diff options
| -rw-r--r-- | .gitattributes | 3 | ||||
| -rw-r--r-- | 26697-8.txt | 7552 | ||||
| -rw-r--r-- | 26697-8.zip | bin | 0 -> 135332 bytes | |||
| -rw-r--r-- | 26697-h.zip | bin | 0 -> 2317441 bytes | |||
| -rw-r--r-- | 26697-h/26697-h.htm | 10476 | ||||
| -rw-r--r-- | 26697-h/images/fig_01.png | bin | 0 -> 76941 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_02.png | bin | 0 -> 40383 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_03.png | bin | 0 -> 74536 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_04.png | bin | 0 -> 18383 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_05.png | bin | 0 -> 19334 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_06.png | bin | 0 -> 13952 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_07.png | bin | 0 -> 20467 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_08.png | bin | 0 -> 15880 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_09-14.png | bin | 0 -> 27532 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_15.png | bin | 0 -> 41243 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_16.png | bin | 0 -> 44270 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_17.png | bin | 0 -> 74960 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_18.png | bin | 0 -> 77521 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_19.png | bin | 0 -> 71327 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_20.png | bin | 0 -> 69139 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_21.png | bin | 0 -> 77084 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_22.png | bin | 0 -> 78037 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_23.png | bin | 0 -> 54403 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_24.png | bin | 0 -> 53421 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_25.png | bin | 0 -> 48547 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_26.png | bin | 0 -> 55754 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_27.png | bin | 0 -> 54376 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_28.png | bin | 0 -> 50168 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_29.png | bin | 0 -> 53796 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_30.png | bin | 0 -> 60742 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_31.png | bin | 0 -> 105447 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_32.png | bin | 0 -> 124761 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_33.png | bin | 0 -> 52637 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_34.png | bin | 0 -> 89017 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_35.png | bin | 0 -> 28688 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_36.png | bin | 0 -> 11492 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_37.png | bin | 0 -> 59107 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_38.png | bin | 0 -> 70943 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_39.png | bin | 0 -> 61776 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_40.png | bin | 0 -> 44296 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_41.png | bin | 0 -> 30325 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_42.png | bin | 0 -> 57906 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_43.png | bin | 0 -> 33533 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_44.png | bin | 0 -> 48199 bytes | |||
| -rw-r--r-- | 26697-h/images/fig_45.png | bin | 0 -> 70728 bytes | |||
| -rw-r--r-- | 26697.txt | 7552 | ||||
| -rw-r--r-- | 26697.zip | bin | 0 -> 135265 bytes | |||
| -rw-r--r-- | LICENSE.txt | 11 | ||||
| -rw-r--r-- | README.md | 2 |
49 files changed, 25596 insertions, 0 deletions
diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/26697-8.txt b/26697-8.txt new file mode 100644 index 0000000..5d48eba --- /dev/null +++ b/26697-8.txt @@ -0,0 +1,7552 @@ +The Project Gutenberg EBook of Principles of Mining, by Herbert C. Hoover + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Principles of Mining + Valuation, Organization and Administration + +Author: Herbert C. Hoover + +Release Date: September 24, 2008 [EBook #26697] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK PRINCIPLES OF MINING *** + + + + +Produced by Robert J. Hall + + + + +PRINCIPLES OF MINING + ++--------------------------------------------------------------+ +| Published by the | +| McGraw-Hill Book Company | +| New York | +| | +| Successors to the Book Departments of the | +| McGraw Publishing Company Hill Publishing Company | +| | +| Publishers of Books for | +| Electrical World The Engineering and Mining Journal | +| Engineering Record Power and The Engineer | +| Electric Railway Journal American Machinist | +| Metallurgical and Chemical Engineering | ++--------------------------------------------------------------+ + + + + +PRINCIPLES OF MINING + +VALUATION, ORGANIZATION AND ADMINISTRATION + +COPPER, GOLD, LEAD, SILVER, TIN AND ZINC + + +BY + +HERBERT C. HOOVER + +_Member American Institute of Mining Engineers, Mining and Metallurgical +Society of America, Société des Ingénieurs Civils de France, Fellow +Royal Geographical Society, etc._ + +First Edition + +_FOURTH THOUSAND_ + +McGRAW-HILL BOOK COMPANY + +239 WEST 39TH STREET, NEW YORK + +BOUVERIE STREET, LONDON, E.C. + +1909 + + + + +PREFACE. + +This volume is a condensation of a series of lectures delivered +in part at Stanford and in part at Columbia Universities. It is +intended neither for those wholly ignorant of mining, nor for those +long experienced in the profession. + +The bulk of the material presented is the common heritage of the +profession, and if any one may think there is insufficient reference +to previous writers, let him endeavor to find to whom the origin +of our methods should be credited. The science has grown by small +contributions of experience since, or before, those unnamed Egyptian +engineers, whose works prove their knowledge of many fundamentals +of mine engineering six thousand eight hundred years ago. If I +have contributed one sentence to the accumulated knowledge of a +thousand generations of engineers, or have thrown one new ray of +light on the work, I shall have done my share. + +I therefore must acknowledge my obligations to all those who have +gone before, to all that has been written that I have read, to +those engineers with whom I have been associated for many years, +and in particular to many friends for kindly reply to inquiry upon +points herein discussed. + + + + +CONTENTS. + +CHAPTER 1. + +Valuation of Copper, Gold, Lead, Silver, Tin, and Zinc Lode Mines + +Determination of average metal content; sampling, assay plans, +calculations of averages, percentage of errors in estimate from +sampling. + +CHAPTER II. + +Mine Valuation (_Continued_) + +Calculation of quantities of ore, and classification of ore in sight. + +CHAPTER III. + +Mine Valuation (_Continued_) + +Prospective value. Extension in depth; origin and structural character +of the deposit; secondary enrichment; development in neighboring +mines; depth of exhaustion. + +CHAPTER IV. + +Mine Valuation (_Continued_) + +Recoverable percentage of the gross assay value; price of metals; +cost of production. + +CHAPTER V. + +Mine Valuation (_Continued_) + +Redemption or amortization of capital and interest. + +CHAPTER VI. + +Mine Valuation (_Concluded_) + +Valuation of mines with little or no ore in sight; valuations on +second-hand data; general conduct of examinations; reports. + +CHAPTER VII. + +Development of Mines + +Entry to the mine; tunnels; vertical, inclined, and combined shafts; +location and number of shafts. + +CHAPTER VIII. + +Development of Mines (_Continued_) + +Shape and size of shafts; speed of sinking; tunnels. + +CHAPTER IX. + +Development of Mines (_Concluded_) + +Subsidiary development: stations; crosscuts; levels; interval between +levels; protection of levels; winzes and rises. Development in the +prospecting stage; drilling. + +CHAPTER X. + +Stoping + +Methods of ore-breaking; underhand stopes; overhand stopes; combined +stope. Valuing ore in course of breaking. + +CHAPTER XI. + +Methods of Supporting Excavation + +Timbering; filling with waste; filling with broken ore; pillars +of ore; artificial pillars; caving system. + +CHAPTER XII. + +Mechanical Equipment + +Conditions bearing on mine equipment; winding appliances; haulage +equipment in shafts; lateral underground transport; transport in +stopes. + +CHAPTER XIII. + +Mechanical Equipment (_Continued_) + +Drainage: controlling factors; volume and head of water; flexibility; +reliability; power conditions; mechanical efficiency; capital outlay. +Systems of drainage,--steam pumps, compressed-air pumps, electrical +pumps, rod-driven pumps, bailing; comparative value of various +systems. + +CHAPTER XIV. + +Mechanical Equipment (_Concluded_) + +Machine drilling: power transmission; compressed air _vs._ electricity; +air drills; machine _vs._ hand drilling. Workshops. Improvement in +equipment. + +CHAPTER XV. + +Ratio of Output to the Mine + +Determination of possible maximum; limiting factors; cost of equipment; +life of the mine; mechanical inefficiency of patchwork plant; +overproduction of base metal; security of investment. + +CHAPTER XVI. + +Administration + +Labor efficiency; skill; intelligence; application coördination; +contract work; labor unions; real basis of wages. + +CHAPTER XVII. + +Administration (_Continued_) + +Accounts and technical data and reports; working costs; division +of expenditure; inherent limitations in accuracy of working costs; +working cost sheets. General technical data; labor, supplies, power, +surveys, sampling, and assaying. + +CHAPTER XVIII. + +Administration (_Concluded_) + +Administrative reports. + +CHAPTER XIX. + +The Amount of Risk in Mining Investments + +Risk in valuation of mines; in mines as compared with other commercial +enterprises. + +CHAPTER XX. + +The Character, Training, and Obligations of the Mining Engineering +Profession + +Index + + + + +PRINCIPLES OF MINING. + +CHAPTER I. + +Valuation of Copper, Gold, Lead, Silver, Tin, and Zinc Lode Mines. + +DETERMINATION OF AVERAGE METAL CONTENT; SAMPLING, ASSAY PLANS, +CALCULATIONS OF AVERAGES, PERCENTAGE OF ERRORS IN ESTIMATE FROM +SAMPLING. + +The following discussion is limited to _in situ_ deposits of copper, +gold, lead, silver, tin, and zinc. The valuation of alluvial deposits, +iron, coal, and other mines is each a special science to itself and +cannot be adequately discussed in common with the type of deposits +mentioned above. + +The value of a metal mine of the order under discussion depends +upon:-- + +_a_. The profit that may be won from ore exposed; +_b_. The prospective profit to be derived from extension of the + ore beyond exposures; +_c_. The effect of a higher or lower price of metal (except in + gold mines); +_d_. The efficiency of the management during realization. + +The first may be termed the positive value, and can be approximately +determined by sampling or test-treatment runs. The second and the +third may be termed the speculative values, and are largely a matter +of judgment based on geological evidence and the industrial outlook. +The fourth is a question of development, equipment, and engineering +method adapted to the prospects of the enterprise, together with +capable executive control of these works. + +It should be stated at the outset that it is utterly impossible to +accurately value any mine, owing to the many speculative factors +involved. The best that can be done is to state that the value +lies between certain limits, and that various stages above the +minimum given represent various degrees of risk. Further, it would +be but stating truisms to those engaged in valuing mines to repeat +that, because of the limited life of every mine, valuation of such +investments cannot be based upon the principle of simple interest; +nor that any investment is justified without a consideration of +the management to ensue. Yet the ignorance of these essentials +is so prevalent among the public that they warrant repetition on +every available occasion. + +To such an extent is the realization of profits indicated from +the other factors dependent upon the subsequent management of the +enterprise that the author considers a review of underground engineering +and administration from an economic point of view an essential to +any essay upon the subject. While the metallurgical treatment of +ores is an essential factor in mine economics, it is considered that +a detailed discussion of the myriad of processes under hypothetic +conditions would lead too far afield. Therefore the discussion is +largely limited to underground and administrative matters. + +The valuation of mines arises not only from their change of ownership, +but from the necessity in sound administration for a knowledge +of some of the fundamentals of valuation, such as ore reserves +and average values, that managerial and financial policy may be +guided aright. Also with the growth of corporate ownership there +is a demand from owners and stockholders for periodic information +as to the intrinsic condition of their properties. + +The growth of a body of speculators and investors in mining stocks +and securities who desire professional guidance which cannot be based +upon first-hand data is creating further demand on the engineer. +Opinions in these cases must be formed on casual visits or second-hand +information, and a knowledge of men and things generally. Despite +the feeling of some engineers that the latter employment is not +properly based professionally, it is an expanding phase of engineers' +work, and must be taken seriously. Although it lacks satisfactory +foundation for accurate judgment, yet the engineer can, and should, +give his experience to it when the call comes, out of interest +to the industry as a whole. Not only can he in a measure protect +the lamb, by insistence on no investment without the provision of +properly organized data and sound administration for his client, but +he can do much to direct the industry from gambling into industrial +lines. + +An examination of the factors which arise on the valuation of mines +involves a wide range of subjects. For purposes of this discussion +they may be divided into the following heads:-- + +1. _Determination of Average Metal Contents of the Ore._ +2. _Determination of Quantities of Ore._ +3. _Prospective Value._ +4. _Recoverable Percentage of Gross Value._ +5. _Price of Metals._ +6. _Cost of Production._ +7. _Redemption or Amortization of Capital and Interest._ +8. _Valuation of Mines without Ore in Sight._ +9. _General Conduct of Examination and Reports._ + +DETERMINATION OF AVERAGE METAL CONTENTS OF THE ORE. + +Three means of determination of the average metal content of standing +ore are in use--Previous Yield, Test-treatment Runs, and Sampling. + +PREVIOUS YIELD.--There are certain types of ore where the previous +yield from known space becomes the essential basis of determination +of quantity and metal contents of ore standing and of the future +probabilities. Where metals occur like plums in a pudding, sampling +becomes difficult and unreliable, and where experience has proved +a sort of regularity of recurrence of these plums, dependence must +necessarily be placed on past records, for if their reliability is +to be questioned, resort must be had to extensive test-treatment +runs. The Lake Superior copper mines and the Missouri lead and zinc +mines are of this type of deposit. On the other sorts of deposits +the previous yield is often put forward as of important bearing +on the value of the ore standing, but such yield, unless it can +be _authentically_ connected with blocks of ore remaining, is not +necessarily a criterion of their contents. Except in the cases +mentioned, and as a check on other methods of determination, it +has little place in final conclusions. + +TEST PARCELS.--Treatment on a considerable scale of sufficiently +regulated parcels, although theoretically the ideal method, is, +however, not often within the realm of things practical. In examination +on behalf of intending purchasers, the time, expense, or opportunity +to fraud are usually prohibitive, even where the plant and facilities +for such work exist. Even in cases where the engineer in management +of producing mines is desirous of determining the value of standing +ore, with the exception of deposits of the type mentioned above, +it is ordinarily done by actual sampling, because separate mining +and treatment of test lots is generally inconvenient and expensive. +As a result, the determination of the value of standing ore is, +in the great majority of cases, done by sampling and assaying. + +SAMPLING.--The whole theory of sampling is based on the distribution +of metals through the ore-body with more or less regularity, so +that if small portions, that is samples, be taken from a sufficient +number of points, their average will represent fairly closely the +unit value of the ore. If the ore is of the extreme type of irregular +metal distribution mentioned under "previous yield," then sampling +has no place. + +How frequently samples must be taken, the manner of taking them, +and the quantity that constitutes a fair sample, are matters that +vary with each mine. So much depends upon the proper performance +of this task that it is in fact the most critical feature of mine +examination. Ten samples properly taken are more valuable than +five hundred slovenly ones, like grab samples, for such a number +of bad ones would of a surety lead to wholly wrong conclusions. +Given a good sampling and a proper assay plan, the valuation of a +mine is two-thirds accomplished. It should be an inflexible principle +in examinations for purchase that every sample must be taken under +the personal supervision of the examining engineer or his trusted +assistants. Aside from throwing open the doors to fraud, the average +workman will not carry out the work in a proper manner, unless +under constant supervision, because of his lack of appreciation of +the issues involved. Sampling is hard, uncongenial, manual labor. +It requires a deal of conscientiousness to take enough samples and +to take them thoroughly. The engineer does not exist who, upon +completion of this task, considers that he has got too many, and +most wish that they had taken more. + +The accuracy of sampling as a method of determining the value of +standing ore is a factor of the number of samples taken. The average, +for example, of separate samples from each square inch would be +more accurate than those from each alternate square inch. However, +the accumulated knowledge and experience as to the distribution +of metals through ore has determined approximately the manner of +taking such samples, and the least number which will still by the +law of averages secure a degree of accuracy commensurate with the +other factors of estimation. + +As metals are distributed through ore-bodies of fissure origin +with most regularity on lines parallel to the strike and dip, an +equal portion of ore from every point along cross-sections at right +angles to the strike will represent fairly well the average values +for a certain distance along the strike either side of these +cross-sections. In massive deposits, sample sections are taken +in all directions. The intervals at which sample sections must +be cut is obviously dependent upon the general character of the +deposit. If the values are well distributed, a longer interval +may be employed than in one subject to marked fluctuations. As +a general rule, five feet is the distance most accepted. This, +in cases of regular distribution of values, may be stretched to +ten feet, or in reverse may be diminished to two or three feet. + +The width of ore which may be included for one sample is dependent +not only upon the width of the deposit, but also upon its character. +Where the ore is wider than the necessary stoping width, the sample +should be regulated so as to show the possible locus of values. +The metal contents may be, and often are, particularly in deposits +of the impregnation or replacement type, greater along some streak +in the ore-body, and this difference may be such as to make it +desirable to stope only a portion of the total thickness. For deposits +narrower than the necessary stoping width the full breadth of ore +should be included in one sample, because usually the whole of +the deposit will require to be broken. + +In order that a payable section may not possibly be diluted with +material unnecessary to mine, if the deposit is over four feet and +under eight feet, the distance across the vein or lode is usually +divided into two samples. If still wider, each is confined to a +span of about four feet, not only for the reason given above, but +because the more numerous the samples, the greater the accuracy. +Thus, in a deposit twenty feet wide it may be taken as a good guide +that a test section across the ore-body should be divided into +five parts. + +As to the physical details of sample taking, every engineer has +his own methods and safeguards against fraud and error. In a large +organization of which the writer had for some years the direction, +and where sampling of mines was constantly in progress on an extensive +scale, not only in contemplation of purchase, but where it was also +systematically conducted in operating mines for working data, he +adopted the above general lines and required the following details. + +A fresh face of ore is first broken and then a trench cut about +five inches wide and two inches deep. This trench is cut with a +hammer and moil, or, where compressed air is available and the +rock hard, a small air-drill of the hammer type is used. The spoil +from the trench forms the sample, and it is broken down upon a +large canvas cloth. Afterwards it is crushed so that all pieces +will pass a half-inch screen, mixed and quartered, thus reducing the +weight to half. Whether it is again crushed and quartered depends +upon what the conditions are as to assaying. If convenient to assay +office, as on a going mine, the whole of the crushing and quartering +work can be done at that office, where there are usually suitable +mechanical appliances. If the samples must be taken a long distance, +the bulk for transport can be reduced by finer breaking and repeated +quartering, until there remain only a few ounces. + +PRECAUTIONS AGAINST FRAUD.--Much has been written about the precautions +to be taken against fraud in cases of valuations for purchase. The +best safeguards are an alert eye and a strong right arm. However, +certain small details help. A large leather bag, arranged to lock +after the order of a mail sack, into which samples can be put +underground and which is never unfastened except by responsible +men, not only aids security but relieves the mind. A few samples +of country rock form a good check, and notes as to the probable +value of the ore, from inspection when sampling, are useful. A +great help in examination is to have the assays or analyses done +coincidentally with the sampling. A doubt can then always be settled +by resampling at once, and much knowledge can be gained which may +relieve so exhaustive a program as might be necessary were results +not known until after leaving the mine. + +ASSAY OF SAMPLES.--Two assays, or as the case may be, analyses, +are usually made of every sample and their average taken. In the +case of erratic differences a third determination is necessary. + +ASSAY PLANS.--An assay plan is a plan of the workings, with the +location, assay value, and width of the sample entered upon it. In +a mine with a narrow vein or ore-body, a longitudinal section is +sufficient base for such entries, but with a greater width than one +sample span it is desirable to make preliminary plans of separate +levels, winzes, etc., and to average the value of the whole payable +widths on such plans before entry upon a longitudinal section. Such +a longitudinal section will, through the indicated distribution +of values, show the shape of the ore-body--a step necessary in +estimating quantities and of the most fundamental importance in +estimating the probabilities of ore extension beyond the range of +the openings. The final assay plan should show the average value +of the several blocks of ore, and it is from these averages that +estimates of quantities must be made up. + +CALCULATIONS OF AVERAGES.--The first step in arriving at average +values is to reduce erratic high assays to the general tenor of +other adjacent samples. This point has been disputed at some length, +more often by promoters than by engineers, but the custom is very +generally and rightly adopted. Erratically high samples may indicate +presence of undue metal in the assay attributable to unconscious +salting, for if the value be confined to a few large particles +they may find their way through all the quartering into the assay. +Or the sample may actually indicate rich spots of ore; but in any +event experience teaches that no dependence can be put upon regular +recurrence of such abnormally rich spots. As will be discussed +under percentage of error in sampling, samples usually indicate +higher than the true value, even where erratic assays have been +eliminated. There are cases of profitable mines where the values +were all in spots, and an assay plan would show 80% of the assays +_nil_, yet these pockets were so rich as to give value to the whole. +Pocket mines, as stated before, are beyond valuation by sampling, +and aside from the previous yield recourse must be had to actual +treatment runs on every block of ore separately. + +After reduction of erratic assays, a preliminary study of the runs of +value or shapes of the ore-bodies is necessary before any calculation +of averages. A preliminary delineation of the boundaries of the +payable areas on the assay plan will indicate the sections of the +mine which are unpayable, and from which therefore samples can +be rightly excluded in arriving at an average of the payable ore +(Fig. 1). In a general way, only the ore which must be mined need +be included in averaging. + +The calculation of the average assay value of standing ore from +samples is one which seems to require some statement of elementals. +Although it may seem primitive, it can do no harm to recall that if +a dump of two tons of ore assaying twenty ounces per ton be added +to a dump of five tons averaging one ounce per ton, the result has +not an average assay of twenty-one ounces divided by the number of +dumps. Likewise one sample over a width of two feet, assaying twenty +ounces per ton, if averaged with another sample over a width of five +feet, assaying one ounce, is no more twenty-one ounces divided by +two samples than in the case of the two dumps. If common sense were +not sufficient demonstration of this, it can be shown algebraically. +Were samples equidistant from each other, and were they of equal +width, the average value would be the simple arithmetical mean of +the assays. But this is seldom the case. The number of instances, +not only in practice but also in technical literature, where the +fundamental distinction between an arithmetical and a geometrical +mean is lost sight of is amazing. + +To arrive at the average value of samples, it is necessary, in +effect, to reduce them to the actual quantity of the metal and volume +of ore represented by each. The method of calculation therefore +is one which gives every sample an importance depending upon the +metal content of the volume of ore it represents. + +The volume of ore appertaining to any given sample can be considered +as a prismoid, the dimensions of which may be stated as follows:-- + + _W_ = Width in feet of ore sampled. + _L_ = Length in feet of ore represented by the sample. + _D_ = Depth into the block to which values are assumed to penetrate. + +We may also let:-- + + _C_ = The number of cubic feet per ton of ore. + _V_ = Assay value of the sample. + +Then _WLD_/C_ = tonnage of the prismoid.* + _V WLD_/C_ = total metal contents. + +[Footnote *: Strictly, the prismoidal formula should be used, but +it complicates the study unduly, and for practical purposes the +above may be taken as the volume.] + +The average value of a number of samples is the total metal contents +of their respective prismoids, divided by the total tonnage of +these prismoids. If we let _W_, _W_1, _V_, _V_1 etc., represent +different samples, we have:-- + +_V(_WLD_/_C_) + _V_1 (_W_1 _L_1 _D_1/_C_) + _V_2 (_W_2 _L_2 _D_2/_C_) +--------------------------------------------------------------------- + _WLD_/_C_ + _W_1 _L_1 _D_1/_C_ + _W_2 _L_2 _D_2/_C_ += average value. + +This may be reduced to:-- + +(_VWLD_) + (_V_1 _W_1 _L_1 _D_1) + (_V_2 _W_2 _L_2 _D_2,), etc. +--------------------------------------------------------------- + (_WLD_) + (_W_1 _L_1 _D_1) + (_W_2 _L_2 _D_2), etc. + +As a matter of fact, samples actually represent the value of +the outer shell of the block of ore only, and the continuity of +the same values through the block is a geological assumption. +From the outer shell, all the values can be taken to penetrate +equal distances into the block, and therefore _D_, _D_1, _D_2 +may be considered as equal and the equation becomes:-- + +(_VWL_) + (_V_1 _W_1 _L_1) + (_V_2 _W_2 _L_2), etc. +--------------------------------------------------- + (_WL_) + (_W_1 _L_1) + (_W_2 _L_2), etc. + +The length of the prismoid base _L_ for any given sample will be +a distance equal to one-half the sum of the distances to the two +adjacent samples. As a matter of practice, samples are usually taken +at regular intervals, and the lengths _L_, _L_1, _L_2 becoming thus +equal can in such case be eliminated, and the equation becomes:-- + +(_VW_) + (_V_1 _W_1) + (_V_2 _W_2), etc. +---------------------------------------- + _W_ + _W_1 + _W_2 , etc. + +The name "assay foot" or "foot value" has been given to the relation +_VW_, that is, the assay value multiplied by the width sampled.[*] +It is by this method that all samples must be averaged. The same +relation obviously can be evolved by using an inch instead of a +foot, and in narrow veins the assay inch is generally used. + +[Footnote *: An error will be found in this method unless the two +end samples be halved, but in a long run of samples this may be +disregarded.] + +Where the payable cross-section is divided into more than one sample, +the different samples in the section must be averaged by the above +formula, before being combined with the adjacent section. Where +the width sampled is narrower than the necessary stoping width, +and where the waste cannot be broken separately, the sample value +must be diluted to a stoping width. To dilute narrow samples to +a stoping width, a blank value over the extra width which it is +necessary to include must be averaged with the sample from the +ore on the above formula. Cases arise where, although a certain +width of waste must be broken with the ore, it subsequently can +be partially sorted out. Practically nothing but experience on +the deposit itself will determine how far this will restore the +value of the ore to the average of the payable seam. In any event, +no sorting can eliminate all such waste; and it is necessary to +calculate the value on the breaking width, and then deduct from +the gross tonnage to be broken a percentage from sorting. There +is always an allowance to be made in sorting for a loss of good +ore with the discards. + +PERCENTAGE OF ERROR IN ESTIMATES FROM SAMPLING.--It must be remembered +that the whole theory of estimation by sampling is founded upon +certain assumptions as to evenness of continuity and transition +in value and volume. It is but a basis for an estimate, and an +estimate is not a statement of fact. It cannot therefore be too +forcibly repeated that an estimate is inherently but an approximation, +take what care one may in its founding. While it is possible to +refine mathematical calculation of averages to almost any nicety, +beyond certain essentials it adds nothing to accuracy and is often +misleading. + +It is desirable to consider where errors are most likely to creep +in, assuming that all fundamental data are both accurately taken +and considered. Sampling of ore _in situ_ in general has a tendency +to give higher average value than the actual reduction of the ore +will show. On three West Australian gold mines, in records covering +a period of over two years, where sampling was most exhaustive as +a daily régime of the mines, the values indicated by sampling were +12% higher than the mill yield plus the contents of the residues. +On the Witwatersrand gold mines, the actual extractable value is +generally considered to be about 78 to 80% of the average shown +by sampling, while the mill extractions are on average about 90 +to 92% of the head value coming to the mill. In other words, there +is a constant discrepancy of about 10 to 12% between the estimated +value as indicated by mine samples, and the actual value as shown +by yield plus the residues. At Broken Hill, on three lead mines, +the yield is about 12% less than sampling would indicate. This +constancy of error in one direction has not been so generally +acknowledged as would be desirable, and it must be allowed for +in calculating final results. The causes of the exaggeration seem +to be:-- + +_First_, inability to stope a mine to such fine limitations of +width, or exclusion of unpayable patches, as would appear practicable +when sampling, that is by the inclusion when mining of a certain +amount of barren rock. Even in deposits of about normal stoping +width, it is impossible to prevent the breaking of a certain amount +of waste, even if the ore occurrence is regularly confined by walls. + +If the mine be of the impregnation type, such as those at Goldfield, +or Kalgoorlie, with values like plums in a pudding, and the stopes +themselves directed more by assays than by any physical differences +in the ore, the discrepancy becomes very much increased. In mines +where the range of values is narrower than the normal stoping width, +some wall rock must be broken. Although it is customary to allow for +this in calculating the average value from samples, the allowance +seldom seems enough. In mines where the ore is broken on to the +top of stopes filled with waste, there is some loss underground +through mixture with the filling. + +_Second_, the metal content of ores, especially when in the form of +sulphides, is usually more friable than the matrix, and in actual +breaking of samples an undue proportion of friable material usually +creeps in. This is true more in lead, copper, and zinc, than in +gold ores. On several gold mines, however, tests on accumulated +samples for their sulphide percentage showed a distinctly greater +ratio than the tenor of the ore itself in the mill. As the gold is +usually associated with the sulphides, the samples showed higher +values than the mill. + +In general, some considerable factor of safety must be allowed +after arriving at calculated average of samples,--how much it is +difficult to say, but, in any event, not less than 10%. + + + + +CHAPTER II. + +Mine Valuation (_Continued_). + +CALCULATION OF QUANTITIES OF ORE, AND CLASSIFICATION OF ORE IN SIGHT. + +As mines are opened by levels, rises, etc., through the ore, an +extension of these workings has the effect of dividing it into +"blocks." The obvious procedure in determining tonnages is to calculate +the volume and value of each block separately. Under the law of +averages, the multiplicity of these blocks tends in proportion +to their number to compensate the percentage of error which might +arise in the sampling or estimating of any particular one. The +shapes of these blocks, on longitudinal section, are often not +regular geometrical figures. As a matter of practice, however, they +can be subdivided into such figures that the total will approximate +the whole with sufficient closeness for calculations of their areas. + +The average width of the ore in any particular block is the arithmetical +mean of the width of the sample sections in it,[*] if the samples be +an equal distance apart. If they are not equidistant, the average +width is the sum of the areas between samples, divided by the total +length sampled. The cubic foot contents of a particular block is +obviously the width multiplied by the area of its longitudinal +section. + +[Footnote *: This is not strictly true unless the sum of the widths +of the two end-sections be divided by two and the result incorporated +in calculating the means. In a long series that error is of little +importance.] + +The ratio of cubic feet to tons depends on the specific gravity +of the ore, its porosity, and moisture. The variability of ores +throughout the mine in all these particulars renders any method +of calculation simply an approximation in the end. The factors +which must remain unknown necessarily lead the engineer to the +provision of a margin of safety, which makes mathematical refinement +and algebraic formulæ ridiculous. + +There are in general three methods of determination of the specific +volume of ores:-- + +_First_, by finding the true specific gravity of a sufficient number +of representative specimens; this, however, would not account for +the larger voids in the ore-body and in any event, to be anything +like accurate, would be as expensive as sampling and is therefore +of little more than academic interest. + +_Second_, by determining the weight of quantities broken from measured +spaces. This also would require several tests from different portions +of the mine, and, in examinations, is usually inconvenient and +difficult. Yet it is necessary in cases of unusual materials, such +as leached gossans, and it is desirable to have it done sooner +or later in going mines, as a check. + +_Third_, by an approximation based upon a calculation from the +specific gravities of the predominant minerals in the ore. Ores +are a mixture of many minerals; the proportions vary through the +same ore-body. Despite this, a few partial analyses, which are +usually available from assays of samples and metallurgical tests, +and a general inspection as to the compactness of the ore, give a +fairly reliable basis for approximation, especially if a reasonable +discount be allowed for safety. In such discount must be reflected +regard for the porosity of the ore, and the margin of safety necessary +may vary from 10 to 25%. If the ore is of unusual character, as +in leached deposits, as said before, resort must be had to the +second method. + +The following table of the weights per cubic foot and the number +of cubic feet per ton of some of the principal ore-forming minerals +and gangue rocks will be useful for approximating the weight of +a cubic foot of ore by the third method. Weights are in pounds +avoirdupois, and two thousand pounds are reckoned to the ton. + +============================================ + | | Number of + | Weight per | Cubic Feet + | Cubic Foot | per Ton of + | | 2000 lb. +------------------|------------|------------ +Antimony | 417.50 | 4.79 + Sulphide | 285.00 | 7.01 +Arsenical Pyrites | 371.87 | 5.37 +Barium Sulphate | 278.12 | 7.19 +Calcium: | | + Fluorite | 198.75 | 10.06 + Gypsum | 145.62 | 13.73 + Calcite | 169.37 | 11.80 +Copper | 552.50 | 3.62 + Calcopyrite | 262.50 | 7.61 + Bornite | 321.87 | 6.21 + Malachite | 247.50 | 8.04 + Azurite | 237.50 | 8.42 + Chrysocolla | 132.50 | 15.09 +Iron (Cast) | 450.00 | 4.44 + Magnetite | 315.62 | 6.33 + Hematite | 306.25 | 6.53 + Limonite | 237.50 | 8.42 + Pyrite | 312.50 | 6.40 + Carbonate | 240.62 | 8.31 +Lead | 710.62 | 2.81 + Galena | 468.75 | 4.27 + Carbonate | 406.87 | 4.81 +Manganese Oxide | 268.75 | 6.18 + Rhodonite | 221.25 | 9.04 +Magnesite | 187.50 | 10.66 + Dolomite | 178.12 | 11.23 +Quartz | 165.62 | 12.07 +Quicksilver | 849.75 | 2.35 + Cinnabar | 531.25 | 3.76 + Sulphur | 127.12 | 15.74 +Tin | 459.00 | 4.35 + Oxide | 418.75 | 4.77 +Zinc | 437.50 | 4.57 + Blende | 253.12 | 7.90 + Carbonate | 273.12 | 7.32 + Silicate | 215.62 | 9.28 +Andesite | 165.62 | 12.07 +Granite | 162.62 | 12.30 +Diabase | 181.25 | 11.03 +Diorite | 171.87 | 11.63 +Slates | 165.62 | 12.07 +Sandstones | 162.50 | 12.30 +Rhyolite | 156.25 | 12.80 +============================================ + +The specific gravity of any particular mineral has a considerable +range, and a medium has been taken. The possible error is +inconsequential for the purpose of these calculations. + +For example, a representative gold ore may contain in the main +96% quartz, and 4% iron pyrite, and the weight of the ore may be +deduced as follows:-- + + Quartz, 96% x 12.07 = 11.58 + Iron Pyrite, 4% x 6.40 = .25 + ----- + 11.83 cubic feet per ton. + +Most engineers, to compensate porosity, would allow twelve to thirteen +cubic feet per ton. + +CLASSIFICATION OF ORE IN SIGHT. + +The risk in estimates of the average value of standing ore is dependent +largely upon how far values disclosed by sampling are assumed to +penetrate beyond the tested face, and this depends upon the geological +character of the deposit. From theoretical grounds and experience, +it is known that such values will have some extension, and the +assumption of any given distance is a calculation of risk. The +multiplication of development openings results in an increase of +sampling points available and lessens the hazards. The frequency +of such openings varies in different portions of every mine, and +thus there are inequalities of risk. It is therefore customary in +giving estimates of standing ore to classify the ore according +to the degree of risk assumed, either by stating the number of +sides exposed or by other phrases. Much discussion and ink have +been devoted to trying to define what risk may be taken in such +matters, that is in reality how far values may be assumed to penetrate +into the unbroken ore. Still more has been consumed in attempts +to coin terms and make classifications which will indicate what +ratio of hazard has been taken in stating quantities and values. + +The old terms "ore in sight" and "profit in sight" have been of +late years subject to much malediction on the part of engineers +because these expressions have been so badly abused by the charlatans +of mining in attempts to cover the flights of their imaginations. A +large part of Volume X of the "Institution of Mining and Metallurgy" +has been devoted to heaping infamy on these terms, yet not only +have they preserved their places in professional nomenclature, +but nothing has been found to supersede them. + +Some general term is required in daily practice to cover the whole +field of visible ore, and if the phrase "ore in sight" be defined, +it will be easier to teach the laymen its proper use than to abolish +it. In fact, the substitutes are becoming abused as much as the +originals ever were. All convincing expressions will be misused +by somebody. + +The legitimate direction of reform has been to divide the general +term of "ore in sight" into classes, and give them names which will +indicate the variable amount of risk of continuity in different parts +of the mine. As the frequency of sample points, and consequently the +risk of continuity, will depend upon the detail with which the mine +is cut into blocks by the development openings, and upon the number +of sides of such blocks which are accessible, most classifications +of the degree of risk of continuity have been defined in terms of +the number of sides exposed in the blocks. Many phrases have been +coined to express such classifications; those most currently used +are the following:-- + +Positive Ore \ Ore exposed on four sides in blocks of a size +Ore Developed / variously prescribed. +Ore Blocked Out Ore exposed on three sides within reasonable + distance of each other. +Probable Ore \ +Ore Developing / Ore exposed on two sides. + +Possible Ore \ The whole or a part of the ore below the +Ore Expectant / lowest level or beyond the range of vision. + +No two of these parallel expressions mean quite the same thing; +each more or less overlies into another class, and in fact none +of them is based upon a logical footing for such a classification. +For example, values can be assumed to penetrate some distance from +every sampled face, even if it be only ten feet, so that ore exposed +on one side will show some "positive" or "developed" ore which, on +the lines laid down above, might be "probable" or even "possible" +ore. Likewise, ore may be "fully developed" or "blocked out" so far +as it is necessary for stoping purposes with modern wide intervals +between levels, and still be in blocks too large to warrant an +assumption of continuity of values to their centers (Fig. 1). As +to the third class of "possible" ore, it conveys an impression +of tangibility to a nebulous hazard, and should never be used in +connection with positive tonnages. This part of the mine's value +comes under extension of the deposit a long distance beyond openings, +which is a speculation and cannot be defined in absolute tons without +exhaustive explanation of the risks attached, in which case any +phrase intended to shorten description is likely to be misleading. + +[Illustration: Fig. 1.--Longitudinal section of a mine, showing +classification of the exposed ore. Scale, 400 feet = 1 inch.] + +Therefore empirical expressions in terms of development openings +cannot be made to cover a geologic factor such as the distribution +of metals through a rock mass. The only logical basis of ore +classification for estimation purposes is one which is founded +on the chances of the values penetrating from the surface of the +exposures for each particular mine. Ore that may be calculated +upon to a certainty is that which, taking into consideration the +character of the deposit, can be said to be so sufficiently surrounded +by sampled faces that the distance into the mass to which values +are assumed to extend is reduced to a minimum risk. Ore so far +removed from the sampled face as to leave some doubt, yet affording +great reason for expectation of continuity, is "probable" ore. +The third class of ore mentioned, which is that depending upon +extension of the deposit and in which, as said above, there is great +risk, should be treated separately as the speculative value of the +mine. Some expressions are desirable for these classifications, and +the writer's own preference is for the following, with a definition +based upon the controlling factor itself. + +They are:-- + +Proved Ore Ore where there is practically no risk of + failure of continuity. + +Probable Ore Ore where there is some risk, yet warrantable + justification for assumption of continuity. + +Prospective Ore Ore which cannot be included in the above + classes, nor definitely known or stated in + any terms of tonnage. + +What extent of openings, and therefore of sample faces, is required +for the ore to be called "proved" varies naturally with the type +of deposit,--in fact with each mine. In a general way, a fair rule +in gold quartz veins below influence of secondary alteration is +that no point in the block shall be over fifty feet from the points +sampled. In limestone or andesite replacements, as by gold or lead +or copper, the radius must be less. In defined lead and copper +lodes, or in large lenticular bodies such as the Tennessee copper +mines, the radius may often be considerably greater,--say one hundred +feet. In gold deposits of such extraordinary regularity of values +as the Witwatersrand bankets, it can well be two hundred or two +hundred and fifty feet. + +"Probable ore" should be ore which entails continuity of values +through a greater distance than the above, and such distance must +depend upon the collateral evidence from the character of the deposit, +the position of openings, etc. + +Ore beyond the range of the "probable" zone is dependent upon the +extension of the deposit beyond the realm of development and will +be discussed separately. + +Although the expression "ore in sight" may be deprecated, owing to +its abuse, some general term to cover both "positive" and "probable" +ore is desirable; and where a general term is required, it is the +intention herein to hold to the phrase "ore in sight" under the +limitations specified. + + + + +CHAPTER III. + +Mine Valuation (_Continued_). + +PROSPECTIVE VALUE.[*] EXTENSION IN DEPTH; ORIGIN AND STRUCTURAL +CHARACTER OF THE DEPOSIT; SECONDARY ENRICHMENT; DEVELOPMENT IN +NEIGHBORING MINES; DEPTH OF EXHAUSTION. + +[Footnote *: The term "extension in depth" is preferred by many +to the phrase "prospective value." The former is not entirely +satisfactory, as it has a more specific than general application. +It is, however, a current miner's phrase, and is more expressive. +In this discussion "extension in depth" is used synonymously, and +it may be taken to include not alone the downward prolongation of +the ore below workings, but also the occasional cases of lateral +extension beyond the range of development work. The commonest instance +is continuance below the bottom level. In any event, to the majority +of cases of different extension the same reasoning applies.] + +It is a knotty problem to value the extension of a deposit beyond +a short distance from the last opening. A short distance beyond +it is "proved ore," and for a further short distance is "probable +ore." Mines are very seldom priced at a sum so moderate as that +represented by the profit to be won from the ore in sight, and what +value should be assigned to this unknown portion of the deposit +admits of no certainty. No engineer can approach the prospective +value of a mine with optimism, yet the mining industry would be +non-existent to-day were it approached with pessimism. Any value +assessed must be a matter of judgment, and this judgment based on +geological evidence. Geology is not a mathematical science, and +to attach a money equivalence to forecasts based on such evidence +is the most difficult task set for the mining engineer. It is here +that his view of geology must differ from that of his financially +more irresponsible brother in the science. The geologist, contributing +to human knowledge in general, finds his most valuable field in the +examination of mines largely exhausted. The engineer's most valuable +work arises from his ability to anticipate in the youth of the mine +the symptoms of its old age. The work of our geologic friends is, +however, the very foundation on which we lay our forecasts. + +Geologists have, as the result of long observation, propounded for +us certain hypotheses which, while still hypotheses, have proved +to account so widely for our underground experience that no engineer +can afford to lose sight of them. Although there is a lack of safety +in fixed theories as to ore deposition, and although such conclusions +cannot be translated into feet and metal value, they are nevertheless +useful weights on the scale where probabilities are to be weighed. + +A method in vogue with many engineers is, where the bottom level +is good, to assume the value of the extension in depth as a sum +proportioned to the profit in sight, and thus evade the use of +geological evidence. The addition of various percentages to the +profit in sight has been used by engineers, and proposed in technical +publications, as varying from 25 to 50%. That is, they roughly +assess the extension in depth to be worth one-fifth to one-third +of the whole value of an equipped mine. While experience may have +sometimes demonstrated this to be a practical method, it certainly +has little foundation in either science or logic, and the writer's +experience is that such estimates are untrue in practice. The quantity +of ore which may be in sight is largely the result of managerial +policy. A small mill on a large mine, under rapid development, +will result in extensive ore-reserves, while a large mill eating +away rapidly on the same mine under the same scale of development +would leave small reserves. On the above scheme of valuation the +extension in depth would be worth very different sums, even when the +deepest level might be at the same horizon in both cases. Moreover, +no mine starts at the surface with a large amount of ore in sight. +Yet as a general rule this is the period when its extension is most +valuable, for when the deposit is exhausted to 2000 feet, it is +not likely to have such extension in depth as when opened one hundred +feet, no matter what the ore-reserves may be. Further, such bases +of valuation fail to take into account the widely varying geologic +character of different mines, and they disregard any collateral +evidence either of continuity from neighboring development, or from +experience in the district. Logically, the prospective value can +be simply a factor of how _far_ the ore in the individual mine +may be expected to extend, and not a factor of the remnant of ore +that may still be unworked above the lowest level. + +An estimation of the chances of this extension should be based +solely on the local factors which bear on such extension, and these +are almost wholly dependent upon the character of the deposit. +These various geological factors from a mining engineer's point +of view are:-- + +1. The origin and structural character of the ore-deposit. +2. The position of openings in relation to secondary alteration. +3. The size of the deposit. +4. The depth to which the mine has already been exhausted. +5. The general experience of the district for continuity and + the development of adjoining mines. + +THE ORIGIN AND STRUCTURAL CHARACTER OF THE DEPOSIT.--In a general +way, the ore-deposits of the order under discussion originate primarily +through the deposition of metals from gases or solutions circulating +along avenues in the earth's crust.[*] The original source of metals +is a matter of great disagreement, and does not much concern the +miner. To him, however, the origin and character of the avenue +of circulation, the enclosing rock, the influence of the rocks +on the solution, and of the solutions on the rocks, have a great +bearing on the probable continuity of the volume and value of the +ore. + +[Footnote *: The class of magmatic segregations is omitted, as +not being of sufficiently frequent occurrence in payable mines to +warrant troubling with it here.] + +All ore-deposits vary in value and, in the miner's view, only those +portions above the pay limit are ore-bodies, or ore-shoots. The +localization of values into such pay areas in an ore-deposit are +apparently influenced by: + +1. The distribution of the open spaces created by structural + movement, fissuring, or folding as at Bendigo. +2. The intersection of other fractures which, by mingling of + solutions from different sources, provided precipitating + conditions, as shown by enrichments at cross-veins. +3. The influence of the enclosing rocks by:-- + (a) Their solubility, and therefore susceptibility to replacement. + (b) Their influence as a precipitating agent on solutions. + (c) Their influence as a source of metal itself. + (d) Their texture, in its influence on the character of + the fracture. In homogeneous rocks the tendency + is to open clean-cut fissures; in friable + rocks, zones of brecciation; in slates or schistose + rocks, linked lenticular open spaces;--these + influences exhibiting themselves in miner's terms + respectively in "well-defined fissure veins," + "lodes," and "lenses." + (e) The physical character of the rock mass and the + dynamic forces brought to bear upon it. This + is a difficult study into the physics of stress in + cases of fracturing, but its local application has + not been without results of an important order. +4. Secondary alteration near the surface, more fully discussed + later. + +It is evident enough that the whole structure of the deposit is +a necessary study, and even a digest of the subject is not to be +compressed into a few paragraphs. + +From the point of view of continuity of values, ore-deposits may +be roughly divided into three classes. They are:-- + +1. Deposits of the infiltration type in porous beds, such as + Lake Superior copper conglomerates and African gold bankets. +2. Deposits of the fissure vein type, such as California quartz veins. +3. Replacement or impregnation deposits on the lines of fissuring + or otherwise. + +In a general way, the uniformity of conditions of deposition in +the first class has resulted in the most satisfactory continuity of +ore and of its metal contents. In the second, depending much upon +the profundity of the earth movements involved, there is laterally +and vertically a reasonable basis for expectation of continuity +but through much less distance than in the first class. + +The third class of deposits exhibits widely different phenomena +as to continuity and no generalization is of any value. In gold +deposits of this type in West Australia, Colorado, and Nevada, +continuity far beyond a sampled face must be received with the +greatest skepticism. Much the same may be said of most copper +replacements in limestone. On the other hand the most phenomenal +regularity of values have been shown in certain Utah and Arizona +copper mines, the result of secondary infiltration in porphyritic +gangues. The Mississippi Valley lead and zinc deposits, while irregular +in detail, show remarkable continuity by way of reoccurrence over +wide areas. The estimation of the prospective value of mines where +continuity of production is dependent on reoccurrence of ore-bodies +somewhat proportional to the area, such as these Mississippi deposits +or to some extent as in Cobalt silver veins, is an interesting +study, but one that offers little field for generalization. + +THE POSITION OF THE OPENINGS IN RELATION TO SECONDARY ALTERATION.--The +profound alteration of the upper section of ore-deposits by oxidation +due to the action of descending surface waters, and their associated +chemical agencies, has been generally recognized for a great many +years. Only recently, however, has it been appreciated that this +secondary alteration extends into the sulphide zone as well. The +bearing of the secondary alteration, both in the oxidized and upper +sulphide zones, is of the most sweeping economic character. In +considering extension of values in depth, it demands the most rigorous +investigation. Not only does the metallurgical character of the ores +change with oxidation, but the complex reactions due to descending +surface waters cause leaching and a migration of metals from one +horizon to another lower down, and also in many cases a redistribution +of their sequence in the upper zones of the deposit. + +The effect of these agencies has been so great in many cases as +to entirely alter the character of the mine and extension in depth +has necessitated a complete reëquipment. For instance, the Mt. +Morgan gold mine, Queensland, has now become a copper mine; the +copper mines at Butte were formerly silver mines; Leadville has +become largely a zinc producer instead of lead. + +From this alteration aspect ore-deposits may be considered to have +four horizons:-- + +1. The zone near the outcrop, where the dominating feature + is oxidation and leaching of the soluble minerals. +2. A lower horizon, still in the zone of oxidation, where the + predominant feature is the deposition of metals as native, + oxides, and carbonates. +3. The upper horizon of the sulphide zone, where the special + feature is the enrichment due to secondary deposition + as sulphides. +4. The region below these zones of secondary alteration, where + the deposit is in its primary state. + +These zones are seldom sharply defined, nor are they always all +in evidence. How far they are in evidence will depend, among other +things, upon the amount and rapidity of erosion, the structure and +mineralogical character of the deposit, and upon the enclosing +rock. + +If erosion is extremely rapid, as in cold, wet climates, and rough +topography, or as in the case of glaciation of the Lake copper +deposits, denudation follows close on the heels of alteration, +and the surface is so rapidly removed that we may have the primary +ore practically at the surface. Flat, arid regions present the +other extreme, for denudation is much slower, and conditions are +most perfect for deep penetration of oxidizing agencies, and the +consequent alteration and concentration of the metals. + +The migration of metals from the top of the oxidized zone leaves +but a barren cap for erosion. The consequent effect of denudation +that lags behind alteration is to raise slowly the concentrated +metals toward the surface, and thus subject them to renewed attack +and repeated migration. In this manner we can account for the enormous +concentration of values in the lower oxidized and upper sulphide +zones overlying very lean sulphides in depth. + +Some minerals are more freely soluble and more readily precipitated +than others. From this cause there is in complex metal deposits a +rearrangement of horizontal sequence, in addition to enrichment at +certain horizons and impoverishment at others. The whole subject +is one of too great complexity for adequate consideration in this +discussion. No engineer is properly equipped to give judgment on +extension in depth without a thorough grasp of the great principles +laid down by Van Hise, Emmons, Lindgren, Weed, and others. We may, +however, briefly examine some of the theoretical effects of such +alteration. + +Zinc, iron, and lead sulphides are a common primary combination. +These metals are rendered soluble from their usual primary forms +by oxidizing agencies, in the order given. They reprecipitate as +sulphides in the reverse sequence. The result is the leaching of +zinc and iron readily in the oxidized zone, thus differentially +enriching the lead which lags behind, and a further extension of +the lead horizon is provided by the early precipitation of such +lead as does migrate. Therefore, the lead often predominates in +the second and the upper portion of the third zone, with the zinc +and iron below. Although the action of all surface waters is toward +oxidation and carbonation of these metals, the carbonate development +of oxidized zones is more marked when the enclosing rocks are +calcareous. + +In copper-iron deposits, the comparatively easy decomposition and +solubility and precipitation of the copper and some iron salts +generally result in more extensive impoverishment of these metals +near the surface, and more predominant enrichment at a lower horizon +than is the case with any other metals. The barren "iron hat" at the +first zone, the carbonates and oxides at the second, the enrichment +with secondary copper sulphides at the top of the third, and the +occurrence of secondary copper-iron sulphides below, are often +most clearly defined. In the easy recognition of the secondary +copper sulphides, chalcocite, bornite, etc., the engineer finds a +finger-post on the road to extension in depth; and the directions +upon this post are not to be disregarded. The number of copper +deposits enriched from unpayability in the first zone to a profitable +character in the next two, and unpayability again in the fourth, +is legion. + +Silver occurs most abundantly in combination with either lead, +copper, iron, or gold. As it resists oxidation and solution more +strenuously than copper and iron, its tendency when in combination +with them is to lag behind in migration. There is thus a differential +enrichment of silver in the upper two zones, due to the reduction +in specific gravity of the ore by the removal of associated metals. +Silver does migrate somewhat, however, and as it precipitates more +readily than copper, lead, zinc, or iron, its tendency when in +combination with them is towards enrichment above the horizons of +enrichment of these metals. When it is in combination with lead +and zinc, its very ready precipitation from solution by the galena +leaves it in combination more predominantly with the lead. The +secondary enrichment of silver deposits at the top of the sulphide +zone is sometimes a most pronounced feature, and it seems to be +the explanation of the origin of many "bonanzas." + +In gold deposits, the greater resistance to solubility of this +metal than most of the others, renders the phenomena of migration to +depth less marked. Further than this, migration is often interfered +with by the more impervious quartz matrix of many gold deposits. +Where gold is associated with large quantities of base metals, +however, the leaching of the latter in the oxidized zone leaves the +ore differentially richer, and as gold is also slightly soluble, +in such cases the migration of the base metals does carry some of +the gold. In the instance especially of impregnation or replacement +deposits, where the matrix is easily permeable, the upper sulphide +zone is distinctly richer than lower down, and this enrichment is +accompanied by a considerable increase in sulphides and tellurides. +The predominant characteristic of alteration in gold deposits is, +however, enrichment in the oxidized zone with the maximum values +near the surface. The reasons for this appear to be that gold in its +resistance to oxidation and wholesale migration gives opportunities +to a sort of combined mechanical and chemical enrichment. + +In dry climates, especially, the gentleness of erosion allows of +more thorough decomposition of the outcroppings, and a mechanical +separation of the gold from the detritus. It remains on or near +the deposit, ready to be carried below, mechanically or otherwise. +In wet climates this is less pronounced, for erosion bears away +the croppings before such an extensive decomposition and freeing +of the gold particles. The West Australian gold fields present an +especially prominent example of this type of superficial enrichment. +During the last fifteen years nearly eight hundred companies have +been formed for working mines in this region. Although from four +hundred of these high-grade ore has been produced, some thirty-three +only have ever paid dividends. The great majority have been unpayable +below oxidation,--a distance of one or two hundred feet. The writer's +unvarying experience with gold is that it is richer in the oxidized +zone than at any point below. While cases do occur of gold deposits +richer in the upper sulphide zone than below, even the upper sulphides +are usually poorer than the oxidized region. In quartz veins +preëminently, evidence of enrichment in the third zone is likely +to be practically absent. + +Tin ores present an anomaly among the base metals under discussion, +in that the primary form of this metal in most workable deposits +is an oxide. Tin in this form is most difficult of solution from +ground agencies, as witness the great alluvial deposits, often of +considerable geologic age. In consequence the phenomena of migration +and enrichment are almost wholly absent, except such as are due +to mechanical penetration of tin from surface decomposition of +the matrix akin to that described in gold deposits. + +In general, three or four essential facts from secondary alteration +must be kept in view when prognosticating extensions. + + Oxidation usually alters treatment problems, and oxidized ore + of the same grade as sulphides can often be treated more cheaply. + This is not universal. Low-grade ores of lead, copper, and zinc + may be treatable by concentration when in the form of sulphides, + and may be valueless when oxidized, even though of the same grade. + + Copper ores generally show violent enrichment at the base of the + oxidized, and at the top of the sulphide zone. + + Lead-zinc ores show lead enrichment and zinc impoverishment in + the oxidized zone but have usually less pronounced enrichment + below water level than copper. The rearrangement of the metals + by the deeper migration of the zinc, also renders them + metallurgically of less value with depth. + + Silver deposits are often differentially enriched in the oxidized + zone, and at times tend to concentrate in the upper sulphide zone. + + Gold deposits usually decrease in value from the surface through + the whole of the three alteration zones. + +SIZE OF DEPOSITS.--The proverb of a relation between extension +in depth and size of ore-bodies expresses one of the oldest of +miners' beliefs. It has some basis in experience, especially in +fissure veins, but has little foundation in theory and is applicable +over but limited areas and under limited conditions. + +From a structural view, the depth of fissuring is likely to be more +or less in proportion to its length and breadth and therefore the +volume of vein filling with depth is likely to be proportional to +length and width of the fissure. As to the distribution of values, +if we eliminate the influence of changing wall rocks, or other +precipitating agencies which often cause the values to arrange +themselves in "floors," and of secondary alteration, there may be +some reason to assume distribution of values of an extent equal +vertically to that displayed horizontally. There is, as said, more +reason in experience for this assumption than in theory. A study +of the shape of a great many ore-shoots in mines of fissure type +indicates that when the ore-shoots or ore-bodies are approaching +vertical exhaustion they do not end abruptly, but gradually shorten +and decrease in value, their bottom boundaries being more often +wedge-shaped than even lenticular. If this could be taken as the usual +occurrence, it would be possible (eliminating the evident exceptions +mentioned above) to state roughly that the minimum extension of an +ore-body or ore-shoot in depth below any given horizon would be +a distance represented by a radius equal to one-half its length. By +length is not meant necessarily the length of a horizontal section, +but of one at right angles to the downward axis. + +On these grounds, which have been reënforced by much experience among +miners, the probabilities of extension are somewhat in proportion +to the length and width of each ore-body. For instance, in the A +mine, with an ore-shoot 1000 feet long and 10 feet wide, on its +bottom level, the minimum extension under this hypothesis would +be a wedge-shaped ore-body with its deepest point 500 feet below +the lowest level, or a minimum of say 200,000 tons. Similarly, +the B mine with five ore-bodies, each 300 hundred feet long and +10 feet wide, exposed on its lowest level, would have a minimum of +five wedges 100 feet deep at their deepest points, or say 50,000 +tons. This is not proposed as a formula giving the total amount of +extension in depth, but as a sort of yardstick which has experience +behind it. This experience applies in a much less degree to deposits +originating from impregnation along lines of fissuring and not at +all to replacements. + +DEVELOPMENT IN NEIGHBORING MINES.--Mines of a district are usually +found under the same geological conditions, and show somewhat the same +habits as to extension in depth or laterally, and especially similar +conduct of ore-bodies and ore-shoots. As a practical criterion, one +of the most intimate guides is the actual development in adjoining +mines. For instance, in Kalgoorlie, the Great Boulder mine is (March, +1908) working the extension of Ivanhoe lodes at points 500 feet +below the lowest level in the Ivanhoe; likewise, the Block 10 lead +mine at Broken Hill is working the Central ore-body on the Central +boundary some 350 feet below the Central workings. Such facts as +these must have a bearing on assessing the downward extension. + +DEPTH OF EXHAUSTION.--All mines become completely exhausted at +some point in depth. Therefore the actual distance to which ore +can be expected to extend below the lowest level grows less with +every deeper working horizon. The really superficial character of +ore-deposits, even outside of the region of secondary enrichment +is becoming every year better recognized. The prospector's idea +that "she gets richer deeper down," may have some basis near the +surface in some metals, but it is not an idea which prevails in +the minds of engineers who have to work in depth. The writer, with +some others, prepared a list of several hundred dividend-paying +metal mines of all sorts, extending over North and South America, +Australasia, England, and Africa. Notes were made as far as possible +of the depths at which values gave out, and also at which dividends +ceased. Although by no means a complete census, the list indicated +that not 6% of mines (outside banket) that have yielded profits, +ever made them from ore won below 2000 feet. Of mines that paid +dividends, 80% did not show profitable value below 1500 feet, and +a sad majority died above 500. Failures at short depths may be +blamed upon secondary enrichment, but the majority that reached +below this influence also gave out. The geological reason for such +general unseemly conduct is not so evident. + +CONCLUSION.--As a practical problem, the assessment of prospective +value is usually a case of "cut and try." The portion of the capital +to be invested, which depends upon extension, will require so many +tons of ore of the same value as that indicated by the standing +ore, in order to justify the price. To produce this tonnage at +the continued average size of the ore-bodies will require their +extension in depth so many feet--or the discovery of new ore-bodies +of a certain size. The five geological weights mentioned above +may then be put into the scale and a basis of judgment reached. + + + + +CHAPTER IV. + +Mine Valuation (_Continued_). + +RECOVERABLE PERCENTAGE OF THE GROSS ASSAY VALUE; PRICE OF METALS; +COST OF PRODUCTION. + +The method of treatment for the ore must be known before a mine +can be valued, because a knowledge of the recoverable percentage +is as important as that of the gross value of the ore itself. The +recoverable percentage is usually a factor of working costs. Practically +every ore can be treated and all the metal contents recovered, but +the real problem is to know the method and percentage of recovery +which will yield the most remunerative result, if any. This limit to +profitable recovery regulates the amount of metal which should be +lost, and the amount of metal which consequently must be deducted +from the gross value before the real net value of the ore can be +calculated. Here, as everywhere else in mining, a compromise has to +be made with nature, and we take what we can get--profitably. For +instance, a copper ore may be smelted and a 99% recovery obtained. +Under certain conditions this might be done at a loss, while the +same ore might be concentrated before smelting and yield a profit +with a 70% recovery. An additional 20% might be obtained by roasting +and leaching the residues from concentration, but this would probably +result in an expenditure far greater than the value of the 20% +recovered. If the ore is not already under treatment on the mine, +or exactly similar ore is not under treatment elsewhere, with known +results, the method must be determined experimentally, either by +the examining engineer or by a special metallurgist. + +Where partially treated products, such as concentrates, are to be +sold, not only will there be further losses, but deductions will +be made by the smelter for deleterious metals and other charges. +All of these factors must be found out,--and a few sample smelting +returns from a similar ore are useful. + +To cover the whole field of metallurgy and discuss what might apply, +and how it might apply, under a hundred supposititious conditions +would be too great a digression from the subject in hand. It is +enough to call attention here to the fact that the residues from +every treatment carry some metal, and that this loss has to be +deducted from the gross value of the ore in any calculations of +net values. + +PRICE OF METALS. + +Unfortunately for the mining engineer, not only has he to weigh +the amount of risk inherent in calculations involved in the mine +itself, but also that due to fluctuations in the value of metals. +If the ore is shipped to custom works, he has to contemplate also +variations in freights and smelting charges. Gold from the mine +valuer's point of view has no fluctuations. It alone among the +earth's products gives no concern as to the market price. The price +to be taken for all other metals has to be decided before the mine +can be valued. This introduces a further speculation and, as in +all calculations of probabilities, amounts to an estimate of the +amount of risk. In a free market the law of supply and demand governs +the value of metals as it does that of all other commodities. So +far, except for tariff walls and smelting rings, there is a free +market in the metals under discussion. + +The demand for metals varies with the unequal fluctuations of the +industrial tides. The sea of commercial activity is subject to +heavy storms, and the mine valuer is compelled to serve as weather +prophet on this ocean of trouble. High prices, which are the result +of industrial booms, bring about overproduction, and the collapse of +these begets a shrinkage of demand, wherein consequently the tide +of price turns back. In mining for metals each pound is produced +actually at a different cost. In case of an oversupply of base metals +the price will fall until it has reached a point where a portion of +the production is no longer profitable, and the equilibrium is +established through decline in output. However, in the backward +swing, due to lingering overproduction, prices usually fall lower +than the cost of producing even a much-diminished supply. There is +at this point what we may call the "basic" price, that at which +production is insufficient and the price rises again. The basic +price which is due to this undue backward swing is no more the +real price of the metal to be contemplated over so long a term +of years than is the highest price. At how much above the basic +price of depressed times the product can be safely expected to +find a market is the real question. Few mines can be bought or +valued at this basic price. An indication of what this is can be +gained from a study of fluctuations over a long term of years. + +It is common to hear the average price over an extended period +considered the "normal" price, but this basis for value is one which +must be used with discretion, for it is not the whole question when +mining. The "normal" price is the average price over a long term. +The lives of mines, and especially ore in sight, may not necessarily +enjoy the period of this "normal" price. The engineer must balance +his judgments by the immediate outlook of the industrial weather. +When lead was falling steadily in December, 1907, no engineer would +accept the price of that date, although it was then below "normal"; +his product might go to market even lower yet. + +It is desirable to ascertain what the basic and normal prices are, +for between them lies safety. Since 1884 there have been three cycles +of commercial expansion and contraction. If the average prices +are taken for these three cycles separately (1885-95), 1895-1902, +1902-08) it will be seen that there has been a steady advance in +prices. For the succeeding cycles lead on the London Exchange,[*] +the freest of the world's markets was £12 12_s._ 4_d._, £13 3_s._ +7_d._, and £17 7_s._ 0_d._ respectively; zinc, £17 14_s._ 10_d._, +£19 3_s._ 8_d._, and £23 3_s._ 0_d._; and standard copper, £48 16_s._ +0_d._, £59 10_s._ 0_d._, and £65 7_s._ 0_d._ It seems, therefore, +that a higher standard of prices can be assumed as the basic and +normal than would be indicated if the general average of, say, +twenty years were taken. During this period, the world's gold output +has nearly quadrupled, and, whether the quantitative theory of +gold be accepted or not, it cannot be denied that there has been +a steady increase in the price of commodities. In all base-metal +mining it is well to remember that the production of these metals +is liable to great stimulus at times from the discovery of new +deposits or new processes of recovery from hitherto unprofitable +ores. It is therefore for this reason hazardous in the extreme +to prophesy what prices will be far in the future, even when the +industrial weather is clear. But some basis must be arrived at, +and from the available outlook it would seem that the following +metal prices are justifiable for some time to come, provided the +present tariff schedules are maintained in the United States: + +[Footnote *: All London prices are based on the long ton of 2,240 +lbs. Much confusion exists in the copper trade as to the classification +of the metal. New York prices are quoted in electrolytic and "Lake"; +London's in "Standard." "Standard" has now become practically an +arbitrary term peculiar to London, for the great bulk of copper +dealt in is "electrolytic" valued considerably over "Standard."] + +========================================================================== + | Lead | Spelter | Copper | Tin | Silver + |------------|----------|----------|----------|--------------- + |London| N.Y.|Lon.| N.Y.|Lon.| N.Y.|Lon.| N.Y.| Lon. | N.Y. + | Ton |Pound|Ton |Pound|Ton |Pound|Ton |Pound|Per oz.|Per oz. +------------|------|-----|----|-----|----|-----|----|-----|-------|------- +Basic Price | £11. |$.035|£17 |$.040|£52 |$.115|£100|$.220| 22_d._|$.44 +Normal Price| 13.5| .043| 21 | .050| 65 | .140| 130| .290| 26 | .52 +========================================================================== + +In these figures the writer has not followed strict averages, but +has taken the general outlook combined with the previous records. +The likelihood of higher prices for lead is more encouraging than +for any other metal, as no new deposits of importance have come +forward for years, and the old mines are reaching considerable +depths. Nor does the frenzied prospecting of the world's surface +during the past ten years appear to forecast any very disturbing +developments. The zinc future is not so bright, for metallurgy +has done wonders in providing methods of saving the zinc formerly +discarded from lead ores, and enormous supplies will come forward +when required. The tin outlook is encouraging, for the supply from +a mining point of view seems unlikely to more than keep pace with +the world's needs. In copper the demand is growing prodigiously, +but the supplies of copper ores and the number of copper mines +that are ready to produce whenever normal prices recur was never +so great as to-day. One very hopeful fact can be deduced for the +comfort of the base metal mining industry as a whole. If the growth +of demand continues through the next thirty years in the ratio of +the past three decades, the annual demand for copper will be over +3,000,000 tons, of lead over 1,800,000 tons, of spelter 2,800,000 +tons, of tin 250,000 tons. Where such stupendous amounts of these +metals are to come from at the present range of prices, and even +with reduced costs of production, is far beyond any apparent source +of supply. The outlook for silver prices is in the long run not +bright. As the major portion of the silver produced is a bye product +from base metals, any increase in the latter will increase the +silver production despite very much lower prices for the precious +metal. In the meantime the gradual conversion of all nations to +the gold standard seems a matter of certainty. Further, silver +may yet be abandoned as a subsidiary coinage inasmuch as it has +now but a token value in gold standard countries if denuded of +sentiment. + +COST OF PRODUCTION. + +It is hardly necessary to argue the relative importance of the +determination of the cost of production and the determination of +the recoverable contents of the ore. Obviously, the aim of mine +valuation is to know the profits to be won, and the profit is the +value of the metal won, less the cost of production. + +The cost of production embraces development, mining, treatment, +management. Further than this, it is often contended that, as the +capital expended in purchase and equipment must be redeemed within +the life of the mine, this item should also be included in production +costs. It is true that mills, smelters, shafts, and all the +paraphernalia of a mine are of virtually negligible value when it +is exhausted; and that all mines are exhausted sometime and every +ton taken out contributes to that exhaustion; and that every ton of +ore must bear its contribution to the return of the investment, +as well as profit upon it. Therefore it may well be said that the +redemption of the capital and its interest should be considered +in costs per ton. The difficulty in dealing with the subject from +the point of view of production cost arises from the fact that, +except possibly in the case of banket gold and some conglomerate +copper mines, the life of a metal mine is unknown beyond the time +required to exhaust the ore reserves. The visible life at the time +of purchase or equipment may be only three or four years, yet the +average equipment has a longer life than this, and the anticipation +for every mine is also for longer duration than the bare ore in sight. +For clarity of conclusions in mine valuation the most advisable +course is to determine the profit in sight irrespective of capital +redemption in the first instance. The questions of capital redemption, +purchase price, or equipment cost can then be weighed against the +margin of profit. One phase of redemption will be further discussed +under "Amortization of Capital" and "Ratio of Output to the Mine." + +The cost of production depends upon many things, such as the cost of +labor, supplies, the size of the ore-body, the treatment necessary, +the volume of output, etc.; and to discuss them all would lead +into a wilderness of supposititious cases. If the mine is a going +concern, from which reliable data can be obtained, the problem is +much simplified. If it is virgin, the experience of other mines +in the same region is the next resource; where no such data can be +had, the engineer must fall back upon the experience with mines +still farther afield. Use is sometimes made of the "comparison ton" +in calculating costs upon mines where data of actual experience +are not available. As costs will depend in the main upon items +mentioned above, if the known costs of a going mine elsewhere be +taken as a basis, and subtractions and additions made for more +unfavorable or favorable effect of the differences in the above +items, a fairly close result can be approximated. + +Mine examinations are very often inspired by the belief that extended +operations or new metallurgical applications to the mine will expand +the profits. In such cases the paramount questions are the reduction +of costs by better plant, larger outputs, new processes, or alteration +of metallurgical basis and better methods. If every item of previous +expenditure be gone over and considered, together with the equipment, +and method by which it was obtained, the possible savings can be +fairly well deduced, and justification for any particular line +of action determined. One view of this subject will be further +discussed under "Ratio of Output to the Mine." The conditions which +govern the working costs are on every mine so special to itself, +that no amount of advice is very useful. Volumes of advice have +been published on the subject, but in the main their burden is +not to underestimate. + +In considering the working costs of base-metal mines, much depends +upon the opportunity for treatment in customs works, smelters, +etc. Such treatment means a saving of a large portion of equipment +cost, and therefore of the capital to be invested and subsequently +recovered. The economics of home treatment must be weighed against +the sum which would need to be set aside for redemption of the +plant, and unless there is a very distinct advantage to be had by +the former, no risks should be taken. More engineers go wrong by +the erection of treatment works where other treatment facilities +are available, than do so by continued shipping. There are many +mines where the cost of equipment could never be returned, and +which would be valueless unless the ore could be shipped. Another +phase of foreign treatment arises from the necessity or advantage +of a mixture of ores,--the opportunity of such mixtures often gives +the public smelter an advantage in treatment with which treatment +on the mine could never compete. + +Fluctuation in the price of base metals is a factor so much to be +taken into consideration, that it is desirable in estimating mine +values to reduce the working costs to a basis of a "per unit" of +finished metal. This method has the great advantage of indicating +so simply the involved risks of changing prices that whoso runs +may read. Where one metal predominates over the other to such an +extent as to form the "backbone" of the value of the mine, the +value of the subsidiary metals is often deducted from the cost of +the principal metal, in order to indicate more plainly the varying +value of the mine with the fluctuating prices of the predominant +metal. For example, it is usual to state that the cost of copper +production from a given ore will be so many cents per pound, or so +many pounds sterling per ton. Knowing the total metal extractable +from the ore in sight, the profits at given prices of metal can +be readily deduced. The point at which such calculation departs +from the "per-ton-of-ore" unto the per-unit-cost-of-metal basis, +usually lies at the point in ore dressing where it is ready for the +smelter. To take a simple case of a lead ore averaging 20%: this +is to be first concentrated and the lead reduced to a concentrate +averaging 70% and showing a recovery of 75% of the total metal +content. The cost per ton of development, mining, concentration, +management, is to this point say $4 per ton of original crude ore. +The smelter buys the concentrate for 95% of the value of the metal, +less the smelting charge of $15 per ton, or there is a working +cost of a similar sum by home equipment. In this case 4.66 tons of +ore are required to produce one ton of concentrates, and therefore +each ton of concentrates costs $18.64. This amount, added to the +smelting charge, gives a total of $33.64 for the creation of 70% +of one ton of finished lead, or equal to 2.40 cents per pound which +can be compared with the market price less 5%. If the ore were +to contain 20 ounces of silver per ton, of which 15 ounces were +recovered into the leady concentrates, and the smelter price for +the silver were 50 cents per ounce, then the $7.50 thus recovered +would be subtracted from $33.64, making the apparent cost of the +lead 1.86 cents per pound. + + + + +CHAPTER V. + +Mine Valuation (_Continued_). + +REDEMPTION OR AMORTIZATION OF CAPITAL AND INTEREST. + +It is desirable to state in some detail the theory of amortization +before consideration of its application in mine valuation. + +As every mine has a limited life, the capital invested in it must +be redeemed during the life of the mine. It is not sufficient that +there be a bare profit over working costs. In this particular, +mines differ wholly from many other types of investment, such as +railways. In the latter, if proper appropriation is made for +maintenance, the total income to the investor can be considered as +interest or profit; but in mines, a portion of the annual income +must be considered as a return of capital. Therefore, before the +yield on a mine investment can be determined, a portion of the +annual earnings must be set aside in such a manner that when the +mine is exhausted the original investment will have been restored. +If we consider the date due for the return of the capital as the time +when the mine is exhausted, we may consider the annual instalments +as payments before the due date, and they can be put out at compound +interest until the time for restoration arrives. If they be invested +in safe securities at the usual rate of about 4%, the addition of +this amount of compound interest will assist in the repayment of +the capital at the due date, so that the annual contributions to +a sinking fund need not themselves aggregate the total capital to +be restored, but may be smaller by the deficiency which will be +made up by their interest earnings. Such a system of redemption +of capital is called "Amortization." + +Obviously it is not sufficient for the mine investor that his capital +shall have been restored, but there is required an excess earning +over and above the necessities of this annual funding of capital. +What rate of excess return the mine must yield is a matter of the +risks in the venture and the demands of the investor. Mining business +is one where 7% above provision for capital return is an absolute +minimum demanded by the risks inherent in mines, even where the +profit in sight gives warranty to the return of capital. Where +the profit in sight (which is the only real guarantee in mine +investment) is below the price of the investment, the annual return +should increase in proportion. There are thus two distinct directions +in which interest must be computed,--first, the internal influence +of interest in the amortization of the capital, and second, the +percentage return upon the whole investment after providing for +capital return. + +There are many limitations to the introduction of such refinements +as interest calculations in mine valuation. It is a subject not +easy to discuss with finality, for not only is the term of years +unknown, but, of more importance, there are many factors of a highly +speculative order to be considered in valuing. It may be said that +a certain life is known in any case from the profit in sight, and +that in calculating this profit a deduction should be made from +the gross profit for loss of interest on it pending recovery. This +is true, but as mines are seldom dealt with on the basis of profit +in sight alone, and as the purchase price includes usually some +proportion for extension in depth, an unknown factor is introduced +which outweighs the known quantities. Therefore the application of +the culminative effect of interest accumulations is much dependent +upon the sort of mine under consideration. In most cases of uncertain +continuity in depth it introduces a mathematical refinement not +warranted by the speculative elements. For instance, in a mine +where the whole value is dependent upon extension of the deposit +beyond openings, and where an expected return of at least 50% per +annum is required to warrant the risk, such refinement would be +absurd. On the other hand, in a Witwatersrand gold mine, in gold +and tin gravels, or in massive copper mines such as Bingham and +Lake Superior, where at least some sort of life can be approximated, +it becomes a most vital element in valuation. + +In general it may be said that the lower the total annual return +expected upon the capital invested, the greater does the amount +demanded for amortization become in proportion to this total income, +and therefore the greater need of its introduction in calculations. +Especially is this so where the cost of equipment is large +proportionately to the annual return. Further, it may be said that +such calculations are of decreasing use with increasing proportion of +speculative elements in the price of the mine. The risk of extension in +depth, of the price of metal, etc., may so outweigh the comparatively +minor factors here introduced as to render them useless of attention. + +In the practical conduct of mines or mining companies, sinking +funds for amortization of capital are never established. In the +vast majority of mines of the class under discussion, the ultimate +duration of life is unknown, and therefore there is no basis upon +which to formulate such a definite financial policy even were it +desired. Were it possible to arrive at the annual sum to be set +aside, the stockholders of the mining type would prefer to do their +own reinvestment. The purpose of these calculations does not lie +in the application of amortization to administrative finance. It +is nevertheless one of the touchstones in the valuation of certain +mines or mining investments. That is, by a sort of inversion such +calculations can be made to serve as a means to expose the amount +of risk,--to furnish a yardstick for measuring the amount of risk +in the very speculations of extension in depth and price of metals +which attach to a mine. Given the annual income being received, +or expected, the problem can be formulated into the determination +of how many years it must be continued in order to amortize the +investment and pay a given rate of profit. A certain length of +life is evident from the ore in sight, which may be called the +life in sight. If the term of years required to redeem the capital +and pay an interest upon it is greater than the life in sight, +then this extended life must come from extension in depth, or ore +from other direction, or increased price of metals. If we then take +the volume and profit on the ore as disclosed we can calculate the +number of feet the deposit must extend in depth, or additional tonnage +that must be obtained of the same grade, or the different prices of +metal that must be secured, in order to satisfy the demanded term +of years. These demands in actual measure of ore or feet or higher +price can then be weighed against the geological and industrial +probabilities. + +The following tables and examples may be of assistance in these +calculations. + +Table 1. To apply this table, the amount of annual income or dividend +and the term of years it will last must be known or estimated factors. +It is then possible to determine the _present_ value of this annual +income after providing for amortization and interest on the investment +at various rates given, by multiplying the annual income by the +factor set out. + +A simple illustration would be that of a mine earning a profit of +$200,000 annually, and having a total of 1,000,000 tons in sight, +yielding a profit of $2 a ton, or a total profit in sight of $2,000,000, +thus recoverable in ten years. On a basis of a 7% return on the +investment and amortization of capital (Table I), the factor is +6.52 x $200,000 = $1,304,000 as the present value of the gross +profits exposed. That is, this sum of $1,304,000, if paid for the +mine, would be repaid out of the profit in sight, together with +7% interest if the annual payments into sinking fund earn 4%. + +TABLE I. + +Present Value of an Annual Dividend Over -- Years at --% and Replacing +Capital by Reinvestment of an Annual Sum at 4%. + +======================================================= + Years | 5% | 6% | 7% | 8% | 9% | 10% +-------|-------|-------|-------|-------|-------|------- + 1 | .95 | .94 | .93 | .92 | .92 | .91 + 2 | 1.85 | 1.82 | 1.78 | 1.75 | 1.72 | 1.69 + 3 | 2.70 | 2.63 | 2.56 | 2.50 | 2.44 | 2.38 + 4 | 3.50 | 3.38 | 3.27 | 3.17 | 3.07 | 2.98 + 5 | 4.26 | 4.09 | 3.93 | 3.78 | 3.64 | 3.51 + 6 | 4.98 | 4.74 | 4.53 | 4.33 | 4.15 | 3.99 + 7 | 5.66 | 5.36 | 5.09 | 4.84 | 4.62 | 4.41 + 8 | 6.31 | 5.93 | 5.60 | 5.30 | 5.04 | 4.79 + 9 | 6.92 | 6.47 | 6.08 | 5.73 | 5.42 | 5.14 + 10 | 7.50 | 6.98 | 6.52 | 6.12 | 5.77 | 5.45 + | | | | | | + 11 | 8.05 | 7.45 | 6.94 | 6.49 | 6.09 | 5.74 + 12 | 8.58 | 7.90 | 7.32 | 6.82 | 6.39 | 6.00 + 13 | 9.08 | 8.32 | 7.68 | 7.13 | 6.66 | 6.24 + 14 | 9.55 | 8.72 | 8.02 | 7.42 | 6.91 | 6.46 + 15 | 10.00 | 9.09 | 8.34 | 7.79 | 7.14 | 6.67 + 16 | 10.43 | 9.45 | 8.63 | 7.95 | 7.36 | 6.86 + 17 | 10.85 | 9.78 | 8.91 | 8.18 | 7.56 | 7.03 + 18 | 11.24 | 10.10 | 9.17 | 8.40 | 7.75 | 7.19 + 19 | 11.61 | 10.40 | 9.42 | 8.61 | 7.93 | 7.34 + 20 | 11.96 | 10.68 | 9.65 | 8.80 | 8.09 | 7.49 + | | | | | | + 21 | 12.30 | 10.95 | 9.87 | 8.99 | 8.24 | 7.62 + 22 | 12.62 | 11.21 | 10.08 | 9.16 | 8.39 | 7.74 + 23 | 12.93 | 11.45 | 10.28 | 9.32 | 8.52 | 7.85 + 24 | 13.23 | 11.68 | 10.46 | 9.47 | 8.65 | 7.96 + 25 | 13.51 | 11.90 | 10.64 | 9.61 | 8.77 | 8.06 + 26 | 13.78 | 12.11 | 10.80 | 9.75 | 8.88 | 8.16 + 27 | 14.04 | 12.31 | 10.96 | 9.88 | 8.99 | 8.25 + 28 | 14.28 | 12.50 | 11.11 | 10.00 | 9.09 | 8.33 + 29 | 14.52 | 12.68 | 11.25 | 10.11 | 9.18 | 8.41 + 30 | 14.74 | 12.85 | 11.38 | 10.22 | 9.27 | 8.49 + | | | | | | + 31 | 14.96 | 13.01 | 11.51 | 10.32 | 9.36 | 8.56 + 32 | 15.16 | 13.17 | 11.63 | 10.42 | 9.44 | 8.62 + 33 | 15.36 | 13.31 | 11.75 | 10.51 | 9.51 | 8.69 + 34 | 15.55 | 13.46 | 11.86 | 10.60 | 9.59 | 8.75 + 35 | 15.73 | 13.59 | 11.96 | 10.67 | 9.65 | 8.80 + 36 | 15.90 | 13.72 | 12.06 | 10.76 | 9.72 | 8.86 + 37 | 16.07 | 13.84 | 12.16 | 10.84 | 9.78 | 8.91 + 38 | 16.22 | 13.96 | 12.25 | 10.91 | 9.84 | 8.96 + 39 | 16.38 | 14.07 | 12.34 | 10.98 | 9.89 | 9.00 + 40 | 16.52 | 14.18 | 12.42 | 11.05 | 9.95 | 9.05 +======================================================= +Condensed from Inwood's Tables. + +Table II is practically a compound discount table. That is, by +it can be determined the present value of a fixed sum payable at +the end of a given term of years, interest being discounted at +various given rates. Its use may be illustrated by continuing the +example preceding. + +TABLE II. + +Present Value of $1, or £1, payable in -- Years, Interest taken +at --%. + +=================================== +Years | 4% | 5% | 6% | 7% +------|------|------|------|------- + 1 | .961 | .952 | .943 | .934 + 2 | .924 | .907 | .890 | .873 + 3 | .889 | .864 | .840 | .816 + 4 | .854 | .823 | .792 | .763 + 5 | .821 | .783 | .747 | .713 + 6 | .790 | .746 | .705 | .666 + 7 | .760 | .711 | .665 | .623 + 8 | .731 | .677 | .627 | .582 + 9 | .702 | .645 | .592 | .544 + 10 | .675 | .614 | .558 | .508 + | | | | + 11 | .649 | .585 | .527 | .475 + 12 | .625 | .557 | .497 | .444 + 13 | .600 | .530 | .469 | .415 + 14 | .577 | .505 | .442 | .388 + 15 | .555 | .481 | .417 | .362 + 16 | .534 | .458 | .394 | .339 + 17 | .513 | .436 | .371 | .316 + 18 | .494 | .415 | .350 | .296 + 19 | .475 | .396 | .330 | .276 + 20 | .456 | .377 | .311 | .258 + | | | | + 21 | .439 | .359 | .294 | .241 + 22 | .422 | .342 | .277 | .266 + 23 | .406 | .325 | .262 | .211 + 24 | .390 | .310 | .247 | .197 + 25 | .375 | .295 | .233 | .184 + 26 | .361 | .281 | .220 | .172 + 27 | .347 | .268 | .207 | .161 + 28 | .333 | .255 | .196 | .150 + 29 | .321 | .243 | .184 | .140 + 30 | .308 | .231 | .174 | .131 + | | | | + 31 | .296 | .220 | .164 | .123 + 32 | .285 | .210 | .155 | .115 + 33 | .274 | .200 | .146 | .107 + 34 | .263 | .190 | .138 | .100 + 35 | .253 | .181 | .130 | .094 + 36 | .244 | .172 | .123 | .087 + 37 | .234 | .164 | .116 | .082 + 38 | .225 | .156 | .109 | .076 + 39 | .216 | .149 | .103 | .071 + 40 | .208 | .142 | .097 | .067 +=================================== +Condensed from Inwood's Tables. + +If such a mine is not equipped, and it is assumed that $200,000 +are required to equip the mine, and that two years are required +for this equipment, the value of the ore in sight is still less, +because of the further loss of interest in delay and the cost of +equipment. In this case the present value of $1,304,000 in two +years, interest at 7%, the factor is .87 X 1,304,000 = $1,134,480. +From this comes off the cost of equipment, or $200,000, leaving +$934,480 as the present value of the profit in sight. A further +refinement could be added by calculating the interest chargeable +against the $200,000 equipment cost up to the time of production. + +TABLE III. +=========================================================================== + Annual | Number of years of life required to yield--% interest, and in + Rate of | addition to furnish annual instalments which, if reinvested at +Dividend.| 4% will return the original investment at the end of the period. +---------|----------------------------------------------------------------- + % | 5% | 6% | 7% | 8% | 9% | 10% + | | | | | | + 6 | 41.0 | | | | | + 7 | 28.0 | 41.0 | | | | + 8 | 21.6 | 28.0 | 41.0 | | | + 9 | 17.7 | 21.6 | 28.0 | 41.0 | | + 10 | 15.0 | 17.7 | 21.6 | 28.0 | 41.0 | + | | | | | | + 11 | 13.0 | 15.0 | 17.7 | 21.6 | 28.0 | 41.0 + 12 | 11.5 | 13.0 | 15.0 | 17.7 | 21.6 | 28.0 + 13 | 10.3 | 11.5 | 13.0 | 15.0 | 17.7 | 21.6 + 14 | 9.4 | 10.3 | 11.5 | 13.0 | 15.0 | 17.7 + 15 | 8.6 | 9.4 | 10.3 | 11.5 | 13.0 | 15.0 + | | | | | | + 16 | 7.9 | 8.6 | 9.4 | 10.3 | 11.5 | 13.0 + 17 | 7.3 | 7.9 | 8.6 | 9.4 | 10.3 | 11.5 + 18 | 6.8 | 7.3 | 7.9 | 8.6 | 9.4 | 10.3 + 19 | 6.4 | 6.8 | 7.3 | 7.9 | 8.6 | 9.4 + 20 | 6.0 | 6.4 | 6.8 | 7.3 | 7.9 | 8.6 + | | | | | | + 21 | 5.7 | 6.0 | 6.4 | 6.8 | 7.3 | 7.9 + 22 | 5.4 | 5.7 | 6.0 | 6.4 | 6.8 | 7.3 + 23 | 5.1 | 5.4 | 5.7 | 6.0 | 6.4 | 6.8 + 24 | 4.9 | 5.1 | 5.4 | 5.7 | 6.0 | 6.4 + 25 | 4.7 | 4.9 | 5.1 | 5.4 | 5.7 | 6.0 + | | | | | | + 26 | 4.5 | 4.7 | 4.9 | 5.1 | 5.4 | 5.7 + 27 | 4.3 | 4.5 | 4.7 | 4.9 | 5.1 | 5.4 + 28 | 4.1 | 4.3 | 4.5 | 4.7 | 4.9 | 5.1 + 29 | 3.9 | 4.1 | 4.3 | 4.5 | 4.7 | 4.9 + 30 | 3.8 | 3.9 | 4.1 | 4.3 | 4.5 | 4.7 +=========================================================================== + +Table III. This table is calculated by inversion of the factors +in Table I, and is the most useful of all such tables, as it is +a direct calculation of the number of years that a given rate of +income on the investment must continue in order to amortize the +capital (the annual sinking fund being placed at compound interest +at 4%) and to repay various rates of interest on the investment. The +application of this method in testing the value of dividend-paying +shares is very helpful, especially in weighing the risks involved in +the portion of the purchase or investment unsecured by the profit +in sight. Given the annual percentage income on the investment from +the dividends of the mine (or on a non-producing mine assuming a +given rate of production and profit from the factors exposed), by +reference to the table the number of years can be seen in which +this percentage must continue in order to amortize the investment +and pay various rates of interest on it. As said before, the ore +in sight at a given rate of exhaustion can be reduced to terms of +life in sight. This certain period deducted from the total term +of years required gives the life which must be provided by further +discovery of ore, and this can be reduced to tons or feet of extension +of given ore-bodies and a tangible position arrived at. The test +can be applied in this manner to the various prices which must +be realized from the base metal in sight to warrant the price. + +Taking the last example and assuming that the mine is equipped, +and that the price is $2,000,000, the yearly return on the price is +10%. If it is desired besides amortizing or redeeming the capital to +secure a return of 7% on the investment, it will be seen by reference +to the table that there will be required a life of 21.6 years. As the +life visible in the ore in sight is ten years, then the extensions +in depth must produce ore for 11.6 years longer--1,160,000 tons. If +the ore-body is 1,000 feet long and 13 feet wide, it will furnish +of gold ore 1,000 tons per foot of depth; hence the ore-body must +extend 1,160 feet deeper to justify the price. Mines are seldom so +simple a proposition as this example. There are usually probabilities +of other ore; and in the case of base metal, then variability of price +and other elements must be counted. However, once the extension +in depth which is necessary is determined for various assumptions +of metal value, there is something tangible to consider and to +weigh with the five geological weights set out in Chapter III. + +The example given can be expanded to indicate not only the importance +of interest and redemption in the long extension in depth required, +but a matter discussed from another point of view under "Ratio of +Output." If the plant on this mine were doubled and the earnings +increased to 20% ($400,000 per annum) (disregarding the reduction +in working expenses that must follow expansion of equipment), it +will be found that the life required to repay the purchase +money,--$2,000,000,--and 7% interest upon it, is about 6.8 years. + +As at this increased rate of production there is in the ore in +sight a life of five years, the extension in depth must be depended +upon for 1.8 years, or only 360,000 tons,--that is, 360 feet of +extension. Similarly, the present value of the ore in sight is +$268,000 greater if the mine be given double the equipment, for +thus the idle money locked in the ore is brought into the interest +market at an earlier date. Against this increased profit must be +weighed the increased cost of equipment. The value of low grade +mines, especially, is very much a factor of the volume of output +contemplated. + + + + +CHAPTER VI. + +Mine Valuation (_Concluded_). + +VALUATION OF MINES WITH LITTLE OR NO ORE IN SIGHT; VALUATIONS ON +SECOND-HAND DATA; GENERAL CONDUCT OF EXAMINATIONS; REPORTS. + +A large number of examinations arise upon prospecting ventures +or partially developed mines where the value is almost wholly +prospective. The risks in such enterprises amount to the possible loss +of the whole investment, and the possible returns must consequently +be commensurate. Such business is therefore necessarily highly +speculative, but not unjustifiable, as the whole history of the +industry attests; but this makes the matter no easier for the mine +valuer. Many devices of financial procedure assist in the limitation +of the sum risked, and offer a middle course to the investor between +purchase of a wholly prospective value and the loss of a possible +opportunity to profit by it. The usual form is an option to buy the +property after a period which permits a certain amount of development +work by the purchaser before final decision as to purchase. + +Aside from young mines such enterprises often arise from the possibility +of lateral extension of the ore-deposit outside the boundaries of +the property of original discovery (Fig. 3), in which cases there +is often no visible ore within the property under consideration +upon which to found opinion. In regions where vertical side lines +obtain, there is always the possibility of a "deep level" in inclined +deposits. Therefore the ground surrounding known deposits has a +certain speculative value, upon which engineers are often called to +pass judgment. Except in such unusual occurrences as South African +bankets, or Lake Superior coppers, prospecting for deep level of +extension is also a highly speculative phase of mining. + +The whole basis of opinion in both classes of ventures must be +the few geological weights,--the geology of the property and the +district, the development of surrounding mines, etc. In any event, +there is a very great percentage of risk, and the profit to be gained +by success must be, proportionally to the expenditure involved, +very large. It is no case for calculating amortization and other +refinements. It is one where several hundreds or thousands of per +cent hoped for on the investment is the only justification. + +OPINIONS AND VALUATIONS UPON SECOND-HAND DATA. + +Some one may come forward and deprecate the bare suggestion of an +engineer's offering an opinion when he cannot have proper first-hand +data. But in these days we have to deal with conditions as well as +theories of professional ethics. The growing ownership of mines +by companies, that is by corporations composed of many individuals, +and with their stocks often dealt in on the public exchanges, has +resulted in holders whose interest is not large enough to warrant +their undertaking the cost of exhaustive examinations. The system +has produced an increasing class of mining speculators and investors +who are finding and supplying the enormous sums required to work +our mines,--sums beyond the reach of the old-class single-handed +mining men. Every year the mining investors of the new order are +coming more and more to the engineer for advice, and they should +be encouraged, because such counsel can be given within limits, +and these limits tend to place the industry upon a sounder footing +of ownership. As was said before, the lamb can be in a measure +protected. The engineer's interest is to protect him, so that the +industry which concerns his own life-work may be in honorable repute, +and that capital may be readily forthcoming for its expansion. +Moreover, by constant advice to the investor as to what constitutes +a properly presented and managed project, the arrangement of such +proper presentation and management will tend to become an _a priori_ +function of the promoter. + +Sometimes the engineer can make a short visit to the mine for data +purposes,--more often he cannot. In the former case, he can resolve +for himself an approximation upon all the factors bearing on value, +except the quality of the ore. For this, aside from inspection of +the ore itself, a look at the plans is usually enlightening. A +longitudinal section of the mine showing a continuous shortening of +the stopes with each succeeding level carries its own interpretation. +In the main, the current record of past production and estimates +of the management as to ore-reserves, etc., can be accepted in +ratio to the confidence that can be placed in the men who present +them. It then becomes a case of judgment of men and things, and +here no rule applies. + +Advice must often be given upon data alone, without inspection +of the mine. Most mining data present internal evidence as to +credibility. The untrustworthy and inexperienced betray themselves +in their every written production. Assuming the reliability of data, +the methods already discussed for weighing the ultimate value of +the property can be applied. It would be possible to cite hundreds +of examples of valuation based upon second-hand data. Three will, +however, sufficiently illustrate. First, the R mine at Johannesburg. +With the regularity of this deposit, the development done, and +a study of the workings on the neighboring mines and in deeper +ground, it is a not unfair assumption that the reefs will maintain +size and value throughout the area. The management is sound, and +all the data are given in the best manner. The life of the mine +is estimated at six years, with some probabilities of further ore +from low-grade sections. The annual earnings available for dividends +are at the rate of about £450,000 per annum. The capital is £440,000 +in £1 shares. By reference to the table on page 46 it will be seen +that the present value of £450,000 spread over six years to return +capital at the end of that period, and give 7% dividends in the +meantime, is 4.53 x £450,000 = £2,036,500 ÷ 440,000 = £4 12_s_. +7_d_. per share. So that this mine, on the assumption of continuity +of values, will pay about 7% and return the price. Seven per cent +is, however, not deemed an adequate return for the risks of labor +troubles, faults, dykes, or poor patches. On a 9% basis, the mine +is worth about £4 4_s_. per share. + +Second, the G mine in Nevada. It has a capital of $10,000,000 in +$1 shares, standing in the market at 50 cents each. The reserves +are 250,000 tons, yielding a profit for yearly division of $7 per +ton. It has an annual capacity of about 100,000 tons, or $700,000 +net profit, equal to 14% on the market value. In order to repay +the capital value of $5,000,000 and 8% per annum, it will need +a life of (Table III) 13 years, of which 2-1/2 are visible. The +size of the ore-bodies indicates a yield of about 1,100 tons per +foot of depth. At an exhaustion rate of 100,000 tons per annum, +the mine would need to extend to a depth of over a thousand feet +below the present bottom. There is always a possibility of finding +parallel bodies or larger volumes in depth, but it would be a sanguine +engineer indeed who would recommend the stock, even though it pays +an apparent 14%. + +Third, the B mine, with a capital of $10,000,000 in 2,000,000 shares +of $5 each. The promoters state that the mine is in the slopes of +the Andes in Peru; that there are 6,000,000 tons of "ore blocked +out"; that two assays by the assayers of the Bank of England average +9% copper; that the copper can be produced at five cents per pound; +that there is thus a profit of $10,000,000 in sight. The evidences +are wholly incompetent. It is a gamble on statements of persons +who have not the remotest idea of sound mining. + +GENERAL CONDUCT OF EXAMINATION. + +Complete and exhaustive examination, entailing extensive sampling, +assaying, and metallurgical tests, is very expensive and requires +time. An unfavorable report usually means to the employer absolute +loss of the engineer's fee and expenses. It becomes then the initial +duty of the latter to determine at once, by the general conditions +surrounding the property, how far the expenditure for exhaustive +examination is warranted. There is usually named a money valuation +for the property, and thus a peg is afforded upon which to hang +conclusions. Very often collateral factors with a preliminary sampling, +or indeed no sampling at all, will determine the whole business. +In fact, it is becoming very common to send younger engineers to +report as to whether exhaustive examination by more expensive men +is justified. + +In the course of such preliminary inspection, the ore-bodies may +prove to be too small to insure adequate yield on the price, even +assuming continuity in depth and represented value. They may be +so difficult to mine as to make costs prohibitive, or they may +show strong signs of "petering out." The ore may present visible +metallurgical difficulties which make it unprofitable in any event. +A gold ore may contain copper or arsenic, so as to debar cyanidation, +where this process is the only hope of sufficiently moderate costs. +A lead ore may be an amorphous compound with zinc, and successful +concentration or smelting without great penalties may be precluded. +A copper ore may carry a great excess of silica and be at the same +time unconcentratable, and there may be no base mineral supply +available for smelting mixture. The mine may be so small or so +isolated that the cost of equipment will never be justified. Some +of these conditions may be determined as unsurmountable, assuming +a given value for the ore, and may warrant the rejection of the +mine at the price set. + +It is a disagreeable thing to have a disappointed promoter heap +vituperation on an engineer's head because he did not make an exhaustive +examination. Although it is generally desirable to do some sampling +to give assurance to both purchaser and vendor of conscientiousness, +a little courage of conviction, when this is rightly and adequately +grounded, usually brings its own reward. + +Supposing, however, that conditions are right and that the mine is +worth the price, subject to confirmation of values, the determination +of these cannot be undertaken unless time and money are available +for the work. As was said, a sampling campaign is expensive, and +takes time, and no engineer has the moral right to undertake an +examination unless both facilities are afforded. Curtailment is +unjust, both to himself and to his employer. + +How much time and outlay are required to properly sample a mine +is obviously a question of its size, and the character of its ore. +An engineer and one principal assistant can conduct two sampling +parties. In hard rock it may be impossible to take more than five +samples a day for each party. But, in average ore, ten samples for +each is reasonable work. As the number of samples is dependent +upon the footage of openings on the deposit, a rough approximation +can be made in advance, and a general idea obtained as to the time +required. This period must be insisted upon. + +REPORTS. + +Reports are to be read by the layman, and their first qualities +should be simplicity of terms and definiteness of conclusions. +Reports are usually too long, rather than too short. The essential +facts governing the value of a mine can be expressed on one sheet +of paper. It is always desirable, however, that the groundwork data +and the manner of their determination should be set out with such +detail that any other engineer could come to the same conclusion +if he accepted the facts as accurately determined. In regard to the +detailed form of reports, the writer's own preference is for a single +page summarizing the main factors, and an assay plan, reduced to a +longitudinal section where possible. Then there should be added, +for purposes of record and for submission to other engineers, a +set of appendices going into some details as to the history of +the mine, its geology, development, equipment, metallurgy, and +management. A list of samples should be given with their location, +and the tonnages and values of each separate block. A presentation +should be made of the probabilities of extension in depth, together +with recommendations for working the mine. + +GENERAL SUMMARY. + +The bed-rock value which attaches to a mine is the profit to be +won from proved ore and in which the price of metal is calculated +at some figure between "basic" and "normal." This we may call the +"_A_" value. Beyond this there is the speculative value of the +mine. If the value of the "probable" ore be represented by _X_, +the value of extension of the ore by _Y_, and a higher price for +metal than the price above assumed represented by _Z_, then if +the mine be efficiently managed the value of the mine is _A_ + +_X_ + _Y_ + _Z_. What actual amounts should be attached to _X, +Y, Z_ is a matter of judgment. There is no prescription for good +judgment. Good judgment rests upon a proper balancing of evidence. +The amount of risk in _X, Y, Z_ is purely a question of how much +these factors are required to represent in money,--in effect, how +much more ore must be found, or how many feet the ore must extend +in depth; or in convertible terms, what life in years the mine +must have, or how high the price of metal must be. In forming an +opinion whether these requirements will be realized, _X, Y, Z_ +must be balanced in a scale whose measuring standards are the five +geological weights and the general industrial outlook. The wise +engineer will put before his clients the scale, the weights, and +the conclusion arrived at. The shrewd investor will require to +know these of his adviser. + + + + +CHAPTER VII. + +Development of Mines. + +ENTRY TO THE MINE; TUNNELS; VERTICAL, INCLINED, AND COMBINED SHAFTS; +LOCATION AND NUMBER OF SHAFTS. + +Development is conducted for two purposes: first, to search for +ore; and second, to open avenues for its extraction. Although both +objects are always more or less in view, the first predominates +in the early life of mines, the prospecting stage, and the second +in its later life, the producing stage. It is proposed to discuss +development designed to embrace extended production purposes first, +because development during the prospecting stage is governed by +the same principles, but is tempered by the greater degree of +uncertainty as to the future of the mine, and is, therefore, of +a more temporary character. + +ENTRY TO THE MINE. + +There are four methods of entry: by tunnel, vertical shaft, inclined +shaft, or by a combination of the last two, that is, by a shaft +initially vertical then turned to an incline. Combined shafts are +largely a development of the past few years to meet "deep level" +conditions, and have been rendered possible only by skip-winding. The +angle in such shafts (Fig. 2) is now generally made on a parabolic +curve, and the speed of winding is then less diminished by the +bend. + +The engineering problems which present themselves under "entry" +may be divided into those of:-- + + 1. Method. + 2. Location. + 3. Shape and size. + +The resolution of these questions depends upon the:-- + + a. Degree of dip of the deposit. + b. Output of ore to be provided for. + c. Depth at which the deposit is to be attacked. + d. Boundaries of the property. + e. Surface topography. + f. Cost. + g. Operating efficiency. + h. Prospects of the mine. + +[Illustration: Fig. 2.--Showing arrangement of the bend in combined +shafts.] + +From the point of view of entrance, the coöperation of a majority +of these factors permits the division of mines into certain broad +classes. The type of works demanded for moderate depths (say vertically +2,500 to 3,000 feet) is very different from that required for great +depths. To reach great depths, the size of shafts must greatly +expand, to provide for extended ventilation, pumping, and winding +necessities. Moreover inclined shafts of a degree of flatness possible +for moderate depths become too long to be used economically from +the surface. The vast majority of metal-mining shafts fall into +the first class, those of moderate depths. Yet, as time goes on +and ore-deposits are exhausted to lower planes, problems of depth +will become more common. One thing, however, cannot be too much +emphasized, especially on mines to be worked from the outcrop, and +that is, that no engineer is warranted, owing to the speculation +incidental to extension in depth, in initiating early in the mine's +career shafts of such size or equipment as would be available for +great depths. Moreover, the proper location of a shaft so as to +work economically extension of the ore-bodies is a matter of no +certainty, and therefore shafts of speculative mines are tentative +in any event. + +Another line of division from an engineering view is brought about +by a combination of three of the factors mentioned. This is the +classification into "outcrop" and "deep-level" mines. The former +are those founded upon ore-deposits to be worked from or close +to the surface. The latter are mines based upon the extension in +depth of ore-bodies from outcrop mines. Such projects are not so +common in America, where the law in most districts gives the outcrop +owner the right to follow ore beyond his side-lines, as in countries +where the boundaries are vertical on all sides. They do, however, +arise not alone in the few American sections where the side-lines +are vertical boundaries, but in other parts owing to the pitch of +ore-bodies through the end lines (Fig. 3). More especially do such +problems arise in America in effect, where the ingress questions +have to be revised for mines worked out in the upper levels (Fig. +7). + +[Illustration: Fig. 3.--Longitudinal section showing "deep level" +project arising from dip of ore-body through end-line.] + +If from a standpoint of entrance questions, mines are first classified +into those whose works are contemplated for moderate depths, and those +in which work is contemplated for great depth, further clarity in +discussion can be gained by subdivision into the possible cases arising +out of the factors of location, dip, topography, and boundaries. + +MINES OF MODERATE DEPTHS. + +Case I. Deposits where topographic conditions permit the + alternatives of shaft or tunnel. +Case II. Vertical or horizontal deposits, the only practical + means of attaining which is by a vertical shaft. +Case III. Inclined deposits to be worked from near the surface. + There are in such instances the alternatives of either + a vertical or an inclined shaft. +Case IV. Inclined deposits which must be attacked in depth, + that is, deep-level projects. There are the alternatives + of a compound shaft or of a vertical shaft, and + in some cases of an incline from the surface. + +MINES TO GREAT DEPTHS. + +Case V. Vertical or horizontal deposits, the only way of reaching + which is by a vertical shaft. +Case VI. Inclined deposits. In such cases the alternatives are + a vertical or a compound shaft. + +CASE I.--Although for logical arrangement tunnel entry has been +given first place, to save repetition it is proposed to consider +it later. With few exceptions, tunnels are a temporary expedient +in the mine, which must sooner or later be opened by a shaft. + +CASE II. VERTICAL OR HORIZONTAL DEPOSITS.--These require no discussion +as to manner of entry. There is no justifiable alternative to a +vertical shaft (Fig. 4). + +[Illustration: Fig. 4.--Cross-sections showing entry to vertical +or horizontal deposits. Case II.] + +[Illustration: Fig. 5.--Cross-section showing alternative shafts +to inclined deposit to be worked from surface. Case III.] + +CASE III. INCLINED DEPOSITS WHICH ARE INTENDED TO BE WORKED FROM +THE OUTCROP, OR FROM NEAR IT (Fig. 5).--The choice of inclined or +vertical shaft is dependent upon relative cost of construction, +subsequent operation, and the useful life of the shaft, and these +matters are largely governed by the degree of dip. Assuming a shaft +of the same size in either alternative, the comparative cost per +foot of sinking is dependent largely on the breaking facilities +of the rock under the different directions of attack. In this, +the angles of the bedding or joint planes to the direction of the +shaft outweigh other factors. The shaft which takes the greatest +advantage of such lines of breaking weakness will be the cheapest +per foot to sink. In South African experience, where inclined shafts +are sunk parallel to the bedding planes of hard quartzites, the cost +per foot appears to be in favor of the incline. On the other hand, +sinking shafts across tight schists seems to be more advantageous +than parallel to the bedding planes, and inclines following the +dip cost more per foot than vertical shafts. + +An inclined shaft requires more footage to reach a given point +of depth, and therefore it would entail a greater total expense +than a vertical shaft, assuming they cost the same per foot. The +excess amount will be represented by the extra length, and this +will depend upon the flatness of the dip. With vertical shafts, +however, crosscuts to the deposit are necessary. In a comparative +view, therefore, the cost of the crosscuts must be included with +that of the vertical shaft, as they would be almost wholly saved +in an incline following near the ore. + +The factor of useful life for the shaft enters in deciding as to +the advisability of vertical shafts on inclined deposits, from the +fact that at some depth one of two alternatives has to be chosen. +The vertical shaft, when it reaches a point below the deposit where +the crosscuts are too long (_C_, Fig. 5), either becomes useless, +or must be turned on an incline at the intersection with the ore +(_B_). The first alternative means ultimately a complete loss of +the shaft for working purposes. The latter has the disadvantage +that the bend interferes slightly with haulage. + +The following table will indicate an hypothetical extreme case,--not +infrequently met. In it a vertical shaft 1,500 feet in depth is taken +as cutting the deposit at the depth of 750 feet, the most favored +position so far as aggregate length of crosscuts is concerned. The +cost of crosscutting is taken at $20 per foot and that of sinking +the vertical shaft at $75 per foot. The incline is assumed for two +cases at $75 and $100 per foot respectively. The stoping height +upon the ore between levels is counted at 125 feet. + + Dip of | Depth of | Length of |No. of Crosscuts| Total Length +Deposit from | Vertical | Incline | Required from | of Crosscuts, + Horizontal | Shaft | Required | V Shaft | Feet +-------------|-------------|-------------|----------------|--------------- + 80° | 1,500 | 1,522 | 11 | 859 + 70° | 1,500 | 1,595 | 12 | 1,911 + 60° | 1,500 | 1,732 | 13 | 3,247 + 50° | 1,500 | 1,058 | 15 | 5,389 + 40° | 1,500 | 2,334 | 18 | 8,038 + 30° | 1,500 | 3,000 | 23 | 16,237 +========================================================================== + Cost of |Cost Vertical| Total Cost | Cost of Incline|Cost of Incline +Crosscuts $20| Shaft $75 | of Vertical | $75 per Foot | $100 per Foot + per Foot | per Foot |and Crosscuts| | +-------------|-------------|-------------|----------------|--------------- + $17,180 | $112,500 | $129,680 | $114,150 | $152,200 + 38,220 | 112,500 | 150,720 | 118,625 | 159,500 + 64,940 | 112,500 | 177,440 | 129,900 | 172,230 + 107,780 | 112,500 | 220,280 | 114,850 | 195,800 + 178,760 | 112,500 | 291,260 | 175,050 | 233,400 + 324,740 | 112,500 | 437,240 | 225,000 | 300,000 + +From the above examples it will be seen that the cost of crosscuts +put at ordinary level intervals rapidly outruns the extra expense +of increased length of inclines. If, however, the conditions are +such that crosscuts from a vertical shaft are not necessary at so +frequent intervals, then in proportion to the decrease the advantages +sway to the vertical shaft. Most situations wherein the crosscuts +can be avoided arise in mines worked out in the upper levels and +fall under Case IV, that of deep-level projects. + +There can be no doubt that vertical shafts are cheaper to operate +than inclines: the length of haul from a given depth is less; much +higher rope speed is possible, and thus the haulage hours are less +for the same output; the wear and tear on ropes, tracks, or guides +is not so great, and pumping is more economical where the Cornish +order of pump is used. On the other hand, with a vertical shaft +must be included the cost of operating crosscuts. On mines where +the volume of ore does not warrant mechanical haulage, the cost of +tramming through the extra distance involved is an expense which +outweighs any extra operating outlay in the inclined shaft itself. +Even with mechanical haulage in crosscuts, it is doubtful if there +is anything in favor of the vertical shaft on this score. + +[Illustration: Fig. 6.--Cross-section showing auxiliary vertical +outlet.] + +In deposits of very flat dips, under 30°, the case arises where the +length of incline is so great that the saving on haulage through +direct lift warrants a vertical shaft as an auxiliary outlet in +addition to the incline (Fig. 6). In such a combination the crosscut +question is eliminated. The mine is worked above and below the +intersection by incline, and the vertical shaft becomes simply a +more economical exit and an alternative to secure increased output. +The North Star mine at Grass Valley is an illustration in point. Such +a positive instance borders again on Case IV, deep-level projects. + +In conclusion, it is the writer's belief that where mines are to +be worked from near the surface, coincidentally with sinking, and +where, therefore, crosscuts from a vertical shaft would need to be +installed frequently, inclines are warranted in all dips under 75° +and over 30°. Beyond 75° the best alternative is often undeterminable. +In the range under 30° and over 15°, although inclines are primarily +necessary for actual delivery of ore from levels, they can often +be justifiably supplemented by a vertical shaft as a relief to a +long haul. In dips of less than 15°, as in those over 75°, the +advantages again trend strongly in favor of the vertical shaft. There +arise, however, in mountainous countries, topographic conditions +such as the dip of deposits into the mountain, which preclude any +alternative on an incline at any angled dip. + +CASE IV. INCLINED DEPOSITS WHICH MUST BE ATTACKED IN DEPTH (Fig. +7).--There are two principal conditions in which such properties +exist: first, mines being operated, or having been previously worked, +whose method of entry must be revised; second, those whose ore-bodies +to be attacked do not outcrop within the property. + +The first situation may occur in mines of inadequate shaft capacity +or wrong location; in mines abandoned and resurrected; in mines +where a vertical shaft has reached its limit of useful extensions, +having passed the place of economical crosscutting; or in mines in +flat deposits with inclines whose haul has become too long to be +economical. Three alternatives present themselves in such cases: a +new incline from the surface (_A B F_, Fig. 7), or a vertical shaft +combined with incline extension (_C D F_), or a simple vertical +shaft (_H G_). A comparison can be first made between the simple +incline and the combined shaft. The construction of an incline from +the surface to the ore-body will be more costly than a combined +shaft, for until the horizon of the ore is reached (at _D_) no +crosscuts are required in the vertical section, while the incline +must be of greater length to reach the same horizon. The case arises, +however, where inclines can be sunk through old stopes, and thus +more cheaply constructed than vertical shafts through solid rock; +and also the case of mountainous topographic conditions mentioned +above. + +[Illustration: Fig. 7.--Cross-section of inclined deposit which +must be attacked in depth.] + +From an operating point of view, the bend in combined shafts (at +_D_) gives rise to a good deal of wear and tear on ropes and gear. +The possible speed of winding through a combined shaft is, however, +greater than a simple incline, for although haulage speed through +the incline section (_D F_) and around the bend of the combined +shaft is about the same as throughout a simple incline (_A F_), the +speed can be accelerated in the vertical portion (_D C_) above that +feasible did the incline extend to the surface. There is therefore an +advantage in this regard in the combined shaft. The net advantages +of the combined over the inclined shaft depend on the comparative +length of the two alternative routes from the intersection (_D_) +to the surface. Certainly it is not advisable to sink a combined +shaft to cut a deposit at 300 feet in depth if a simple incline +can be had to the surface. On the other hand, a combined shaft +cutting the deposit at 1,000 feet will be more advisable than a +simple incline 2,000 feet long to reach the same point. The matter +is one for direct calculation in each special case. In general, there +are few instances of really deep-level projects where a complete +incline from the surface is warranted. + +In most situations of this sort, and in all of the second type +(where the outcrop is outside the property), actual choice usually +lies between combined shafts (_C D F_) and entire vertical shafts (_H +G_). The difference between a combined shaft and a direct vertical +shaft can be reduced to a comparison of the combined shaft below +the point of intersection (_D_) with that portion of a vertical +shaft which would cover the same horizon. The question then becomes +identical with that of inclined _versus_ verticals, as stated in Case +III, with the offsetting disadvantage of the bend in the combined +shaft. If it is desired to reach production at the earliest date, +the lower section of a simple vertical shaft must have crosscuts +to reach the ore lying above the horizon of its intersection (_E_). +If production does not press, the ore above the intersection (_EB_) +can be worked by rises from the horizon of intersection (_E_). +In the use of rises, however, there follow the difficulties of +ventilation and lowering the ore down to the shaft, which brings +expenses to much the same thing as operating through crosscuts. + +The advantages of combined over simple vertical shafts are earlier +production, saving of either rises or crosscuts, and the ultimate +utility of the shaft to any depth. The disadvantages are the cost +of the extra length of the inclined section, slower winding, and +greater wear and tear within the inclined section and especially +around the bend. All these factors are of variable import, depending +upon the dip. On very steep dips,--over 70°,--the net result is in +favor of the simple vertical shaft. On other dips it is in favor +of the combined shaft. + +CASES V AND VI. MINES TO BE WORKED TO GREAT DEPTHS,--OVER 3,000 +FEET.--In Case V, with vertical or horizontal deposits, there is +obviously no desirable alternative to vertical shafts. + +In Case VI, with inclined deposits, there are the alternatives +of a combined or of a simple vertical shaft. A vertical shaft in +locations (_H_, Fig. 7) such as would not necessitate extension in +depth by an incline, would, as in Case IV, compel either crosscuts +to the ore or inclines up from the horizon of intersection (_E_). +Apart from delay in coming to production and the consequent loss of +interest on capital, the ventilation problems with this arrangement +would be appalling. Moreover, the combined shaft, entering the deposit +near its shallowest point, offers the possibility of a separate +haulage system on the inclined and on the vertical sections, and +such separate haulage is usually advisable at great depths. In +such instances, the output to be handled is large, for no mine of +small output is likely to be contemplated at such depth. Several +moderate-sized inclines from the horizon of intersection have been +suggested (_EF_, _DG_, _CH_, Fig. 8) to feed a large primary shaft +(_AB_), which thus becomes the trunk road. This program would cheapen +lateral haulage underground, as mechanical traction can be used +in the main level, (_EC_), and horizontal haulage costs can be +reduced on the lower levels. Moreover, separate winding engines +on the two sections increase the capacity, for the effect is that +of two trains instead of one running on a single track. + +SHAFT LOCATION.--Although the prime purpose in locating a shaft +is obviously to gain access to the largest volume of ore within +the shortest haulage distance, other conditions also enter, such +as the character of the surface and the rock to be intersected, +the time involved before reaching production, and capital cost. +As shafts must bear two relations to a deposit,--one as to the +dip and the other as to the strike,--they may be considered from +these aspects. Vertical shafts must be on the hanging-wall side +of the outcrop if the deposit dips at all. In any event, the shaft +should be far enough away to be out of the reach of creeps. An +inclined shaft may be sunk either on the vein, in which case a +pillar of ore must be left to support the shaft; or, instead, it +may be sunk a short distance in the footwall, and where necessary +the excavation above can be supported by filling. Following the +ore has the advantage of prospecting in sinking, and in many cases +the softness of the ground in the region of the vein warrants this +procedure. It has, however, the disadvantage that a pillar of ore +is locked up until the shaft is ready for abandonment. Moreover, as +veins or lodes are seldom of even dip, an inclined shaft, to have +value as a prospecting opening, or to take advantage of breaking +possibilities in the lode, will usually be crooked, and an incline +irregular in detail adds greatly to the cost of winding and maintenance. +These twin disadvantages usually warrant a straight incline in the +footwall. Inclines are not necessarily of the same dip throughout, +but for reasonably economical haulage change of angle must take +place gradually. + +[Illustration: Fig. 8.--Longitudinal section showing shaft arrangement +proposed for very deep inclined deposits.] + +In the case of deep-level projects on inclined deposits, demanding +combined or vertical shafts, the first desideratum is to locate +the vertical section as far from the outcrop as possible, and thus +secure the most ore above the horizon of intersection. This, however, +as stated before, would involve the cost of crosscuts or rises and +would cause delay in production, together with the accumulation +of capital charges. How important the increment of interest on +capital may become during the period of opening the mine may be +demonstrated by a concrete case. For instance, the capital of a +company or the cost of the property is, say, $1,000,000, and where +opening the mine for production requires four years, the aggregate +sum of accumulated compound interest at 5% (and most operators +want more from a mining investment) would be $216,000. Under such +circumstances, if a year or two can be saved in getting to production +by entering the property at a higher horizon, the difference in +accumulated interest will more than repay the infinitesimal extra +cost of winding through a combined shaft of somewhat increased +length in the inclined section. + +The unknown character of the ore in depth is always a sound reason +for reaching it as quickly and as cheaply as possible. In result, +such shafts are usually best located when the vertical section +enters the upper portion of the deposit. + +The objective in location with regard to the strike of the ore-bodies +is obviously to have an equal length of lateral ore-haul in every +direction from the shaft. It is easier to specify than to achieve +this, for in all speculative deposits ore-shoots are found to pursue +curious vagaries as they go down. Ore-bodies do not reoccur with +the same locus as in the upper levels, and generally the chances +to go wrong are more numerous than those to go right. + +NUMBER OF SHAFTS.--The problem of whether the mine is to be opened +by one or by two shafts of course influences location. In metal +mines under Cases II and III (outcrop properties) the ore output +requirements are seldom beyond the capacity of one shaft. Ventilation +and escape-ways are usually easily managed through the old stopes. +Under such circumstances, the conditions warranting a second shaft +are the length of underground haul and isolation of ore-bodies or +veins. Lateral haulage underground is necessarily disintegrated by +the various levels, and usually has to be done by hand. By shortening +this distance of tramming and by consolidation of the material +from all levels at the surface, where mechanical haulage can be +installed, a second shaft is often justified. There is therefore +an economic limitation to the radius of a single shaft, regardless +of the ability of the shaft to handle the total output. + +Other questions also often arise which are of equal importance +to haulage costs. Separate ore-shoots or ore-bodies or parallel +deposits necessitate, if worked from one shaft, constant levels +through unpayable ground and extra haul as well, or ore-bodies may +dip away from the original shaft along the strike of the deposit +and a long haulage through dead levels must follow. For instance, +levels and crosscuts cost roughly one-quarter as much per foot as +shafts. Therefore four levels in barren ground, to reach a parallel +vein or isolated ore-body 1,000 feet away, would pay for a shaft +1,000 feet deep. At a depth of 1,000 feet, at least six levels +might be necessary. The tramming of ore by hand through such a +distance would cost about double the amount to hoist it through +a shaft and transport it mechanically to the dressing plant at +surface. The aggregate cost and operation of barren levels therefore +soon pays for a second shaft. If two or more shafts are in question, +they must obviously be set so as to best divide the work. + +Under Cases IV, V, and VI,--that is, deep-level projects,--ventilation +and escape become most important considerations. Even where the +volume of ore is within the capacity of a single shaft, another +usually becomes a necessity for these reasons. Their location is +affected not only by the locus of the ore, but, as said, by the time +required to reach it. Where two shafts are to be sunk to inclined +deposits, it is usual to set one so as to intersect the deposit at +a lower point than the other. Production can be started from the +shallower, before the second is entirely ready. The ore above the +horizon of intersection of the deeper shaft is thus accessible from +the shallower shaft, and the difficulty of long rises or crosscuts +from that deepest shaft does not arise. + + + + +CHAPTER VIII. + +Development of Mines (_Continued_). + +SHAPE AND SIZE OF SHAFTS; SPEED OF SINKING; TUNNELS. + +SHAPE OF SHAFTS.--Shafts may be round or rectangular.[*] Round +vertical shafts are largely applied to coal-mines, and some engineers +have advocated their usefulness to the mining of the metals under +discussion. Their great advantages lie in their structural strength, +in the large amount of free space for ventilation, and in the fact +that if walled with stone, brick, concrete, or steel, they can be +made water-tight so as to prevent inflow from water-bearing strata, +even when under great pressure. The round walled shafts have a longer +life than timbered shafts. All these advantages pertain much more to +mining coal or iron than metals, for unsound, wet ground is often +the accompaniment of coal-measures, and seldom troubles metal-mines. +Ventilation requirements are also much greater in coal-mines. From +a metal-miner's standpoint, round shafts are comparatively much +more expensive than the rectangular timbered type.[**] For a larger +area must be excavated for the same useful space, and if support +is needed, satisfactory walling, which of necessity must be brick, +stone, concrete, or steel, cannot be cheaply accomplished under +the conditions prevailing in most metal regions. Although such +shafts would have a longer life, the duration of timbered shafts +is sufficient for most metal mines. It follows that, as timber +is the cheapest and all things considered the most advantageous +means of shaft support for the comparatively temporary character +of metal mines, to get the strains applied to the timbers in the +best manner, and to use the minimum amount of it consistent with +security, and to lose the least working space, the shaft must be +constructed on rectangular lines. + +[Footnote *: Octagonal shafts were sunk in Mexico in former times. +At each face of the octagon was a whim run by mules, and hauling +leather buckets.] + +[Footnote **: The economic situation is rapidly arising in a number +of localities that steel beams can be usefully used instead of +timber. The same arguments apply to this type of support that apply +to timber.] + +The variations in timbered shaft design arise from the possible +arrangement of compartments. Many combinations can be imagined, +of which Figures 9, 10, 11, 12, 13, and 14 are examples. + +[Illustration: FIG. 9. FIG. 10. FIG. 11. FIG. 12. FIG. 13. FIG. +14.] + +The arrangement of compartments shown in Figures 9, 10, 11, and +13 gives the greatest strength. It permits timbering to the best +advantage, and avoids the danger underground involved in crossing +one compartment to reach another. It is therefore generally adopted. +Any other arrangement would obviously be impossible in inclined +or combined shafts. + +SIZE OF SHAFTS.--In considering the size of shafts to be installed, +many factors are involved. They are in the main:-- + + _a_. Amount of ore to be handled. + _b_. Winding plant. + _c_. Vehicle of transport. + _d_. Depth. + _e_. Number of men to be worked underground. + _f_. Amount of water. + _g_. Ventilation. + _h_. Character of the ground. + _i_. Capital outlay. + _j_. Operating expense. + +It is not to be assumed that these factors have been stated in +the order of relative importance. More or less emphasis will be +attached to particular factors by different engineers, and under +different circumstances. It is not possible to suggest any arbitrary +standard for calculating their relative weight, and they are so +interdependent as to preclude separate discussion. The usual result +is a compromise between the demands of all. + +Certain factors, however, dictate a minimum position, which may +be considered as a datum from which to start consideration. + +_First_, a winding engine, in order to work with any economy, must +be balanced, that is, a descending empty skip or cage must assist +in pulling up a loaded one. Therefore, except in mines of very +small output, at least two compartments must be made for hoisting +purposes. Water has to be pumped from most mines, escape-ways are +necessary, together with room for wires and air-pipes, so that at +least one more compartment must be provided for these objects. +We have thus three compartments as a sound minimum for any shaft +where more than trivial output is required. + +_Second_, there is a certain minimum size of shaft excavation below +which there is very little economy in actual rock-breaking.[*] +In too confined a space, holes cannot be placed to advantage for +the blast, men cannot get round expeditiously, and spoil cannot be +handled readily. The writer's own experience leads him to believe +that, in so far as rock-breaking is concerned, to sink a shaft +fourteen to sixteen feet long by six to seven feet wide outside +the timbers, is as cheap as to drive any smaller size within the +realm of consideration, and is more rapid. This size of excavation +permits of three compartments, each about four to five feet inside +the timbers. + +[Footnote *: Notes on the cost of shafts in various regions which +have been personally collected show a remarkable decrease in the +cost per cubic foot of material excavated with increased size of +shaft. Variations in skill, in economic conditions, and in method +of accounting make data regarding different shafts of doubtful +value, but the following are of interest:-- + +In Australia, eight shafts between 10 and 11 feet long by 4 to +5 feet wide cost an average of $1.20 per cubic foot of material +excavated. Six shafts 13 to 14 feet long by 4 to 5 feet wide cost +an average of $0.95 per cubic foot; seven shafts 14 to 16 feet +long and 5 to 7 feet wide cost an average of $0.82 per cubic foot. +In South Africa, eleven shafts 18 to 19 feet long by 7 to 8 feet +wide cost an average of $0.82 per cubic foot; five shafts 21 to +25 feet long by 8 feet wide, cost $0.74; and seven shafts 28 feet +by 8 feet cost $0.60 per cubic foot.] + +The cost of timber, it is true, is a factor of the size of shaft, +but the labor of timbering does not increase in the same ratio. +In any event, the cost of timber is only about 15% of the actual +shaft cost, even in localities of extremely high prices. + +_Third_, three reasons are rapidly making the self-dumping skip +the almost universal shaft-vehicle, instead of the old cage for +cars. First, there is a great economy in labor for loading into +and discharging from a shaft; second, there is more rapid despatch +and discharge and therefore a larger number of possible trips; +third, shaft-haulage is then independent of delays in arrival of +cars at stations, while tramming can be done at any time and +shaft-haulage can be concentrated into certain hours. Cages to +carry mine cars and handle the same load as a skip must either +be big enough to take two cars, which compels a much larger shaft +than is necessary with skips, or they must be double-decked, which +renders loading arrangements underground costly to install and +expensive to work. For all these reasons, cages can be justified only +on metal mines of such small tonnage that time is no consideration +and where the saving of men is not to be effected. In compartments +of the minimum size mentioned above (four to five feet either way) +a skip with a capacity of from two to five tons can be installed, +although from two to three tons is the present rule. Lighter loads +than this involve more trips, and thus less hourly capacity, and, +on the other hand, heavier loads require more costly engines. This +matter is further discussed under "Haulage Appliances." + +We have therefore as the economic minimum a shaft of three compartments +(Fig. 9), each four to five feet square. When the maximum tonnage +is wanted from such a shaft at the least operating cost, it should +be equipped with loading bins and skips. + +The output capacity of shafts of this size and equipment will depend +in a major degree upon the engine employed, and in a less degree +upon the hauling depth. The reason why depth is a subsidiary factor +is that the rapidity with which a load can be drawn is not wholly a +factor of depth. The time consumed in hoisting is partially expended +in loading, in acceleration and retardation of the engine, and in +discharge of the load. These factors are constant for any depth, +and extra distance is therefore accomplished at full speed of the +engine. + +Vertical shafts will, other things being equal, have greater capacity +than inclines, as winding will be much faster and length of haul less +for same depth. Since engines have, however, a great tractive ability +on inclines, by an increase in the size of skip it is usually possible +partially to equalize matters. Therefore the size of inclines for +the same output need not differ materially from vertical shafts. + +The maximum capacity of a shaft whose equipment is of the character +and size given above, will, as stated, decrease somewhat with extension +in depth of the haulage horizon. At 500 feet, such a shaft if vertical +could produce 70 to 80 tons per hour comfortably with an engine +whose winding speed was 700 feet per minute. As men and material +other than ore have to be handled in and out of the mine, and +shaft-sinking has to be attended to, the winding engine cannot +be employed all the time on ore. Twelve hours of actual daily +ore-winding are all that can be expected without auxiliary help. +This represents a capacity from such a depth of 800 to 1,000 tons +per day. A similar shaft, under ordinary working conditions, with +an engine speed of 2,000 feet per minute, should from, say, 3,000 +feet have a capacity of about 400 to 600 tons daily. + +It is desirable to inquire at what stages the size of shaft should +logically be enlarged in order to attain greater capacity. A +considerable measure of increase can be obtained by relieving the +main hoisting engine of all or part of its collateral duties. Where +the pumping machinery is not elaborate, it is often possible to +get a small single winding compartment into the gangway without +materially increasing the size of the shaft if the haulage compartments +be made somewhat narrower (Fig. 10). Such a compartment would be +operated by an auxiliary engine for sinking, handling tools and +material, and assisting in handling men. If this arrangement can +be effected, the productive time of the main engine can be expanded +to about twenty hours with an addition of about two-thirds to the +output. + +Where the exigencies of pump and gangway require more than two +and one-half feet of shaft length, the next stage of expansion +becomes four full-sized compartments (Fig. 11). By thus enlarging the +auxiliary winding space, some assistance may be given to ore-haulage +in case of necessity. The mine whose output demands such haulage +provisions can usually stand another foot of width to the shaft, +so that the dimensions come to about 21 feet to 22 feet by 7 feet +to 8 feet outside the timbers. Such a shaft, with three- to four-ton +skips and an appropriate engine, will handle up to 250 tons per +hour from a depth of 1,000 feet. + +The next logical step in advance is the shaft of five compartments +with four full-sized haulage ways (Fig. 13), each of greater size +than in the above instance. In this case, the auxiliary engine +becomes a balanced one, and can be employed part of the time upon +ore-haulage. Such a shaft will be about 26 feet to 28 feet long +by 8 feet wide outside the timbers, when provision is made for +one gangway. The capacity of such shafts can be up to 4,000 tons a +day, depending on the depth and engine. When very large quantities +of water are to be dealt with and rod-driven pumps to be used, +two pumping compartments are sometimes necessary, but other forms +of pumps do not require more than one compartment,--an additional +reason for their use. + +For depths greater than 3,000 feet, other factors come into play. +Ventilation questions become of more import. The mechanical problems +on engines and ropes become involved, and their sum-effect is to +demand much increased size and a greater number of compartments. +The shafts at Johannesburg intended as outlets for workings 5,000 +feet deep are as much as 46 feet by 9 feet outside timbers. + +It is not purposed to go into details as to sinking methods or +timbering. While important matters, they would unduly prolong this +discussion. Besides, a multitude of treatises exist on these subjects +and cover all the minutiæ of such work. + +SPEED OF SINKING.--Mines may be divided into two cases,--those +being developed only, and those being operated as well as developed. +In the former, the entrance into production is usually dependent +upon the speed at which the shaft is sunk. Until the mine is earning +profits, there is a loss of interest on the capital involved, which, +in ninety-nine instances out of a hundred, warrants any reasonable +extra expenditure to induce more rapid progress. In the case of +mines in operation, the volume of ore available to treatment or +valuation is generally dependent to a great degree upon the rapidity +of the extension of workings in depth. It will be demonstrated +later that, both from a financial and a technical standpoint, the +maximum development is the right one and that unremitting extension +in depth is not only justifiable but necessary. + +Speed under special conditions or over short periods has a more +romantic than practical interest, outside of its value as a stimulant +to emulation. The thing that counts is the speed which can be maintained +over the year. Rapidity of sinking depends mainly on:-- + +_a_. Whether the shaft is or is not in use for operating the + mine. +_b_. The breaking character of the rock. +_c_. The amount of water. + +The delays incident to general carrying of ore and men are such that +the use of the main haulage engine for shaft-sinking is practically +impossible, except on mines with small tonnage output. Even with a +separate winch or auxiliary winding-engine, delays are unavoidable +in a working shaft, especially as it usually has more water to contend +with than one not in use for operating the mine. The writer's own +impression is that an average of 40 feet per month is the maximum +possibility for year in and out sinking under such conditions. In +fact, few going mines manage more than 400 feet a year. In cases +of clean shaft-sinking, where every energy is bent to speed, 150 +feet per month have been averaged for many months. Special cases +have occurred where as much as 213 feet have been achieved in a +single month. With ordinary conditions, 1,200 feet in a year is +very good work. Rock awkward to break, and water especially, lowers +the rate of progress very materially. Further reference to speed +will be found in the chapter on "Drilling Methods." + +TUNNEL ENTRY.--The alternative of entry to a mine by tunnel is +usually not a question of topography altogether, but, like everything +else in mining science, has to be tempered to meet the capital +available and the expenditure warranted by the value showing. + +In the initial prospecting of a mine, tunnels are occasionally +overdone by prospectors. Often more would be proved by a few inclines. +As the pioneer has to rely upon his right arm for hoisting and +drainage, the tunnel offers great temptations, even when it is +long and gains but little depth. At a more advanced stage of +development, the saving of capital outlay on hoisting and pumping +equipment, at a time when capital is costly to secure, is often +sufficient justification for a tunnel entry. But at the stage where +the future working of ore below a tunnel-level must be contemplated, +other factors enter. For ore below tunnel-level a shaft becomes +necessary, and in cases where a tunnel enters a few hundred feet +below the outcrop the shaft should very often extend to the surface, +because internal shafts, winding from tunnel-level, require large +excavations to make room for the transfer of ore and for winding +gear. The latter must be operated by transmitted power, either +that of steam, water, electricity, or air. Where power has to be +generated on the mine, the saving by the use of direct steam, generated +at the winding gear, is very considerable. Moreover, the cost of +haulage through a shaft for the extra distance from tunnel-level +to the surface is often less than the cost of transferring the +ore and removing it through the tunnel. The load once on the +winding-engine, the consumption of power is small for the extra +distance, and the saving of labor is of consequence. On the other +hand, where drainage problems arise, they usually outweigh all +other considerations, for whatever the horizon entered by tunnel, +the distance from that level to the surface means a saving of +water-pumpage against so much head. The accumulation of such constant +expense justifies a proportioned capital outlay. In other words, +the saving of this extra pumping will annually redeem the cost of +a certain amount of tunnel, even though it be used for drainage +only. + +In order to emphasize the rapidity with which such a saving of +constant expense will justify capital outlay, one may tabulate the +result of calculations showing the length of tunnel warranted with +various hypothetical factors of quantity of water and height of lift +eliminated from pumping. In these computations, power is taken at +the low rate of $60 per horsepower-year, the cost of tunneling at +an average figure of $20 per foot, and the time on the basis of +a ten-year life for the mine. + +Feet of Tunnel Paid for in 10 Years with Under-mentioned Conditions. + +============================================================= + Feet of | 100,000 | 200,000 | 300,000 | 500,000 |1,000,000 +Water Lift | Gallons | Gallons | Gallons | Gallons | Gallons + Avoided |per Diem |per Diem |per Diem |per Diem |per Diem +-----------|---------|---------|---------|---------|--------- + 100 | 600 | 1,200 | 1,800 | 3,000 | 6,000 + 200 | 1,200 | 2,400 | 3,600 | 6,000 | 12,000 + 300 | 1,800 | 3,600 | 5,400 | 9,000 | 18,000 + 500 | 3,000 | 6,000 | 9,000 | 15,000 | 30,000 + 1,000 | 6,000 | 12,000 | 18,000 | 30,000 | 60,000 +============================================================= + +The size of tunnels where ore-extraction is involved depends upon +the daily tonnage output required, and the length of haul. The +smallest size that can be economically driven and managed is about +6-1/2 feet by 6 feet inside the timbers. Such a tunnel, with single +track for a length of 1,000 feet, with one turn-out, permits handling +up to 500 tons a day with men and animals. If the distance be longer +or the tonnage greater, a double track is required, which necessitates +a tunnel at least 8 feet wide by 6-1/2 feet to 7 feet high, inside +the timbers. + +There are tunnel projects of a much more impressive order than those +designed to operate upper levels of mines; that is, long crosscut +tunnels designed to drain and operate mines at very considerable +depths, such as the Sutro tunnel at Virginia City. The advantage +of these tunnels is very great, especially for drainage, and they +must be constructed of large size and equipped with appliances +for mechanical haulage. + + + + +CHAPTER IX. + +Development of Mines (_Concluded_). + +SUBSIDIARY DEVELOPMENT;--STATIONS; CROSSCUTS; LEVELS; INTERVAL +BETWEEN LEVELS; PROTECTION OF LEVELS; WINZES AND RISES. DEVELOPMENT +IN THE PROSPECTING STAGE; DRILLING. + +SUBSIDIARY DEVELOPMENT. + +Stations, crosscuts, levels, winzes, and rises follow after the +initial entry. They are all expensive, and the least number that +will answer is the main desideratum. + +STATIONS.--As stations are the outlets of the levels to the shaft, +their size and construction is a factor of the volume and character +of the work at the levels which they are to serve. If no timber +is to be handled, and little ore, and this on cages, the stations +need be no larger than a good sized crosscut. Where timber is to +be let down, they must be ten to fifteen feet higher than the floor +of the crosscut. Where loading into skips is to be provided for, +bins must be cut underneath and sufficient room be provided to +shift the mine cars comfortably. Such bins are built of from 50 to +500 tons' capacity in order to contain some reserve for hoisting +purposes, and in many cases separate bins must be provided on opposite +sides of the shaft for ore and waste. It is a strong argument in +favor of skips, that with this means of haulage storage capacity +at the stations is possible, and the hoisting may then go on +independently of trucking and, as said before, there are no idle +men at the stations. + +[Illustration: Fig. 15.--Cross-section of station arrangement for +skip-haulage in vertical shaft.] + +[Illustration: Fig. 16.--Cross-section of station arrangement for +skip-haulage in vertical shaft.] + +It is always desirable to concentrate the haulage to the least +number of levels, for many reasons. Among them is that, where haulage +is confined to few levels, storage-bins are not required at every +station. Figures 15, 16, 17, and 18 illustrate various arrangements +of loading bins. + +CROSSCUTS.--Crosscuts are for two purposes, for roadway connection +of levels to the shaft or to other levels, and for prospecting +purposes. The number of crosscuts for roadways can sometimes be +decreased by making the connections with the shaft at every second +or even every third level, thus not only saving in the construction +cost of crosscuts and stations, but also in the expenses of scattered +tramming. The matter becomes especially worth considering where +the quantity of ore that can thus be accumulated warrants mule +or mechanical haulage. This subject will be referred to later on. + +[Illustration: Fig. 17.--Arrangement of loading chutes in vertical +shaft.] + +On the second purpose of crosscuts,--that of prospecting,--one +observation merits emphasis. This is, that the tendency of ore-fissures +to be formed in parallels warrants more systematic crosscutting +into the country rock than is done in many mines. + +[Illustration: Fig. 18.--Cross-section of station arrangement for +skip-haulage in inclined shaft.] + +LEVELS. + +The word "level" is another example of miners' adaptations in +nomenclature. Its use in the sense of tunnels driven in the direction +of the strike of the deposit has better, but less used, synonyms in +the words "drifts" or "drives." The term "level" is used by miners +in two senses, in that it is sometimes applied to all openings on one +horizon, crosscuts included. Levels are for three purposes,--for a +stoping base; for prospecting the deposit; and for roadways. As a +prospecting and a stoping base it is desirable that the level should +be driven on the deposit; as a roadway, that it should constitute +the shortest distance between two points and be in the soundest +ground. On narrow, erratic deposits the levels usually must serve +all three purposes at once; but in wider and more regular deposits +levels are often driven separately for roadways from the level +which forms the stoping base and prospecting datum. + +There was a time when mines were worked by driving the level on ore +and enlarging it top and bottom as far as the ground would stand, +then driving the next level 15 to 20 feet below, and repeating the +operation. This interval gradually expanded, but for some reason +100 feet was for years assumed to be the proper distance between +levels. Scattered over every mining camp on earth are thousands +of mines opened on this empirical figure, without consideration +of the reasons for it or for any other distance. + +The governing factors in determining the vertical interval between +levels are the following:-- + + _a_. The regularity of the deposit. + _b_. The effect of the method of excavation of winzes and rises. + _c_. The dip and the method of stoping. + +REGULARITY OF THE DEPOSIT.--From a prospecting point of view the +more levels the better, and the interval therefore must be determined +somewhat by the character of the deposit. In erratic deposits there +is less risk of missing ore with frequent levels, but it does not +follow that every level need be a through roadway to the shaft or +even a stoping base. In such deposits, intermediate levels for +prospecting alone are better than complete levels, each a roadway. +Nor is it essential, even where frequent levels are required for +a stoping base, that each should be a main haulage outlet to the +shaft. In some mines every third level is used as a main roadway, +the ore being poured from the intermediate ones down to the haulage +line. Thus tramming and shaft work, as stated before, can be +concentrated. + +EFFECT OF METHOD OF EXCAVATING WINZES AND RISES.--With hand drilling +and hoisting, winzes beyond a limited depth become very costly to +pull spoil out of, and rises too high become difficult to ventilate, +so that there is in such cases a limit to the interval desirable +between levels, but these difficulties largely disappear where +air-winches and air-drills are used. + +THE DIP AND METHOD OF STOPING.--The method of stoping is largely +dependent upon the dip, and indirectly thus affects level intervals. +In dips under that at which material will "flow" in the stopes--about +45° to 50°--the interval is greatly dependent on the method of +stope-transport. Where ore is to be shoveled from stopes to the +roadway, the levels must be comparatively close together. Where +deposits are very flat, under 20°, and walls fairly sound, it is +often possible to use a sort of long wall system of stoping and to +lay tracks in the stopes with self-acting inclines to the levels. +In such instances, the interval can be expanded to 250 or even 400 +feet. In dips between 20° and 45°, tracks are not often possible, +and either shoveling or "bumping troughs"[*] are the only help +to transport. With shoveling, intervals of 100 feet[**] are most +common, and with troughs the distance can be expanded up to 150 +or 175 feet. + +[Footnote *: Page 136.] + +[Footnote **: Intervals given are measured on the dip.] + +In dips of over 40° to 50°, depending on the smoothness of the foot +wall, the distance can again be increased, as stope-transport is +greatly simplified, since the stope materials fall out by gravity. +In timbered stopes, in dips over about 45°, intervals of 150 to +200 feet are possible. In filled stopes intervals of over 150 feet +present difficulties in the maintenance of ore-passes, for the wear +and tear of longer use often breaks the timbers. In shrinkage-stopes, +where no passes are to be maintained and few winzes put through, the +interval is sometimes raised to 250 feet. The subject is further +discussed under "Stoping." + +Another factor bearing on level intervals is the needed insurance +of sufficient points of stoping attack to keep up a certain output. +This must particularly influence the manager whose mine has but +little ore in reserve. + +[Illustration: Fig. 19.] + +PROTECTION OF LEVELS.--Until recent years, timbering and occasional +walling was the only method for the support of the roof, and for +forming a platform for a stoping base. Where the rock requires no +support sublevels can be used as a stoping base, and timbering +for such purpose avoided altogether (Figs. 38, 39, 42). In such +cases the main roadway can then be driven on straight lines, either +in the walls or in the ore, and used entirely for haulage. The +subheading for a stoping base is driven far enough above or below +the roadway (depending on whether overhand or underhand stoping +is to be used) to leave a supporting pillar which is penetrated +by short passes for ore. In overhand stopes, the ore is broken +directly on the floor of an upper sublevel; and in underhand stopes, +broken directly from the bottom of the sublevel. The method entails +leaving a pillar of ore which can be recovered only with difficulty +in mines where stope-support is necessary. The question of its +adoption is then largely one of the comparative cost of timbering, +the extra cost of the sublevel, and the net value of the ore left. +In bad swelling veins, or badly crushing walls, where constant +repair to timbers would be necessary, the use of a sublevel is a +most useful alternative. It is especially useful with stopes to +be left open or worked by shrinkage-stoping methods. + +If the haulage level, however, is to be the stoping base, some +protection to the roadway must be provided. There are three systems +in use,--by wood stulls or sets (Figs. 19, 30, 43), by dry-walling +with timber caps (Fig. 35), and in some localities by steel sets. +Stulls are put up in various ways, and, as their use entails the +least difficulty in taking the ore out from beneath the level, +they are much favored, but are applicable only in comparatively +narrow deposits. + +WINZES AND RISES. + +These two kinds of openings for connecting two horizons in a mine +differ only in their manner of construction. A winze is sunk underhand, +while a rise is put up overhand. When the connection between levels +is completed, a miner standing at the bottom usually refers to +the opening as a rise, and when he goes to the top he calls it +a winze. This confusion in terms makes it advisable to refer to +all such completed openings as winzes, regardless of how they are +constructed. + +In actual work, even disregarding water, it costs on the average +about 30% less to raise than to sink such openings, for obviously +the spoil runs out or is assisted by gravity in one case, and in +the other has to be shoveled and hauled up. Moreover, it is easier +to follow the ore in a rise than in a winze. It usually happens, +however, that in order to gain time both things are done, and for +prospecting purposes sinking is necessary. + +The number of winzes required depends upon the method of stoping +adopted, and is mentioned under "Stoping." After stoping, the number +necessary to be maintained open depends upon the necessities of +ventilation, of escape, and of passageways for material to be used +below. Where stopes are to be filled with waste, more winzes must +be kept open than when other methods are used, and these winzes +must be in sufficient alignment to permit the continuous flow of +material down past the various levels. In order that the winzes +should deliver timber and filling to the most advantageous points, +they should, in dipping ore-bodies, be as far as possible on the +hanging wall side. + +DEVELOPMENT IN THE EARLY PROSPECTING STAGE. + +The prime objects in the prospecting stage are to expose the ore +and to learn regarding the ore-bodies something of their size, their +value, metallurgical character, location, dip, strike, etc.,--so much +at least as may be necessary to determine the works most suitable +for their extraction or values warranting purchase. In outcrop mines +there is one rule, and that is "follow the ore." Small temporary +inclines following the deposit, even though they are eventually +useless; are nine times out of ten justified. + +In prospecting deep-level projects, it is usually necessary to +layout work which can be subsequently used in operating the mine, +because the depth involves works of such considerable scale, even +for prospecting, that the initial outlay does not warrant any +anticipation of revision. Such works have to be located and designed +after a study of the general geology as disclosed in adjoining mines. +Practically the only method of supplementing such information is +by the use of churn- and diamond-drills. + +DRILLING.--Churn-drills are applicable only to comparatively shallow +deposits of large volume. They have an advantage over the diamond +drill in exposing a larger section and in their application to +loose material; but inability to determine the exact horizon of +the spoil does not lend them to narrow deposits, and in any event +results are likely to be misleading from the finely ground state of +the spoil. They are, however, of very great value for preliminary +prospecting to shallow horizons. + +Two facts in diamond-drilling have to be borne in mind: the indication +of values is liable to be misleading, and the deflection of the drill +is likely to carry it far away from its anticipated destination. +A diamond-drill secures a small section which is sufficiently large +to reveal the geology, but the values disclosed in metal mines must +be accepted with reservations. The core amounts to but a little +sample out of possibly large amounts of ore, which is always of +variable character, and the core is most unlikely to represent +the average of the deposit. Two diamond-drill holes on the Oroya +Brownhill mine both passed through the ore-body. One apparently +disclosed unpayable values, the other seemingly showed ore forty +feet in width assaying $80 per ton. Neither was right. On the other +hand, the predetermination of the location of the ore-body justified +expenditure. A recent experiment at Johannesburg of placing a copper +wedge in the hole at a point above the ore-body and deflecting +the drill on reintroducing it, was successful in giving a second +section of the ore at small expense. + +The deflection of diamond-drill holes from the starting angle is +almost universal. It often amounts to a considerable wandering +from the intended course. The amount of such deflection varies +with no seeming rule, but it is probable that it is especially +affected by the angle at which stratification or lamination planes +are inclined to the direction of the hole. A hole has been known +to wander in a depth of 1,500 feet more than 500 feet from the +point intended. Various instruments have been devised for surveying +deep holes, and they should be brought into use before works are +laid out on the basis of diamond-drill results, although none of +the inventions are entirely satisfactory. + + + + +CHAPTER X. + +Stoping. + +METHODS OF ORE-BREAKING; UNDERHAND STOPES; OVERHAND STOPES; COMBINED +STOPE. VALUING ORE IN COURSE OF BREAKING. + +There is a great deal of confusion in the application of the word +"stoping." It is used not only specifically to mean the actual +ore-breaking, but also in a general sense to indicate all the operations +of ore-breaking, support of excavations, and transportation between +levels. It is used further as a noun to designate the hole left +when the ore is taken out. Worse still, it is impossible to adhere +to miners' terms without employing it in every sense, trusting +to luck and the context to make the meaning clear. + +The conditions which govern the method of stoping are in the main:-- + + _a_. The dip. + _b_. The width of the deposit. + _c_. The character of the walls. + _d_. The cost of materials. + _e_. The character of the ore. + +Every mine, and sometimes every stope in a mine, is a problem special +to itself. Any general consideration must therefore be simply an +inquiry into the broad principles which govern the adaptability of +special methods. A logical arrangement of discussion is difficult, +if not wholly impossible, because the factors are partially +interdependent and of varying importance. + +For discussion the subject may be divided into: + + 1. Methods of ore-breaking. + 2. Methods of supporting excavation. + 3. Methods of transport in stopes. + +METHODS OF ORE-BREAKING. + +The manner of actual ore-breaking is to drill and blast off slices +from the block of ground under attack. As rock obviously breaks +easiest when two sides are free, that is, when corners can be broken +off, the detail of management for blasts is therefore to set the holes +so as to preserve a corner for the next cut; and as a consequence +the face of the stope shapes into a series of benches (Fig. +22),--inverted benches in the case of overhand stopes (Figs. 20, +21). The size of these benches will in a large measure depend on +the depth of the holes. In wide stopes with machine-drills they +vary from 7 to 10 feet; in narrow stopes with hand-holes, from +two to three feet. + +[Illustration: Fig. 20.] + +The position of the men in relation to the working face gives rise +to the usual primary classification of the methods of stoping. +They are:-- + + 1. Underhand stopes, + 2. Overhand stopes, + 3. Combined stopes. + +These terms originated from the direction of the drill-holes, but +this is no longer a logical basis of distinction, for underhand +holes in overhand stopes,--as in rill-stoping,--are used entirely +in some mines (Fig. 21). + +[Illustration: Fig. 21.] + +UNDERHAND STOPES.--Underhand stopes are those in which the ore +is broken downward from the levels. Inasmuch as this method has +the advantage of allowing the miner to strike his blows downward +and to stand upon the ore when at work, it was almost universal +before the invention of powder; and was applied more generally +before the invention of machine-drills than since. It is never +rightly introduced unless the stope is worked back from winzes +through which the ore broken can be let down to the level below, +as shown in Figures 22 and 23. + +[Illustration: Fig. 22.] + +This system can be advantageously applied only in the rare cases +in which the walls require little or no support, and where very +little or no waste requiring separation is broken with the ore +in the stopes. To support the walls in bad ground in underhand +stopes would be far more costly than with overhand stopes, for +square-set timbering would be most difficult to introduce, and +to support the walls with waste and stulls would be even more +troublesome. Any waste broken must needs be thrown up to the level +above or be stored upon specially built stages--again a costly +proceeding. + +A further drawback lies in the fact that the broken ore follows +down the face of the stope, and must be shoveled off each bench. +It thus all arrives at a single point,--the winze,--and must be +drawn from a single ore-pass into the level. This usually results +not only in more shoveling but in a congestion at the passes not +present in overhand stoping, for with that method several chutes +are available for discharging ore into the levels. Where the walls +require no support and no selection is desired in the stopes, the +advantage of the men standing on the solid ore to work, and of +having all down holes and therefore drilled wet, gives this method +a distinct place. In using this system, in order to protect the +men, a pillar is often left under the level by driving a sublevel, +the pillar being easily recoverable later. The method of sublevels +is of advantage largely in avoiding the timbering of levels. + +[Illustration: Fig. 23.--Longitudinal section of an underhand stope.] + +OVERHAND STOPES.--By far the greatest bulk of ore is broken overhand, +that is broken upward from one level to the next above. There are +two general forms which such stopes are given,--"horizontal" and +"rill." + +[Illustration: Fig. 24.--Horizontal-cut overhand stope--longitudinal +section.] + +The horizontal "flat-back" or "long-wall" stope, as it is variously +called, shown in Figure 24, is operated by breaking the ore in slices +parallel with the levels. In rill-stoping the ore is cut back from +the winzes in such a way that a pyramid-shaped room is created, +with its apex in the winze and its base at the level (Figs. 25 and +26). Horizontal or flat-backed stopes can be applied to almost any +dip, while "rill-stoping" finds its most advantageous application +where the dip is such that the ore will "run," or where it can be +made to "run" with a little help. The particular application of +the two systems is dependent not only on the dip but on the method +of supporting the excavation and the ore. With rill-stoping, it is +possible to cut the breaking benches back horizontally from the +winzes (Fig. 25), or to stagger the cuts in such a manner as to +take the slices in a descending angle (Figs. 21 and 26). + +[Illustration: Fig. 25.--Rill-cut overhand stope--longitudinal section.] + +In the "rill" method of incline cuts, all the drill-holes are "down" +holes (Fig. 21), and can be drilled wet, while in horizontal cuts +or flat-backed stopes, at least part of the holes must be "uppers" +(Fig. 20). Aside from the easier and cheaper drilling and setting +up of machines with this kind of "cut," there is no drill dust,--a +great desideratum in these days of miners' phthisis. A further +advantage in the "rill" cut arises in cases where horizontal jointing +planes run through the ore of a sort from which unduly large masses +break away in "flat-back" stopes. By the descending cut of the +"rill" method these calamities can be in a measure avoided. In +cases of dips over 40º the greatest advantage in "rill" stoping +arises from the possibility of pouring filling or timber into the +stope from above with less handling, because the ore and material +will run down the sides of the pyramid (Figs. 32 and 34). Thus +not only is there less shoveling required, but fewer ore-passes +and a less number of preliminary winzes are necessary, and a wider +level interval is possible. This matter will be gone into more +fully later. + +[Illustration: Fig. 26.--Rill-cut overhand stope-longitudinal section.] + +COMBINED STOPES.--A combined stope is made by the coincident working +of the underhand and "rill" method (Fig. 27). This order of stope +has the same limitations in general as the underhand kind. For +flat veins with strong walls, it has a great superiority in that +the stope is carried back more or less parallel with the winzes, +and thus broken ore after blasting lies in a line on the gradient +of the stope. It is, therefore, conveniently placed for mechanical +stope haulage. A further advantage is gained in that winzes may +be placed long distances apart, and that men are not required, +either when at work or passing to and from it, to be ever far from +the face, and they are thus in the safest ground, so that timber +and filling protection which may be otherwise necessary is not +required. This method is largely used in South Africa. + +[Illustration: Fig. 27.--Longitudinal section of a combined stope.] + +MINIMUM WIDTH OF STOPES.--The minimum stoping width which can be +consistently broken with hand-holes is about 30 inches, and this +only where there is considerable dip to the ore. This space is +so narrow that it is of doubtful advantage in any case, and 40 +inches is more common in narrow mines, especially where worked +with white men. Where machine-drills are used about 4 feet is the +minimum width feasible. + +RESUING.--In very narrow veins where a certain amount of wall-rock +must be broken to give working space, it pays under some circumstances +to advance the stope into the wall-rock ahead of the ore, thus +stripping the ore and enabling it to be broken separately. This +permits of cleaner selection of the ore; but it is a problem to +be worked out in each case, as to whether rough sorting of some +waste in the stopes, or further sorting at surface with inevitable +treatment of some waste rock, is more economical than separate +stoping cuts and inevitably wider stopes. + +VALUING ORE IN COURSE OF BREAKING.--There are many ores whose payability +can be determined by inspection, but there are many of which it cannot. +Continuous assaying is in the latter cases absolutely necessary +to avoid the treatment of valueless material. In such instances, +sampling after each stoping-cut is essential, the unprofitable ore +being broken down and used as waste. Where values fade into the +walls, as in impregnation deposits, the width of stopes depends +upon the limit of payability. In these cases, drill-holes are put +into the walls and the drillings assayed. If the ore is found +profitable, the holes are blasted out. The gauge of what is profitable +in such situations is not dependent simply upon the average total +working costs of the mine, for ore in that position can be said to +cost nothing for development work and administration; moreover, +it is usually more cheaply broken than the average breaking cost, +men and machines being already on the spot. + + + + +CHAPTER XI. + +Methods of Supporting Excavation. + +TIMBERING; FILLING WITH WASTE; FILLING WITH BROKEN ORE; PILLARS +OF ORE; ARTIFICIAL PILLARS; CAVING SYSTEM. + +Most stopes require support to be given to the walls and often to +the ore itself. Where they do require support there are five principal +methods of accomplishing it. The application of any particular method +depends upon the dip, width of ore-body, character of the ore and +walls, and cost of materials. The various systems are by:-- + + 1. Timbering. + 2. Filling with waste. + 3. Filling with broken ore subsequently withdrawn. + 4. Pillars of ore. + 5. Artificial pillars built of timbers and waste. + 6. Caving. + +TIMBERING.--At one time timbering was the almost universal means of +support in such excavations, but gradually various methods for the +economical application of waste and ore itself have come forward, +until timbering is fast becoming a secondary device. Aside from +economy in working without it, the dangers of creeps, or crushing, +and of fires are sufficient incentives to do away with wood as +far as possible. + +There are three principal systems of timber support to excavations,--by +stulls, square-sets, and cribs. + +Stulls are serviceable only where the deposit is so narrow that +the opening can be bridged by single timbers between wall and wall +(Figs. 28 and 43). This system can be applied to any dip and is most +useful in narrow deposits where the walls are not too heavy. Stulls +in inclined deposits are usually set at a slightly higher angle than +that perpendicular to the walls, in order that the vertical pressure +of the hanging wall will serve to tighten them in position. The +"stull" system can, in inclined deposits, be further strengthened by +building waste pillars against them, in which case the arrangement +merges into the system of artificial pillars. + +[Illustration: Fig. 28.--Longitudinal section of stull-supported +stope.] + +[Illustration: Fig. 29.--Longitudinal section showing square-set +timbering.] + +[Illustration: Fig. 30.--Square-set timbering on inclined ore-body. +Showing ultimate strain on timbers.] + +Square-sets (Figs. 29 and 30), that is, trusses built in the opening +as the ore is removed, are applicable to almost any dip or width +of ore, but generally are applied only in deposits too wide, or to +rock too heavy, for stulls. Such trusses are usually constructed on +vertical and horizontal lines, and while during actual ore-breaking +the strains are partially vertical, ultimately, however, when the +weight of the walls begins to be felt, these strains, except in +vertical deposits, come at an angle to lines of strength in the +trusses, and therefore timber constructions of this type present +little ultimate resistance (Fig. 30). Square-set timbers are sometimes +set to present the maximum resistance to the direction of strain, +but the difficulties of placing them in position and variations in +the direction of strain on various parts of the stope do not often +commend the method. As a general rule square-sets on horizontal +lines answer well enough for the period of actual ore-breaking. The +crushing or creeps is usually some time later; and if the crushing +may damage the whole mine, their use is fraught with danger. +Reënforcement by building in waste is often resorted to. When done +fully, it is difficult to see the utility of the enclosed timber, +for entire waste-filling would in most cases be cheaper and equally +efficient. + +[Illustration: Fig. 31.--"Cribs."] + +There is always, with wood constructions, as said before, the very +pertinent danger of subsequent crushing and of subsidence in after +years, and the great risk of fires. Both these disasters have cost +Comstock and Broken Hill mines, directly or indirectly, millions of +dollars, and the outlay on timber and repairs one way or another +would have paid for the filling system ten times over. There are +cases where, by virtue of the cheapness of timber, "square-setting" +is the most economical method. Again, there are instances where the +ore lies in such a manner--particularly in limestone replacements--as +to preclude other means of support. These cases are being yearly +more and more evaded by the ingenuity of engineers in charge. The +author believes it soon will be recognized that the situation is +rare indeed where complete square-setting is necessarily without an +economical alternative. An objection is sometimes raised to filling +in favor of timber, in that if it become desirable to restope the +walls for low-grade ore left behind, such stopes could only be +entered by drawing the filling, with consequent danger of total +collapse. Such a contingency can be provided for in large ore-bodies +by installing an outer shell of sets of timber around the periphery +of the stope and filling the inside with waste. If the crushing +possibilities are too great for this method then, the subsequent +recovery of ore is hopeless in any event. In narrow ore-bodies +with crushing walls recovery of ore once left behind is not often +possible. + +The third sort of timber constructions are cribs, a "log-house" sort +of structure usually filled with waste, and more fully discussed +under artificial pillars (Fig. 31). The further comparative merits +of timbering with other methods will be analyzed as the different +systems are described. + +FILLING WITH WASTE.--The system of filling stope-excavations completely +with waste in alternating progress with ore-breaking is of wide +and increasingly general application (Figs. 32, 33, 34, 35). + +Although a certain amount of waste is ordinarily available in the +stopes themselves, or from development work in the mine, such a +supply must usually be supplemented from other directions. Treatment +residues afford the easiest and cheapest handled material. Quarried +rock ranks next, and in default of any other easy supply, materials +from crosscuts driven into the stope-walls are sometimes resorted +to. + +In working the system to the best advantage, the winzes through +the block of ore under attack are kept in alignment with similar +openings above, in order that filling may be poured through the +mine from the surface or any intermediate point. Winzes to be used +for filling should be put on the hanging-wall side of the area to +be filled, for the filling poured down will then reach the foot-wall +side of the stopes with a minimum of handling. In some instances, +one special winze is arranged for passing all filling from the +surface to a level above the principal stoping operations; and +it is then distributed along the levels into the winzes, and thus +to the operating stopes, by belt-conveyors. + +[Illustration: Fig. 32.--Longitudinal section. Rill stope filled +with waste.] + +[Illustration: Fig. 33.--Longitudinal section. Horizontal stope +filled with waste.] + +[Illustration: Fig. 34.--Longitudinal section. Waste-filled stope +with dry-walling of levels and passes.] + +In this system of stope support the ore is broken at intervals +alternating with filling. If there is danger of much loss from +mixing broken ore and filling, "sollars" of boards or poles are +laid on the waste. If the ore is very rich, old canvas or cowhides +are sometimes put under the boards. Before the filling interval, +the ore passes are built close to the face above previous filling +and their tops covered temporarily to prevent their being filled +with running waste. If the walls are bad, the filling is kept close +to the face. If the unbroken ore requires support, short stulls +set on the waste (as in Fig. 39) are usually sufficient until the +next cut is taken off, when the timber can be recovered. If stulls +are insufficient, cribs or bulkheads (Fig. 31) are also used and +often buried in the filling. + +[Illustration: Fig. 35.--Cross-section of Fig. 34 on line _A-B_.] + +Both flat-backed and rill-stope methods of breaking are employed in +conjunction with filled stopes. The advantages of the rill-stopes +are so patent as to make it difficult to understand why they are +not universally adopted when the dip permits their use at all. In +rill-stopes (Figs. 32 and 34) the waste flows to its destination +with a minimum of handling. Winzes and ore-passes are not required +with the same frequency as in horizontal breaking, and the broken +ore always lies on the slope towards the passes and is therefore +also easier to shovel. In flat-backed stopes (Fig. 33) winzes must +be put in every 50 feet or so, while in rill-stopes they can be +double this distance apart. The system is applicable by modification +to almost any width of ore. It finds its most economical field +where the dip of the stope floor is over 45°, when waste and ore, +with the help of the "rill," will flow to their destination. For +dips from under about 45° to about 30° or 35°, where the waste +and ore will not "flow" easily, shoveling can be helped by the +use of the "rill" system and often evaded altogether, if flow be +assisted by a sheet-iron trough described in the discussion of +stope transport. Further saving in shoveling can be gained in this +method, by giving a steeper pitch to the filling winzes and to the +ore-passes, by starting them from crosscuts in the wall, and by +carrying them at greater angles than the pitch of the ore (Fig. +36). These artifices combined have worked out most economically +on several mines within the writer's experience, with the dip as +flat as 30°. For very flat dips, where filling is to be employed, +rill-stoping has no advantage over flat-backed cuts, and in such +cases it is often advisable to assist stope transport by temporary +tracks and cars which obviously could not be worked on the tortuous +contour of a rill-stope, so that for dips under 30° advantage lies +with "flat-backed" ore-breaking. + +[Illustration: Fig. 36.--Cross-section showing method of steepening +winzes and ore passes.] + +On very wide ore-bodies where the support of the standing ore itself +becomes a great problem, the filling system can be applied by combining +it with square-setting. In this case the stopes are carried in +panels laid out transversally to the strike as wide as the standing +strength of the ore permits. On both sides of each panel a fence +of lagged square-sets is carried up and the area between is filled +with waste. The panels are stoped out alternately. The application +of this method at Broken Hill will be described later. (See pages +120 and Figs. 41 and 42.) The same type of wide ore-body can be +managed also on the filling system by the use of frequent "bulkheads" +to support the ore (Fig. 31). + +Compared with timbering methods, filling has the great advantage +of more effective support to the mine, less danger of creeps, and +absolute freedom from the peril of fire. The relative expense of +the two systems is determined by the cost of materials and labor. +Two extreme cases illustrate the result of these economic factors +with sufficient clearness. It is stated that the cost of timbering +stopes on the Le Roi Mine by square-sets is about 21 cents per +ton of ore excavated. In the Ivanhoe mine of West Australia the +cost of filling stopes with tailings is about 22 cents per ton +of ore excavated. At the former mine the average cost of timber +is under $10 per M board-measure, while at the latter its price +would be $50 per M board-measure; although labor is about of the +same efficiency and wage, the cost in the Ivanhoe by square-setting +would be about 65 cents per ton of ore broken. In the Le Roi, on the +other hand, no residues are available for filling. To quarry rock +or drive crosscuts into the walls might make this system cost 65 +cents per ton of ore broken if applied to that mine. The comparative +value of the filling method with other systems will be discussed +later. + +FILLING WITH BROKEN ORE SUBSEQUENTLY WITHDRAWN.--This order of support +is called by various names, the favorite being "shrinkage-stoping." +The method is to break the ore on to the roof of the level, and by +thus filling the stope with broken ore, provide temporary support +to the walls and furnish standing floor upon which to work in making +the next cut (Figs. 37, 38, and 39.) As broken material occupies 30 +to 40% more space than rock _in situ_, in order to provide working +space at the face, the broken ore must be drawn from along the level +after each cut. When the area attacked is completely broken through +from level to level, the stope will be full of loose broken ore, +which is then entirely drawn off. + +A block to be attacked by this method requires preliminary winzes +only at the extremities of the stope,--for entry and for ventilation. +Where it is desired to maintain the winzes after stoping, they +must either be strongly timbered and lagged on the stope side, +be driven in the walls, or be protected by a pillar of ore (Fig. +37). The settling ore and the crushing after the stope is empty +make it difficult to maintain timbered winzes. + +[Illustration: Fig. 37.--Longitudinal section of stope filled with +broken ore.] + +Where it can be done without danger to the mine, the empty stopes +are allowed to cave. If such crushing would be dangerous, either +the walls must be held up by pillars of unbroken ore, as in the +Alaska Treadwell, where large "rib" pillars are left, or the open +spaces must be filled with waste. Filling the empty stope is usually +done by opening frequent passes along the base of the filled stope +above, and allowing the material of the upper stope to flood the +lower one. This program continued upwards through the mine allows +the whole filling of the mine to descend gradually and thus requires +replenishment only into the top. The old stopes in the less critical +and usually exhausted territory nearer the surface are sometimes +left without replenishing their filling. + +The weight of broken ore standing at such a high angle as to settle +rapidly is very considerable upon the level; moreover, at the moment +when the stope is entirely drawn off, the pressure of the walls +as well is likely to be very great. The roadways in this system +therefore require more than usual protection. Three methods are +used: (_a_) timbering; (_b_) driving a sublevel in the ore above +the main roadway as a stoping-base, thus leaving a pillar of ore +over the roadway (Fig. 39); (_c_) by dry-walling the levels, as in +the Baltic mine, Michigan (Figs. 34 and 35). By the use of sublevels +the main roadways are sometimes driven in the walls (Fig. 38) and in +many cases all timbering is saved. To recover pillars left below +sublevels is a rather difficult task, especially if the old stope +above is caved or filled. The use of pillars in substitution for +timber, if the pillars are to be lost, is simply a matter of economics +as to whether the lost ore would repay the cost of other devices. + +[Illustration: Fig. 38.--Cross-section of "shrinkage" stope.] + +Frequent ore-chutes through the level timbers, or from the sublevels, +are necessary to prevent lodgment of broken ore between such passes, +because it is usually too dangerous for men to enter the emptying +stope to shovel out the lodged remnants. Where the ore-body is +wide, and in order that there may be no lodgment of ore, the timbers +over the level are set so as to form a trough along the level; +or where pillars are left, they are made "A"-shaped between the +chutes, as indicated in Figure 37. + +[Illustration: Fig. 39.--Cross-section of "shrinkage" stope.] + +The method of breaking the ore in conjunction with this means of +support in comparatively narrow deposits can be on the rill, in order +to have the advantage of down holes. Usually, however, flat-back +or horizontal cuts are desirable, as in such an arrangement it +is less troublesome to regulate the drawing of the ore so as to +provide proper head room. Where stopes are wide, ore is sometimes +cut arch-shaped from wall to wall to assure its standing. Where +this method of support is not of avail, short, sharply tapering +stulls are put in from the broken ore to the face (Fig. 39). When +the cut above these stulls is taken out, they are pulled up and +are used again. + +This method of stoping is only applicable when:-- + +1. The deposit dips over 60°, and thus broken material will freely +settle downward to be drawn off from the bottom. + +2. The ore is consistently payable in character. No selection can be +done in breaking, as all material broken must be drawn off together. + +3. The hanging wall is strong, and will not crush or spall off waste +into the ore. + +4. The ore-body is regular in size, else loose ore will lodge on +the foot wall. Stopes opened in this manner when partially empty +are too dangerous for men to enter for shoveling out remnants. + +The advantages of this system over others, where it is applicable, +are:-- + +(_a_) A greater distance between levels can be operated and few +winzes and rises are necessary, thus a great saving of development +work can be effected. A stope 800 to 1000 feet long can be operated +with a winze at either end and with levels 200 or 220 feet apart. + +(_b_) There is no shoveling in the stopes at all. + +(_c_) No timber is required. As compared with timbering by stulling, +it will apply to stopes too wide and walls too heavy for this method. +Moreover, little staging is required for working the face, since +ore can be drawn from below in such a manner as to allow just the +right head room. + +(_d_) Compared to the system of filling with waste, coincidentally +with breaking (second method), it saves altogether in some cases +the cost of filling. In any event, it saves the cost of ore-passes, +of shoveling into them, and of the detailed distribution of the +filling. + +Compared with other methods, the system has the following disadvantages, +that: + +_A_. The ore requires to be broken in the stopes to a degree of +fineness which will prevent blocking of the chutes at the level. +When pieces too large reach the chutes, nothing will open them but +blasting,--to the damage of timbers and chutes. Some large rocks +are always liable to be buried in the course of ore-breaking. + +_B_. Practically no such perfection of walls exists, but some spalling +of waste into the ore will take place. A crushing of the walls +would soon mean the loss of large amounts of ore. + +_C_. There is no possibility of regulating the mixture of grade +of ore by varying the working points. It is months after the ore +is broken before it can reach the levels. + +_D_. The breaking of 60% more ore than immediate treatment demands +results in the investment of a considerable sum of money. An equilibrium +is ultimately established in a mine worked on this system when a +certain number of stopes full of completely broken ore are available +for entire withdrawal, and there is no further accumulation. But, +in any event, a considerable amount of broken ore must be held in +reserve. In one mine worked on this plan, with which the writer +has had experience, the annual production is about 250,000 tons +and the broken ore represents an investment which, at 5%, means +an annual loss of interest amounting to 7 cents per ton of ore +treated. + +_E_. A mine once started on the system is most difficult to alter, +owing to the lack of frequent winzes or passes. Especially is this +so if the only alternative is filling, for an alteration to the +system of filling coincident with breaking finds the mine short +of filling winzes. As the conditions of walls and ore often alter +with depth, change of system may be necessary and the situation +may become very embarrassing. + +_F_. The restoping of the walls for lower-grade ore at a later +period is impossible, for the walls of the stope will be crushed, +or, if filled with waste, will usually crush when it is drawn off +to send to a lower stope. + +The system has much to recommend it where conditions are favorable. +Like all other alternative methods of mining, it requires the most +careful study in the light of the special conditions involved. In many +mines it can be used for some stopes where not adaptable generally. +It often solves the problem of blind ore-bodies, for they can by +this means be frequently worked with an opening underneath only. +Thus the cost of driving a roadway overhead is avoided, which would +be required if timber or coincident filling were the alternatives. +In such cases ventilation can be managed without an opening above, +by so directing the current of air that it will rise through a +winze from the level below, flow along the stope and into the level +again at the further end of the stope through another winze. + +[Illustration: Fig. 40.--Longitudinal section. Ore-pillar support +in narrow stopes.] + +SUPPORT BY PILLARS OF ORE.--As a method of mining metals of the +sort under discussion, the use of ore-pillars except in conjunction +with some other means of support has no general application. To +use them without assistance implies walls sufficiently strong to +hold between pillars; to leave them permanently anywhere implies +that the ore abandoned would not repay the labor and the material +of a substitute. There are cases of large, very low-grade mines +where to abandon one-half the ore as pillars is more profitable +than total extraction, but the margin of payability in such ore must +be very, very narrow. Unpayable spots are always left as pillars, +for obvious reasons. Permanent ore-pillars as an adjunct to other +methods of support are in use. Such are the rib-pillars in the +Alaska Treadwell, the form of which is indicated by the upward +extension of the pillars adjacent to the winzes, shown in Figure +37. Always a careful balance must be cast as to the value of the ore +left, and as to the cost of a substitute, because every ore-pillar +can be removed at some outlay. Temporary pillars are not unusual, +particularly to protect roadways and shafts. They are, when left +for these purposes, removed ultimately, usually by beginning at +the farther end and working back to the final exit. + +[Illustration: Fig. 41.--Horizontal plan at levels of Broken Hill. +Method of alternate stopes and ore-pillars.] + +[Illustration: Fig. 42.--Longitudinal section of Figure 41.] + +A form of temporary ore-pillars in very wide deposits is made use +of in conjunction with both filling and timbering (Figs. 37, 39, +40). In the use of temporary pillars for ore-bodies 100 to 250 +feet wide at Broken Hill, stopes are carried up at right angles +to the strike, each fifty feet wide and clear across the ore-body +(Figs. 41 and 42). A solid pillar of the same width is left in the +first instance between adjacent stopes, and the initial series of +stopes are walled with one square-set on the sides as the stope is +broken upward. The room between these two lines of sets is filled +with waste alternating with ore-breaking in the usual filling method. +When the ore from the first group of alternate stopes (_ABC_, Fig. +42) is completely removed, the pillars are stoped out and replaced +with waste. The square-sets of the first set of stopes thus become +the boundaries of the second set. Entry and ventilation are obtained +through these lines of square-sets, and the ore is passed out of +the stopes through them. + +[Illustration: Fig. 43.--Cross-section of stull support with waste +reënforcement.] + +ARTIFICIAL PILLARS.--This system also implies a roof so strong +as not to demand continuous support. Artificial pillars are built +in many different ways. The method most current in fairly narrow +deposits is to reënforce stulls by packing waste above them (Figs. +43 and 44). Not only is it thus possible to economize in stulls by +using the waste which accumulates underground, but the principle +applies also to cases where the stulls alone are not sufficient +support, and yet where complete filling or square-setting is +unnecessary. When the conditions are propitious for this method, it +has the comparative advantage over timber systems of saving timber, +and over filling systems of saving imported filling. Moreover, +these constructions being pillar-shaped (Fig. 44), the intervals +between them provide outlets for broken ore, and specially built +passes are unnecessary. The method has two disadvantages as against +the square-set or filling process, in that more staging must be +provided from which to work, and in stopes over six feet the erection +of machine-drill columns is tedious and costly in time and wages. + +[Illustration: Fig. 44.--Longitudinal section of stull and waste +pillars.] + +In wide deposits of markedly flat, irregular ore-bodies, where a +definite system is difficult and where timber is expensive, cribs +of cord-wood or logs filled with waste after the order shown in +Figure 31, often make fairly sound pillars. They will not last +indefinitely and are best adapted to the temporary support of the +ore-roof pending filling. The increased difficulty in setting up +machine drills in such stopes adds to the breaking costs,--often +enough to warrant another method of support. + +[Illustration: Fig. 45.--Sublevel caving system.] + +CAVING SYSTEMS.--This method, with variations, has been applied +to large iron deposits, to the Kimberley diamond mines, to some +copper mines, but in general it has little application to the metal +mines under consideration, as few ore-bodies are of sufficiently +large horizontal area. The system is dependent upon a large area of +loose or "heavy" ground pressing directly on the ore with weight, +such that if the ore be cut into pillars, these will crush. The +details of the system vary, but in general the _modus operandi_ +is to prepare roadways through the ore, and from the roadways to +put rises, from which sublevels are driven close under the floating +mass of waste and ore,--sometimes called the "matte" (Fig. 45). +The pillars between these sublevels are then cut away until the +weight above crushes them down. When all the crushed ore which +can be safely reached is extracted, retreat is made and another +series of subopenings is then driven close under the "matte." The +pillar is reduced until it crushes and the operation is repeated. +Eventually the bottom strata of the "matte" become largely ore, +and a sort of equilibrium is reached when there is not much loss +in this direction. "Top slicing" is a variation of the above method +by carrying a horizontal stope from the rises immediately under the +matte, supporting the floating material with timber. At Kimberley +the system is varied in that galleries are run out to the edge of +the diamond-iferous area and enlarged until the pillar between +crushes. + +In the caving methods, between 40 and 50% of the ore is removed +by the preliminary openings, and as they are all headings of some +sort, the average cost per ton of this particular ore is higher +than by ordinary stoping methods. On the other hand, the remaining +50 to 60% of the ore costs nothing to break, and the average cost +is often remarkably low. As said, the system implies bodies of large +horizontal area. They must start near enough to the surface that +the whole superincumbent mass may cave and give crushing weight, +or the immediately overhanging roof must easily cave. All of these +are conditions not often met with in mines of the character under +review. + + + + +CHAPTER XII. + +Mechanical Equipment. + +CONDITIONS BEARING ON MINE EQUIPMENT; WINDING APPLIANCES; HAULAGE +EQUIPMENT IN SHAFTS; LATERAL UNDERGROUND TRANSPORT; TRANSPORT IN +STOPES. + +There is no type of mechanical engineering which presents such +complexities in determination of the best equipment as does that of +mining. Not only does the economic side dominate over pure mechanics, +but machines must be installed and operated under difficulties which +arise from the most exceptional and conflicting conditions, none of +which can be entirely satisfied. Compromise between capital outlay, +operating efficiency, and conflicting demands is the key-note of +the work. + +These compromises are brought about by influences which lie outside +the questions of mechanics of individual machines, and are mainly +as follows:-- + + 1. Continuous change in horizon of operations. + 2. Uncertain life of the enterprise. + 3. Care and preservation of human life. + 4. Unequal adaptability of power transmission mediums. + 5. Origin of power. + +_First._--The depth to be served and the volume of ore and water +to be handled, are not only unknown at the initial equipment, but +they are bound to change continuously in quantity, location, and +horizon with the extension of the workings. + +_Second._--From the mine manager's point of view, which must embrace +that of the mechanical engineer, further difficulty presents itself +because the life of the enterprise is usually unknown, and therefore +a manifest necessity arises for an economic balance of capital +outlay and of operating efficiency commensurate with the prospects +of the mine. Moreover, the initial capital is often limited, and +makeshifts for this reason alone must be provided. In net result, +no mineral deposit of speculative ultimate volume of ore warrants +an initial equipment of the sort that will meet every eventuality, +or of the kind that will give even the maximum efficiency which +a free choice of mining machinery could obtain. + +_Third._--In the design and selection of mining machines, the safety +of human life, the preservation of the health of workmen under +conditions of limited space and ventilation, together with reliability +and convenience in installing and working large mechanical tools, +all dominate mechanical efficiency. For example, compressed-air +transmission of power best meets the requirements of drilling, +yet the mechanical losses in the generation, the transmission, +and the application of compressed air probably total, from first +to last, 70 to 85%. + +_Fourth._--All machines, except those for shaft haulage, must be +operated by power transmitted from the surface, as obviously power +generation underground is impossible. The conversion of power into +a transmission medium and its transmission are, at the outset, +bound to be the occasions of loss. Not only are the various forms +of transmission by steam, electricity, compressed air, or rods, of +different efficiency, but no one system lends itself to universal +or economical application to all kinds of mining machines. Therefore +it is not uncommon to find three or four different media of power +transmission employed on the same mine. To illustrate: from the +point of view of safety, reliability, control, and in most cases +economy as well, we may say that direct steam is the best motive +force for winding-engines; that for mechanical efficiency and +reliability, rods constitute the best media of power transmission +to pumps; that, considering ventilation and convenience, compressed +air affords the best medium for drills. Yet there are other conditions +as to character of the work, volume of water or ore, and the origin +of power which must in special instances modify each and every one +of these generalizations. For example, although pumping water with +compressed air is mechanically the most inefficient of devices, +it often becomes the most advantageous, because compressed air may +be of necessity laid on for other purposes, and the extra power +required to operate a small pump may be thus most cheaply provided. + +_Fifth._--Further limitations and modifications arise out of the +origin of power, for the sources of power have an intimate bearing on +the type of machine and media of transmission. This very circumstance +often compels giving away efficiency and convenience in some machines +to gain more in others. This is evident enough if the principal +origins of power generation be examined. They are in the main as +follows:-- + +_a_. Water-power available at the mine. +_b_. Water-power available at a less distance than three + or four miles. +_c_. Water-power available some miles away, thus necessitating + electrical transmission (or purchased electrical power). +_d_. Steam-power to be generated at the mine. +_e_. Gas-power to be generated at the mine. + +_a_. With water-power at the mine, winding engines can be operated +by direct hydraulic application with a gain in economy over direct +steam, although with the sacrifice of control and reliability. Rods +for pumps can be driven directly with water, but this superiority +in working economy means, as discussed later, a loss of flexibility +and increased total outlay over other forms of transmission to pumps. +As compressed air must be transmitted for drills, the compressor +would be operated direct from water-wheels, but with less control +in regularity of pressure delivery. + +_b_. With water-power a short distance from the mine, it would +normally be transmitted either by compressed air or by electricity. +Compressed-air transmission would better satisfy winding and drilling +requirements, but would show a great comparative loss in efficiency +over electricity when applied to pumping. Despite the latter drawback, +air transmission is a method growing in favor, especially in view +of the advance made in effecting compression by falling water. + +_c_. In the situation of transmission too far for using compressed +air, there is no alternative but electricity. In these cases, direct +electric winding is done, but under such disadvantages that it +requires a comparatively very cheap power to take precedence over +a subsidiary steam plant for this purpose. Electric air-compressors +work under the material disadvantage of constant speed on a variable +load, but this installation is also a question of economics. The +pumping service is well performed by direct electrical pumps. + +_d_. In this instance, winding and air-compression are well accomplished +by direct steam applications; but pumping is beset with wholly +undesirable alternatives, among which it is difficult to choose. + +_e_. With internal combustion engines, gasoline (petrol) motors +have more of a position in experimental than in systematic mining, +for their application to winding and pumping and drilling is fraught +with many losses. The engine must be under constant motion, and +that, too, with variable loads. Where power from producer gas is +used, there is a greater possibility of installing large equipments, +and it is generally applied to the winding and lesser units by +conversion into compressed air or electricity as an intermediate +stage. + +One thing becomes certain from these examples cited, that the right +installation for any particular portion of the mine's equipment cannot +be determined without reference to all the others. The whole system +of power generation for surface work, as well as the transmission +underground, must be formulated with regard to furnishing the best +total result from all the complicated primary and secondary motors, +even at the sacrifice of some members. + +Each mine is a unique problem, and while it would be easy to sketch +an ideal plant, there is no mine within the writer's knowledge +upon which the ideal would, under the many variable conditions, +be the most economical of installation or the most efficient of +operation. The dominant feature of the task is an endeavor to find +a compromise between efficiency and capital outlay. The result is +a series of choices between unsatisfying alternatives, a number of +which are usually found to have been wrong upon further extension +of the mine in depth. + +In a general way, it may be stated that where power is generated +on the mine, economy in labor of handling fuel, driving engines, +generation and condensing steam where steam is used, demand a +consolidated power plant for the whole mine equipment. The principal +motors should be driven direct by steam or gas, with power distribution +by electricity to all outlying surface motors and sometimes to +underground motors, and also to some underground motors by compressed +air. + +Much progress has been made in the past few years in the perfection +of larger mining tools. Inherently many of our devices are of a +wasteful character, not only on account of the need of special +forms of transmission, but because they are required to operate +under greatly varying loads. As an outcome of transmission losses +and of providing capacity to cope with heavy peak loads, their +efficiency on the basis of actual foot-pounds of work accomplished +is very low. + +The adoption of electric transmission in mine work, while in certain +phases beneficial, has not decreased the perplexity which arises +from many added alternatives, none of which are as yet a complete or +desirable answer to any mine problem. When a satisfactory electric +drill is invented, and a method is evolved of applying electricity +to winding-engines that will not involve such abnormal losses due +to high peak load then we will have a solution to our most difficult +mechanical problems, and electricity will deserve the universal +blessing which it has received in other branches of mechanical +engineering. + +It is not intended to discuss mine equipment problems from the +machinery standpoint,--there are thousands of different devices,--but +from the point of view of the mine administrator who finds in the +manufactory the various machines which are applicable, and whose +work then becomes that of choosing, arranging, and operating these +tools. + +The principal mechanical questions of a mine may be examined under +the following heads:-- + + 1. Shaft haulage. + 2. Lateral underground transport. + 3. Drainage. + 4. Rock drilling. + 5. Workshops. + 6. Improvements in equipment. + +SHAFT HAULAGE. + +WINDING APPLIANCES.--No device has yet been found to displace the +single load pulled up the shaft by winding a rope on a drum. Of +driving mechanisms for drum motors the alternatives are the +steam-engine, the electrical motor, and infrequently water-power +or gas engines. + +All these have to cope with one condition which, on the basis of +work accomplished, gives them a very low mechanical efficiency. +This difficulty is that the load is intermittent, and it must be +started and accelerated at the point of maximum weight, and from +that moment the power required diminishes to less than nothing +at the end of the haul. A large number of devices are in use to +equalize partially the inequalities of the load at different stages +of the lift. The main lines of progress in this direction have +been:-- + +_a_. The handling of two cages or skips with one engine + or motor, the descending skip partially balancing + the ascending one. +_b_. The use of tail-ropes or balance weights to compensate + the increasing weight of the descending rope. +_c_. The use of skips instead of cages, thus permitting of + a greater percentage of paying load. +_d_. The direct coupling of the motor to the drum shaft. +_e_. The cone-shaped construction of drums,--this latter + being now largely displaced by the use of the tail-rope. + +The first and third of these are absolutely essential for anything +like economy and speed; the others are refinements depending on +the work to be accomplished and the capital available. + +Steam winding-engines require large cylinders to start the load, +but when once started the requisite power is much reduced and the +load is too small for steam economy. The throttling of the engine +for controlling speed and reversing the engine at periodic stoppages +militates against the maximum expansion and condensation of the +steam and further increases the steam consumption. In result, the +best of direct compound condensing engines consume from 60 to 100 +pounds of steam per horse-power hour, against a possible efficiency +of such an engine working under constant load of less than 16 pounds +of steam per horse-power hour. + +It is only within very recent years that electrical motors have +been applied to winding. Even yet, all things considered, this +application is of doubtful value except in localities of extremely +cheap electrical power. The constant speed of alternating current +motors at once places them at a disadvantage for this work of high +peak and intermittent loads. While continuous-current motors can +be made to partially overcome this drawback, such a current, where +power is purchased or transmitted a long distance, is available +only by conversion, which further increases the losses. However, +schemes of electrical winding are in course of development which +bid fair, by a sort of storage of power in heavy fly-wheels or +storage batteries after the peak load, to reduce the total power +consumption; but the very high first cost so far prevents their +very general adoption for metal mining. + +Winding-engines driven by direct water- or gas-power are of too rare +application to warrant much discussion. Gasoline driven hoists have a +distinct place in prospecting and early-stage mining, especially in +desert countries where transport and fuel conditions are onerous, +for both the machines and their fuel are easy of transport. As direct +gas-engines entail constant motion of the engine at the power demand +of the peak load, they are hopeless in mechanical efficiency. + +Like all other motors in mining, the size and arrangement of the +motor and drum are dependent upon the duty which they will be called +upon to perform. This is primarily dependent upon the depth to be +hoisted from, the volume of the ore, and the size of the load. +For shallow depths and tonnages up to, say, 200 tons daily, geared +engines have a place on account of their low capital cost. Where +great rope speed is not essential they are fully as economical as +direct-coupled engines. With great depths and greater capacities, +speed becomes a momentous factor, and direct-coupled engines are +necessary. Where the depth exceeds 3,000 feet, another element +enters which has given rise to much debate and experiment; that +is, the great increase of starting load due to the increased length +and size of ropes and the drum space required to hold it. So far +the most advantageous device seems to be the Whiting hoist, a +combination of double drums and tail rope. + +On mines worked from near the surface, where depth is gained by +the gradual exhaustion of the ore, the only prudent course is to +put in a new hoist periodically, when the demand for increased +winding speed and power warrants. The lack of economy in winding +machines is greatly augmented if they are much over-sized for the +duty. An engine installed to handle a given tonnage to a depth of +3,000 feet will have operated with more loss during the years the +mine is progressing from the surface to that depth than several +intermediate-sized engines would have cost. On most mines the +uncertainty of extension in depth would hardly warrant such a +preliminary equipment. More mines are equipped with over-sized +than with under-sized engines. For shafts on going metal mines +where the future is speculative, an engine will suffice whose size +provides for an extension in depth of 1,000 feet beyond that reached +at the time of its installation. The cost of the engine will depend +more largely upon the winding speed desired than upon any other +one factor. The proper speed to be arranged is obviously dependent +upon the depth of the haulage, for it is useless to have an engine +able to wind 3,000 feet a minute on a shaft 500 feet deep, since it +could never even get under way; and besides, the relative operating +loss, as said, would be enormous. + +HAULAGE EQUIPMENT IN THE SHAFT.--Originally, material was hoisted +through shafts in buckets. Then came the cage for transporting mine +cars, and in more recent years the "skip" has been developed. The +aggrandized bucket or "kibble" of the Cornishman has practically +disappeared, but the cage still remains in many mines. The advantages +of the skip over the cage are many. Some of them are:-- + + _a_. It permits 25 to 40% greater load of material in + proportion to the dead weight of the vehicle. + _b_. The load can be confined within a smaller horizontal + space, thus the area of the shaft need not be so great + for large tonnages. + _c_. Loading and discharging are more rapid, and the latter + is automatic, thus permitting more trips per hour and + requiring less labor. + _d_. Skips must be loaded from bins underground, and by + providing in the bins storage capacity, shaft haulage is + rendered independent of the lateral transport in the + mine, and there are no delays to the engine awaiting + loads. The result is that ore-winding can be concentrated + into fewer hours, and indirect economies in labor + and power are thus effected. + _e_. Skips save the time of the men engaged in the lateral + haulage, as they have no delay waiting for the winding + engine. + +Loads equivalent to those from skips are obtained in some mines +by double-decked cages; but, aside from waste weight of the cage, +this arrangement necessitates either stopping the engine to load the +lower deck, or a double-deck loading station. Double-deck loading +stations are as costly to install and more expensive to work than +skip-loading station ore-bins. Cages are also constructed large +enough to take as many as four trucks on one deck. This entails a +shaft compartment double the size required for skips of the same +capacity, and thus enormously increases shaft cost without gaining +anything. + +Altogether the advantages of the skip are so certain and so important +that it is difficult to see the justification for the cage under +but a few conditions. These conditions are those which surround +mines of small output where rapidity of haulage is no object, where +the cost of station-bins can thus be evaded, and the convenience +of the cage for the men can still be preserved. The easy change +of the skip to the cage for hauling men removes the last objection +on larger mines. There occurs also the situation in which ore is +broken under contract at so much per truck, and where it is desirable +to inspect the contents of the truck when discharging it, but even +this objection to the skip can be obviated by contracting on a +cubic-foot basis. + +Skips are constructed to carry loads of from two to seven tons, +the general tendency being toward larger loads every year. One +of the most feasible lines of improvement in winding is in the +direction of larger loads and less speed, for in this way the sum +total of dead weight of the vehicle and rope to the tonnage of +ore hauled will be decreased, and the efficiency of the engine +will be increased by a less high peak demand, because of this less +proportion of dead weight and the less need of high acceleration. + +LATERAL UNDERGROUND TRANSPORT. + +Inasmuch as the majority of metal mines dip at considerable angles, +the useful life of a roadway in a metal mine is very short because +particular horizons of ore are soon exhausted. Therefore any method +of transport has to be calculated upon a very quick redemption of +the capital laid out. Furthermore, a roadway is limited in its +daily traffic to the product of the stopes which it serves. + +MEN AND ANIMALS.--Some means of transport must be provided, and +the basic equipment is light tracks with push-cars, in capacity +from half a ton to a ton. The latter load is, however, too heavy +to be pushed by one man. As but one car can be pushed at a time, +hand-trucking is both slow and expensive. At average American or +Australian wages, the cost works out between 25 and 35 cents a +ton per mile. An improvement of growing import where hand-trucking +is necessary is the overhead mono-rail instead of the track. + +If the supply to any particular roadway is such as to fully employ +horses or mules, the number of cars per trip can be increased up +to seven or eight. In this case the expense, including wages of +the men and wear, tear, and care of mules, will work out roughly +at from 7 to 10 cents per ton mile. Manifestly, if the ore-supply +to a particular roadway is insufficient to keep a mule busy, the +economy soon runs off. + +MECHANICAL HAULAGE.--Mechanical haulage is seldom applicable to +metal mines, for most metal deposits dip at considerable angles, +and therefore, unlike most coal-mines, the horizon of haulage must +frequently change, and there are no main arteries along which haulage +continues through the life of the mine. Any mechanical system entails +a good deal of expense for installation, and the useful life of +any particular roadway, as above said, is very short. Moreover, +the crooked roadways of most metal mines present difficulties of +negotiation not to be overlooked. In order to use such systems it +is necessary to condense the haulage to as few roadways as possible. +Where the tonnage on one level is not sufficient to warrant other +than men or animals, it sometimes pays (if the dip is steep enough) +to dump everything through winzes from one to two levels to a main +road below where mechanical equipment can be advantageously provided. +The cost of shaft-winding the extra depth is inconsiderable compared +to other factors, for the extra vertical distance of haulage can +be done at a cost of one or two cents per ton mile. Moreover, from +such an arrangement follows the concentration of shaft-bins, and of +shaft labor, and winding is accomplished without so much shifting +as to horizon, all of which economies equalize the extra distance +of the lift. + +There are three principal methods of mechanical transport in use:-- + + 1. Cable-ways. + 2. Compressed-air locomotives. + 3. Electrical haulage. + +Cable-ways or endless ropes are expensive to install, and to work +to the best advantage require double tracks and fairly straight +roads. While they are economical in operation and work with little +danger to operatives, the limitations mentioned preclude them from +adoption in metal mines, except in very special circumstances such +as main crosscuts or adit tunnels, where the haulage is straight +and concentrated from many sources of supply. + +Compressed-air locomotives are somewhat heavy and cumbersome, and +therefore require well-built tracks with heavy rails, but they +have very great advantages for metal mine work. They need but a +single track and are of low initial cost where compressed air is +already a requirement of the mine. No subsidiary line equipment is +needed, and thus they are free to traverse any road in the mine and +can be readily shifted from one level to another. Their mechanical +efficiency is not so low in the long run as might appear from the +low efficiency of pneumatic machines generally, for by storage of +compressed air at the charging station a more even rate of energy +consumption is possible than in the constant cable and electrical +power supply which must be equal to the maximum demand, while the +air-plant consumes but the average demand. + +Electrical haulage has the advantage of a much more compact locomotive +and the drawback of more expensive track equipment, due to the +necessity of transmission wire, etc. It has the further disadvantages +of uselessness outside the equipped haulage way and of the dangers +of the live wire in low and often wet tunnels. + +In general, compressed-air locomotives possess many attractions +for metal mine work, where air is in use in any event and where +any mechanical system is at all justified. Any of the mechanical +systems where tonnage is sufficient in quantity to justify their +employment will handle material for from 1.5 to 4 cents per ton +mile. + +TRACKS.--Tracks for hand, mule, or rope haulage are usually built +with from 12- to 16-pound rails, but when compressed-air or electrical +locomotives are to be used, less than 24-pound rails are impossible. +As to tracks in general, it may be said that careful laying out +with even grades and gentle curves repays itself many times over in +their subsequent operation. Further care in repair and lubrication +of cars will often make a difference of 75% in the track resistance. + +TRANSPORT IN STOPES.--Owing to the even shorter life of individual +stopes than levels, the actual transport of ore or waste in them is +often a function of the aboriginal shovel plus gravity. As shoveling +is the most costly system of transport known, any means of stoping +that decreases the need for it has merit. Shrinkage-stoping eliminates +it altogether. In the other methods, gravity helps in proportion to +the steepness of the dip. When the underlie becomes too flat for +the ore to "run," transport can sometimes be helped by pitching +the ore-passes at a steeper angle than the dip (Fig. 36). In some +cases of flat deposits, crosscuts into the walls, or even levels +under the ore-body, are justifiable. The more numerous the ore-passes, +the less the lateral shoveling, but as passes cost money for +construction and for repair, there is a nice economic balance in +their frequency. + +Mechanical haulage in stopes has been tried and finds a field under +some conditions. In dips under 25° and possessing fairly sound +hanging-wall, where long-wall or flat-back cuts are employed, temporary +tracks can often be laid in the stopes and the ore run in cars to +the main passes. In such cases, the tracks are pushed up close +to the face after each cut. Further self-acting inclines to lower +cars to the levels can sometimes be installed to advantage. This +arrangement also permits greater intervals between levels and less +number of ore-passes. For dips between 25° and 50° where the mine +is worked without stope support or with occasional pillars, a very +useful contrivance is the sheet-iron trough--about eighteen inches +wide and six inches deep--made in sections ten or twelve feet long +and readily bolted together. In dips 35° to 50° this trough, laid +on the foot-wall, gives a sufficiently smooth surface for the ore +to run upon. When the dip is flat, the trough, if hung from plugs +in the hanging-wall, may be swung backward and forward. The use of +this "bumping-trough" saves much shoveling. For handling filling +or ore in flat runs it deserves wider adoption. It is, of course, +inapplicable in passes as a "bumping-trough," but can be fixed to +give smooth surface. In flat mines it permits a wider interval +between levels and therefore saves development work. The life of +this contrivance is short when used in open stopes, owing to the +dangers of bombardment from blasting. + +In dips steeper than 50° much of the shoveling into passes can be +saved by rill-stoping, as described on page 100. Where flat-backed +stopes are used in wide ore-bodies with filling, temporary tracks +laid on the filling to the ore-passes are useful, for they permit +wider intervals between passes. + +In that underground engineer's paradise, the Witwatersrand, where +the stopes require neither timber nor filling, the long, moderately +pitched openings lend themselves particularly to the swinging iron +troughs, and even endless wire ropes have been found advantageous +in certain cases. + +Where the roof is heavy and close support is required, and where +the deposits are very irregular in shape and dip, there is little +hope of mechanical assistance in stope transport. + + + + +CHAPTER XIII. + +Mechanical Equipment. (_Continued_). + +DRAINAGE: CONTROLLING FACTORS; VOLUME AND HEAD OF WATER; FLEXIBILITY; +RELIABILITY; POWER CONDITIONS; MECHANICAL EFFICIENCY; CAPITAL OUTLAY. +SYSTEMS OF DRAINAGE,--STEAM PUMPS, COMPRESSED-AIR PUMPS, ELECTRICAL +PUMPS, ROD-DRIVEN PUMPS, BAILING; COMPARATIVE VALUE OF VARIOUS +SYSTEMS. + +With the exception of drainage tunnels--more fully described in +Chapter VIII--all drainage must be mechanical. As the bulk of mine +water usually lies near the surface, saving in pumping can sometimes +be effected by leaving a complete pillar of ore under some of the +upper levels. In many deposits, however, the ore has too many channels +to render this of much avail. + +There are six factors which enter into a determination of mechanical +drainage systems for metal mines:-- + + 1. Volume and head of water. + 2. Flexibility to fluctuation in volume and head. + 3. Reliability. + 4. Capital cost. + 5. The general power conditions. + 6. Mechanical efficiency. + +In the drainage appliances, more than in any other feature of the +equipment, must mechanical efficiency be subordinated to the other +issues. + +FLEXIBILITY.--Flexibility in plant is necessary because volume and +head of water are fluctuating factors. In wet regions the volume +of water usually increases for a certain distance with the extension +of openings in depth. In dry climates it generally decreases with the +downward extension of the workings after a certain depth. Moreover, +as depth progresses, the water follows the openings more or less +and must be pumped against an ever greater head. In most cases +the volume varies with the seasons. What increase will occur, from +what horizon it must be lifted, and what the fluctuations in volume +are likely to be, are all unknown at the time of installation. If +a pumping system were to be laid out for a new mine, which would +peradventure meet every possible contingency, the capital outlay would +be enormous, and the operating efficiency would be very low during +the long period in which it would be working below its capacity. The +question of flexibility does not arise so prominently in coal-mines, +for the more or less flat deposits give a fixed factor of depth. +The flow is also more steady, and the volume can be in a measure +approximated from general experience. + +RELIABILITY.--The factor of reliability was at one time of more +importance than in these days of high-class manufacture of many +different pumping systems. Practically speaking, the only insurance +from flooding in any event lies in the provision of a relief system +of some sort,--duplicate pumps, or the simplest and most usual +thing, bailing tanks. Only Cornish and compressed-air pumps will +work with any security when drowned, and electrical pumps are easily +ruined. + +GENERAL POWER CONDITIONS.--The question of pumping installation +is much dependent upon the power installation and other power +requirements of the mine. For instance, where electrical power is +purchased or generated by water-power, then electrical pumps have +every advantage. Or where a large number of subsidiary motors can be +economically driven from one central steam- or gas-driven electrical +generation plant, they again have a strong call,--especially if +the amount of water to be handled is moderate. Where the water +is of limited volume and compressed-air plant a necessity for the +mine, then air-driven pumps may be the most advantageous, etc. + +MECHANICAL EFFICIENCY.--The mechanical efficiency of drainage machinery +is very largely a question of method of power application. The +actual pump can be built to almost the same efficiency for any +power application, and with the exception of the limited field +of bailing with tanks, mechanical drainage is a matter of pumps. +All pumps must be set below their load, barring a few possible +feet of suction lift, and they are therefore perforce underground, +and in consequence all power must be transmitted from the surface. +Transmission itself means loss of power varying from 10 to 60%, +depending upon the medium used. It is therefore the choice of +transmission medium that largely governs the mechanical efficiency. + +SYSTEMS OF DRAINAGE.--The ideal pumping system for metal mines +would be one which could be built in units and could be expanded +or contracted unit by unit with the fluctuation in volume; which +could also be easily moved to meet the differences of lifts; and +in which each independent unit could be of the highest mechanical +efficiency and would require but little space for erection. Such +an ideal is unobtainable among any of the appliances with which +the writer is familiar. + +The wide variations in the origin of power, in the form of transmission, +and in the method of final application, and the many combinations +of these factors, meet the demands for flexibility, efficiency, +capital cost, and reliability in various degrees depending upon +the environment of the mine. Power nowadays is generated primarily +with steam, water, and gas. These origins admit the transmission of +power to the pumps by direct steam, compressed air, electricity, +rods, or hydraulic columns. + +DIRECT STEAM-PUMPS.--Direct steam has the disadvantage of radiated +heat in the workings, of loss by the radiation, and, worse still, +of the impracticability of placing and operating a highly efficient +steam-engine underground. It is all but impossible to derive benefit +from the vacuum, as any form of surface condenser here is impossible, +and there can be no return of the hot soft water to the boilers. + +Steam-pumps fall into two classes, rotary and direct-acting; the former +have the great advantage of permitting the use of steam expansively +and affording some field for effective use of condensation, but +they are more costly, require much room, and are not fool-proof. +The direct-acting pumps have all the advantage of compactness and +the disadvantage of being the most inefficient of pumping machines +used in mining. Taking the steam consumption of a good surface +steam plant at 15 pounds per horse-power hour, the efficiency of +rotary pumps with well-insulated pipes is probably not over 50%, +and of direct-acting pumps from 40% down to 10%. + +The advantage of all steam-pumps lies in the low capital outlay,--hence +their convenient application to experimental mining and temporary +pumping requirements. For final equipment they afford a great deal +of flexibility, for if properly constructed they can be, with slight +alteration, moved from one horizon to another without loss of relative +efficiency. Thus the system can be rearranged for an increased +volume of water, by decreasing the lift and increasing the number +of pumps from different horizons. + +COMPRESSED-AIR PUMPS.--Compressed-air transmission has an application +similar to direct steam, but it is of still lower mechanical efficiency, +because of the great loss in compression. It has the superiority +of not heating the workings, and there is no difficulty as to the +disposal of the exhaust, as with steam. Moreover, such pumps will +work when drowned. Compressed air has a distinct place for minor +pumping units, especially those removed from the shaft, for they +can be run as an adjunct to the air-drill system of the mine, and +by this arrangement much capital outlay may be saved. The cost of +the extra power consumed by such an arrangement is less than the +average cost of compressed-air power, because many of the compressor +charges have to be paid anyway. When compressed air is water-generated, +they have a field for permanent installations. The efficiency of +even rotary air-driven pumps, based on power delivered into a good +compressor, is probably not over 25%. + +ELECTRICAL PUMPS.--Electrical pumps have somewhat less flexibility +than steam- or air-driven apparatus, in that the speed of the pumps can +be varied only within small limits. They have the same great advantage +in the easy reorganization of the system to altered conditions of +water-flow. Electricity, when steam-generated, has the handicap +of the losses of two conversions, the actual pump efficiency being +about 60% in well-constructed plants; the efficiency is therefore +greater than direct steam or compressed air. Where the mine is +operated with water-power, purchased electric current, or where +there is an installation of electrical generating plant by steam or +gas for other purposes, electrically driven pumps take precedence +over all others on account of their combined moderate capital outlay, +great flexibility, and reasonable efficiency. + +In late years, direct-coupled, electric-driven centrifugal pumps +have entered the mining field, but their efficiency, despite makers' +claims, is low. While they show comparatively good results on low +lifts the slip increases with the lift. In heads over 200 feet +their efficiency is probably not 30% of the power delivered to the +electrical generator. Their chief attractions are small capital +cost and the compact size which admits of easy installation. + +ROD-DRIVEN PUMPS.--Pumps of the Cornish type in vertical shafts, +if operated to full load and if driven by modern engines, have +an efficiency much higher than any other sort of installation, +and records of 85 to 90% are not unusual. The highest efficiency +in these pumps yet obtained has been by driving the pump with rope +transmission from a high-speed triple expansion engine, and in +this plant an actual consumption of only 17 pounds of steam per +horse-power hour for actual water lifted has been accomplished. + +To provide, however, for increase of flow and change of horizon, +rod-driven pumps must be so overpowered at the earlier stage of +the mine that they operate with great loss. Of all pumping systems +they are the most expensive to provide. They have no place in crooked +openings and only work in inclines with many disadvantages. + +In general their lack of flexibility is fast putting them out of +the metal miner's purview. Where the pumping depth and volume of +water are approximately known, as is often the case in coal mines, +this, the father of all pumps, still holds its own. + +HYDRAULIC PUMPS.--Hydraulic pumps, in which a column of water is +used as the transmission fluid from a surface pump to a corresponding +pump underground has had some adoption in coal mines, but little +in metal mines. They have a certain amount of flexibility but low +efficiency, and are not likely to have much field against electrical +pumps. + +BAILING.--Bailing deserves to be mentioned among drainage methods, +for under certain conditions it is a most useful system, and at +all times a mine should be equipped with tanks against accident +to the pumps. Where the amount of water is limited,--up to, say, +50,000 gallons daily,--and where the ore output of the mine permits +the use of the winding-engine for part of the time on water haulage, +there is in the method an almost total saving of capital outlay. +Inasmuch as the winding-engine, even when the ore haulage is finished +for the day, must be under steam for handling men in emergencies, +and as the labor of stokers, engine-drivers, shaft-men, etc., is +therefore necessary, the cost of power consumed by bailing is not +great, despite the low efficiency of winding-engines. + +COMPARISON OF VARIOUS SYSTEMS.--If it is assumed that flexibility, +reliability, mechanical efficiency, and capital cost can each be +divided into four figures of relative importance,--_A_, _B_, _C_, +and _D_, with _A_ representing the most desirable result,--it is +possible to indicate roughly the comparative values of various +pumping systems. It is not pretended that the four degrees are of +equal import. In all cases the factor of general power conditions +on the mine may alter the relative positions. + +==================================================================== + |Direct|Compressed| |Steam-| | + |Steam | Air |Electricity|Driven|Hydraulic|Bailing + |Pumps | | | Rods | Columns | Tanks +-------------|------|----------|-----------|------|---------|------- +Flexibility. | _A_ | _A_ | _B_ | _D_ | _B_ | _A_ +Reliability. | _B_ | _B_ | _B_ | _A_ | _D_ | _A_ +Mechanical | | | | | | + Efficiency.| _C_ | _D_ | _B_ | _A_ | _C_ | _D_ +Capital Cost | _A_ | _B_ | _B_ | _D_ | _D_ | -- +==================================================================== + +As each mine has its special environment, it is impossible to formulate +any final conclusion on a subject so involved. The attempt would lead +to a discussion of a thousand supposititious cases and hypothetical +remedies. Further, the description alone of pumping machines would +fill volumes, and the subject will never be exhausted. The engineer +confronted with pumping problems must marshal all the alternatives, +count his money, and apply the tests of flexibility, reliability, +efficiency, and cost, choose the system of least disadvantages, +and finally deprecate the whole affair, for it is but a parasite +growth on the mine. + + + + +CHAPTER XIV. + +Mechanical Equipment (_Concluded_). + +MACHINE DRILLING: POWER TRANSMISSION; COMPRESSED AIR _VS_. ELECTRICITY; +AIR DRILLS; MACHINE _VS_. HAND DRILLING. WORK-SHOPS. IMPROVEMENT +IN EQUIPMENT. + +For over two hundred years from the introduction of drill-holes +for blasting by Caspar Weindel in Hungary, to the invention of +the first practicable steam percussion drill by J. J. Crouch of +Philadelphia, in 1849, all drilling was done by hand. Since Crouch's +time a host of mechanical drills to be actuated by all sorts of +power have come forward, and even yet the machine-drill has not +reached a stage of development where it can displace hand-work +under all conditions. Steam-power was never adapted to underground +work, and a serviceable drill for this purpose was not found until +compressed air for transmission was demonstrated by Dommeiller +on the Mt. Cenis tunnel in 1861. + +The ideal requirements for a drill combine:-- + + a. Power transmission adapted to underground conditions. + b. Lightness. + c. Simplicity of construction. + d. Strength. + e. Rapidity and strength of blow. + f. Ease of erection. + g. Reliability. + h. Mechanical efficiency. + i. Low capital cost. + +No drill invented yet fills all these requirements, and all are +a compromise on some point. + +POWER TRANSMISSION; COMPRESSED AIR _vs_. ELECTRICITY.--The only +transmissions adapted to underground drill-work are compressed +air and electricity, and as yet an electric-driven drill has not +been produced which meets as many of the requirements of the metal +miner as do compressed-air drills. The latter, up to date, have +superiority in simplicity, lightness, ease of erection, reliability, +and strength over electric machines. Air has another advantage in +that it affords some assistance to ventilation, but it has the +disadvantage of remarkably low mechanical efficiency. The actual +work performed by the standard 3-3/4-inch air-drill probably does +not amount to over two or three horse-power against from fifteen to +eighteen horse-power delivered into the compressor, or mechanical +efficiency of less than 25%. As electrical power can be delivered to +the drill with much less loss than compressed air, the field for a +more economical drill on this line is wide enough to create eventually +the proper tool to apply it. The most satisfactory electric drill +produced has been the Temple drill, which is really an air-drill +driven by a small electrically-driven compressor placed near the +drill itself. But even this has considerable deficiencies in mining +work; the difficulties of setting up, especially for stoping work, +and the more cumbersome apparatus to remove before blasting are +serious drawbacks. It has deficiencies in reliability and greater +complication of machinery than direct air. + +AIR-COMPRESSION.--The method of air-compression so long accomplished +only by power-driven pistons has now an alternative in some situations +by the use of falling water. This latter system is a development +of the last twelve years, and, due to the low initial outlay and +extremely low operating costs, bids fair in those regions where +water head is available not only to displace the machine compressor, +but also to extend the application of compressed air to mine motors +generally, and to stay in some environments the encroachment of +electricity into the compressed-air field. Installations of this +sort in the West Kootenay, B.C., and at the Victoria copper mine, +Michigan, are giving results worthy of careful attention. + +Mechanical air-compressors are steam-, water-, electrical-, and +gas-driven, the alternative obviously depending on the source and +cost of power. Electrical- and gas- and water-driven compressors +work under the disadvantage of constant speed motors and respond +little to the variation in load, a partial remedy for which lies +in enlarged air-storage capacity. Inasmuch as compressed air, so +far as our knowledge goes at present, must be provided for drills, +it forms a convenient transmission of power to various motors +underground, such as small pumps, winches, or locomotives. As stated +in discussing those machines, it is not primarily a transmission +of even moderate mechanical efficiency for such purposes; but as +against the installation and operation of independent transmission, +such as steam or electricity, the economic advantage often compensates +the technical losses. Where such motors are fixed, as in pumps +and winches, a considerable gain in efficiency can be obtained by +reheating. + +It is not proposed to enter a discussion of mechanical details of +air-compression, more than to call attention to the most common +delinquency in the installation of such plants. This deficiency +lies in insufficient compression capacity for the needs of the +mine and consequent effective operation of drills, for with under +75 pounds pressure the drills decrease remarkably in rapidity of +stroke and force of the blow. The consequent decrease in actual +accomplishment is far beyond the ratio that might be expected on +the basis of mere difference of pressure. Another form of the same +chronic ill lies in insufficient air-storage capacity to provide +for maintenance of pressure against moments when all drills or +motors in the mine synchronize in heavy demand for air, and thus +lower the pressure at certain periods. + +AIR-DRILLS.--Air-drills are from a mechanical point of view broadly +of two types,--the first, in which the drill is the piston extension; +and the second, a more recent development for mining work, in which +the piston acts as a hammer striking the head of the drill. From an +economic point of view drills may be divided into three classes. +First, heavy drills, weighing from 150 to 400 pounds, which require +two men for their operation; second, "baby" drills of the piston type, +weighing from 110 to 150 pounds, requiring one man with occasional +assistance in setting up; and third, very light drills almost wholly +of the hammer type. This type is built in two forms: a heavier +type for mounting on columns, weighing about 80 pounds; and a type +after the order of the pneumatic riveter, weighing as low as 20 +pounds and worked without mounting. + +The weight and consequent mobility of a drill, aside from labor +questions, have a marked effect on costs, for the lighter the drill +the less difficulty and delay in erection, and consequent less +loss of time and less tendency to drill holes from one radius, +regardless of pointing to take best advantage of breaking planes. +Moreover, smaller diameter and shorter holes consume less explosives +per foot advanced or per ton broken. The best results in tonnage +broken and explosive consumed, if measured by the foot of drill-hole +necessary, can be accomplished from hand-drilling and the lighter +the machine drill, assuming equal reliability, the nearer it +approximates these advantages. + +The blow, and therefore size and depth of hole and rapidity of +drilling, are somewhat dependent upon the size of cylinders and +length of stroke, and therefore the heavier types are better adapted +to hard ground and to the deep holes of some development points. +Their advantages over the other classes lie chiefly in this ability +to bore exceedingly hard material and in the greater speed of advance +possible in development work; but except for these two special +purposes they are not as economical per foot advanced or per ton +of ore broken as the lighter drills. + +The second class, where men can be induced to work them one man per +drill, saves in labor and gains in mobility. Many tests show great +economy of the "baby" type of piston drills in average ground over +the heavier machines for stoping and for most lateral development. +All piston types are somewhat cumbersome and the heavier types +require at least four feet of head room. The "baby" type can be +operated in less space than this, but for narrow stopes they do +not lend themselves with the same facility as the third class. + +The third class of drills is still in process of development, but +it bids fair to displace much of the occupation of the piston types +of drill. Aside from being a one-man drill, by its mobility it +will apparently largely reproduce the advantage of hand-drilling +in ability to place short holes from the most advantageous angles +and for use in narrow places. As compared with other drills it +bids fair to require less time for setting up and removal and for +change of bits; to destroy less steel by breakages; to dull the +bits less rapidly per foot of hole; to be more economical of power; +to require much less skill in operation, for judgment is less called +upon in delivering speed; and to evade difficulties of fissured +ground, etc. And finally the cost is only one-half, initially and +for spares. Its disadvantage so far is a lack of reliability due to +lightness of construction, but this is very rapidly being overcome. +This type, however, is limited in depth of hole possible, for, +from lack of positive reverse movement, there is a tendency for +the spoil to pack around the bit, and as a result about four feet +seems the limit. + +The performance of a machine-drill under show conditions may be +anything up to ten or twelve feet of hole per hour on rock such +as compact granite; but in underground work a large proportion of +the time is lost in picking down loose ore, setting up machines, +removal for blasting, clearing away spoil, making adjustments, +etc. The amount of lost time is often dependent upon the width of +stope or shaft and the method of stoping. Situations which require +long drill columns or special scaffolds greatly accentuate the loss +of time. Further, the difficulties in setting up reflect indirectly +on efficiency to a greater extent in that a larger proportion of +holes are drilled from one radius and thus less adapted to the +best breaking results than where the drill can easily be reset from +various angles. + +The usual duty of a heavy drill per eight-hour shift using two men +is from 20 to 40 feet of hole, depending upon the rock, facilities +for setting up, etc., etc.[*] The lighter drills have a less average +duty, averaging from 15 to 25 feet per shift. + +[Footnote *: Over the year 1907 in twenty-eight mines compiled +from Alaska to Australia, an average of 23.5 feet was drilled per +eight-hour shift by machines larger than three-inch cylinder.] + +MACHINE _vs_. HAND-DRILLING.--The advantages of hand-drilling over +machine-drilling lie, first, in the total saving of power, the +absence of capital cost, repairs, depreciation, etc., on power, +compresser and drill plant; second, the time required for setting +up machine-drills does not warrant frequent blasts, so that a number +of holes on one radius are a necessity, and therefore machine-holes +generally cannot be pointed to such advantage as hand-holes. Hand-holes +can be set to any angle, and by thus frequent blasting yield greater +tonnage per foot of hole. Third, a large number of comparative +statistics from American, South African, and Australian mines show +a saving of about 25% in explosives for the same tonnage or foot +of advance by hand-holes over medium and heavy drill-holes. + +The duty of a skilled white man, single-handed, in rock such as +is usually met below the zone of oxidation, is from 5 to 7 feet +per shift, depending on the rock and the man. Two men hand-drilling +will therefore do from 1/4 to 2/3 of the same footage of holes +that can be done by two men with a heavy machine-drill, and two +men hand-drilling will do from 1/5 to 1/2 the footage of two men +with two light drills. + +The saving in labor of from 75 to 33% by machine-drilling may or +may not be made up by the other costs involved in machine-work. +The comparative value of machine- and hand-drilling is not subject +to sweeping generalization. A large amount of data from various +parts of the world, with skilled white men, shows machine-work +to cost from half as much per ton or foot advanced as hand-work +to 25% more than handwork, depending on the situation, type of +drill, etc. In a general way hand-work can more nearly compete +with heavy machines than light ones. The situations where hand-work +can compete with even light machines are in very narrow stopes where +drills cannot be pointed to advantage, and where the increased +working space necessary for machine drills results in breaking more +waste. Further, hand-drilling can often compete with machine-work +in wide stopes where long columns or platforms must be used and +therefore there is much delay in taking down, reërection, etc. + +Many other factors enter into a comparison, however, for +machine-drilling produces a greater number of deeper holes and +permits larger blasts and therefore more rapid progress. In driving +levels under average conditions monthly footage is from two to +three times as great with heavy machines as by hand-drilling, and +by lighter machines a somewhat less proportion of greater speed. +The greater speed obtained in development work, the greater tonnage +obtained per man in stoping, with consequent reduction in the number +of men employed, and in reduction of superintendence and general +charges are indirect advantages for machine-drilling not to be +overlooked. + +The results obtained in South Africa by hand-drilling in shafts, +and its very general adoption there, seem to indicate that better +speed and more economical work can be obtained in that way in very +large shafts than by machine-drilling. How far special reasons +there apply to smaller shafts or labor conditions elsewhere have +yet to be demonstrated. In large-dimension shafts demanding a large +number of machines, the handling of long machine bars and machines +generally results in a great loss of time. The large charges in +deep holes break the walls very irregularly; misfires cause more +delay; timbering is more difficult in the face of heavy blasting +charges; and the larger amount of spoil broken at one time delays +renewed drilling, and altogether the advantages seem to lie with +hand-drilling in shafts of large horizontal section. + +The rapid development of special drills for particular conditions +has eliminated the advantage of hand-work in many situations during +the past ten years, and the invention of the hammer type of drill +bids fair to render hand-drilling a thing of the past. One +generalization is possible, and that is, if drills are run on 40-50 +pounds' pressure they are no economy over hand-drilling. + +WORKSHOPS. + +In addition to the ordinary blacksmithy, which is a necessity, +the modern tendency has been to elaborate the shops on mines to +cover machine-work, pattern-making and foundry-work, in order that +delays may be minimized by quick repairs. To provide, however, +for such contingencies a staff of men must be kept larger than +the demand of average requirements. The result is an effort to +provide jobs or to do work extravagantly or unnecessarily well. +In general, it is an easy spot for fungi to start growing on the +administration, and if custom repair shops are available at all, +mine shops can be easily overdone. + +A number of machines are now in use for sharpening drills. +Machine-sharpening is much cheaper than hand-work, although the drills +thus sharpened are rather less efficient owing to the difficulty of +tempering them to the same nicety; however, the net results are +in favor of the machines. + +IMPROVEMENT IN EQUIPMENT. + +Not only is every mine a progressive industry until the bottom +gives out, but the technology of the industry is always progressing, +so that the manager is almost daily confronted with improvements +which could be made in his equipment that would result in decreasing +expenses or increasing metal recovery. There is one test to the +advisability of such alterations: How long will it take to recover +the capital outlay from the savings effected? and over and above +this recovery of capital there must be some very considerable gain. +The life of mines is at least secured over the period exposed in +the ore-reserves, and if the proposed alteration will show its +recovery and profit in that period, then it is certainly justified. +If it takes longer than this on the average speculative ore-deposit, +it is a gamble on finding further ore. As a matter of practical +policy it will be found that an improvement in equipment which +requires more than three or four years to redeem itself out of +saving, is usually a mechanical or metallurgical refinement the +indulgence in which is very doubtful. + + + + +CHAPTER XV. + +Ratio of Output to the Mine. + +DETERMINATION OF THE POSSIBLE MAXIMUM; LIMITING FACTORS; COST OF +EQUIPMENT; LIFE OF THE MINE; MECHANICAL INEFFICIENCY OF PATCHWORK +PLANT; OVERPRODUCTION OF BASE METAL; SECURITY OF INVESTMENT. + +The output obtainable from a given mine is obviously dependent +not only on the size of the deposit, but also on the equipment +provided,--in which equipment means the whole working appliances, +surface and underground. + +A rough and ready idea of output possibilities of inclined deposits +can be secured by calculating the tonnage available per foot of +depth from the horizontal cross-section of the ore-bodies exposed +and assuming an annual depth of exhaustion, or in horizontal deposits +from an assumption of a given area of exhaustion. Few mines, at the +time of initial equipment, are developed to an extent from which +their possibilities in production are evident, for wise finance +usually leads to the erection of some equipment and production before +development has been advanced to a point that warrants a large or +final installation. Moreover, even were the full possibilities of +the mine known, the limitations of finance usually necessitate a +less plant to start with than is finally contemplated. Therefore +output and equipment are usually growing possibilities during the +early life of a mine. + +There is no better instance in mine engineering where pure theory +must give way to practical necessities of finance than in the +determination of the size of equipment and therefore output. Moreover, +where finance even is no obstruction, there are other limitations +of a very practical order which must dominate the question of the +size of plant giving the greatest technical economy. It is, however, +useful to state the theoretical considerations in determining the +ultimate volume of output and therefore the size of equipments, +for the theory will serve to illuminate the practical limitations. +The discussion will also again demonstrate that all engineering +is a series of compromises with natural and economic forces. + +OUTPUT GIVING LEAST PRODUCTION COST.--As one of the most important +objectives is to work the ore at the least cost per ton, it is +not difficult to demonstrate that the minimum working costs can +be obtained only by the most intensive production. To prove this, +it need only be remembered that the working expenses of a mine +are of two sorts: one is a factor of the tonnage handled, such as +stoping and ore-dressing; the other is wholly or partially dependent +upon time. A large number of items are of this last order. Pumping +and head-office expenses are almost entirely charges independent +of the tonnage handled. Superintendence and staff salaries and +the like are in a large proportion dependent upon time. Many other +elements of expense, such as the number of engine-drivers, etc., do +not increase proportionately to increase in tonnage. These charges, +or the part of them dependent upon time apart from tonnage, may be +termed the "fixed charges." + +There is another fixed charge more obscure yet no less certain. +Ore standing in a mine is like money in a bank drawing no interest, +and this item of interest may be considered a "fixed charge," for +if the ore were realized earlier, this loss could be partially +saved. This subject is further referred to under "Amortization." + +If, therefore, the time required to exhaust the mine be prolonged +by the failure to maintain the maximum output, the total cost of +working it will be greater by the fixed charges over such an increased +period. Conversely, by equipping on a larger scale, the mine will +be exhausted more quickly, a saving in total cost can be made, and +the ultimate profit can be increased by an amount corresponding +to the time saved from the ravages of fixed charges. In fine, the +working costs may be reduced by larger operations, and therefore +the value of the mine increased. + +The problem in practice usually takes the form of the relative +superiority of more or of fewer units of plant, and it can be considered +in more detail if the production be supposed to consist of units +averaging say 100 tons per day each. The advantage of more units +over less will be that the extra ones can be produced free of fixed +charges, for these are an expense already involved in the lesser +units. This extra production will also enjoy the interest which +can be earned over the period of its earlier production. Moreover, +operations on a larger scale result in various minor economies +throughout the whole production, not entirely included in the type +of expenditure mentioned as "fixed charges." We may call these +various advantages the "saving of fixed charges" due to larger-scale +operations. The saving of fixed charges amounts to very considerable +sums. In general the items of working cost alone, mentioned above, +which do not increase proportionately to the tonnage, aggregate +from 10 to 25% of the total costs. Where much pumping is involved, +the percentage will become even greater. + +The question of the value of the mine as affected by the volume +of output becomes very prominent in low-grade mines, where, if +equipped for output on too small a scale, no profits at all could +be earned, and a sufficient production is absolutely imperative +for any gain. There are many mines in every country which with +one-third of their present rate of production would lose money. +That is, the fixed charges, if spread over small output, would be +so great per ton that the profit would be extinguished by them. + +In the theoretical view, therefore, it would appear clear that +the greatest ultimate profit from a mine can be secured only by +ore extraction under the highest pressure. As a corollary to this +it follows that development must proceed with the maximum speed. +Further, it follows that the present value of a mine is at least +partially a factor of the volume of output contemplated. + +FACTORS LIMITING THE OUTPUT. + +Although the above argument can be academically defended, there +are, as said at the start, practical limitations to the maximum +intensity of production, arising out of many other considerations +to which weight must be given. In the main, there are five principal +limitations:-- + + 1. Cost of equipment. + 2. Life of the mine. + 3. Mechanical inefficiency of patchwork plant. + 4. Overproduction of base metal. + 5. Security of investment. + +COST OF EQUIPMENT.--The "saving of fixed charges" can only be obtained +by larger equipment, which represents an investment. Mining works, +shafts, machinery, treatment plants, and all the paraphernalia cost +large sums of money. They become either worn out or practically +valueless through the exhaustion of the mines. Even surface machinery +when in good condition will seldom realize more than one-tenth of its +expense if useless at its original site. All mines are ephemeral; +therefore virtually the entire capital outlay of such works must +be redeemed during the life of the mine, and the interest on it +must also be recovered. + +The certain life, with the exception of banket and a few other +types of deposit, is that shown by the ore in sight, plus something +for extension of the deposit beyond exposures. So, against the +"savings" to be made, must be set the cost of obtaining them, for +obviously it is of no use investing a dollar to save a total of +ninety cents. The economies by increased production are, however, +of such an important character that the cost of almost any number +of added units (within the ability of the mine to supply them) +can be redeemed from these savings in a few years. For instance, +in a Californian gold mine where the working expenses are $3 and +the fixed charges are at the low rate of 30 cents per ton, one +unit of increased production would show a saving of over $10,000 +per annum from the saving of fixed charges. In about three years +this sum would repay the cost of the additional treatment equipment. +If further shaft capacity were required, the period would be much +extended. On a Western copper mine, where the costs are $8 and the +fixed charges are 80 cents per ton, one unit of increased production +would effect a saving of the fixed charges equal to the cost of +the extra unit in about three years. That is, the total sum would +amount to $80,000, or enough to provide almost any type of mechanical +equipment for such additional tonnage. + +The first result of vigorous development is to increase the ore in +sight,--the visible life of the mine. When such visible life has +been so lengthened that the period in which the "saving of fixed +charges" will equal the amount involved in expansion of equipment, +then from the standpoint of this limitation only is the added +installation justified. The equipment if expanded on this practice +will grow upon the heels of rapid development until the maximum +production from the mine is reached, and a kind of equilibrium +establishes itself. + +Conversely, this argument leads to the conclusion that, regardless +of other considerations, an equipment, and therefore output, should +not be expanded beyond the redemption by way of "saving from fixed +charges" of the visible or certain life of the mine. In those mines, +such as at the Witwatersrand, where there is a fairly sound assurance +of definite life, it is possible to calculate at once the size of +plant which by saving of "fixed charges" will be eventually the +most economical, but even here the other limitations step in to +vitiate such policy of management,--chiefly the limitation through +security of investment. + +LIFE OF THE MINE.--If carried to its logical extreme, the above +program means a most rapid exhaustion of the mine. The maximum output +will depend eventually upon the rapidity with which development +work may be extended. As levels and other subsidiary development +openings can be prepared in inclined deposits much more quickly +than the shaft can be sunk, the critical point is the shaft-sinking. +As a shaft may by exertion be deepened at least 400 feet a year on +a going mine, the provision of an equipment to eat up the ore-body +at this rate of sinking means very early exhaustion indeed. In +fact, had such a theory of production been put into practice by +our forefathers, the mining profession might find difficulty in +obtaining employment to-day. Such rapid exhaustion would mean a +depletion of the mineral resources of the state at a pace which +would be alarming. + +MECHANICAL INEFFICIENCY OF PATCHWORK PLANT.--Mine equipments on +speculative mines (the vast majority) are often enough patchwork, +for they usually grow from small beginnings; but any scheme of +expansion based upon the above doctrine would need to be modified +to the extent that additions could be in units large in ratio to +previous installations, or their patchwork character would be still +further accentuated. It would be impossible to maintain mechanical +efficiency under detail expansion. + +OVERPRODUCTION OF BASE METAL.--Were this intensity of production of +general application to base metal mines it would flood the markets, +and, by an overproduction of metal depress prices to a point where +the advantages of such large-scale operations would quickly vanish. +The theoretical solution in this situation would be, if metals +fell below normal prices, let the output be reduced, or let the +products be stored until the price recovers. From a practical point +of view either alternative is a policy difficult to face. + +In the first case, reduction of output means an increase of working +expenses by the spread of fixed charges over less tonnage, and +this in the face of reduced metal prices. It may be contended, +however, that a falling metal market is usually the accompaniment +of a drop in all commodities, wherefore working costs can be reduced +somewhat in such times of depression, thereby partially compensating +the other elements making for increased costs. Falls in commodities +are also the accompaniment of hard times. Consideration of one's +workpeople and the wholesale slaughter of dividends to the then +needy stockholders, resulting from a policy of reduced production, +are usually sufficient deterrents to diminished output. + +The second alternative, that of storing metal, means equally a +loss of dividends by the investment of a large sum in unrealized +products, and the interest on this sum. The detriment to the market +of large amounts of unsold metal renders such a course not without +further disadvantages. + +SECURITY OF INVESTMENT.--Another point of view antagonistic to +such wholesale intensity of production, and one worthy of careful +consideration, is that of the investor in mines. The root-value of +mining stocks is, or should be, the profit in sight. If the policy +of greatest economy in production costs be followed as outlined +above, the economic limit of ore-reserves gives an apparently very +short life, for the ore in sight will never represent a life beyond +the time required to justify more plant. Thus the "economic limit +of ore in reserve" will be a store equivalencing a period during +which additional equipment can be redeemed from the "saving of +fixed charges," or three or four years, usually. + +The investor has the right to say that he wants the guarantee of +longer life to his investment,--he will in effect pay insurance for +it by a loss of some ultimate profit. That this view, contradictory +to the economics of the case, is not simply academic, can be observed +by any one who studies what mines are in best repute on any stock +exchange. All engineers must wish to have the industry under them +in high repute. The writer knows of several mines paying 20% on +their stocks which yet stand lower in price on account of short +ore-reserves than mines paying less annual returns. The speculator, +who is an element not to be wholly disregarded, wishes a rise in +his mining stock, and if development proceeds at a pace in advance +of production, he will gain a legitimate rise through the increase +in ore-reserves. + +The investor's and speculator's idea of the desirability of a proved +long life readily supports the technical policy of high-pressure +development work, but not of expansion of production, for they +desire an increasing ore-reserve. Even the metal operator who is +afraid of overproduction does not object to increased ore-reserves. +On the point of maximum intensity of development work in a mine all +views coincide. The mining engineer, if he takes a Machiavellian +view, must agree with the investor and the metal dealer, for the +engineer is a "fixed charge" the continuance of which is important +to his daily needs. + +The net result of all these limitations is therefore an invariable +compromise upon some output below the possible maximum. The initial +output to be contemplated is obviously one upon which the working +costs will be low enough to show a margin of profit. The medium +between these two extremes is determinable by a consideration of +the limitations set out,--and the cash available. When the volume +of output is once determined, it must be considered as a factor +in valuation, as discussed under "Amortization." + + + + +CHAPTER XVI. + +Administration. + +LABOR EFFICIENCY; SKILL; INTELLIGENCE; APPLICATION COORDINATION; +CONTRACT WORK; LABOR UNIONS; REAL BASIS OF WAGES. + +The realization from a mine of the profits estimated from the other +factors in the case is in the end dependent upon the management. +Good mine management is based upon three elementals: first, sound +engineering; second, proper coördination and efficiency of every human +unit; third, economy in the purchase and consumption of supplies. + +The previous chapters have been devoted to a more or less extended +exposition of economic engineering. While the second and third +requirements are equally important, they range in many ways out of +the engineering and into the human field. For this latter reason +no complete manual will ever be published upon "How to become a +Good Mine Manager." + +It is purposed, however, to analyze some features of these second +and third fundamentals, especially in their interdependent phases, +and next to consider the subject of mine statistics, for the latter +are truly the microscopes through which the competence of the +administration must be examined. + +The human units in mine organization can be divided into officers +and men. The choice of mine officers is the assembling of specialized +brains. Their control, stimulation, and inspiration is the main work +of the administrative head. Success in the selection and control of +staff is the index of executive ability. There are no mathematical, +mechanical, or chemical formulas for dealing with the human mind +or human energies. + +LABOR.--The whole question of handling labor can be reduced to +the one term "efficiency." Not only does the actual labor outlay +represent from 60 to 70% of the total underground expenses, but +the capacity or incapacity of its units is responsible for wider +fluctuations in production costs than the bare predominance in +expenditure might indicate. The remaining expense is for supplies, +such as dynamite, timber, steel, power, etc., and the economical +application of these materials by the workman has the widest bearing +upon their consumption. + +Efficiency of the mass is the resultant of that of each individual +under a direction which coördinates effectively all units. The +lack of effectiveness in one individual diminishes the returns +not simply from that man alone; it lowers the results from numbers +of men associated with the weak member through the delaying and +clogging of their work, and of the machines operated by them. +Coördination of work is a necessary factor of final efficiency. This +is a matter of organization and administration. The most zealous +stoping-gang in the world if associated with half the proper number +of truckers must fail to get the desired result. + +Efficiency in the single man is the product of three factors,--skill, +intelligence, and application. A great proportion of underground +work in a mine is of a type which can be performed after a fashion +by absolutely unskilled and even unintelligent men, as witness the +breaking-in of savages of low average mentality, like the South +African Kaffirs. Although most duties can be performed by this +crudest order of labor, skill and intelligence can be applied to +it with such economic results as to compensate for the difference +in wage. The reason for this is that the last fifty years have seen +a substitution of labor-saving machines for muscle. Such machines +displace hundreds of raw laborers. Not only do they initially cost +large sums, but they require large expenditure for power and up-keep. +These fixed charges against the machine demand that it shall be +worked at its maximum. For interest, power, and up-keep go on in +any event, and the saving on crude labor displaced is not so great +but that it quickly disappears if the machine is run under its +capacity. To get its greatest efficiency, a high degree of skill +and intelligence is required. Nor are skill and intelligence alone +applicable to labor-saving devices themselves, because drilling and +blasting rock and executing other works underground are matters +in which experience and judgment in the individual workman count +to the highest degree. + +How far skill affects production costs has had a thorough demonstration +in West Australia. For a time after the opening of those mines +only a small proportion of experienced men were obtainable. During +this period the rock broken per man employed underground did not +exceed the rate of 300 tons a year. In the large mines it has now, +after some eight years, attained 600 to 700 tons. + +How far intelligence is a factor indispensable to skill can be well +illustrated by a comparison of the results obtained from working +labor of a low mental order, such as Asiatics and negroes, with those +achieved by American or Australian miners. In a general way, it may +be stated with confidence that the white miners above mentioned +can, under the same physical conditions, and with from five to ten +times the wage, produce the same economic result,--that is, an +equal or lower cost per unit of production. Much observation and +experience in working Asiatics and negroes as well as Americans +and Australians in mines, leads the writer to the conclusion that, +averaging actual results, one white man equals from two to three +of the colored races, even in the simplest forms of mine work such +as shoveling or tramming. In the most highly skilled branches, +such as mechanics, the average ratio is as one to seven, or in +extreme cases even eleven. The question is not entirely a comparison +of bare efficiency individually; it is one of the sum total of +results. In mining work the lower races require a greatly increased +amount of direction, and this excess of supervisors consists of +men not in themselves directly productive. There is always, too, +a waste of supplies, more accidents, and more ground to be kept +open for accommodating increased staff, and the maintenance of +these openings must be paid for. There is an added expense for +handling larger numbers in and out of the mine, and the lower +intelligence reacts in many ways in lack of coördination and inability +to take initiative. Taking all divisions of labor together, the +ratio of efficiency as measured in amount of output works out from +four to five colored men as the equivalent of one white man of the +class stated. The ratio of costs, for reasons already mentioned, +and in other than quantity relation, figures still more in favor +of the higher intelligence. + +The following comparisons, which like all mine statistics must +necessarily be accepted with reservation because of some dissimilarity +of economic surroundings, are yet on sufficiently common ground +to demonstrate the main issue,--that is, the bearing of inherent +intelligence in the workmen and their consequent skill. Four groups +of gold mines have been taken, from India, West Australia, South +Africa, and Western America. All of those chosen are of the same +stoping width, 4 to 5 feet. All are working in depth and with every +labor-saving device available. All dip at about the same angle and +are therefore in much the same position as to handling rock. The +other conditions are against the white-manned mines and in favor of +the colored. That is, the Indian mines have water-generated electric +power and South Africa has cheaper fuel than either the American or +Australian examples. In both the white-manned groups, the stopes +are supported, while in the others no support is required. + +======================================================================= + | Tons of | Average |Tons | + | Material | Number of Men | per |Cost per + Group of Mines | Excavated | Employed | Man | Ton of + |over Period|---------------| per |Material + |Compiled[5]|Colored| White |Annum| Broken +----------------------------|-----------|-------|-------|-----|-------- +Four Kolar mines[1] | 963,950 | 13,611| 302 | 69.3| $3.85 +Six Australian mines[2] | 1,027,718 | -- | 1,534 |669.9| 2.47 +Three Witwatersrand mines[3]| 2,962,640 | 13,560| 1,595 |195.5| 2.68 +Five American mines[4] | 1,089,500 | -- | 1,524 |713.3| 1.92 +======================================================================= + +[Footnote 1: Indian wages average about 20 cents per day.] + +[Footnote 2: White men's wages average about $3 per day.] + +[Footnote 3: About two-fifths of the colored workers were negroes, +and three-fifths Chinamen. Negroes average about 60 cents, and +Chinamen about 45 cents per day, including keep.] + +[Footnote 4: Wages about $3.50. Tunnel entry in two mines.] + +[Footnote 5: Includes rock broken in development work. + +In the case of the specified African mines, the white labor is +employed almost wholly in positions of actual or semi-superintendence, +such as one white man in charge of two or three drills. + +In the Indian case, in addition to the white men who are wholly +in superintendence, there were of the natives enumerated some 1000 +in positions of semi-superintendence, as contractors or headmen, +working-gangers, etc.] + +One issue arises out of these facts, and that is that no engineer +or investor in valuing mines is justified in anticipating lower +costs in regions where cheap labor exists. + +In supplement to sheer skill and intelligence, efficiency can be +gained only by the application of the man himself. A few months ago +a mine in California changed managers. The new head reduced the number +employed one-third without impairing the amount of work accomplished. +This was not the result of higher skill or intelligence in the men, +but in the manager. Better application and coördination were secured +from the working force. Inspiration to increase of exertion is +created less by "driving" than by recognition of individual effort, +in larger pay, and by extending justifiable hope of promotion. A +great factor in the proficiency of the mine manager is his ability +to create an _esprit-de-corps_ through the whole staff, down to +the last tool boy. Friendly interest in the welfare of the men +and stimulation by competitions between various works and groups +all contribute to this end. + +CONTRACT WORK.--The advantage both to employer and employed of +piece work over wage needs no argument. In a general way, contract +work honorably carried out puts a premium upon individual effort, +and thus makes for efficiency. There are some portions of mine +work which cannot be contracted, but the development, stoping, +and trucking can be largely managed in this way, and these items +cover 65 to 75% of the total labor expenditure underground. + +In development there are two ways of basing contracts,--the first +on the footage of holes drilled, and the second on the footage +of heading advanced. In contract-stoping there are four methods +depending on the feet of hole drilled, on tonnage, on cubic space, +and on square area broken. + +All these systems have their rightful application, conditioned upon +the class of labor and character of the deposit. + +In the "hole" system, the holes are "pointed" by some mine official +and are blasted by a special crew. The miner therefore has little +interest in the result of the breaking. If he is a skilled white +man, the hours which he has wherein to contemplate the face usually +enable him to place holes to better advantage than the occasional +visiting foreman. With colored labor, the lack of intelligence in +placing holes and blasting usually justifies contracts per "foot +drilled." Then the holes are pointed and blasted by superintending +men. + +On development work with the foot-hole system, unless two working +faces can be provided for each contracting party, they are likely +to lose time through having finished their round of holes before the +end of the shift. As blasting must be done outside the contractor's +shifts, it means that one shift per day must be set aside for the +purpose. Therefore not nearly such progress can be made as where +working the face with three shifts. For these reasons, the "hole" +system is not so advantageous in development as the "foot of advance" +basis. + +In stoping, the "hole" system has not only a wider, but a sounder +application. In large ore-bodies where there are waste inclusions, +it has one superiority over any system of excavation measurement, +namely, that the miner has no interest in breaking waste into the +ore. + +The plan of contracting stopes by the ton has the disadvantage +that either the ore produced by each contractor must be weighed +separately, or truckers must be trusted to count correctly, and to +see that the cars are full. Moreover, trucks must be inspected for +waste,--a thing hard to do underground. So great are these detailed +difficulties that many mines are sending cars to the surface in +cages when they should be equipped for bin-loading and self-dumping +skips. + +The method of contracting by the cubic foot of excavation saves +all necessity for determining the weight of the output of each +contractor. Moreover, he has no object in mixing waste with the ore, +barring the breaking of the walls. This system therefore requires +the least superintendence, permits the modern type of hoisting, +and therefore leaves little justification for the survival of the +tonnage basis. + +Where veins are narrow, stoping under contract by the square foot +or fathom measured parallel to the walls has an advantage. The miner +has no object then in breaking wall-rock, and the thoroughness of +the ore-extraction is easily determined by inspection. + +BONUS SYSTEMS.--By giving cash bonuses for special accomplishment, +much the same results can be obtained in some departments as by +contracting. A bonus per foot of heading gained above a minimum, +or an excess of trucks trammed beyond a minimum, or prizes for +the largest amount done during the week or month in special works +or in different shifts,--all these have a useful application in +creating efficiency. A high level of results once established is +easily maintained. + +LABOR UNIONS.--There is another phase of the labor question which +must be considered and that is the general relations of employer +and employed. In these days of largely corporate proprietorship, +the owners of mines are guided in their relations with labor by +engineers occupying executive positions. On them falls the +responsibility in such matters, and the engineer becomes thus a +buffer between labor and capital. As corporations have grown, so +likewise have the labor unions. In general, they are normal and +proper antidotes for unlimited capitalistic organization. + +Labor unions usually pass through two phases. First, the inertia +of the unorganized labor is too often stirred only by demagogic +means. After organization through these and other agencies, the +lack of balance in the leaders often makes for injustice in demands, +and for violence to obtain them and disregard of agreements entered +upon. As time goes on, men become educated in regard to the rights +of their employers, and to the reflection of these rights in ultimate +benefit to labor itself. Then the men, as well as the intelligent +employer, endeavor to safeguard both interests. When this stage +arrives, violence disappears in favor of negotiation on economic +principles, and the unions achieve their greatest real gains. Given +a union with leaders who can control the members, and who are disposed +to approach differences in a business spirit, there are few sounder +positions for the employer, for agreements honorably carried out +dismiss the constant harassments of possible strikes. Such unions +exist in dozens of trades in this country, and they are entitled to +greater recognition. The time when the employer could ride roughshod +over his labor is disappearing with the doctrine of "_laissez faire_," +on which it was founded. The sooner the fact is recognized, the +better for the employer. The sooner some miners' unions develop +from the first into the second stage, the more speedily will their +organizations secure general respect and influence.[*] + +[Footnote *: Some years of experience with compulsory arbitration +in Australia and New Zealand are convincing that although the law +there has many defects, still it is a step in the right direction, +and the result has been of almost unmixed good to both sides. One +of its minor, yet really great, benefits has been a considerable +extinction of the parasite who lives by creating violence.] + +The crying need of labor unions, and of some employers as well, +is education on a fundamental of economics too long disregarded +by all classes and especially by the academic economist. When the +latter abandon the theory that wages are the result of supply and +demand, and recognize that in these days of international flow of +labor, commodities and capital, the real controlling factor in +wages is efficiency, then such an educational campaign may become +possible. Then will the employer and employee find a common ground +on which each can benefit. There lives no engineer who has not +seen insensate dispute as to wages where the real difficulty was +inefficiency. No administrator begrudges a division with his men +of the increased profit arising from increased efficiency. But +every administrator begrudges the wage level demanded by labor +unions whose policy is decreased efficiency in the false belief +that they are providing for more labor. + + + + +CHAPTER XVII. + +Administration (_Continued_). + +ACCOUNTS AND TECHNICAL DATA AND REPORTS; WORKING COSTS; DIVISION +OF EXPENDITURE; INHERENT LIMITATIONS IN ACCURACY OF WORKING COSTS; +WORKING COST SHEETS. GENERAL TECHNICAL DATA; LABOR, SUPPLIES, POWER, +SURVEYS, SAMPLING, AND ASSAYING. + +First and foremost, mine accounts are for guidance in the distribution +of expenditure and in the collection of revenue; secondly, they +are to determine the financial progress of the enterprise, its +profit or loss; and thirdly, they are to furnish statistical data to +assist the management in its interminable battle to reduce expenses +and increase revenue, and to enable the owner to determine the +efficiency of his administrators. Bookkeeping _per se_ is no part +of this discussion. The fundamental purpose of that art is to cover +the first two objects, and, as such, does not differ from its +application to other commercial concerns. + +In addition to these accounting matters there is a further type +of administrative report of equal importance--that is the periodic +statements as to the physical condition of the property, the results +of exploration in the mine, and the condition of the equipment. + +ACCOUNTS. + +The special features of mine accounting reports which are a development +to meet the needs of this particular business are the determination +of working costs, and the final presentation of these data in a +form available for comparative purposes. + +The subject may be discussed under:-- + + 1. Classes of mine expenditure. + 2. Working costs. + 3. The dissection of expenditures departmentally. + 4. Inherent limitations in the accuracy of working costs. + 5. Working cost sheets. + +In a wide view, mine expenditures fall into three classes, which +maybe termed the "fixed charges," "proportional charges," and "suspense +charges" or "capital expenditure." "Fixed charges" are those which, +like pumping and superintendence, depend upon time rather than +tonnage and material handled. They are expenditures that would not +decrease relatively to output. "Proportional charges" are those +which, like ore-breaking, stoping, supporting stopes, and tramming, +are a direct coefficient of the ore extracted. "Suspense charges" are +those which are an indirect factor of the cost of the ore produced, +such as equipment and development. These expenditures are preliminary +to output, and they thus represent a storage of expense to be charged +off when the ore is won. This outlay is often called "capital +expenditure." Such a term, though in common use, is not strictly +correct, for the capital value vanishes when the ore is extracted, +but in conformity with current usage the term "capital expenditure" +will be adopted. + +Except for the purpose of special inquiry, such as outlined under +the chapter on "Ratio of Output," "fixed charges" are not customarily +a special division in accounts. In a general way, such expenditures, +combined with the "proportional charges," are called "revenue +expenditure," as distinguished from the capital, or "suspense," +expenditures. In other words, "revenue" expenditures are those +involved in the daily turnover of the business and resulting in +immediate returns. The inherent difference in character of revenue +and capital expenditures is responsible for most of the difficulties +in the determination of working costs, and most of the discussion +on the subject. + +WORKING COSTS.--"Working costs" are a division of expenditure for +some unit,--the foot of opening, ton of ore, a pound of metal, +cubic yard or fathom of material excavated, or some other measure. +The costs per unit are usually deduced for each month and each +year. They are generally determined for each of the different +departments of the mine or special works separately. Further, the +various sorts of expenditure in these departments are likewise +segregated. + +In metal mining the ton is the universal unit of distribution for +administrative purpose, although the pound of metal is often used +to indicate final financial results. The object of determination of +"working costs" is fundamentally for comparative purposes. Together +with other technical data, they are the nerves of the administration, +for by comparison of detailed and aggregate results with other mines +and internally in the same mine, over various periods and between +different works, a most valuable check on efficiency is possible. +Further, there is one collateral value in all statistical data not +to be overlooked, which is that the knowledge of its existence +induces in the subordinate staff both solicitude and emulation. + +The fact must not be lost sight of, however, that the wide variations +in physical and economic environment are so likely to vitiate +conclusions from comparisons of statistics from two mines or from +two detailed works on the same mine, or even from two different +months on the same work, that the greatest care and discrimination +are demanded in their application. Moreover, the inherent difficulties +in segregating and dividing the accounts which underlie such data, +render it most desirable to offer some warning regarding the limits +to which segregation and division may be carried to advantage. + +As working costs are primarily for comparisons, in order that they +may have value for this purpose they must include only such items +of expenditure as will regularly recur. If this limitation were more +generally recognized, a good deal of dispute and polemics on the +subject might be saved. For this reason it is quite impossible that +all the expenditure on the mine should be charged into working costs, +particularly some items that arise through "capital expenditure." + +THE DISSECTION OF EXPENDITURES DEPARTMENTALLY.--The final division +in the dissection of the mine expenditure is in the main:-- + + /(1) General Expenses. / Ore-breaking. \ + | | Supporting Stopes. | Various +_Revenue._< (2) Ore Extraction. < Trucking Ore. | expenditures + | \ Hoisting. | for labor, + \(3) Pumping. | supplies, power, + / Shaft-sinking. | repairs, etc., + | Station-cutting. > worked out per + | Crosscutting. | ton or foot + /(4) Development. < Driving. | advanced +_Capital | | Rising. | over each + or < | Winzes. | department. +Suspense._ | \ Diamond Drilling. / + | + | (5) Construction and \ Various Works. + \ Equipment. / + +The detailed dissection of expenditures in these various departments +with view to determine amount of various sorts of expenditure over +the department, or over some special work in that department, is +full of unsolvable complications. The allocation of the direct +expenditure of labor and supplies applied to the above divisions or +special departments in them, is easily accomplished, but beyond this +point two sorts of difficulties immediately arise and offer infinite +field for opinion and method. The first of these difficulties arises +from supplementary departments on the mine, such as "power," "repairs +and maintenance," "sampling and assaying." These departments must +be "spread" over the divisions outlined above, for such charges +are in part or whole a portion of the expense of these divisions. +Further, all of these "spread" departments are applied to surface +as well as to underground works, and must be divided not only over +the above departments but also over the surface departments,--not +under discussion here. The common method is to distribute "power" on +a basis of an approximation of the amount used in each department; +to distribute "repairs and maintenance," either on a basis of shop +returns, or a distribution over all departments on the basis of +the labor employed in those departments, on the theory that such +repairs arise in this proportion; to distribute sampling and assaying +over the actual points to which they relate at the average cost +per sample or assay. + +"General expenses," that is, superintendence, etc., are often not +included in the final departments as above, but are sometimes "spread" +in an attempt to charge a proportion of superintendence to each +particular work. As, however, such "spreading" must take place +on the basis of the relative expenditure in each department, the +result is of little value, for such a basis does not truly represent +the proportion of general superintendence, etc., devoted to each +department. If they are distributed over all departments, capital +as well as revenue, on the basis of total expenditure, they inflate +the "capital expenditure" departments against a day of reckoning when +these charges come to be distributed over working costs. Although it +may be contended that the capital departments also require supervision, +such a practice is a favorite device for showing apparently low +working costs in the revenue departments. The most courageous way +is not to distribute general expenses at all, but to charge them +separately and directly to revenue accounts and thus wholly into +working costs. + +The second problem is to reduce the "suspense" or capital charges +to a final cost per ton, and this is no simple matter. Development +expenditures bear a relation to the tonnage developed and not to +that extracted in any particular period. If it is desired to preserve +any value for comparative purposes in the mining costs, such outlay +must be charged out on the basis of the tonnage developed, and such +portion of the ore as is extracted must be written off at this +rate; otherwise one month may see double the amount of development +in progress which another records, and the underground costs would +be swelled or diminished thereby in a way to ruin their comparative +value from month to month. The ore developed cannot be satisfactorily +determined at short intervals, but it can be known at least annually, +and a price may be deduced as to its cost per ton. In many mines +a figure is arrived at by estimating ore-reserves at the end of +the year, and this figure is used during the succeeding year as a +"redemption of development" and as such charged to working costs, +and thus into revenue account in proportion to the tonnage extracted. +This matter is further elaborated in some mines, in that winzes +and rises are written off at one rate, levels and crosscuts at +another, and shafts at one still lower, on the theory that they +lost their usefulness in this progression as the ore is extracted. +This course, however, is a refinement hardly warranted. + +Plant and equipment constitute another "suspense" account even +harder to charge up logically to tonnage costs, for it is in many +items dependent upon the life of the mine, which is an unknown +factor. Most managers debit repairs and maintenance directly to +the revenue account and leave the reduction of the construction +outlay to an annual depreciation on the final balance sheet, on the +theory that the plant is maintained out of costs to its original +value. This subject will be discussed further on. + +INHERENT LIMITATIONS IN ACCURACY OF WORKING COSTS.--There are three +types of such limitations which arise in the determination of costs +and render too detailed dissection of such costs hopeless of accuracy +and of little value for comparative purposes. They are, first, the +difficulty of determining all of even direct expenditure on any +particular crosscut, stope, haulage, etc.; second, the leveling effect +of distributing the "spread" expenditures, such as power, repairs, +etc.; and third, the difficulties arising out of the borderland +of various departments. + +Of the first of these limitations the instance may be cited that +foremen and timekeepers can indicate very closely the destination of +labor expense, and also that of some of the large items of supply, +such as timber and explosives, but the distribution of minor supplies, +such as candles, drills, picks, and shovels, is impossible of accurate +knowledge without an expense wholly unwarranted by the information +gained. To determine at a particular crosscut the exact amount of +steel, and of tools consumed, and the cost of sharpening them, +would entail their separate and special delivery to the same place +of attack and a final weighing-up to learn the consumption. + +Of the second sort of limitations, the effect of "spread" expenditure, +the instance may be given that the repairs and maintenance are done by +many men at work on timbers, tracks, machinery, etc. It is hopeless +to try and tell how much of their work should be charged specifically +to detailed points. In the distribution of power may be taken the +instance of air-drills. Although the work upon which the drill is +employed can be known, the power required for compression usually +comes from a common power-plant, so that the portion of power debited +to the air compressor is an approximation. The assumption of an +equal consumption of air by all drills is a further approximation. +In practice, therefore, many expenses are distributed on the theory +that they arise in proportion to the labor employed, or the machines +used in the various departments. The net result is to level down +expensive points and level up inexpensive ones. + +The third sort of limitation of accounting difficulty referred +to, arises in determining into which department are actually to be +allocated the charges which lie in the borderland between various +primary classes of expenditure. For instance, in ore won from +development,--in some months three times as much development may +be in ore as in other months. If the total expense of development +work which yields ore be charged to stoping account, and if cost +be worked out on the total tonnage of ore hoisted, then the stoping +cost deduced will be erratic, and the true figures will be obscured. +On the other hand, if all development is charged to 'capital account' +and the stoping cost worked out on all ore hoisted, it will include +a fluctuating amount of ore not actually paid for by the revenue +departments or charged into costs. This fluctuation either way +vitiates the whole comparative value of the stoping costs. In the +following system a compromise is reached by crediting "development" +with an amount representing the ore won from development at the +average cost of stoping, and by charging this amount into "stoping." +A number of such questions arise where the proper division is simply +a matter of opinion. + +The result of all these limitations is that a point in detail is +quickly reached where no further dissection of expenditure is justified, +since it becomes merely an approximation. The writer's own impression +is that without an unwarrantable number of accountants, no manager +can tell with any accuracy the cost of any particular stope, or +of any particular development heading. Therefore, aside from some +large items, such detailed statistics, if given, are to be taken +with great reserve. + +WORKING COST SHEETS.--There are an infinite number of forms of +working cost sheets, practically every manager having a system of +his own. To be of greatest value, such sheets should show on their +face the method by which the "spread" departments are handled, and +how revenue and suspense departments are segregated. When too much +detail is presented, it is but a waste of accounting and consequent +expense. Where to draw the line in this regard is, however, a matter +of great difficulty. No cost sheet is entirely satisfactory. The +appended sheet is in use at a number of mines. It is no more perfect +than many others. It will be noticed that the effect of this system +is to throw the general expenses into the revenue expenditures, +and as little as possible into the "suspense" account. + +GENERAL TECHNICAL DATA. + +For the purposes of efficient management, the information gathered +under this head is of equal, if not superior, importance to that +under "working costs." Such data fall generally under the following +heads:-- + +LABOR.--Returns of the shifts worked in the various departments +for each day and for the month; worked out on a monthly basis of +footage progress, tonnage produced or tons handled per man; also +where possible the footage of holes drilled, worked out per man +and per machine. + +SUPPLIES.--Daily returns of supplies used; the principal items +worked out monthly in quantity per foot of progress, or per ton +of ore produced. + +POWER.--Fuel, lubricant, etc., consumed in steam production, worked +out into units of steam produced, and this production allocated to +the various engines. Where electrical power is used, the consumption +of the various motors is set out. + +SURVEYS.--The need of accurate plans requires no discussion. Aside +from these, the survey-office furnishes the returns of development +footage, measurements under contracts, and the like. + +SAMPLING AND ASSAYING.--Mine sampling and assaying fall under two +heads,--the determination of the value of standing ore, and of +products from the mine. The sampling and assaying on a going mine +call for the same care and method as in cases of valuation of the +mine for purchase,--the details of which have been presented under +"Mine Valuation,"--for through it, guidance must not only be had to +the value of the mine and for reports to owners, but the detailed +development and ore extraction depend on an absolute knowledge of +where the values lie. + + + + +CHAPTER XVIII. + +ADMINISTRATION (_Concluded_). + +ADMINISTRATIVE REPORTS. + +In addition to financial returns showing the monthly receipts, +expenditures, and working costs, there must be in proper administration +periodic reports from the officers of the mine to the owners or +directors as to the physical progress of the enterprise. Such reports +must embrace details of ore extraction, metal contents, treatment +recoveries, construction of equipment, and the results of underground +development. The value of mines is so much affected by the monthly +or even daily result of exploration that reports of such work are +needed very frequently,--weekly or even daily if critical work is +in progress. These reports must show the width, length, and value +of the ore disclosed. + +The tangible result of development work is the tonnage and grade +of ore opened up. How often this stock-taking should take place +is much dependent upon the character of the ore. The result of +exploration in irregular ore-bodies often does not, over short +periods, show anything tangible in definite measurable tonnage, +but at least annually the ore reserve can be estimated. + +In mines owned by companies, the question arises almost daily as +to how much of and how often the above information should be placed +before stockholders (and therefore the public) by the directors. In +a general way, any company whose shares are offered on the stock +exchange is indirectly inviting the public to become partners in the +business, and these partners are entitled to all the information +which affects the value of their property and are entitled to it +promptly. Moreover, mining is a business where competition is so +obscure and so much a matter of indifference, that suppression +of important facts in documents for public circulation has no +justification. On the other hand, both the technical progress of +the industry and its position in public esteem demand the fullest +disclosure and greatest care in preparation of reports. Most +stockholders' ignorance of mining technology and of details of +their particular mine demands a great deal of care and discretion +in the preparation of these public reports that they may not be +misled. Development results may mean little or much, depending +upon the location of the work done in relation to the ore-bodies, +etc., and this should be clearly set forth. + +The best opportunity of clear, well-balanced statements lies in +the preparation of the annual report and accounts. Such reports +are of three parts:-- + +1. The "profit and loss" account, or the "revenue account." +2. The balance sheet; that is, the assets and liabilities + statement. +3. The reports of the directors, manager, and consulting + engineer. + +The first two items are largely matters of bookkeeping. They or +the report should show the working costs per ton for the year. +What must be here included in costs is easier of determination +than in the detailed monthly cost sheets of the administration; +for at the annual review, it is not difficult to assess the amount +chargeable to development. Equipment expenditure, however, presents +an annual difficulty, for, as said, the distribution of this item +is a factor of the life of the mine, and that is unknown. If such +a plant has been paid for out of the earnings, there is no object +in carrying it on the company's books as an asset, and most +well-conducted companies write it off at once. On the other hand, +where the plant is paid for out of capital provided for the purpose, +even to write off depreciation means that a corresponding sum of +cash must be held in the company's treasury in order to balance +the accounts,--in other words, depreciation in such an instance +becomes a return of capital. The question then is one of policy +in the company's finance, and in neither case is it a matter which +can be brought into working costs and leave them any value for +comparative purposes. Indeed, the true cost of working the ore +from any mine can only be told when the mine is exhausted; then +the dividends can be subtracted from the capital sunk and metal +sold, and the difference divided over the total tonnage produced. + +The third section of the report affords wide scope for the best +efforts of the administration. This portion of the report falls +into three divisions: (_a_) the construction and equipment work +of the year, (_b_) the ore extraction and treatment, and (_c_) +the results of development work. + +The first requires a statement of the plant constructed, its object +and accomplishment; the second a disclosure of tonnage produced, +values, metallurgical and mechanical efficiency. The third is of +the utmost importance to the stockholder, and is the one most often +disregarded and obscured. Upon this hinges the value of the property. +There is no reason why, with plans and simplicity of terms, such +reports cannot be presented in a manner from which the novice can +judge of the intrinsic position of the property. A statement of +the tonnage of ore-reserves and their value, or of the number of +years' supply of the current output, together with details of ore +disclosed in development work, and the working costs, give the +ground data upon which any stockholder who takes interest in his +investment may judge for himself. Failure to provide such data +will some day be understood by the investing public as a _prima +facie_ index of either incapacity or villainy. By the insistence of +the many engineers in administration of mines upon the publication +of such data, and by the insistence of other engineers upon such +data for their clients before investment, and by the exposure of +the delinquents in the press, a more practicable "protection of +investors" can be reached than by years of academic discussion. + + + + +CHAPTER XIX. + +The Amount of Risk in Mining Investments. + +RISK IN VALUATION OF MINES; IN MINES AS COMPARED WITH OTHER COMMERCIAL +ENTERPRISES. + +From the constant reiteration of the risks and difficulties involved +in every step of mining enterprise from the valuation of the mine +to its administration as a going concern, the impression may be +gained that the whole business is one great gamble; in other words, +that the point whereat certainties stop and conjecture steps in +is so vital as to render the whole highly speculative. + +Far from denying that mining is, in comparison with better-class +government bonds, a speculative type of investment, it is desirable +to avow and emphasize the fact. But it is none the less well to +inquire what degree of hazard enters in and how it compares with +that in other forms of industrial enterprise. + +Mining business, from an investment view, is of two sorts,--prospecting +ventures and developed mines; that is, mines where little or no ore is +exposed, and mines where a definite quantity of ore is measurable or can +be reasonably anticipated. The great hazards and likewise the Aladdin +caves of mining are mainly confined to the first class. Although all +mines must pass through the prospecting stage, the great industry +of metal production is based on developed mines, and it is these +which should come into the purview of the non-professional investor. +The first class should be reserved invariably for speculators, and +a speculator may be defined as one who hazards all to gain much. +It is with mining as an investment, however, that this discussion +is concerned. + +RISK IN VALUATION OF MINES.--Assuming a competent collection of +data and efficient management of the property, the risks in valuing +are from step to step:-- + +1. The risk of continuity in metal contents beyond sample + faces. +2. The risk of continuity in volume through the blocks + estimated. +3. The risk of successful metallurgical treatment. +4. The risk of metal prices, in all but gold. +5. The risk of properly estimating costs. +6. The risk of extension of the ore beyond exposures. +7. The risk of management. + +As to the continuity of values and volumes through the estimated +area, the experience of hundreds of engineers in hundreds of mines +has shown that when the estimates are based on properly secured +data for "proved ore," here at least there is absolutely no hazard. +Metallurgical treatment, if determined by past experience on the +ore itself, carries no chance; and where determined by experiment, +the risk is eliminated if the work be sufficiently exhaustive. The +risk of metal price is simply a question of how conservative a +figure is used in estimating. It can be eliminated if a price low +enough be taken. Risk of extension in depth or beyond exposures +cannot be avoided. It can be reduced in proportion to the distance +assumed. Obviously, if no extension is counted, there is nothing +chanced. The risk of proper appreciation of costs is negligible where +experience in the district exists. Otherwise, it can be eliminated +if a sufficiently large allowance is taken. The risk of failure to +secure good management can be eliminated if proved men are chosen. + +There is, therefore, a basic value to every mine. The "proved" +ore taken on known metallurgical grounds, under known conditions +of costs on minimum prices of metals, has a value as certain as +that of money in one's own vault. This is the value previously +referred to as the "_A_" value. If the price (and interest on it +pending recovery) falls within this amount, there is no question +that the mine is worth the price. What the risk is in mining is +simply what amount the price of the investment demands shall be +won from extension of the deposit beyond known exposures, or what +higher price of metal must be realized than that calculated in +the "_A_" value. The demands on this _X, Y_ portion of the mine +can be converted into tons of ore, life of production, or higher +prices, and these can be weighed with the geological weights and +the industrial outlook. + +MINES COMPARED TO OTHER COMMERCIAL ENTERPRISES.--The profits from +a mining venture over and above the bed-rock value _A_, that is, +the return to be derived from more extensive ore-recovery and a +higher price of metal, may be compared to the value included in +other forms of commercial enterprise for "good-will." Such forms of +enterprise are valued on a basis of the amount which will replace +the net assets plus (or minus) an amount for "good-will," that is, +the earning capacity. This good-will is a speculation of varying +risk depending on the character of the enterprise. For natural +monopolies, like some railways and waterworks, the risk is less +and for shoe factories more. Even natural monopolies are subject +to the risks of antagonistic legislation and industrial storms. +But, eliminating this class of enterprise, the speculative value +of a good-will involves a greater risk than prospective value in +mines, if properly measured; because the dangers of competition +and industrial storms do not enter to such a degree, nor is the +future so dependent upon the human genius of the founder or manager. +Mining has reached such a stage of development as a science that +management proceeds upon comparatively well-known lines. It is +subject to known checks through the opportunity of comparisons +by which efficiency can be determined in a manner more open for +the investor to learn than in any other form of industry. While +in mining an estimate of a certain minimum of extension in depth, +as indicated by collateral factors, may occasionally fall short, +it will, in nine cases out of ten, be exceeded. If investment in +mines be spread over ten cases, similarly valued as to minimum of +extension, the risk has been virtually eliminated. The industry, +if reduced to the above basis for financial guidance, is a more +profitable business and is one of less hazards than competitive +forms of commercial enterprises. + +In view of what has been said before, it may be unnecessary to refer +again to the subject, but the constant reiteration by wiseacres +that the weak point in mining investments lies in their short life +and possible loss of capital, warrants a repetition that the _A, +B, C_ of proper investment in mines is to be assured, by the "_A_" +value, of a return of the whole or major portion of the capital. +The risk of interest and profit may be deferred to the _X, Y_ value, +and in such case it is on a plane with "good-will." It should be said +at once to that class who want large returns on investment without +investigation as to merits, or assurance as to the management of the +business, that there is no field in this world for the employment +of their money at over 4%. + +Unfortunately for the reputation of the mining industry, and metal +mines especially, the business is often not conducted or valued on +lines which have been outlined in these chapters. There is often +the desire to sell stocks beyond their value. There is always the +possibility that extension in depth will reveal a glorious Eldorado. +It occasionally does, and the report echoes round the world for years, +together with tributes to the great judgment of the exploiters. The +volume of sound allures undue numbers of the venturesome, untrained, +and ill-advised public to the business, together with a mob of +camp-followers whose objective is to exploit the ignorant by preying +on their gambling instincts. Thus a considerable section of metal +mining industry is in the hands of these classes, and a cloud of +disrepute hangs ever in the horizon. + +There has been a great educational campaign in progress during the +past few years through the technical training of men for conduct +of the industry, by the example of reputable companies in regularly +publishing the essential facts upon which the value of their mines +is based, and through understandable nontechnical discussion in +and by some sections of the financial and general press. The real +investor is being educated to distinguish between reputable concerns +and the counters of gamesters. Moreover, yearly, men of technical +knowledge are taking a stronger and more influential part in mining +finance and in the direction of mining and exploration companies. +The net result of these forces will be to put mining on a better +plane. + + + + +CHAPTER XX. + +The Character, Training, and Obligations of the Mining Engineering +Profession. + +In a discussion of some problems of metal mining from the point +of view of the direction of mining operations it may not be amiss +to discuss the character of the mining engineering profession in +its bearings on training and practice, and its relations to the +public. + +The most dominant characteristic of the mining engineering profession +is the vast preponderance of the commercial over the technical in +the daily work of the engineer. For years a gradual evolution has +been in progress altering the larger demands on this branch of the +engineering profession from advisory to executive work. The mining +engineer is no longer the technician who concocts reports and blue +prints. It is demanded of him that he devise the finance, construct +and manage the works which he advises. The demands of such executive +work are largely commercial; although the commercial experience +and executive ability thus become one pier in the foundation of +training, the bridge no less requires two piers, and the second +is based on technical knowledge. Far from being deprecated, these +commercial phases cannot be too strongly emphasized. On the other +hand, I am far from contending that our vocation is a business +rather than a profession. + +For many years after the dawn of modern engineering, the members +of our profession were men who rose through the ranks of workmen, +and as a result, we are to this day in the public mind a sort of +superior artisan, for to many the engine-driver is equally an engineer +with the designer of the engine, yet their real relation is but as +the hand to the brain. At a later period the recruits entered by +apprenticeship to those men who had established their intellectual +superiority to their fellow-workers. These men were nearly always +employed in an advisory way--subjective to the executive head. + +During the last few decades, the advance of science and the complication +of industry have demanded a wholly broader basis of scientific and +general training for its leaders. Executive heads are demanded who +have technical training. This has resulted in the establishment of +special technical colleges, and compelled a place for engineering +in the great universities. The high intelligence demanded by the +vocation itself, and the revolution in training caused by the +strengthening of its foundations in general education, has finally, +beyond all question, raised the work of application of science to +industry to the dignity of a profession on a par with the law, +medicine, and science. It demands of its members equally high mental +attainments,--and a more rigorous training and experience. Despite +all this, industry is conducted for commercial purposes, and leaves +no room for the haughty intellectual superiority assumed by some +professions over business callings. + +There is now demanded of the mining specialist a wide knowledge +of certain branches of civil, mechanical, electrical, and chemical +engineering, geology, economics, the humanities, and what not; and +in addition to all this, engineering sense, executive ability, +business experience, and financial insight. Engineering sense is +that fine blend of honesty, ingenuity, and intuition which is a +mental endowment apart from knowledge and experience. Its possession +is the test of the real engineer. It distinguishes engineering as +a profession from engineering as a trade. It is this sense that +elevates the possessor to the profession which is, of all others, +the most difficult and the most comprehensive. Financial insight can +only come by experience in the commercial world. Likewise must come +the experience in technical work which gives balance to theoretical +training. Executive ability is that capacity to coördinate and command +the best results from other men,--it is a natural endowment. which +can be cultivated only in actual use. + +The practice of mine engineering being so large a mixture of business, +it follows that the whole of the training of this profession cannot +be had in schools and universities. The commercial and executive +side of the work cannot be taught; it must be absorbed by actual +participation in the industry. Nor is it impossible to rise to +great eminence in the profession without university training, as +witness some of our greatest engineers. The university can do much; +it can give a broad basis of knowledge and mental training, and can +inculcate moral feeling, which entitles men to lead their fellows. It +can teach the technical fundamentals of the multifold sciences which +the engineer should know and must apply. But after the university +must come a schooling in men and things equally thorough and more +arduous. + +In this predominating demand for commercial qualifications over +the technical ones, the mining profession has differentiated to +a great degree from its brother engineering branches. That this +is true will be most apparent if we examine the course through +which engineering projects march, and the demands of each stage +on their road to completion. + +The life of all engineering projects in a general way may be divided +into five phases:[*]-- + +[Footnote *: These phases do not necessarily proceed step by step. +For an expanding works especially, all of them may be in process +at the same time, but if each item be considered to itself, this +is the usual progress, or should be when properly engineered.] + + 1. Determination of the value of the project. + 2. Determination of the method of attack. + 3. The detailed delineation of method, means, and tools. + 4. The execution of the works. + 5. The operation of the completed works. + +These various stages of the resolution of an engineering project +require in each more or less of every quality of intellect, training, +and character. At the different stages, certain of these qualities +are in predominant demand: in the first stage, financial insight; +in the second, "engineering sense"; in the third, training and +experience; in the fourth and fifth, executive ability. + +A certain amount of compass over the project during the whole +five stages is required by all branches of the engineering +profession,--harbor, canal, railway, waterworks, bridge, mechanical, +electrical, etc.; but in none of them so completely and in such +constant combination is this demanded as in mining. + +The determination of the commercial value of projects is a greater +section of the mining engineer's occupation than of the other +engineering branches. Mines are operated only to earn immediate +profits. No question of public utility enters, so that all mining +projects have by this necessity to be from the first weighed from +a profit point of view alone. The determination of this question +is one which demands such an amount of technical knowledge and +experience that those who are not experts cannot enter the +field,--therefore the service of the engineer is always demanded in +their satisfactory solution. Moreover, unlike most other engineering +projects, mines have a faculty of changing owners several times +during their career, so that every one has to survive a periodic +revaluation. From the other branches of engineering, the electrical +engineer is the most often called upon to weigh the probabilities +of financial success of the enterprise, but usually his presence +in this capacity is called upon only at the initial stage, for +electrical enterprises seldom change hands. The mechanical and +chemical branches are usually called upon for purely technical +service on the demand of the operator, who decides the financial +problems for himself, or upon works forming but units in undertakings +where the opinion on the financial advisability is compassed by some +other branch of the engineering profession. The other engineering +branches, even less often, are called in for financial advice, +and in those branches involving works of public utility the +profit-and-loss phase scarcely enters at all. + +Given that the project has been determined upon, and that the enterprise +has entered upon the second stage, that of determination of method of +attack, the immediate commercial result limits the mining engineer's +every plan and design to a greater degree than it does the other +engineering specialists. The question of capital and profit dogs +his every footstep, for all mines are ephemeral; the life of any +given mine is short. Metal mines have indeed the shortest lives of +any. While some exceptional ones may produce through one generation, +under the stress of modern methods a much larger proportion extend +only over a decade or two. But of more pertinent force is the fact +that as the certain life of a metal mine can be positively known in +most cases but a short period beyond the actual time required to +exhaust the ore in sight, not even a decade of life to the enterprise +is available for the estimates of the mining engineer. Mining works +are of no value when the mine is exhausted; the capital invested +must be recovered in very short periods, and therefore all mining +works must be of the most temporary character that will answer. +The mining engineer cannot erect a works that will last as long as +possible; it is to last as long as the mine only, and, in laying +it out, forefront in his mind must be the question, Can its cost +be redeemed in the period of use of which I am certain it will +find employment? If not, will some cheaper device, which gives +less efficiency, do? The harbor engineer, the railway engineer, +the mechanical engineer, build as solidly as they can, for the +demand for the work will exist till after their materials are worn +out, however soundly they construct. + +Our engineer cousins can, in a greater degree by study and +investigation, marshal in advance the factors with which they have +to deal. The mining engineer's works, on the other hand, depend at +all times on many elements which, from the nature of things, must +remain unknown. No mine is laid bare to study and resolve in advance. +We have to deal with conditions buried in the earth. Especially in +metal mines we cannot know, when our works are initiated, what +the size, mineralization, or surroundings of the ore-bodies will +be. We must plunge into them and learn,--and repent. Not only is +the useful life of our mining works indeterminate, but the very +character of them is uncertain in advance. All our works must be in +a way doubly tentative, for they are subject to constant alterations +as they proceed. + +Not only does this apply to our initial plans, but to our daily +amendment of them as we proceed into the unknown. Mining engineering +is, therefore, never ended with the initial determination of a method. +It is called upon daily to replan and reconceive, coincidentally with +the daily progress of the constructions and operation. Weary with +disappointment in his wisest conception, many a mining engineer +looks jealously upon his happier engineering cousin, who, when he +designs a bridge, can know its size, its strains, and its cost, +and can wash his hands of it finally when the contractor steps +in to its construction. And, above all, it is no concern of his +whether it will pay. Did he start to build a bridge over a water, +the width or depth or bottom of which he could not know in advance, +and require to get its cost back in ten years, with a profit, his +would be a task of similar harassments. + +As said before, it is becoming more general every year to employ +the mining engineer as the executive head in the operation of mining +engineering projects, that is, in the fourth and fifth stages of +the enterprise. He is becoming the foreman, manager, and president +of the company, or as it may be contended by some, the executive +head is coming to have technical qualifications. Either way, in +no branch of enterprise founded on engineering is the operative +head of necessity so much a technical director. Not only is this +caused by the necessity of executive knowledge before valuations +can be properly done, but the incorporation of the executive work +with the technical has been brought about by several other forces. +We have a type of works which, by reason of the new conditions +and constant revisions which arise from pushing into the unknown +coincidentally with operating, demands an intimate continuous daily +employment of engineering sense and design through the whole history +of the enterprise. These works are of themselves of a character +which requires a constant vigilant eye on financial outcome. The +advances in metallurgy, and the decreased cost of production by +larger capacities, require yearly larger, more complicated, and +more costly plants. Thus, larger and larger capitals are required, +and enterprise is passing from the hands of the individual to the +financially stronger corporation. This altered position as to the +works and finance has made keener demands, both technically and in +an administrative way, for the highly trained man. In the early +stages of American mining, with the moderate demand on capital and +the simpler forms of engineering involved, mining was largely a +matter of individual enterprise and ownership. These owners were +men to whom experience had brought some of the needful technical +qualifications. They usually held the reins of business management +in their own hands and employed the engineer subjectively, when +they employed him at all. They were also, as a rule, distinguished +by their contempt for university-trained engineers. + +The gradually increasing employment of the engineer as combined +executive and technical head, was largely of American development. +Many English and European mines still maintain the two separate +bureaus, the technical and the financial. Such organization is open +to much objection from the point of view of the owner's interests, +and still more from that of the engineer. In such an organization the +latter is always subordinate to the financial control,--hence the +least paid and least respected. When two bureaus exist, the technical +lacks that balance of commercial purpose which it should have. The +ambition of the theoretical engineer, divorced from commercial +result, is complete technical nicety of works and low production +costs without the regard for capital outlay which the commercial +experience and temporary character of mining constructions demand. +On the other hand, the purely financial bureau usually begrudges +the capital outlay which sound engineering may warrant. The result +is an administration that is not comparable to the single head with +both qualifications and an even balance in both spheres. In America, +we still have a relic of this form of administration in the consulting +mining engineer, but barring his functions as a valuer of mines, he +is disappearing in connection with the industry, in favor of the +manager, or the president of the company, who has administrative +control. The mining engineer's field of employment is therefore not +only wider by this general inclusion of administrative work, but +one of more responsibility. While he must conduct all five phases +of engineering projects coincidentally, the other branches of the +profession are more or less confined to one phase or another. They +can draw sharper limitations of their engagements or specialization +and confine themselves to more purely technical work. The civil +engineer may construct railway or harbor works; the mechanical +engineer may design and build engines; the naval architect may +build ships; but given that he designed to do the work in the most +effectual manner, it is no concern of his whether they subsequently +earn dividends. He does not have to operate them, to find the income, +to feed the mill, or sell the product. The profit and loss does +not hound his footsteps after his construction is complete. + +Although it is desirable to emphasize the commercial side of the +practice of the mining engineer's profession, there are other sides +of no less moment. There is the right of every red-blooded man to +be assured that his work will be a daily satisfaction to himself; +that it is a work which is contributing to the welfare and advance +of his country; and that it will build for him a position of dignity +and consequence among his fellows. + +There are the moral and public obligations upon the profession. +There are to-day the demands upon the engineers which are the demands +upon their positions as leaders of a great industry. In an industry +that lends itself so much to speculation and chicanery, there is the +duty of every engineer to diminish the opportunity of the vulture +so far as is possible. Where he can enter these lists has been +suggested in the previous pages. Further than to the "investor" +in mines, he has a duty to his brothers in the profession. In no +profession does competition enter so obscurely, nor in no other +are men of a profession thrown into such terms of intimacy in +professional work. From these causes there has arisen a freedom of +disclosure of technical results and a comradery of members greater +than that in any other profession. No profession is so subject to +the capriciousness of fortune, and he whose position is assured +to-day is not assured to-morrow unless it be coupled with a +consideration of those members not so fortunate. Especially is +there an obligation to the younger members that they may have +opportunity of training and a right start in the work. + +The very essence of the profession is that it calls upon its members +to direct men. They are the officers in the great industrial army. +From the nature of things, metal mines do not, like our cities and +settlements, lie in those regions covered deep in rich soils. Our +mines must be found in the mountains and deserts where rocks are +exposed to search. Thus they lie away from the centers of comfort +and culture,--they are the outposts of civilization. The engineer +is an officer on outpost duty, and in these places he is the camp +leader. By his position as a leader in the community he has a +chieftainship that carries a responsibility besides mere mine +management. His is the responsibility of example in fair dealing +and good government in the community. + +In but few of its greatest works does the personality of its real +creator reach the ears of the world; the real engineer does not +advertise himself. But the engineering profession generally rises +yearly in dignity and importance as the rest of the world learns +more of where the real brains of industrial progress are. The time +will come when people will ask, not who paid for a thing, but who +built it. + +To the engineer falls the work of creating from the dry bones of +scientific fact the living body of industry. It is he whose intellect +and direction bring to the world the comforts and necessities of +daily need. Unlike the doctor, his is not the constant struggle +to save the weak. Unlike the soldier, destruction is not his prime +function. Unlike the lawyer, quarrels are not his daily bread. +Engineering is the profession of creation and of construction, of +stimulation of human effort and accomplishment. + + + + +INDEX. + +Accounts. +Administration. +Administrative reports. +Air-compression. + -drills. +Alteration, secondary. +Alternative shafts to inclined deposit. +Amortization of capital and interest. +Animals for underground transport. +Annual demand for base metals. + report. +Artificial pillars. +Assay foot. + inch. + of samples. + plans. +Assaying. +A value of mine. +Averages, calculation. + +Bailing. +Balance sheet. +Basic price. + value of mine. +Benches. +Bend in combined shafts. +Bins. +Blocked-out ore. +Blocks. +Bonanzas, origin. +Bonus systems, of work. +Breaking ore. +Broken Hill, levels. + ore-pillars. +Bumping-trough. + +Cable-ways. +Cages. +Calculation of averages. + of quantities of ore. +Capital expenditure. +Caving systems. +Churn-drills. +Chutes, loading, in vertical shaft. +Classification of ore in sight. +Combined shaft. + stopes. +Commercial value of projects, determination. +Compartments for shaft. +Compressed-air locomotives. + -air pumps. + _vs_. electricity for drills. +Content, average metal, determining. + metal, differences. +Contract work. +Copper, annual demand. + deposits. + ores, enrichment. +Cost of entry into mine. + of equipment. + production. + per foot of sinking. + working. +Cribs. +Crosscuts. +Cross-section of inclined deposit which must be attacked in depth. + showing auxiliary vertical outlet. +Crouch, J. J. +Cubic feet per ton of ore. + foot contents of block. + +Deep-level mines. +Demand for metals. +Departmental dissection of expenditures. +Deposits, _in situ_. + ore, classes. + regularity. + size. + structure. +Depth of exhaustion. +Determination of average metal contents of ore. +Development in early prospecting stage. + in neighboring mines. + of mines. +Diamond-drilling. +Diluting narrow samples to a stoping width. +Dip. +Direct-acting steam-pumps. +Distribution of values. +Dividend, annual, present value. +Dommeiler. +Down holes. +Drainage. + comparison of different systems. + systems. +Drifts. +Drill, requirements. +Drilling. +Drives. +Dry walling with timber caps. + +Efficiency, factors of. + of mass. +Electrical haulage. + pumps. +Electricity for drills. +Engine, size for winding appliances. +Engineer, mining, as executive. +Engineering projects, phases of. +Enrichment. + at cross-veins. +Entry, to mine. + to vertical or horizontal deposits. +Equipment, cost. + improvements. + mechanical. +Erosion. +Error, percentage in estimates from sampling. +Escape. +Examination of mining property. +Excavation, supporting. +Exhaustion, depth. +Expenditures, departmental dissection. + mine. +Extension in depth. + +Factor of safety in calculating averages of samples. +Filling. + system combined with square-setting. + with broken ore subsequently withdrawn. + waste. +Fissure veins. +Fissuring. + depth. +Fixed charges. +Flat-back stope. +Flexibility in drainage system. +Floors. +Folding. +Foot-drilled system of contract work. + -hole system of contract work. + of advance system of contract work. + value. +Fraud, precautions against in sampling. + +General expenses. +Gold deposits. + deposits, alteration. + enrichment. + +Hammer type of drill. +Hand-drilling. + -trucking. +Haulage, electrical. + equipment in shaft. + mechanical. +Hole system of contract work. +Horizons of ore-deposits. +Horizontal deposits, entry. + stope. + filled with waste. +Hydraulic pumps. + +Impregnation deposits. +Inch, assay. +Inclined deposits to be worked from outcrop or near it. + deposits which must be attacked in depth. + shaft. +Inclines. + capacity. +Infiltration type of deposits. +Intelligence as factor of skill. +Interest calculations in mine valuation. +Intervals, level. +Inwood's tables. +Iron hat. + leaching. +Ivanhoe mine, West Australia. + +Kibble. + +Labor, general technical data. + handling. + unions. +Lateral underground transport. +Le Roi mine. +Lead, annual demand. + deposits. + enriching. + prices, 1884-1908. + -zinc ores, enrichment. +Lenses. +Levels. + intervals. + of Broken Hill. + protection. +Life, in sight. + of mine. +Locomotives, compressed-air. +Lode mines, valuation. +Lodes. +Long-wall stope. + +Machine-drill, performance. + drilling. + _vs_. hand-drilling. +Management, mine. +Matte. +Mechanical efficiency of drainage machinery. + equipment. +Men for underground transport. +Metal content, determining. + contents, differences. + demand for. + mine, value. + price. +Mines compared to other commercial enterprises. + equipment. + expenditures. +Mines--_continued._ + life of. + metal, value of. + of moderate depths. + to be worked to great depths. + valuation. +Mining engineering profession. +Mt. Cenis tunnel. +Morgan gold mine. + +Normal price. + +Obligations of engineering profession. +Openings, position in relation to secondary alteration. +Ore, average width in block. + blocked-out. + -bodies. + shapes. + -breaking, methods. + calculation of quantities of. + -chutes in shrinkage-stoping. + -deposits, classes. + determination of average metal contents. + developed. + developing. + expectant. + in sight. + sight, classification. + -pillars. + support in narrow stopes. + -shoots. + weight of a cubic foot. + width for one sample. +Origin of deposit. +Outcrop mines. +Output, factors limiting. + giving least production cost. + maximum, determination. +Overhand stapes. +Overproduction of base metal. +Oxidation. + +Patchwork plant, mechanical inefficiency of. +Pay areas, formation. +Pillars, artificial. +Positive ore. + value of metal mine. +Possible ore. +Power conditions. + general technical data. + sources. + transmission. +Preliminary inspection. +Previous yield. +Price of metals. +Probable ore. +Producing stage of mine. +Production, cost. +Profit and loss account. + factors determining. + in sight. +Proportional charges. +Prospecting stage of mine. +Prospective ore. + value. +Protection of levels. +Proved ore. +Pumping systems. +Pumps, compressed-air. + electrical. + hydraulic. + rod-driven. + +Ratio of output to mine. +Recoverable percentage of gross assay value. +Recovery of ore. +Rectangular shaft. +Redemption of capital and interest. +Reduction of output. +Regularity of deposit. +Reliability of drainage system. +Replacement. +Reports. + administrative. +Resuing. +Revenue account. +Rill-cut overhand stope. + method of incline cuts. + -stopes. + filled with waste. + -stoping. +Rises. +Risk in mining investments. + in valuation of mines. +Roadways, protecting in shrinkage-stoping. +Rod-driven pumps. +Rotary steam-pumps. +Round vertical shafts. +Runs of value. + test-treatment. + +Safety, factor of, in calculating averages of samples. +Sample, assay of. + average value. + narrow, diluting to a stoping width. + sections. + taking, physical details. + manner of taking. +Sampling. + accuracy. + percentage of error in estimates from. + precautions against fraud. +Saving of fixed charges. +Secondary alteration. + enrichment. +Security of investment. +Self-dumping skip. +Sets. +Shafts. + arrangement for very deep inclined shafts. + compartments. + different depths. + haulage. + location. + number. + output capacity. + shape. + size. +Shrinkage-stope. + -stoping. + advantages. + disadvantages. + when applicable. +Silver deposits. + deposits, enrichment. + prices. +Sinking, speed. +Size of deposit. +Skill, effect on production cost. +Skips. + balanced. + haulage in vertical shaft. +Sollars. +Solubility of minerals. +Specific volume of ores. +Speculative values of metal mine. + value of mine. +Spelter, annual demand. +Square-set. + -set timbering. +Stations. + arrangement for skip haulage in vertical shaft. +Steam-pumps, direct. +Steepening winzes and ore passes. +Stope filled with broken ore. + minimum width. +Stoping. + contract systems. +Storing metal. +Structural character of deposit. +Structure of deposit. +Stull and waste pillars. + support with waste reënforcement. + -supported stope. +Stulls. + wood. +Subheading. +Sublevel caving system. +Subsidiary development. +Superficial enrichment. +Supplies, general technical data. +Support by pillars of ore. +Supporting excavation. +Surveys. +Suspense charges. + +Test parcels. + sections. + -treatment runs. +Timber, cost. +Timbered shaft design. +Timbering. +Tin, annual demand. + deposits. + ore, migration and enrichment. +Tools. +Top slicing. +Tracks. +Transport in stopes. +Tunnel entry. + feet paid for in 10 years. + size. + +Underhand stopes. +Uppers. + +Valuation, mine. + of lode mines. + mines, risk in. + mines with little or no ore in sight. + on second-hand data. +Value, average, of samples. + discrepancy between estimated and actual. + distribution. + of extension in depth, estimating. + positive, of metal mine. + present, of an annual dividend. + of $1 or £1, payable in -- years. + runs of. + speculative, of metal mine. +Valuing ore in course of breaking. +Ventilation. +Vertical deposits, entry. + interval between levels. + shafts. + capacity. +Volume, specific, of ores. + +Waste-filled stope. +Water-power. +Weight per cubic foot of ore. +Weindel, Caspar. +Whiting hoist. +Width of ore for one sample. +Winding appliances. +Winzes. + in shrinkage-stoping. + to be used for filling. +Working cost. + inherent limitations in accuracy of. + sheets. +Workshops. + +Yield, previous. +Years of life required to yield --% interest. + +Zinc deposits. + leaching. + + + + + + +End of Project Gutenberg's Principles of Mining, by Herbert C. Hoover + +*** END OF THIS PROJECT GUTENBERG EBOOK PRINCIPLES OF MINING *** + +***** This file should be named 26697-8.txt or 26697-8.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/2/6/6/9/26697/ + +Produced by Robert J. Hall + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +https://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, is critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at https://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +https://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at https://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit https://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/26697-8.zip b/26697-8.zip Binary files differnew file mode 100644 index 0000000..e0d2f94 --- /dev/null +++ b/26697-8.zip diff --git a/26697-h.zip b/26697-h.zip Binary files differnew file mode 100644 index 0000000..67553cb --- /dev/null +++ b/26697-h.zip diff --git a/26697-h/26697-h.htm b/26697-h/26697-h.htm new file mode 100644 index 0000000..aea9265 --- /dev/null +++ b/26697-h/26697-h.htm @@ -0,0 +1,10476 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"> +<html> +<head> +<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> +<title>Principles of Mining</title> + <style type="text/css"> + <!-- + body { background: white; color: black; + margin-left: 15%; margin-right: 15%; } + h1 { text-align: center; margin-top: 4em; } + h2 { text-align: center; margin-top: 2em; } + h3 { text-align: center; font-size: medium; + font-weight: normal; } + p { margin-top: 0.3em; margin-bottom: 0.3em; } + p.indent { text-indent: 1em; text-align: justify; } + p.bindent { text-indent: -1em; padding-left: 2em; + text-align: justify; } + p.center { text-align: center; } + p.center_gap { text-align: center; + margin-top: 2em; margin-bottom: 2em; } + p.footnote { font-size: smaller; text-align: justify; } + p.subtitle { font-size: larger; text-align: center; } + p.bigtitle { text-align: center; font-size: x-large; } + p.author { text-align: center; + margin-top: 2em; margin-bottom: 2em; } + p.bquote { margin-left: 4em; margin-right: 4em; } + p.big { font-size: x-large; text-align: center; + margin-top: 2em; margin-bottom: 2em; } + p.indmgn { font-size: smaller; margin: 1em 0em 0em 0em; + text-align: justify; } + p.index { font-size: smaller; margin: 0em; + text-align: justify; } + p.index2 { font-size: smaller; margin: 0em 0em 0em 2em; + text-align: justify; } + p.index4 { font-size: smaller; margin: 0em 0em 0em 4em; + text-align: justify; } + table.plate { border: solid black 1px; width: 100%; } + table.summary { margin-left: auto; margin-right: auto; + margin-top: 1em; margin-bottom: 1em; } + table.bquote { margin-left: 4em; } + table.center { margin-left: auto; margin-right: auto; + margin-top: 0.5em; margin-bottom: 0.5em; } + table.ctrclps { margin-left: auto; margin-right: auto; + margin-top: 0.5em; margin-bottom: 0.5em; + border-collapse: collapse; } + table.image { margin-left: auto; margin-right: auto; + margin-top: 1em; margin-bottom: 1em; } + th.center_btrb { border-top: solid black 1px; + border-right: solid black 1px; + border-bottom: solid black 1px; } + th.center_btb { border-top: solid black 1px; + border-bottom: solid black 1px; } + th.left_btb { text-align: left; border-top: solid black 1px; + border-bottom: solid black 1px; } + td.br { border-right: solid black 1px; } + td.brb { border-right: solid black 1px; + border-bottom: solid black 1px; } + td.center_br { text-align: center; border-right: solid black 1px; } + td.brb { border-right: solid black 1px; + border-bottom: solid black 1px; } + td.center_brb { text-align: center; border-right: solid black 1px; + border-bottom: solid black 1px; } + td.center_bb { text-align: center; border-bottom: solid black 1px; } + td.topleft { text-align: left; vertical-align: top; } + td.topright { text-align: right; vertical-align: top; } + td.left { text-align: left; } + td.left_br { text-align: left; border-right: solid black 1px; } + td.left_brb { text-align: left; border-right: solid black 1px; + border-bottom: solid black 1px; } + td.justify { text-align: justify; } + td.center { text-align: center; } + td.right { text-align: right; } + td.right_bb { text-align: right; border-bottom: solid black 1px; } + td.sc { font-variant: small-caps; text-align: justify; } + td.summary { text-indent: -1em; padding-left: 1em; + text-align: justify; } + td.indent { padding-left: 1em; text-indent: 1em; + text-align: justify; } + td.forward { padding-left: 1em; text-indent: -1em; + text-align: justify; } + td.caption { font-size: smaller; text-align: center; } + span.sc { font-variant: small-caps; } + span.page { position: absolute; left: 92%; right: auto; + text-align: right; text-indent: 0em; + color: gray; background: white; + font-size: 9px; font-weight: normal; } + --> + </style> +</head> + +<body> + + +<pre> + +The Project Gutenberg EBook of Principles of Mining, by Herbert C. Hoover + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Principles of Mining + Valuation, Organization and Administration + +Author: Herbert C. Hoover + +Release Date: September 24, 2008 [EBook #26697] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK PRINCIPLES OF MINING *** + + + + +Produced by Robert J. Hall + + + + + +</pre> + + +<p class="big"> +PRINCIPLES OF MINING +</p> + +<table class="plate"> +<tr><td class="center" colspan="2">Published by the<br> + McGraw-Hill Book Company<br>New York</td></tr> +<tr><td colspan="2"> </td></tr> +<tr><td class="center" colspan="2">Successors to the Book + Departments of the</td></tr> +<tr><td class="left">McGraw Publishing Company</td> + <td class="right">Hill Publishing Company</td></tr> +<tr><td colspan="2"> </td></tr> +<tr><td class="left">Electrical World</td> + <td class="right">The Engineering and Mining Journal</td></tr> +<tr><td class="left">Engineering Record</td> + <td class="right">Power and The Engineer</td></tr> +<tr><td class="left">Electric Railway Journal</td> + <td class="right">American Machinist</td></tr> +<tr><td class="center" colspan="2">Metallurgical and Chemical + Engineering</td></tr> +</table> + +<h1>PRINCIPLES OF MINING</h1> + +<p class="subtitle"> +VALUATION, ORGANIZATION AND ADMINISTRATION +</p> + +<p class="center"> +COPPER, GOLD, LEAD, SILVER, TIN AND ZINC +</p> + +<p class="center_gap"> +<span style="font-size: smaller;">BY</span><br> +HERBERT C. HOOVER +</p> + +<p class="center_gap" style="font-size: smaller;"> +<i>Member American Institute of Mining Engineers, Mining and +Metallurgical Society of America, Société des +Ingénieurs Civils de France, Fellow Royal Geographical Society, +etc.</i> +</p> + +<p class="center_gap"> +<span class="sc">First Edition</span><br> +<i>FOURTH THOUSAND</i> +</p> + +<p class="center_gap"> +<b>McGRAW-HILL BOOK COMPANY</b><br> +239 WEST 39TH STREET, NEW YORK<br> +BOUVERIE STREET, LONDON, E.C.<br> +1909 +</p> + +<h2><a name="page_iii"><span class="page">Page iii</span></a> +PREFACE.</h2> + +<p class="indent"> +This volume is a condensation of a series of lectures delivered +in part at Stanford and in part at Columbia Universities. It is +intended neither for those wholly ignorant of mining, nor for those +long experienced in the profession. +</p> + +<p class="indent"> +The bulk of the material presented is the common heritage of the +profession, and if any one may think there is insufficient reference +to previous writers, let him endeavor to find to whom the origin +of our methods should be credited. The science has grown by small +contributions of experience since, or before, those unnamed Egyptian +engineers, whose works prove their knowledge of many fundamentals +of mine engineering six thousand eight hundred years ago. If I +have contributed one sentence to the accumulated knowledge of a +thousand generations of engineers, or have thrown one new ray of +light on the work, I shall have done my share. +</p> + +<p class="indent"> +I therefore must acknowledge my obligations to all those who have +gone before, to all that has been written that I have read, to +those engineers with whom I have been associated for many years, +and in particular to many friends for kindly reply to inquiry upon +points herein discussed. +</p> + +<h2><a name="page_v"><span class="page">Page v</span></a> +CONTENTS.</h2> + +<table> +<tr><td class="center"><a href="#page_1">CHAPTER 1.</a></td></tr> +<tr><td class="sc">Valuation of Copper, Gold, Lead, Silver, Tin, and + Zinc Lode Mines</td></tr> +<tr><td class="indent">Determination of average metal content; + sampling, assay plans, calculations of averages, percentage of + errors in estimate from sampling.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_13">CHAPTER II.</a></td></tr> +<tr><td><span class="sc">Mine Valuation</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Calculation of quantities of ore, and + classification of ore in sight.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_21">CHAPTER III.</a></td></tr> +<tr><td><span class="sc">Mine Valuation</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Prospective value. Extension in depth; origin + and structural character of the deposit; secondary enrichment; + development in neighboring mines; depth of exhaustion.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_34">CHAPTER IV.</a></td></tr> +<tr><td><span class="sc">Mine Valuation</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Recoverable percentage of the gross assay + value; price of metals; cost of production.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_42">CHAPTER V.</a></td></tr> +<tr><td><span class="sc">Mine Valuation</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Redemption or amortization of capital and + interest.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_51">CHAPTER VI.</a></td></tr> +<tr><td><span class="sc">Mine Valuation</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Valuation of mines with little or no ore + in sight; valuations on second-hand data; general conduct of + examinations; reports.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_58">CHAPTER VII.</a></td></tr> +<tr><td><span class="sc">Development of Mines</span></td></tr> +<tr><td class="indent">Entry to the mine; tunnels; vertical, inclined, + and combined shafts; location and number of shafts. + <a name="page_vi"><span class="page">Page vi</span></a> + </td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_74">CHAPTER VIII.</a></td></tr> +<tr><td><span class="sc">Development of Mines</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Shape and size of shafts; speed of sinking; + tunnels.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_84">CHAPTER IX.</a></td></tr> +<tr><td><span class="sc">Development of Mines</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Subsidiary development: stations; crosscuts; + levels; interval between levels; protection of levels; winzes and + rises. Development in the prospecting stage; drilling.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_94">CHAPTER X.</a></td></tr> +<tr><td class="sc">Stoping</td></tr> +<tr><td class="indent">Methods of ore-breaking; underhand stopes; + overhand stopes; combined stope. Valuing ore in course of + breaking.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_103">CHAPTER XI.</a></td></tr> +<tr><td class="sc">Methods of Supporting Excavation</td></tr> +<tr><td class="indent">Timbering; filling with waste; filling + with broken ore; pillars of ore; artificial pillars; caving + system.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_124">CHAPTER XII.</a></td></tr> +<tr><td class="sc">Mechanical Equipment</td></tr> +<tr><td class="indent">Conditions bearing on mine equipment; + winding appliances; haulage equipment in shafts; lateral + underground transport; transport in stopes.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_138">CHAPTER XIII.</a></td></tr> +<tr><td><span class="sc">Mechanical Equipment</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Drainage: controlling factors; volume + and head of water; flexibility; reliability; power conditions; + mechanical efficiency; capital outlay. Systems of + drainage,—steam pumps, compressed-air pumps, electrical + pumps, rod-driven pumps, bailing; comparative value of various + systems.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_145">CHAPTER XIV.</a></td></tr> +<tr><td><span class="sc">Mechanical Equipment</span> + (<i>Concluded</i>)</td></tr> +<tr><td class="indent">Machine drilling: power transmission; + compressed air <i>vs.</i> electricity; air drills; + machine <i>vs.</i> hand drilling. Workshops. Improvement in + equipment. + <a name="page_vii"><span class="page">Page vii</span></a> + </td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_153">CHAPTER XV.</a></td></tr> +<tr><td class="sc">Ratio of Output to the Mine</td></tr> +<tr><td class="indent">Determination of possible maximum; + limiting factors; cost of equipment; life of the mine; + mechanical inefficiency of patchwork plant; overproduction + of base metal; security of investment.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_161">CHAPTER XVI.</a></td></tr> +<tr><td class="sc">Administration</td></tr> +<tr><td class="indent">Labor efficiency; skill; intelligence; + application coördination; contract work; labor unions; + real basis of wages.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_169">CHAPTER XVII.</a></td></tr> +<tr><td><span class="sc">Administration</span> + (<i>Continued</i>)</td></tr> +<tr><td class="indent">Accounts and technical data and reports; + working costs; division of expenditure; inherent limitations in + accuracy of working costs; working cost sheets. General technical + data; labor, supplies, power, surveys, sampling, and + assaying.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_178">CHAPTER XVIII.</a></td></tr> +<tr><td><span class="sc">Administration</span> + (<i>Concluded</i>)</td></tr> +<tr><td class="indent">Administrative reports.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_178">CHAPTER XIX.</a></td></tr> +<tr><td class="sc">The Amount of Risk in Mining Investments</td></tr> +<tr><td class="indent">Risk in valuation of mines; in mines as + compared with other commercial enterprises.</td></tr> + +<tr><td> </tr> +<tr><td class="center"><a href="#page_185">CHAPTER XX.</a></td></tr> +<tr><td class="sc">The Character, Training, and Obligations of the + Mining Engineering Profession</td></tr> + +<tr><td> </tr> +<tr><td class="sc"><a href="#page_195">Index</a></td></tr> +</table> + +<p class="big"> +<a name="page_1"><span class="page">Page 1</span></a> +PRINCIPLES OF MINING. +</p> + +<h2>CHAPTER I.</h2> + +<p class="center"> +<span class="sc">Valuation of Copper, Gold, Lead, Silver, Tin, + and Zinc Lode Mines.</span> +</p> + +<table class="summary"><tr><td class="summary"> +DETERMINATION OF AVERAGE METAL CONTENT; SAMPLING, ASSAY PLANS, +CALCULATIONS OF AVERAGES, PERCENTAGE OF ERRORS IN ESTIMATE FROM +SAMPLING. +</td></tr></table> + +<p class="indent"> +The following discussion is limited to <i>in situ</i> deposits +of copper, gold, lead, silver, tin, and zinc. The valuation of +alluvial deposits, iron, coal, and other mines is each a special +science to itself and cannot be adequately discussed in common +with the type of deposits mentioned above. +</p> + +<p class="indent"> +The value of a metal mine of the order under discussion depends +upon:— +</p> + +<ol style="list-style-type: lower-alpha;"> +<li>The profit that may be won from ore exposed;</li> +<li>The prospective profit to be derived from extension of + the ore beyond exposures;</li> +<li>The effect of a higher or lower price of metal (except + in gold mines);</li> +<li>The efficiency of the management during realization.</li> +</ol> + +<p class="indent"> +The first may be termed the positive value, and can be approximately +determined by sampling or test-treatment runs. The second and the +third may be termed the speculative values, and are largely a matter +of judgment based on geological evidence and the industrial outlook. +The fourth is a question of development, equipment, and engineering +method adapted to the prospects of the enterprise, together with +capable executive control of these works. +</p> + +<p class="indent"> +<a name="page_2"><span class="page">Page 2</span></a> It should be +stated at the outset that it is utterly impossible to accurately +value any mine, owing to the many speculative factors involved. +The best that can be done is to state that the value lies between +certain limits, and that various stages above the minimum given +represent various degrees of risk. Further, it would be but stating +truisms to those engaged in valuing mines to repeat that, because +of the limited life of every mine, valuation of such investments +cannot be based upon the principle of simple interest; nor that any +investment is justified without a consideration of the management +to ensue. Yet the ignorance of these essentials is so prevalent +among the public that they warrant repetition on every available +occasion. +</p> + +<p class="indent"> +To such an extent is the realization of profits indicated from +the other factors dependent upon the subsequent management of the +enterprise that the author considers a review of underground engineering +and administration from an economic point of view an essential to +any essay upon the subject. While the metallurgical treatment of +ores is an essential factor in mine economics, it is considered that +a detailed discussion of the myriad of processes under hypothetic +conditions would lead too far afield. Therefore the discussion is +largely limited to underground and administrative matters. +</p> + +<p class="indent"> +The valuation of mines arises not only from their change of ownership, +but from the necessity in sound administration for a knowledge +of some of the fundamentals of valuation, such as ore reserves +and average values, that managerial and financial policy may be +guided aright. Also with the growth of corporate ownership there +is a demand from owners and stockholders for periodic information +as to the intrinsic condition of their properties. +</p> + +<p class="indent"> +The growth of a body of speculators and investors in mining stocks +and securities who desire professional guidance which cannot be based +upon first-hand data is creating further demand on the engineer. +Opinions in these cases must be formed on casual visits or second-hand +information, and a knowledge of men and things generally. Despite the +feeling of some engineers that the latter employment is not properly +based professionally, it is an expanding phase of engineers' work, and +must be <a name="page_3"><span class="page">Page 3</span></a> taken +seriously. Although it lacks satisfactory foundation for accurate +judgment, yet the engineer can, and should, give his experience to +it when the call comes, out of interest to the industry as a whole. +Not only can he in a measure protect the lamb, by insistence on no +investment without the provision of properly organized data and +sound administration for his client, but he can do much to direct +the industry from gambling into industrial lines. +</p> + +<p class="indent"> +An examination of the factors which arise on the valuation of mines +involves a wide range of subjects. For purposes of this discussion +they may be divided into the following heads:— +</p> + +<ol> +<li><i>Determination of Average Metal Contents of the Ore.</i></li> +<li><i>Determination of Quantities of Ore.</i></li> +<li><i>Prospective Value.</i></li> +<li><i>Recoverable Percentage of Gross Value.</i></li> +<li><i>Price of Metals.</i></li> +<li><i>Cost of Production.</i></li> +<li><i>Redemption or Amortization of Capital and Interest.</i></li> +<li><i>Valuation of Mines without Ore in Sight.</i></li> +<li><i>General Conduct of Examination and Reports.</i></li> +</ol> + +<p class="center"> +DETERMINATION OF AVERAGE METAL CONTENTS OF THE ORE. +</p> + +<p class="indent"> +Three means of determination of the average metal content of standing +ore are in use—Previous Yield, Test-treatment Runs, and Sampling. +</p> + +<p class="indent"> +<b>Previous Yield.</b>—There are certain types of ore where +the previous yield from known space becomes the essential basis +of determination of quantity and metal contents of ore standing +and of the future probabilities. Where metals occur like plums in +a pudding, sampling becomes difficult and unreliable, and where +experience has proved a sort of regularity of recurrence of these +plums, dependence must necessarily be placed on past records, for +if their reliability is to be questioned, resort must be had to +extensive test-treatment runs. The Lake Superior copper mines and +the Missouri lead and zinc mines are of this type of deposit. On +the other sorts of deposits the previous <a name="page_4"><span +class="page">Page 4</span></a> yield is often put forward as of +important bearing on the value of the ore standing, but such yield, +unless it can be <i>authentically</i> connected with blocks of +ore remaining, is not necessarily a criterion of their contents. +Except in the cases mentioned, and as a check on other methods +of determination, it has little place in final conclusions. +</p> + +<p class="indent"> +<b>Test Parcels.</b>—Treatment on a considerable scale of +sufficiently regulated parcels, although theoretically the ideal +method, is, however, not often within the realm of things practical. +In examination on behalf of intending purchasers, the time, expense, +or opportunity to fraud are usually prohibitive, even where the +plant and facilities for such work exist. Even in cases where the +engineer in management of producing mines is desirous of determining +the value of standing ore, with the exception of deposits of the +type mentioned above, it is ordinarily done by actual sampling, +because separate mining and treatment of test lots is generally +inconvenient and expensive. As a result, the determination of the +value of standing ore is, in the great majority of cases, done +by sampling and assaying. +</p> + +<p class="indent"> +<b>Sampling.</b>—The whole theory of sampling is based on +the distribution of metals through the ore-body with more or less +regularity, so that if small portions, that is samples, be taken +from a sufficient number of points, their average will represent +fairly closely the unit value of the ore. If the ore is of the +extreme type of irregular metal distribution mentioned under "previous +yield," then sampling has no place. +</p> + +<p class="indent"> +How frequently samples must be taken, the manner of taking them, +and the quantity that constitutes a fair sample, are matters that +vary with each mine. So much depends upon the proper performance +of this task that it is in fact the most critical feature of mine +examination. Ten samples properly taken are more valuable than +five hundred slovenly ones, like grab samples, for such a number +of bad ones would of a surety lead to wholly wrong conclusions. +Given a good sampling and a proper assay plan, the valuation of a +mine is two-thirds accomplished. It should be an inflexible principle +in examinations for purchase that every sample must be taken under +the personal <a name="page_5"><span class="page">Page 5</span></a> +supervision of the examining engineer or his trusted assistants. +Aside from throwing open the doors to fraud, the average workman +will not carry out the work in a proper manner, unless under constant +supervision, because of his lack of appreciation of the issues +involved. Sampling is hard, uncongenial, manual labor. It requires +a deal of conscientiousness to take enough samples and to take +them thoroughly. The engineer does not exist who, upon completion +of this task, considers that he has got too many, and most wish +that they had taken more. +</p> + +<p class="indent"> +The accuracy of sampling as a method of determining the value of +standing ore is a factor of the number of samples taken. The average, +for example, of separate samples from each square inch would be +more accurate than those from each alternate square inch. However, +the accumulated knowledge and experience as to the distribution +of metals through ore has determined approximately the manner of +taking such samples, and the least number which will still by the +law of averages secure a degree of accuracy commensurate with the +other factors of estimation. +</p> + +<p class="indent"> +As metals are distributed through ore-bodies of fissure origin +with most regularity on lines parallel to the strike and dip, an +equal portion of ore from every point along cross-sections at right +angles to the strike will represent fairly well the average values +for a certain distance along the strike either side of these +cross-sections. In massive deposits, sample sections are taken +in all directions. The intervals at which sample sections must +be cut is obviously dependent upon the general character of the +deposit. If the values are well distributed, a longer interval +may be employed than in one subject to marked fluctuations. As +a general rule, five feet is the distance most accepted. This, +in cases of regular distribution of values, may be stretched to +ten feet, or in reverse may be diminished to two or three feet. +</p> + +<p class="indent"> +The width of ore which may be included for one sample is dependent +not only upon the width of the deposit, but also upon its character. +Where the ore is wider than the necessary stoping width, the sample +should be regulated so as to show the <a name="page_6"><span +class="page">Page 6</span></a> possible locus of values. The metal +contents may be, and often are, particularly in deposits of the +impregnation or replacement type, greater along some streak in the +ore-body, and this difference may be such as to make it desirable +to stope only a portion of the total thickness. For deposits narrower +than the necessary stoping width the full breadth of ore should be +included in one sample, because usually the whole of the deposit +will require to be broken. +</p> + +<p class="indent"> +In order that a payable section may not possibly be diluted with +material unnecessary to mine, if the deposit is over four feet and +under eight feet, the distance across the vein or lode is usually +divided into two samples. If still wider, each is confined to a +span of about four feet, not only for the reason given above, but +because the more numerous the samples, the greater the accuracy. +Thus, in a deposit twenty feet wide it may be taken as a good guide +that a test section across the ore-body should be divided into +five parts. +</p> + +<p class="indent"> +As to the physical details of sample taking, every engineer has +his own methods and safeguards against fraud and error. In a large +organization of which the writer had for some years the direction, +and where sampling of mines was constantly in progress on an extensive +scale, not only in contemplation of purchase, but where it was also +systematically conducted in operating mines for working data, he +adopted the above general lines and required the following details. +</p> + +<p class="indent"> +A fresh face of ore is first broken and then a trench cut about +five inches wide and two inches deep. This trench is cut with a +hammer and moil, or, where compressed air is available and the +rock hard, a small air-drill of the hammer type is used. The spoil +from the trench forms the sample, and it is broken down upon a +large canvas cloth. Afterwards it is crushed so that all pieces +will pass a half-inch screen, mixed and quartered, thus reducing the +weight to half. Whether it is again crushed and quartered depends +upon what the conditions are as to assaying. If convenient to assay +office, as on a going mine, the whole of the crushing and quartering +work can be done at that office, where there are usually suitable +mechanical appliances. If the samples <a name="page_7"><span +class="page">Page 7</span></a> must be taken a long distance, the +bulk for transport can be reduced by finer breaking and repeated +quartering, until there remain only a few ounces. +</p> + +<p class="indent"> +<b>Precautions against Fraud.</b>—Much has been written about +the precautions to be taken against fraud in cases of valuations +for purchase. The best safeguards are an alert eye and a strong +right arm. However, certain small details help. A large leather +bag, arranged to lock after the order of a mail sack, into which +samples can be put underground and which is never unfastened except +by responsible men, not only aids security but relieves the mind. +A few samples of country rock form a good check, and notes as to +the probable value of the ore, from inspection when sampling, are +useful. A great help in examination is to have the assays or analyses +done coincidentally with the sampling. A doubt can then always be +settled by resampling at once, and much knowledge can be gained +which may relieve so exhaustive a program as might be necessary +were results not known until after leaving the mine. +</p> + +<p class="indent"> +<b>Assay of Samples.</b>—Two assays, or as the case may be, +analyses, are usually made of every sample and their average taken. +In the case of erratic differences a third determination is necessary. +</p> + +<p class="indent"> +<b>Assay Plans.</b>—An assay plan is a plan of the workings, +with the location, assay value, and width of the sample entered +upon it. In a mine with a narrow vein or ore-body, a longitudinal +section is sufficient base for such entries, but with a greater +width than one sample span it is desirable to make preliminary +plans of separate levels, winzes, etc., and to average the value +of the whole payable widths on such plans before entry upon a +longitudinal section. Such a longitudinal section will, through +the indicated distribution of values, show the shape of the +ore-body—a step necessary in estimating quantities and of +the most fundamental importance in estimating the probabilities +of ore extension beyond the range of the openings. The final assay +plan should show the average value of the several blocks of ore, +and it is from these averages that estimates of quantities must +be made up. +</p> + +<p class="indent"> +<a name="page_8"><span class="page">Page 8</span></a> <b>Calculations +of Averages.</b>—The first step in arriving at average values +is to reduce erratic high assays to the general tenor of other +adjacent samples. This point has been disputed at some length, +more often by promoters than by engineers, but the custom is very +generally and rightly adopted. Erratically high samples may indicate +presence of undue metal in the assay attributable to unconscious +salting, for if the value be confined to a few large particles +they may find their way through all the quartering into the assay. +Or the sample may actually indicate rich spots of ore; but in any +event experience teaches that no dependence can be put upon regular +recurrence of such abnormally rich spots. As will be discussed +under percentage of error in sampling, samples usually indicate +higher than the true value, even where erratic assays have been +eliminated. There are cases of profitable mines where the values +were all in spots, and an assay plan would show 80% of the assays +<i>nil</i>, yet these pockets were so rich as to give value to +the whole. Pocket mines, as stated before, are beyond valuation +by sampling, and aside from the previous yield recourse must be +had to actual treatment runs on every block of ore separately. +</p> + +<p class="indent"> +After reduction of erratic assays, a preliminary study of the runs of +value or shapes of the ore-bodies is necessary before any calculation +of averages. A preliminary delineation of the boundaries of the +payable areas on the assay plan will indicate the sections of the +mine which are unpayable, and from which therefore samples can +be rightly excluded in arriving at an average of the payable ore +(Fig. 1). In a general way, only the ore which must be mined need +be included in averaging. +</p> + +<p class="indent"> +The calculation of the average assay value of standing ore from +samples is one which seems to require some statement of elementals. +Although it may seem primitive, it can do no harm to recall that if +a dump of two tons of ore assaying twenty ounces per ton be added +to a dump of five tons averaging one ounce per ton, the result +has not an average assay of twenty-one ounces divided by the number +of dumps. Likewise one sample over a width of two feet, assaying +twenty ounces per ton, if averaged with another sample over a width +of five feet, assaying <a name="page_9"><span class="page">Page +9</span></a> one ounce, is no more twenty-one ounces divided by +two samples than in the case of the two dumps. If common sense were +not sufficient demonstration of this, it can be shown algebraically. +Were samples equidistant from each other, and were they of equal +width, the average value would be the simple arithmetical mean of +the assays. But this is seldom the case. The number of instances, +not only in practice but also in technical literature, where the +fundamental distinction between an arithmetical and a geometrical +mean is lost sight of is amazing. +</p> + +<p class="indent"> +To arrive at the average value of samples, it is necessary, in +effect, to reduce them to the actual quantity of the metal and volume +of ore represented by each. The method of calculation therefore +is one which gives every sample an importance depending upon the +metal content of the volume of ore it represents. +</p> + +<p class="indent"> +The volume of ore appertaining to any given sample can be considered +as a prismoid, the dimensions of which may be stated as follows:— +</p> + +<table> +<tr><td rowspan="3"> </td> + <td class="topright"><i>W</i></td> + <td class="topright">=</td> + <td>Width in feet of ore sampled.</td></tr> +<tr><td class="topright"><i>L</i></td> + <td class="topright">=</td> + <td>Length in feet of ore represented by the sample.</td></tr> +<tr><td class="topright"><i>D</i></td> + <td class="topright">=</td> + <td>Depth into the block to which values are assumed to + penetrate.</td></tr> + +<tr><td colspan="4">We may also let:—</td></tr> + +<tr><td rowspan="2"> </td> + <td class="topright"><i>C</i></td> + <td class="topright">=</td> + <td>The number of cubic feet per ton of ore.</td></tr> +<tr><td class="topright"><i>V</i></td> + <td class="topright">=</td> + <td>Assay value of the sample.</td></tr> +<tr><td class="topright" rowspan="2">Then</td> + <td class="topright"><i>WLD</i>/<i>C</i></td> + <td class="topright">=</td> + <td>tonnage of the prismoid.[*]</td></tr> +<tr><td class="topright"><i>V WLD</i>/<i>C</i></td> + <td class="topright">=</td> + <td>total metal contents.</td></tr> +</table> + +<p class="footnote"> +[Footnote *: Strictly, the prismoidal formula should be used, but +it complicates the study unduly, and for practical purposes the +above may be taken as the volume.] +</p> + +<p class="indent"> +The average value of a number of samples is the total metal contents +of their respective prismoids, divided by the total tonnage of these +prismoids. If we let <i>W</i>, <i>W</i><sub>1</sub>, <i>V</i>, +<i>V</i><sub>1</sub> etc., represent different samples, we have:— +</p> + +<table class="center"> +<tr><td class="center" style="border-bottom: solid black 1px;"> + <i>V</i>(<i>WLD</i>/<i>C</i>) + + <i>V</i><sub>1</sub>(<i>W</i><sub>1</sub> <i>L</i><sub>1</sub> + <i>D</i><sub>1</sub>/<i>C</i>) + + <i>V</i><sub>2</sub>(<i>W</i><sub>2</sub> <i>L</i><sub>2</sub> + <i>D</i><sub>2</sub>/<i>C</i>) +</td><td rowspan="2"> = average value.</td></tr> + +<tr><td class="center"> + <i>WLD</i>/<i>C</i> + + <i>W</i><sub>1</sub><i>L</i><sub>1</sub><i>D</i><sub>1</sub>/<i>C</i> + + <i>W</i><sub>2</sub><i>L</i><sub>2</sub><i>D</i><sub>2</sub>/<i>C</i> + <a name="page_10"><span class="page">Page 10</span></a> +</td></tr> +</table> + +<p class="indent"> +This may be reduced to:— +</p> + +<table class="center"> +<tr><td class="center" style="border-bottom: solid black 1px;"> +(<i>VWLD</i>) + +(<i>V</i><sub>1</sub> <i>W</i><sub>1</sub> <i>L</i><sub>1</sub> + <i>D</i><sub>1</sub>) + +(<i>V</i><sub>2</sub> <i>W</i><sub>2</sub> <i>L</i><sub>2</sub> + <i>D</i><sub>2</sub>,), etc.</td></tr> +<tr><td class="center"> +(<i>WLD</i>) + +(<i>W</i><sub>1</sub><i>L</i><sub>1</sub><i>D</i><sub>1</sub>) + +(<i>W</i><sub>2</sub><i>L</i><sub>2</sub><i>D</i><sub>2</sub>), etc. +</td></tr> +</table> + +<p class="indent"> +As a matter of fact, samples actually represent the value of the +outer shell of the block of ore only, and the continuity of the +same values through the block is a geological assumption. From the +outer shell, all the values can be taken to penetrate equal distances +into the block, and therefore <i>D</i>, <i>D</i><sub>1</sub>, +<i>D</i><sub>2</sub> may be considered as equal and the equation +becomes:— +</p> + +<table class="center"> +<tr><td class="center" style="border-bottom: solid black 1px;"> +(<i>VWL</i>) + +(<i>V</i><sub>1</sub><i>W</i><sub>1</sub><i>L</i><sub>1</sub>) + +(<i>V</i><sub>2</sub><i>W</i><sub>2</sub><i>L</i><sub>2</sub>), etc. +</td></tr> +<tr><td class="center"> +(<i>WL</i>) + (<i>W</i><sub>1</sub><i>L</i><sub>1</sub>) + +(<i>W</i><sub>2</sub><i>L</i><sub>2</sub>), etc. +</td></tr> +</table> + +<p class="indent"> +The length of the prismoid base <i>L</i> for any given sample will +be a distance equal to one-half the sum of the distances to the two +adjacent samples. As a matter of practice, samples are usually taken +at regular intervals, and the lengths <i>L</i>, <i>L</i><sub>1</sub>, +<i>L</i><sub>2</sub> becoming thus equal can in such case be eliminated, +and the equation becomes:— +</p> + +<table class="center"> +<tr><td class="center" style="border-bottom: solid black 1px;"> +(<i>VW</i>) + (<i>V</i><sub>1</sub><i>W</i><sub>1</sub>) + +(<i>V</i><sub>2</sub><i>W</i><sub>2</sub>), etc.</td></tr> +<tr><td class="center"> +<i>W</i> + <i>W</i><sub>1</sub> + <i>W</i><sub>2</sub>, etc. +</td></tr> +</table> + +<p class="indent"> +The name "assay foot" or "foot value" has been given to the relation +<i>VW</i>, that is, the assay value multiplied by the width sampled.[*] +It is by this method that all samples must be averaged. The same +relation obviously can be evolved by using an inch instead of a +foot, and in narrow veins the assay inch is generally used. +</p> + +<p class="footnote"> +[Footnote *: An error will be found in this method unless the two +end samples be halved, but in a long run of samples this may be +disregarded.] +</p> + +<p class="indent"> +Where the payable cross-section is divided into more than one sample, +the different samples in the section must be averaged by the above +formula, before being combined with the adjacent <a name="page_11"><span +class="page">Page 11</span></a> section. Where the width sampled +is narrower than the necessary stoping width, and where the waste +cannot be broken separately, the sample value must be diluted to a +stoping width. To dilute narrow samples to a stoping width, a blank +value over the extra width which it is necessary to include must be +averaged with the sample from the ore on the above formula. Cases +arise where, although a certain width of waste must be broken with +the ore, it subsequently can be partially sorted out. Practically +nothing but experience on the deposit itself will determine how +far this will restore the value of the ore to the average of the +payable seam. In any event, no sorting can eliminate all such waste; +and it is necessary to calculate the value on the breaking width, +and then deduct from the gross tonnage to be broken a percentage +from sorting. There is always an allowance to be made in sorting +for a loss of good ore with the discards. +</p> + +<p class="indent"> +<b>Percentage of Error in Estimates from Sampling.</b>—It +must be remembered that the whole theory of estimation by sampling +is founded upon certain assumptions as to evenness of continuity and +transition in value and volume. It is but a basis for an estimate, +and an estimate is not a statement of fact. It cannot therefore +be too forcibly repeated that an estimate is inherently but an +approximation, take what care one may in its founding. While it is +possible to refine mathematical calculation of averages to almost +any nicety, beyond certain essentials it adds nothing to accuracy +and is often misleading. +</p> + +<p class="indent"> +It is desirable to consider where errors are most likely to creep +in, assuming that all fundamental data are both accurately taken and +considered. Sampling of ore <i>in situ</i> in general has a tendency +to give higher average value than the actual reduction of the ore +will show. On three West Australian gold mines, in records covering +a period of over two years, where sampling was most exhaustive as a +daily régime of the mines, the values indicated by sampling +were 12% higher than the mill yield plus the contents of the residues. +On the Witwatersrand gold mines, the actual extractable value is +generally considered to be about 78 to 80% of the average shown +by sampling, while the mill extractions are on average about 90 +to 92% of the head value <a name="page_12"><span class="page">Page +12</span></a> coming to the mill. In other words, there is a constant +discrepancy of about 10 to 12% between the estimated value as indicated +by mine samples, and the actual value as shown by yield plus the +residues. At Broken Hill, on three lead mines, the yield is about +12% less than sampling would indicate. This constancy of error in +one direction has not been so generally acknowledged as would be +desirable, and it must be allowed for in calculating final results. +The causes of the exaggeration seem to be:— +</p> + +<p class="indent"> +<i>First</i>, inability to stope a mine to such fine limitations of +width, or exclusion of unpayable patches, as would appear practicable +when sampling, that is by the inclusion when mining of a certain +amount of barren rock. Even in deposits of about normal stoping +width, it is impossible to prevent the breaking of a certain amount +of waste, even if the ore occurrence is regularly confined by walls. +</p> + +<p class="indent"> +If the mine be of the impregnation type, such as those at Goldfield, +or Kalgoorlie, with values like plums in a pudding, and the stopes +themselves directed more by assays than by any physical differences +in the ore, the discrepancy becomes very much increased. In mines +where the range of values is narrower than the normal stoping width, +some wall rock must be broken. Although it is customary to allow for +this in calculating the average value from samples, the allowance +seldom seems enough. In mines where the ore is broken on to the +top of stopes filled with waste, there is some loss underground +through mixture with the filling. +</p> + +<p class="indent"> +<i>Second</i>, the metal content of ores, especially when in the +form of sulphides, is usually more friable than the matrix, and in +actual breaking of samples an undue proportion of friable material +usually creeps in. This is true more in lead, copper, and zinc, than +in gold ores. On several gold mines, however, tests on accumulated +samples for their sulphide percentage showed a distinctly greater +ratio than the tenor of the ore itself in the mill. As the gold is +usually associated with the sulphides, the samples showed higher +values than the mill. +</p> + +<p class="indent"> +In general, some considerable factor of safety must be allowed +after arriving at calculated average of samples,—how much +it is difficult to say, but, in any event, not less than 10%. +</p> + +<h2><a name="page_13"><span class="page">Page 13</span></a> +CHAPTER II.</h2> + +<p class="center"> +<span class="sc">Mine Valuation</span> (<i>Continued</i>). +</p> + +<table class="summary"><tr><td class="summary"> +CALCULATION OF QUANTITIES OF ORE, AND CLASSIFICATION OF ORE IN +SIGHT. +</td></tr></table> + +<p class="indent"> +As mines are opened by levels, rises, etc., through the ore, an +extension of these workings has the effect of dividing it into +"blocks." The obvious procedure in determining tonnages is to calculate +the volume and value of each block separately. Under the law of +averages, the multiplicity of these blocks tends in proportion +to their number to compensate the percentage of error which might +arise in the sampling or estimating of any particular one. The +shapes of these blocks, on longitudinal section, are often not +regular geometrical figures. As a matter of practice, however, they +can be subdivided into such figures that the total will approximate +the whole with sufficient closeness for calculations of their areas. +</p> + +<p class="indent"> +The average width of the ore in any particular block is the arithmetical +mean of the width of the sample sections in it,[*] if the samples be +an equal distance apart. If they are not equidistant, the average +width is the sum of the areas between samples, divided by the total +length sampled. The cubic foot contents of a particular block is +obviously the width multiplied by the area of its longitudinal +section. +</p> + +<p class="footnote"> +[Footnote *: This is not strictly true unless the sum of the widths +of the two end-sections be divided by two and the result incorporated +in calculating the means. In a long series that error is of little +importance.] +</p> + +<p class="indent"> +The ratio of cubic feet to tons depends on the specific gravity +of the ore, its porosity, and moisture. The variability of ores +throughout the mine in all these particulars renders any method +of calculation simply an approximation in the end. The factors +which must remain unknown necessarily lead the engineer to the +<a name="page_14"><span class="page">Page 14</span></a> +provision of a margin of safety, which makes mathematical refinement +and algebraic formulæ ridiculous. +</p> + +<p class="indent"> +There are in general three methods of determination of the specific +volume of ores:— +</p> + +<p class="indent"> +<i>First</i>, by finding the true specific gravity of a sufficient +number of representative specimens; this, however, would not account +for the larger voids in the ore-body and in any event, to be anything +like accurate, would be as expensive as sampling and is therefore +of little more than academic interest. +</p> + +<p class="indent"> +<i>Second</i>, by determining the weight of quantities broken from +measured spaces. This also would require several tests from different +portions of the mine, and, in examinations, is usually inconvenient +and difficult. Yet it is necessary in cases of unusual materials, +such as leached gossans, and it is desirable to have it done sooner +or later in going mines, as a check. +</p> + +<p class="indent"> +<i>Third</i>, by an approximation based upon a calculation from +the specific gravities of the predominant minerals in the ore. +Ores are a mixture of many minerals; the proportions vary through +the same ore-body. Despite this, a few partial analyses, which +are usually available from assays of samples and metallurgical +tests, and a general inspection as to the compactness of the ore, +give a fairly reliable basis for approximation, especially if a +reasonable discount be allowed for safety. In such discount must +be reflected regard for the porosity of the ore, and the margin of +safety necessary may vary from 10 to 25%. If the ore is of unusual +character, as in leached deposits, as said before, resort must be +had to the second method. +</p> + +<p class="indent"> +The following table of the weights per cubic foot and the number +of cubic feet per ton of some of the principal ore-forming minerals +and gangue rocks will be useful for approximating the weight of +a cubic foot of ore by the third method. Weights are in pounds +avoirdupois, and two thousand pounds are reckoned to the ton. +</p> + +<table class="ctrclps"> +<tr><th class="center_btrb"> </th> + <th class="center_btrb"><span class="sc">Weight per<br> + Cubic Foot</span></th> + <th class="center_btb"><span class="sc">Number of<br> + Cubic Feet<br>per Ton of<br>2000 lb.</span> + <a name="page_15"><span class="page">Page 15</span></a> + </th></tr> +<tr><td class="br">Antimony</td> + <td class="center_br">417.50</td> + <td class="center">4.79</td></tr> +<tr><td class="br" style="padding-left: 2em;">Sulphide</td> + <td class="center_br">285.00</td> + <td class="center">7.01</td></tr> +<tr><td class="br">Arsenical Pyrites</td> + <td class="center_br">371.87</td> + <td class="center">5.37</td></tr> +<tr><td class="br">Barium Sulphate</td> + <td class="center_br">278.12</td> + <td class="center">7.19</td></tr> +<tr><td class="br">Calcium:</td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="br" style="padding-left: 2em;">Fluorite</td> + <td class="center_br">198.75</td> + <td class="center">10.06</td></tr> +<tr><td class="br" style="padding-left: 2em;">Gypsum</td> + <td class="center_br">145.62</td> + <td class="center">13.73</td></tr> +<tr><td class="br" style="padding-left: 2em;">Calcite</td> + <td class="center_br">169.37</td> + <td class="center">11.80</td></tr> +<tr><td class="br">Copper</td> + <td class="center_br">552.50</td> + <td class="center">3.62</td></tr> +<tr><td class="br" style="padding-left: 2em;">Calcopyrite</td> + <td class="center_br">262.50</td> + <td class="center">7.61</td></tr> +<tr><td class="br" style="padding-left: 2em;">Bornite</td> + <td class="center_br">321.87</td> + <td class="center">6.21</td></tr> +<tr><td class="br" style="padding-left: 2em;">Malachite</td> + <td class="center_br">247.50</td> + <td class="center">8.04</td></tr> +<tr><td class="br" style="padding-left: 2em;">Azurite</td> + <td class="center_br">237.50</td> + <td class="center">8.42</td></tr> +<tr><td class="br" style="padding-left: 2em;">Chrysocolla</td> + <td class="center_br">132.50</td> + <td class="center">15.09</td></tr> +<tr><td class="br">Iron (Cast)</td> + <td class="center_br">450.00</td> + <td class="center">4.44</td></tr> +<tr><td class="br" style="padding-left: 2em;">Magnetite</td> + <td class="center_br">315.62</td> + <td class="center">6.33</td></tr> +<tr><td class="br" style="padding-left: 2em;">Hematite</td> + <td class="center_br">306.25</td> + <td class="center">6.53</td></tr> +<tr><td class="br" style="padding-left: 2em;">Limonite</td> + <td class="center_br">237.50</td> + <td class="center">8.42</td></tr> +<tr><td class="br" style="padding-left: 2em;">Pyrite</td> + <td class="center_br">312.50</td> + <td class="center">6.40</td></tr> +<tr><td class="br" style="padding-left: 2em;">Carbonate</td> + <td class="center_br">240.62</td> + <td class="center">8.31</td></tr> +<tr><td class="br">Lead</td> + <td class="center_br">710.62</td> + <td class="center">2.81</td></tr> +<tr><td class="br" style="padding-left: 2em;">Galena + <td class="center_br">468.75</td> + <td class="center">4.27</td></tr> +<tr><td class="br" style="padding-left: 2em;">Carbonate + <td class="center_br">406.87</td> + <td class="center">4.81</td></tr> +<tr><td class="br">Manganese Oxide</td> + <td class="center_br">268.75</td> + <td class="center">6.18</td></tr> +<tr><td class="br" style="padding-left: 2em;">Rhodonite</td> + <td class="center_br">221.25</td> + <td class="center">9.04</td></tr> +<tr><td class="br">Magnesite</td> + <td class="center_br">187.50</td> + <td class="center">10.66</td></tr> +<tr><td class="br" style="padding-left: 2em;">Dolomite</td> + <td class="center_br">178.12</td> + <td class="center">11.23</td></tr> +<tr><td class="br">Quartz</td> + <td class="center_br">165.62</td> + <td class="center">12.07</td></tr> +<tr><td class="br">Quicksilver</td> + <td class="center_br">849.75</td> + <td class="center">2.35</td></tr> +<tr><td class="br" style="padding-left: 2em;">Cinnabar</td> + <td class="center_br">531.25</td> + <td class="center">3.76</td></tr> +<tr><td class="br" style="padding-left: 2em;">Sulphur</td> + <td class="center_br">127.12</td> + <td class="center">15.74</td></tr> +<tr><td class="br">Tin</td> + <td class="center_br">459.00</td> + <td class="center">4.35</td></tr> +<tr><td class="br" style="padding-left: 2em;">Oxide</td> + <td class="center_br">418.75</td> + <td class="center">4.77</td></tr> +<tr><td class="br">Zinc</td> + <td class="center_br">437.50</td> + <td class="center">4.57</td></tr> +<tr><td class="br" style="padding-left: 2em;">Blende</td> + <td class="center_br">253.12</td> + <td class="center">7.90</td></tr> +<tr><td class="br" style="padding-left: 2em;">Carbonate</td> + <td class="center_br">273.12</td> + <td class="center">7.32</td></tr> +<tr><td class="br" style="padding-left: 2em;">Silicate</td> + <td class="center_br">215.62</td> + <td class="center">9.28</td></tr> +<tr><td class="br">Andesite</td> + <td class="center_br">165.62</td> + <td class="center">12.07</td></tr> +<tr><td class="br">Granite</td> + <td class="center_br">162.62</td> + <td class="center">12.30</td></tr> +<tr><td class="br">Diabase</td> + <td class="center_br">181.25</td> + <td class="center">11.03</td></tr> +<tr><td class="br">Diorite</td> + <td class="center_br">171.87</td> + <td class="center">11.63</td></tr> +<tr><td class="br">Slates</td> + <td class="center_br">165.62</td> + <td class="center">12.07</td></tr> +<tr><td class="br">Sandstones</td> + <td class="center_br">162.50</td> + <td class="center">12.30</td></tr> +<tr><td class="brb">Rhyolite</td> + <td class="center_brb">156.25</td> + <td class="center_bb">12.80</td></tr> +</table> + +<p class="footnote"> +The specific gravity of any particular mineral has a considerable +range, and a medium has been taken. The possible error is +inconsequential for the purpose of these calculations. +</p> + +<p class="indent"> +<a name="page_16"><span class="page">Page 16</span></a> For example, +a representative gold ore may contain in the main 96% quartz, and +4% iron pyrite, and the weight of the ore may be deduced as +follows:— +</p> + +<table class="ctrclps"> +<tr><td>Quartz,</td><td class="right">96% ×</td> + <td class="right">12.07</td><td> = </td> + <td class="right">11.58</td><td> </td></tr> +<tr><td>Iron Pyrite,</td><td class="right">4% ×</td> + <td class="right">6.40</td><td> = </td> + <td class="right_bb">.25</td><td> </td></tr> +<tr><td colspan="4"> </td><td class="right">11.83</td> + <td>cubic feet per ton.</td></tr> +</table> + +<p class="indent"> +Most engineers, to compensate porosity, would allow twelve to thirteen +cubic feet per ton. +</p> + +<h3>CLASSIFICATION OF ORE IN SIGHT.</h3> + +<p class="indent"> +The risk in estimates of the average value of standing ore is dependent +largely upon how far values disclosed by sampling are assumed to +penetrate beyond the tested face, and this depends upon the geological +character of the deposit. From theoretical grounds and experience, +it is known that such values will have some extension, and the +assumption of any given distance is a calculation of risk. The +multiplication of development openings results in an increase of +sampling points available and lessens the hazards. The frequency +of such openings varies in different portions of every mine, and +thus there are inequalities of risk. It is therefore customary in +giving estimates of standing ore to classify the ore according +to the degree of risk assumed, either by stating the number of +sides exposed or by other phrases. Much discussion and ink have +been devoted to trying to define what risk may be taken in such +matters, that is in reality how far values may be assumed to penetrate +into the unbroken ore. Still more has been consumed in attempts +to coin terms and make classifications which will indicate what +ratio of hazard has been taken in stating quantities and values. +</p> + +<p class="indent"> +The old terms "ore in sight" and "profit in sight" have been of +late years subject to much malediction on the part of engineers +because these expressions have been so badly abused by the charlatans +of mining in attempts to cover the flights of their imaginations. A +large part of Volume X of the "Institution of Mining and Metallurgy" +has been devoted to heaping infamy on <a name="page_17"><span +class="page">Page 17</span></a> these terms, yet not only have they +preserved their places in professional nomenclature, but nothing +has been found to supersede them. +</p> + +<p class="indent"> +Some general term is required in daily practice to cover the whole +field of visible ore, and if the phrase "ore in sight" be defined, +it will be easier to teach the laymen its proper use than to abolish +it. In fact, the substitutes are becoming abused as much as the +originals ever were. All convincing expressions will be misused +by somebody. +</p> + +<p class="indent"> +The legitimate direction of reform has been to divide the general +term of "ore in sight" into classes, and give them names which will +indicate the variable amount of risk of continuity in different parts +of the mine. As the frequency of sample points, and consequently the +risk of continuity, will depend upon the detail with which the mine +is cut into blocks by the development openings, and upon the number +of sides of such blocks which are accessible, most classifications +of the degree of risk of continuity have been defined in terms of +the number of sides exposed in the blocks. Many phrases have been +coined to express such classifications; those most currently used +are the following:— +</p> + +<table class="center" style="border-collapse: collapse;"> +<tr><td>Positive Ore</td> + <td rowspan="2" style="border-top: solid black 1px; + border-bottom: solid black 1px;"> </td> + <td rowspan="2" style="border-left: solid black 1px; + padding-left: 1em;">Ore exposed on four sides in blocks of + a size variously prescribed.</td></tr> +<tr><td>Ore Developed</td></tr> +<tr><td colspan="2">Ore Blocked Out</td> + <td style="padding-left: 1em;">Ore exposed on three sides + within reasonable distance of each other.</td></tr> +<tr><td>Probable Ore</td> + <td rowspan="2" style="border-top: solid black 1px; + border-bottom: solid black 1px;"> </td> + <td rowspan="2" style="border-left: solid black 1px; + padding-left: 1em;">Ore exposed on two sides.</td></tr> +<tr><td>Ore Developing</td></tr> +<tr><td colspan="3"> </tr> +<tr><td>Possible Ore</td> + <td rowspan="2" style="border-top: solid black 1px; + border-bottom: solid black 1px;"> </td> + <td rowspan="2" style="border-left: solid black 1px; + padding-left: 1em;">The whole or a part of the ore below + the lowest level or beyond the range of vision.</td></tr> +<tr><td>Ore Expectant</td></tr> +</table> + +<p class="indent"> +No two of these parallel expressions mean quite the same thing; +each more or less overlies into another class, and in fact none +of them is based upon a logical footing for such a classification. +For example, values can be assumed to penetrate some distance from +every sampled face, even if it be only ten feet, so that ore exposed +on one side will show some "positive" or "developed" ore which, +on the lines laid down above, might be <a name="page_18"><span +class="page">Page 18</span></a> "probable" or even "possible" ore. +Likewise, ore may be "fully developed" or "blocked out" so far as +it is necessary for stoping purposes with modern wide intervals +between levels, and still be in blocks too large to warrant an +assumption of continuity of values to their centers (Fig. 1). As +to the third class of "possible" ore, it conveys an impression +of tangibility to a nebulous hazard, and should never be used in +connection with positive tonnages. This part of the mine's value +comes under extension of the deposit a long distance beyond openings, +which is a speculation and cannot be defined in absolute tons without +exhaustive explanation of the risks attached, in which case any +phrase intended to shorten description is likely to be misleading. +</p> + +<table class="image" style="width: 677px;"> +<tr><td><a name="fig_01"> + <img src="images/fig_01.png" width="677" height="466" alt="Fig. 1"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> + 1.—Longitudinal section of a mine, showing classification of + the exposed ore. Scale, 400 feet = 1 inch.</td></tr> +</table> + +<p class="indent"> +Therefore empirical expressions in terms of development openings +cannot be made to cover a geologic factor such as the <a +name="page_19"><span class="page">Page 19</span></a> distribution +of metals through a rock mass. The only logical basis of ore +classification for estimation purposes is one which is founded +on the chances of the values penetrating from the surface of the +exposures for each particular mine. Ore that may be calculated +upon to a certainty is that which, taking into consideration the +character of the deposit, can be said to be so sufficiently surrounded +by sampled faces that the distance into the mass to which values +are assumed to extend is reduced to a minimum risk. Ore so far +removed from the sampled face as to leave some doubt, yet affording +great reason for expectation of continuity, is "probable" ore. +The third class of ore mentioned, which is that depending upon +extension of the deposit and in which, as said above, there is great +risk, should be treated separately as the speculative value of the +mine. Some expressions are desirable for these classifications, and +the writer's own preference is for the following, with a definition +based upon the controlling factor itself. +</p> + +<p class="indent"> +They are:— +</p> + +<table class="center"> +<tr><td class="topleft">Proved Ore</td> + <td class="forward" style="padding-left: 2em;">Ore where there + is practically no risk of failure of continuity.</td></tr> +<tr><td class="topleft">Probable Ore</td> + <td class="forward" style="padding-left: 2em;">Ore where there + is some risk, yet warrantable justification for assumption of + continuity.</td></tr> +<tr><td class="topleft">Prospective Ore</td> + <td class="forward" style="padding-left: 2em;">Ore which cannot + be included in the above classes, nor definitely known or + stated in any terms of tonnage.</td></tr> +</table> + +<p class="indent"> +What extent of openings, and therefore of sample faces, is required +for the ore to be called "proved" varies naturally with the type +of deposit,—in fact with each mine. In a general way, a fair +rule in gold quartz veins below influence of secondary alteration +is that no point in the block shall be over fifty feet from the +points sampled. In limestone or andesite replacements, as by gold +or lead or copper, the radius must be less. In defined lead and +copper lodes, or in large lenticular bodies such as the Tennessee +copper mines, the radius may often be considerably greater,—say +one hundred feet. In gold deposits of <a name="page_20"><span +class="page">Page 20</span></a> such extraordinary regularity of +values as the Witwatersrand bankets, it can well be two hundred +or two hundred and fifty feet. +</p> + +<p class="indent"> +"Probable ore" should be ore which entails continuity of values +through a greater distance than the above, and such distance must +depend upon the collateral evidence from the character of the deposit, +the position of openings, etc. +</p> + +<p class="indent"> +Ore beyond the range of the "probable" zone is dependent upon the +extension of the deposit beyond the realm of development and will +be discussed separately. +</p> + +<p class="indent"> +Although the expression "ore in sight" may be deprecated, owing to +its abuse, some general term to cover both "positive" and "probable" +ore is desirable; and where a general term is required, it is the +intention herein to hold to the phrase "ore in sight" under the +limitations specified. +</p> + +<h2><a name="page_21"><span class="page">Page 21</span></a> +CHAPTER III.</h2> + +<p class="center"> +<span class="sc">Mine Valuation</span> (<i>Continued</i>). +</p> + +<table class="summary"><tr><td class="summary"> +PROSPECTIVE VALUE.[*] EXTENSION IN DEPTH; ORIGIN AND STRUCTURAL +CHARACTER OF THE DEPOSIT; SECONDARY ENRICHMENT; DEVELOPMENT IN +NEIGHBORING MINES; DEPTH OF EXHAUSTION. +</td></tr></table> + +<p class="footnote"> +[Footnote *: The term "extension in depth" is preferred by many +to the phrase "prospective value." The former is not entirely +satisfactory, as it has a more specific than general application. +It is, however, a current miner's phrase, and is more expressive. +In this discussion "extension in depth" is used synonymously, and +it may be taken to include not alone the downward prolongation of +the ore below workings, but also the occasional cases of lateral +extension beyond the range of development work. The commonest instance +is continuance below the bottom level. In any event, to the majority +of cases of different extension the same reasoning applies.] +</p> + +<p class="indent"> +It is a knotty problem to value the extension of a deposit beyond +a short distance from the last opening. A short distance beyond +it is "proved ore," and for a further short distance is "probable +ore." Mines are very seldom priced at a sum so moderate as that +represented by the profit to be won from the ore in sight, and what +value should be assigned to this unknown portion of the deposit +admits of no certainty. No engineer can approach the prospective +value of a mine with optimism, yet the mining industry would be +non-existent to-day were it approached with pessimism. Any value +assessed must be a matter of judgment, and this judgment based on +geological evidence. Geology is not a mathematical science, and +to attach a money equivalence to forecasts based on such evidence +is the most difficult task set for the mining engineer. It is here +that his view of geology must differ from that of his financially +more irresponsible brother in the science. The geologist, contributing +to human knowledge in general, finds his most valuable field in +the examination of mines largely exhausted. The engineer's most +valuable <a name="page_22"><span class="page">Page 22</span></a> +work arises from his ability to anticipate in the youth of the +mine the symptoms of its old age. The work of our geologic friends +is, however, the very foundation on which we lay our forecasts. +</p> + +<p class="indent"> +Geologists have, as the result of long observation, propounded for +us certain hypotheses which, while still hypotheses, have proved +to account so widely for our underground experience that no engineer +can afford to lose sight of them. Although there is a lack of safety +in fixed theories as to ore deposition, and although such conclusions +cannot be translated into feet and metal value, they are nevertheless +useful weights on the scale where probabilities are to be weighed. +</p> + +<p class="indent"> +A method in vogue with many engineers is, where the bottom level +is good, to assume the value of the extension in depth as a sum +proportioned to the profit in sight, and thus evade the use of +geological evidence. The addition of various percentages to the +profit in sight has been used by engineers, and proposed in technical +publications, as varying from 25 to 50%. That is, they roughly +assess the extension in depth to be worth one-fifth to one-third +of the whole value of an equipped mine. While experience may have +sometimes demonstrated this to be a practical method, it certainly +has little foundation in either science or logic, and the writer's +experience is that such estimates are untrue in practice. The quantity +of ore which may be in sight is largely the result of managerial +policy. A small mill on a large mine, under rapid development, +will result in extensive ore-reserves, while a large mill eating +away rapidly on the same mine under the same scale of development +would leave small reserves. On the above scheme of valuation the +extension in depth would be worth very different sums, even when the +deepest level might be at the same horizon in both cases. Moreover, +no mine starts at the surface with a large amount of ore in sight. +Yet as a general rule this is the period when its extension is +most valuable, for when the deposit is exhausted to 2000 feet, it +is not likely to have such extension in depth as when opened one +hundred feet, no matter what the ore-reserves may be. Further, such +bases of valuation fail to take into account <a name="page_23"><span +class="page">Page 23</span></a> the widely varying geologic character +of different mines, and they disregard any collateral evidence either +of continuity from neighboring development, or from experience +in the district. Logically, the prospective value can be simply a +factor of how <i>far</i> the ore in the individual mine may be +expected to extend, and not a factor of the remnant of ore that +may still be unworked above the lowest level. +</p> + +<p class="indent"> +An estimation of the chances of this extension should be based +solely on the local factors which bear on such extension, and these +are almost wholly dependent upon the character of the deposit. +These various geological factors from a mining engineer's point +of view are:— +</p> + +<ol> +<li>The origin and structural character of the ore-deposit.</li> +<li>The position of openings in relation to secondary alteration.</li> +<li>The size of the deposit.</li> +<li>The depth to which the mine has already been exhausted.</li> +<li>The general experience of the district for continuity and the + development of adjoining mines.</li> +</ol> + +<p class="indent"> +<b>The Origin and Structural Character of the Deposit.</b>—In a +general way, the ore-deposits of the order under discussion originate +primarily through the deposition of metals from gases or solutions +circulating along avenues in the earth's crust.[*] The original +source of metals is a matter of great disagreement, and does not +much concern the miner. To him, however, the origin and character +of the avenue of circulation, the enclosing rock, the influence +of the rocks on the solution, and of the solutions on the rocks, +have a great bearing on the probable continuity of the volume and +value of the ore. +</p> + +<p class="footnote"> +[Footnote *: The class of magmatic segregations is omitted, as +not being of sufficiently frequent occurrence in payable mines to +warrant troubling with it here.] +</p> + +<p class="indent"> +All ore-deposits vary in value and, in the miner's view, only those +portions above the pay limit are ore-bodies, or ore-shoots. The +localization of values into such pay areas in an ore-deposit are +apparently influenced by: +</p> + +<ol> +<li>The distribution of the open spaces created by structural + movement, fissuring, or folding as at Bendigo. +<a name="page_24"><span class="page">Page 24</span></a></li> +<li>The intersection of other fractures which, by mingling of + solutions from different sources, provided precipitating + conditions, as shown by enrichments at cross-veins.</li> +<li>The influence of the enclosing rocks by:— + <ol style="list-style-type: lower-alpha;"> + <li>Their solubility, and therefore susceptibility to + replacement.</li> + <li>Their influence as a precipitating agent on solutions.</li> + <li>Their influence as a source of metal itself.</li> + <li>Their texture, in its influence on the character of + the fracture. In homogeneous rocks the tendency + is to open clean-cut fissures; in friable + rocks, zones of brecciation; in slates or schistose + rocks, linked lenticular open spaces;—these + influences exhibiting themselves in miner's terms + respectively in "well-defined fissure veins," + "lodes," and "lenses."</li> + <li>The physical character of the rock mass and the + dynamic forces brought to bear upon it. This + is a difficult study into the physics of stress in + cases of fracturing, but its local application has + not been without results of an important order.</li> + </ol></li> +<li>Secondary alteration near the surface, more fully discussed + later.</li> +</ol> + +<p class="indent"> +It is evident enough that the whole structure of the deposit is +a necessary study, and even a digest of the subject is not to be +compressed into a few paragraphs. +</p> + +<p class="indent"> +From the point of view of continuity of values, ore-deposits may +be roughly divided into three classes. They are:— +</p> + +<ol> +<li>Deposits of the infiltration type in porous beds, such as + Lake Superior copper conglomerates and African gold bankets.</li> +<li>Deposits of the fissure vein type, such as California quartz + veins.</li> +<li>Replacement or impregnation deposits on the lines of fissuring + or otherwise.</li> +</ol> + +<p class="indent"> +<a name="page_25"><span class="page">Page 25</span></a> In a general +way, the uniformity of conditions of deposition in the first class +has resulted in the most satisfactory continuity of ore and of its +metal contents. In the second, depending much upon the profundity +of the earth movements involved, there is laterally and vertically +a reasonable basis for expectation of continuity but through much +less distance than in the first class. +</p> + +<p class="indent"> +The third class of deposits exhibits widely different phenomena +as to continuity and no generalization is of any value. In gold +deposits of this type in West Australia, Colorado, and Nevada, +continuity far beyond a sampled face must be received with the +greatest skepticism. Much the same may be said of most copper +replacements in limestone. On the other hand the most phenomenal +regularity of values have been shown in certain Utah and Arizona +copper mines, the result of secondary infiltration in porphyritic +gangues. The Mississippi Valley lead and zinc deposits, while irregular +in detail, show remarkable continuity by way of reoccurrence over +wide areas. The estimation of the prospective value of mines where +continuity of production is dependent on reoccurrence of ore-bodies +somewhat proportional to the area, such as these Mississippi deposits +or to some extent as in Cobalt silver veins, is an interesting +study, but one that offers little field for generalization. +</p> + +<p class="indent"> +<b>The Position of the Openings in Relation to Secondary +Alteration.</b>—The profound alteration of the upper section +of ore-deposits by oxidation due to the action of descending surface +waters, and their associated chemical agencies, has been generally +recognized for a great many years. Only recently, however, has it +been appreciated that this secondary alteration extends into the +sulphide zone as well. The bearing of the secondary alteration, both +in the oxidized and upper sulphide zones, is of the most sweeping +economic character. In considering extension of values in depth, +it demands the most rigorous investigation. Not only does the +metallurgical character of the ores change with oxidation, but the +complex reactions due to descending surface waters cause leaching +and a migration of metals from one horizon to another lower down, and +also in many <a name="page_26"><span class="page">Page 26</span></a> +cases a redistribution of their sequence in the upper zones of the +deposit. +</p> + +<p class="indent"> +The effect of these agencies has been so great in many cases as +to entirely alter the character of the mine and extension in depth +has necessitated a complete reëquipment. For instance, the +Mt. Morgan gold mine, Queensland, has now become a copper mine; +the copper mines at Butte were formerly silver mines; Leadville +has become largely a zinc producer instead of lead. +</p> + +<p class="indent"> +From this alteration aspect ore-deposits may be considered to have +four horizons:— +</p> + +<ol> +<li>The zone near the outcrop, where the dominating feature + is oxidation and leaching of the soluble minerals.</li> +<li>A lower horizon, still in the zone of oxidation, where the + predominant feature is the deposition of metals as native, + oxides, and carbonates.</li> +<li>The upper horizon of the sulphide zone, where the special + feature is the enrichment due to secondary deposition + as sulphides.</li> +<li>The region below these zones of secondary alteration, where + the deposit is in its primary state.</li> +</ol> + +<p class="indent"> +These zones are seldom sharply defined, nor are they always all +in evidence. How far they are in evidence will depend, among other +things, upon the amount and rapidity of erosion, the structure and +mineralogical character of the deposit, and upon the enclosing +rock. +</p> + +<p class="indent"> +If erosion is extremely rapid, as in cold, wet climates, and rough +topography, or as in the case of glaciation of the Lake copper +deposits, denudation follows close on the heels of alteration, +and the surface is so rapidly removed that we may have the primary +ore practically at the surface. Flat, arid regions present the +other extreme, for denudation is much slower, and conditions are +most perfect for deep penetration of oxidizing agencies, and the +consequent alteration and concentration of the metals. +</p> + +<p class="indent"> +The migration of metals from the top of the oxidized zone <a +name="page_27"><span class="page">Page 27</span></a> leaves but a +barren cap for erosion. The consequent effect of denudation that +lags behind alteration is to raise slowly the concentrated metals +toward the surface, and thus subject them to renewed attack and +repeated migration. In this manner we can account for the enormous +concentration of values in the lower oxidized and upper sulphide +zones overlying very lean sulphides in depth. +</p> + +<p class="indent"> +Some minerals are more freely soluble and more readily precipitated +than others. From this cause there is in complex metal deposits a +rearrangement of horizontal sequence, in addition to enrichment at +certain horizons and impoverishment at others. The whole subject +is one of too great complexity for adequate consideration in this +discussion. No engineer is properly equipped to give judgment on +extension in depth without a thorough grasp of the great principles +laid down by Van Hise, Emmons, Lindgren, Weed, and others. We may, +however, briefly examine some of the theoretical effects of such +alteration. +</p> + +<p class="indent"> +Zinc, iron, and lead sulphides are a common primary combination. +These metals are rendered soluble from their usual primary forms +by oxidizing agencies, in the order given. They reprecipitate as +sulphides in the reverse sequence. The result is the leaching of +zinc and iron readily in the oxidized zone, thus differentially +enriching the lead which lags behind, and a further extension of +the lead horizon is provided by the early precipitation of such +lead as does migrate. Therefore, the lead often predominates in +the second and the upper portion of the third zone, with the zinc +and iron below. Although the action of all surface waters is toward +oxidation and carbonation of these metals, the carbonate development +of oxidized zones is more marked when the enclosing rocks are +calcareous. +</p> + +<p class="indent"> +In copper-iron deposits, the comparatively easy decomposition and +solubility and precipitation of the copper and some iron salts +generally result in more extensive impoverishment of these metals +near the surface, and more predominant enrichment at a lower horizon +than is the case with any other metals. The barren "iron hat" at +the first zone, the carbonates and oxides <a name="page_28"><span +class="page">Page 28</span></a> at the second, the enrichment with +secondary copper sulphides at the top of the third, and the occurrence +of secondary copper-iron sulphides below, are often most clearly +defined. In the easy recognition of the secondary copper sulphides, +chalcocite, bornite, etc., the engineer finds a finger-post on +the road to extension in depth; and the directions upon this post +are not to be disregarded. The number of copper deposits enriched +from unpayability in the first zone to a profitable character in +the next two, and unpayability again in the fourth, is legion. +</p> + +<p class="indent"> +Silver occurs most abundantly in combination with either lead, +copper, iron, or gold. As it resists oxidation and solution more +strenuously than copper and iron, its tendency when in combination +with them is to lag behind in migration. There is thus a differential +enrichment of silver in the upper two zones, due to the reduction +in specific gravity of the ore by the removal of associated metals. +Silver does migrate somewhat, however, and as it precipitates more +readily than copper, lead, zinc, or iron, its tendency when in +combination with them is towards enrichment above the horizons of +enrichment of these metals. When it is in combination with lead +and zinc, its very ready precipitation from solution by the galena +leaves it in combination more predominantly with the lead. The +secondary enrichment of silver deposits at the top of the sulphide +zone is sometimes a most pronounced feature, and it seems to be +the explanation of the origin of many "bonanzas." +</p> + +<p class="indent"> +In gold deposits, the greater resistance to solubility of this +metal than most of the others, renders the phenomena of migration to +depth less marked. Further than this, migration is often interfered +with by the more impervious quartz matrix of many gold deposits. +Where gold is associated with large quantities of base metals, +however, the leaching of the latter in the oxidized zone leaves the +ore differentially richer, and as gold is also slightly soluble, +in such cases the migration of the base metals does carry some of +the gold. In the instance especially of impregnation or replacement +deposits, where the matrix is easily permeable, the upper sulphide +zone is distinctly richer than lower down, and this enrichment is <a +name="page_29"><span class="page">Page 29</span></a> accompanied by +a considerable increase in sulphides and tellurides. The predominant +characteristic of alteration in gold deposits is, however, enrichment +in the oxidized zone with the maximum values near the surface. +The reasons for this appear to be that gold in its resistance to +oxidation and wholesale migration gives opportunities to a sort +of combined mechanical and chemical enrichment. +</p> + +<p class="indent"> +In dry climates, especially, the gentleness of erosion allows of +more thorough decomposition of the outcroppings, and a mechanical +separation of the gold from the detritus. It remains on or near +the deposit, ready to be carried below, mechanically or otherwise. +In wet climates this is less pronounced, for erosion bears away +the croppings before such an extensive decomposition and freeing +of the gold particles. The West Australian gold fields present an +especially prominent example of this type of superficial enrichment. +During the last fifteen years nearly eight hundred companies have +been formed for working mines in this region. Although from four +hundred of these high-grade ore has been produced, some thirty-three +only have ever paid dividends. The great majority have been unpayable +below oxidation,—a distance of one or two hundred feet. The +writer's unvarying experience with gold is that it is richer in +the oxidized zone than at any point below. While cases do occur of +gold deposits richer in the upper sulphide zone than below, even +the upper sulphides are usually poorer than the oxidized region. +In quartz veins preëminently, evidence of enrichment in the +third zone is likely to be practically absent. +</p> + +<p class="indent"> +Tin ores present an anomaly among the base metals under discussion, +in that the primary form of this metal in most workable deposits +is an oxide. Tin in this form is most difficult of solution from +ground agencies, as witness the great alluvial deposits, often of +considerable geologic age. In consequence the phenomena of migration +and enrichment are almost wholly absent, except such as are due +to mechanical penetration of tin from surface decomposition of +the matrix akin to that described in gold deposits. +</p> + +<p class="indent"> +<a name="page_30"><span class="page">Page 30</span></a> In general, +three or four essential facts from secondary alteration must be +kept in view when prognosticating extensions. +</p> + +<p class="bindent"> +Oxidation usually alters treatment problems, and oxidized ore +of the same grade as sulphides can often be treated more cheaply. +This is not universal. Low-grade ores of lead, copper, and zinc +may be treatable by concentration when in the form of sulphides, +and may be valueless when oxidized, even though of the same grade. +</p> + +<p class="bindent"> +Copper ores generally show violent enrichment at the base of the +oxidized, and at the top of the sulphide zone. +</p> + +<p class="bindent"> +Lead-zinc ores show lead enrichment and zinc impoverishment in +the oxidized zone but have usually less pronounced enrichment +below water level than copper. The rearrangement of the metals +by the deeper migration of the zinc, also renders them +metallurgically of less value with depth. +</p> + +<p class="bindent"> +Silver deposits are often differentially enriched in the oxidized +zone, and at times tend to concentrate in the upper sulphide zone. +</p> + +<p class="bindent"> +Gold deposits usually decrease in value from the surface through +the whole of the three alteration zones. +</p> + +<p class="indent"> +<b>Size of Deposits.</b>—The proverb of a relation between +extension in depth and size of ore-bodies expresses one of the oldest +of miners' beliefs. It has some basis in experience, especially in +fissure veins, but has little foundation in theory and is applicable +over but limited areas and under limited conditions. +</p> + +<p class="indent"> +From a structural view, the depth of fissuring is likely to be more +or less in proportion to its length and breadth and therefore the +volume of vein filling with depth is likely to be proportional to +length and width of the fissure. As to the distribution of values, +if we eliminate the influence of changing <a name="page_31"><span +class="page">Page 31</span></a> wall rocks, or other precipitating +agencies which often cause the values to arrange themselves in +"floors," and of secondary alteration, there may be some reason +to assume distribution of values of an extent equal vertically +to that displayed horizontally. There is, as said, more reason in +experience for this assumption than in theory. A study of the shape +of a great many ore-shoots in mines of fissure type indicates that +when the ore-shoots or ore-bodies are approaching vertical exhaustion +they do not end abruptly, but gradually shorten and decrease in +value, their bottom boundaries being more often wedge-shaped than +even lenticular. If this could be taken as the usual occurrence, +it would be possible (eliminating the evident exceptions mentioned +above) to state roughly that the minimum extension of an ore-body +or ore-shoot in depth below any given horizon would be a distance +represented by a radius equal to one-half its length. By length +is not meant necessarily the length of a horizontal section, but +of one at right angles to the downward axis. +</p> + +<p class="indent"> +On these grounds, which have been reënforced by much experience +among miners, the probabilities of extension are somewhat in proportion +to the length and width of each ore-body. For instance, in the A +mine, with an ore-shoot 1000 feet long and 10 feet wide, on its +bottom level, the minimum extension under this hypothesis would +be a wedge-shaped ore-body with its deepest point 500 feet below +the lowest level, or a minimum of say 200,000 tons. Similarly, +the B mine with five ore-bodies, each 300 hundred feet long and +10 feet wide, exposed on its lowest level, would have a minimum of +five wedges 100 feet deep at their deepest points, or say 50,000 +tons. This is not proposed as a formula giving the total amount of +extension in depth, but as a sort of yardstick which has experience +behind it. This experience applies in a much less degree to deposits +originating from impregnation along lines of fissuring and not at +all to replacements. +</p> + +<p class="indent"> +<b>Development in Neighboring Mines.</b>—Mines of a district +are usually found under the same geological conditions, and show +somewhat the same habits as to extension in depth or laterally, +and especially similar conduct of ore-bodies and ore-shoots. <a +name="page_32"><span class="page">Page 32</span></a> As a practical +criterion, one of the most intimate guides is the actual development +in adjoining mines. For instance, in Kalgoorlie, the Great Boulder +mine is (March, 1908) working the extension of Ivanhoe lodes at +points 500 feet below the lowest level in the Ivanhoe; likewise, the +Block 10 lead mine at Broken Hill is working the Central ore-body +on the Central boundary some 350 feet below the Central workings. +Such facts as these must have a bearing on assessing the downward +extension. +</p> + +<p class="indent"> +<b>Depth of Exhaustion.</b>—All mines become completely exhausted +at some point in depth. Therefore the actual distance to which ore +can be expected to extend below the lowest level grows less with +every deeper working horizon. The really superficial character of +ore-deposits, even outside of the region of secondary enrichment +is becoming every year better recognized. The prospector's idea +that "she gets richer deeper down," may have some basis near the +surface in some metals, but it is not an idea which prevails in +the minds of engineers who have to work in depth. The writer, with +some others, prepared a list of several hundred dividend-paying +metal mines of all sorts, extending over North and South America, +Australasia, England, and Africa. Notes were made as far as possible +of the depths at which values gave out, and also at which dividends +ceased. Although by no means a complete census, the list indicated +that not 6% of mines (outside banket) that have yielded profits, +ever made them from ore won below 2000 feet. Of mines that paid +dividends, 80% did not show profitable value below 1500 feet, and +a sad majority died above 500. Failures at short depths may be +blamed upon secondary enrichment, but the majority that reached +below this influence also gave out. The geological reason for such +general unseemly conduct is not so evident. +</p> + +<p class="indent"> +<b>Conclusion.</b>—As a practical problem, the assessment of +prospective value is usually a case of "cut and try." The portion +of the capital to be invested, which depends upon extension, will +require so many tons of ore of the same value as that indicated by the +standing ore, in order to justify the price. <a name="page_33"><span +class="page">Page 33</span></a> To produce this tonnage at the +continued average size of the ore-bodies will require their extension +in depth so many feet—or the discovery of new ore-bodies of +a certain size. The five geological weights mentioned above may +then be put into the scale and a basis of judgment reached. +</p> + +<h2><a name="page_34"><span class="page">Page 34</span></a> +CHAPTER IV.</h2> + +<p class="center"> +<span class="sc">Mine Valuation</span> (<i>Continued</i>). +</p> + +<table class="summary"><tr><td class="summary"> +RECOVERABLE PERCENTAGE OF THE GROSS ASSAY VALUE; PRICE OF METALS; +COST OF PRODUCTION. +</td></tr></table> + +<p class="indent"> +The method of treatment for the ore must be known before a mine +can be valued, because a knowledge of the recoverable percentage +is as important as that of the gross value of the ore itself. The +recoverable percentage is usually a factor of working costs. Practically +every ore can be treated and all the metal contents recovered, but +the real problem is to know the method and percentage of recovery +which will yield the most remunerative result, if any. This limit to +profitable recovery regulates the amount of metal which should be +lost, and the amount of metal which consequently must be deducted +from the gross value before the real net value of the ore can be +calculated. Here, as everywhere else in mining, a compromise has to +be made with nature, and we take what we can get—profitably. +For instance, a copper ore may be smelted and a 99% recovery obtained. +Under certain conditions this might be done at a loss, while the +same ore might be concentrated before smelting and yield a profit +with a 70% recovery. An additional 20% might be obtained by roasting +and leaching the residues from concentration, but this would probably +result in an expenditure far greater than the value of the 20% +recovered. If the ore is not already under treatment on the mine, +or exactly similar ore is not under treatment elsewhere, with known +results, the method must be determined experimentally, either by +the examining engineer or by a special metallurgist. +</p> + +<p class="indent"> +Where partially treated products, such as concentrates, are to be +sold, not only will there be further losses, but <a name="page_35"><span +class="page">Page 35</span></a> deductions will be made by the +smelter for deleterious metals and other charges. All of these +factors must be found out,—and a few sample smelting returns +from a similar ore are useful. +</p> + +<p class="indent"> +To cover the whole field of metallurgy and discuss what might apply, +and how it might apply, under a hundred supposititious conditions +would be too great a digression from the subject in hand. It is +enough to call attention here to the fact that the residues from +every treatment carry some metal, and that this loss has to be +deducted from the gross value of the ore in any calculations of +net values. +</p> + +<h3>PRICE OF METALS.</h3> + +<p class="indent"> +Unfortunately for the mining engineer, not only has he to weigh +the amount of risk inherent in calculations involved in the mine +itself, but also that due to fluctuations in the value of metals. +If the ore is shipped to custom works, he has to contemplate also +variations in freights and smelting charges. Gold from the mine +valuer's point of view has no fluctuations. It alone among the +earth's products gives no concern as to the market price. The price +to be taken for all other metals has to be decided before the mine +can be valued. This introduces a further speculation and, as in +all calculations of probabilities, amounts to an estimate of the +amount of risk. In a free market the law of supply and demand governs +the value of metals as it does that of all other commodities. So +far, except for tariff walls and smelting rings, there is a free +market in the metals under discussion. +</p> + +<p class="indent"> +The demand for metals varies with the unequal fluctuations of the +industrial tides. The sea of commercial activity is subject to +heavy storms, and the mine valuer is compelled to serve as weather +prophet on this ocean of trouble. High prices, which are the result +of industrial booms, bring about overproduction, and the collapse of +these begets a shrinkage of demand, wherein consequently the tide +of price turns back. In mining for metals each pound is produced +actually at a different cost. In case of an oversupply of base metals +the price will fall until it has reached <a name="page_36"><span +class="page">Page 36</span></a> a point where a portion of the +production is no longer profitable, and the equilibrium is established +through decline in output. However, in the backward swing, due +to lingering overproduction, prices usually fall lower than the +cost of producing even a much-diminished supply. There is at this +point what we may call the "basic" price, that at which production +is insufficient and the price rises again. The basic price which +is due to this undue backward swing is no more the real price of +the metal to be contemplated over so long a term of years than is +the highest price. At how much above the basic price of depressed +times the product can be safely expected to find a market is the +real question. Few mines can be bought or valued at this basic +price. An indication of what this is can be gained from a study +of fluctuations over a long term of years. +</p> + +<p class="indent"> +It is common to hear the average price over an extended period +considered the "normal" price, but this basis for value is one which +must be used with discretion, for it is not the whole question when +mining. The "normal" price is the average price over a long term. +The lives of mines, and especially ore in sight, may not necessarily +enjoy the period of this "normal" price. The engineer must balance +his judgments by the immediate outlook of the industrial weather. +When lead was falling steadily in December, 1907, no engineer would +accept the price of that date, although it was then below "normal"; +his product might go to market even lower yet. +</p> + +<p class="indent"> +It is desirable to ascertain what the basic and normal prices are, +for between them lies safety. Since 1884 there have been three cycles +of commercial expansion and contraction. If the average prices +are taken for these three cycles separately (1885-95), 1895-1902, +1902-08) it will be seen that there has been a steady advance in +prices. For the succeeding cycles lead on the London Exchange,[*] +the freest of the world's <a name="page_37"><span class="page">Page +37</span></a> markets was £12 12<i>s.</i> 4<i>d.</i>, £13 +3<i>s.</i> 7<i>d.</i>, and £17 7<i>s.</i> 0<i>d.</i> respectively; +zinc, £17 14<i>s.</i> 10<i>d.</i>, £19 3<i>s.</i> +8<i>d.</i>, and £23 3<i>s.</i> 0<i>d.</i>; and standard copper, +£48 16<i>s.</i> 0<i>d.</i>, £59 10<i>s.</i> 0<i>d.</i>, +and £65 7<i>s.</i> 0<i>d.</i> It seems, therefore, that a +higher standard of prices can be assumed as the basic and normal +than would be indicated if the general average of, say, twenty +years were taken. During this period, the world's gold output has +nearly quadrupled, and, whether the quantitative theory of gold be +accepted or not, it cannot be denied that there has been a steady +increase in the price of commodities. In all base-metal mining it +is well to remember that the production of these metals is liable +to great stimulus at times from the discovery of new deposits or +new processes of recovery from hitherto unprofitable ores. It is +therefore for this reason hazardous in the extreme to prophesy +what prices will be far in the future, even when the industrial +weather is clear. But some basis must be arrived at, and from the +available outlook it would seem that the following metal prices +are justifiable for some time to come, provided the present tariff +schedules are maintained in the United States: +</p> + +<p class="footnote"> +[Footnote *: All London prices are based on the long ton of 2,240 +lbs. Much confusion exists in the copper trade as to the classification +of the metal. New York prices are quoted in electrolytic and "Lake"; +London's in "Standard." "Standard" has now become practically an +arbitrary term peculiar to London, for the great bulk of copper +dealt in is "electrolytic" valued considerably over "Standard."] +</p> + +<table class="ctrclps" style="margin-top: 1em; margin-bottom: 1em;"> +<tr><th rowspan="2" class="center_btrb"> </th> + <th colspan="2" class="center_btrb"><span class="sc">Lead + </span></th> + <th colspan="2" class="center_btrb"><span class="sc">Spelter + </span></th> + <th colspan="2" class="center_btrb"><span class="sc">Copper + </span></th> + <th colspan="2"class="center_btrb"><span class="sc">Tin + </span></th> + <th colspan="2"class="center_btb"><span class="sc">Silver + </span></th></tr> +<tr><th class="center_btrb">London Ton</th> + <th class="center_btrb">N.Y. Pound</th> + <th class="center_btrb">Lon. Ton</th> + <th class="center_btrb">N.Y. Pound</th> + <th class="center_btrb">Lon. Ton</th> + <th class="center_btrb">N.Y. Pound</th> + <th class="center_btrb">Lon. Ton</th> + <th class="center_btrb">N.Y. Pound</th> + <th class="center_btrb">Lon. Per oz.</th> + <th class="center_btb">N.Y. Per oz.</th></tr> +<tr><td class="left_br">Basic Price</td> + <td class="center_br">£11.</td> + <td class="center_br">$.035</td> + <td class="center_br">£17</td> + <td class="center_br">$.040</td> + <td class="center_br">£52</td> + <td class="center_br">$.115</td> + <td class="center_br">£100</td> + <td class="center_br">$.220</td> + <td class="center_br">22<i>d.</i></td> + <td class="center">$.44</td></tr> +<tr><td class="left_brb">Normal Price</td> + <td class="center_brb">13.5</td> + <td class="center_brb">.043</td> + <td class="center_brb">21</td> + <td class="center_brb">.050</td> + <td class="center_brb">65</td> + <td class="center_brb">.140</td> + <td class="center_brb">130</td> + <td class="center_brb">.290</td> + <td class="center_brb">26</td> + <td class="center_bb">.52</td></tr> +</table> + +<p class="indent"> +In these figures the writer has not followed strict averages, but +has taken the general outlook combined with the previous records. +The likelihood of higher prices for lead is more encouraging than +for any other metal, as no new deposits of importance have come +forward for years, and the old mines are reaching considerable +depths. Nor does the frenzied prospecting of the world's surface +during the past ten years appear to forecast any very disturbing +developments. The zinc future is not so bright, for metallurgy has +done wonders <a name="page_38"><span class="page">Page 38</span></a> +in providing methods of saving the zinc formerly discarded from lead +ores, and enormous supplies will come forward when required. The +tin outlook is encouraging, for the supply from a mining point of +view seems unlikely to more than keep pace with the world's needs. +In copper the demand is growing prodigiously, but the supplies +of copper ores and the number of copper mines that are ready to +produce whenever normal prices recur was never so great as to-day. +One very hopeful fact can be deduced for the comfort of the base +metal mining industry as a whole. If the growth of demand continues +through the next thirty years in the ratio of the past three decades, +the annual demand for copper will be over 3,000,000 tons, of lead +over 1,800,000 tons, of spelter 2,800,000 tons, of tin 250,000 +tons. Where such stupendous amounts of these metals are to come +from at the present range of prices, and even with reduced costs +of production, is far beyond any apparent source of supply. The +outlook for silver prices is in the long run not bright. As the major +portion of the silver produced is a bye product from base metals, any +increase in the latter will increase the silver production despite +very much lower prices for the precious metal. In the meantime the +gradual conversion of all nations to the gold standard seems a +matter of certainty. Further, silver may yet be abandoned as a +subsidiary coinage inasmuch as it has now but a token value in +gold standard countries if denuded of sentiment. +</p> + +<h3>COST OF PRODUCTION.</h3> + +<p class="indent"> +It is hardly necessary to argue the relative importance of the +determination of the cost of production and the determination of +the recoverable contents of the ore. Obviously, the aim of mine +valuation is to know the profits to be won, and the profit is the +value of the metal won, less the cost of production. +</p> + +<p class="indent"> +The cost of production embraces development, mining, treatment, +management. Further than this, it is often contended that, as the +capital expended in purchase and <a name="page_39"><span +class="page">Page 39</span></a> equipment must be redeemed within +the life of the mine, this item should also be included in production +costs. It is true that mills, smelters, shafts, and all the +paraphernalia of a mine are of virtually negligible value when it +is exhausted; and that all mines are exhausted sometime and every +ton taken out contributes to that exhaustion; and that every ton of +ore must bear its contribution to the return of the investment, +as well as profit upon it. Therefore it may well be said that the +redemption of the capital and its interest should be considered +in costs per ton. The difficulty in dealing with the subject from +the point of view of production cost arises from the fact that, +except possibly in the case of banket gold and some conglomerate +copper mines, the life of a metal mine is unknown beyond the time +required to exhaust the ore reserves. The visible life at the time +of purchase or equipment may be only three or four years, yet the +average equipment has a longer life than this, and the anticipation +for every mine is also for longer duration than the bare ore in sight. +For clarity of conclusions in mine valuation the most advisable +course is to determine the profit in sight irrespective of capital +redemption in the first instance. The questions of capital redemption, +purchase price, or equipment cost can then be weighed against the +margin of profit. One phase of redemption will be further discussed +under "Amortization of Capital" and "Ratio of Output to the Mine." +</p> + +<p class="indent"> +The cost of production depends upon many things, such as the cost of +labor, supplies, the size of the ore-body, the treatment necessary, +the volume of output, etc.; and to discuss them all would lead +into a wilderness of supposititious cases. If the mine is a going +concern, from which reliable data can be obtained, the problem is +much simplified. If it is virgin, the experience of other mines +in the same region is the next resource; where no such data can be +had, the engineer must fall back upon the experience with mines +still farther afield. Use is sometimes made of the "comparison ton" +in calculating costs upon mines where data of actual experience +are not available. As costs will depend in the main upon items +mentioned above, if the <a name="page_40"><span class="page">Page +40</span></a> known costs of a going mine elsewhere be taken as a +basis, and subtractions and additions made for more unfavorable or +favorable effect of the differences in the above items, a fairly +close result can be approximated. +</p> + +<p class="indent"> +Mine examinations are very often inspired by the belief that extended +operations or new metallurgical applications to the mine will expand +the profits. In such cases the paramount questions are the reduction +of costs by better plant, larger outputs, new processes, or alteration +of metallurgical basis and better methods. If every item of previous +expenditure be gone over and considered, together with the equipment, +and method by which it was obtained, the possible savings can be +fairly well deduced, and justification for any particular line +of action determined. One view of this subject will be further +discussed under "Ratio of Output to the Mine." The conditions which +govern the working costs are on every mine so special to itself, +that no amount of advice is very useful. Volumes of advice have +been published on the subject, but in the main their burden is +not to underestimate. +</p> + +<p class="indent"> +In considering the working costs of base-metal mines, much depends +upon the opportunity for treatment in customs works, smelters, +etc. Such treatment means a saving of a large portion of equipment +cost, and therefore of the capital to be invested and subsequently +recovered. The economics of home treatment must be weighed against +the sum which would need to be set aside for redemption of the +plant, and unless there is a very distinct advantage to be had by +the former, no risks should be taken. More engineers go wrong by +the erection of treatment works where other treatment facilities +are available, than do so by continued shipping. There are many +mines where the cost of equipment could never be returned, and +which would be valueless unless the ore could be shipped. Another +phase of foreign treatment arises from the necessity or advantage +of a mixture of ores,—the opportunity of such mixtures often +gives the public smelter an advantage in treatment with which treatment +on the mine could never compete. +</p> + +<p class="indent"> +Fluctuation in the price of base metals is a factor so much to +<a name="page_41"><span class="page">Page 41</span></a> be taken +into consideration, that it is desirable in estimating mine values +to reduce the working costs to a basis of a "per unit" of finished +metal. This method has the great advantage of indicating so simply +the involved risks of changing prices that whoso runs may read. +Where one metal predominates over the other to such an extent as +to form the "backbone" of the value of the mine, the value of the +subsidiary metals is often deducted from the cost of the principal +metal, in order to indicate more plainly the varying value of the +mine with the fluctuating prices of the predominant metal. For +example, it is usual to state that the cost of copper production +from a given ore will be so many cents per pound, or so many pounds +sterling per ton. Knowing the total metal extractable from the +ore in sight, the profits at given prices of metal can be readily +deduced. The point at which such calculation departs from the +"per-ton-of-ore" unto the per-unit-cost-of-metal basis, usually +lies at the point in ore dressing where it is ready for the smelter. +To take a simple case of a lead ore averaging 20%: this is to be +first concentrated and the lead reduced to a concentrate averaging +70% and showing a recovery of 75% of the total metal content. The +cost per ton of development, mining, concentration, management, is +to this point say $4 per ton of original crude ore. The smelter +buys the concentrate for 95% of the value of the metal, less the +smelting charge of $15 per ton, or there is a working cost of a +similar sum by home equipment. In this case 4.66 tons of ore are +required to produce one ton of concentrates, and therefore each ton +of concentrates costs $18.64. This amount, added to the smelting +charge, gives a total of $33.64 for the creation of 70% of one ton +of finished lead, or equal to 2.40 cents per pound which can be +compared with the market price less 5%. If the ore were to contain +20 ounces of silver per ton, of which 15 ounces were recovered +into the leady concentrates, and the smelter price for the silver +were 50 cents per ounce, then the $7.50 thus recovered would be +subtracted from $33.64, making the apparent cost of the lead 1.86 +cents per pound. +</p> + +<h2><a name="page_42"><span class="page">Page 42</span></a> +CHAPTER V.</h2> + +<p class="center"> +<span class="sc">Mine Valuation</span> (<i>Continued</i>). +</p> + +<table class="summary"><tr><td class="summary"> +REDEMPTION OR AMORTIZATION OF CAPITAL AND INTEREST. +</td></tr></table> + +<p class="indent"> +It is desirable to state in some detail the theory of amortization +before consideration of its application in mine valuation. +</p> + +<p class="indent"> +As every mine has a limited life, the capital invested in it must +be redeemed during the life of the mine. It is not sufficient that +there be a bare profit over working costs. In this particular, +mines differ wholly from many other types of investment, such as +railways. In the latter, if proper appropriation is made for +maintenance, the total income to the investor can be considered as +interest or profit; but in mines, a portion of the annual income +must be considered as a return of capital. Therefore, before the +yield on a mine investment can be determined, a portion of the +annual earnings must be set aside in such a manner that when the +mine is exhausted the original investment will have been restored. +If we consider the date due for the return of the capital as the time +when the mine is exhausted, we may consider the annual instalments +as payments before the due date, and they can be put out at compound +interest until the time for restoration arrives. If they be invested +in safe securities at the usual rate of about 4%, the addition of +this amount of compound interest will assist in the repayment of +the capital at the due date, so that the annual contributions to +a sinking fund need not themselves aggregate the total capital to +be restored, but may be smaller by the deficiency which will be +made up by their interest earnings. Such a system of redemption +of capital is called "Amortization." +</p> + +<p class="indent"> +Obviously it is not sufficient for the mine investor that his capital +shall have been restored, but there is required an excess earning +over and above the necessities of this annual funding of <a +name="page_43"><span class="page">Page 43</span></a> capital. What +rate of excess return the mine must yield is a matter of the risks +in the venture and the demands of the investor. Mining business +is one where 7% above provision for capital return is an absolute +minimum demanded by the risks inherent in mines, even where the +profit in sight gives warranty to the return of capital. Where the +profit in sight (which is the only real guarantee in mine investment) +is below the price of the investment, the annual return should +increase in proportion. There are thus two distinct directions in +which interest must be computed,—first, the internal influence +of interest in the amortization of the capital, and second, the +percentage return upon the whole investment after providing for +capital return. +</p> + +<p class="indent"> +There are many limitations to the introduction of such refinements +as interest calculations in mine valuation. It is a subject not +easy to discuss with finality, for not only is the term of years +unknown, but, of more importance, there are many factors of a highly +speculative order to be considered in valuing. It may be said that +a certain life is known in any case from the profit in sight, and +that in calculating this profit a deduction should be made from +the gross profit for loss of interest on it pending recovery. This +is true, but as mines are seldom dealt with on the basis of profit +in sight alone, and as the purchase price includes usually some +proportion for extension in depth, an unknown factor is introduced +which outweighs the known quantities. Therefore the application of +the culminative effect of interest accumulations is much dependent +upon the sort of mine under consideration. In most cases of uncertain +continuity in depth it introduces a mathematical refinement not +warranted by the speculative elements. For instance, in a mine +where the whole value is dependent upon extension of the deposit +beyond openings, and where an expected return of at least 50% per +annum is required to warrant the risk, such refinement would be +absurd. On the other hand, in a Witwatersrand gold mine, in gold +and tin gravels, or in massive copper mines such as Bingham and +Lake Superior, where at least some sort of life can be approximated, +it becomes a most vital element in valuation. +</p> + +<p class="indent"> +<a name="page_44"><span class="page">Page 44</span></a> In general +it may be said that the lower the total annual return expected upon +the capital invested, the greater does the amount demanded for +amortization become in proportion to this total income, and therefore +the greater need of its introduction in calculations. Especially +is this so where the cost of equipment is large proportionately to +the annual return. Further, it may be said that such calculations +are of decreasing use with increasing proportion of speculative +elements in the price of the mine. The risk of extension in depth, +of the price of metal, etc., may so outweigh the comparatively minor +factors here introduced as to render them useless of attention. +</p> + +<p class="indent"> +In the practical conduct of mines or mining companies, sinking +funds for amortization of capital are never established. In the +vast majority of mines of the class under discussion, the ultimate +duration of life is unknown, and therefore there is no basis upon +which to formulate such a definite financial policy even were it +desired. Were it possible to arrive at the annual sum to be set +aside, the stockholders of the mining type would prefer to do their +own reinvestment. The purpose of these calculations does not lie +in the application of amortization to administrative finance. It +is nevertheless one of the touchstones in the valuation of certain +mines or mining investments. That is, by a sort of inversion such +calculations can be made to serve as a means to expose the amount +of risk,—to furnish a yardstick for measuring the amount +of risk in the very speculations of extension in depth and price +of metals which attach to a mine. Given the annual income being +received, or expected, the problem can be formulated into the +determination of how many years it must be continued in order to +amortize the investment and pay a given rate of profit. A certain +length of life is evident from the ore in sight, which may be called +the life in sight. If the term of years required to redeem the +capital and pay an interest upon it is greater than the life in +sight, then this extended life must come from extension in depth, or +ore from other direction, or increased price of metals. If we then +take the volume and profit on the ore as disclosed we can calculate +the number of feet the deposit must extend in depth, or additional +tonnage <a name="page_45"><span class="page">Page 45</span></a> +that must be obtained of the same grade, or the different prices of +metal that must be secured, in order to satisfy the demanded term +of years. These demands in actual measure of ore or feet or higher +price can then be weighed against the geological and industrial +probabilities. +</p> + +<p class="indent"> +The following tables and examples may be of assistance in these +calculations. +</p> + +<p class="indent"> +Table 1. To apply this table, the amount of annual income or dividend +and the term of years it will last must be known or estimated factors. +It is then possible to determine the <i>present</i> value of this +annual income after providing for amortization and interest on +the investment at various rates given, by multiplying the annual +income by the factor set out. +</p> + +<p class="indent"> +A simple illustration would be that of a mine earning a profit of +$200,000 annually, and having a total of 1,000,000 tons in sight, +yielding a profit of $2 a ton, or a total profit in sight of $2,000,000, +thus recoverable in ten years. On a basis of a 7% return on the +investment and amortization of capital (Table I), the factor is +6.52 x $200,000 = $1,304,000 as the present value of the gross +profits exposed. That is, this sum of $1,304,000, if paid for the +mine, would be repaid out of the profit in sight, together with +7% interest if the annual payments into sinking fund earn 4%. +</p> + +<h3><a name="page_46"><span class="page">Page 46</span></a> +TABLE I.</h3> + +<p class="indent"> +<span class="sc">Present Value of an Annual Dividend Over — +Years at —% and Replacing Capital by Reinvestment of an Annual +Sum at 4%.</span> +</p> + +<table class="ctrclps" style="width: 100%;"> +<tr><th class="center_btrb"><span class="sc">Years</span></th> + <th class="center_btrb">5%</th> + <th class="center_btrb">6%</th> + <th class="center_btrb">7%</th> + <th class="center_btrb">8%</th> + <th class="center_btrb">9%</th> + <th class="center_btb">10%</th></tr> +<tr><td class="center_br">1</td> + <td class="center_br">.95</td> + <td class="center_br">.94</td> + <td class="center_br">.93</td> + <td class="center_br">.92</td> + <td class="center_br">.92</td> + <td class="center">.91</td></tr> +<tr><td class="center_br">2</td> + <td class="center_br">1.85</td> + <td class="center_br">1.82</td> + <td class="center_br">1.78</td> + <td class="center_br">1.75</td> + <td class="center_br">1.72</td> + <td class="center">1.69</td></tr> +<tr><td class="center_br">3</td> + <td class="center_br">2.70</td> + <td class="center_br">2.63</td> + <td class="center_br">2.56</td> + <td class="center_br">2.50</td> + <td class="center_br">2.44</td> + <td class="center">2.38</td></tr> +<tr><td class="center_br">4</td> + <td class="center_br">3.50</td> + <td class="center_br">3.38</td> + <td class="center_br">3.27</td> + <td class="center_br">3.17</td> + <td class="center_br">3.07</td> + <td class="center">2.98</td></tr> +<tr><td class="center_br">5</td> + <td class="center_br">4.26</td> + <td class="center_br">4.09</td> + <td class="center_br">3.93</td> + <td class="center_br">3.78</td> + <td class="center_br">3.64</td> + <td class="center">3.51</td></tr> +<tr><td class="center_br">6</td> + <td class="center_br">4.98</td> + <td class="center_br">4.74</td> + <td class="center_br">4.53</td> + <td class="center_br">4.33</td> + <td class="center_br">4.15</td> + <td class="center">3.99</td></tr> +<tr><td class="center_br">7</td> + <td class="center_br">5.66</td> + <td class="center_br">5.36</td> + <td class="center_br">5.09</td> + <td class="center_br">4.84</td> + <td class="center_br">4.62</td> + <td class="center">4.41</td></tr> +<tr><td class="center_br">8</td> + <td class="center_br">6.31</td> + <td class="center_br">5.93</td> + <td class="center_br">5.60</td> + <td class="center_br">5.30</td> + <td class="center_br">5.04</td> + <td class="center">4.79</td></tr> +<tr><td class="center_br">9</td> + <td class="center_br">6.92</td> + <td class="center_br">6.47</td> + <td class="center_br">6.08</td> + <td class="center_br">5.73</td> + <td class="center_br">5.42</td> + <td class="center">5.14</td></tr> +<tr><td class="center_br">10</td> + <td class="center_br">7.50</td> + <td class="center_br">6.98</td> + <td class="center_br">6.52</td> + <td class="center_br">6.12</td> + <td class="center_br">5.77</td> + <td class="center">5.45</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">11</td> + <td class="center_br">8.05</td> + <td class="center_br">7.45</td> + <td class="center_br">6.94</td> + <td class="center_br">6.49</td> + <td class="center_br">6.09</td> + <td class="center">5.74</td></tr> +<tr><td class="center_br">12</td> + <td class="center_br">8.58</td> + <td class="center_br">7.90</td> + <td class="center_br">7.32</td> + <td class="center_br">6.82</td> + <td class="center_br">6.39</td> + <td class="center">6.00</td></tr> +<tr><td class="center_br">13</td> + <td class="center_br">9.08</td> + <td class="center_br">8.32</td> + <td class="center_br">7.68</td> + <td class="center_br">7.13</td> + <td class="center_br">6.66</td> + <td class="center">6.24</td></tr> +<tr><td class="center_br">14</td> + <td class="center_br">9.55</td> + <td class="center_br">8.72</td> + <td class="center_br">8.02</td> + <td class="center_br">7.42</td> + <td class="center_br">6.91</td> + <td class="center">6.46</td></tr> +<tr><td class="center_br">15</td> + <td class="center_br">10.00</td> + <td class="center_br">9.09</td> + <td class="center_br">8.34</td> + <td class="center_br">7.79</td> + <td class="center_br">7.14</td> + <td class="center">6.67</td></tr> +<tr><td class="center_br">16</td> + <td class="center_br">10.43</td> + <td class="center_br">9.45</td> + <td class="center_br">8.63</td> + <td class="center_br">7.95</td> + <td class="center_br">7.36</td> + <td class="center">6.86</td></tr> +<tr><td class="center_br">17</td> + <td class="center_br">10.85</td> + <td class="center_br">9.78</td> + <td class="center_br">8.91</td> + <td class="center_br">8.18</td> + <td class="center_br">7.56</td> + <td class="center">7.03</td></tr> +<tr><td class="center_br">18</td> + <td class="center_br">11.24</td> + <td class="center_br">10.10</td> + <td class="center_br">9.17</td> + <td class="center_br">8.40</td> + <td class="center_br">7.75</td> + <td class="center">7.19</td></tr> +<tr><td class="center_br">19</td> + <td class="center_br">11.61</td> + <td class="center_br">10.40</td> + <td class="center_br">9.42</td> + <td class="center_br">8.61</td> + <td class="center_br">7.93</td> + <td class="center">7.34</td></tr> +<tr><td class="center_br">20</td> + <td class="center_br">11.96</td> + <td class="center_br">10.68</td> + <td class="center_br">9.65</td> + <td class="center_br">8.80</td> + <td class="center_br">8.09</td> + <td class="center">7.49</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">21</td> + <td class="center_br">12.30</td> + <td class="center_br">10.95</td> + <td class="center_br">9.87</td> + <td class="center_br">8.99</td> + <td class="center_br">8.24</td> + <td class="center">7.62</td></tr> +<tr><td class="center_br">22</td> + <td class="center_br">12.62</td> + <td class="center_br">11.21</td> + <td class="center_br">10.08</td> + <td class="center_br">9.16</td> + <td class="center_br">8.39</td> + <td class="center">7.74</td></tr> +<tr><td class="center_br">23</td> + <td class="center_br">12.93</td> + <td class="center_br">11.45</td> + <td class="center_br">10.28</td> + <td class="center_br">9.32</td> + <td class="center_br">8.52</td> + <td class="center">7.85</td></tr> +<tr><td class="center_br">24</td> + <td class="center_br">13.23</td> + <td class="center_br">11.68</td> + <td class="center_br">10.46</td> + <td class="center_br">9.47</td> + <td class="center_br">8.65</td> + <td class="center">7.96</td></tr> +<tr><td class="center_br">25</td> + <td class="center_br">13.51</td> + <td class="center_br">11.90</td> + <td class="center_br">10.64</td> + <td class="center_br">9.61</td> + <td class="center_br">8.77</td> + <td class="center">8.06</td></tr> +<tr><td class="center_br">26</td> + <td class="center_br">13.78</td> + <td class="center_br">12.11</td> + <td class="center_br">10.80</td> + <td class="center_br">9.75</td> + <td class="center_br">8.88</td> + <td class="center">8.16</td></tr> +<tr><td class="center_br">27</td> + <td class="center_br">14.04</td> + <td class="center_br">12.31</td> + <td class="center_br">10.96</td> + <td class="center_br">9.88</td> + <td class="center_br">8.99</td> + <td class="center">8.25</td></tr> +<tr><td class="center_br">28</td> + <td class="center_br">14.28</td> + <td class="center_br">12.50</td> + <td class="center_br">11.11</td> + <td class="center_br">10.00</td> + <td class="center_br">9.09</td> + <td class="center">8.33</td></tr> +<tr><td class="center_br">29</td> + <td class="center_br">14.52</td> + <td class="center_br">12.68</td> + <td class="center_br">11.25</td> + <td class="center_br">10.11</td> + <td class="center_br">9.18</td> + <td class="center">8.41</td></tr> +<tr><td class="center_br">30</td> + <td class="center_br">14.74</td> + <td class="center_br">12.85</td> + <td class="center_br">11.38</td> + <td class="center_br">10.22</td> + <td class="center_br">9.27</td> + <td class="center">8.49</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">31</td> + <td class="center_br">14.96</td> + <td class="center_br">13.01</td> + <td class="center_br">11.51</td> + <td class="center_br">10.32</td> + <td class="center_br">9.36</td> + <td class="center">8.56</td></tr> +<tr><td class="center_br">32</td> + <td class="center_br">15.16</td> + <td class="center_br">13.17</td> + <td class="center_br">11.63</td> + <td class="center_br">10.42</td> + <td class="center_br">9.44</td> + <td class="center">8.62</td></tr> +<tr><td class="center_br">33</td> + <td class="center_br">15.36</td> + <td class="center_br">13.31</td> + <td class="center_br">11.75</td> + <td class="center_br">10.51</td> + <td class="center_br">9.51</td> + <td class="center">8.69</td></tr> +<tr><td class="center_br">34</td> + <td class="center_br">15.55</td> + <td class="center_br">13.46</td> + <td class="center_br">11.86</td> + <td class="center_br">10.60</td> + <td class="center_br">9.59</td> + <td class="center">8.75</td></tr> +<tr><td class="center_br">35</td> + <td class="center_br">15.73</td> + <td class="center_br">13.59</td> + <td class="center_br">11.96</td> + <td class="center_br">10.67</td> + <td class="center_br">9.65</td> + <td class="center">8.80</td></tr> +<tr><td class="center_br">36</td> + <td class="center_br">15.90</td> + <td class="center_br">13.72</td> + <td class="center_br">12.06</td> + <td class="center_br">10.76</td> + <td class="center_br">9.72</td> + <td class="center">8.86</td></tr> +<tr><td class="center_br">37</td> + <td class="center_br">16.07</td> + <td class="center_br">13.84</td> + <td class="center_br">12.16</td> + <td class="center_br">10.84</td> + <td class="center_br">9.78</td> + <td class="center">8.91</td></tr> +<tr><td class="center_br">38</td> + <td class="center_br">16.22</td> + <td class="center_br">13.96</td> + <td class="center_br">12.25</td> + <td class="center_br">10.91</td> + <td class="center_br">9.84</td> + <td class="center">8.96</td></tr> +<tr><td class="center_br">39</td> + <td class="center_br">16.38</td> + <td class="center_br">14.07</td> + <td class="center_br">12.34</td> + <td class="center_br">10.98</td> + <td class="center_br">9.89</td> + <td class="center">9.00</td></tr> +<tr><td class="center_brb">40</td> + <td class="center_brb">16.52</td> + <td class="center_brb">14.18</td> + <td class="center_brb">12.42</td> + <td class="center_brb">11.05</td> + <td class="center_brb">9.95</td> + <td class="center_bb">9.05</td></tr> +<tr><td colspan="7" style="font-size: smaller; text-align: center"> + Condensed from Inwood's Tables.</td></tr> +</table> + +<p class="indent"> +<a name="page_47"><span class="page">Page 47</span></a> Table II +is practically a compound discount table. That is, by it can be +determined the present value of a fixed sum payable at the end +of a given term of years, interest being discounted at various +given rates. Its use may be illustrated by continuing the example +preceding. +</p> + +<h3>TABLE II.</h3> + +<p class="indent"> +<span class="sc">Present Value of $1, or £1, payable in — +Years, Interest taken at —%.</span> +</p> + +<table class="ctrclps" style="width: 100%;"> +<tr><th class="center_btrb"><span class="sc">Years</span></th> + <th class="center_btrb">4%</th> + <th class="center_btrb">5%</th> + <th class="center_btrb">6%</th> + <th class="center_btb">7%</th></tr> +<tr><td class="center_br">1</td> + <td class="center_br">.961</td> + <td class="center_br">.952</td> + <td class="center_br">.943</td> + <td class="center">.934</td></tr> +<tr><td class="center_br">2</td> + <td class="center_br">.924</td> + <td class="center_br">.907</td> + <td class="center_br">.890</td> + <td class="center">.873</td></tr> +<tr><td class="center_br">3</td> + <td class="center_br">.889</td> + <td class="center_br">.864</td> + <td class="center_br">.840</td> + <td class="center">.816</td></tr> +<tr><td class="center_br">4</td> + <td class="center_br">.854</td> + <td class="center_br">.823</td> + <td class="center_br">.792</td> + <td class="center">.763</td></tr> +<tr><td class="center_br">5</td> + <td class="center_br">.821</td> + <td class="center_br">.783</td> + <td class="center_br">.747</td> + <td class="center">.713</td></tr> +<tr><td class="center_br">6</td> + <td class="center_br">.790</td> + <td class="center_br">.746</td> + <td class="center_br">.705</td> + <td class="center">.666</td></tr> +<tr><td class="center_br">7</td> + <td class="center_br">.760</td> + <td class="center_br">.711</td> + <td class="center_br">.665</td> + <td class="center">.623</td></tr> +<tr><td class="center_br">8</td> + <td class="center_br">.731</td> + <td class="center_br">.677</td> + <td class="center_br">.627</td> + <td class="center">.582</td></tr> +<tr><td class="center_br">9</td> + <td class="center_br">.702</td> + <td class="center_br">.645</td> + <td class="center_br">.592</td> + <td class="center">.544</td></tr> +<tr><td class="center_br">10</td> + <td class="center_br">.675</td> + <td class="center_br">.614</td> + <td class="center_br">.558</td> + <td class="center">.508</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">11</td> + <td class="center_br">.649</td> + <td class="center_br">.585</td> + <td class="center_br">.527</td> + <td class="center">.475</td></tr> +<tr><td class="center_br">12</td> + <td class="center_br">.625</td> + <td class="center_br">.557</td> + <td class="center_br">.497</td> + <td class="center">.444</td></tr> +<tr><td class="center_br">13</td> + <td class="center_br">.600</td> + <td class="center_br">.530</td> + <td class="center_br">.469</td> + <td class="center">.415</td></tr> +<tr><td class="center_br">14</td> + <td class="center_br">.577</td> + <td class="center_br">.505</td> + <td class="center_br">.442</td> + <td class="center">.388</td></tr> +<tr><td class="center_br">15</td> + <td class="center_br">.555</td> + <td class="center_br">.481</td> + <td class="center_br">.417</td> + <td class="center">.362</td></tr> +<tr><td class="center_br">16</td> + <td class="center_br">.534</td> + <td class="center_br">.458</td> + <td class="center_br">.394</td> + <td class="center">.339</td></tr> +<tr><td class="center_br">17</td> + <td class="center_br">.513</td> + <td class="center_br">.436</td> + <td class="center_br">.371</td> + <td class="center">.316</td></tr> +<tr><td class="center_br">18</td> + <td class="center_br">.494</td> + <td class="center_br">.415</td> + <td class="center_br">.350</td> + <td class="center">.296</td></tr> +<tr><td class="center_br">19</td> + <td class="center_br">.475</td> + <td class="center_br">.396</td> + <td class="center_br">.330</td> + <td class="center">.276</td></tr> +<tr><td class="center_br">20</td> + <td class="center_br">.456</td> + <td class="center_br">.377</td> + <td class="center_br">.311</td> + <td class="center">.258</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">21</td> + <td class="center_br">.439</td> + <td class="center_br">.359</td> + <td class="center_br">.294</td> + <td class="center">.241</td></tr> +<tr><td class="center_br">22</td> + <td class="center_br">.422</td> + <td class="center_br">.342</td> + <td class="center_br">.277</td> + <td class="center">.266</td></tr> +<tr><td class="center_br">23</td> + <td class="center_br">.406</td> + <td class="center_br">.325</td> + <td class="center_br">.262</td> + <td class="center">.211</td></tr> +<tr><td class="center_br">24</td> + <td class="center_br">.390</td> + <td class="center_br">.310</td> + <td class="center_br">.247</td> + <td class="center">.197</td></tr> +<tr><td class="center_br">25</td> + <td class="center_br">.375</td> + <td class="center_br">.295</td> + <td class="center_br">.233</td> + <td class="center">.184</td></tr> +<tr><td class="center_br">26</td> + <td class="center_br">.361</td> + <td class="center_br">.281</td> + <td class="center_br">.220</td> + <td class="center">.172</td></tr> +<tr><td class="center_br">27</td> + <td class="center_br">.347</td> + <td class="center_br">.268</td> + <td class="center_br">.207</td> + <td class="center">.161</td></tr> +<tr><td class="center_br">28</td> + <td class="center_br">.333</td> + <td class="center_br">.255</td> + <td class="center_br">.196</td> + <td class="center">.150</td></tr> +<tr><td class="center_br">29</td> + <td class="center_br">.321</td> + <td class="center_br">.243</td> + <td class="center_br">.184</td> + <td class="center">.140</td></tr> +<tr><td class="center_br">30</td> + <td class="center_br">.308</td> + <td class="center_br">.231</td> + <td class="center_br">.174</td> + <td class="center">.131</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">31</td> + <td class="center_br">.296</td> + <td class="center_br">.220</td> + <td class="center_br">.164</td> + <td class="center">.123</td></tr> +<tr><td class="center_br">32</td> + <td class="center_br">.285</td> + <td class="center_br">.210</td> + <td class="center_br">.155</td> + <td class="center">.115</td></tr> +<tr><td class="center_br">33</td> + <td class="center_br">.274</td> + <td class="center_br">.200</td> + <td class="center_br">.146</td> + <td class="center">.107</td></tr> +<tr><td class="center_br">34</td> + <td class="center_br">.263</td> + <td class="center_br">.190</td> + <td class="center_br">.138</td> + <td class="center">.100</td></tr> +<tr><td class="center_br">35</td> + <td class="center_br">.253</td> + <td class="center_br">.181</td> + <td class="center_br">.130</td> + <td class="center">.094</td></tr> +<tr><td class="center_br">36</td> + <td class="center_br">.244</td> + <td class="center_br">.172</td> + <td class="center_br">.123</td> + <td class="center">.087</td></tr> +<tr><td class="center_br">37</td> + <td class="center_br">.234</td> + <td class="center_br">.164</td> + <td class="center_br">.116</td> + <td class="center">.082</td></tr> +<tr><td class="center_br">38</td> + <td class="center_br">.225</td> + <td class="center_br">.156</td> + <td class="center_br">.109</td> + <td class="center">.076</td></tr> +<tr><td class="center_br">39</td> + <td class="center_br">.216</td> + <td class="center_br">.149</td> + <td class="center_br">.103</td> + <td class="center">.071</td></tr> +<tr><td class="center_brb">40</td> + <td class="center_brb">.208</td> + <td class="center_brb">.142</td> + <td class="center_brb">.097</td> + <td class="center_bb">.067</td></tr> +<tr><td colspan="7" style="font-size: smaller; text-align: center;"> + Condensed from Inwood's Tables.</td></tr> +</table> + +<p class="indent"> +<a name="page_48"><span class="page">Page 48</span></a> If such a +mine is not equipped, and it is assumed that $200,000 are required +to equip the mine, and that two years are required for this equipment, +the value of the ore in sight is still less, because of the further +loss of interest in delay and the cost of equipment. In this case +the present value of $1,304,000 in two years, interest at 7%, the +factor is .87 X 1,304,000 = $1,134,480. From this comes off the +cost of equipment, or $200,000, leaving $934,480 as the present +value of the profit in sight. A further refinement could be added by +calculating the interest chargeable against the $200,000 equipment +cost up to the time of production. +</p> + +<h3>TABLE III.</h3> + +<table class="ctrclps"> +<tr><th class="center_btrb">Annual Rate of Dividend.</th> + <th class="left_btb" colspan="6">Number of years of life + required to yield—% interest, and in addition to furnish + annual instalments which, if reinvested at 4% will return the + original investment at the end of the period.</th></tr> +<tr><td class="center_br">%</td> + <td class="center_br">5%</td> + <td class="center_br">6%</td> + <td class="center_br">7%</td> + <td class="center_br">8%</td> + <td class="center_br">9%</td> + <td class="center">10%</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">6</td> + <td class="center_br">41.0</td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">7</td> + <td class="center_br">28.0</td> + <td class="center_br">41.0</td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">8</td> + <td class="center_br">21.6</td> + <td class="center_br">28.0</td> + <td class="center_br">41.0</td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">9</td> + <td class="center_br">17.7</td> + <td class="center_br">21.6</td> + <td class="center_br">28.0</td> + <td class="center_br">41.0</td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">10</td> + <td class="center_br">15.0</td> + <td class="center_br">17.7</td> + <td class="center_br">21.6</td> + <td class="center_br">28.0</td> + <td class="center_br">41.0</td> + <td class="center"> </td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">11</td> + <td class="center_br">13.0</td> + <td class="center_br">15.0</td> + <td class="center_br">17.7</td> + <td class="center_br">21.6</td> + <td class="center_br">28.0</td> + <td class="center">41.0</td></tr> +<tr><td class="center_br">12</td> + <td class="center_br">11.5</td> + <td class="center_br">13.0</td> + <td class="center_br">15.0</td> + <td class="center_br">17.7</td> + <td class="center_br">21.6</td> + <td class="center">28.0</td></tr> +<tr><td class="center_br">13</td> + <td class="center_br">10.3</td> + <td class="center_br">11.5</td> + <td class="center_br">13.0</td> + <td class="center_br">15.0</td> + <td class="center_br">17.7</td> + <td class="center">21.6</td></tr> +<tr><td class="center_br">14</td> + <td class="center_br">9.4</td> + <td class="center_br">10.3</td> + <td class="center_br">11.5</td> + <td class="center_br">13.0</td> + <td class="center_br">15.0</td> + <td class="center">17.7</td></tr> +<tr><td class="center_br">15</td> + <td class="center_br">8.6</td> + <td class="center_br">9.4</td> + <td class="center_br">10.3</td> + <td class="center_br">11.5</td> + <td class="center_br">13.0</td> + <td class="center">15.0</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">16</td> + <td class="center_br">7.9</td> + <td class="center_br">8.6</td> + <td class="center_br">9.4</td> + <td class="center_br">10.3</td> + <td class="center_br">11.5</td> + <td class="center">13.0</td></tr> +<tr><td class="center_br">17</td> + <td class="center_br">7.3</td> + <td class="center_br">7.9</td> + <td class="center_br">8.6</td> + <td class="center_br">9.4</td> + <td class="center_br">10.3</td> + <td class="center">11.5</td></tr> +<tr><td class="center_br">18</td> + <td class="center_br">6.8</td> + <td class="center_br">7.3</td> + <td class="center_br">7.9</td> + <td class="center_br">8.6</td> + <td class="center_br">9.4</td> + <td class="center">10.3</td></tr> +<tr><td class="center_br">19</td> + <td class="center_br">6.4</td> + <td class="center_br">6.8</td> + <td class="center_br">7.3</td> + <td class="center_br">7.9</td> + <td class="center_br">8.6</td> + <td class="center">9.4</td></tr> +<tr><td class="center_br">20</td> + <td class="center_br">6.0</td> + <td class="center_br">6.4</td> + <td class="center_br">6.8</td> + <td class="center_br">7.3</td> + <td class="center_br">7.9</td> + <td class="center">8.6</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">21</td> + <td class="center_br">5.7</td> + <td class="center_br">6.0</td> + <td class="center_br">6.4</td> + <td class="center_br">6.8</td> + <td class="center_br">7.3</td> + <td class="center">7.9</td></tr> +<tr><td class="center_br">22</td> + <td class="center_br">5.4</td> + <td class="center_br">5.7</td> + <td class="center_br">6.0</td> + <td class="center_br">6.4</td> + <td class="center_br">6.8</td> + <td class="center">7.3</td></tr> +<tr><td class="center_br">23</td> + <td class="center_br">5.1</td> + <td class="center_br">5.4</td> + <td class="center_br">5.7</td> + <td class="center_br">6.0</td> + <td class="center_br">6.4</td> + <td class="center">6.8</td></tr> +<tr><td class="center_br">24</td> + <td class="center_br">4.9</td> + <td class="center_br">5.1</td> + <td class="center_br">5.4</td> + <td class="center_br">5.7</td> + <td class="center_br">6.0</td> + <td class="center">6.4</td></tr> +<tr><td class="center_br">25</td> + <td class="center_br">4.7</td> + <td class="center_br">4.9</td> + <td class="center_br">5.1</td> + <td class="center_br">5.4</td> + <td class="center_br">5.7</td> + <td class="center">6.0</td></tr> +<tr><td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center_br"> </td> + <td class="center"> </td></tr> +<tr><td class="center_br">26</td> + <td class="center_br">4.5</td> + <td class="center_br">4.7</td> + <td class="center_br">4.9</td> + <td class="center_br">5.1</td> + <td class="center_br">5.4</td> + <td class="center">5.7</td></tr> +<tr><td class="center_br">27</td> + <td class="center_br">4.3</td> + <td class="center_br">4.5</td> + <td class="center_br">4.7</td> + <td class="center_br">4.9</td> + <td class="center_br">5.1</td> + <td class="center">5.4</td></tr> +<tr><td class="center_br">28</td> + <td class="center_br">4.1</td> + <td class="center_br">4.3</td> + <td class="center_br">4.5</td> + <td class="center_br">4.7</td> + <td class="center_br">4.9</td> + <td class="center">5.1</td></tr> +<tr><td class="center_br">29</td> + <td class="center_br">3.9</td> + <td class="center_br">4.1</td> + <td class="center_br">4.3</td> + <td class="center_br">4.5</td> + <td class="center_br">4.7</td> + <td class="center">4.9</td></tr> +<tr><td class="center_brb">30</td> + <td class="center_brb">3.8</td> + <td class="center_brb">3.9</td> + <td class="center_brb">4.1</td> + <td class="center_brb">4.3</td> + <td class="center_brb">4.5</td> + <td class="center_bb">4.7</td></tr> +</table> + +<p class="indent"> +<a name="page_49"><span class="page">Page 49</span></a> Table III. +This table is calculated by inversion of the factors in Table I, and +is the most useful of all such tables, as it is a direct calculation +of the number of years that a given rate of income on the investment +must continue in order to amortize the capital (the annual sinking +fund being placed at compound interest at 4%) and to repay various +rates of interest on the investment. The application of this method +in testing the value of dividend-paying shares is very helpful, +especially in weighing the risks involved in the portion of the +purchase or investment unsecured by the profit in sight. Given +the annual percentage income on the investment from the dividends +of the mine (or on a non-producing mine assuming a given rate of +production and profit from the factors exposed), by reference to +the table the number of years can be seen in which this percentage +must continue in order to amortize the investment and pay various +rates of interest on it. As said before, the ore in sight at a +given rate of exhaustion can be reduced to terms of life in sight. +This certain period deducted from the total term of years required +gives the life which must be provided by further discovery of ore, and +this can be reduced to tons or feet of extension of given ore-bodies +and a tangible position arrived at. The test can be applied in this +manner to the various prices which must be realized from the base +metal in sight to warrant the price. +</p> + +<p class="indent"> +Taking the last example and assuming that the mine is equipped, +and that the price is $2,000,000, the yearly return on the price is +10%. If it is desired besides amortizing or redeeming the capital to +secure a return of 7% on the investment, it will be seen by reference +to the table that there will be required a life of 21.6 years. As the +life visible in the ore in sight is ten years, then the extensions in +depth must produce ore for 11.6 years longer—1,160,000 tons. +If the ore-body is 1,000 feet long and 13 feet wide, it will furnish +of gold ore 1,000 tons per foot of depth; hence the ore-body must +extend 1,160 feet deeper to justify the price. Mines are seldom so +simple a proposition as this example. There are usually probabilities +of other ore; and in the case of base metal, then variability of price +and other elements must be counted. However, once the extension +in depth <a name="page_50"><span class="page">Page 50</span></a> +which is necessary is determined for various assumptions of metal +value, there is something tangible to consider and to weigh with +the five geological weights set out in Chapter III. +</p> + +<p class="indent"> +The example given can be expanded to indicate not only the importance +of interest and redemption in the long extension in depth required, +but a matter discussed from another point of view under "Ratio of +Output." If the plant on this mine were doubled and the earnings +increased to 20% ($400,000 per annum) (disregarding the reduction +in working expenses that must follow expansion of equipment), it +will be found that the life required to repay the purchase +money,—$2,000,000,—and 7% interest upon it, is about +6.8 years. +</p> + +<p class="indent"> +As at this increased rate of production there is in the ore in +sight a life of five years, the extension in depth must be depended +upon for 1.8 years, or only 360,000 tons,—that is, 360 feet +of extension. Similarly, the present value of the ore in sight is +$268,000 greater if the mine be given double the equipment, for +thus the idle money locked in the ore is brought into the interest +market at an earlier date. Against this increased profit must be +weighed the increased cost of equipment. The value of low grade +mines, especially, is very much a factor of the volume of output +contemplated. +</p> + +<h2><a name="page_51"><span class="page">Page 51</span></a> +CHAPTER VI.</h2> + +<p class="center"> +<span class="sc">Mine Valuation</span> (<i>Concluded</i>). +</p> + +<table class="summary"><tr><td class="summary"> +VALUATION OF MINES WITH LITTLE OR NO ORE IN SIGHT; VALUATIONS ON +SECOND-HAND DATA; GENERAL CONDUCT OF EXAMINATIONS; REPORTS. +</td></tr></table> + +<p class="indent"> +A large number of examinations arise upon prospecting ventures +or partially developed mines where the value is almost wholly +prospective. The risks in such enterprises amount to the possible loss +of the whole investment, and the possible returns must consequently +be commensurate. Such business is therefore necessarily highly +speculative, but not unjustifiable, as the whole history of the +industry attests; but this makes the matter no easier for the mine +valuer. Many devices of financial procedure assist in the limitation +of the sum risked, and offer a middle course to the investor between +purchase of a wholly prospective value and the loss of a possible +opportunity to profit by it. The usual form is an option to buy the +property after a period which permits a certain amount of development +work by the purchaser before final decision as to purchase. +</p> + +<p class="indent"> +Aside from young mines such enterprises often arise from the possibility +of lateral extension of the ore-deposit outside the boundaries of +the property of original discovery (Fig. 3), in which cases there +is often no visible ore within the property under consideration +upon which to found opinion. In regions where vertical side lines +obtain, there is always the possibility of a "deep level" in inclined +deposits. Therefore the ground surrounding known deposits has a +certain speculative value, upon which engineers are often called to +pass judgment. Except in such unusual occurrences as South African +bankets, or Lake Superior coppers, prospecting for deep level of +extension is also a highly speculative phase of mining. +</p> + +<p class="indent"> +<a name="page_52"><span class="page">Page 52</span></a> The whole +basis of opinion in both classes of ventures must be the few geological +weights,—the geology of the property and the district, the +development of surrounding mines, etc. In any event, there is a very +great percentage of risk, and the profit to be gained by success +must be, proportionally to the expenditure involved, very large. +It is no case for calculating amortization and other refinements. +It is one where several hundreds or thousands of per cent hoped +for on the investment is the only justification. +</p> + +<h3>OPINIONS AND VALUATIONS UPON SECOND-HAND DATA.</h3> + +<p class="indent"> +Some one may come forward and deprecate the bare suggestion of an +engineer's offering an opinion when he cannot have proper first-hand +data. But in these days we have to deal with conditions as well as +theories of professional ethics. The growing ownership of mines +by companies, that is by corporations composed of many individuals, +and with their stocks often dealt in on the public exchanges, has +resulted in holders whose interest is not large enough to warrant +their undertaking the cost of exhaustive examinations. The system +has produced an increasing class of mining speculators and investors +who are finding and supplying the enormous sums required to work our +mines,—sums beyond the reach of the old-class single-handed +mining men. Every year the mining investors of the new order are +coming more and more to the engineer for advice, and they should +be encouraged, because such counsel can be given within limits, +and these limits tend to place the industry upon a sounder footing +of ownership. As was said before, the lamb can be in a measure +protected. The engineer's interest is to protect him, so that the +industry which concerns his own life-work may be in honorable repute, +and that capital may be readily forthcoming for its expansion. +Moreover, by constant advice to the investor as to what constitutes +a properly presented and managed project, the arrangement of such +proper presentation and management will tend to become an <i>a +priori</i> function of the promoter. +</p> + +<p class="indent"> +<a name="page_53"><span class="page">Page 53</span></a> Sometimes +the engineer can make a short visit to the mine for data +purposes,—more often he cannot. In the former case, he can +resolve for himself an approximation upon all the factors bearing on +value, except the quality of the ore. For this, aside from inspection +of the ore itself, a look at the plans is usually enlightening. A +longitudinal section of the mine showing a continuous shortening of +the stopes with each succeeding level carries its own interpretation. +In the main, the current record of past production and estimates +of the management as to ore-reserves, etc., can be accepted in +ratio to the confidence that can be placed in the men who present +them. It then becomes a case of judgment of men and things, and +here no rule applies. +</p> + +<p class="indent"> +Advice must often be given upon data alone, without inspection +of the mine. Most mining data present internal evidence as to +credibility. The untrustworthy and inexperienced betray themselves +in their every written production. Assuming the reliability of data, +the methods already discussed for weighing the ultimate value of +the property can be applied. It would be possible to cite hundreds +of examples of valuation based upon second-hand data. Three will, +however, sufficiently illustrate. First, the R mine at Johannesburg. +With the regularity of this deposit, the development done, and +a study of the workings on the neighboring mines and in deeper +ground, it is a not unfair assumption that the reefs will maintain +size and value throughout the area. The management is sound, and +all the data are given in the best manner. The life of the mine +is estimated at six years, with some probabilities of further ore +from low-grade sections. The annual earnings available for dividends +are at the rate of about £450,000 per annum. The capital is +£440,000 in £1 shares. By reference to the table on +page 46 it will be seen that the present value of £450,000 +spread over six years to return capital at the end of that period, +and give 7% dividends in the meantime, is 4.53 x £450,000 = +£2,036,500 ÷ 440,000 = £4 12<i>s</i>. 7<i>d</i>. +per share. So that this mine, on the assumption of continuity of +values, will pay about 7% and return the price. Seven per cent +is, however, not deemed an adequate return for the risks of labor +<a name="page_54"><span class="page">Page 54</span></a> troubles, +faults, dykes, or poor patches. On a 9% basis, the mine is worth +about £4 4<i>s</i>. per share. +</p> + +<p class="indent"> +Second, the G mine in Nevada. It has a capital of $10,000,000 in +$1 shares, standing in the market at 50 cents each. The reserves +are 250,000 tons, yielding a profit for yearly division of $7 per +ton. It has an annual capacity of about 100,000 tons, or $700,000 +net profit, equal to 14% on the market value. In order to repay +the capital value of $5,000,000 and 8% per annum, it will need +a life of (Table III) 13 years, of which 2-1/2 are visible. The +size of the ore-bodies indicates a yield of about 1,100 tons per +foot of depth. At an exhaustion rate of 100,000 tons per annum, +the mine would need to extend to a depth of over a thousand feet +below the present bottom. There is always a possibility of finding +parallel bodies or larger volumes in depth, but it would be a sanguine +engineer indeed who would recommend the stock, even though it pays +an apparent 14%. +</p> + +<p class="indent"> +Third, the B mine, with a capital of $10,000,000 in 2,000,000 shares +of $5 each. The promoters state that the mine is in the slopes of +the Andes in Peru; that there are 6,000,000 tons of "ore blocked +out"; that two assays by the assayers of the Bank of England average +9% copper; that the copper can be produced at five cents per pound; +that there is thus a profit of $10,000,000 in sight. The evidences +are wholly incompetent. It is a gamble on statements of persons +who have not the remotest idea of sound mining. +</p> + +<h3>GENERAL CONDUCT OF EXAMINATION.</h3> + +<p class="indent"> +Complete and exhaustive examination, entailing extensive sampling, +assaying, and metallurgical tests, is very expensive and requires +time. An unfavorable report usually means to the employer absolute +loss of the engineer's fee and expenses. It becomes then the initial +duty of the latter to determine at once, by the general conditions +surrounding the property, how far the expenditure for exhaustive +examination is warranted. There is usually named a money valuation +for the property, and thus a peg is afforded upon which to hang +conclusions. Very often collateral factors with a preliminary sampling, +or indeed no <a name="page_55"><span class="page">Page 55</span></a> +sampling at all, will determine the whole business. In fact, it +is becoming very common to send younger engineers to report as to +whether exhaustive examination by more expensive men is justified. +</p> + +<p class="indent"> +In the course of such preliminary inspection, the ore-bodies may +prove to be too small to insure adequate yield on the price, even +assuming continuity in depth and represented value. They may be +so difficult to mine as to make costs prohibitive, or they may +show strong signs of "petering out." The ore may present visible +metallurgical difficulties which make it unprofitable in any event. +A gold ore may contain copper or arsenic, so as to debar cyanidation, +where this process is the only hope of sufficiently moderate costs. +A lead ore may be an amorphous compound with zinc, and successful +concentration or smelting without great penalties may be precluded. +A copper ore may carry a great excess of silica and be at the same +time unconcentratable, and there may be no base mineral supply +available for smelting mixture. The mine may be so small or so +isolated that the cost of equipment will never be justified. Some +of these conditions may be determined as unsurmountable, assuming +a given value for the ore, and may warrant the rejection of the +mine at the price set. +</p> + +<p class="indent"> +It is a disagreeable thing to have a disappointed promoter heap +vituperation on an engineer's head because he did not make an exhaustive +examination. Although it is generally desirable to do some sampling +to give assurance to both purchaser and vendor of conscientiousness, +a little courage of conviction, when this is rightly and adequately +grounded, usually brings its own reward. +</p> + +<p class="indent"> +Supposing, however, that conditions are right and that the mine is +worth the price, subject to confirmation of values, the determination +of these cannot be undertaken unless time and money are available +for the work. As was said, a sampling campaign is expensive, and +takes time, and no engineer has the moral right to undertake an +examination unless both facilities are afforded. Curtailment is +unjust, both to himself and to his employer. +</p> + +<p class="indent"> +<a name="page_56"><span class="page">Page 56</span></a> How much +time and outlay are required to properly sample a mine is obviously +a question of its size, and the character of its ore. An engineer +and one principal assistant can conduct two sampling parties. In +hard rock it may be impossible to take more than five samples a +day for each party. But, in average ore, ten samples for each is +reasonable work. As the number of samples is dependent upon the +footage of openings on the deposit, a rough approximation can be +made in advance, and a general idea obtained as to the time required. +This period must be insisted upon. +</p> + +<h3>REPORTS.</h3> + +<p class="indent"> +Reports are to be read by the layman, and their first qualities +should be simplicity of terms and definiteness of conclusions. +Reports are usually too long, rather than too short. The essential +facts governing the value of a mine can be expressed on one sheet +of paper. It is always desirable, however, that the groundwork data +and the manner of their determination should be set out with such +detail that any other engineer could come to the same conclusion +if he accepted the facts as accurately determined. In regard to the +detailed form of reports, the writer's own preference is for a single +page summarizing the main factors, and an assay plan, reduced to a +longitudinal section where possible. Then there should be added, +for purposes of record and for submission to other engineers, a +set of appendices going into some details as to the history of +the mine, its geology, development, equipment, metallurgy, and +management. A list of samples should be given with their location, +and the tonnages and values of each separate block. A presentation +should be made of the probabilities of extension in depth, together +with recommendations for working the mine. +</p> + +<h3>GENERAL SUMMARY.</h3> + +<p class="indent"> +The bed-rock value which attaches to a mine is the profit to be +won from proved ore and in which the price of metal is calculated +at some figure between "basic" and "normal." This we may call the +"<i>A</i>" value. Beyond this there is the speculative <a +name="page_57"><span class="page">Page 57</span></a> value of the +mine. If the value of the "probable" ore be represented by <i>X</i>, +the value of extension of the ore by <i>Y</i>, and a higher price +for metal than the price above assumed represented by <i>Z</i>, +then if the mine be efficiently managed the value of the mine is +<i>A</i> + <i>X</i> + <i>Y</i> + <i>Z</i>. What actual amounts +should be attached to <i>X, Y, Z</i> is a matter of judgment. There +is no prescription for good judgment. Good judgment rests upon +a proper balancing of evidence. The amount of risk in <i>X, Y, +Z</i> is purely a question of how much these factors are required +to represent in money,—in effect, how much more ore must +be found, or how many feet the ore must extend in depth; or in +convertible terms, what life in years the mine must have, or how +high the price of metal must be. In forming an opinion whether these +requirements will be realized, <i>X, Y, Z</i> must be balanced in a +scale whose measuring standards are the five geological weights +and the general industrial outlook. The wise engineer will put before +his clients the scale, the weights, and the conclusion arrived at. +The shrewd investor will require to know these of his adviser. +</p> + +<h2><a name="page_58"><span class="page">Page 58</span></a> +CHAPTER VII.</h2> + +<p class="center"> +<span class="sc">Development of Mines.</span> +</p> + +<table class="summary"><tr><td class="summary"> +ENTRY TO THE MINE; TUNNELS; VERTICAL, INCLINED, AND COMBINED SHAFTS; +LOCATION AND NUMBER OF SHAFTS. +</td></tr></table> + +<p class="indent"> +Development is conducted for two purposes: first, to search for +ore; and second, to open avenues for its extraction. Although both +objects are always more or less in view, the first predominates +in the early life of mines, the prospecting stage, and the second +in its later life, the producing stage. It is proposed to discuss +development designed to embrace extended production purposes first, +because development during the prospecting stage is governed by +the same principles, but is tempered by the greater degree of +uncertainty as to the future of the mine, and is, therefore, of +a more temporary character. +</p> + +<h3>ENTRY TO THE MINE.</h3> + +<p class="indent"> +There are four methods of entry: by tunnel, vertical shaft, inclined +shaft, or by a combination of the last two, that is, by a shaft +initially vertical then turned to an incline. Combined shafts are +largely a development of the past few years to meet "deep level" +conditions, and have been rendered possible only by skip-winding. The +angle in such shafts (Fig. 2) is now generally made on a parabolic +curve, and the speed of winding is then less diminished by the +bend. +</p> + +<p class="indent"> +The engineering problems which present themselves under "entry" +may be divided into those of:— +</p> + +<ol> + <li>Method.</li> + <li>Location.</li> + <li>Shape and size.</li> +</ol> + +<p class="indent"> +<a name="page_59"><span class="page">Page 59</span></a> The resolution +of these questions depends upon the:— +</p> + +<table style="margin: 1em;"> +<tr><td>a.</td><td>Degree of dip of the deposit.</td></tr> +<tr><td>b.</td><td>Output of ore to be provided for.</td></tr> +<tr><td>c.</td><td>Depth at which the deposit is to be attacked.</td></tr> +<tr><td>d.</td><td>Boundaries of the property.</td></tr> +<tr><td>e.</td><td>Surface topography.</td></tr> +<tr><td>f.</td><td>Cost.</td></tr> +<tr><td>g.</td><td>Operating efficiency.</td></tr> +<tr><td>h.</td><td>Prospects of the mine.</td></tr> +</table> + +<table class="image" style="width: 411px;"> +<tr><td><a name="fig_02"> + <img src="images/fig_02.png" width="411" height="710" alt="Fig. 2"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> 2.—Showing +arrangement of the bend in combined shafts.</td></tr> +</table> + +<p class="indent"> +<a name="page_60"><span class="page">Page 60</span></a> From the +point of view of entrance, the coöperation of a majority of +these factors permits the division of mines into certain broad +classes. The type of works demanded for moderate depths (say vertically +2,500 to 3,000 feet) is very different from that required for great +depths. To reach great depths, the size of shafts must greatly +expand, to provide for extended ventilation, pumping, and winding +necessities. Moreover inclined shafts of a degree of flatness possible +for moderate depths become too long to be used economically from +the surface. The vast majority of metal-mining shafts fall into +the first class, those of moderate depths. Yet, as time goes on +and ore-deposits are exhausted to lower planes, problems of depth +will become more common. One thing, however, cannot be too much +emphasized, especially on mines to be worked from the outcrop, and +that is, that no engineer is warranted, owing to the speculation +incidental to extension in depth, in initiating early in the mine's +career shafts of such size or equipment as would be available for +great depths. Moreover, the proper location of a shaft so as to +work economically extension of the ore-bodies is a matter of no +certainty, and therefore shafts of speculative mines are tentative +in any event. +</p> + +<p class="indent"> +Another line of division from an engineering view is brought about +by a combination of three of the factors mentioned. This is the +classification into "outcrop" and "deep-level" mines. The former +are those founded upon ore-deposits to be worked from or close +to the surface. The latter are mines based upon the extension in +depth of ore-bodies from outcrop mines. Such projects are not so +common in America, where the law in most districts gives the outcrop +owner the right to follow ore beyond his side-lines, as in countries +where the boundaries are vertical on all sides. They do, however, +arise not alone in the few American sections where the side-lines +are vertical boundaries, but in other parts owing to the pitch of +ore-bodies through the end lines (Fig. 3). More especially do such +problems arise in America in effect, where the ingress questions +have to be revised for mines worked out in the upper levels (Fig. +7).<a name="page_61"><span class="page">Page 61</span></a></p> + +<table class="image" style="width: 751px;"> +<tr><td><a name="fig_03"> + <img src="images/fig_03.png" width="751" height="558" alt="Fig. 3"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +3.—Longitudinal section showing "deep level" project arising +from dip of ore-body through end-line.</td></tr> +</table> + +<p class="indent"> +If from a standpoint of entrance questions, mines are first <a +name="page_62"><span class="page">Page 62</span></a> classified +into those whose works are contemplated for moderate depths, and +those in which work is contemplated for great depth, further clarity +in discussion can be gained by subdivision into the possible cases +arising out of the factors of location, dip, topography, and boundaries. +</p> + +<h3>MINES OF MODERATE DEPTHS.</h3> + +<table style="width: 100%;"> +<tr><td class="topright">Case I.</td> + <td class="justify">Deposits where topographic conditions permit + the alternatives of shaft or tunnel.</td></tr> +<tr><td class="topright">Case II.</td> + <td class="justify">Vertical or horizontal deposits, the only + practical means of attaining which is by a vertical + shaft.</td></tr> +<tr><td class="topright">Case III.</td> + <td class="justify">Inclined deposits to be worked from near the + surface. There are in such instances the alternatives of either + a vertical or an inclined shaft.</td></tr> +<tr><td class="topright">Case IV.</td> + <td class="justify">Inclined deposits which must be attacked in + depth, that is, deep-level projects. There are the alternatives + of a compound shaft or of a vertical shaft, and in some cases + of an incline from the surface.</td></tr> +</table> + +<h3>MINES TO GREAT DEPTHS.</h3> + +<table style="width: 100%;"> +<tr><td class="topright">Case V.</td> + <td class="justify">Vertical or horizontal deposits, the only way + of reaching which is by a vertical shaft.</td></tr> +<tr><td class="topright">Case VI.</td> + <td class="justify">Inclined deposits. In such cases the + alternatives are a vertical or a compound shaft.</td></tr> +</table> + +<p class="indent"> +<b>Case I.</b>—Although for logical arrangement tunnel entry +has been given first place, to save repetition it is proposed to +consider it later. With few exceptions, tunnels are a temporary +expedient in the mine, which must sooner or later be opened by +a shaft. +</p> + +<p class="indent"> +<b>Case II. Vertical or Horizontal Deposits.</b>—These require +no discussion as to manner of entry. There is no justifiable alternative +to a vertical shaft (Fig. 4). +<a name="page_63"><span class="page">Page 63</span></a></p> + +<table class="image" style="width: 523px;"> +<tr><td><a name="fig_04"> + <img src="images/fig_04.png" width="523" height="415" alt="Fig. 4"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +4.—Cross-sections showing entry to vertical or horizontal +deposits. Case II.</td></tr> +</table> + +<table class="image" style="width: 560px;"> +<tr><td><a name="fig_05"> + <img src="images/fig_05.png" width="560" height="426" alt="Fig. 5"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +5.—Cross-section showing alternative shafts to inclined +deposit to be worked from surface. Case III.</td></tr> +</table> + +<p class="indent"> +<b>Case III. Inclined Deposits which are intended to be worked +from the Outcrop, or from near It</b> (Fig. 5).—The choice +of inclined or vertical shaft is dependent upon relative cost of <a +name="page_64"><span class="page">Page 64</span></a> construction, +subsequent operation, and the useful life of the shaft, and these +matters are largely governed by the degree of dip. Assuming a shaft +of the same size in either alternative, the comparative cost per +foot of sinking is dependent largely on the breaking facilities +of the rock under the different directions of attack. In this, +the angles of the bedding or joint planes to the direction of the +shaft outweigh other factors. The shaft which takes the greatest +advantage of such lines of breaking weakness will be the cheapest +per foot to sink. In South African experience, where inclined shafts +are sunk parallel to the bedding planes of hard quartzites, the cost +per foot appears to be in favor of the incline. On the other hand, +sinking shafts across tight schists seems to be more advantageous +than parallel to the bedding planes, and inclines following the +dip cost more per foot than vertical shafts. +</p> + +<p class="indent"> +An inclined shaft requires more footage to reach a given point +of depth, and therefore it would entail a greater total expense +than a vertical shaft, assuming they cost the same per foot. The +excess amount will be represented by the extra length, and this +will depend upon the flatness of the dip. With vertical shafts, +however, crosscuts to the deposit are necessary. In a comparative +view, therefore, the cost of the crosscuts must be included with +that of the vertical shaft, as they would be almost wholly saved +in an incline following near the ore. +</p> + +<p class="indent"> +The factor of useful life for the shaft enters in deciding as to +the advisability of vertical shafts on inclined deposits, from the +fact that at some depth one of two alternatives has to be chosen. +The vertical shaft, when it reaches a point below the deposit where +the crosscuts are too long (<i>C</i>, Fig. 5), either becomes useless, +or must be turned on an incline at the intersection with the ore +(<i>B</i>). The first alternative means ultimately a complete loss +of the shaft for working purposes. The latter has the disadvantage +that the bend interferes slightly with haulage. +</p> + +<p class="indent"> +The following table will indicate an hypothetical extreme +case,—not infrequently met. In it a vertical shaft 1,500 +feet in depth is taken as cutting the deposit at the depth of 750 +feet, <a name="page_65"><span class="page">Page 65</span></a> the +most favored position so far as aggregate length of crosscuts is +concerned. The cost of crosscutting is taken at $20 per foot and +that of sinking the vertical shaft at $75 per foot. The incline +is assumed for two cases at $75 and $100 per foot respectively. +The stoping height upon the ore between levels is counted at 125 +feet. +</p> + +<table class="ctrclps" style="margin-top: 1em; margin-bottom: 1em;"> +<tr><th class="center_btrb"><span class="sc">Dip of Deposit from + Horizontal</span></th> + <th class="center_btrb"><span class="sc">Depth of Vertical + Shaft</span></th> + <th class="center_btrb"><span class="sc">Length of Incline + Required</span></th> + <th class="center_btrb"><span class="sc">No. of Crosscuts + Required from V Shaft</span></th> + <th class="center_btb"><span class="sc">Total Length of + Crosscuts, Feet</span></th></tr> +<tr><td class="center_br">80°</td> + <td class="center_br">1,500</td> + <td class="center_br">1,522</td> + <td class="center_br">11</td> + <td class="center">859</td></tr> +<tr><td class="center_br">70°</td> + <td class="center_br">1,500</td> + <td class="center_br">1,595</td> + <td class="center_br">12</td> + <td class="center">1,911</td></tr> +<tr><td class="center_br">60°</td> + <td class="center_br">1,500</td> + <td class="center_br">1,732</td> + <td class="center_br">13</td> + <td class="center">3,247</td></tr> +<tr><td class="center_br">50°</td> + <td class="center_br">1,500</td> + <td class="center_br">1,058</td> + <td class="center_br">15</td> + <td class="center">5,389</td></tr> +<tr><td class="center_br">40°</td> + <td class="center_br">1,500</td> + <td class="center_br">2,334</td> + <td class="center_br">18</td> + <td class="center">8,038</td></tr> +<tr><td class="center_br">30°</td> + <td class="center_br">1,500</td> + <td class="center_br">3,000</td> + <td class="center_br">23</td> + <td class="center">16,237</td></tr> +<tr><th class="center_btrb"><span class="sc">Cost of Crosscuts $20 + per Foot</span></th> + <th class="center_btrb"><span class="sc">Cost Vertical Shaft + $75 per Foot</span></th> + <th class="center_btrb"><span class="sc">Total Cost of Vertical + and Crosscuts</span></th> + <th class="center_btrb"><span class="sc">Cost of Incline $75 + per Foot</span></th> + <th class="center_btb"><span class="sc">Cost of Incline $100 + per Foot</span></th></tr> +<tr><td class="center_br">$17,180</td> + <td class="center_br">$112,500</td> + <td class="center_br">$129,680</td> + <td class="center_br">$114,150</td> + <td class="center">$152,200</td></tr> +<tr><td class="center_br">38,220</td> + <td class="center_br">112,500</td> + <td class="center_br">150,720</td> + <td class="center_br">118,625</td> + <td class="center">159,500</td></tr> +<tr><td class="center_br">64,940</td> + <td class="center_br">112,500</td> + <td class="center_br">177,440</td> + <td class="center_br">129,900</td> + <td class="center">172,230</td></tr> +<tr><td class="center_br">107,780</td> + <td class="center_br">112,500</td> + <td class="center_br">220,280</td> + <td class="center_br">114,850</td> + <td class="center">195,800</td></tr> +<tr><td class="center_br">178,760</td> + <td class="center_br">112,500</td> + <td class="center_br">291,260</td> + <td class="center_br">175,050</td> + <td class="center">233,400</td></tr> +<tr><td class="center_brb">324,740</td> + <td class="center_brb">112,500</td> + <td class="center_brb">437,240</td> + <td class="center_brb">225,000</td> + <td class="center_bb">300,000</td></tr> +</table> + +<p class="indent"> +From the above examples it will be seen that the cost of crosscuts +put at ordinary level intervals rapidly outruns the extra expense +of increased length of inclines. If, however, the conditions are +such that crosscuts from a vertical shaft are not necessary at so +frequent intervals, then in proportion to the decrease the advantages +sway to the vertical shaft. Most situations wherein the crosscuts +can be avoided arise in mines worked out in the upper levels and +fall under Case IV, that of deep-level projects. +</p> + +<p class="indent"> +There can be no doubt that vertical shafts are cheaper to operate +than inclines: the length of haul from a given depth is less; much +higher rope speed is possible, and thus the haulage hours are less for +the same output; the wear and tear on ropes, <a name="page_66"><span +class="page">Page 66</span></a> tracks, or guides is not so great, +and pumping is more economical where the Cornish order of pump is +used. On the other hand, with a vertical shaft must be included +the cost of operating crosscuts. On mines where the volume of ore +does not warrant mechanical haulage, the cost of tramming through +the extra distance involved is an expense which outweighs any extra +operating outlay in the inclined shaft itself. Even with mechanical +haulage in crosscuts, it is doubtful if there is anything in favor +of the vertical shaft on this score. +</p> + +<table class="image" style="width: 619px;"> +<tr><td><a name="fig_06"> + <img src="images/fig_06.png" width="619" height="279" alt="Fig. 6"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +6.—Cross-section showing auxiliary vertical outlet.</td></tr> +</table> + +<p class="indent"> +In deposits of very flat dips, under 30°, the case arises where +the length of incline is so great that the saving on haulage through +direct lift warrants a vertical shaft as an auxiliary outlet in +addition to the incline (Fig. 6). In such a combination the crosscut +question is eliminated. The mine is worked above and below the +intersection by incline, and the vertical shaft becomes simply a +more economical exit and an alternative to secure increased output. +The North Star mine at Grass Valley is an illustration in point. Such +a positive instance borders again on Case IV, deep-level projects. +</p> + +<p class="indent"> +In conclusion, it is the writer's belief that where mines are to +be worked from near the surface, coincidentally with sinking, and +where, therefore, crosscuts from a vertical shaft would need to +be installed frequently, inclines are warranted in all dips under +75° and over 30°. Beyond 75° the best alternative is +often <a name="page_67"><span class="page">Page 67</span></a> +undeterminable. In the range under 30° and over 15°, although +inclines are primarily necessary for actual delivery of ore from +levels, they can often be justifiably supplemented by a vertical +shaft as a relief to a long haul. In dips of less than 15°, +as in those over 75°, the advantages again trend strongly in +favor of the vertical shaft. There arise, however, in mountainous +countries, topographic conditions such as the dip of deposits into +the mountain, which preclude any alternative on an incline at any +angled dip. +</p> + +<p class="indent"> +<b>Case IV. Inclined Deposits which must be attacked in Depth</b> +(Fig. 7).—There are two principal conditions in which such +properties exist: first, mines being operated, or having been previously +worked, whose method of entry must be revised; second, those whose +ore-bodies to be attacked do not outcrop within the property. +</p> + +<p class="indent"> +The first situation may occur in mines of inadequate shaft capacity +or wrong location; in mines abandoned and resurrected; in mines +where a vertical shaft has reached its limit of useful extensions, +having passed the place of economical crosscutting; or in mines in +flat deposits with inclines whose haul has become too long to be +economical. Three alternatives present themselves in such cases: a +new incline from the surface (<i>A B F</i>, Fig. 7), or a vertical +shaft combined with incline extension (<i>C D F</i>), or a simple +vertical shaft (<i>H G</i>). A comparison can be first made between +the simple incline and the combined shaft. The construction of an +incline from the surface to the ore-body will be more costly than +a combined shaft, for until the horizon of the ore is reached (at +<i>D</i>) no crosscuts are required in the vertical section, while +the incline must be of greater length to reach the same horizon. +The case arises, however, where inclines can be sunk through old +stopes, and thus more cheaply constructed than vertical shafts +through solid rock; and also the case of mountainous topographic +conditions mentioned above. +</p> + +<table class="image" style="width: 539px;"> +<tr><td><a name="fig_07"> + <img src="images/fig_07.png" width="539" height="592" alt="Fig. 7"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +7.—Cross-section of inclined deposit which must be attacked +in depth.</td></tr> +</table> + +<p class="indent"> +From an operating point of view, the bend in combined shafts (at +<i>D</i>) gives rise to a good deal of wear and tear on ropes and +gear. The possible speed of winding through a combined shaft is, +however, greater than a simple incline, for although haulage speed +through <a name="page_68"><span class="page">Page 68</span></a> the +incline section (<i>D F</i>) and around the bend of the combined +shaft is about the same as throughout a simple incline (<i>A F</i>), +the speed can be accelerated in the vertical portion (<i>D C</i>) +above that feasible did the incline extend to the surface. There +is therefore an advantage in this regard in the combined shaft. The +net advantages of the combined over the inclined shaft depend on the +comparative length of the two alternative routes from the intersection +(<i>D</i>) to the surface. Certainly it is not advisable to sink a +combined shaft to cut a deposit at 300 feet in depth if a simple +incline can be had to the surface. On the <a name="page_69"><span +class="page">Page 69</span></a> other hand, a combined shaft cutting +the deposit at 1,000 feet will be more advisable than a simple +incline 2,000 feet long to reach the same point. The matter is +one for direct calculation in each special case. In general, there +are few instances of really deep-level projects where a complete +incline from the surface is warranted. +</p> + +<p class="indent"> +In most situations of this sort, and in all of the second type +(where the outcrop is outside the property), actual choice usually +lies between combined shafts (<i>C D F</i>) and entire vertical +shafts (<i>H G</i>). The difference between a combined shaft and a +direct vertical shaft can be reduced to a comparison of the combined +shaft below the point of intersection (<i>D</i>) with that portion +of a vertical shaft which would cover the same horizon. The question +then becomes identical with that of inclined <i>versus</i> verticals, +as stated in Case III, with the offsetting disadvantage of the +bend in the combined shaft. If it is desired to reach production +at the earliest date, the lower section of a simple vertical shaft +must have crosscuts to reach the ore lying above the horizon of +its intersection (<i>E</i>). If production does not press, the ore +above the intersection (<i>EB</i>) can be worked by rises from the +horizon of intersection (<i>E</i>). In the use of rises, however, +there follow the difficulties of ventilation and lowering the ore +down to the shaft, which brings expenses to much the same thing +as operating through crosscuts. +</p> + +<p class="indent"> +The advantages of combined over simple vertical shafts are earlier +production, saving of either rises or crosscuts, and the ultimate +utility of the shaft to any depth. The disadvantages are the cost +of the extra length of the inclined section, slower winding, and +greater wear and tear within the inclined section and especially +around the bend. All these factors are of variable import, depending +upon the dip. On very steep dips,—over 70°,—the +net result is in favor of the simple vertical shaft. On other dips +it is in favor of the combined shaft. +</p> + +<p class="indent"> +<b>Cases V and VI. Mines to be worked to Great Depths,—over +3,000 Feet.</b>—In Case V, with vertical or horizontal deposits, +there is obviously no desirable alternative to vertical shafts. +</p> + +<p class="indent"> +In Case VI, with inclined deposits, there are the alternatives <a +name="page_70"><span class="page">Page 70</span></a> of a combined +or of a simple vertical shaft. A vertical shaft in locations (<i>H</i>, +Fig. 7) such as would not necessitate extension in depth by an +incline, would, as in Case IV, compel either crosscuts to the ore +or inclines up from the horizon of intersection (<i>E</i>). Apart +from delay in coming to production and the consequent loss of interest +on capital, the ventilation problems with this arrangement would +be appalling. Moreover, the combined shaft, entering the deposit +near its shallowest point, offers the possibility of a separate +haulage system on the inclined and on the vertical sections, and +such separate haulage is usually advisable at great depths. In +such instances, the output to be handled is large, for no mine of +small output is likely to be contemplated at such depth. Several +moderate-sized inclines from the horizon of intersection have been +suggested (<i>EF</i>, <i>DG</i>, <i>CH</i>, Fig. 8) to feed a large +primary shaft (<i>AB</i>), which thus becomes the trunk road. This +program would cheapen lateral haulage underground, as mechanical +traction can be used in the main level, (<i>EC</i>), and horizontal +haulage costs can be reduced on the lower levels. Moreover, separate +winding engines on the two sections increase the capacity, for the +effect is that of two trains instead of one running on a single +track. +</p> + +<p class="indent"> +<b>Shaft Location.</b>—Although the prime purpose in locating +a shaft is obviously to gain access to the largest volume of ore +within the shortest haulage distance, other conditions also enter, +such as the character of the surface and the rock to be intersected, +the time involved before reaching production, and capital cost. As +shafts must bear two relations to a deposit,—one as to the +dip and the other as to the strike,—they may be considered +from these aspects. Vertical shafts must be on the hanging-wall +side of the outcrop if the deposit dips at all. In any event, the +shaft should be far enough away to be out of the reach of creeps. +An inclined shaft may be sunk either on the vein, in which case a +pillar of ore must be left to support the shaft; or, instead, it +may be sunk a short distance in the footwall, and where necessary +the excavation above can be supported by filling. Following the +ore has the advantage of prospecting in sinking, and in many cases +the softness of the ground in the region <a name="page_71"><span +class="page">Page 71</span></a> of the vein warrants this procedure. +It has, however, the disadvantage that a pillar of ore is locked +up until the shaft is ready for abandonment. Moreover, as veins or +lodes are seldom of even dip, an inclined shaft, to have value as a +prospecting opening, or to take advantage of breaking possibilities +in the lode, will usually be crooked, and an incline irregular in +detail adds greatly to the cost of winding and maintenance. These +twin disadvantages usually warrant a straight incline in the footwall. +Inclines are not necessarily of the same dip throughout, but for <a +name="page_72"><span class="page">Page 72</span></a> reasonably +economical haulage change of angle must take place gradually. +</p> + +<table class="image" style="width: 556px;"> +<tr><td><a name="fig_08"> + <img src="images/fig_08.png" width="556" height="610" alt="Fig. 8"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +8.—Longitudinal section showing shaft arrangement proposed +for very deep inclined deposits.</td></tr> +</table> + +<p class="indent"> +In the case of deep-level projects on inclined deposits, demanding +combined or vertical shafts, the first desideratum is to locate +the vertical section as far from the outcrop as possible, and thus +secure the most ore above the horizon of intersection. This, however, +as stated before, would involve the cost of crosscuts or rises and +would cause delay in production, together with the accumulation +of capital charges. How important the increment of interest on +capital may become during the period of opening the mine may be +demonstrated by a concrete case. For instance, the capital of a +company or the cost of the property is, say, $1,000,000, and where +opening the mine for production requires four years, the aggregate +sum of accumulated compound interest at 5% (and most operators +want more from a mining investment) would be $216,000. Under such +circumstances, if a year or two can be saved in getting to production +by entering the property at a higher horizon, the difference in +accumulated interest will more than repay the infinitesimal extra +cost of winding through a combined shaft of somewhat increased +length in the inclined section. +</p> + +<p class="indent"> +The unknown character of the ore in depth is always a sound reason +for reaching it as quickly and as cheaply as possible. In result, +such shafts are usually best located when the vertical section +enters the upper portion of the deposit. +</p> + +<p class="indent"> +The objective in location with regard to the strike of the ore-bodies +is obviously to have an equal length of lateral ore-haul in every +direction from the shaft. It is easier to specify than to achieve +this, for in all speculative deposits ore-shoots are found to pursue +curious vagaries as they go down. Ore-bodies do not reoccur with +the same locus as in the upper levels, and generally the chances +to go wrong are more numerous than those to go right. +</p> + +<p class="indent"> +<b>Number of Shafts.</b>—The problem of whether the mine is +to be opened by one or by two shafts of course influences location. +In metal mines under Cases II and III (outcrop properties) the ore +output requirements are seldom beyond the capacity of one shaft. +Ventilation and escape-ways are usually easily managed through the +old stopes. Under such circumstances, the <a name="page_73"><span +class="page">Page 73</span></a> conditions warranting a second shaft +are the length of underground haul and isolation of ore-bodies or +veins. Lateral haulage underground is necessarily disintegrated by +the various levels, and usually has to be done by hand. By shortening +this distance of tramming and by consolidation of the material +from all levels at the surface, where mechanical haulage can be +installed, a second shaft is often justified. There is therefore +an economic limitation to the radius of a single shaft, regardless +of the ability of the shaft to handle the total output. +</p> + +<p class="indent"> +Other questions also often arise which are of equal importance +to haulage costs. Separate ore-shoots or ore-bodies or parallel +deposits necessitate, if worked from one shaft, constant levels +through unpayable ground and extra haul as well, or ore-bodies may +dip away from the original shaft along the strike of the deposit +and a long haulage through dead levels must follow. For instance, +levels and crosscuts cost roughly one-quarter as much per foot as +shafts. Therefore four levels in barren ground, to reach a parallel +vein or isolated ore-body 1,000 feet away, would pay for a shaft +1,000 feet deep. At a depth of 1,000 feet, at least six levels +might be necessary. The tramming of ore by hand through such a +distance would cost about double the amount to hoist it through +a shaft and transport it mechanically to the dressing plant at +surface. The aggregate cost and operation of barren levels therefore +soon pays for a second shaft. If two or more shafts are in question, +they must obviously be set so as to best divide the work. +</p> + +<p class="indent"> +Under Cases IV, V, and VI,—that is, deep-level +projects,—ventilation and escape become most important +considerations. Even where the volume of ore is within the capacity +of a single shaft, another usually becomes a necessity for these +reasons. Their location is affected not only by the locus of the +ore, but, as said, by the time required to reach it. Where two +shafts are to be sunk to inclined deposits, it is usual to set one +so as to intersect the deposit at a lower point than the other. +Production can be started from the shallower, before the second +is entirely ready. The ore above the horizon of intersection of +the deeper shaft is thus accessible from the shallower shaft, and +the difficulty of long rises or crosscuts from that deepest shaft +does not arise. +</p> + +<h2><a name="page_74"><span class="page">Page 74</span></a> +CHAPTER VIII.</h2> + +<p class="center"> +<span class="sc">Development of Mines</span> (<i>Continued</i>). +</p> + +<table class="summary"><tr><td class="summary"> +SHAPE AND SIZE OF SHAFTS; SPEED OF SINKING; TUNNELS. +</td></tr></table> + +<p class="indent"> +<b>Shape of Shafts.</b>—Shafts may be round or rectangular.[*] +Round vertical shafts are largely applied to coal-mines, and some +engineers have advocated their usefulness to the mining of the metals +under discussion. Their great advantages lie in their structural +strength, in the large amount of free space for ventilation, and in +the fact that if walled with stone, brick, concrete, or steel, they +can be made water-tight so as to prevent inflow from water-bearing +strata, even when under great pressure. The round walled shafts have +a longer life than timbered shafts. All these advantages pertain +much more to mining coal or iron than metals, for unsound, wet +ground is often the accompaniment of coal-measures, and seldom +troubles metal-mines. Ventilation requirements are also much greater +in coal-mines. From a metal-miner's standpoint, round shafts are +comparatively much more expensive than the rectangular timbered +type.[**] For a larger area must be excavated for the same useful +space, and if support is needed, satisfactory walling, which of +necessity must be brick, stone, concrete, or steel, cannot be cheaply +accomplished under the conditions prevailing in most metal regions. +Although such shafts would have a longer life, the duration of +timbered shafts is sufficient for most metal mines. It follows +that, as timber is the cheapest and all things considered the most +advantageous means of shaft support for the comparatively temporary +character of metal mines, to get the strains applied to the timbers +in the <a name="page_75"><span class="page">Page 75</span></a> +best manner, and to use the minimum amount of it consistent with +security, and to lose the least working space, the shaft must be +constructed on rectangular lines. +</p> + +<p class="footnote"> +[Footnote *: Octagonal shafts were sunk in Mexico in former times. +At each face of the octagon was a whim run by mules, and hauling +leather buckets.] +</p> + +<p class="footnote"> +[Footnote **: The economic situation is rapidly arising in a number +of localities that steel beams can be usefully used instead of +timber. The same arguments apply to this type of support that apply +to timber.] +</p> + +<p class="indent"> +The variations in timbered shaft design arise from the possible +arrangement of compartments. Many combinations can be imagined, +of which Figures 9, 10, 11, 12, 13, and 14 are examples. +</p> + +<table class="image" style="width: 525px;"> +<tr><td><a name="fig_09-14"> + <img src="images/fig_09-14.png" width="525" height="553" + alt="Fig. 9-14"></a></td></tr> +</table> + +<p class="indent"> +The arrangement of compartments shown in Figures 9, 10, 11, and +13 gives the greatest strength. It permits timbering to the best +advantage, and avoids the danger underground involved in crossing +one compartment to reach another. It is therefore generally adopted. +Any other arrangement would obviously be impossible in inclined +or combined shafts. +</p> + +<p class="indent"> +<a name="page_76"><span class="page">Page 76</span></a> <b>Size of +Shafts.</b>—In considering the size of shafts to be installed, +many factors are involved. They are in the main:— +</p> + +<table style="margin-left: 2em; border-collapse: collapse;"> +<tr><td><i>a</i>.</td><td>Amount of ore to be handled.</td></tr> +<tr><td><i>b</i>.</td><td>Winding plant.</td></tr> +<tr><td><i>c</i>.</td><td>Vehicle of transport.</td></tr> +<tr><td><i>d</i>.</td><td>Depth.</td></tr> +<tr><td><i>e</i>.</td><td>Number of men to be worked underground.</td></tr> +<tr><td><i>f</i>.</td><td>Amount of water.</td></tr> +<tr><td><i>g</i>.</td><td>Ventilation.</td></tr> +<tr><td><i>h</i>.</td><td>Character of the ground.</td></tr> +<tr><td><i>i</i>.</td><td>Capital outlay.</td></tr> +<tr><td><i>j</i>.</td><td>Operating expense.</td></tr> +</table> + +<p class="indent"> +It is not to be assumed that these factors have been stated in +the order of relative importance. More or less emphasis will be +attached to particular factors by different engineers, and under +different circumstances. It is not possible to suggest any arbitrary +standard for calculating their relative weight, and they are so +interdependent as to preclude separate discussion. The usual result +is a compromise between the demands of all. +</p> + +<p class="indent"> +Certain factors, however, dictate a minimum position, which may +be considered as a datum from which to start consideration. +</p> + +<p class="indent"> +<i>First</i>, a winding engine, in order to work with any economy, +must be balanced, that is, a descending empty skip or cage must +assist in pulling up a loaded one. Therefore, except in mines of very +small output, at least two compartments must be made for hoisting +purposes. Water has to be pumped from most mines, escape-ways are +necessary, together with room for wires and air-pipes, so that at +least one more compartment must be provided for these objects. +We have thus three compartments as a sound minimum for any shaft +where more than trivial output is required. +</p> + +<p class="indent"> +<i>Second</i>, there is a certain minimum size of shaft excavation +below which there is very little economy in actual rock-breaking.[*] +<a name="page_77"><span class="page">Page 77</span></a> In too +confined a space, holes cannot be placed to advantage for the blast, +men cannot get round expeditiously, and spoil cannot be handled +readily. The writer's own experience leads him to believe that, +in so far as rock-breaking is concerned, to sink a shaft fourteen +to sixteen feet long by six to seven feet wide outside the timbers, +is as cheap as to drive any smaller size within the realm of +consideration, and is more rapid. This size of excavation permits +of three compartments, each about four to five feet inside the +timbers. +</p> + +<p class="footnote"> +[Footnote *: Notes on the cost of shafts in various regions which +have been personally collected show a remarkable decrease in the +cost per cubic foot of material excavated with increased size of +shaft. Variations in skill, in economic conditions, and in method +of accounting make data regarding different shafts of doubtful +value, but the following are of interest:— +</p> + +<p class="indent"> +In Australia, eight shafts between 10 and 11 feet long by 4 to +5 feet wide cost an average of $1.20 per cubic foot of material +excavated. Six shafts 13 to 14 feet long by 4 to 5 feet wide cost +an average of $0.95 per cubic foot; seven shafts 14 to 16 feet +long and 5 to 7 feet wide cost an average of $0.82 per cubic foot. +In South Africa, eleven shafts 18 to 19 feet long by 7 to 8 feet +wide cost an average of $0.82 per cubic foot; five shafts 21 to +25 feet long by 8 feet wide, cost $0.74; and seven shafts 28 feet +by 8 feet cost $0.60 per cubic foot.] +</p> + +<p class="indent"> +The cost of timber, it is true, is a factor of the size of shaft, +but the labor of timbering does not increase in the same ratio. +In any event, the cost of timber is only about 15% of the actual +shaft cost, even in localities of extremely high prices. +</p> + +<p class="indent"> +<i>Third</i>, three reasons are rapidly making the self-dumping +skip the almost universal shaft-vehicle, instead of the old cage +for cars. First, there is a great economy in labor for loading +into and discharging from a shaft; second, there is more rapid +despatch and discharge and therefore a larger number of possible +trips; third, shaft-haulage is then independent of delays in arrival +of cars at stations, while tramming can be done at any time and +shaft-haulage can be concentrated into certain hours. Cages to +carry mine cars and handle the same load as a skip must either be +big enough to take two cars, which compels a much larger shaft than +is necessary with skips, or they must be double-decked, which renders +loading arrangements underground costly to install and expensive to +work. For all these reasons, cages can be justified only on metal +mines of such small tonnage that time is no consideration and where +the saving of men is not to be effected. In compartments of the +minimum size mentioned above (four to five feet either way) a skip +with a capacity of from <a name="page_78"><span class="page">Page +78</span></a> two to five tons can be installed, although from +two to three tons is the present rule. Lighter loads than this +involve more trips, and thus less hourly capacity, and, on the +other hand, heavier loads require more costly engines. This matter +is further discussed under "Haulage Appliances." +</p> + +<p class="indent"> +We have therefore as the economic minimum a shaft of three compartments +(Fig. 9), each four to five feet square. When the maximum tonnage +is wanted from such a shaft at the least operating cost, it should +be equipped with loading bins and skips. +</p> + +<p class="indent"> +The output capacity of shafts of this size and equipment will depend +in a major degree upon the engine employed, and in a less degree +upon the hauling depth. The reason why depth is a subsidiary factor +is that the rapidity with which a load can be drawn is not wholly a +factor of depth. The time consumed in hoisting is partially expended +in loading, in acceleration and retardation of the engine, and in +discharge of the load. These factors are constant for any depth, +and extra distance is therefore accomplished at full speed of the +engine. +</p> + +<p class="indent"> +Vertical shafts will, other things being equal, have greater capacity +than inclines, as winding will be much faster and length of haul less +for same depth. Since engines have, however, a great tractive ability +on inclines, by an increase in the size of skip it is usually possible +partially to equalize matters. Therefore the size of inclines for +the same output need not differ materially from vertical shafts. +</p> + +<p class="indent"> +The maximum capacity of a shaft whose equipment is of the character +and size given above, will, as stated, decrease somewhat with extension +in depth of the haulage horizon. At 500 feet, such a shaft if vertical +could produce 70 to 80 tons per hour comfortably with an engine +whose winding speed was 700 feet per minute. As men and material +other than ore have to be handled in and out of the mine, and +shaft-sinking has to be attended to, the winding engine cannot +be employed all the time on ore. Twelve hours of actual daily +ore-winding are all that can be expected without auxiliary help. +This represents a capacity from such a depth of 800 to 1,000 tons +per day. A similar shaft, under ordinary working conditions, with +an <a name="page_79"><span class="page">Page 79</span></a> engine +speed of 2,000 feet per minute, should from, say, 3,000 feet have +a capacity of about 400 to 600 tons daily. +</p> + +<p class="indent"> +It is desirable to inquire at what stages the size of shaft should +logically be enlarged in order to attain greater capacity. A +considerable measure of increase can be obtained by relieving the +main hoisting engine of all or part of its collateral duties. Where +the pumping machinery is not elaborate, it is often possible to +get a small single winding compartment into the gangway without +materially increasing the size of the shaft if the haulage compartments +be made somewhat narrower (Fig. 10). Such a compartment would be +operated by an auxiliary engine for sinking, handling tools and +material, and assisting in handling men. If this arrangement can +be effected, the productive time of the main engine can be expanded +to about twenty hours with an addition of about two-thirds to the +output. +</p> + +<p class="indent"> +Where the exigencies of pump and gangway require more than two +and one-half feet of shaft length, the next stage of expansion +becomes four full-sized compartments (Fig. 11). By thus enlarging the +auxiliary winding space, some assistance may be given to ore-haulage +in case of necessity. The mine whose output demands such haulage +provisions can usually stand another foot of width to the shaft, +so that the dimensions come to about 21 feet to 22 feet by 7 feet +to 8 feet outside the timbers. Such a shaft, with three- to four-ton +skips and an appropriate engine, will handle up to 250 tons per +hour from a depth of 1,000 feet. +</p> + +<p class="indent"> +The next logical step in advance is the shaft of five compartments +with four full-sized haulage ways (Fig. 13), each of greater size +than in the above instance. In this case, the auxiliary engine +becomes a balanced one, and can be employed part of the time upon +ore-haulage. Such a shaft will be about 26 feet to 28 feet long +by 8 feet wide outside the timbers, when provision is made for +one gangway. The capacity of such shafts can be up to 4,000 tons a +day, depending on the depth and engine. When very large quantities +of water are to be dealt with and rod-driven pumps to be used, two +pumping compartments are sometimes necessary, but other forms of +pumps do not require more than one compartment,—an additional +reason for their use. +</p> + +<p class="indent"> +<a name="page_80"><span class="page">Page 80</span></a> For depths +greater than 3,000 feet, other factors come into play. Ventilation +questions become of more import. The mechanical problems on engines +and ropes become involved, and their sum-effect is to demand much +increased size and a greater number of compartments. The shafts +at Johannesburg intended as outlets for workings 5,000 feet deep +are as much as 46 feet by 9 feet outside timbers. +</p> + +<p class="indent"> +It is not purposed to go into details as to sinking methods or +timbering. While important matters, they would unduly prolong this +discussion. Besides, a multitude of treatises exist on these subjects +and cover all the minutiæ of such work. +</p> + +<p class="indent"> +<b>Speed of Sinking.</b>—Mines may be divided into two +cases,—those being developed only, and those being operated +as well as developed. In the former, the entrance into production +is usually dependent upon the speed at which the shaft is sunk. +Until the mine is earning profits, there is a loss of interest +on the capital involved, which, in ninety-nine instances out of a +hundred, warrants any reasonable extra expenditure to induce more +rapid progress. In the case of mines in operation, the volume of +ore available to treatment or valuation is generally dependent to +a great degree upon the rapidity of the extension of workings in +depth. It will be demonstrated later that, both from a financial +and a technical standpoint, the maximum development is the right +one and that unremitting extension in depth is not only justifiable +but necessary. +</p> + +<p class="indent"> +Speed under special conditions or over short periods has a more +romantic than practical interest, outside of its value as a stimulant +to emulation. The thing that counts is the speed which can be maintained +over the year. Rapidity of sinking depends mainly on:— +</p> + +<table style="margin-left: 1em;"> +<tr><td><i>a</i>.</td> + <td>Whether the shaft is or is not in use for operating the + mine.</td></tr> +<tr><td><i>b</i>.</td><td>The breaking character of the rock.</td></tr> +<tr><td><i>c</i>.</td><td>The amount of water.</td></tr> +</table> + +<p class="indent"> +The delays incident to general carrying of ore and men are such +that the use of the main haulage engine for shaft-sinking is <a +name="page_81"><span class="page">Page 81</span></a> practically +impossible, except on mines with small tonnage output. Even with a +separate winch or auxiliary winding-engine, delays are unavoidable +in a working shaft, especially as it usually has more water to contend +with than one not in use for operating the mine. The writer's own +impression is that an average of 40 feet per month is the maximum +possibility for year in and out sinking under such conditions. In +fact, few going mines manage more than 400 feet a year. In cases +of clean shaft-sinking, where every energy is bent to speed, 150 +feet per month have been averaged for many months. Special cases +have occurred where as much as 213 feet have been achieved in a +single month. With ordinary conditions, 1,200 feet in a year is +very good work. Rock awkward to break, and water especially, lowers +the rate of progress very materially. Further reference to speed +will be found in the chapter on "Drilling Methods." +</p> + +<p class="indent"> +<b>Tunnel Entry.</b>—The alternative of entry to a mine by +tunnel is usually not a question of topography altogether, but, +like everything else in mining science, has to be tempered to meet +the capital available and the expenditure warranted by the value +showing. +</p> + +<p class="indent"> +In the initial prospecting of a mine, tunnels are occasionally +overdone by prospectors. Often more would be proved by a few inclines. +As the pioneer has to rely upon his right arm for hoisting and +drainage, the tunnel offers great temptations, even when it is +long and gains but little depth. At a more advanced stage of +development, the saving of capital outlay on hoisting and pumping +equipment, at a time when capital is costly to secure, is often +sufficient justification for a tunnel entry. But at the stage where +the future working of ore below a tunnel-level must be contemplated, +other factors enter. For ore below tunnel-level a shaft becomes +necessary, and in cases where a tunnel enters a few hundred feet +below the outcrop the shaft should very often extend to the surface, +because internal shafts, winding from tunnel-level, require large +excavations to make room for the transfer of ore and for winding +gear. The latter must be operated by transmitted power, either that +of steam, water, electricity, or air. Where power has to be generated +on the <a name="page_82"><span class="page">Page 82</span></a> mine, +the saving by the use of direct steam, generated at the winding +gear, is very considerable. Moreover, the cost of haulage through +a shaft for the extra distance from tunnel-level to the surface +is often less than the cost of transferring the ore and removing +it through the tunnel. The load once on the winding-engine, the +consumption of power is small for the extra distance, and the saving +of labor is of consequence. On the other hand, where drainage problems +arise, they usually outweigh all other considerations, for whatever +the horizon entered by tunnel, the distance from that level to +the surface means a saving of water-pumpage against so much head. +The accumulation of such constant expense justifies a proportioned +capital outlay. In other words, the saving of this extra pumping +will annually redeem the cost of a certain amount of tunnel, even +though it be used for drainage only. +</p> + +<p class="indent" style="margin-bottom: 1em;"> +In order to emphasize the rapidity with which such a saving of +constant expense will justify capital outlay, one may tabulate the +result of calculations showing the length of tunnel warranted with +various hypothetical factors of quantity of water and height of lift +eliminated from pumping. In these computations, power is taken at +the low rate of $60 per horsepower-year, the cost of tunneling at +an average figure of $20 per foot, and the time on the basis of +a ten-year life for the mine. +</p> + +<table class="ctrclps"> +<caption><span class="sc">Feet of Tunnel Paid for in 10 Years with + Under-mentioned Conditions.</span></caption> +<tr><th class="center_btrb"><span class="sc">Feet of Water Lift + Avoided</span></th> + <th class="center_btrb"><span class="sc">100,000 Gallons + per Diem</span></th> + <th class="center_btrb"><span class="sc">200,000 Gallons + per Diem</span></th> + <th class="center_btrb"><span class="sc">300,000 Gallons + per Diem</span></th> + <th class="center_btrb"><span class="sc">500,000 Gallons + per Diem</span></th> + <th class="center_btb"><span class="sc">1,000,000 Gallons + per Diem</span></th> +<tr><td class="center_br">100</td> + <td class="center_br">600</td> + <td class="center_br">1,200</td> + <td class="center_br">1,800</td> + <td class="center_br">3,000</td> + <td class="center">6,000</td></tr> +<tr><td class="center_br">200</td> + <td class="center_br">1,200</td> + <td class="center_br">2,400</td> + <td class="center_br">3,600</td> + <td class="center_br">6,000</td> + <td class="center">12,000</td></tr> +<tr><td class="center_br">300</td> + <td class="center_br">1,800</td> + <td class="center_br">3,600</td> + <td class="center_br">5,400</td> + <td class="center_br">9,000</td> + <td class="center">18,000</td></tr> +<tr><td class="center_br">500</td> + <td class="center_br">3,000</td> + <td class="center_br">6,000</td> + <td class="center_br">9,000</td> + <td class="center_br">15,000</td> + <td class="center">30,000</td></tr> +<tr><td class="center_brb">1,000</td> + <td class="center_brb">6,000</td> + <td class="center_brb">12,000</td> + <td class="center_brb">18,000</td> + <td class="center_brb">30,000</td> + <td class="center_bb">60,000</td></tr> +</table> + +<p class="indent" style="margin-top: 1em;"> +The size of tunnels where ore-extraction is involved depends upon the +daily tonnage output required, and the length of <a name="page_83"><span +class="page">Page 83</span></a> haul. The smallest size that can +be economically driven and managed is about 6-1/2 feet by 6 feet +inside the timbers. Such a tunnel, with single track for a length +of 1,000 feet, with one turn-out, permits handling up to 500 tons a +day with men and animals. If the distance be longer or the tonnage +greater, a double track is required, which necessitates a tunnel at +least 8 feet wide by 6-1/2 feet to 7 feet high, inside the timbers. +</p> + +<p class="indent"> +There are tunnel projects of a much more impressive order than those +designed to operate upper levels of mines; that is, long crosscut +tunnels designed to drain and operate mines at very considerable +depths, such as the Sutro tunnel at Virginia City. The advantage +of these tunnels is very great, especially for drainage, and they +must be constructed of large size and equipped with appliances +for mechanical haulage. +</p> + +<h2><a name="page_84"><span class="page">Page 84</span></a> +CHAPTER IX.</h2> + +<p class="center"> +<span class="sc">Development of Mines</span> (<i>Concluded</i>). +</p> + +<table class="summary"><tr><td class="summary"> +SUBSIDIARY DEVELOPMENT;—STATIONS; CROSSCUTS; LEVELS; INTERVAL +BETWEEN LEVELS; PROTECTION OF LEVELS; WINZES AND RISES. DEVELOPMENT +IN THE PROSPECTING STAGE; DRILLING. +</td></tr></table> + +<h3>SUBSIDIARY DEVELOPMENT.</h3> + +<p class="indent"> +Stations, crosscuts, levels, winzes, and rises follow after the +initial entry. They are all expensive, and the least number that +will answer is the main desideratum. +</p> + +<p class="indent"> +<b>Stations.</b>—As stations are the outlets of the levels +to the shaft, their size and construction is a factor of the volume +and character of the work at the levels which they are to serve. +If no timber is to be handled, and little ore, and this on cages, +the stations need be no larger than a good sized crosscut. Where +timber is to be let down, they must be ten to fifteen feet higher +than the floor of the crosscut. Where loading into skips is to be +provided for, bins must be cut underneath and sufficient room be +provided to shift the mine cars comfortably. Such bins are built +of from 50 to 500 tons' capacity in order to contain some reserve +for hoisting purposes, and in many cases separate bins must be +provided on opposite sides of the shaft for ore and waste. It is a +strong argument in favor of skips, that with this means of haulage +storage capacity at the stations is possible, and the hoisting may +then go on independently of trucking and, as said before, there +are no idle men at the stations. +<a name="page_85"><span class="page">Page 85</span></a></p> + +<table class="image" style="width: 469px;"> +<tr><td><a name="fig_15"> + <img src="images/fig_15.png" width="469" height="429" alt="Fig. 15"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +15.—Cross-section of station arrangement for skip-haulage in +vertical shaft.</td></tr> +</table> + +<table class="image" style="width: 640px;"> +<tr><td><a name="fig_16"> + <img src="images/fig_16.png" width="640" height="403" alt="Fig. 16"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +16.—Cross-section of station arrangement for skip-haulage in +vertical shaft.</td></tr> +</table> + +<p class="indent"> +It is always desirable to concentrate the haulage to the least +number of levels, for many reasons. Among them is that, where haulage +is confined to few levels, storage-bins are <a name="page_86"><span +class="page">Page 86</span></a> not required at every station. +Figures 15, 16, 17, and 18 illustrate various arrangements of loading +bins. +</p> + +<p class="indent"> +<b>Crosscuts.</b>—Crosscuts are for two purposes, for roadway +connection of levels to the shaft or to other levels, and for +prospecting purposes. The number of crosscuts for roadways can +sometimes be decreased by making the connections with the shaft +at every second or even every third level, thus not only saving in +the construction cost of crosscuts and stations, but also in the +expenses of scattered tramming. The matter becomes especially worth +considering where the quantity of ore that can thus be accumulated +warrants mule or mechanical haulage. This subject will be referred +to later on. +</p> + +<table class="image" style="width: 429px;"> +<tr><td><a name="fig_17"> + <img src="images/fig_17.png" width="429" height="453" alt="Fig. 17"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +17.—Arrangement of loading chutes in vertical shaft.</td></tr> +</table> + +<p class="indent"> +On the second purpose of crosscuts,—that of prospecting,—one +observation merits emphasis. This is, that the tendency of ore-fissures +to be formed in parallels warrants <a name="page_87"><span +class="page">Page 87</span></a> more systematic crosscutting into +the country rock than is done in many mines. +</p> + +<table class="image" style="width: 530px;"> +<tr><td><a name="fig_18"> + <img src="images/fig_18.png" width="530" height="585" alt="Fig. 18"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +18.—Cross-section of station arrangement for skip-haulage in +inclined shaft.</td></tr> +</table> + +<h3>LEVELS.</h3> + +<p class="indent"> +The word "level" is another example of miners' adaptations in +nomenclature. Its use in the sense of tunnels driven in the direction +of the strike of the deposit has better, but less used, synonyms in +the words "drifts" or "drives." The term "level" is used by miners +in two senses, in that it is sometimes applied to all openings on one +horizon, crosscuts included. Levels are for three purposes,—for +a stoping <a name="page_88"><span class="page">Page 88</span></a> +base; for prospecting the deposit; and for roadways. As a prospecting +and a stoping base it is desirable that the level should be driven +on the deposit; as a roadway, that it should constitute the shortest +distance between two points and be in the soundest ground. On narrow, +erratic deposits the levels usually must serve all three purposes +at once; but in wider and more regular deposits levels are often +driven separately for roadways from the level which forms the stoping +base and prospecting datum. +</p> + +<p class="indent"> +There was a time when mines were worked by driving the level on ore +and enlarging it top and bottom as far as the ground would stand, +then driving the next level 15 to 20 feet below, and repeating the +operation. This interval gradually expanded, but for some reason +100 feet was for years assumed to be the proper distance between +levels. Scattered over every mining camp on earth are thousands +of mines opened on this empirical figure, without consideration +of the reasons for it or for any other distance. +</p> + +<p class="indent"> +The governing factors in determining the vertical interval between +levels are the following:— +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td><i>a</i>.</td><td>The regularity of the deposit.</td></tr> +<tr><td><i>b</i>.</td><td>The effect of the method of excavation of + winzes and rises.</td></tr> +<tr><td><i>c</i>.</td><td>The dip and the method of stoping.</td></tr> +</table> + +<p class="indent"> +<b>Regularity of the Deposit.</b>—From a prospecting point +of view the more levels the better, and the interval therefore +must be determined somewhat by the character of the deposit. In +erratic deposits there is less risk of missing ore with frequent +levels, but it does not follow that every level need be a through +roadway to the shaft or even a stoping base. In such deposits, +intermediate levels for prospecting alone are better than complete +levels, each a roadway. Nor is it essential, even where frequent +levels are required for a stoping base, that each should be a main +haulage outlet to the shaft. In some mines every third level is used +as a main roadway, the ore being poured from the intermediate ones +down to the <a name="page_89"><span class="page">Page 89</span></a> +haulage line. Thus tramming and shaft work, as stated before, can +be concentrated. +</p> + +<p class="indent"> +<b>Effect of Method of Excavating Winzes and Rises.</b>—With +hand drilling and hoisting, winzes beyond a limited depth become +very costly to pull spoil out of, and rises too high become difficult +to ventilate, so that there is in such cases a limit to the interval +desirable between levels, but these difficulties largely disappear +where air-winches and air-drills are used. +</p> + +<p class="indent"> +<b>The Dip and Method of Stoping.</b>—The method of stoping +is largely dependent upon the dip, and indirectly thus affects +level intervals. In dips under that at which material will "flow" +in the stopes—about 45° to 50°—the interval +is greatly dependent on the method of stope-transport. Where ore +is to be shoveled from stopes to the roadway, the levels must be +comparatively close together. Where deposits are very flat, under +20°, and walls fairly sound, it is often possible to use a sort +of long wall system of stoping and to lay tracks in the stopes +with self-acting inclines to the levels. In such instances, the +interval can be expanded to 250 or even 400 feet. In dips between +20° and 45°, tracks are not often possible, and either +shoveling or "bumping troughs"[*] are the only help to transport. +With shoveling, intervals of 100 feet[**] are most common, and +with troughs the distance can be expanded up to 150 or 175 feet. +</p> + +<p class="footnote"> +[Footnote *: Page 136.] +</p> + +<p class="footnote"> +[Footnote **: Intervals given are measured on the dip.] +</p> + +<p class="indent"> +In dips of over 40° to 50°, depending on the smoothness of +the foot wall, the distance can again be increased, as stope-transport +is greatly simplified, since the stope materials fall out by gravity. +In timbered stopes, in dips over about 45°, intervals of 150 +to 200 feet are possible. In filled stopes intervals of over 150 +feet present difficulties in the maintenance of ore-passes, for +the wear and tear of longer use often breaks the timbers. In +shrinkage-stopes, where no passes are to be maintained and few +winzes put through, the interval is sometimes raised to 250 feet. +The subject is further discussed under "Stoping." +</p> + +<p class="indent"> +Another factor bearing on level intervals is the needed <a +name="page_90"><span class="page">Page 90</span></a> insurance of +sufficient points of stoping attack to keep up a certain output. +This must particularly influence the manager whose mine has but +little ore in reserve. +</p> + +<table class="image" style="width: 530px;"> +<tr><td><a name="fig_19"> + <img src="images/fig_19.png" width="530" height="585" alt="Fig. 19"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> 19.</td></tr> +</table> + +<p class="indent"> +<b>Protection of Levels.</b>—Until recent years, timbering +and occasional walling was the only method for the support of the +roof, and for forming a platform for a stoping base. Where the +rock requires no support sublevels can be used as a stoping base, +and timbering for such purpose avoided altogether (Figs. 38, 39, +42). In such cases the main roadway can then be driven on straight +lines, either in the walls or in the ore, and used entirely for +haulage. The subheading for a stoping base is driven far enough above +or below the roadway (depending on whether overhand or underhand +stoping is to be used) to leave a supporting pillar which is penetrated +by short passes for ore. In overhand stopes, the ore is broken +directly on the floor of an upper sublevel; and in underhand stopes, +broken directly from the bottom of the sublevel. The method <a +name="page_91"><span class="page">Page 91</span></a> entails leaving +a pillar of ore which can be recovered only with difficulty in mines +where stope-support is necessary. The question of its adoption is +then largely one of the comparative cost of timbering, the extra +cost of the sublevel, and the net value of the ore left. In bad +swelling veins, or badly crushing walls, where constant repair +to timbers would be necessary, the use of a sublevel is a most +useful alternative. It is especially useful with stopes to be left +open or worked by shrinkage-stoping methods. +</p> + +<p class="indent"> +If the haulage level, however, is to be the stoping base, some +protection to the roadway must be provided. There are three systems +in use,—by wood stulls or sets (Figs. 19, 30, 43), by dry-walling +with timber caps (Fig. 35), and in some localities by steel sets. +Stulls are put up in various ways, and, as their use entails the +least difficulty in taking the ore out from beneath the level, +they are much favored, but are applicable only in comparatively +narrow deposits. +</p> + +<h3>WINZES AND RISES.</h3> + +<p class="indent"> +These two kinds of openings for connecting two horizons in a mine +differ only in their manner of construction. A winze is sunk underhand, +while a rise is put up overhand. When the connection between levels +is completed, a miner standing at the bottom usually refers to +the opening as a rise, and when he goes to the top he calls it +a winze. This confusion in terms makes it advisable to refer to +all such completed openings as winzes, regardless of how they are +constructed. +</p> + +<p class="indent"> +In actual work, even disregarding water, it costs on the average +about 30% less to raise than to sink such openings, for obviously +the spoil runs out or is assisted by gravity in one case, and in +the other has to be shoveled and hauled up. Moreover, it is easier +to follow the ore in a rise than in a winze. It usually happens, +however, that in order to gain time both things are done, and for +prospecting purposes sinking is necessary. +</p> + +<p class="indent"> +<a name="page_92"><span class="page">Page 92</span></a> The number +of winzes required depends upon the method of stoping adopted, and +is mentioned under "Stoping." After stoping, the number necessary +to be maintained open depends upon the necessities of ventilation, +of escape, and of passageways for material to be used below. Where +stopes are to be filled with waste, more winzes must be kept open than +when other methods are used, and these winzes must be in sufficient +alignment to permit the continuous flow of material down past the +various levels. In order that the winzes should deliver timber and +filling to the most advantageous points, they should, in dipping +ore-bodies, be as far as possible on the hanging wall side. +</p> + +<h3>DEVELOPMENT IN THE EARLY PROSPECTING STAGE.</h3> + +<p class="indent"> +The prime objects in the prospecting stage are to expose the ore +and to learn regarding the ore-bodies something of their size, +their value, metallurgical character, location, dip, strike, +etc.,—so much at least as may be necessary to determine the +works most suitable for their extraction or values warranting purchase. +In outcrop mines there is one rule, and that is "follow the ore." +Small temporary inclines following the deposit, even though they +are eventually useless; are nine times out of ten justified. +</p> + +<p class="indent"> +In prospecting deep-level projects, it is usually necessary to +layout work which can be subsequently used in operating the mine, +because the depth involves works of such considerable scale, even +for prospecting, that the initial outlay does not warrant any +anticipation of revision. Such works have to be located and designed +after a study of the general geology as disclosed in adjoining mines. +Practically the only method of supplementing such information is +by the use of churn- and diamond-drills. +</p> + +<p class="indent"> +<b>Drilling.</b>—Churn-drills are applicable only to comparatively +shallow deposits of large volume. They have an advantage over the +diamond drill in exposing a larger section and in their application +to loose material; but inability to <a name="page_93"><span +class="page">Page 93</span></a> determine the exact horizon of +the spoil does not lend them to narrow deposits, and in any event +results are likely to be misleading from the finely ground state of +the spoil. They are, however, of very great value for preliminary +prospecting to shallow horizons. +</p> + +<p class="indent"> +Two facts in diamond-drilling have to be borne in mind: the indication +of values is liable to be misleading, and the deflection of the drill +is likely to carry it far away from its anticipated destination. +A diamond-drill secures a small section which is sufficiently large +to reveal the geology, but the values disclosed in metal mines must +be accepted with reservations. The core amounts to but a little +sample out of possibly large amounts of ore, which is always of +variable character, and the core is most unlikely to represent +the average of the deposit. Two diamond-drill holes on the Oroya +Brownhill mine both passed through the ore-body. One apparently +disclosed unpayable values, the other seemingly showed ore forty +feet in width assaying $80 per ton. Neither was right. On the other +hand, the predetermination of the location of the ore-body justified +expenditure. A recent experiment at Johannesburg of placing a copper +wedge in the hole at a point above the ore-body and deflecting +the drill on reintroducing it, was successful in giving a second +section of the ore at small expense. +</p> + +<p class="indent"> +The deflection of diamond-drill holes from the starting angle is +almost universal. It often amounts to a considerable wandering +from the intended course. The amount of such deflection varies +with no seeming rule, but it is probable that it is especially +affected by the angle at which stratification or lamination planes +are inclined to the direction of the hole. A hole has been known +to wander in a depth of 1,500 feet more than 500 feet from the +point intended. Various instruments have been devised for surveying +deep holes, and they should be brought into use before works are +laid out on the basis of diamond-drill results, although none of +the inventions are entirely satisfactory. +</p> + +<h2><a name="page_94"><span class="page">Page 94</span></a> +CHAPTER X.</h2> + +<p class="center"> +<span class="sc">Stoping.</span> +</p> + +<table class="summary"><tr><td class="summary"> +METHODS OF ORE-BREAKING; UNDERHAND STOPES; OVERHAND STOPES; COMBINED +STOPE. VALUING ORE IN COURSE OF BREAKING. +</td></tr></table> + +<p class="indent"> +There is a great deal of confusion in the application of the word +"stoping." It is used not only specifically to mean the actual +ore-breaking, but also in a general sense to indicate all the operations +of ore-breaking, support of excavations, and transportation between +levels. It is used further as a noun to designate the hole left +when the ore is taken out. Worse still, it is impossible to adhere +to miners' terms without employing it in every sense, trusting +to luck and the context to make the meaning clear. +</p> + +<p class="indent"> +The conditions which govern the method of stoping are in the +main:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td><i>a</i>.</td><td>The dip.</td></tr> +<tr><td><i>b</i>.</td><td>The width of the deposit.</td></tr> +<tr><td><i>c</i>.</td><td>The character of the walls.</td></tr> +<tr><td><i>d</i>.</td><td>The cost of materials.</td></tr> +<tr><td><i>e</i>.</td><td>The character of the ore.</td></tr> +</table> + +<p class="indent"> +Every mine, and sometimes every stope in a mine, is a problem special +to itself. Any general consideration must therefore be simply an +inquiry into the broad principles which govern the adaptability of +special methods. A logical arrangement of discussion is difficult, +if not wholly impossible, because the factors are partially +interdependent and of varying importance. +</p> + +<p class="indent"> +For discussion the subject may be divided into: +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Methods of ore-breaking.</td></tr> +<tr><td>2.</td><td>Methods of supporting excavation.</td></tr> +<tr><td>3.</td><td>Methods of transport in stopes.</td></tr> +</table> + +<h3><a name="page_95"><span class="page">Page 95</span></a> +METHODS OF ORE-BREAKING.</h3> + +<p class="indent"> +The manner of actual ore-breaking is to drill and blast off slices +from the block of ground under attack. As rock obviously breaks +easiest when two sides are free, that is, when corners can be broken +off, the detail of management for blasts is therefore to set the holes +so as to preserve a corner for the next cut; and as a consequence +the face of the stope shapes into a series of benches (Fig. +22),—inverted benches in the case of overhand stopes (Figs. +20, 21). The size of these benches will in a large measure depend +on the depth of the holes. In wide stopes with machine-drills they +vary from 7 to 10 feet; in narrow stopes with hand-holes, from +two to three feet. +</p> + +<table class="image" style="width: 490px;"> +<tr><td><a name="fig_20"> + <img src="images/fig_20.png" width="490" height="468" alt="Fig. 20"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> 20.</td></tr> +</table> + +<p class="indent"> +The position of the men in relation to the working face <a +name="page_96"><span class="page">Page 96</span></a> gives rise +to the usual primary classification of the methods of stoping. +They are:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Underhand stopes,</td></tr> +<tr><td>2.</td><td>Overhand stopes,</td></tr> +<tr><td>3.</td><td>Combined stopes.</td></tr> +</table> + +<p class="indent"> +These terms originated from the direction of the drill-holes, but +this is no longer a logical basis of distinction, for underhand +holes in overhand stopes,—as in rill-stoping,—are used +entirely in some mines (Fig. 21). +</p> + +<table class="image" style="width: 559px;"> +<tr><td><a name="fig_21"> + <img src="images/fig_21.png" width="559" height="471" alt="Fig. 21"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> 21.</td></tr> +</table> + +<p class="indent"> +<b>Underhand Stopes.</b>—Underhand stopes are those in which +the ore is broken downward from the levels. Inasmuch as this method +has the advantage of allowing the miner to strike his blows downward +and to stand upon the ore when at work, it was almost universal +before the invention of powder; and was <a name="page_97"><span +class="page">Page 97</span></a> applied more generally before the +invention of machine-drills than since. It is never rightly introduced +unless the stope is worked back from winzes through which the ore +broken can be let down to the level below, as shown in Figures +22 and 23. +</p> + +<table class="image" style="width: 448px;"> +<tr><td><a name="fig_22"> + <img src="images/fig_22.png" width="448" height="464" alt="Fig. 22"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> 22.</td></tr> +</table> + +<p class="indent"> +This system can be advantageously applied only in the rare cases +in which the walls require little or no support, and where very +little or no waste requiring separation is broken with the ore +in the stopes. To support the walls in bad ground in underhand +stopes would be far more costly than with overhand stopes, for +square-set timbering would be most difficult to introduce, and +to support the walls with waste and stulls would be even more +troublesome. Any waste broken must needs be thrown up to the level +above or be stored upon specially built stages—again a costly +proceeding. +</p> + +<p class="indent"> +A further drawback lies in the fact that the broken ore <a +name="page_98"><span class="page">Page 98</span></a> follows down +the face of the stope, and must be shoveled off each bench. It +thus all arrives at a single point,—the winze,—and +must be drawn from a single ore-pass into the level. This usually +results not only in more shoveling but in a congestion at the passes +not present in overhand stoping, for with that method several chutes +are available for discharging ore into the levels. Where the walls +require no support and no selection is desired in the stopes, the +advantage of the men standing on the solid ore to work, and of +having all down holes and therefore drilled wet, gives this method +a distinct place. In using this system, in order to protect the +men, a pillar is often left under the level by driving a sublevel, +the pillar being easily recoverable later. The method of sublevels +is of advantage largely in avoiding the timbering of levels. +</p> + +<table class="image" style="width: 478px;"> +<tr><td><a name="fig_23"> + <img src="images/fig_23.png" width="478" height="280" alt="Fig. 23"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +23.—Longitudinal section of an underhand stope.</td></tr> +</table> + +<p class="indent"> +<b>Overhand Stopes.</b>—By far the greatest bulk of ore is +broken overhand, that is broken upward from one level to the next +above. There are two general forms which such stopes are +given,—"horizontal" and "rill." +</p> + +<table class="image" style="width: 506px;"> +<tr><td><a name="fig_24"> + <img src="images/fig_24.png" width="506" height="288" alt="Fig. 24"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +24.—Horizontal-cut overhand stope—longitudinal +section.</td></tr> +</table> + +<p class="indent"> +The horizontal "flat-back" or "long-wall" stope, as it is variously +called, shown in Figure 24, is operated by breaking the ore in slices +parallel with the levels. In rill-stoping the ore is cut back from +the winzes in such a way that a pyramid-shaped room is created, +with its apex in the winze and its base <a name="page_99"><span +class="page">Page 99</span></a> at the level (Figs. 25 and 26). +Horizontal or flat-backed stopes can be applied to almost any dip, +while "rill-stoping" finds its most advantageous application where +the dip is such that the ore will "run," or where it can be made +to "run" with a little help. The particular application of the +two systems is dependent not only on the dip but on the method of +supporting the excavation and the ore. With rill-stoping, it is +possible to <a name="page_100"><span class="page">Page 100</span></a> +cut the breaking benches back horizontally from the winzes (Fig. +25), or to stagger the cuts in such a manner as to take the slices +in a descending angle (Figs. 21 and 26). +</p> + +<table class="image" style="width: 502px;"> +<tr><td><a name="fig_25"> + <img src="images/fig_25.png" width="502" height="279" alt="Fig. 25"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +25.—Rill-cut overhand stope—longitudinal +section.</td></tr> +</table> + +<p class="indent"> +In the "rill" method of incline cuts, all the drill-holes are "down" +holes (Fig. 21), and can be drilled wet, while in horizontal cuts +or flat-backed stopes, at least part of the holes must be "uppers" +(Fig. 20). Aside from the easier and cheaper drilling and setting up +of machines with this kind of "cut," there is no drill dust,—a +great desideratum in these days of miners' phthisis. A further +advantage in the "rill" cut arises in cases where horizontal jointing +planes run through the ore of a sort from which unduly large masses +break away in "flat-back" stopes. By the descending cut of the +"rill" method these calamities can be in a measure avoided. In +cases of dips over 40° the greatest advantage in "rill" stoping +arises from the possibility of pouring filling or timber into the +stope from above with less handling, because the ore and material +will run down the sides of the pyramid (Figs. 32 and 34). Thus +not only is there less shoveling required, but fewer ore-passes +and a less number of preliminary winzes are necessary, and a wider +level interval is possible. This matter will be gone into more +fully later. +</p> + +<table class="image" style="width: 529px;"> +<tr><td><a name="fig_26"> + <img src="images/fig_26.png" width="529" height="296" alt="Fig. 26"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +26.—Rill-cut overhand stope-longitudinal section.</td></tr> +</table> + +<p class="indent"> +<a name="page_101"><span class="page">Page 101</span></a> <b>Combined +Stopes.</b>—A combined stope is made by the coincident working +of the underhand and "rill" method (Fig. 27). This order of stope +has the same limitations in general as the underhand kind. For +flat veins with strong walls, it has a great superiority in that +the stope is carried back more or less parallel with the winzes, +and thus broken ore after blasting lies in a line on the gradient +of the stope. It is, therefore, conveniently placed for mechanical +stope haulage. A further advantage is gained in that winzes may +be placed long distances apart, and that men are not required, +either when at work or passing to and from it, to be ever far from +the face, and they are thus in the safest ground, so that timber +and filling protection which may be otherwise necessary is not +required. This method is largely used in South Africa. +</p> + +<table class="image" style="width: 498px;"> +<tr><td><a name="fig_27"> + <img src="images/fig_27.png" width="498" height="273" alt="Fig. 27"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +27.—Longitudinal section of a combined stope.</td></tr> +</table> + +<p class="indent"> +<b>Minimum Width of Stopes.</b>—The minimum stoping width +which can be consistently broken with hand-holes is about 30 inches, +and this only where there is considerable dip to the ore. This +space is so narrow that it is of doubtful advantage in any case, +and 40 inches is more common in narrow mines, especially where +worked with white men. Where machine-drills are used about 4 feet +is the minimum width feasible. +</p> + +<p class="indent"> +<b>Resuing.</b>—In very narrow veins where a certain amount +of wall-rock must be broken to give working space, it pays under +<a name="page_102"><span class="page">Page 102</span></a> some +circumstances to advance the stope into the wall-rock ahead of the +ore, thus stripping the ore and enabling it to be broken separately. +This permits of cleaner selection of the ore; but it is a problem +to be worked out in each case, as to whether rough sorting of some +waste in the stopes, or further sorting at surface with inevitable +treatment of some waste rock, is more economical than separate +stoping cuts and inevitably wider stopes. +</p> + +<p class="indent"> +<b>Valuing Ore in Course of Breaking.</b>—There are many +ores whose payability can be determined by inspection, but there +are many of which it cannot. Continuous assaying is in the latter +cases absolutely necessary to avoid the treatment of valueless +material. In such instances, sampling after each stoping-cut is +essential, the unprofitable ore being broken down and used as waste. +Where values fade into the walls, as in impregnation deposits, the +width of stopes depends upon the limit of payability. In these +cases, drill-holes are put into the walls and the drillings assayed. +If the ore is found profitable, the holes are blasted out. The +gauge of what is profitable in such situations is not dependent +simply upon the average total working costs of the mine, for ore +in that position can be said to cost nothing for development work +and administration; moreover, it is usually more cheaply broken +than the average breaking cost, men and machines being already +on the spot. +</p> + +<h2><a name="page_103"><span class="page">Page 103</span></a> +CHAPTER XI.</h2> + +<p class="center"> +<span class="sc">Methods of Supporting Excavation.</span> +</p> + +<table class="summary"><tr><td class="summary"> +TIMBERING; FILLING WITH WASTE; FILLING WITH BROKEN ORE; PILLARS +OF ORE; ARTIFICIAL PILLARS; CAVING SYSTEM. +</td></tr></table> + +<p class="indent"> +Most stopes require support to be given to the walls and often to +the ore itself. Where they do require support there are five principal +methods of accomplishing it. The application of any particular method +depends upon the dip, width of ore-body, character of the ore and +walls, and cost of materials. The various systems are by:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Timbering.</td></tr> +<tr><td>2.</td><td>Filling with waste.</td></tr> +<tr><td>3.</td><td>Filling with broken ore subsequently + withdrawn.</td></tr> +<tr><td>4.</td><td>Pillars of ore.</td></tr> +<tr><td>5.</td><td>Artificial pillars built of timbers and + waste.</td></tr> +<tr><td>6.</td><td>Caving.</td></tr> +</table> + +<p class="indent"> +<b>Timbering.</b>—At one time timbering was the almost universal +means of support in such excavations, but gradually various methods +for the economical application of waste and ore itself have come +forward, until timbering is fast becoming a secondary device. Aside +from economy in working without it, the dangers of creeps, or crushing, +and of fires are sufficient incentives to do away with wood as far +as possible. +</p> + +<p class="indent"> +There are three principal systems of timber support to +excavations,—by stulls, square-sets, and cribs. +</p> + +<p class="indent"> +Stulls are serviceable only where the deposit is so narrow that +the opening can be bridged by single timbers between wall and wall +(Figs. 28 and 43). This system can be applied to any dip and is +most useful in narrow deposits where the walls are not too heavy. +Stulls in inclined deposits are usually set at a slightly higher +<a name="page_104"><span class="page">Page 104</span></a> angle +than that perpendicular to the walls, in order that the vertical +pressure of the hanging wall will serve to tighten them in position. +The "stull" system can, in inclined deposits, be further strengthened +by building waste pillars against them, in which case the arrangement +merges into the system of artificial pillars. +</p> + +<table class="image" style="width: 470px;"> +<tr><td><a name="fig_28"> + <img src="images/fig_28.png" width="470" height="290" alt="Fig. 28"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +28.—Longitudinal section of stull-supported stope.</td></tr> +</table> + +<table class="image" style="width: 558px;"> +<tr><td><a name="fig_29"> + <img src="images/fig_29.png" width="558" height="247" alt="Fig. 29"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +29.—Longitudinal section showing square-set timbering.</td></tr> +</table> + +<table class="image" style="width: 585px;"> +<tr><td><a name="fig_30"> + <img src="images/fig_30.png" width="585" height="538" alt="Fig. 30"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +30.—Square-set timbering on inclined ore-body. Showing ultimate +strain on timbers.</td></tr> +</table> + +<p class="indent"> +Square-sets (Figs. 29 and 30), that is, trusses built in the opening +as the ore is removed, are applicable to almost any dip or width +of ore, but generally are applied only in deposits too wide, or to +rock too heavy, for stulls. Such trusses are usually constructed on +<a name="page_105"><span class="page">Page 105</span></a> vertical +and horizontal lines, and while during actual ore-breaking the +strains are partially vertical, ultimately, however, when the weight +of the walls begins to be felt, these strains, except in vertical +deposits, come at an angle to lines of strength in the trusses, +and therefore timber constructions of this type present little +ultimate resistance (Fig. 30). Square-set timbers are sometimes +set to present the maximum resistance to the direction of strain, +but the difficulties of placing them in position and variations in +the direction of strain on various parts of the stope do not often +commend the method. As a general rule square-sets on horizontal +lines answer well enough for the period of actual ore-breaking. The +crushing or creeps is usually some time later; <a name="page_106"><span +class="page">Page 106</span></a> and if the crushing may damage the +whole mine, their use is fraught with danger. Reënforcement +by building in waste is often resorted to. When done fully, it is +difficult to see the utility of the enclosed timber, for entire +waste-filling would in most cases be cheaper and equally efficient. +</p> + +<table class="image" style="width: 638px;"> +<tr><td><a name="fig_31"> + <img src="images/fig_31.png" width="638" height="413" alt="Fig. 31"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +31.—"Cribs."</td></tr> +</table> + +<p class="indent"> +There is always, with wood constructions, as said before, the very +pertinent danger of subsequent crushing and of subsidence in after +years, and the great risk of fires. Both these disasters have cost +Comstock and Broken Hill mines, directly or indirectly, millions of +dollars, and the outlay on timber and repairs one way or another +would have paid for the filling system ten times over. There are +cases where, by virtue of the cheapness of timber, "square-setting" +is the most economical method. Again, there are instances where +the ore lies in such a manner—particularly in limestone +replacements—as to preclude other means of support. These +cases are being yearly more and more evaded by the ingenuity of +engineers in charge. The author believes it soon will <a +name="page_107"><span class="page">Page 107</span></a> be recognized +that the situation is rare indeed where complete square-setting +is necessarily without an economical alternative. An objection +is sometimes raised to filling in favor of timber, in that if it +become desirable to restope the walls for low-grade ore left behind, +such stopes could only be entered by drawing the filling, with +consequent danger of total collapse. Such a contingency can be +provided for in large ore-bodies by installing an outer shell of +sets of timber around the periphery of the stope and filling the +inside with waste. If the crushing possibilities are too great +for this method then, the subsequent recovery of ore is hopeless +in any event. In narrow ore-bodies with crushing walls recovery +of ore once left behind is not often possible. +</p> + +<p class="indent"> +The third sort of timber constructions are cribs, a "log-house" sort +of structure usually filled with waste, and more fully discussed +under artificial pillars (Fig. 31). The further comparative merits +of timbering with other methods will be analyzed as the different +systems are described. +</p> + +<p class="indent"> +<b>Filling with Waste.</b>—The system of filling stope-excavations +completely with waste in alternating progress with ore-breaking is +of wide and increasingly general application (Figs. 32, 33, 34, +35). +</p> + +<p class="indent"> +Although a certain amount of waste is ordinarily available in the +stopes themselves, or from development work in the mine, such a +supply must usually be supplemented from other directions. Treatment +residues afford the easiest and cheapest handled material. Quarried +rock ranks next, and in default of any other easy supply, materials +from crosscuts driven into the stope-walls are sometimes resorted +to. +</p> + +<p class="indent"> +In working the system to the best advantage, the winzes through +the block of ore under attack are kept in alignment with similar +openings above, in order that filling may be poured through the +mine from the surface or any intermediate point. Winzes to be used +for filling should be put on the hanging-wall side of the area to +be filled, for the filling poured down will then reach the foot-wall +side of the stopes with a minimum of handling. In some instances, one +special winze is arranged for passing all filling from the surface +to a level above the principal stoping <a name="page_108"> +<span class="page">Page 108</span></a><a name="page_109"><span +class="page">Page 109</span></a> operations; and it is then distributed +along the levels into the winzes, and thus to the operating stopes, +by belt-conveyors. +</p> + +<table class="image" style="width: 647px;"> +<tr><td><a name="fig_32"> + <img src="images/fig_32.png" width="647" height="460" alt="Fig. 32"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +32.—Longitudinal section. Rill stope filled with waste.</td></tr> +</table> + +<table class="image" style="width: 495px;"> +<tr><td><a name="fig_33"> + <img src="images/fig_33.png" width="495" height="263" alt="Fig. 33"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +33.—Longitudinal section. Horizontal stope filled with +waste.</td></tr> +</table> + +<table class="image" style="width: 456px;"> +<tr><td><a name="fig_34"> + <img src="images/fig_34.png" width="456" height="473" alt="Fig. 34"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +34.—Longitudinal section. Waste-filled stope with dry-walling +of levels and passes.</td></tr> +</table> + +<p class="indent"> +In this system of stope support the ore is broken at intervals +alternating with filling. If there is danger of much loss from +mixing broken ore and filling, "sollars" of boards or poles are +laid on the waste. If the ore is very rich, old canvas or cowhides +are sometimes put under the boards. Before the filling interval, +the ore passes are built close to the face above previous filling +and their tops covered temporarily to prevent their being filled +with running waste. If the walls are bad, the filling is kept close +to the face. If the unbroken ore requires support, short stulls +set on the waste (as in Fig. 39) are usually sufficient until the +next cut is taken off, when the timber can be recovered. If stulls +are insufficient, cribs or bulkheads (Fig. 31) are also used and +often buried in the filling. +</p> + +<table class="image" style="width: 284px;"> +<tr><td><a name="fig_35"> + <img src="images/fig_35.png" width="284" height="476" alt="Fig. 35"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +35.—Cross-section of Fig. 34 on line <i>A-B</i>. +<a name="page_110"><span class="page">Page 110</span></a> +</td></tr> +</table> + +<p class="indent"> +Both flat-backed and rill-stope methods of breaking are employed in +conjunction with filled stopes. The advantages of the rill-stopes +are so patent as to make it difficult to understand why they are +not universally adopted when the dip permits their use at all. In +rill-stopes (Figs. 32 and 34) the waste flows to its destination +with a minimum of handling. Winzes and ore-passes are not required +with the same frequency as in horizontal breaking, and the broken +ore always lies on the slope towards the passes and is therefore +also easier to shovel. In flat-backed stopes (Fig. 33) winzes must +be put in every 50 feet or so, while in rill-stopes they can be +double this distance apart. The system is applicable by modification +to almost any width of ore. It finds its most economical field +where the dip of the stope floor is over 45°, when waste and +ore, with the help of the "rill," will flow to their destination. +For dips from under about 45° to about 30° or 35°, +<a name="page_111"><span class="page">Page 111</span></a> where +the waste and ore will not "flow" easily, shoveling can be helped +by the use of the "rill" system and often evaded altogether, if +flow be assisted by a sheet-iron trough described in the discussion +of stope transport. Further saving in shoveling can be gained in +this method, by giving a steeper pitch to the filling winzes and +to the ore-passes, by starting them from crosscuts in the wall, and +by carrying them at greater angles than the pitch of the ore (Fig. +36). These artifices combined have worked out most economically on +several mines within the writer's experience, with the dip as flat +as 30°. For very flat dips, where filling is to be employed, +rill-stoping has no advantage over flat-backed cuts, and in such +cases it is often advisable to assist stope transport by temporary +tracks and cars which obviously could not be worked on the tortuous +contour of a rill-stope, so that for dips under 30° advantage +lies with "flat-backed" ore-breaking. +</p> + +<table class="image" style="width: 498px;"> +<tr><td><a name="fig_36"> + <img src="images/fig_36.png" width="498" height="343" alt="Fig. 36"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> 36.—Cross-section +showing method of steepening winzes and ore passes.</td></tr> +</table> + +<p class="indent"> +On very wide ore-bodies where the support of the standing ore itself +becomes a great problem, the filling system can be applied by combining +it with square-setting. In this case the stopes are carried in +panels laid out transversally to the strike as wide as the standing +strength of the ore permits. On both sides of each panel a fence +of lagged square-sets is carried up and <a name="page_112"><span +class="page">Page 112</span></a> the area between is filled with +waste. The panels are stoped out alternately. The application of +this method at Broken Hill will be described later. (See pages +120 and Figs. 41 and 42.) The same type of wide ore-body can be +managed also on the filling system by the use of frequent "bulkheads" +to support the ore (Fig. 31). +</p> + +<p class="indent"> +Compared with timbering methods, filling has the great advantage +of more effective support to the mine, less danger of creeps, and +absolute freedom from the peril of fire. The relative expense of +the two systems is determined by the cost of materials and labor. +Two extreme cases illustrate the result of these economic factors +with sufficient clearness. It is stated that the cost of timbering +stopes on the Le Roi Mine by square-sets is about 21 cents per +ton of ore excavated. In the Ivanhoe mine of West Australia the +cost of filling stopes with tailings is about 22 cents per ton +of ore excavated. At the former mine the average cost of timber +is under $10 per M board-measure, while at the latter its price +would be $50 per M board-measure; although labor is about of the +same efficiency and wage, the cost in the Ivanhoe by square-setting +would be about 65 cents per ton of ore broken. In the Le Roi, on the +other hand, no residues are available for filling. To quarry rock +or drive crosscuts into the walls might make this system cost 65 +cents per ton of ore broken if applied to that mine. The comparative +value of the filling method with other systems will be discussed +later. +</p> + +<p class="indent"> +<b>Filling with Broken Ore subsequently Withdrawn.</b>—This +order of support is called by various names, the favorite being +"shrinkage-stoping." The method is to break the ore on to the roof +of the level, and by thus filling the stope with broken ore, provide +temporary support to the walls and furnish standing floor upon which +to work in making the next cut (Figs. 37, 38, and 39.) As broken +material occupies 30 to 40% more space than rock <i>in situ</i>, in +order to provide working space at the face, the broken ore must be +drawn from along the level after each cut. When the area attacked +is completely broken through from level to level, the stope will +be full of loose broken ore, which is then entirely drawn off. +</p> + +<p class="indent"> +<a name="page_113"><span class="page">Page 113</span></a> A block +to be attacked by this method requires preliminary winzes only at +the extremities of the stope,—for entry and for ventilation. +Where it is desired to maintain the winzes after stoping, they +must either be strongly timbered and lagged on the stope side, +be driven in the walls, or be protected by a pillar of ore (Fig. +37). The settling ore and the crushing after the stope is empty +make it difficult to maintain timbered winzes. +</p> + +<table class="image" style="width: 466px;"> +<tr><td><a name="fig_37"> + <img src="images/fig_37.png" width="466" height="283" alt="Fig. 37"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +37.—Longitudinal section of stope filled with broken +ore.</td></tr> +</table> + +<p class="indent"> +Where it can be done without danger to the mine, the empty stopes +are allowed to cave. If such crushing would be dangerous, either +the walls must be held up by pillars of unbroken ore, as in the +Alaska Treadwell, where large "rib" pillars are left, or the open +spaces must be filled with waste. Filling the empty stope is usually +done by opening frequent passes along the base of the filled stope +above, and allowing the material of the upper stope to flood the +lower one. This program continued upwards through the mine allows +the whole filling of the mine to descend gradually and thus requires +replenishment only into the top. The old stopes in the less critical +and usually exhausted territory nearer the surface are sometimes +left without replenishing their filling. +</p> + +<p class="indent"> +The weight of broken ore standing at such a high angle as to settle +rapidly is very considerable upon the level; moreover, at the moment +when the stope is entirely drawn off, the pressure <a +name="page_114"><span class="page">Page 114</span></a> of the walls +as well is likely to be very great. The roadways in this system +therefore require more than usual protection. Three methods are +used: (<i>a</i>) timbering; (<i>b</i>) driving a sublevel in the +ore above the main roadway as a stoping-base, thus leaving a pillar +of ore over the roadway (Fig. 39); (<i>c</i>) by dry-walling the +levels, as in the Baltic mine, Michigan (Figs. 34 and 35). By the +use of sublevels the main roadways are sometimes driven in the +walls (Fig. 38) and in many cases all timbering is saved. To recover +pillars left below sublevels is a rather difficult task, especially +if the old stope above is caved or filled. The use of pillars in +substitution for timber, if the pillars are to be lost, is simply +a matter of economics as to whether the lost ore would repay the +cost of other devices. +</p> + +<table class="image" style="width: 517px;"> +<tr><td><a name="fig_38"> + <img src="images/fig_38.png" width="517" height="507" alt="Fig. 38"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +38.—Cross-section of "shrinkage" stope.</td></tr> +</table> + +<p class="indent"> +<a name="page_115"><span class="page">Page 115</span></a> Frequent +ore-chutes through the level timbers, or from the sublevels, are +necessary to prevent lodgment of broken ore between such passes, +because it is usually too dangerous for men to enter the emptying +stope to shovel out the lodged remnants. Where the ore-body is +wide, and in order that there may be no lodgment of ore, the timbers +over the level are set so as to form a trough along the level; +or where pillars are left, they are made "A"-shaped between the +chutes, as indicated in Figure 37. +</p> + +<table class="image" style="width: 395px;"> +<tr><td><a name="fig_39"> + <img src="images/fig_39.png" width="395" height="560" alt="Fig. 39"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +39.—Cross-section of "shrinkage" stope.</td></tr> +</table> + +<p class="indent"> +The method of breaking the ore in conjunction with this means of +support in comparatively narrow deposits can be on the rill, in order +to have the advantage of down holes. Usually, however, flat-back or +horizontal cuts are desirable, as in such <a name="page_116"><span +class="page">Page 116</span></a> an arrangement it is less troublesome +to regulate the drawing of the ore so as to provide proper head +room. Where stopes are wide, ore is sometimes cut arch-shaped from +wall to wall to assure its standing. Where this method of support +is not of avail, short, sharply tapering stulls are put in from +the broken ore to the face (Fig. 39). When the cut above these +stulls is taken out, they are pulled up and are used again. +</p> + +<p class="indent"> +This method of stoping is only applicable when:— +</p> + +<p class="indent"> +1. The deposit dips over 60°, and thus broken material will +freely settle downward to be drawn off from the bottom. +</p> + +<p class="indent"> +2. The ore is consistently payable in character. No selection can be +done in breaking, as all material broken must be drawn off together. +</p> + +<p class="indent"> +3. The hanging wall is strong, and will not crush or spall off waste +into the ore. +</p> + +<p class="indent"> +4. The ore-body is regular in size, else loose ore will lodge on +the foot wall. Stopes opened in this manner when partially empty +are too dangerous for men to enter for shoveling out remnants. +</p> + +<p class="indent"> +The advantages of this system over others, where it is applicable, +are:— +</p> + +<p class="indent"> +(<i>a</i>) A greater distance between levels can be operated and few +winzes and rises are necessary, thus a great saving of development +work can be effected. A stope 800 to 1000 feet long can be operated +with a winze at either end and with levels 200 or 220 feet apart. +</p> + +<p class="indent"> +(<i>b</i>) There is no shoveling in the stopes at all. +</p> + +<p class="indent"> +(<i>c</i>) No timber is required. As compared with timbering by +stulling, it will apply to stopes too wide and walls too heavy +for this method. Moreover, little staging is required for working +the face, since ore can be drawn from below in such a manner as +to allow just the right head room. +</p> + +<p class="indent"> +(<i>d</i>) Compared to the system of filling with waste, coincidentally +with breaking (second method), it saves altogether in some cases the +cost of filling. In any event, it saves the cost of ore-passes, +of shoveling into them, and of the detailed distribution of the +filling. +</p> + +<p class="indent"> +<a name="page_117"><span class="page">Page 117</span></a> Compared +with other methods, the system has the following disadvantages, +that: +</p> + +<p class="indent"> +<i>A</i>. The ore requires to be broken in the stopes to a degree +of fineness which will prevent blocking of the chutes at the level. +When pieces too large reach the chutes, nothing will open them but +blasting,—to the damage of timbers and chutes. Some large +rocks are always liable to be buried in the course of ore-breaking. +</p> + +<p class="indent"> +<i>B</i>. Practically no such perfection of walls exists, but some +spalling of waste into the ore will take place. A crushing of the +walls would soon mean the loss of large amounts of ore. +</p> + +<p class="indent"> +<i>C</i>. There is no possibility of regulating the mixture of +grade of ore by varying the working points. It is months after the +ore is broken before it can reach the levels. +</p> + +<p class="indent"> +<i>D</i>. The breaking of 60% more ore than immediate treatment +demands results in the investment of a considerable sum of money. +An equilibrium is ultimately established in a mine worked on this +system when a certain number of stopes full of completely broken +ore are available for entire withdrawal, and there is no further +accumulation. But, in any event, a considerable amount of broken +ore must be held in reserve. In one mine worked on this plan, with +which the writer has had experience, the annual production is about +250,000 tons and the broken ore represents an investment which, +at 5%, means an annual loss of interest amounting to 7 cents per +ton of ore treated. +</p> + +<p class="indent"> +<i>E</i>. A mine once started on the system is most difficult to +alter, owing to the lack of frequent winzes or passes. Especially +is this so if the only alternative is filling, for an alteration +to the system of filling coincident with breaking finds the mine +short of filling winzes. As the conditions of walls and ore often +alter with depth, change of system may be necessary and the situation +may become very embarrassing. +</p> + +<p class="indent"> +<i>F</i>. The restoping of the walls for lower-grade ore at a later +period is impossible, for the walls of the stope will be crushed, +or, if filled with waste, will usually crush when it is drawn off +to send to a lower stope. +</p> + +<p class="indent"> +The system has much to recommend it where conditions <a +name="page_118"><span class="page">Page 118</span></a> are favorable. +Like all other alternative methods of mining, it requires the most +careful study in the light of the special conditions involved. In many +mines it can be used for some stopes where not adaptable generally. +It often solves the problem of blind ore-bodies, for they can by +this means be frequently worked with an opening underneath only. +Thus the cost of driving a roadway overhead is avoided, which would +be required if timber or coincident filling were the alternatives. +In such cases ventilation can be managed without an opening above, +by so directing the current of air that it will rise through a +winze from the level below, flow along the stope and into the level +again at the further end of the stope through another winze. +</p> + +<table class="image" style="width: 510px;"> +<tr><td><a name="fig_40"> + <img src="images/fig_40.png" width="510" height="280" alt="Fig. 40"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +40.—Longitudinal section. Ore-pillar support in narrow +stopes.</td></tr> +</table> + +<p class="indent"> +<b>Support by Pillars of Ore.</b>—As a method of mining metals of +the sort under discussion, the use of ore-pillars except in conjunction +with some other means of support has no general application. To +use them without assistance implies walls sufficiently strong to +hold between pillars; to leave them permanently anywhere implies +that the ore abandoned would not repay the labor and the material of +a substitute. There are cases of large, very low-grade mines where +to abandon one-half the ore as pillars is more profitable than total +extraction, but the margin of payability in such ore must be very, +very narrow. Unpayable spots are always left as pillars, for obvious +reasons. <a name="page_119"><span class="page">Page 119</span></a> +Permanent ore-pillars as an adjunct to other methods of support +are in use. Such are the rib-pillars in the Alaska Treadwell, the +form of which is indicated by the upward extension of the pillars +adjacent to the winzes, shown in Figure 37. Always a careful balance +must be cast as to the value of the ore left, and as to the cost +of a substitute, because every ore-pillar can be removed at some +outlay. Temporary pillars are not unusual, particularly to protect +roadways and shafts. They are, when left for these purposes, removed +ultimately, usually by beginning at the farther end and working +back to the final exit. +</p> + +<table class="image" style="width: 516px;"> +<tr><td><a name="fig_41"> + <img src="images/fig_41.png" width="516" height="208" alt="Fig. 41"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +41.—Horizontal plan at levels of Broken Hill. Method of +alternate stopes and ore-pillars.</td></tr> +</table> + +<table class="image" style="width: 511px;"> +<tr><td><a name="fig_42"> + <img src="images/fig_42.png" width="511" height="245" alt="Fig. 42"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +42.—Longitudinal section of Figure 41.</td></tr> +</table> + +<p class="indent"> +A form of temporary ore-pillars in very wide deposits is made use of +in conjunction with both filling and timbering (Figs. 37, 39, 40). In +the use of temporary pillars for ore-bodies <a name="page_120"><span +class="page">Page 120</span></a> 100 to 250 feet wide at Broken +Hill, stopes are carried up at right angles to the strike, each +fifty feet wide and clear across the ore-body (Figs. 41 and 42). +A solid pillar of the same width is left in the first instance +between adjacent stopes, and the initial series of stopes are walled +with one square-set on the sides as the stope is broken upward. The +room between these two lines of sets is filled with waste alternating +with ore-breaking in the usual filling method. When the ore from the +first group of alternate stopes (<i>ABC</i>, Fig. 42) is completely +removed, the pillars are stoped out and replaced with waste. The +square-sets of the first set of stopes thus become the boundaries +of the second set. Entry and ventilation are obtained through these +<a name="page_121"><span class="page">Page 121</span></a> lines +of square-sets, and the ore is passed out of the stopes through +them. +</p> + +<table class="image" style="width: 412px;"> +<tr><td><a name="fig_43"> + <img src="images/fig_43.png" width="412" height="532" alt="Fig. 43"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +43.—Cross-section of stull support with waste +reënforcement.</td></tr> +</table> + +<p class="indent"> +<b>Artificial Pillars.</b>—This system also implies a roof +so strong as not to demand continuous support. Artificial pillars +are built in many different ways. The method most current in fairly +narrow deposits is to reënforce stulls by packing waste above +them (Figs. 43 and 44). Not only is it thus possible to economize +in stulls by using the waste which accumulates underground, but +the principle applies also to cases where the stulls alone are not +sufficient support, and yet where complete filling or square-setting +is unnecessary. When the conditions are propitious for this method, it +has the comparative advantage over timber systems of saving timber, +and over filling systems of saving imported filling. Moreover, +these constructions being pillar-shaped (Fig. 44), the intervals +between them provide outlets for broken ore, and specially built +passes are unnecessary. The method has two disadvantages as against +the square-set or filling process, in that more staging must be +provided from which to work, and in stopes over six feet the erection +of machine-drill columns is tedious and costly in time and wages. +</p> + +<table class="image" style="width: 469px;"> +<tr><td><a name="fig_44"> + <img src="images/fig_44.png" width="469" height="267" alt="Fig. 44"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +44.—Longitudinal section of stull and waste pillars.</td></tr> +</table> + +<p class="indent"> +In wide deposits of markedly flat, irregular ore-bodies, where a +definite system is difficult and where timber is expensive, cribs +of cord-wood or logs filled with waste after the order shown in <a +name="page_122"><span class="page">Page 122</span></a> Figure 31, +often make fairly sound pillars. They will not last indefinitely +and are best adapted to the temporary support of the ore-roof pending +filling. The increased difficulty in setting up machine drills +in such stopes adds to the breaking costs,—often enough to +warrant another method of support. +</p> + +<table class="image" style="width: 513px;"> +<tr><td><a name="fig_45"> + <img src="images/fig_45.png" width="513" height="541" alt="Fig. 45"> + </a></td></tr> +<tr><td class="caption"><span class="sc">Fig.</span> +45.—Sublevel caving system.</td></tr> +</table> + +<p class="indent"> +<b>Caving Systems.</b>—This method, with variations, has been +applied to large iron deposits, to the Kimberley diamond mines, +to some copper mines, but in general it has little application +to the metal mines under consideration, as few ore-bodies are of +sufficiently large horizontal area. The system is dependent upon +a large area of loose or "heavy" ground pressing directly on the +ore with weight, such that if the ore be cut into pillars, <a +name="page_123"><span class="page">Page 123</span></a> these will +crush. The details of the system vary, but in general the <i>modus +operandi</i> is to prepare roadways through the ore, and from the +roadways to put rises, from which sublevels are driven close under +the floating mass of waste and ore,—sometimes called the +"matte" (Fig. 45). The pillars between these sublevels are then +cut away until the weight above crushes them down. When all the +crushed ore which can be safely reached is extracted, retreat is +made and another series of subopenings is then driven close under +the "matte." The pillar is reduced until it crushes and the operation +is repeated. Eventually the bottom strata of the "matte" become +largely ore, and a sort of equilibrium is reached when there is +not much loss in this direction. "Top slicing" is a variation of +the above method by carrying a horizontal stope from the rises +immediately under the matte, supporting the floating material with +timber. At Kimberley the system is varied in that galleries are +run out to the edge of the diamond-iferous area and enlarged until +the pillar between crushes. +</p> + +<p class="indent"> +In the caving methods, between 40 and 50% of the ore is removed +by the preliminary openings, and as they are all headings of some +sort, the average cost per ton of this particular ore is higher +than by ordinary stoping methods. On the other hand, the remaining +50 to 60% of the ore costs nothing to break, and the average cost +is often remarkably low. As said, the system implies bodies of large +horizontal area. They must start near enough to the surface that +the whole superincumbent mass may cave and give crushing weight, +or the immediately overhanging roof must easily cave. All of these +are conditions not often met with in mines of the character under +review. +</p> + +<h2><a name="page_124"><span class="page">Page 124</span></a> +CHAPTER XII.</h2> + +<p class="center"> +<span class="sc">Mechanical Equipment.</span> +</p> + +<table class="summary"><tr><td class="summary"> +CONDITIONS BEARING ON MINE EQUIPMENT; WINDING APPLIANCES; HAULAGE +EQUIPMENT IN SHAFTS; LATERAL UNDERGROUND TRANSPORT; TRANSPORT IN +STOPES. +</td></tr></table> + +<p class="indent"> +There is no type of mechanical engineering which presents such +complexities in determination of the best equipment as does that of +mining. Not only does the economic side dominate over pure mechanics, +but machines must be installed and operated under difficulties which +arise from the most exceptional and conflicting conditions, none of +which can be entirely satisfied. Compromise between capital outlay, +operating efficiency, and conflicting demands is the key-note of +the work. +</p> + +<p class="indent"> +These compromises are brought about by influences which lie outside +the questions of mechanics of individual machines, and are mainly +as follows:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Continuous change in horizon of + operations.</td></tr> +<tr><td>2.</td><td>Uncertain life of the enterprise.</td></tr> +<tr><td>3.</td><td>Care and preservation of human life.</td></tr> +<tr><td>4.</td><td>Unequal adaptability of power transmission + mediums.</td></tr> +<tr><td>5.</td><td>Origin of power.</td></tr> +</table> + +<p class="indent"> +<i>First.</i>—The depth to be served and the volume of ore and +water to be handled, are not only unknown at the initial equipment, +but they are bound to change continuously in quantity, location, +and horizon with the extension of the workings. +</p> + +<p class="indent"> +<i>Second.</i>—From the mine manager's point of view, which +must embrace that of the mechanical engineer, further difficulty +presents itself because the life of the enterprise is usually unknown, +and therefore a manifest necessity arises for an economic balance +of capital outlay and of operating efficiency commensurate with <a +name="page_125"><span class="page">Page 125</span></a> the prospects +of the mine. Moreover, the initial capital is often limited, and +makeshifts for this reason alone must be provided. In net result, +no mineral deposit of speculative ultimate volume of ore warrants +an initial equipment of the sort that will meet every eventuality, +or of the kind that will give even the maximum efficiency which +a free choice of mining machinery could obtain. +</p> + +<p class="indent"> +<i>Third.</i>—In the design and selection of mining machines, +the safety of human life, the preservation of the health of workmen +under conditions of limited space and ventilation, together with +reliability and convenience in installing and working large mechanical +tools, all dominate mechanical efficiency. For example, compressed-air +transmission of power best meets the requirements of drilling, yet +the mechanical losses in the generation, the transmission, and +the application of compressed air probably total, from first to +last, 70 to 85%. +</p> + +<p class="indent"> +<i>Fourth.</i>—All machines, except those for shaft haulage, +must be operated by power transmitted from the surface, as obviously +power generation underground is impossible. The conversion of power +into a transmission medium and its transmission are, at the outset, +bound to be the occasions of loss. Not only are the various forms +of transmission by steam, electricity, compressed air, or rods, of +different efficiency, but no one system lends itself to universal +or economical application to all kinds of mining machines. Therefore +it is not uncommon to find three or four different media of power +transmission employed on the same mine. To illustrate: from the +point of view of safety, reliability, control, and in most cases +economy as well, we may say that direct steam is the best motive +force for winding-engines; that for mechanical efficiency and +reliability, rods constitute the best media of power transmission +to pumps; that, considering ventilation and convenience, compressed +air affords the best medium for drills. Yet there are other conditions +as to character of the work, volume of water or ore, and the origin +of power which must in special instances modify each and every +one of these generalizations. For example, although pumping water +with compressed air is mechanically the most inefficient of <a +name="page_126"><span class="page">Page 126</span></a> devices, +it often becomes the most advantageous, because compressed air may +be of necessity laid on for other purposes, and the extra power +required to operate a small pump may be thus most cheaply provided. +</p> + +<p class="indent"> +<i>Fifth.</i>—Further limitations and modifications arise out +of the origin of power, for the sources of power have an intimate +bearing on the type of machine and media of transmission. This very +circumstance often compels giving away efficiency and convenience +in some machines to gain more in others. This is evident enough +if the principal origins of power generation be examined. They +are in the main as follows:— +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td><i>a</i>.</td><td>Water-power available at the mine.</td></tr> +<tr><td><i>b</i>.</td><td>Water-power available at a less distance + than three or four miles.</td></tr> +<tr><td><i>c</i>.</td><td>Water-power available some miles away, + thus necessitating electrical transmission (or purchased + electrical power).</td></tr> +<tr><td><i>d</i>.</td><td>Steam-power to be generated at the + mine.</td></tr> +<tr><td><i>e</i>.</td><td>Gas-power to be generated at the + mine.</td></tr> +</table> + +<p class="indent"> +<i>a</i>. With water-power at the mine, winding engines can be +operated by direct hydraulic application with a gain in economy +over direct steam, although with the sacrifice of control and +reliability. Rods for pumps can be driven directly with water, but +this superiority in working economy means, as discussed later, a +loss of flexibility and increased total outlay over other forms of +transmission to pumps. As compressed air must be transmitted for +drills, the compressor would be operated direct from water-wheels, +but with less control in regularity of pressure delivery. +</p> + +<p class="indent"> +<i>b</i>. With water-power a short distance from the mine, it would +normally be transmitted either by compressed air or by electricity. +Compressed-air transmission would better satisfy winding and drilling +requirements, but would show a great comparative loss in efficiency +over electricity when applied to pumping. Despite the latter drawback, +air transmission is a method growing in favor, especially in view +of the advance made in effecting compression by falling water. +</p> + +<p class="indent"> +<a name="page_127"><span class="page">Page 127</span></a> <i>c</i>. +In the situation of transmission too far for using compressed air, +there is no alternative but electricity. In these cases, direct +electric winding is done, but under such disadvantages that it +requires a comparatively very cheap power to take precedence over +a subsidiary steam plant for this purpose. Electric air-compressors +work under the material disadvantage of constant speed on a variable +load, but this installation is also a question of economics. The +pumping service is well performed by direct electrical pumps. +</p> + +<p class="indent"> +<i>d</i>. In this instance, winding and air-compression are well +accomplished by direct steam applications; but pumping is beset +with wholly undesirable alternatives, among which it is difficult +to choose. +</p> + +<p class="indent"> +<i>e</i>. With internal combustion engines, gasoline (petrol) motors +have more of a position in experimental than in systematic mining, +for their application to winding and pumping and drilling is fraught +with many losses. The engine must be under constant motion, and +that, too, with variable loads. Where power from producer gas is +used, there is a greater possibility of installing large equipments, +and it is generally applied to the winding and lesser units by +conversion into compressed air or electricity as an intermediate +stage. +</p> + +<p class="indent"> +One thing becomes certain from these examples cited, that the right +installation for any particular portion of the mine's equipment cannot +be determined without reference to all the others. The whole system +of power generation for surface work, as well as the transmission +underground, must be formulated with regard to furnishing the best +total result from all the complicated primary and secondary motors, +even at the sacrifice of some members. +</p> + +<p class="indent"> +Each mine is a unique problem, and while it would be easy to sketch +an ideal plant, there is no mine within the writer's knowledge +upon which the ideal would, under the many variable conditions, +be the most economical of installation or the most efficient of +operation. The dominant feature of the task is an endeavor to find +a compromise between efficiency and capital outlay. The result is +a series of choices <a name="page_128"><span class="page">Page +128</span></a> between unsatisfying alternatives, a number of which +are usually found to have been wrong upon further extension of +the mine in depth. +</p> + +<p class="indent"> +In a general way, it may be stated that where power is generated +on the mine, economy in labor of handling fuel, driving engines, +generation and condensing steam where steam is used, demand a +consolidated power plant for the whole mine equipment. The principal +motors should be driven direct by steam or gas, with power distribution +by electricity to all outlying surface motors and sometimes to +underground motors, and also to some underground motors by compressed +air. +</p> + +<p class="indent"> +Much progress has been made in the past few years in the perfection +of larger mining tools. Inherently many of our devices are of a +wasteful character, not only on account of the need of special +forms of transmission, but because they are required to operate +under greatly varying loads. As an outcome of transmission losses +and of providing capacity to cope with heavy peak loads, their +efficiency on the basis of actual foot-pounds of work accomplished +is very low. +</p> + +<p class="indent"> +The adoption of electric transmission in mine work, while in certain +phases beneficial, has not decreased the perplexity which arises +from many added alternatives, none of which are as yet a complete or +desirable answer to any mine problem. When a satisfactory electric +drill is invented, and a method is evolved of applying electricity +to winding-engines that will not involve such abnormal losses due +to high peak load then we will have a solution to our most difficult +mechanical problems, and electricity will deserve the universal +blessing which it has received in other branches of mechanical +engineering. +</p> + +<p class="indent"> +It is not intended to discuss mine equipment problems from the +machinery standpoint,—there are thousands of different +devices,—but from the point of view of the mine administrator +who finds in the manufactory the various machines which are applicable, +and whose work then becomes that of choosing, arranging, and operating +these tools. +</p> + +<p class="indent"> +<a name="page_129"><span class="page">Page 129</span></a> The principal +mechanical questions of a mine may be examined under the following +heads:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Shaft haulage.</td></tr> +<tr><td>2.</td><td>Lateral underground transport.</td></tr> +<tr><td>3.</td><td>Drainage.</td></tr> +<tr><td>4.</td><td>Rock drilling.</td></tr> +<tr><td>5.</td><td>Workshops.</td></tr> +<tr><td>6.</td><td>Improvements in equipment.</td></tr> +</table> + +<h3>SHAFT HAULAGE.</h3> + +<p class="indent"> +<b>Winding Appliances.</b>—No device has yet been found to +displace the single load pulled up the shaft by winding a rope on +a drum. Of driving mechanisms for drum motors the alternatives are +the steam-engine, the electrical motor, and infrequently water-power +or gas engines. +</p> + +<p class="indent"> +All these have to cope with one condition which, on the basis of +work accomplished, gives them a very low mechanical efficiency. +This difficulty is that the load is intermittent, and it must be +started and accelerated at the point of maximum weight, and from +that moment the power required diminishes to less than nothing +at the end of the haul. A large number of devices are in use to +equalize partially the inequalities of the load at different stages +of the lift. The main lines of progress in this direction have +been:— +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td class="topleft"><i>a</i>.</td> + <td>The handling of two cages or skips with one engine or + motor, the descending skip partially balancing the + ascending one.</td></tr> +<tr><td class="topleft"><i>b</i>.</td> + <td>The use of tail-ropes or balance weights to compensate + the increasing weight of the descending rope.</td></tr> +<tr><td class="topleft"><i>c</i>.</td> + <td>The use of skips instead of cages, thus permitting of + a greater percentage of paying load.</td></tr> +<tr><td class="topleft"><i>d</i>.</td> + <td>The direct coupling of the motor to the drum shaft.</td></tr> +<tr><td class="topleft"><i>e</i>.</td> + <td>The cone-shaped construction of drums,—this latter + being now largely displaced by the use of the + tail-rope.</td></tr> +</table> + +<p class="indent"> +The first and third of these are absolutely essential for anything like +economy and speed; the others are refinements <a name="page_130"><span +class="page">Page 130</span></a> depending on the work to be +accomplished and the capital available. +</p> + +<p class="indent"> +Steam winding-engines require large cylinders to start the load, +but when once started the requisite power is much reduced and the +load is too small for steam economy. The throttling of the engine +for controlling speed and reversing the engine at periodic stoppages +militates against the maximum expansion and condensation of the +steam and further increases the steam consumption. In result, the +best of direct compound condensing engines consume from 60 to 100 +pounds of steam per horse-power hour, against a possible efficiency +of such an engine working under constant load of less than 16 pounds +of steam per horse-power hour. +</p> + +<p class="indent"> +It is only within very recent years that electrical motors have +been applied to winding. Even yet, all things considered, this +application is of doubtful value except in localities of extremely +cheap electrical power. The constant speed of alternating current +motors at once places them at a disadvantage for this work of high +peak and intermittent loads. While continuous-current motors can +be made to partially overcome this drawback, such a current, where +power is purchased or transmitted a long distance, is available +only by conversion, which further increases the losses. However, +schemes of electrical winding are in course of development which +bid fair, by a sort of storage of power in heavy fly-wheels or +storage batteries after the peak load, to reduce the total power +consumption; but the very high first cost so far prevents their +very general adoption for metal mining. +</p> + +<p class="indent"> +Winding-engines driven by direct water- or gas-power are of too rare +application to warrant much discussion. Gasoline driven hoists have a +distinct place in prospecting and early-stage mining, especially in +desert countries where transport and fuel conditions are onerous, +for both the machines and their fuel are easy of transport. As direct +gas-engines entail constant motion of the engine at the power demand +of the peak load, they are hopeless in mechanical efficiency. +</p> + +<p class="indent"> +Like all other motors in mining, the size and arrangement <a +name="page_131"><span class="page">Page 131</span></a> of the motor +and drum are dependent upon the duty which they will be called +upon to perform. This is primarily dependent upon the depth to +be hoisted from, the volume of the ore, and the size of the load. +For shallow depths and tonnages up to, say, 200 tons daily, geared +engines have a place on account of their low capital cost. Where +great rope speed is not essential they are fully as economical as +direct-coupled engines. With great depths and greater capacities, +speed becomes a momentous factor, and direct-coupled engines are +necessary. Where the depth exceeds 3,000 feet, another element +enters which has given rise to much debate and experiment; that +is, the great increase of starting load due to the increased length +and size of ropes and the drum space required to hold it. So far +the most advantageous device seems to be the Whiting hoist, a +combination of double drums and tail rope. +</p> + +<p class="indent"> +On mines worked from near the surface, where depth is gained by +the gradual exhaustion of the ore, the only prudent course is to +put in a new hoist periodically, when the demand for increased +winding speed and power warrants. The lack of economy in winding +machines is greatly augmented if they are much over-sized for the +duty. An engine installed to handle a given tonnage to a depth of +3,000 feet will have operated with more loss during the years the +mine is progressing from the surface to that depth than several +intermediate-sized engines would have cost. On most mines the +uncertainty of extension in depth would hardly warrant such a +preliminary equipment. More mines are equipped with over-sized +than with under-sized engines. For shafts on going metal mines +where the future is speculative, an engine will suffice whose size +provides for an extension in depth of 1,000 feet beyond that reached +at the time of its installation. The cost of the engine will depend +more largely upon the winding speed desired than upon any other +one factor. The proper speed to be arranged is obviously dependent +upon the depth of the haulage, for it is useless to have an engine +able to wind 3,000 feet a minute on a shaft 500 feet deep, since it +could never <a name="page_132"><span class="page">Page 132</span></a> +even get under way; and besides, the relative operating loss, as +said, would be enormous. +</p> + +<p class="indent"> +<b>Haulage Equipment in the Shaft.</b>—Originally, material +was hoisted through shafts in buckets. Then came the cage for +transporting mine cars, and in more recent years the "skip" has +been developed. The aggrandized bucket or "kibble" of the Cornishman +has practically disappeared, but the cage still remains in many +mines. The advantages of the skip over the cage are many. Some +of them are:— +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td class="topleft"><i>a</i>.</td> + <td>It permits 25 to 40% greater load of material in + proportion to the dead weight of the vehicle.</td></tr> +<tr><td class="topleft"><i>b</i>.</td> + <td>The load can be confined within a smaller horizontal + space, thus the area of the shaft need not be so great + for large tonnages.</td></tr> +<tr><td class="topleft"><i>c</i>.</td> + <td>Loading and discharging are more rapid, and the latter + is automatic, thus permitting more trips per hour and + requiring less labor. +<tr><td class="topleft"><i>d</i>.</td> + <td>Skips must be loaded from bins underground, and by + providing in the bins storage capacity, shaft haulage is + rendered independent of the lateral transport in the + mine, and there are no delays to the engine awaiting + loads. The result is that ore-winding can be concentrated + into fewer hours, and indirect economies in labor + and power are thus effected.</td></tr> +<tr><td class="topleft"><i>e</i>.</td> + <td>Skips save the time of the men engaged in the lateral + haulage, as they have no delay waiting for the winding + engine.</td></tr> +</table> + +<p class="indent"> +Loads equivalent to those from skips are obtained in some mines +by double-decked cages; but, aside from waste weight of the cage, +this arrangement necessitates either stopping the engine to load the +lower deck, or a double-deck loading station. Double-deck loading +stations are as costly to install and more expensive to work than +skip-loading station ore-bins. Cages are also constructed large +enough to take as many as four trucks on one deck. This entails a +shaft compartment double the size required for skips of the same +capacity, and thus enormously increases shaft cost without gaining +anything. +</p> + +<p class="indent"> +<a name="page_133"><span class="page">Page 133</span></a> Altogether +the advantages of the skip are so certain and so important that +it is difficult to see the justification for the cage under but +a few conditions. These conditions are those which surround mines +of small output where rapidity of haulage is no object, where the +cost of station-bins can thus be evaded, and the convenience of +the cage for the men can still be preserved. The easy change of +the skip to the cage for hauling men removes the last objection +on larger mines. There occurs also the situation in which ore is +broken under contract at so much per truck, and where it is desirable +to inspect the contents of the truck when discharging it, but even +this objection to the skip can be obviated by contracting on a +cubic-foot basis. +</p> + +<p class="indent"> +Skips are constructed to carry loads of from two to seven tons, +the general tendency being toward larger loads every year. One +of the most feasible lines of improvement in winding is in the +direction of larger loads and less speed, for in this way the sum +total of dead weight of the vehicle and rope to the tonnage of +ore hauled will be decreased, and the efficiency of the engine +will be increased by a less high peak demand, because of this less +proportion of dead weight and the less need of high acceleration. +</p> + +<h3>LATERAL UNDERGROUND TRANSPORT.</h3> + +<p class="indent"> +Inasmuch as the majority of metal mines dip at considerable angles, +the useful life of a roadway in a metal mine is very short because +particular horizons of ore are soon exhausted. Therefore any method +of transport has to be calculated upon a very quick redemption of +the capital laid out. Furthermore, a roadway is limited in its +daily traffic to the product of the stopes which it serves. +</p> + +<p class="indent"> +<b>Men and Animals.</b>—Some means of transport must be provided, +and the basic equipment is light tracks with push-cars, in capacity +from half a ton to a ton. The latter load is, however, too heavy +to be pushed by one man. As but one car can be pushed at a time, +hand-trucking is both slow and expensive. At average American or +Australian wages, the cost works out <a name="page_134"><span +class="page">Page 134</span></a> between 25 and 35 cents a ton +per mile. An improvement of growing import where hand-trucking is +necessary is the overhead mono-rail instead of the track. +</p> + +<p class="indent"> +If the supply to any particular roadway is such as to fully employ +horses or mules, the number of cars per trip can be increased up +to seven or eight. In this case the expense, including wages of +the men and wear, tear, and care of mules, will work out roughly +at from 7 to 10 cents per ton mile. Manifestly, if the ore-supply +to a particular roadway is insufficient to keep a mule busy, the +economy soon runs off. +</p> + +<p class="indent"> +<b>Mechanical Haulage.</b>—Mechanical haulage is seldom applicable +to metal mines, for most metal deposits dip at considerable angles, +and therefore, unlike most coal-mines, the horizon of haulage must +frequently change, and there are no main arteries along which haulage +continues through the life of the mine. Any mechanical system entails +a good deal of expense for installation, and the useful life of +any particular roadway, as above said, is very short. Moreover, +the crooked roadways of most metal mines present difficulties of +negotiation not to be overlooked. In order to use such systems it +is necessary to condense the haulage to as few roadways as possible. +Where the tonnage on one level is not sufficient to warrant other +than men or animals, it sometimes pays (if the dip is steep enough) +to dump everything through winzes from one to two levels to a main +road below where mechanical equipment can be advantageously provided. +The cost of shaft-winding the extra depth is inconsiderable compared +to other factors, for the extra vertical distance of haulage can +be done at a cost of one or two cents per ton mile. Moreover, from +such an arrangement follows the concentration of shaft-bins, and of +shaft labor, and winding is accomplished without so much shifting +as to horizon, all of which economies equalize the extra distance +of the lift. +</p> + +<p class="indent"> +There are three principal methods of mechanical transport in use:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Cable-ways.</td></tr> +<tr><td>2.</td><td>Compressed-air locomotives.</td></tr> +<tr><td>3.</td><td>Electrical haulage.</td></tr> +</table> + +<p class="indent"> +<a name="page_135"><span class="page">Page 135</span></a> Cable-ways +or endless ropes are expensive to install, and to work to the best +advantage require double tracks and fairly straight roads. While +they are economical in operation and work with little danger to +operatives, the limitations mentioned preclude them from adoption +in metal mines, except in very special circumstances such as main +crosscuts or adit tunnels, where the haulage is straight and +concentrated from many sources of supply. +</p> + +<p class="indent"> +Compressed-air locomotives are somewhat heavy and cumbersome, and +therefore require well-built tracks with heavy rails, but they +have very great advantages for metal mine work. They need but a +single track and are of low initial cost where compressed air is +already a requirement of the mine. No subsidiary line equipment is +needed, and thus they are free to traverse any road in the mine and +can be readily shifted from one level to another. Their mechanical +efficiency is not so low in the long run as might appear from the +low efficiency of pneumatic machines generally, for by storage of +compressed air at the charging station a more even rate of energy +consumption is possible than in the constant cable and electrical +power supply which must be equal to the maximum demand, while the +air-plant consumes but the average demand. +</p> + +<p class="indent"> +Electrical haulage has the advantage of a much more compact locomotive +and the drawback of more expensive track equipment, due to the +necessity of transmission wire, etc. It has the further disadvantages +of uselessness outside the equipped haulage way and of the dangers +of the live wire in low and often wet tunnels. +</p> + +<p class="indent"> +In general, compressed-air locomotives possess many attractions +for metal mine work, where air is in use in any event and where +any mechanical system is at all justified. Any of the mechanical +systems where tonnage is sufficient in quantity to justify their +employment will handle material for from 1.5 to 4 cents per ton +mile. +</p> + +<p class="indent"> +<b>Tracks.</b>—Tracks for hand, mule, or rope haulage are +usually built with from 12- to 16-pound rails, but when compressed-air +or electrical locomotives are to be used, less than 24-pound rails +<a name="page_136"><span class="page">Page 136</span></a> are +impossible. As to tracks in general, it may be said that careful +laying out with even grades and gentle curves repays itself many +times over in their subsequent operation. Further care in repair +and lubrication of cars will often make a difference of 75% in +the track resistance. +</p> + +<p class="indent"> +<b>Transport in Stopes.</b>—Owing to the even shorter life +of individual stopes than levels, the actual transport of ore or +waste in them is often a function of the aboriginal shovel plus +gravity. As shoveling is the most costly system of transport known, +any means of stoping that decreases the need for it has merit. +Shrinkage-stoping eliminates it altogether. In the other methods, +gravity helps in proportion to the steepness of the dip. When the +underlie becomes too flat for the ore to "run," transport can sometimes +be helped by pitching the ore-passes at a steeper angle than the +dip (Fig. 36). In some cases of flat deposits, crosscuts into the +walls, or even levels under the ore-body, are justifiable. The +more numerous the ore-passes, the less the lateral shoveling, but +as passes cost money for construction and for repair, there is +a nice economic balance in their frequency. +</p> + +<p class="indent"> +Mechanical haulage in stopes has been tried and finds a field under +some conditions. In dips under 25° and possessing fairly sound +hanging-wall, where long-wall or flat-back cuts are employed, temporary +tracks can often be laid in the stopes and the ore run in cars to +the main passes. In such cases, the tracks are pushed up close +to the face after each cut. Further self-acting inclines to lower +cars to the levels can sometimes be installed to advantage. This +arrangement also permits greater intervals between levels and less +number of ore-passes. For dips between 25° and 50° where the +mine is worked without stope support or with occasional pillars, a +very useful contrivance is the sheet-iron trough—about eighteen +inches wide and six inches deep—made in sections ten or twelve +feet long and readily bolted together. In dips 35° to 50° +this trough, laid on the foot-wall, gives a sufficiently smooth +surface for the ore to run upon. When the dip is flat, the trough, +if hung from plugs in the hanging-wall, may be swung backward and +forward. The use of this "bumping-trough" saves much shoveling. For +handling <a name="page_137"><span class="page">Page 137</span></a> +filling or ore in flat runs it deserves wider adoption. It is, of +course, inapplicable in passes as a "bumping-trough," but can be +fixed to give smooth surface. In flat mines it permits a wider +interval between levels and therefore saves development work. The +life of this contrivance is short when used in open stopes, owing +to the dangers of bombardment from blasting. +</p> + +<p class="indent"> +In dips steeper than 50° much of the shoveling into passes can +be saved by rill-stoping, as described on page 100. Where flat-backed +stopes are used in wide ore-bodies with filling, temporary tracks +laid on the filling to the ore-passes are useful, for they permit +wider intervals between passes. +</p> + +<p class="indent"> +In that underground engineer's paradise, the Witwatersrand, where +the stopes require neither timber nor filling, the long, moderately +pitched openings lend themselves particularly to the swinging iron +troughs, and even endless wire ropes have been found advantageous +in certain cases. +</p> + +<p class="indent"> +Where the roof is heavy and close support is required, and where +the deposits are very irregular in shape and dip, there is little +hope of mechanical assistance in stope transport. +</p> + +<h2><a name="page_138"><span class="page">Page 138</span></a> +CHAPTER XIII.</h2> + +<p class="center"> +<span class="sc">Mechanical Equipment.</span> (<i>Continued</i>). +</p> + +<table class="summary"><tr><td class="summary"> +DRAINAGE: CONTROLLING FACTORS; VOLUME AND HEAD OF WATER; FLEXIBILITY; +RELIABILITY; POWER CONDITIONS; MECHANICAL EFFICIENCY; CAPITAL OUTLAY. +SYSTEMS OF DRAINAGE,—STEAM PUMPS, COMPRESSED-AIR PUMPS, ELECTRICAL +PUMPS, ROD-DRIVEN PUMPS, BAILING; COMPARATIVE VALUE OF VARIOUS +SYSTEMS. +</td></tr></table> + +<p class="indent"> +With the exception of drainage tunnels—more fully described +in Chapter VIII—all drainage must be mechanical. As the bulk +of mine water usually lies near the surface, saving in pumping can +sometimes be effected by leaving a complete pillar of ore under +some of the upper levels. In many deposits, however, the ore has +too many channels to render this of much avail. +</p> + +<p class="indent"> +There are six factors which enter into a determination of mechanical +drainage systems for metal mines:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Volume and head of water.</td></tr> +<tr><td>2.</td><td>Flexibility to fluctuation in volume and + head.</td></tr> +<tr><td>3.</td><td>Reliability.</td></tr> +<tr><td>4.</td><td>Capital cost.</td></tr> +<tr><td>5.</td><td>The general power conditions.</td></tr> +<tr><td>6.</td><td>Mechanical efficiency.</td></tr> +</table> + +<p class="indent"> +In the drainage appliances, more than in any other feature of the +equipment, must mechanical efficiency be subordinated to the other +issues. +</p> + +<p class="indent"> +<b>Flexibility.</b>—Flexibility in plant is necessary because +volume and head of water are fluctuating factors. In wet regions the +volume of water usually increases for a certain distance with the +extension of openings in depth. In dry climates it generally decreases +with the downward extension of the workings <a name="page_139"><span +class="page">Page 139</span></a> after a certain depth. Moreover, +as depth progresses, the water follows the openings more or less +and must be pumped against an ever greater head. In most cases +the volume varies with the seasons. What increase will occur, from +what horizon it must be lifted, and what the fluctuations in volume +are likely to be, are all unknown at the time of installation. If a +pumping system were to be laid out for a new mine, which would +peradventure meet every possible contingency, the capital outlay would +be enormous, and the operating efficiency would be very low during +the long period in which it would be working below its capacity. The +question of flexibility does not arise so prominently in coal-mines, +for the more or less flat deposits give a fixed factor of depth. +The flow is also more steady, and the volume can be in a measure +approximated from general experience. +</p> + +<p class="indent"> +<b>Reliability.</b>—The factor of reliability was at one time +of more importance than in these days of high-class manufacture +of many different pumping systems. Practically speaking, the only +insurance from flooding in any event lies in the provision of a +relief system of some sort,—duplicate pumps, or the simplest +and most usual thing, bailing tanks. Only Cornish and compressed-air +pumps will work with any security when drowned, and electrical +pumps are easily ruined. +</p> + +<p class="indent"> +<b>General Power Conditions.</b>—The question of pumping +installation is much dependent upon the power installation and other +power requirements of the mine. For instance, where electrical power +is purchased or generated by water-power, then electrical pumps have +every advantage. Or where a large number of subsidiary motors can be +economically driven from one central steam- or gas-driven electrical +generation plant, they again have a strong call,—especially +if the amount of water to be handled is moderate. Where the water +is of limited volume and compressed-air plant a necessity for the +mine, then air-driven pumps may be the most advantageous, etc. +</p> + +<p class="indent"> +<b>Mechanical Efficiency.</b>—The mechanical efficiency of +drainage machinery is very largely a question of method of power +application. The actual pump can be built to almost the same efficiency +for any power application, and with the exception of <a +name="page_140"><span class="page">Page 140</span></a> the limited +field of bailing with tanks, mechanical drainage is a matter of +pumps. All pumps must be set below their load, barring a few possible +feet of suction lift, and they are therefore perforce underground, +and in consequence all power must be transmitted from the surface. +Transmission itself means loss of power varying from 10 to 60%, +depending upon the medium used. It is therefore the choice of +transmission medium that largely governs the mechanical efficiency. +</p> + +<p class="indent"> +<b>Systems of Drainage.</b>—The ideal pumping system for +metal mines would be one which could be built in units and could +be expanded or contracted unit by unit with the fluctuation in +volume; which could also be easily moved to meet the differences of +lifts; and in which each independent unit could be of the highest +mechanical efficiency and would require but little space for erection. +Such an ideal is unobtainable among any of the appliances with +which the writer is familiar. +</p> + +<p class="indent"> +The wide variations in the origin of power, in the form of transmission, +and in the method of final application, and the many combinations +of these factors, meet the demands for flexibility, efficiency, +capital cost, and reliability in various degrees depending upon +the environment of the mine. Power nowadays is generated primarily +with steam, water, and gas. These origins admit the transmission of +power to the pumps by direct steam, compressed air, electricity, +rods, or hydraulic columns. +</p> + +<p class="indent"> +<b>Direct Steam-pumps.</b>—Direct steam has the disadvantage +of radiated heat in the workings, of loss by the radiation, and, +worse still, of the impracticability of placing and operating a +highly efficient steam-engine underground. It is all but impossible +to derive benefit from the vacuum, as any form of surface condenser +here is impossible, and there can be no return of the hot soft +water to the boilers. +</p> + +<p class="indent"> +Steam-pumps fall into two classes, rotary and direct-acting; the former +have the great advantage of permitting the use of steam expansively +and affording some field for effective use of condensation, but +they are more costly, require much room, and are not fool-proof. +The direct-acting pumps have all the advantage of compactness and +the disadvantage of being the most <a name="page_141"><span +class="page">Page 141</span></a> inefficient of pumping machines +used in mining. Taking the steam consumption of a good surface +steam plant at 15 pounds per horse-power hour, the efficiency of +rotary pumps with well-insulated pipes is probably not over 50%, +and of direct-acting pumps from 40% down to 10%. +</p> + +<p class="indent"> +The advantage of all steam-pumps lies in the low capital +outlay,—hence their convenient application to experimental +mining and temporary pumping requirements. For final equipment they +afford a great deal of flexibility, for if properly constructed +they can be, with slight alteration, moved from one horizon to +another without loss of relative efficiency. Thus the system can +be rearranged for an increased volume of water, by decreasing the +lift and increasing the number of pumps from different horizons. +</p> + +<p class="indent"> +<b>Compressed-air Pumps.</b>—Compressed-air transmission has +an application similar to direct steam, but it is of still lower +mechanical efficiency, because of the great loss in compression. +It has the superiority of not heating the workings, and there is +no difficulty as to the disposal of the exhaust, as with steam. +Moreover, such pumps will work when drowned. Compressed air has a +distinct place for minor pumping units, especially those removed +from the shaft, for they can be run as an adjunct to the air-drill +system of the mine, and by this arrangement much capital outlay +may be saved. The cost of the extra power consumed by such an +arrangement is less than the average cost of compressed-air power, +because many of the compressor charges have to be paid anyway. When +compressed air is water-generated, they have a field for permanent +installations. The efficiency of even rotary air-driven pumps, +based on power delivered into a good compressor, is probably not +over 25%. +</p> + +<p class="indent"> +<b>Electrical Pumps.</b>—Electrical pumps have somewhat less +flexibility than steam- or air-driven apparatus, in that the speed +of the pumps can be varied only within small limits. They have the +same great advantage in the easy reorganization of the system to +altered conditions of water-flow. Electricity, when steam-generated, +has the handicap of the losses of two conversions, the actual pump +efficiency being about 60% in well-constructed <a name="page_142"><span +class="page">Page 142</span></a> plants; the efficiency is therefore +greater than direct steam or compressed air. Where the mine is +operated with water-power, purchased electric current, or where +there is an installation of electrical generating plant by steam or +gas for other purposes, electrically driven pumps take precedence +over all others on account of their combined moderate capital outlay, +great flexibility, and reasonable efficiency. +</p> + +<p class="indent"> +In late years, direct-coupled, electric-driven centrifugal pumps +have entered the mining field, but their efficiency, despite makers' +claims, is low. While they show comparatively good results on low +lifts the slip increases with the lift. In heads over 200 feet +their efficiency is probably not 30% of the power delivered to the +electrical generator. Their chief attractions are small capital +cost and the compact size which admits of easy installation. +</p> + +<p class="indent"> +<b>Rod-driven Pumps.</b>—Pumps of the Cornish type in vertical +shafts, if operated to full load and if driven by modern engines, +have an efficiency much higher than any other sort of installation, +and records of 85 to 90% are not unusual. The highest efficiency +in these pumps yet obtained has been by driving the pump with rope +transmission from a high-speed triple expansion engine, and in +this plant an actual consumption of only 17 pounds of steam per +horse-power hour for actual water lifted has been accomplished. +</p> + +<p class="indent"> +To provide, however, for increase of flow and change of horizon, +rod-driven pumps must be so overpowered at the earlier stage of +the mine that they operate with great loss. Of all pumping systems +they are the most expensive to provide. They have no place in crooked +openings and only work in inclines with many disadvantages. +</p> + +<p class="indent"> +In general their lack of flexibility is fast putting them out of +the metal miner's purview. Where the pumping depth and volume of +water are approximately known, as is often the case in coal mines, +this, the father of all pumps, still holds its own. +</p> + +<p class="indent"> +<b>Hydraulic Pumps.</b>—Hydraulic pumps, in which a column +of water is used as the transmission fluid from a surface pump +to a corresponding pump underground has had some adoption in <a +name="page_143"><span class="page">Page 143</span></a> coal mines, +but little in metal mines. They have a certain amount of flexibility +but low efficiency, and are not likely to have much field against +electrical pumps. +</p> + +<p class="indent"> +<b>Bailing.</b>—Bailing deserves to be mentioned among drainage +methods, for under certain conditions it is a most useful system, and +at all times a mine should be equipped with tanks against accident +to the pumps. Where the amount of water is limited,—up to, +say, 50,000 gallons daily,—and where the ore output of the +mine permits the use of the winding-engine for part of the time +on water haulage, there is in the method an almost total saving of +capital outlay. Inasmuch as the winding-engine, even when the ore +haulage is finished for the day, must be under steam for handling +men in emergencies, and as the labor of stokers, engine-drivers, +shaft-men, etc., is therefore necessary, the cost of power consumed +by bailing is not great, despite the low efficiency of winding-engines. +</p> + +<p class="indent"> +<b>Comparison of Various Systems.</b>—If it is assumed that +flexibility, reliability, mechanical efficiency, and capital cost +can each be divided into four figures of relative +importance,—<i>A</i>, <i>B</i>, <i>C</i>, and <i>D</i>, with +<i>A</i> representing the most desirable result,—it is possible +to indicate roughly the comparative values of various pumping systems. +It is not pretended that the four degrees are of equal import. In +all cases the factor of general power conditions on the mine may +alter the relative positions. +</p> + +<table class="ctrclps"> +<tr><th class="center_btrb"> </th> + <th class="center_btrb"><span class="sc">Direct Steam + Pumps</span></th> + <th class="center_btrb"><span class="sc">Compressed + Air</span></th> + <th class="center_btrb"><span class="sc">Elec-<br>tricity</span></th> + <th class="center_btrb"><span class="sc">Steam-<br>Driven + Rods</span></th> + <th class="center_btrb"><span class="sc">Hydraulic + Columns</span></th> + <th class="center_btb"><span class="sc">Bailing + Rods</span></th></tr> +<tr><td class="left_br">Flexibility</td> + <td class="center_br"><i>A</i></td> + <td class="center_br"><i>A</i></td> + <td class="center_br"><i>B</i></td> + <td class="center_br"><i>D</i></td> + <td class="center_br"><i>B</i></td> + <td class="center"><i>A</i></td></tr> +<tr><td class="left_br">Reliability</td> + <td class="center_br"><i>B</i></td> + <td class="center_br"><i>B</i></td> + <td class="center_br"><i>B</i></td> + <td class="center_br"><i>A</i></td> + <td class="center_br"><i>D</i></td> + <td class="center"><i>A</i></td></tr> +<tr><td class="left_br">Mechanical Efficiency</td> + <td class="center_br"><i>C</i></td> + <td class="center_br"><i>D</i></td> + <td class="center_br"><i>B</i></td> + <td class="center_br"><i>A</i></td> + <td class="center_br"><i>C</i></td> + <td class="center"><i>D</i></td></tr> +<tr><td class="left_brb">Capital Cost</td> + <td class="center_brb"><i>A</i></td> + <td class="center_brb"><i>B</i></td> + <td class="center_brb"><i>B</i></td> + <td class="center_brb"><i>D</i></td> + <td class="center_brb"><i>D</i></td> + <td class="center_bb">—</td></tr> +</table> + +<p class="indent"> +As each mine has its special environment, it is impossible to formulate +any final conclusion on a subject so involved. The attempt would lead +to a discussion of a thousand supposititious <a name="page_144"><span +class="page">Page 144</span></a> cases and hypothetical remedies. +Further, the description alone of pumping machines would fill volumes, +and the subject will never be exhausted. The engineer confronted +with pumping problems must marshal all the alternatives, count his +money, and apply the tests of flexibility, reliability, efficiency, +and cost, choose the system of least disadvantages, and finally +deprecate the whole affair, for it is but a parasite growth on +the mine. +</p> + +<h2><a name="page_145"><span class="page">Page 145</span></a> +CHAPTER XIV.</h2> + +<p class="center"> +<span class="sc">Mechanical Equipment</span> (<i>Concluded</i>). +</p> + +<table class="summary"><tr><td class="summary"> +MACHINE DRILLING: POWER TRANSMISSION; COMPRESSED AIR <i>VS</i>. +ELECTRICITY; AIR DRILLS; MACHINE <i>VS</i>. HAND DRILLING. WORK-SHOPS. +IMPROVEMENT IN EQUIPMENT. +</td></tr></table> + +<p class="indent"> +For over two hundred years from the introduction of drill-holes +for blasting by Caspar Weindel in Hungary, to the invention of +the first practicable steam percussion drill by J. J. Crouch of +Philadelphia, in 1849, all drilling was done by hand. Since Crouch's +time a host of mechanical drills to be actuated by all sorts of +power have come forward, and even yet the machine-drill has not +reached a stage of development where it can displace hand-work +under all conditions. Steam-power was never adapted to underground +work, and a serviceable drill for this purpose was not found until +compressed air for transmission was demonstrated by Dommeiller +on the Mt. Cenis tunnel in 1861. +</p> + +<p class="indent"> +The ideal requirements for a drill combine:— +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td><i>a.</i></td><td>Power transmission adapted to underground + conditions.</td></tr> +<tr><td><i>b.</i></td><td>Lightness.</td></tr> +<tr><td><i>c.</i></td><td>Simplicity of construction.</td></tr> +<tr><td><i>d.</i></td><td>Strength.</td></tr> +<tr><td><i>e.</i></td><td>Rapidity and strength of blow.</td></tr> +<tr><td><i>f.</i></td><td>Ease of erection.</td></tr> +<tr><td><i>g.</i></td><td>Reliability.</td></tr> +<tr><td><i>h.</i></td><td>Mechanical efficiency.</td></tr> +<tr><td><i>i.</i></td><td>Low capital cost.</td></tr> +</table> + +<p class="indent"> +No drill invented yet fills all these requirements, and all are +a compromise on some point. +</p> + +<p class="indent"> +<b>Power Transmission; Compressed Air</b> <i>vs</i>. +<b>Electricity.</b>—The only transmissions adapted to underground +drill-work are compressed <a name="page_146"><span class="page">Page +146</span></a> air and electricity, and as yet an electric-driven +drill has not been produced which meets as many of the requirements +of the metal miner as do compressed-air drills. The latter, up to +date, have superiority in simplicity, lightness, ease of erection, +reliability, and strength over electric machines. Air has another +advantage in that it affords some assistance to ventilation, but +it has the disadvantage of remarkably low mechanical efficiency. +The actual work performed by the standard 3-3/4-inch air-drill +probably does not amount to over two or three horse-power against +from fifteen to eighteen horse-power delivered into the compressor, +or mechanical efficiency of less than 25%. As electrical power can +be delivered to the drill with much less loss than compressed air, +the field for a more economical drill on this line is wide enough to +create eventually the proper tool to apply it. The most satisfactory +electric drill produced has been the Temple drill, which is really +an air-drill driven by a small electrically-driven compressor placed +near the drill itself. But even this has considerable deficiencies +in mining work; the difficulties of setting up, especially for +stoping work, and the more cumbersome apparatus to remove before +blasting are serious drawbacks. It has deficiencies in reliability +and greater complication of machinery than direct air. +</p> + +<p class="indent"> +<b>Air-compression.</b>—The method of air-compression so long +accomplished only by power-driven pistons has now an alternative +in some situations by the use of falling water. This latter system +is a development of the last twelve years, and, due to the low +initial outlay and extremely low operating costs, bids fair in +those regions where water head is available not only to displace the +machine compressor, but also to extend the application of compressed +air to mine motors generally, and to stay in some environments +the encroachment of electricity into the compressed-air field. +Installations of this sort in the West Kootenay, B.C., and at the +Victoria copper mine, Michigan, are giving results worthy of careful +attention. +</p> + +<p class="indent"> +Mechanical air-compressors are steam-, water-, electrical-, and +gas-driven, the alternative obviously depending on the source and cost +of power. Electrical- and gas- and water-driven <a name="page_147"><span +class="page">Page 147</span></a> compressors work under the disadvantage +of constant speed motors and respond little to the variation in load, +a partial remedy for which lies in enlarged air-storage capacity. +Inasmuch as compressed air, so far as our knowledge goes at present, +must be provided for drills, it forms a convenient transmission of +power to various motors underground, such as small pumps, winches, +or locomotives. As stated in discussing those machines, it is not +primarily a transmission of even moderate mechanical efficiency +for such purposes; but as against the installation and operation +of independent transmission, such as steam or electricity, the +economic advantage often compensates the technical losses. Where +such motors are fixed, as in pumps and winches, a considerable +gain in efficiency can be obtained by reheating. +</p> + +<p class="indent"> +It is not proposed to enter a discussion of mechanical details of +air-compression, more than to call attention to the most common +delinquency in the installation of such plants. This deficiency +lies in insufficient compression capacity for the needs of the +mine and consequent effective operation of drills, for with under +75 pounds pressure the drills decrease remarkably in rapidity of +stroke and force of the blow. The consequent decrease in actual +accomplishment is far beyond the ratio that might be expected on +the basis of mere difference of pressure. Another form of the same +chronic ill lies in insufficient air-storage capacity to provide +for maintenance of pressure against moments when all drills or +motors in the mine synchronize in heavy demand for air, and thus +lower the pressure at certain periods. +</p> + +<p class="indent"> +<b>Air-drills.</b>—Air-drills are from a mechanical point +of view broadly of two types,—the first, in which the drill +is the piston extension; and the second, a more recent development +for mining work, in which the piston acts as a hammer striking the +head of the drill. From an economic point of view drills may be +divided into three classes. First, heavy drills, weighing from 150 +to 400 pounds, which require two men for their operation; second, +"baby" drills of the piston type, weighing from 110 to 150 pounds, +requiring one man with occasional assistance in setting up; and +third, very light drills almost wholly of the <a name="page_148"><span +class="page">Page 148</span></a> hammer type. This type is built in +two forms: a heavier type for mounting on columns, weighing about +80 pounds; and a type after the order of the pneumatic riveter, +weighing as low as 20 pounds and worked without mounting. +</p> + +<p class="indent"> +The weight and consequent mobility of a drill, aside from labor +questions, have a marked effect on costs, for the lighter the drill +the less difficulty and delay in erection, and consequent less +loss of time and less tendency to drill holes from one radius, +regardless of pointing to take best advantage of breaking planes. +Moreover, smaller diameter and shorter holes consume less explosives +per foot advanced or per ton broken. The best results in tonnage +broken and explosive consumed, if measured by the foot of drill-hole +necessary, can be accomplished from hand-drilling and the lighter +the machine drill, assuming equal reliability, the nearer it +approximates these advantages. +</p> + +<p class="indent"> +The blow, and therefore size and depth of hole and rapidity of +drilling, are somewhat dependent upon the size of cylinders and +length of stroke, and therefore the heavier types are better adapted +to hard ground and to the deep holes of some development points. +Their advantages over the other classes lie chiefly in this ability +to bore exceedingly hard material and in the greater speed of advance +possible in development work; but except for these two special +purposes they are not as economical per foot advanced or per ton +of ore broken as the lighter drills. +</p> + +<p class="indent"> +The second class, where men can be induced to work them one man per +drill, saves in labor and gains in mobility. Many tests show great +economy of the "baby" type of piston drills in average ground over +the heavier machines for stoping and for most lateral development. +All piston types are somewhat cumbersome and the heavier types +require at least four feet of head room. The "baby" type can be +operated in less space than this, but for narrow stopes they do +not lend themselves with the same facility as the third class. +</p> + +<p class="indent"> +The third class of drills is still in process of development, but +it bids fair to displace much of the occupation of the piston types +of drill. Aside from being a one-man drill, by its mobility it will +apparently largely reproduce the advantage of hand-drilling <a +name="page_149"><span class="page">Page 149</span></a> in ability +to place short holes from the most advantageous angles and for +use in narrow places. As compared with other drills it bids fair +to require less time for setting up and removal and for change of +bits; to destroy less steel by breakages; to dull the bits less +rapidly per foot of hole; to be more economical of power; to require +much less skill in operation, for judgment is less called upon in +delivering speed; and to evade difficulties of fissured ground, +etc. And finally the cost is only one-half, initially and for spares. +Its disadvantage so far is a lack of reliability due to lightness +of construction, but this is very rapidly being overcome. This +type, however, is limited in depth of hole possible, for, from +lack of positive reverse movement, there is a tendency for the +spoil to pack around the bit, and as a result about four feet seems +the limit. +</p> + +<p class="indent"> +The performance of a machine-drill under show conditions may be +anything up to ten or twelve feet of hole per hour on rock such +as compact granite; but in underground work a large proportion of +the time is lost in picking down loose ore, setting up machines, +removal for blasting, clearing away spoil, making adjustments, +etc. The amount of lost time is often dependent upon the width of +stope or shaft and the method of stoping. Situations which require +long drill columns or special scaffolds greatly accentuate the loss +of time. Further, the difficulties in setting up reflect indirectly +on efficiency to a greater extent in that a larger proportion of +holes are drilled from one radius and thus less adapted to the +best breaking results than where the drill can easily be reset from +various angles. +</p> + +<p class="indent"> +The usual duty of a heavy drill per eight-hour shift using two men +is from 20 to 40 feet of hole, depending upon the rock, facilities +for setting up, etc., etc.[*] The lighter drills have a less average +duty, averaging from 15 to 25 feet per shift. +</p> + +<p class="footnote"> +[Footnote *: Over the year 1907 in twenty-eight mines compiled +from Alaska to Australia, an average of 23.5 feet was drilled per +eight-hour shift by machines larger than three-inch cylinder.] +</p> + +<p class="indent"> +<b>Machine</b> <i>vs</i>. <b>Hand-Drilling.</b>—The advantages +of hand-drilling over machine-drilling lie, first, in the total saving +of power, the absence of capital cost, repairs, depreciation, etc., +on power, compresser <a name="page_150"><span class="page">Page +150</span></a> and drill plant; second, the time required for setting +up machine-drills does not warrant frequent blasts, so that a number +of holes on one radius are a necessity, and therefore machine-holes +generally cannot be pointed to such advantage as hand-holes. Hand-holes +can be set to any angle, and by thus frequent blasting yield greater +tonnage per foot of hole. Third, a large number of comparative +statistics from American, South African, and Australian mines show +a saving of about 25% in explosives for the same tonnage or foot +of advance by hand-holes over medium and heavy drill-holes. +</p> + +<p class="indent"> +The duty of a skilled white man, single-handed, in rock such as +is usually met below the zone of oxidation, is from 5 to 7 feet +per shift, depending on the rock and the man. Two men hand-drilling +will therefore do from 1/4 to 2/3 of the same footage of holes +that can be done by two men with a heavy machine-drill, and two +men hand-drilling will do from 1/5 to 1/2 the footage of two men +with two light drills. +</p> + +<p class="indent"> +The saving in labor of from 75 to 33% by machine-drilling may or +may not be made up by the other costs involved in machine-work. +The comparative value of machine- and hand-drilling is not subject +to sweeping generalization. A large amount of data from various +parts of the world, with skilled white men, shows machine-work +to cost from half as much per ton or foot advanced as hand-work +to 25% more than handwork, depending on the situation, type of +drill, etc. In a general way hand-work can more nearly compete +with heavy machines than light ones. The situations where hand-work +can compete with even light machines are in very narrow stopes where +drills cannot be pointed to advantage, and where the increased +working space necessary for machine drills results in breaking more +waste. Further, hand-drilling can often compete with machine-work +in wide stopes where long columns or platforms must be used and +therefore there is much delay in taking down, reërection, +etc. +</p> + +<p class="indent"> +Many other factors enter into a comparison, however, for +machine-drilling produces a greater number of deeper holes and +permits larger blasts and therefore more rapid progress. In driving +<a name="page_151"><span class="page">Page 151</span></a> levels +under average conditions monthly footage is from two to three times +as great with heavy machines as by hand-drilling, and by lighter +machines a somewhat less proportion of greater speed. The greater +speed obtained in development work, the greater tonnage obtained +per man in stoping, with consequent reduction in the number of men +employed, and in reduction of superintendence and general charges +are indirect advantages for machine-drilling not to be overlooked. +</p> + +<p class="indent"> +The results obtained in South Africa by hand-drilling in shafts, +and its very general adoption there, seem to indicate that better +speed and more economical work can be obtained in that way in very +large shafts than by machine-drilling. How far special reasons +there apply to smaller shafts or labor conditions elsewhere have +yet to be demonstrated. In large-dimension shafts demanding a large +number of machines, the handling of long machine bars and machines +generally results in a great loss of time. The large charges in +deep holes break the walls very irregularly; misfires cause more +delay; timbering is more difficult in the face of heavy blasting +charges; and the larger amount of spoil broken at one time delays +renewed drilling, and altogether the advantages seem to lie with +hand-drilling in shafts of large horizontal section. +</p> + +<p class="indent"> +The rapid development of special drills for particular conditions +has eliminated the advantage of hand-work in many situations during +the past ten years, and the invention of the hammer type of drill +bids fair to render hand-drilling a thing of the past. One +generalization is possible, and that is, if drills are run on 40-50 +pounds' pressure they are no economy over hand-drilling. +</p> + +<h3>WORKSHOPS.</h3> + +<p class="indent"> +In addition to the ordinary blacksmithy, which is a necessity, +the modern tendency has been to elaborate the shops on mines to +cover machine-work, pattern-making and foundry-work, in order that +delays may be minimized by quick repairs. To provide, however, for +such contingencies a staff of men must be kept larger than the +demand of average requirements. The result <a name="page_152"><span +class="page">Page 152</span></a> is an effort to provide jobs or +to do work extravagantly or unnecessarily well. In general, it is +an easy spot for fungi to start growing on the administration, +and if custom repair shops are available at all, mine shops can +be easily overdone. +</p> + +<p class="indent"> +A number of machines are now in use for sharpening drills. +Machine-sharpening is much cheaper than hand-work, although the drills +thus sharpened are rather less efficient owing to the difficulty of +tempering them to the same nicety; however, the net results are +in favor of the machines. +</p> + +<h3>IMPROVEMENT IN EQUIPMENT.</h3> + +<p class="indent"> +Not only is every mine a progressive industry until the bottom +gives out, but the technology of the industry is always progressing, +so that the manager is almost daily confronted with improvements +which could be made in his equipment that would result in decreasing +expenses or increasing metal recovery. There is one test to the +advisability of such alterations: How long will it take to recover +the capital outlay from the savings effected? and over and above +this recovery of capital there must be some very considerable gain. +The life of mines is at least secured over the period exposed in +the ore-reserves, and if the proposed alteration will show its +recovery and profit in that period, then it is certainly justified. +If it takes longer than this on the average speculative ore-deposit, +it is a gamble on finding further ore. As a matter of practical +policy it will be found that an improvement in equipment which +requires more than three or four years to redeem itself out of +saving, is usually a mechanical or metallurgical refinement the +indulgence in which is very doubtful. +</p> + +<h2><a name="page_153"><span class="page">Page 153</span></a> +CHAPTER XV.</h2> + +<p class="center"> +<span class="sc">Ratio of Output to the Mine.</span> +</p> + +<table class="summary"><tr><td class="summary"> +DETERMINATION OF THE POSSIBLE MAXIMUM; LIMITING FACTORS; COST OF +EQUIPMENT; LIFE OF THE MINE; MECHANICAL INEFFICIENCY OF PATCHWORK +PLANT; OVERPRODUCTION OF BASE METAL; SECURITY OF INVESTMENT. +</td></tr></table> + +<p class="indent"> +The output obtainable from a given mine is obviously dependent +not only on the size of the deposit, but also on the equipment +provided,—in which equipment means the whole working appliances, +surface and underground. +</p> + +<p class="indent"> +A rough and ready idea of output possibilities of inclined deposits +can be secured by calculating the tonnage available per foot of +depth from the horizontal cross-section of the ore-bodies exposed +and assuming an annual depth of exhaustion, or in horizontal deposits +from an assumption of a given area of exhaustion. Few mines, at the +time of initial equipment, are developed to an extent from which +their possibilities in production are evident, for wise finance +usually leads to the erection of some equipment and production before +development has been advanced to a point that warrants a large or +final installation. Moreover, even were the full possibilities of +the mine known, the limitations of finance usually necessitate a +less plant to start with than is finally contemplated. Therefore +output and equipment are usually growing possibilities during the +early life of a mine. +</p> + +<p class="indent"> +There is no better instance in mine engineering where pure theory +must give way to practical necessities of finance than in the +determination of the size of equipment and therefore output. Moreover, +where finance even is no obstruction, there are other limitations +of a very practical order which must dominate the question of the +size of plant giving the greatest technical economy. It is, however, +useful to state the theoretical considerations in determining the +ultimate volume of output and therefore the size of equipments, for +the theory will serve to illuminate the <a name="page_154"><span +class="page">Page 154</span></a> practical limitations. The discussion +will also again demonstrate that all engineering is a series of +compromises with natural and economic forces. +</p> + +<p class="indent"> +<b>Output giving Least Production Cost.</b>—As one of the +most important objectives is to work the ore at the least cost per +ton, it is not difficult to demonstrate that the minimum working +costs can be obtained only by the most intensive production. To prove +this, it need only be remembered that the working expenses of a mine +are of two sorts: one is a factor of the tonnage handled, such as +stoping and ore-dressing; the other is wholly or partially dependent +upon time. A large number of items are of this last order. Pumping +and head-office expenses are almost entirely charges independent of +the tonnage handled. Superintendence and staff salaries and the +like are in a large proportion dependent upon time. Many other +elements of expense, such as the number of engine-drivers, etc., do +not increase proportionately to increase in tonnage. These charges, +or the part of them dependent upon time apart from tonnage, may be +termed the "fixed charges." +</p> + +<p class="indent"> +There is another fixed charge more obscure yet no less certain. +Ore standing in a mine is like money in a bank drawing no interest, +and this item of interest may be considered a "fixed charge," for +if the ore were realized earlier, this loss could be partially +saved. This subject is further referred to under "Amortization." +</p> + +<p class="indent"> +If, therefore, the time required to exhaust the mine be prolonged +by the failure to maintain the maximum output, the total cost of +working it will be greater by the fixed charges over such an increased +period. Conversely, by equipping on a larger scale, the mine will +be exhausted more quickly, a saving in total cost can be made, and +the ultimate profit can be increased by an amount corresponding +to the time saved from the ravages of fixed charges. In fine, the +working costs may be reduced by larger operations, and therefore +the value of the mine increased. +</p> + +<p class="indent"> +The problem in practice usually takes the form of the relative +superiority of more or of fewer units of plant, and it can be considered +in more detail if the production be supposed to consist of units +averaging say 100 tons per day each. The advantage of <a +name="page_155"><span class="page">Page 155</span></a> more units +over less will be that the extra ones can be produced free of fixed +charges, for these are an expense already involved in the lesser +units. This extra production will also enjoy the interest which +can be earned over the period of its earlier production. Moreover, +operations on a larger scale result in various minor economies +throughout the whole production, not entirely included in the type +of expenditure mentioned as "fixed charges." We may call these +various advantages the "saving of fixed charges" due to larger-scale +operations. The saving of fixed charges amounts to very considerable +sums. In general the items of working cost alone, mentioned above, +which do not increase proportionately to the tonnage, aggregate +from 10 to 25% of the total costs. Where much pumping is involved, +the percentage will become even greater. +</p> + +<p class="indent"> +The question of the value of the mine as affected by the volume +of output becomes very prominent in low-grade mines, where, if +equipped for output on too small a scale, no profits at all could +be earned, and a sufficient production is absolutely imperative +for any gain. There are many mines in every country which with +one-third of their present rate of production would lose money. +That is, the fixed charges, if spread over small output, would be +so great per ton that the profit would be extinguished by them. +</p> + +<p class="indent"> +In the theoretical view, therefore, it would appear clear that +the greatest ultimate profit from a mine can be secured only by +ore extraction under the highest pressure. As a corollary to this +it follows that development must proceed with the maximum speed. +Further, it follows that the present value of a mine is at least +partially a factor of the volume of output contemplated. +</p> + +<h3>FACTORS LIMITING THE OUTPUT.</h3> + +<p class="indent"> +Although the above argument can be academically defended, there +are, as said at the start, practical limitations to the maximum +intensity of production, arising out of many other considerations +to which weight must be given. In the main, there are five principal +limitations:— +</p> + +<table style="margin-left: 4em; border-collapse: collapse;"> +<tr><td>1.</td><td>Cost of equipment. + <a name="page_156"><span class="page">Page 156</span></a> + </td></tr> +<tr><td>2.</td><td>Life of the mine.</td></tr> +<tr><td>3.</td><td>Mechanical inefficiency of patchwork + plant.</td></tr> +<tr><td>4.</td><td>Overproduction of base metal.</td></tr> +<tr><td>5.</td><td>Security of investment.</td></tr> +</table> + +<p class="indent"> +<b>Cost of Equipment.</b>—The "saving of fixed charges" can +only be obtained by larger equipment, which represents an investment. +Mining works, shafts, machinery, treatment plants, and all the +paraphernalia cost large sums of money. They become either worn +out or practically valueless through the exhaustion of the mines. +Even surface machinery when in good condition will seldom realize +more than one-tenth of its expense if useless at its original site. +All mines are ephemeral; therefore virtually the entire capital +outlay of such works must be redeemed during the life of the mine, +and the interest on it must also be recovered. +</p> + +<p class="indent"> +The certain life, with the exception of banket and a few other +types of deposit, is that shown by the ore in sight, plus something +for extension of the deposit beyond exposures. So, against the +"savings" to be made, must be set the cost of obtaining them, for +obviously it is of no use investing a dollar to save a total of +ninety cents. The economies by increased production are, however, +of such an important character that the cost of almost any number +of added units (within the ability of the mine to supply them) +can be redeemed from these savings in a few years. For instance, +in a Californian gold mine where the working expenses are $3 and +the fixed charges are at the low rate of 30 cents per ton, one +unit of increased production would show a saving of over $10,000 +per annum from the saving of fixed charges. In about three years +this sum would repay the cost of the additional treatment equipment. +If further shaft capacity were required, the period would be much +extended. On a Western copper mine, where the costs are $8 and the +fixed charges are 80 cents per ton, one unit of increased production +would effect a saving of the fixed charges equal to the cost of +the extra unit in about three years. That is, the total sum would +amount to $80,000, or enough to provide <a name="page_157"><span +class="page">Page 157</span></a> almost any type of mechanical +equipment for such additional tonnage. +</p> + +<p class="indent"> +The first result of vigorous development is to increase the ore +in sight,—the visible life of the mine. When such visible +life has been so lengthened that the period in which the "saving +of fixed charges" will equal the amount involved in expansion of +equipment, then from the standpoint of this limitation only is +the added installation justified. The equipment if expanded on +this practice will grow upon the heels of rapid development until +the maximum production from the mine is reached, and a kind of +equilibrium establishes itself. +</p> + +<p class="indent"> +Conversely, this argument leads to the conclusion that, regardless +of other considerations, an equipment, and therefore output, should +not be expanded beyond the redemption by way of "saving from fixed +charges" of the visible or certain life of the mine. In those mines, +such as at the Witwatersrand, where there is a fairly sound assurance +of definite life, it is possible to calculate at once the size of +plant which by saving of "fixed charges" will be eventually the +most economical, but even here the other limitations step in to +vitiate such policy of management,—chiefly the limitation +through security of investment. +</p> + +<p class="indent"> +<b>Life of the Mine.</b>—If carried to its logical extreme, +the above program means a most rapid exhaustion of the mine. The +maximum output will depend eventually upon the rapidity with which +development work may be extended. As levels and other subsidiary +development openings can be prepared in inclined deposits much +more quickly than the shaft can be sunk, the critical point is +the shaft-sinking. As a shaft may by exertion be deepened at least +400 feet a year on a going mine, the provision of an equipment +to eat up the ore-body at this rate of sinking means very early +exhaustion indeed. In fact, had such a theory of production been +put into practice by our forefathers, the mining profession might +find difficulty in obtaining employment to-day. Such rapid exhaustion +would mean a depletion of the mineral resources of the state at a +pace which would be alarming. +</p> + +<p class="indent"> +<a name="page_158"><span class="page">Page 158</span></a> <b>Mechanical +Inefficiency of Patchwork Plant.</b>—Mine equipments on +speculative mines (the vast majority) are often enough patchwork, +for they usually grow from small beginnings; but any scheme of +expansion based upon the above doctrine would need to be modified +to the extent that additions could be in units large in ratio to +previous installations, or their patchwork character would be still +further accentuated. It would be impossible to maintain mechanical +efficiency under detail expansion. +</p> + +<p class="indent"> +<b>Overproduction of Base Metal.</b>—Were this intensity +of production of general application to base metal mines it would +flood the markets, and, by an overproduction of metal depress prices +to a point where the advantages of such large-scale operations +would quickly vanish. The theoretical solution in this situation +would be, if metals fell below normal prices, let the output be +reduced, or let the products be stored until the price recovers. From +a practical point of view either alternative is a policy difficult +to face. +</p> + +<p class="indent"> +In the first case, reduction of output means an increase of working +expenses by the spread of fixed charges over less tonnage, and +this in the face of reduced metal prices. It may be contended, +however, that a falling metal market is usually the accompaniment +of a drop in all commodities, wherefore working costs can be reduced +somewhat in such times of depression, thereby partially compensating +the other elements making for increased costs. Falls in commodities +are also the accompaniment of hard times. Consideration of one's +workpeople and the wholesale slaughter of dividends to the then +needy stockholders, resulting from a policy of reduced production, +are usually sufficient deterrents to diminished output. +</p> + +<p class="indent"> +The second alternative, that of storing metal, means equally a +loss of dividends by the investment of a large sum in unrealized +products, and the interest on this sum. The detriment to the market +of large amounts of unsold metal renders such a course not without +further disadvantages. +</p> + +<p class="indent"> +<b>Security of Investment.</b>—Another point of view antagonistic +to such wholesale intensity of production, and one worthy of careful +consideration, is that of the investor in mines. The root-value <a +name="page_159"><span class="page">Page 159</span></a> of mining +stocks is, or should be, the profit in sight. If the policy of +greatest economy in production costs be followed as outlined above, +the economic limit of ore-reserves gives an apparently very short +life, for the ore in sight will never represent a life beyond the +time required to justify more plant. Thus the "economic limit of +ore in reserve" will be a store equivalencing a period during which +additional equipment can be redeemed from the "saving of fixed +charges," or three or four years, usually. +</p> + +<p class="indent"> +The investor has the right to say that he wants the guarantee of +longer life to his investment,—he will in effect pay insurance +for it by a loss of some ultimate profit. That this view, contradictory +to the economics of the case, is not simply academic, can be observed +by any one who studies what mines are in best repute on any stock +exchange. All engineers must wish to have the industry under them +in high repute. The writer knows of several mines paying 20% on +their stocks which yet stand lower in price on account of short +ore-reserves than mines paying less annual returns. The speculator, +who is an element not to be wholly disregarded, wishes a rise in +his mining stock, and if development proceeds at a pace in advance +of production, he will gain a legitimate rise through the increase +in ore-reserves. +</p> + +<p class="indent"> +The investor's and speculator's idea of the desirability of a proved +long life readily supports the technical policy of high-pressure +development work, but not of expansion of production, for they +desire an increasing ore-reserve. Even the metal operator who is +afraid of overproduction does not object to increased ore-reserves. +On the point of maximum intensity of development work in a mine all +views coincide. The mining engineer, if he takes a Machiavellian +view, must agree with the investor and the metal dealer, for the +engineer is a "fixed charge" the continuance of which is important +to his daily needs. +</p> + +<p class="indent"> +The net result of all these limitations is therefore an invariable +compromise upon some output below the possible maximum. The initial +output to be contemplated is obviously one upon which the working +costs will be low enough to show a margin of <a name="page_160"><span +class="page">Page 160</span></a> profit. The medium between these +two extremes is determinable by a consideration of the limitations +set out,—and the cash available. When the volume of output is +once determined, it must be considered as a factor in valuation, +as discussed under "Amortization." +</p> + +<h2><a name="page_161"><span class="page">Page 161</span></a> +CHAPTER XVI.</h2> + +<p class="center"> +<span class="sc">Administration.</span> +</p> + +<table class="summary"><tr><td class="summary"> +LABOR EFFICIENCY; SKILL; INTELLIGENCE; APPLICATION COORDINATION; +CONTRACT WORK; LABOR UNIONS; REAL BASIS OF WAGES. +</td></tr></table> + +<p class="indent"> +The realization from a mine of the profits estimated from the other +factors in the case is in the end dependent upon the management. +Good mine management is based upon three elementals: first, sound +engineering; second, proper coördination and efficiency of +every human unit; third, economy in the purchase and consumption +of supplies. +</p> + +<p class="indent"> +The previous chapters have been devoted to a more or less extended +exposition of economic engineering. While the second and third +requirements are equally important, they range in many ways out of +the engineering and into the human field. For this latter reason +no complete manual will ever be published upon "How to become a +Good Mine Manager." +</p> + +<p class="indent"> +It is purposed, however, to analyze some features of these second +and third fundamentals, especially in their interdependent phases, +and next to consider the subject of mine statistics, for the latter +are truly the microscopes through which the competence of the +administration must be examined. +</p> + +<p class="indent"> +The human units in mine organization can be divided into officers +and men. The choice of mine officers is the assembling of specialized +brains. Their control, stimulation, and inspiration is the main work +of the administrative head. Success in the selection and control of +staff is the index of executive ability. There are no mathematical, +mechanical, or chemical formulas for dealing with the human mind +or human energies. +</p> + +<p class="indent"> +<b>Labor.</b>—The whole question of handling labor can be +reduced to the one term "efficiency." Not only does the actual +labor outlay represent from 60 to 70% of the total underground <a +name="page_162"><span class="page">Page 162</span></a> expenses, +but the capacity or incapacity of its units is responsible for wider +fluctuations in production costs than the bare predominance in +expenditure might indicate. The remaining expense is for supplies, +such as dynamite, timber, steel, power, etc., and the economical +application of these materials by the workman has the widest bearing +upon their consumption. +</p> + +<p class="indent"> +Efficiency of the mass is the resultant of that of each individual +under a direction which coördinates effectively all units. +The lack of effectiveness in one individual diminishes the returns +not simply from that man alone; it lowers the results from numbers +of men associated with the weak member through the delaying and +clogging of their work, and of the machines operated by them. +Coördination of work is a necessary factor of final efficiency. +This is a matter of organization and administration. The most zealous +stoping-gang in the world if associated with half the proper number +of truckers must fail to get the desired result. +</p> + +<p class="indent"> +Efficiency in the single man is the product of three +factors,—skill, intelligence, and application. A great proportion +of underground work in a mine is of a type which can be performed +after a fashion by absolutely unskilled and even unintelligent men, +as witness the breaking-in of savages of low average mentality, like +the South African Kaffirs. Although most duties can be performed by +this crudest order of labor, skill and intelligence can be applied +to it with such economic results as to compensate for the difference +in wage. The reason for this is that the last fifty years have seen +a substitution of labor-saving machines for muscle. Such machines +displace hundreds of raw laborers. Not only do they initially cost +large sums, but they require large expenditure for power and up-keep. +These fixed charges against the machine demand that it shall be +worked at its maximum. For interest, power, and up-keep go on in +any event, and the saving on crude labor displaced is not so great +but that it quickly disappears if the machine is run under its +capacity. To get its greatest efficiency, a high degree of skill +and intelligence is required. Nor are skill and intelligence alone +applicable to labor-saving devices themselves, because drilling and +blasting <a name="page_163"><span class="page">Page 163</span></a> +rock and executing other works underground are matters in which +experience and judgment in the individual workman count to the +highest degree. +</p> + +<p class="indent"> +How far skill affects production costs has had a thorough demonstration +in West Australia. For a time after the opening of those mines +only a small proportion of experienced men were obtainable. During +this period the rock broken per man employed underground did not +exceed the rate of 300 tons a year. In the large mines it has now, +after some eight years, attained 600 to 700 tons. +</p> + +<p class="indent"> +How far intelligence is a factor indispensable to skill can be well +illustrated by a comparison of the results obtained from working +labor of a low mental order, such as Asiatics and negroes, with those +achieved by American or Australian miners. In a general way, it may +be stated with confidence that the white miners above mentioned +can, under the same physical conditions, and with from five to ten +times the wage, produce the same economic result,—that is, +an equal or lower cost per unit of production. Much observation +and experience in working Asiatics and negroes as well as Americans +and Australians in mines, leads the writer to the conclusion that, +averaging actual results, one white man equals from two to three +of the colored races, even in the simplest forms of mine work such +as shoveling or tramming. In the most highly skilled branches, +such as mechanics, the average ratio is as one to seven, or in +extreme cases even eleven. The question is not entirely a comparison +of bare efficiency individually; it is one of the sum total of +results. In mining work the lower races require a greatly increased +amount of direction, and this excess of supervisors consists of +men not in themselves directly productive. There is always, too, a +waste of supplies, more accidents, and more ground to be kept open +for accommodating increased staff, and the maintenance of these +openings must be paid for. There is an added expense for handling +larger numbers in and out of the mine, and the lower intelligence +reacts in many ways in lack of coördination and inability to +take initiative. Taking all divisions of labor together, the ratio +of efficiency as measured in amount of output <a name="page_164"><span +class="page">Page 164</span></a> works out from four to five colored +men as the equivalent of one white man of the class stated. The +ratio of costs, for reasons already mentioned, and in other than +quantity relation, figures still more in favor of the higher +intelligence. +</p> + +<p class="indent"> +The following comparisons, which like all mine statistics must +necessarily be accepted with reservation because of some dissimilarity +of economic surroundings, are yet on sufficiently common ground to +demonstrate the main issue,—that is, the bearing of inherent +intelligence in the workmen and their consequent skill. Four groups +of gold mines have been taken, from India, West Australia, South +Africa, and Western America. All of those chosen are of the same +stoping width, 4 to 5 feet. All are working in depth and with every +labor-saving device available. All dip at about the same angle and +are therefore in much the same position as to handling rock. The +other conditions are against the white-manned mines and in favor of +the colored. That is, the Indian mines have water-generated electric +power and South Africa has cheaper fuel than either the American or +Australian examples. In both the white-manned groups, the stopes +are supported, while in the others no support is required. +</p> + +<table class="ctrclps"> +<tr><th rowspan="2" class="center_btrb"><span class="sc">Group of + Mines</span></th> + <th rowspan="2" class="center_btrb"><span class="sc">Tons of + Material Excavated over Period Compiled</span>[5]</th> + <th colspan="2" class="center_btrb"><span class="sc">Average + Number of Men Employed</span></th> + <th rowspan="2" class="center_btrb"><span class="sc">Tons per + Man per Annum</span></th> + <th rowspan="2" class="center_btb"><span class="sc">Cost per + Ton of Material Broken</span></th></tr> +<tr><th class="center_btrb">Colored</th> + <th class="center_btrb">White</th></tr> +<tr><td class="left_br">Four Kolar mines[1]</td> + <td class="center_br">963,950</td> + <td class="center_br">13,611</td> + <td class="center_br">302</td> + <td class="center_br">69.3</td> + <td class="center">$3.85</td></tr> +<tr><td class="left_br">Six Australian mines[2]</td> + <td class="center_br">1,027,718</td> + <td class="center_br">—</td> + <td class="center_br">1,534</td> + <td class="center_br">669.9</td> + <td class="center">2.47</td></tr> +<tr><td class="left_br">Three Witwatersrand mines[3]</td> + <td class="center_br">2,962,640</td> + <td class="center_br">13,560</td> + <td class="center_br">1,595</td> + <td class="center_br">195.5</td> + <td class="center">2.68</td></tr> +<tr><td class="left_brb">Five American mines[4]</td> + <td class="center_brb">1,089,500 + <td class="center_brb">—</td> + <td class="center_brb">1,524</td> + <td class="center_brb">713.3</td> + <td class="center_bb">1.92</td></tr> +</table> + +<p class="footnote"> +[Footnote 1: Indian wages average about 20 cents per day.] +</p> + +<p class="footnote"> +[Footnote 2: White men's wages average about $3 per day.] +</p> + +<p class="footnote"> +[Footnote 3: About two-fifths of the colored workers were negroes, +and three-fifths Chinamen. Negroes average about 60 cents, and +Chinamen about 45 cents per day, including keep.] +</p> + +<p class="footnote"> +[Footnote 4: Wages about $3.50. Tunnel entry in two mines.] +</p> + +<p class="footnote"> +[Footnote 5: Includes rock broken in development work. +</p> + +<p class="indent"> +In the case of the specified African mines, the white labor is +employed almost wholly in positions of actual or semi-superintendence, +such as one white man in charge of two or three drills. +</p> + +<p class="indent"> +In the Indian case, in addition to the white men who are wholly +in superintendence, there were of the natives enumerated some 1000 +in positions of semi-superintendence, as contractors or headmen, +working-gangers, etc.] +</p> + +<p class="indent"> +<a name="page_165"><span class="page">Page 165</span></a> One issue +arises out of these facts, and that is that no engineer or investor +in valuing mines is justified in anticipating lower costs in regions +where cheap labor exists. +</p> + +<p class="indent"> +In supplement to sheer skill and intelligence, efficiency can be +gained only by the application of the man himself. A few months ago +a mine in California changed managers. The new head reduced the number +employed one-third without impairing the amount of work accomplished. +This was not the result of higher skill or intelligence in the men, +but in the manager. Better application and coördination were +secured from the working force. Inspiration to increase of exertion is +created less by "driving" than by recognition of individual effort, +in larger pay, and by extending justifiable hope of promotion. A +great factor in the proficiency of the mine manager is his ability +to create an <i>esprit-de-corps</i> through the whole staff, down +to the last tool boy. Friendly interest in the welfare of the men +and stimulation by competitions between various works and groups +all contribute to this end. +</p> + +<p class="indent"> +<b>Contract Work.</b>—The advantage both to employer and +employed of piece work over wage needs no argument. In a general way, +contract work honorably carried out puts a premium upon individual +effort, and thus makes for efficiency. There are some portions of +mine work which cannot be contracted, but the development, stoping, +and trucking can be largely managed in this way, and these items +cover 65 to 75% of the total labor expenditure underground. +</p> + +<p class="indent"> +In development there are two ways of basing contracts,—the +first on the footage of holes drilled, and the second on the footage +of heading advanced. In contract-stoping there are four methods +depending on the feet of hole drilled, on tonnage, on cubic space, +and on square area broken. +</p> + +<p class="indent"> +All these systems have their rightful application, conditioned upon +the class of labor and character of the deposit. +</p> + +<p class="indent"> +In the "hole" system, the holes are "pointed" by some mine official +and are blasted by a special crew. The miner therefore has little +interest in the result of the breaking. If he is a skilled white man, +the hours which he has wherein to contemplate <a name="page_166"><span +class="page">Page 166</span></a> the face usually enable him to place +holes to better advantage than the occasional visiting foreman. +With colored labor, the lack of intelligence in placing holes and +blasting usually justifies contracts per "foot drilled." Then the +holes are pointed and blasted by superintending men. +</p> + +<p class="indent"> +On development work with the foot-hole system, unless two working +faces can be provided for each contracting party, they are likely +to lose time through having finished their round of holes before the +end of the shift. As blasting must be done outside the contractor's +shifts, it means that one shift per day must be set aside for the +purpose. Therefore not nearly such progress can be made as where +working the face with three shifts. For these reasons, the "hole" +system is not so advantageous in development as the "foot of advance" +basis. +</p> + +<p class="indent"> +In stoping, the "hole" system has not only a wider, but a sounder +application. In large ore-bodies where there are waste inclusions, +it has one superiority over any system of excavation measurement, +namely, that the miner has no interest in breaking waste into the +ore. +</p> + +<p class="indent"> +The plan of contracting stopes by the ton has the disadvantage +that either the ore produced by each contractor must be weighed +separately, or truckers must be trusted to count correctly, and +to see that the cars are full. Moreover, trucks must be inspected +for waste,—a thing hard to do underground. So great are these +detailed difficulties that many mines are sending cars to the surface +in cages when they should be equipped for bin-loading and self-dumping +skips. +</p> + +<p class="indent"> +The method of contracting by the cubic foot of excavation saves +all necessity for determining the weight of the output of each +contractor. Moreover, he has no object in mixing waste with the ore, +barring the breaking of the walls. This system therefore requires +the least superintendence, permits the modern type of hoisting, +and therefore leaves little justification for the survival of the +tonnage basis. +</p> + +<p class="indent"> +Where veins are narrow, stoping under contract by the square foot +or fathom measured parallel to the walls has an advantage. The +miner has no object then in breaking wall-rock, and the <a +name="page_167"><span class="page">Page 167</span></a> thoroughness +of the ore-extraction is easily determined by inspection. +</p> + +<p class="indent"> +<b>Bonus Systems.</b>—By giving cash bonuses for special +accomplishment, much the same results can be obtained in some +departments as by contracting. A bonus per foot of heading gained +above a minimum, or an excess of trucks trammed beyond a minimum, +or prizes for the largest amount done during the week or month +in special works or in different shifts,—all these have a +useful application in creating efficiency. A high level of results +once established is easily maintained. +</p> + +<p class="indent"> +<b>Labor Unions.</b>—There is another phase of the labor +question which must be considered and that is the general relations +of employer and employed. In these days of largely corporate +proprietorship, the owners of mines are guided in their relations +with labor by engineers occupying executive positions. On them +falls the responsibility in such matters, and the engineer becomes +thus a buffer between labor and capital. As corporations have grown, +so likewise have the labor unions. In general, they are normal +and proper antidotes for unlimited capitalistic organization. +</p> + +<p class="indent"> +Labor unions usually pass through two phases. First, the inertia +of the unorganized labor is too often stirred only by demagogic +means. After organization through these and other agencies, the lack +of balance in the leaders often makes for injustice in demands, and +for violence to obtain them and disregard of agreements entered upon. +As time goes on, men become educated in regard to the rights of their +employers, and to the reflection of these rights in ultimate benefit +to labor itself. Then the men, as well as the intelligent employer, +endeavor to safeguard both interests. When this stage arrives, +violence disappears in favor of negotiation on economic principles, +and the unions achieve their greatest real gains. Given a union with +leaders who can control the members, and who are disposed to approach +differences in a business spirit, there are few sounder positions +for the employer, for agreements honorably carried out dismiss the +constant harassments of possible strikes. Such unions exist in dozens +of trades in this country, and they are <a name="page_168"><span +class="page">Page 168</span></a> entitled to greater recognition. +The time when the employer could ride roughshod over his labor is +disappearing with the doctrine of "<i>laissez faire</i>," on which +it was founded. The sooner the fact is recognized, the better for +the employer. The sooner some miners' unions develop from the first +into the second stage, the more speedily will their organizations +secure general respect and influence.[*] +</p> + +<p class="footnote"> +[Footnote *: Some years of experience with compulsory arbitration +in Australia and New Zealand are convincing that although the law +there has many defects, still it is a step in the right direction, +and the result has been of almost unmixed good to both sides. One +of its minor, yet really great, benefits has been a considerable +extinction of the parasite who lives by creating violence.] +</p> + +<p class="indent"> +The crying need of labor unions, and of some employers as well, +is education on a fundamental of economics too long disregarded +by all classes and especially by the academic economist. When the +latter abandon the theory that wages are the result of supply and +demand, and recognize that in these days of international flow of +labor, commodities and capital, the real controlling factor in +wages is efficiency, then such an educational campaign may become +possible. Then will the employer and employee find a common ground +on which each can benefit. There lives no engineer who has not +seen insensate dispute as to wages where the real difficulty was +inefficiency. No administrator begrudges a division with his men +of the increased profit arising from increased efficiency. But +every administrator begrudges the wage level demanded by labor +unions whose policy is decreased efficiency in the false belief +that they are providing for more labor. +</p> + +<h2><a name="page_169"><span class="page">Page 169</span></a> +CHAPTER XVII.</h2> + +<p class="center"> +<span class="sc">Administration</span> (<i>Continued</i>). +</p> + +<table class="summary"><tr><td class="summary"> +ACCOUNTS AND TECHNICAL DATA AND REPORTS; WORKING COSTS; DIVISION +OF EXPENDITURE; INHERENT LIMITATIONS IN ACCURACY OF WORKING COSTS; +WORKING COST SHEETS. GENERAL TECHNICAL DATA; LABOR, SUPPLIES, POWER, +SURVEYS, SAMPLING, AND ASSAYING. +</td></tr></table> + +<p class="indent"> +First and foremost, mine accounts are for guidance in the distribution +of expenditure and in the collection of revenue; secondly, they +are to determine the financial progress of the enterprise, its +profit or loss; and thirdly, they are to furnish statistical data to +assist the management in its interminable battle to reduce expenses +and increase revenue, and to enable the owner to determine the +efficiency of his administrators. Bookkeeping <i>per se</i> is +no part of this discussion. The fundamental purpose of that art +is to cover the first two objects, and, as such, does not differ +from its application to other commercial concerns. +</p> + +<p class="indent"> +In addition to these accounting matters there is a further type +of administrative report of equal importance—that is the +periodic statements as to the physical condition of the property, +the results of exploration in the mine, and the condition of the +equipment. +</p> + +<h3>ACCOUNTS.</h3> + +<p class="indent"> +The special features of mine accounting reports which are a development +to meet the needs of this particular business are the determination +of working costs, and the final presentation of these data in a +form available for comparative purposes. +</p> + +<p class="indent"> +The subject may be discussed under:— +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td>1.</td><td>Classes of mine expenditure.</td></tr> +<tr><td>2.</td><td>Working costs. + <a name="page_170"><span class="page">Page 170</span></a> + </td></tr> +<tr><td>3.</td><td>The dissection of expenditures + departmentally.</td></tr> +<tr><td>4.</td><td>Inherent limitations in the accuracy of working + costs.</td></tr> +<tr><td>5.</td><td>Working cost sheets.</td></tr> +</table> + +<p class="indent"> +In a wide view, mine expenditures fall into three classes, which +maybe termed the "fixed charges," "proportional charges," and "suspense +charges" or "capital expenditure." "Fixed charges" are those which, +like pumping and superintendence, depend upon time rather than +tonnage and material handled. They are expenditures that would not +decrease relatively to output. "Proportional charges" are those +which, like ore-breaking, stoping, supporting stopes, and tramming, +are a direct coefficient of the ore extracted. "Suspense charges" are +those which are an indirect factor of the cost of the ore produced, +such as equipment and development. These expenditures are preliminary +to output, and they thus represent a storage of expense to be charged +off when the ore is won. This outlay is often called "capital +expenditure." Such a term, though in common use, is not strictly +correct, for the capital value vanishes when the ore is extracted, +but in conformity with current usage the term "capital expenditure" +will be adopted. +</p> + +<p class="indent"> +Except for the purpose of special inquiry, such as outlined under +the chapter on "Ratio of Output," "fixed charges" are not customarily +a special division in accounts. In a general way, such expenditures, +combined with the "proportional charges," are called "revenue +expenditure," as distinguished from the capital, or "suspense," +expenditures. In other words, "revenue" expenditures are those +involved in the daily turnover of the business and resulting in +immediate returns. The inherent difference in character of revenue +and capital expenditures is responsible for most of the difficulties +in the determination of working costs, and most of the discussion +on the subject. +</p> + +<p class="indent"> +<b>Working Costs.</b>—"Working costs" are a division of +expenditure for some unit,—the foot of opening, ton of ore, +a pound of metal, cubic yard or fathom of material excavated, or +some other measure. The costs per unit are usually deduced for +each month and each year. They are generally determined for each +of the <a name="page_171"><span class="page">Page 171</span></a> +different departments of the mine or special works separately. +Further, the various sorts of expenditure in these departments are +likewise segregated. +</p> + +<p class="indent"> +In metal mining the ton is the universal unit of distribution for +administrative purpose, although the pound of metal is often used +to indicate final financial results. The object of determination of +"working costs" is fundamentally for comparative purposes. Together +with other technical data, they are the nerves of the administration, +for by comparison of detailed and aggregate results with other mines +and internally in the same mine, over various periods and between +different works, a most valuable check on efficiency is possible. +Further, there is one collateral value in all statistical data not +to be overlooked, which is that the knowledge of its existence +induces in the subordinate staff both solicitude and emulation. +</p> + +<p class="indent"> +The fact must not be lost sight of, however, that the wide variations +in physical and economic environment are so likely to vitiate +conclusions from comparisons of statistics from two mines or from +two detailed works on the same mine, or even from two different +months on the same work, that the greatest care and discrimination +are demanded in their application. Moreover, the inherent difficulties +in segregating and dividing the accounts which underlie such data, +render it most desirable to offer some warning regarding the limits +to which segregation and division may be carried to advantage. +</p> + +<p class="indent"> +As working costs are primarily for comparisons, in order that they +may have value for this purpose they must include only such items +of expenditure as will regularly recur. If this limitation were more +generally recognized, a good deal of dispute and polemics on the +subject might be saved. For this reason it is quite impossible that +all the expenditure on the mine should be charged into working costs, +particularly some items that arise through "capital expenditure." +</p> + +<p class="indent"> +<b>The Dissection of Expenditures Departmentally.</b>—The +final division in the dissection of the mine expenditure is in +the main:— +</p> + +<table style="margin-top: 1em; margin-bottom: 1em; font-size: smaller; + border-collapse: collapse;"> +<tr><td rowspan="3" style="border-right: solid black 1px; + text-align: center;"> + <i>Revenue.</i></td> + <td style="border-top: solid black 1px;"> </td> + <td style="vertical-align: top;">(1) + <a name="page_172"><span class="page">Page 172</span></a></td> + <td colspan="2" style="vertical-align: top;">General Expenses.</td> + <td rowspan="3" style="border-left: solid black 1px; + border-top: solid black 1px; border-bottom: solid black 1px;"> + </td> + <td rowspan="3">Ore-breaking.<br>Supporting Stopes.<br> + Trucking Ore.<br>Hoisting.</td> + <td rowspan="6" style="border-right: solid black 1px; + border-top: solid black 1px; border-bottom: solid black 1px;"> + </td> + <td rowspan="6">Various expenditures for + labor, supplies, power, repairs, etc., worked out per ton or + foot advanced over each department.</td></tr> +<tr><td> </td> + <td style="vertical-align: top;">(2)</td> + <td style="vertical-align: top;">Ore Extraction.</td> + <td style="vertical-align: top; text-align: right;">—</td></tr> +<tr><td style="border-bottom: solid black 1px;"> </td> + <td style="vertical-align: top;">(3)</td> + <td colspan="2" style="vertical-align: top;">Pumping.</td></tr> +<tr><td colspan="7"> </td></tr> +<tr><td colspan="5"> </td> + <td rowspan="2" style="border-left: solid black 1px; + border-top: solid black 1px; border-bottom: solid black 1px;"> + </td> + <td rowspan="2"> + Shaft-sinking.<br>Station-cutting.<br>Crosscutting.<br> + Driving.<br>Rising.<br>Winzes.<br>Diamond Drilling.</td></tr> +<tr><td rowspan="3" style="border-right: solid black 1px; + text-align: center;"> + <i>Capital<br>or<br>Suspense.</i></td> + <td style="border-top: solid black 1px;"> </td> + <td style="vertical-align: top;">(4)</td> + <td style="vertical-align: top;">Development.</td> + <td style="vertical-align: top; text-align: right;">—</td></tr> +<tr><td colspan="7"> </td></tr> +<tr><td style="border-bottom: solid black 1px;"> </td> + <td style="vertical-align: top;">(5)</td> + <td colspan="2" style="vertical-align: top;">Construction and + Equipment.</td> + <td style="border-right: solid black 1px; + border-top: solid black 1px; border-bottom: solid black 1px;"> + </td> + <td>Various Works.</td> + <td colspan="2"> </td></tr> +</table> + +<p class="indent"> +The detailed dissection of expenditures in these various departments +with view to determine amount of various sorts of expenditure over +the department, or over some special work in that department, is +full of unsolvable complications. The allocation of the direct +expenditure of labor and supplies applied to the above divisions or +special departments in them, is easily accomplished, but beyond this +point two sorts of difficulties immediately arise and offer infinite +field for opinion and method. The first of these difficulties arises +from supplementary departments on the mine, such as "power," "repairs +and maintenance," "sampling and assaying." These departments must +be "spread" over the divisions outlined above, for such charges +are in part or whole a portion of the expense of these divisions. +Further, all of these "spread" departments are applied to surface as +well as to underground works, and must be divided not only over the +above departments but also over the surface departments,—not +under discussion here. The common method is to distribute "power" on +a basis of an approximation of the amount used in each department; +to distribute "repairs and maintenance," either on a basis of shop +returns, or a distribution over all departments on the basis of +the labor employed in those departments, on the theory that such +repairs arise in this proportion; to distribute sampling and assaying +over the actual points to which they relate at the average cost +per sample or assay. +</p> + +<p class="indent"> +<a name="page_173"><span class="page">Page 173</span></a> "General +expenses," that is, superintendence, etc., are often not included +in the final departments as above, but are sometimes "spread" in an +attempt to charge a proportion of superintendence to each particular +work. As, however, such "spreading" must take place on the basis of +the relative expenditure in each department, the result is of little +value, for such a basis does not truly represent the proportion of +general superintendence, etc., devoted to each department. If they +are distributed over all departments, capital as well as revenue, +on the basis of total expenditure, they inflate the "capital +expenditure" departments against a day of reckoning when these +charges come to be distributed over working costs. Although it may +be contended that the capital departments also require supervision, +such a practice is a favorite device for showing apparently low +working costs in the revenue departments. The most courageous way +is not to distribute general expenses at all, but to charge them +separately and directly to revenue accounts and thus wholly into +working costs. +</p> + +<p class="indent"> +The second problem is to reduce the "suspense" or capital charges +to a final cost per ton, and this is no simple matter. Development +expenditures bear a relation to the tonnage developed and not to +that extracted in any particular period. If it is desired to preserve +any value for comparative purposes in the mining costs, such outlay +must be charged out on the basis of the tonnage developed, and such +portion of the ore as is extracted must be written off at this +rate; otherwise one month may see double the amount of development +in progress which another records, and the underground costs would +be swelled or diminished thereby in a way to ruin their comparative +value from month to month. The ore developed cannot be satisfactorily +determined at short intervals, but it can be known at least annually, +and a price may be deduced as to its cost per ton. In many mines +a figure is arrived at by estimating ore-reserves at the end of +the year, and this figure is used during the succeeding year as a +"redemption of development" and as such charged to working costs, and +thus into revenue account in proportion to the tonnage extracted. This +matter is further elaborated in some mines, <a name="page_174"><span +class="page">Page 174</span></a> in that winzes and rises are written +off at one rate, levels and crosscuts at another, and shafts at +one still lower, on the theory that they lost their usefulness in +this progression as the ore is extracted. This course, however, +is a refinement hardly warranted. +</p> + +<p class="indent"> +Plant and equipment constitute another "suspense" account even +harder to charge up logically to tonnage costs, for it is in many +items dependent upon the life of the mine, which is an unknown +factor. Most managers debit repairs and maintenance directly to +the revenue account and leave the reduction of the construction +outlay to an annual depreciation on the final balance sheet, on the +theory that the plant is maintained out of costs to its original +value. This subject will be discussed further on. +</p> + +<p class="indent"> +<b>Inherent Limitations in Accuracy of Working Costs.</b>—There +are three types of such limitations which arise in the determination +of costs and render too detailed dissection of such costs hopeless of +accuracy and of little value for comparative purposes. They are, first, +the difficulty of determining all of even direct expenditure on any +particular crosscut, stope, haulage, etc.; second, the leveling effect +of distributing the "spread" expenditures, such as power, repairs, +etc.; and third, the difficulties arising out of the borderland +of various departments. +</p> + +<p class="indent"> +Of the first of these limitations the instance may be cited that +foremen and timekeepers can indicate very closely the destination of +labor expense, and also that of some of the large items of supply, +such as timber and explosives, but the distribution of minor supplies, +such as candles, drills, picks, and shovels, is impossible of accurate +knowledge without an expense wholly unwarranted by the information +gained. To determine at a particular crosscut the exact amount of +steel, and of tools consumed, and the cost of sharpening them, +would entail their separate and special delivery to the same place +of attack and a final weighing-up to learn the consumption. +</p> + +<p class="indent"> +Of the second sort of limitations, the effect of "spread" expenditure, +the instance may be given that the repairs and maintenance are done +by many men at work on timbers, tracks, <a name="page_175"><span +class="page">Page 175</span></a> machinery, etc. It is hopeless to +try and tell how much of their work should be charged specifically +to detailed points. In the distribution of power may be taken the +instance of air-drills. Although the work upon which the drill is +employed can be known, the power required for compression usually +comes from a common power-plant, so that the portion of power debited +to the air compressor is an approximation. The assumption of an +equal consumption of air by all drills is a further approximation. +In practice, therefore, many expenses are distributed on the theory +that they arise in proportion to the labor employed, or the machines +used in the various departments. The net result is to level down +expensive points and level up inexpensive ones. +</p> + +<p class="indent"> +The third sort of limitation of accounting difficulty referred +to, arises in determining into which department are actually to be +allocated the charges which lie in the borderland between various +primary classes of expenditure. For instance, in ore won from +development,—in some months three times as much development +may be in ore as in other months. If the total expense of development +work which yields ore be charged to stoping account, and if cost be +worked out on the total tonnage of ore hoisted, then the stoping +cost deduced will be erratic, and the true figures will be obscured. +On the other hand, if all development is charged to 'capital account' +and the stoping cost worked out on all ore hoisted, it will include +a fluctuating amount of ore not actually paid for by the revenue +departments or charged into costs. This fluctuation either way +vitiates the whole comparative value of the stoping costs. In the +following system a compromise is reached by crediting "development" +with an amount representing the ore won from development at the +average cost of stoping, and by charging this amount into "stoping." +A number of such questions arise where the proper division is simply +a matter of opinion. +</p> + +<p class="indent"> +The result of all these limitations is that a point in detail is +quickly reached where no further dissection of expenditure is justified, +since it becomes merely an approximation. The writer's own impression +is that without an unwarrantable number of accountants, no manager can +tell with any accuracy the <a name="page_176"><span class="page">Page +176</span></a> cost of any particular stope, or of any particular +development heading. Therefore, aside from some large items, such +detailed statistics, if given, are to be taken with great reserve. +</p> + +<p class="indent"> +<b>Working Cost Sheets.</b>—There are an infinite number +of forms of working cost sheets, practically every manager having +a system of his own. To be of greatest value, such sheets should +show on their face the method by which the "spread" departments are +handled, and how revenue and suspense departments are segregated. +When too much detail is presented, it is but a waste of accounting +and consequent expense. Where to draw the line in this regard is, +however, a matter of great difficulty. No cost sheet is entirely +satisfactory. The appended sheet is in use at a number of mines. +It is no more perfect than many others. It will be noticed that +the effect of this system is to throw the general expenses into the +revenue expenditures, and as little as possible into the "suspense" +account. +</p> + +<h3>GENERAL TECHNICAL DATA.</h3> + +<p class="indent"> +For the purposes of efficient management, the information gathered +under this head is of equal, if not superior, importance to that +under "working costs." Such data fall generally under the following +heads:— +</p> + +<p class="indent"> +<b>Labor.</b>—Returns of the shifts worked in the various +departments for each day and for the month; worked out on a monthly +basis of footage progress, tonnage produced or tons handled per +man; also where possible the footage of holes drilled, worked out +per man and per machine. +</p> + +<p class="indent"> +<b>Supplies.</b>—Daily returns of supplies used; the principal +items worked out monthly in quantity per foot of progress, or per +ton of ore produced. +</p> + +<p class="indent"> +<b>Power.</b>—Fuel, lubricant, etc., consumed in steam production, +worked out into units of steam produced, and this production allocated +to the various engines. Where electrical power is used, the consumption +of the various motors is set out. +</p> + +<p class="indent"> +<b>Surveys.</b>—The need of accurate plans requires no discussion. +Aside from these, the survey-office furnishes the returns <a +name="page_177"><span class="page">Page 177</span></a> of development +footage, measurements under contracts, and the like. +</p> + +<p class="indent"> +<b>Sampling and Assaying.</b>—Mine sampling and assaying fall +under two heads,—the determination of the value of standing +ore, and of products from the mine. The sampling and assaying on a +going mine call for the same care and method as in cases of valuation +of the mine for purchase,—the details of which have been +presented under "Mine Valuation,"—for through it, guidance +must not only be had to the value of the mine and for reports to +owners, but the detailed development and ore extraction depend +on an absolute knowledge of where the values lie. +</p> + +<h2><a name="page_178"><span class="page">Page 178</span></a> +CHAPTER XVIII.</h2> + +<p class="center"> +ADMINISTRATION (<i>Concluded</i>). +</p> + +<table class="summary"><tr><td class="summary"> +ADMINISTRATIVE REPORTS. +</td></tr></table> + +<p class="indent"> +In addition to financial returns showing the monthly receipts, +expenditures, and working costs, there must be in proper administration +periodic reports from the officers of the mine to the owners or +directors as to the physical progress of the enterprise. Such reports +must embrace details of ore extraction, metal contents, treatment +recoveries, construction of equipment, and the results of underground +development. The value of mines is so much affected by the monthly +or even daily result of exploration that reports of such work are +needed very frequently,—weekly or even daily if critical +work is in progress. These reports must show the width, length, +and value of the ore disclosed. +</p> + +<p class="indent"> +The tangible result of development work is the tonnage and grade +of ore opened up. How often this stock-taking should take place +is much dependent upon the character of the ore. The result of +exploration in irregular ore-bodies often does not, over short +periods, show anything tangible in definite measurable tonnage, +but at least annually the ore reserve can be estimated. +</p> + +<p class="indent"> +In mines owned by companies, the question arises almost daily as +to how much of and how often the above information should be placed +before stockholders (and therefore the public) by the directors. In +a general way, any company whose shares are offered on the stock +exchange is indirectly inviting the public to become partners in the +business, and these partners are entitled to all the information +which affects the value of their property and are entitled to it +promptly. Moreover, mining is a business where competition is so +obscure and so much a matter of indifference, that suppression of +important <a name="page_179"><span class="page">Page 179</span></a> +facts in documents for public circulation has no justification. +On the other hand, both the technical progress of the industry +and its position in public esteem demand the fullest disclosure +and greatest care in preparation of reports. Most stockholders' +ignorance of mining technology and of details of their particular +mine demands a great deal of care and discretion in the preparation +of these public reports that they may not be misled. Development +results may mean little or much, depending upon the location of +the work done in relation to the ore-bodies, etc., and this should +be clearly set forth. +</p> + +<p class="indent"> +The best opportunity of clear, well-balanced statements lies in +the preparation of the annual report and accounts. Such reports +are of three parts:— +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td class="topleft">1.</td> + <td>The "profit and loss" account, or the "revenue + account."</td></tr> +<tr><td class="topleft">2.</td> + <td>The balance sheet; that is, the assets and liabilities + statement.</td></tr> +<tr><td class="topleft">3.</td> + <td>The reports of the directors, manager, and consulting + engineer.</td></tr> +</table> + +<p class="indent"> +The first two items are largely matters of bookkeeping. They or +the report should show the working costs per ton for the year. +What must be here included in costs is easier of determination +than in the detailed monthly cost sheets of the administration; +for at the annual review, it is not difficult to assess the amount +chargeable to development. Equipment expenditure, however, presents +an annual difficulty, for, as said, the distribution of this item +is a factor of the life of the mine, and that is unknown. If such +a plant has been paid for out of the earnings, there is no object +in carrying it on the company's books as an asset, and most +well-conducted companies write it off at once. On the other hand, +where the plant is paid for out of capital provided for the purpose, +even to write off depreciation means that a corresponding sum of +cash must be held in the company's treasury in order to balance the +accounts,—in other words, depreciation in such an instance +becomes a return of capital. The question then is one of policy in +the company's finance, and in neither case is it a matter which +can be brought into working costs and <a name="page_180"><span +class="page">Page 180</span></a> leave them any value for comparative +purposes. Indeed, the true cost of working the ore from any mine +can only be told when the mine is exhausted; then the dividends +can be subtracted from the capital sunk and metal sold, and the +difference divided over the total tonnage produced. +</p> + +<p class="indent"> +The third section of the report affords wide scope for the best +efforts of the administration. This portion of the report falls +into three divisions: (<i>a</i>) the construction and equipment +work of the year, (<i>b</i>) the ore extraction and treatment, +and (<i>c</i>) the results of development work. +</p> + +<p class="indent"> +The first requires a statement of the plant constructed, its object +and accomplishment; the second a disclosure of tonnage produced, +values, metallurgical and mechanical efficiency. The third is of +the utmost importance to the stockholder, and is the one most often +disregarded and obscured. Upon this hinges the value of the property. +There is no reason why, with plans and simplicity of terms, such +reports cannot be presented in a manner from which the novice can +judge of the intrinsic position of the property. A statement of +the tonnage of ore-reserves and their value, or of the number of +years' supply of the current output, together with details of ore +disclosed in development work, and the working costs, give the +ground data upon which any stockholder who takes interest in his +investment may judge for himself. Failure to provide such data +will some day be understood by the investing public as a <i>prima +facie</i> index of either incapacity or villainy. By the insistence +of the many engineers in administration of mines upon the publication +of such data, and by the insistence of other engineers upon such +data for their clients before investment, and by the exposure of +the delinquents in the press, a more practicable "protection of +investors" can be reached than by years of academic discussion. +</p> + +<h2><a name="page_181"><span class="page">Page 181</span></a> +CHAPTER XIX.</h2> + +<p class="center"> +<span class="sc">The Amount of Risk in Mining Investments.</span> +</p> + +<table class="summary"><tr><td class="summary"> +RISK IN VALUATION OF MINES; IN MINES AS COMPARED WITH OTHER COMMERCIAL +ENTERPRISES. +</td></tr></table> + +<p class="indent"> +From the constant reiteration of the risks and difficulties involved +in every step of mining enterprise from the valuation of the mine +to its administration as a going concern, the impression may be +gained that the whole business is one great gamble; in other words, +that the point whereat certainties stop and conjecture steps in +is so vital as to render the whole highly speculative. +</p> + +<p class="indent"> +Far from denying that mining is, in comparison with better-class +government bonds, a speculative type of investment, it is desirable +to avow and emphasize the fact. But it is none the less well to +inquire what degree of hazard enters in and how it compares with +that in other forms of industrial enterprise. +</p> + +<p class="indent"> +Mining business, from an investment view, is of two +sorts,—prospecting ventures and developed mines; that is, +mines where little or no ore is exposed, and mines where a definite +quantity of ore is measurable or can be reasonably anticipated. +The great hazards and likewise the Aladdin caves of mining are +mainly confined to the first class. Although all mines must pass +through the prospecting stage, the great industry of metal production +is based on developed mines, and it is these which should come +into the purview of the non-professional investor. The first class +should be reserved invariably for speculators, and a speculator may +be defined as one who hazards all to gain much. It is with mining +as an investment, however, that this discussion is concerned. +</p> + +<p class="indent"> +<b>Risk in Valuation of Mines.</b>—Assuming a competent collection +of data and efficient management of the property, the risks in +valuing are from step to step:— +<a name="page_182"><span class="page">Page 182</span></a></p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td class="topleft">1.</td> + <td>The risk of continuity in metal contents beyond sample + faces.</td></tr> +<tr><td class="topleft">2.</td> + <td>The risk of continuity in volume through the blocks + estimated.</td></tr> +<tr><td class="topleft">3.</td> + <td>The risk of successful metallurgical treatment.</td></tr> +<tr><td class="topleft">4.</td> + <td>The risk of metal prices, in all but gold.</td></tr> +<tr><td class="topleft">5.</td> + <td>The risk of properly estimating costs.</td></tr> +<tr><td class="topleft">6.</td> + <td>The risk of extension of the ore beyond exposures.</td></tr> +<tr><td class="topleft">7.</td> + <td>The risk of management.</td></tr> +</table> + +<p class="indent"> +As to the continuity of values and volumes through the estimated +area, the experience of hundreds of engineers in hundreds of mines +has shown that when the estimates are based on properly secured +data for "proved ore," here at least there is absolutely no hazard. +Metallurgical treatment, if determined by past experience on the +ore itself, carries no chance; and where determined by experiment, +the risk is eliminated if the work be sufficiently exhaustive. The +risk of metal price is simply a question of how conservative a +figure is used in estimating. It can be eliminated if a price low +enough be taken. Risk of extension in depth or beyond exposures +cannot be avoided. It can be reduced in proportion to the distance +assumed. Obviously, if no extension is counted, there is nothing +chanced. The risk of proper appreciation of costs is negligible where +experience in the district exists. Otherwise, it can be eliminated +if a sufficiently large allowance is taken. The risk of failure to +secure good management can be eliminated if proved men are chosen. +</p> + +<p class="indent"> +There is, therefore, a basic value to every mine. The "proved" +ore taken on known metallurgical grounds, under known conditions +of costs on minimum prices of metals, has a value as certain as +that of money in one's own vault. This is the value previously +referred to as the "<i>A</i>" value. If the price (and interest on +it pending recovery) falls within this amount, there is no question +that the mine is worth the price. What the risk is in mining is +simply what amount the price of the investment demands shall be won +from extension of the deposit beyond known <a name="page_183"><span +class="page">Page 183</span></a> exposures, or what higher price +of metal must be realized than that calculated in the "<i>A</i>" +value. The demands on this <i>X, Y</i> portion of the mine can be +converted into tons of ore, life of production, or higher prices, +and these can be weighed with the geological weights and the industrial +outlook. +</p> + +<p class="indent"> +<b>Mines compared to Other Commercial Enterprises.</b>—The +profits from a mining venture over and above the bed-rock value +<i>A</i>, that is, the return to be derived from more extensive +ore-recovery and a higher price of metal, may be compared to the value +included in other forms of commercial enterprise for "good-will." Such +forms of enterprise are valued on a basis of the amount which will +replace the net assets plus (or minus) an amount for "good-will," +that is, the earning capacity. This good-will is a speculation of +varying risk depending on the character of the enterprise. For +natural monopolies, like some railways and waterworks, the risk +is less and for shoe factories more. Even natural monopolies are +subject to the risks of antagonistic legislation and industrial +storms. But, eliminating this class of enterprise, the speculative +value of a good-will involves a greater risk than prospective value +in mines, if properly measured; because the dangers of competition +and industrial storms do not enter to such a degree, nor is the +future so dependent upon the human genius of the founder or manager. +Mining has reached such a stage of development as a science that +management proceeds upon comparatively well-known lines. It is +subject to known checks through the opportunity of comparisons +by which efficiency can be determined in a manner more open for +the investor to learn than in any other form of industry. While +in mining an estimate of a certain minimum of extension in depth, +as indicated by collateral factors, may occasionally fall short, +it will, in nine cases out of ten, be exceeded. If investment in +mines be spread over ten cases, similarly valued as to minimum of +extension, the risk has been virtually eliminated. The industry, +if reduced to the above basis for financial guidance, is a more +profitable business and is one of less hazards than competitive +forms of commercial enterprises. +</p> + +<p class="indent"> +In view of what has been said before, it may be unnecessary <a +name="page_184"><span class="page">Page 184</span></a> to refer +again to the subject, but the constant reiteration by wiseacres +that the weak point in mining investments lies in their short life +and possible loss of capital, warrants a repetition that the <i>A, +B, C</i> of proper investment in mines is to be assured, by the +"<i>A</i>" value, of a return of the whole or major portion of the +capital. The risk of interest and profit may be deferred to the <i>X, +Y</i> value, and in such case it is on a plane with "good-will." +It should be said at once to that class who want large returns on +investment without investigation as to merits, or assurance as +to the management of the business, that there is no field in this +world for the employment of their money at over 4%. +</p> + +<p class="indent"> +Unfortunately for the reputation of the mining industry, and metal +mines especially, the business is often not conducted or valued on +lines which have been outlined in these chapters. There is often +the desire to sell stocks beyond their value. There is always the +possibility that extension in depth will reveal a glorious Eldorado. +It occasionally does, and the report echoes round the world for years, +together with tributes to the great judgment of the exploiters. The +volume of sound allures undue numbers of the venturesome, untrained, +and ill-advised public to the business, together with a mob of +camp-followers whose objective is to exploit the ignorant by preying +on their gambling instincts. Thus a considerable section of metal +mining industry is in the hands of these classes, and a cloud of +disrepute hangs ever in the horizon. +</p> + +<p class="indent"> +There has been a great educational campaign in progress during the +past few years through the technical training of men for conduct +of the industry, by the example of reputable companies in regularly +publishing the essential facts upon which the value of their mines +is based, and through understandable nontechnical discussion in +and by some sections of the financial and general press. The real +investor is being educated to distinguish between reputable concerns +and the counters of gamesters. Moreover, yearly, men of technical +knowledge are taking a stronger and more influential part in mining +finance and in the direction of mining and exploration companies. +The net result of these forces will be to put mining on a better +plane. +</p> + +<h2><a name="page_185"><span class="page">Page 185</span></a> +CHAPTER XX.</h2> + +<p class="center"> +<span class="sc">The Character, Training, and Obligations of the +Mining Engineering Profession.</span> +</p> + +<p class="indent"> +In a discussion of some problems of metal mining from the point +of view of the direction of mining operations it may not be amiss +to discuss the character of the mining engineering profession in +its bearings on training and practice, and its relations to the +public. +</p> + +<p class="indent"> +The most dominant characteristic of the mining engineering profession +is the vast preponderance of the commercial over the technical in +the daily work of the engineer. For years a gradual evolution has +been in progress altering the larger demands on this branch of the +engineering profession from advisory to executive work. The mining +engineer is no longer the technician who concocts reports and blue +prints. It is demanded of him that he devise the finance, construct +and manage the works which he advises. The demands of such executive +work are largely commercial; although the commercial experience +and executive ability thus become one pier in the foundation of +training, the bridge no less requires two piers, and the second +is based on technical knowledge. Far from being deprecated, these +commercial phases cannot be too strongly emphasized. On the other +hand, I am far from contending that our vocation is a business +rather than a profession. +</p> + +<p class="indent"> +For many years after the dawn of modern engineering, the members +of our profession were men who rose through the ranks of workmen, +and as a result, we are to this day in the public mind a sort of +superior artisan, for to many the engine-driver is equally an engineer +with the designer of the engine, yet their real relation is but as +the hand to the brain. At a later period the recruits entered by +apprenticeship to those men who had established their intellectual +superiority to their fellow-workers. <a name="page_186"><span +class="page">Page 186</span></a> These men were nearly always employed +in an advisory way—subjective to the executive head. +</p> + +<p class="indent"> +During the last few decades, the advance of science and the complication +of industry have demanded a wholly broader basis of scientific and +general training for its leaders. Executive heads are demanded who +have technical training. This has resulted in the establishment of +special technical colleges, and compelled a place for engineering +in the great universities. The high intelligence demanded by the +vocation itself, and the revolution in training caused by the +strengthening of its foundations in general education, has finally, +beyond all question, raised the work of application of science to +industry to the dignity of a profession on a par with the law, +medicine, and science. It demands of its members equally high mental +attainments,—and a more rigorous training and experience. +Despite all this, industry is conducted for commercial purposes, +and leaves no room for the haughty intellectual superiority assumed +by some professions over business callings. +</p> + +<p class="indent"> +There is now demanded of the mining specialist a wide knowledge +of certain branches of civil, mechanical, electrical, and chemical +engineering, geology, economics, the humanities, and what not; and +in addition to all this, engineering sense, executive ability, +business experience, and financial insight. Engineering sense is +that fine blend of honesty, ingenuity, and intuition which is a +mental endowment apart from knowledge and experience. Its possession +is the test of the real engineer. It distinguishes engineering as +a profession from engineering as a trade. It is this sense that +elevates the possessor to the profession which is, of all others, +the most difficult and the most comprehensive. Financial insight can +only come by experience in the commercial world. Likewise must come +the experience in technical work which gives balance to theoretical +training. Executive ability is that capacity to coördinate and +command the best results from other men,—it is a natural +endowment. which can be cultivated only in actual use. +</p> + +<p class="indent"> +The practice of mine engineering being so large a mixture of business, +it follows that the whole of the training of this <a +name="page_187"><span class="page">Page 187</span></a> profession +cannot be had in schools and universities. The commercial and executive +side of the work cannot be taught; it must be absorbed by actual +participation in the industry. Nor is it impossible to rise to +great eminence in the profession without university training, as +witness some of our greatest engineers. The university can do much; +it can give a broad basis of knowledge and mental training, and can +inculcate moral feeling, which entitles men to lead their fellows. It +can teach the technical fundamentals of the multifold sciences which +the engineer should know and must apply. But after the university +must come a schooling in men and things equally thorough and more +arduous. +</p> + +<p class="indent"> +In this predominating demand for commercial qualifications over +the technical ones, the mining profession has differentiated to +a great degree from its brother engineering branches. That this +is true will be most apparent if we examine the course through +which engineering projects march, and the demands of each stage +on their road to completion. +</p> + +<p class="indent"> +The life of all engineering projects in a general way may be divided +into five phases:[*]— +</p> + +<p class="footnote"> +[Footnote *: These phases do not necessarily proceed step by step. +For an expanding works especially, all of them may be in process +at the same time, but if each item be considered to itself, this +is the usual progress, or should be when properly engineered.] +</p> + +<table style="margin-left: 1em; border-collapse: collapse;"> +<tr><td class="topleft">1.</td> + <td>Determination of the value of the project.</td></tr> +<tr><td class="topleft">2.</td> + <td>Determination of the method of attack.</td></tr> +<tr><td class="topleft">3.</td> + <td>The detailed delineation of method, means, and tools.</td></tr> +<tr><td class="topleft">4.</td> + <td>The execution of the works.</td></tr> +<tr><td class="topleft">5.</td> + <td>The operation of the completed works.</td></tr> +</table> + +<p class="indent"> +These various stages of the resolution of an engineering project +require in each more or less of every quality of intellect, training, +and character. At the different stages, certain of these qualities +are in predominant demand: in the first stage, financial insight; +in the second, "engineering sense"; in the third, training and +experience; in the fourth and fifth, executive ability. +</p> + +<p class="indent"> +A certain amount of compass over the project during the <a +name="page_188"><span class="page">Page 188</span></a> whole five stages +is required by all branches of the engineering profession,—harbor, +canal, railway, waterworks, bridge, mechanical, electrical, etc.; +but in none of them so completely and in such constant combination +is this demanded as in mining. +</p> + +<p class="indent"> +The determination of the commercial value of projects is a greater +section of the mining engineer's occupation than of the other +engineering branches. Mines are operated only to earn immediate +profits. No question of public utility enters, so that all mining +projects have by this necessity to be from the first weighed from +a profit point of view alone. The determination of this question +is one which demands such an amount of technical knowledge and +experience that those who are not experts cannot enter the +field,—therefore the service of the engineer is always demanded +in their satisfactory solution. Moreover, unlike most other engineering +projects, mines have a faculty of changing owners several times +during their career, so that every one has to survive a periodic +revaluation. From the other branches of engineering, the electrical +engineer is the most often called upon to weigh the probabilities +of financial success of the enterprise, but usually his presence +in this capacity is called upon only at the initial stage, for +electrical enterprises seldom change hands. The mechanical and +chemical branches are usually called upon for purely technical +service on the demand of the operator, who decides the financial +problems for himself, or upon works forming but units in undertakings +where the opinion on the financial advisability is compassed by some +other branch of the engineering profession. The other engineering +branches, even less often, are called in for financial advice, +and in those branches involving works of public utility the +profit-and-loss phase scarcely enters at all. +</p> + +<p class="indent"> +Given that the project has been determined upon, and that the enterprise +has entered upon the second stage, that of determination of method of +attack, the immediate commercial result limits the mining engineer's +every plan and design to a greater degree than it does the other +engineering specialists. The question of capital and profit dogs +his every footstep, for all mines are ephemeral; the life of any +given mine is short. <a name="page_189"><span class="page">Page +189</span></a> Metal mines have indeed the shortest lives of any. +While some exceptional ones may produce through one generation, +under the stress of modern methods a much larger proportion extend +only over a decade or two. But of more pertinent force is the fact +that as the certain life of a metal mine can be positively known in +most cases but a short period beyond the actual time required to +exhaust the ore in sight, not even a decade of life to the enterprise +is available for the estimates of the mining engineer. Mining works +are of no value when the mine is exhausted; the capital invested +must be recovered in very short periods, and therefore all mining +works must be of the most temporary character that will answer. +The mining engineer cannot erect a works that will last as long as +possible; it is to last as long as the mine only, and, in laying +it out, forefront in his mind must be the question, Can its cost +be redeemed in the period of use of which I am certain it will +find employment? If not, will some cheaper device, which gives +less efficiency, do? The harbor engineer, the railway engineer, +the mechanical engineer, build as solidly as they can, for the +demand for the work will exist till after their materials are worn +out, however soundly they construct. +</p> + +<p class="indent"> +Our engineer cousins can, in a greater degree by study and +investigation, marshal in advance the factors with which they have +to deal. The mining engineer's works, on the other hand, depend +at all times on many elements which, from the nature of things, +must remain unknown. No mine is laid bare to study and resolve +in advance. We have to deal with conditions buried in the earth. +Especially in metal mines we cannot know, when our works are initiated, +what the size, mineralization, or surroundings of the ore-bodies +will be. We must plunge into them and learn,—and repent. +Not only is the useful life of our mining works indeterminate, +but the very character of them is uncertain in advance. All our +works must be in a way doubly tentative, for they are subject to +constant alterations as they proceed. +</p> + +<p class="indent"> +Not only does this apply to our initial plans, but to our daily +amendment of them as we proceed into the unknown. Mining engineering +is, therefore, never ended with the initial determination <a +name="page_190"><span class="page">Page 190</span></a> of a method. +It is called upon daily to replan and reconceive, coincidentally +with the daily progress of the constructions and operation. Weary +with disappointment in his wisest conception, many a mining engineer +looks jealously upon his happier engineering cousin, who, when he +designs a bridge, can know its size, its strains, and its cost, +and can wash his hands of it finally when the contractor steps +in to its construction. And, above all, it is no concern of his +whether it will pay. Did he start to build a bridge over a water, +the width or depth or bottom of which he could not know in advance, +and require to get its cost back in ten years, with a profit, his +would be a task of similar harassments. +</p> + +<p class="indent"> +As said before, it is becoming more general every year to employ +the mining engineer as the executive head in the operation of mining +engineering projects, that is, in the fourth and fifth stages of +the enterprise. He is becoming the foreman, manager, and president +of the company, or as it may be contended by some, the executive +head is coming to have technical qualifications. Either way, in +no branch of enterprise founded on engineering is the operative +head of necessity so much a technical director. Not only is this +caused by the necessity of executive knowledge before valuations +can be properly done, but the incorporation of the executive work +with the technical has been brought about by several other forces. +We have a type of works which, by reason of the new conditions +and constant revisions which arise from pushing into the unknown +coincidentally with operating, demands an intimate continuous daily +employment of engineering sense and design through the whole history +of the enterprise. These works are of themselves of a character +which requires a constant vigilant eye on financial outcome. The +advances in metallurgy, and the decreased cost of production by +larger capacities, require yearly larger, more complicated, and +more costly plants. Thus, larger and larger capitals are required, +and enterprise is passing from the hands of the individual to the +financially stronger corporation. This altered position as to the +works and finance has made keener demands, both technically and in an +administrative way, for the highly trained <a name="page_191"><span +class="page">Page 191</span></a> man. In the early stages of American +mining, with the moderate demand on capital and the simpler forms +of engineering involved, mining was largely a matter of individual +enterprise and ownership. These owners were men to whom experience +had brought some of the needful technical qualifications. They +usually held the reins of business management in their own hands +and employed the engineer subjectively, when they employed him +at all. They were also, as a rule, distinguished by their contempt +for university-trained engineers. +</p> + +<p class="indent"> +The gradually increasing employment of the engineer as combined +executive and technical head, was largely of American development. +Many English and European mines still maintain the two separate +bureaus, the technical and the financial. Such organization is open +to much objection from the point of view of the owner's interests, +and still more from that of the engineer. In such an organization the +latter is always subordinate to the financial control,—hence the +least paid and least respected. When two bureaus exist, the technical +lacks that balance of commercial purpose which it should have. The +ambition of the theoretical engineer, divorced from commercial +result, is complete technical nicety of works and low production +costs without the regard for capital outlay which the commercial +experience and temporary character of mining constructions demand. +On the other hand, the purely financial bureau usually begrudges +the capital outlay which sound engineering may warrant. The result +is an administration that is not comparable to the single head +with both qualifications and an even balance in both spheres. In +America, we still have a relic of this form of administration in +the consulting mining engineer, but barring his functions as a +valuer of mines, he is disappearing in connection with the industry, +in favor of the manager, or the president of the company, who has +administrative control. The mining engineer's field of employment is +therefore not only wider by this general inclusion of administrative +work, but one of more responsibility. While he must conduct all five +phases of engineering projects coincidentally, the other branches of +the profession are more or less confined to one phase or another. +They can draw sharper <a name="page_192"><span class="page">Page +192</span></a> limitations of their engagements or specialization +and confine themselves to more purely technical work. The civil +engineer may construct railway or harbor works; the mechanical +engineer may design and build engines; the naval architect may +build ships; but given that he designed to do the work in the most +effectual manner, it is no concern of his whether they subsequently +earn dividends. He does not have to operate them, to find the income, +to feed the mill, or sell the product. The profit and loss does +not hound his footsteps after his construction is complete. +</p> + +<p class="indent"> +Although it is desirable to emphasize the commercial side of the +practice of the mining engineer's profession, there are other sides +of no less moment. There is the right of every red-blooded man to +be assured that his work will be a daily satisfaction to himself; +that it is a work which is contributing to the welfare and advance +of his country; and that it will build for him a position of dignity +and consequence among his fellows. +</p> + +<p class="indent"> +There are the moral and public obligations upon the profession. +There are to-day the demands upon the engineers which are the demands +upon their positions as leaders of a great industry. In an industry +that lends itself so much to speculation and chicanery, there is the +duty of every engineer to diminish the opportunity of the vulture +so far as is possible. Where he can enter these lists has been +suggested in the previous pages. Further than to the "investor" +in mines, he has a duty to his brothers in the profession. In no +profession does competition enter so obscurely, nor in no other +are men of a profession thrown into such terms of intimacy in +professional work. From these causes there has arisen a freedom of +disclosure of technical results and a comradery of members greater +than that in any other profession. No profession is so subject to +the capriciousness of fortune, and he whose position is assured +to-day is not assured to-morrow unless it be coupled with a +consideration of those members not so fortunate. Especially is +there an obligation to the younger members that they may have +opportunity of training and a right start in the work. +</p> + +<p class="indent"> +The very essence of the profession is that it calls upon its members to +direct men. They are the officers in the great <a name="page_193"><span +class="page">Page 193</span></a> industrial army. From the nature +of things, metal mines do not, like our cities and settlements, +lie in those regions covered deep in rich soils. Our mines must +be found in the mountains and deserts where rocks are exposed to +search. Thus they lie away from the centers of comfort and +culture,—they are the outposts of civilization. The engineer +is an officer on outpost duty, and in these places he is the camp +leader. By his position as a leader in the community he has a +chieftainship that carries a responsibility besides mere mine +management. His is the responsibility of example in fair dealing +and good government in the community. +</p> + +<p class="indent"> +In but few of its greatest works does the personality of its real +creator reach the ears of the world; the real engineer does not +advertise himself. But the engineering profession generally rises +yearly in dignity and importance as the rest of the world learns +more of where the real brains of industrial progress are. The time +will come when people will ask, not who paid for a thing, but who +built it. +</p> + +<p class="indent"> +To the engineer falls the work of creating from the dry bones of +scientific fact the living body of industry. It is he whose intellect +and direction bring to the world the comforts and necessities of +daily need. Unlike the doctor, his is not the constant struggle +to save the weak. Unlike the soldier, destruction is not his prime +function. Unlike the lawyer, quarrels are not his daily bread. +Engineering is the profession of creation and of construction, of +stimulation of human effort and accomplishment. +</p> + +<h2><a name="page_195"><span class="page">Page 195</span></a> +INDEX.</h2> + +<p class="indmgn">Accounts, <a href="#page_169">169</a>.</p> +<p class="index">Administration, <a href="#page_161">161</a>, + <a href="#page_169">169</a>, <a href="#page_178">178</a>.</p> +<p class="index">Administrative reports, <a href="#page_178">178</a>.</p> +<p class="index">Air-compression, <a href="#page_146">146</a>.</p> +<p class="index2">-drills, <a href="#page_147">147</a>.</p> +<p class="index">Alteration, secondary, <a href="#page_24">24</a>, + <a href="#page_25">25</a>, <a href="#page_26">26</a>, + <a href="#page_30">30</a>.</p> +<p class="index">Alternative shafts to inclined deposit, + <a href="#page_63">63</a>.</p> +<p class="index">Amortization of capital and interest, + <a href="#page_42">42</a>.</p> +<p class="index">Animals for underground transport, + <a href="#page_134">134</a>.</p> +<p class="index">Annual demand for base metals, + <a href="#page_38">38</a>.</p> +<p class="index2">report, <a href="#page_179">179</a>.</p> +<p class="index">Artificial pillars, <a href="#page_121">121</a>.</p> +<p class="index">Assay foot, <a href="#page_10">10</a>.</p> +<p class="index2">inch, <a href="#page_10">10</a>.</p> +<p class="index2">of samples, <a href="#page_7">7</a>.</p> +<p class="index2">plans, <a href="#page_1">1</a>, + <a href="#page_7">7</a>.</p> +<p class="index">Assaying, <a href="#page_177">177</a>.</p> +<p class="index">A value of mine, <a href="#page_56">56</a>.</p> +<p class="index">Averages, calculation, <a href="#page_1">1</a>, + <a href="#page_8">8</a>.</p> + +<p class="indmgn">Bailing, <a href="#page_143">143</a>.</p> +<p class="index">Balance sheet, <a href="#page_179">179</a>.</p> +<p class="index">Basic price, <a href="#page_36">36</a>, + <a href="#page_37">37</a>.</p> +<p class="index2">value of mine, <a href="#page_182">182</a>.</p> +<p class="index">Benches, <a href="#page_95">95</a>.</p> +<p class="index">Bend in combined shafts, <a href="#page_59">59</a>.</p> +<p class="index">Bins, <a href="#page_84">84</a>.</p> +<p class="index">Blocked-out ore, <a href="#page_18">18</a>.</p> +<p class="index">Blocks, <a href="#page_13">13</a>.</p> +<p class="index">Bonanzas, origin, <a href="#page_28">28</a>.</p> +<p class="index">Bonus systems, of work, <a href="#page_167">167</a>.</p> +<p class="index">Breaking ore, <a href="#page_115">115</a>.</p> +<p class="index">Broken Hill, levels, <a href="#page_119">119</a>.</p> +<p class="index2">ore-pillars, <a href="#page_120">120</a>.</p> +<p class="index">Bumping-trough, <a href="#page_89">89</a>, + <a href="#page_136">136</a>.</p> + +<p class="indmgn">Cable-ways, <a href="#page_135">135</a>.</p> +<p class="index">Cages, <a href="#page_132">132</a>.</p> +<p class="index">Calculation of averages, <a href="#page_1">1</a>, + <a href="#page_8">8</a>.</p> +<p class="index2">of quantities of ore, <a href="#page_13">13</a>.</p> +<p class="index">Capital expenditure, <a href="#page_170">170</a>.</p> +<p class="index">Caving systems, <a href="#page_122">122</a>.</p> +<p class="index">Churn-drills, <a href="#page_92">92</a>.</p> +<p class="index">Chutes, loading, in vertical shaft, + <a href="#page_86">86</a>.</p> +<p class="index">Classification of ore in sight, + <a href="#page_13">13</a>, <a href="#page_16">16</a>.</p> +<p class="index">Combined shaft, <a href="#page_58">58</a>, + <a href="#page_67">67</a>, <a href="#page_68">68</a>, + <a href="#page_69">69</a>, <a href="#page_70">70</a>, + <a href="#page_72">72</a>.</p> +<p class="index2">stopes, <a href="#page_96">96</a>, + <a href="#page_101">101</a>.</p> +<p class="index">Commercial value of projects, determination, + <a href="#page_188">188</a>.</p> +<p class="index">Compartments for shaft, <a href="#page_76">76</a>.</p> +<p class="index">Compressed-air locomotives, <a href="#page_135">135</a>.</p> +<p class="index2">-air pumps, <a href="#page_141">141</a>.</p> +<p class="index2"><i>vs</i>. electricity for drills, + <a href="#page_145">145</a>.</p> +<p class="index">Content, average metal, determining, + <a href="#page_1">1</a>.</p> +<p class="index2">metal, differences, <a href="#page_6">6</a>.</p> +<p class="index">Contract work, <a href="#page_165">165</a>.</p> +<p class="index">Copper, annual demand, <a href="#page_38">38</a>.</p> +<p class="index2">deposits, <a href="#page_1">1</a>.</p> +<p class="index2">ores, enrichment, <a href="#page_30">30</a>.</p> +<p class="index">Cost of entry into mine, <a href="#page_65">65</a>.</p> +<p class="index2">of equipment, <a href="#page_156">156</a>.</p> +<p class="index4">production, <a href="#page_38">38</a>, + <a href="#page_39">39</a>.</p> +<p class="index2">per foot of sinking, <a href="#page_64">64</a>.</p> +<p class="index2">working, <a href="#page_40">40</a>, + <a href="#page_170">170</a>.</p> +<p class="index">Cribs, <a href="#page_103">103</a>, + <a href="#page_107">107</a>.</p> +<p class="index">Crosscuts, <a href="#page_86">86</a>.</p> +<p class="index">Cross-section of inclined deposit which must be attacked + in depth, <a href="#page_68">68</a>.</p> +<p class="index2">showing auxiliary vertical outlet, + <a href="#page_66">66</a>.</p> +<p class="index">Crouch, J. J., <a href="#page_145">145</a>.</p> +<p class="index">Cubic feet per ton of ore, <a href="#page_14">14</a>, + <a href="#page_15">15</a>.</p> +<p class="index2">foot contents of block, <a href="#page_13">13</a>.</p> + +<p class="indmgn">Deep-level mines, <a href="#page_60">60</a>.</p> +<p class="index">Demand for metals, <a href="#page_35">35</a>.</p> +<p class="index">Departmental dissection of expenditures, + <a href="#page_171">171</a>.</p> +<p class="index">Deposits, <i>in situ</i>, <a href="#page_1">1</a>.</p> +<p class="index2">ore, classes, <a href="#page_24">24</a>.</p> +<p class="index2">regularity, <a href="#page_88">88</a>.</p> +<p class="index2">size, <a href="#page_30">30</a>.</p> +<p class="index2">structure, <a href="#page_24">24</a>.</p> +<p class="index">Depth of exhaustion, <a href="#page_21">21</a>, + <a href="#page_32">32</a>.<a name="page_196"><span class="page">Page + 196</span></a></p> +<p class="index">Determination of average metal contents of ore, + <a href="#page_3">3</a>.</p> +<p class="index">Development in early prospecting stage, + <a href="#page_92">92</a>.</p> +<p class="index2">in neighboring mines, <a href="#page_21">21</a>, + <a href="#page_31">31</a>.</p> +<p class="index"> of mines, <a href="#page_58">58</a>, + <a href="#page_74">74</a>, <a href="#page_84">84</a>.</p> +<p class="index">Diamond-drilling, <a href="#page_93">93</a>.</p> +<p class="index">Diluting narrow samples to a stoping width, + <a href="#page_11">11</a>.</p> +<p class="index">Dip, <a href="#page_89">89</a>.</p> +<p class="index">Direct-acting steam-pumps, + <a href="#page_140">140</a>.</p> +<p class="index">Distribution of values, <a href="#page_30">30</a>.</p> +<p class="index">Dividend, annual, present value, + <a href="#page_46">46</a>.</p> +<p class="index">Dommeiler, <a href="#page_145">145</a>.</p> +<p class="index">Down holes, <a href="#page_100">100</a>.</p> +<p class="index">Drainage <a href="#page_138">138</a>.</p> +<p class="index2">comparison of different systems, + <a href="#page_143">143</a>.</p> +<p class="index2">systems, <a href="#page_140">140</a>.</p> +<p class="index">Drifts, <a href="#page_87">87</a>.</p> +<p class="index">Drill, requirements, <a href="#page_145">145</a>.</p> +<p class="index">Drilling, <a href="#page_92">92</a>, + <a href="#page_145">145</a>.</p> +<p class="index">Drives, <a href="#page_87">87</a>.</p> +<p class="index">Dry walling with timber caps, + <a href="#page_91">91</a>.</p> + +<p class="indmgn">Efficiency, factors of, <a href="#page_162">162</a>.</p> +<p class="index2">of mass, <a href="#page_162">162</a>.</p> +<p class="index">Electrical haulage, <a href="#page_135">135</a>.</p> +<p class="index2">pumps, <a href="#page_141">141</a>.</p> +<p class="index">Electricity for drills, <a href="#page_145">145</a>.</p> +<p class="index">Engine, size for winding appliances, + <a href="#page_131">131</a>.</p> +<p class="index">Engineer, mining, as executive, + <a href="#page_190">190</a>.</p> +<p class="index">Engineering projects, phases of, + <a href="#page_187">187</a>.</p> +<p class="index">Enrichment, <a href="#page_27">27</a>, + <a href="#page_28">28</a>, <a href="#page_29">29</a>.</p> +<p class="index2">at cross-veins, <a href="#page_24">24</a>.</p> +<p class="index">Entry, to mine, <a href="#page_58">58</a>.</p> +<p class="index2">to vertical or horizontal deposits, + <a href="#page_62">62</a>, <a href="#page_63">63</a>.</p> +<p class="index">Equipment, cost, <a href="#page_156">156</a>.</p> +<p class="index2">improvements, <a href="#page_152">152</a>.</p> +<p class="index2">mechanical, <a href="#page_138">138</a>, + <a href="#page_145">145</a>.</p> +<p class="index">Erosion, <a href="#page_26">26</a>, + <a href="#page_29">29</a>.</p> +<p class="index">Error, percentage in estimates from sampling, + <a href="#page_1">1</a>, <a href="#page_11">11</a>.</p> +<p class="index">Escape, <a href="#page_73">73</a>.</p> +<p class="index">Examination of mining property, + <a href="#page_54">54</a>.</p> +<p class="index">Excavation, supporting, <a href="#page_103">103</a>.</p> +<p class="index">Exhaustion, depth, <a href="#page_32">32</a>.</p> +<p class="index">Expenditures, departmental dissection, + <a href="#page_171">171</a>.</p> +<p class="index2">mine, <a href="#page_170">170</a>.</p> +<p class="index">Extension in depth, <a href="#page_21">21</a>, + <a href="#page_22">22</a>, <a href="#page_28">28</a>.</p> + +<p class="indmgn">Factor of safety in calculating averages of samples, + <a href="#page_12">12</a>.</p> +<p class="index">Filling, <a href="#page_112">112</a>.</p> +<p class="index2">system combined with square-setting, + <a href="#page_111">111</a>.</p> +<p class="index2">with broken ore subsequently withdrawn, + <a href="#page_112">112</a>.</p> +<p class="index2">waste, <a href="#page_107">107</a>.</p> +<p class="index">Fissure veins, <a href="#page_24">24</a>.</p> +<p class="index">Fissuring, <a href="#page_23">23</a>.</p> +<p class="index2">depth, <a href="#page_30">30</a>.</p> +<p class="index">Fixed charges, <a href="#page_154">154</a>, + <a href="#page_170">170</a>.</p> +<p class="index">Flat-back stope, <a href="#page_98">98</a>, + <a href="#page_100">100</a>, <a href="#page_110">110</a>.</p> +<p class="index">Flexibility in drainage system, + <a href="#page_138">138</a>.</p> +<p class="index">Floors, <a href="#page_31">31</a>.</p> +<p class="index">Folding, <a href="#page_23">23</a>.</p> +<p class="index">Foot-drilled system of contract work, + <a href="#page_166">166</a>.</p> +<p class="index2">-hole system of contract work, + <a href="#page_166">166</a>.</p> +<p class="index2">of advance system of contract work, + <a href="#page_166">166</a>.</p> +<p class="index2">value, <a href="#page_10">10</a>.</p> +<p class="index">Fraud, precautions against in sampling, + <a href="#page_7">7</a>.</p> + +<p class="indmgn">General expenses, <a href="#page_173">173</a>.</p> +<p class="index">Gold deposits, <a href="#page_1">1</a>.</p> +<p class="index2">deposits, alteration, <a href="#page_29">29</a>, + <a href="#page_30">30</a>.</p> +<p class="index2">enrichment, <a href="#page_28">28</a>.</p> + +<p class="indmgn">Hammer type of drill, <a href="#page_147">147</a>, + <a href="#page_148">148</a>, <a href="#page_149">149</a>.</p> +<p class="index">Hand-drilling, <a href="#page_149">149</a>.</p> +<p class="index2">-trucking, <a href="#page_133">133</a>.</p> +<p class="index">Haulage, electrical, <a href="#page_135">135</a>.</p> +<p class="index2">equipment in shaft, <a href="#page_132">132</a>.</p> +<p class="index2">mechanical, <a href="#page_134">134</a>.</p> +<p class="index">Hole system of contract work, + <a href="#page_165">165</a>.</p> +<p class="index">Horizons of ore-deposits, <a href="#page_26">26</a>.</p> +<p class="index">Horizontal deposits, entry, <a href="#page_62">62</a>.</p> +<p class="index2">stope, <a href="#page_98">98</a>.</p> +<p class="index2">filled with waste, <a href="#page_108">108</a>.</p> +<p class="index">Hydraulic pumps, <a href="#page_142">142</a>.</p> + +<p class="indmgn">Impregnation deposits, <a href="#page_24">24</a>.</p> +<p class="index">Inch, assay, <a href="#page_10">10</a>.</p> +<p class="index">Inclined deposits to be worked from outcrop or near it, + <a href="#page_62">62</a>.</p> +<p class="index2">deposits which must be attacked in depth, + <a href="#page_67">67</a>.</p> +<p class="index2">shaft, <a href="#page_64">64</a>.</p> +<p class="index">Inclines, <a href="#page_65">65</a>, + <a href="#page_66">66</a>, <a href="#page_67">67</a>, + <a href="#page_68">68</a>.</p> +<p class="index2">capacity, <a href="#page_78">78</a>.<a name="page_197"> + <span class="page">Page 197</span></a></p> +<p class="index">Infiltration type of deposits, + <a href="#page_24">24</a>.</p> +<p class="index">Intelligence as factor of skill, + <a href="#page_163">163</a>, <a href="#page_164">164</a>.</p> +<p class="index">Interest calculations in mine valuation, + <a href="#page_43">43</a>.</p> +<p class="index">Intervals, level, <a href="#page_88">88</a>, + <a href="#page_89">89</a>.</p> +<p class="index">Inwood's tables, <a href="#page_46">46</a>, + <a href="#page_47">47</a>.</p> +<p class="index">Iron hat, <a href="#page_27">27</a>.</p> +<p class="index2">leaching, <a href="#page_27">27</a>.</p> +<p class="index">Ivanhoe mine, West Australia, + <a href="#page_112">112</a>.</p> + +<p class="indmgn">Kibble, <a href="#page_132">132</a>.</p> + +<p class="indmgn">Labor, general technical data, + <a href="#page_176">176</a>.</p> +<p class="index2">handling, <a href="#page_161">161</a>.</p> +<p class="index2">unions, <a href="#page_167">167</a>.</p> +<p class="index">Lateral underground transport, + <a href="#page_133">133</a>.</p> +<p class="index">Le Roi mine, <a href="#page_112">112</a>.</p> +<p class="index">Lead, annual demand, <a href="#page_38">38</a>.</p> +<p class="index2">deposits, <a href="#page_1">1</a>.</p> +<p class="index2">enriching, <a href="#page_27">27</a>.</p> +<p class="index2">prices, 1884-1908, <a href="#page_36">36</a>.</p> +<p class="index2">-zinc ores, enrichment, <a href="#page_30">30</a>.</p> +<p class="index">Lenses, <a href="#page_24">24</a>.</p> +<p class="index">Levels, <a href="#page_87">87</a>.</p> +<p class="index2">intervals, <a href="#page_88">88</a>, + <a href="#page_89">89</a>.</p> +<p class="index2">of Broken Hill, <a href="#page_119">119</a>.</p> +<p class="index2">protection, <a href="#page_90">90</a>.</p> +<p class="index">Life, in sight, <a href="#page_44">44</a>.</p> +<p class="index2">of mine, <a href="#page_157">157</a>.</p> +<p class="index">Locomotives, compressed-air, + <a href="#page_135">135</a>.</p> +<p class="index">Lode mines, valuation, <a href="#page_1">1</a>.</p> +<p class="index">Lodes, <a href="#page_24">24</a>.</p> +<p class="index">Long-wall stope, <a href="#page_98">98</a>.</p> + +<p class="indmgn">Machine-drill, performance, + <a href="#page_149">149</a>.</p> +<p class="index2">drilling, <a href="#page_145">145</a>.</p> +<p class="index2"><i>vs</i>. hand-drilling, + <a href="#page_149">149</a>.</p> +<p class="index">Management, mine, <a href="#page_161">161</a>.</p> +<p class="index">Matte, <a href="#page_123">123</a>.</p> +<p class="index">Mechanical efficiency of drainage machinery, + <a href="#page_139">139</a>.</p> +<p class="index2">equipment, <a href="#page_124">124</a>, + <a href="#page_134">134</a>, <a href="#page_138">138</a>, + <a href="#page_145">145</a>.</p> +<p class="index">Men for underground transport, + <a href="#page_133">133</a>.</p> +<p class="index">Metal content, determining, <a href="#page_1">1</a>, + <a href="#page_3">3</a>.</p> +<p class="index2">contents, differences, <a href="#page_6">6</a>.</p> +<p class="index2">demand for, <a href="#page_35">35</a>.</p> +<p class="index2">mine, value, <a href="#page_1">1</a>.</p> +<p class="index2">price, <a href="#page_35">35</a>, + <a href="#page_37">37</a>.</p> +<p class="index">Mines compared to other commercial enterprises, + <a href="#page_183">183</a>.</p> +<p class="index2">equipment, <a href="#page_124">124</a>.</p> +<p class="index2">expenditures, <a href="#page_170">170</a>.</p> +<p class="index">Mines—<i>continued.</i></p> +<p class="index2">life of, <a href="#page_157">157</a>.</p> +<p class="index2">metal, value of, <a href="#page_1">1</a>.</p> +<p class="index2">of moderate depths, <a href="#page_62">62</a>.</p> +<p class="index2">to be worked to great depths, <a href="#page_62">62</a>, + <a href="#page_69">69</a>.</p> +<p class="index2">valuation, <a href="#page_1">1</a>, + <a href="#page_13">13</a>, <a href="#page_21">21</a>, + <a href="#page_34">34</a>, <a href="#page_42">42</a>, + <a href="#page_51">51</a>.</p> +<p class="index">Mining engineering profession, + <a href="#page_185">185</a>.</p> +<p class="index">Mt. Cenis tunnel, <a href="#page_145">145</a>.</p> +<p class="index">Morgan gold mine, <a href="#page_26">26</a>.</p> + +<p class="indmgn">Normal price, <a href="#page_36">36</a>, + <a href="#page_37">37</a>.</p> + +<p class="indmgn">Obligations of engineering profession, + <a href="#page_192">192</a>.</p> +<p class="index">Openings, position in relation to secondary + alteration, <a href="#page_23">23</a>, <a href="#page_25">25</a>.</p> +<p class="index">Ore, average width in block, + <a href="#page_13">13</a>.</p> +<p class="index2">blocked-out, <a href="#page_17">17</a>.</p> +<p class="index2">-bodies, <a href="#page_23">23</a>.</p> +<p class="index2">shapes, <a href="#page_8">8</a>.</p> +<p class="index2">-breaking, methods, <a href="#page_94">94</a>, + <a href="#page_95">95</a>.</p> +<p class="index2">calculation of quantities of, + <a href="#page_13">13</a>.</p> +<p class="index2">-chutes in shrinkage-stoping, + <a href="#page_115">115</a>.</p> +<p class="index2">-deposits, classes, <a href="#page_24">24</a>.</p> +<p class="index2">determination of average metal contents, + <a href="#page_3">3</a>.</p> +<p class="index2">developed, <a href="#page_17">17</a>.</p> +<p class="index2">developing, <a href="#page_17">17</a>.</p> +<p class="index2">expectant, <a href="#page_17">17</a>.</p> +<p class="index2">in sight, <a href="#page_16">16</a>, + <a href="#page_17">17</a>, <a href="#page_20">20</a>.</p> +<p class="index4">sight, classification, + <a href="#page_13">13</a>, <a href="#page_16">16</a>.</p> +<p class="index2">-pillars, <a href="#page_118">118</a>, + <a href="#page_119">119</a>.</p> +<p class="index4">support in narrow stopes, <a href="#page_118">118</a>.</p> +<p class="index2">-shoots, <a href="#page_23">23</a>.</p> +<p class="index2">weight of a cubic foot, <a href="#page_14">14</a>.</p> +<p class="index2">width for one sample, <a href="#page_5">5</a>.</p> +<p class="index">Origin of deposit, <a href="#page_23">23</a>.</p> +<p class="index">Outcrop mines, <a href="#page_60">60</a>.</p> +<p class="index">Output, factors limiting, + <a href="#page_155">155</a>.</p> +<p class="index2">giving least production cost, + <a href="#page_154">154</a>.</p> +<p class="index2">maximum, determination, <a href="#page_153">153</a>.</p> +<p class="index">Overhand stapes, <a href="#page_96">96</a>, + <a href="#page_98">98</a>, <a href="#page_99">99</a>.</p> +<p class="index">Overproduction of base metal, + <a href="#page_158">158</a>.</p> +<p class="index">Oxidation, <a href="#page_30">30</a>.</p> + +<p class="indmgn">Patchwork plant, mechanical inefficiency of, + <a href="#page_158">158</a>.</p> +<p class="index">Pay areas, formation, <a href="#page_23">23</a>.</p> +<p class="index">Pillars, artificial, <a href="#page_121">121</a>.</p> +<p class="index">Positive ore, <a href="#page_17">17</a>, + <a href="#page_20">20</a>.</p> +<p class="index2">value of metal mine, <a href="#page_1">1</a>.</p> +<p class="index">Possible ore, <a href="#page_17">17</a>. + <a name="page_198"><span class="page">Page 198</span></a></p> +<p class="index">Power conditions, <a href="#page_139">139</a>.</p> +<p class="index2">general technical data, <a href="#page_176">176</a>.</p> +<p class="index2">sources, <a href="#page_126">126</a>.</p> +<p class="index2">transmission, <a href="#page_125">125</a>, + <a href="#page_126">126</a>, <a href="#page_127">127</a>, + <a href="#page_145">145</a>.</p> +<p class="index">Preliminary inspection, <a href="#page_55">55</a>.</p> +<p class="index">Previous yield, <a href="#page_3">3</a>.</p> +<p class="index">Price of metals, <a href="#page_35">35</a>.</p> +<p class="index">Probable ore, <a href="#page_17">17</a>, + <a href="#page_19">19</a>, <a href="#page_20">20</a>, + <a href="#page_21">21</a>.</p> +<p class="index">Producing stage of mine, <a href="#page_58">58</a>.</p> +<p class="index">Production, cost, <a href="#page_38">38</a>, + <a href="#page_39">39</a>.</p> +<p class="index">Profit and loss account, <a href="#page_179">179</a>.</p> +<p class="index2">factors determining, <a href="#page_2">2</a>.</p> +<p class="index2">in sight, <a href="#page_16">16</a>.</p> +<p class="index">Proportional charges, <a href="#page_170">170</a>.</p> +<p class="index">Prospecting stage of mine, <a href="#page_58">58</a>.</p> +<p class="index">Prospective ore, <a href="#page_19">19</a>.</p> +<p class="index2">value, <a href="#page_21">21</a>.</p> +<p class="index">Protection of levels, <a href="#page_90">90</a>.</p> +<p class="index">Proved ore, <a href="#page_19">19</a>, + <a href="#page_21">21</a>.</p> +<p class="index">Pumping systems, <a href="#page_140">140</a>.</p> +<p class="index">Pumps, compressed-air, <a href="#page_141">141</a>.</p> +<p class="index2">electrical, <a href="#page_141">141</a>.</p> +<p class="index2">hydraulic, <a href="#page_142">142</a>.</p> +<p class="index2">rod-driven, <a href="#page_142">142</a>.</p> + +<p class="indmgn">Ratio of output to mine, <a href="#page_153">153</a>.</p> +<p class="index">Recoverable percentage of gross assay value, + <a href="#page_34">34</a>.</p> +<p class="index">Recovery of ore, <a href="#page_107">107</a>.</p> +<p class="index">Rectangular shaft, <a href="#page_74">74</a>.</p> +<p class="index">Redemption of capital and interest, + <a href="#page_42">42</a>.</p> +<p class="index">Reduction of output, <a href="#page_158">158</a>.</p> +<p class="index">Regularity of deposit, <a href="#page_88">88</a>.</p> +<p class="index">Reliability of drainage system, + <a href="#page_139">139</a>.</p> +<p class="index">Replacement, <a href="#page_24">24</a>.</p> +<p class="index">Reports, <a href="#page_56">56</a>.</p> +<p class="index2">administrative, <a href="#page_178">178</a>.</p> +<p class="index">Resuing, <a href="#page_101">101</a>.</p> +<p class="index">Revenue account, <a href="#page_179">179</a>.</p> +<p class="index">Rill-cut overhand stope, <a href="#page_99">99</a>.</p> +<p class="index2">method of incline cuts, <a href="#page_100">100</a>.</p> +<p class="index2">-stopes, <a href="#page_98">98</a>, + <a href="#page_110">110</a>.</p> +<p class="index4">filled with waste, <a href="#page_108">108</a>.</p> +<p class="index2">-stoping, <a href="#page_96">96</a>, + <a href="#page_98">98</a>, <a href="#page_99">99</a>, + <a href="#page_100">100</a>, <a href="#page_137">137</a>.</p> +<p class="index">Rises, <a href="#page_89">89</a>, + <a href="#page_91">91</a>.</p> +<p class="index">Risk in mining investments, + <a href="#page_181">181</a>.</p> +<p class="index2">in valuation of mines, + <a href="#page_181">181</a>.</p> +<p class="index">Roadways, protecting in shrinkage-stoping, + <a href="#page_114">114</a>.</p> +<p class="index">Rod-driven pumps, <a href="#page_142">142</a>.</p> +<p class="index">Rotary steam-pumps, <a href="#page_140">140</a>.</p> +<p class="index">Round vertical shafts, <a href="#page_74">74</a>.</p> +<p class="index">Runs of value, <a href="#page_8">8</a>.</p> +<p class="index2">test-treatment, <a href="#page_3">3</a>.</p> + +<p class="indmgn">Safety, factor of, in calculating averages of samples, + <a href="#page_12">12</a>.</p> +<p class="index">Sample, assay of, <a href="#page_7">7</a>.</p> +<p class="index2">average value, <a href="#page_9">9</a>.</p> +<p class="index2">narrow, diluting to a stoping width, + <a href="#page_11">11</a>.</p> +<p class="index2">sections, <a href="#page_5">5</a>, + <a href="#page_6">6</a>.</p> +<p class="index2">taking, physical details, <a href="#page_6">6</a>.</p> +<p class="index2">manner of taking, <a href="#page_4">4</a>.</p> +<p class="index">Sampling, <a href="#page_1">1</a>, + <a href="#page_3">3</a>, <a href="#page_4">4</a>, + <a href="#page_5">5</a>, <a href="#page_56">56</a>, + <a href="#page_177">177</a>.</p> +<p class="index2">accuracy, <a href="#page_5">5</a>.</p> +<p class="index2">percentage of error in estimates from, + <a href="#page_11">11</a>.</p> +<p class="index2">precautions against fraud, <a href="#page_7">7</a>.</p> +<p class="index">Saving of fixed charges, <a href="#page_155">155</a>.</p> +<p class="index">Secondary alteration, <a href="#page_24">24</a>, + <a href="#page_25">25</a>, <a href="#page_26">26</a>, + <a href="#page_30">30</a>.</p> +<p class="index2">enrichment, <a href="#page_21">21</a>.</p> +<p class="index">Security of investment, <a href="#page_158">158</a>.</p> +<p class="index">Self-dumping skip, <a href="#page_77">77</a>.</p> +<p class="index">Sets, <a href="#page_91">91</a>.</p> +<p class="index">Shafts, <a href="#page_62">62</a>, + <a href="#page_64">64-70</a>.</p> +<p class="index2">arrangement for very deep inclined shafts, + <a href="#page_71">71</a>.</p> +<p class="index2">compartments, <a href="#page_59">59</a>, + <a href="#page_78">78</a>.</p> +<p class="index2">different depths, <a href="#page_60">60</a>.</p> +<p class="index2">haulage, <a href="#page_129">129</a>.</p> +<p class="index2">location, <a href="#page_70">70</a>.</p> +<p class="index2">number, <a href="#page_72">72</a>.</p> +<p class="index2">output capacity, <a href="#page_77">77</a>.</p> +<p class="index2">shape, <a href="#page_74">74</a>.</p> +<p class="index2">size, <a href="#page_76">76</a>, + <a href="#page_79">79</a>.</p> +<p class="index">Shrinkage-stope, <a href="#page_114">114</a>, + <a href="#page_115">115</a>.</p> +<p class="index2">-stoping, <a href="#page_112">112</a>.</p> +<p class="index4">advantages, <a href="#page_117">117</a>.</p> +<p class="index4">disadvantages, <a href="#page_116">116</a>.</p> +<p class="index4">when applicable, <a href="#page_116">116</a>.</p> +<p class="index">Silver deposits, <a href="#page_1">1</a>.</p> +<p class="index2">deposits, enrichment, <a href="#page_28">28</a>, + <a href="#page_30">30</a>.</p> +<p class="index2">prices, <a href="#page_38">38</a>.</p> +<p class="index">Sinking, speed, <a href="#page_80">80</a>.</p> +<p class="index">Size of deposit, <a href="#page_30">30</a>.</p> +<p class="index">Skill, effect on production cost, + <a href="#page_163">163</a>.</p> +<p class="index">Skips, <a href="#page_77">77</a>, + <a href="#page_84">84</a>, <a href="#page_132">132</a>.</p> +<p class="index2">balanced, <a href="#page_129">129</a>.</p> +<p class="index2">haulage in vertical shaft, <a href="#page_85">85</a>.</p> +<p class="index">Sollars, <a href="#page_109">109</a>.</p> +<p class="index">Solubility of minerals, <a href="#page_27">27</a>.</p> +<p class="index">Specific volume of ores, <a href="#page_14">14</a>.</p> +<p class="index">Speculative values of metal mine, + <a href="#page_1">1</a>.</p> +<p class="index2">value of mine, <a href="#page_57">57</a>. + <a name="page_199"><span class="page">Page 199</span></a></p> +<p class="index">Spelter, annual demand, <a href="#page_38">38</a>.</p> +<p class="index">Square-set, <a href="#page_103">103</a>, + <a href="#page_104">104</a>.</p> +<p class="index2">-set timbering, <a href="#page_104">104</a>.</p> +<p class="index">Stations, <a href="#page_84">84</a>.</p> +<p class="index2">arrangement for skip haulage in vertical shaft, + <a href="#page_85">85</a>, <a href="#page_87">87</a>.</p> +<p class="index">Steam-pumps, direct, <a href="#page_140">140</a>.</p> +<p class="index">Steepening winzes and ore passes, + <a href="#page_111">111</a>.</p> +<p class="index">Stope filled with broken ore, + <a href="#page_113">113</a>.</p> +<p class="index2">minimum width, <a href="#page_101">101</a>.</p> +<p class="index">Stoping, <a href="#page_89">89</a>, + <a href="#page_94">94</a>.</p> +<p class="index2">contract systems, <a href="#page_166">166</a>.</p> +<p class="index">Storing metal, <a href="#page_158">158</a>.</p> +<p class="index">Structural character of deposit, + <a href="#page_23">23</a>.</p> +<p class="index">Structure of deposit, <a href="#page_24">24</a>.</p> +<p class="index">Stull and waste pillars, <a href="#page_121">121</a>.</p> +<p class="index2">support with waste reënforcement, + <a href="#page_120">120</a>.</p> +<p class="index2">-supported stope, <a href="#page_104">104</a>.</p> +<p class="index">Stulls, <a href="#page_103">103</a>.</p> +<p class="index2">wood, <a href="#page_91">91</a>.</p> +<p class="index">Subheading, <a href="#page_90">90</a>.</p> +<p class="index">Sublevel caving system, <a href="#page_122">122</a>.</p> +<p class="index">Subsidiary development, <a href="#page_84">84</a>.</p> +<p class="index">Superficial enrichment, <a href="#page_29">29</a>.</p> +<p class="index">Supplies, general technical data, + <a href="#page_176">176</a>.</p> +<p class="index">Support by pillars of ore, <a href="#page_118">118</a>.</p> +<p class="index">Supporting excavation, <a href="#page_103">103</a>.</p> +<p class="index">Surveys, <a href="#page_176">176</a>.</p> +<p class="index">Suspense charges, <a href="#page_170">170</a>.</p> + +<p class="indmgn">Test parcels, <a href="#page_4">4</a>.</p> +<p class="index2">sections, <a href="#page_6">6</a>.</p> +<p class="index2">-treatment runs, <a href="#page_3">3</a>.</p> +<p class="index">Timber, cost, <a href="#page_77">77</a>.</p> +<p class="index">Timbered shaft design, <a href="#page_75">75</a>.</p> +<p class="index">Timbering, <a href="#page_103">103</a>, +<a href="#page_112">112 +</a>.</p> +<p class="index">Tin, annual demand, <a href="#page_38">38</a>.</p> +<p class="index2">deposits, <a href="#page_1">1</a>.</p> +<p class="index2">ore, migration and enrichment, +<a href="#page_29">29</a>.</p> +<p class="index">Tools, <a href="#page_128">128</a>.</p> +<p class="index">Top slicing, <a href="#page_123">123</a>.</p> +<p class="index">Tracks, <a href="#page_135">135</a>.</p> +<p class="index">Transport in stopes, <a href="#page_136">136</a>.</p> +<p class="index">Tunnel entry, <a href="#page_81">81</a>.</p> +<p class="index2">feet paid for in <a href="#page_10">10</a> years, + <a href="#page_82">82</a>.</p> +<p class="index2">size, <a href="#page_82">82</a>.</p> + +<p class="indmgn">Underhand stopes, <a href="#page_96">96</a>, + <a href="#page_98">98</a>.</p> +<p class="index">Uppers, <a href="#page_100">100</a>.</p> + +<p class="indmgn">Valuation, mine, <a href="#page_2">2</a>, + <a href="#page_13">13</a>, <a href="#page_21">21</a>, + <a href="#page_34">34</a>, <a href="#page_42">42</a>, + <a href="#page_51">51</a>.</p> +<p class="index2">of lode mines, <a href="#page_1">1</a>.</p> +<p class="index4">mines, risk in, <a href="#page_181">181</a>.</p> +<p class="index4">mines with little or no ore in sight, + <a href="#page_51">51</a>.</p> +<p class="index2">on second-hand data, <a href="#page_52">52</a>.</p> +<p class="index">Value, average, of samples, <a href="#page_9">9</a>.</p> +<p class="index2">discrepancy between estimated and actual, + <a href="#page_12">12</a>.</p> +<p class="index2">distribution, <a href="#page_31">31</a>.</p> +<p class="index2">of extension in depth, estimating, + <a href="#page_22">22</a>.</p> +<p class="index2">positive, of metal mine, <a href="#page_1">1</a>.</p> +<p class="index2">present, of an annual dividend, + <a href="#page_46">46</a>.</p> +<p class="index4">of $1 or £1, payable in — years, + <a href="#page_47">47</a>.</p> +<p class="index2">runs of, <a href="#page_8">8</a>.</p> +<p class="index2">speculative, of metal mine, <a href="#page_1">1</a>.</p> +<p class="index">Valuing ore in course of breaking, + <a href="#page_102">102</a>.</p> +<p class="index">Ventilation, <a href="#page_72">72</a>, + <a href="#page_73">73</a>.</p> +<p class="index">Vertical deposits, entry, <a href="#page_62">62</a>.</p> +<p class="index2">interval between levels, <a href="#page_88">88</a>.</p> +<p class="index2">shafts, <a href="#page_62">62-70</a>, + <a href="#page_72">72</a>, <a href="#page_85">85</a>, + <a href="#page_86">86</a>.</p> +<p class="index4">capacity, <a href="#page_78">78</a>.</p> +<p class="index">Volume, specific, of ores, <a href="#page_14">14</a>.</p> + +<p class="indmgn">Waste-filled stope, <a href="#page_109">109</a>.</p> +<p class="index">Water-power, <a href="#page_126">126</a>.</p> +<p class="index">Weight per cubic foot of ore, <a href="#page_14">14</a>, + <a href="#page_15">15</a>.</p> +<p class="index">Weindel, Caspar, <a href="#page_145">145</a>.</p> +<p class="index">Whiting hoist, <a href="#page_131">131</a>.</p> +<p class="index">Width of ore for one sample, <a href="#page_5">5</a>.</p> +<p class="index">Winding appliances, <a href="#page_129">129</a>.</p> +<p class="index">Winzes, <a href="#page_89">89</a>, + <a href="#page_91">91</a>.</p> +<p class="index2">in shrinkage-stoping, <a href="#page_113">113</a>.</p> +<p class="index2">to be used for filling, <a href="#page_107">107</a>.</p> +<p class="index">Working cost, <a href="#page_40">40</a>, + <a href="#page_170">170</a>.</p> +<p class="index2">inherent limitations in accuracy of, + <a href="#page_174">174</a>.</p> +<p class="index2">sheets, <a href="#page_176">176</a>.</p> +<p class="index">Workshops, <a href="#page_151">151</a>.</p> + +<p class="indmgn">Yield, previous, <a href="#page_3">3</a>.</p> +<p class="index">Years of life required to yield —% interest, + <a href="#page_48">48</a>.</p> + +<p class="indmgn">Zinc deposits, <a href="#page_1">1</a>.</p> +<p class="index2">leaching, <a href="#page_27">27</a>.</p> + + + + + + + + +<pre> + + + + + +End of Project Gutenberg's Principles of Mining, by Herbert C. Hoover + +*** END OF THIS PROJECT GUTENBERG EBOOK PRINCIPLES OF MINING *** + +***** This file should be named 26697-h.htm or 26697-h.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/2/6/6/9/26697/ + +Produced by Robert J. Hall + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +https://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, is critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at https://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +https://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at https://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit https://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. + + +</pre> + +</body> +</html> diff --git a/26697-h/images/fig_01.png b/26697-h/images/fig_01.png Binary files differnew file mode 100644 index 0000000..7fade8f --- /dev/null +++ b/26697-h/images/fig_01.png diff --git a/26697-h/images/fig_02.png b/26697-h/images/fig_02.png Binary files differnew file mode 100644 index 0000000..a137b79 --- /dev/null +++ b/26697-h/images/fig_02.png diff --git a/26697-h/images/fig_03.png b/26697-h/images/fig_03.png Binary files differnew file mode 100644 index 0000000..5aefb67 --- /dev/null +++ b/26697-h/images/fig_03.png diff --git a/26697-h/images/fig_04.png b/26697-h/images/fig_04.png Binary files differnew file mode 100644 index 0000000..7ac0a72 --- /dev/null +++ b/26697-h/images/fig_04.png diff --git a/26697-h/images/fig_05.png b/26697-h/images/fig_05.png Binary files differnew file mode 100644 index 0000000..613a2f9 --- /dev/null +++ b/26697-h/images/fig_05.png diff --git a/26697-h/images/fig_06.png b/26697-h/images/fig_06.png Binary files differnew file mode 100644 index 0000000..03258dd --- /dev/null +++ b/26697-h/images/fig_06.png diff --git a/26697-h/images/fig_07.png b/26697-h/images/fig_07.png Binary files differnew file mode 100644 index 0000000..146c211 --- /dev/null +++ b/26697-h/images/fig_07.png diff --git a/26697-h/images/fig_08.png b/26697-h/images/fig_08.png Binary files differnew file mode 100644 index 0000000..fcff18c --- /dev/null +++ b/26697-h/images/fig_08.png diff --git a/26697-h/images/fig_09-14.png b/26697-h/images/fig_09-14.png Binary files differnew file mode 100644 index 0000000..915e3ab --- /dev/null +++ b/26697-h/images/fig_09-14.png diff --git a/26697-h/images/fig_15.png b/26697-h/images/fig_15.png Binary files differnew file mode 100644 index 0000000..38dc205 --- /dev/null +++ b/26697-h/images/fig_15.png diff --git a/26697-h/images/fig_16.png b/26697-h/images/fig_16.png Binary files differnew file mode 100644 index 0000000..9912b3e --- /dev/null +++ b/26697-h/images/fig_16.png diff --git a/26697-h/images/fig_17.png b/26697-h/images/fig_17.png Binary files differnew file mode 100644 index 0000000..337b5da --- /dev/null +++ b/26697-h/images/fig_17.png diff --git a/26697-h/images/fig_18.png b/26697-h/images/fig_18.png Binary files differnew file mode 100644 index 0000000..6eef370 --- /dev/null +++ b/26697-h/images/fig_18.png diff --git a/26697-h/images/fig_19.png b/26697-h/images/fig_19.png Binary files differnew file mode 100644 index 0000000..0bab043 --- /dev/null +++ b/26697-h/images/fig_19.png diff --git a/26697-h/images/fig_20.png b/26697-h/images/fig_20.png Binary files differnew file mode 100644 index 0000000..652ee41 --- /dev/null +++ b/26697-h/images/fig_20.png diff --git a/26697-h/images/fig_21.png b/26697-h/images/fig_21.png Binary files differnew file mode 100644 index 0000000..1c0c23e --- /dev/null +++ b/26697-h/images/fig_21.png diff --git a/26697-h/images/fig_22.png b/26697-h/images/fig_22.png Binary files differnew file mode 100644 index 0000000..4ab9c34 --- /dev/null +++ b/26697-h/images/fig_22.png diff --git a/26697-h/images/fig_23.png b/26697-h/images/fig_23.png Binary files differnew file mode 100644 index 0000000..ef3fc41 --- /dev/null +++ b/26697-h/images/fig_23.png diff --git a/26697-h/images/fig_24.png b/26697-h/images/fig_24.png Binary files differnew file mode 100644 index 0000000..ebd6c55 --- /dev/null +++ b/26697-h/images/fig_24.png diff --git a/26697-h/images/fig_25.png b/26697-h/images/fig_25.png Binary files differnew file mode 100644 index 0000000..98d5180 --- /dev/null +++ b/26697-h/images/fig_25.png diff --git a/26697-h/images/fig_26.png b/26697-h/images/fig_26.png Binary files differnew file mode 100644 index 0000000..159603a --- /dev/null +++ b/26697-h/images/fig_26.png diff --git a/26697-h/images/fig_27.png b/26697-h/images/fig_27.png Binary files differnew file mode 100644 index 0000000..10278d2 --- /dev/null +++ b/26697-h/images/fig_27.png diff --git a/26697-h/images/fig_28.png b/26697-h/images/fig_28.png Binary files differnew file mode 100644 index 0000000..b503971 --- /dev/null +++ b/26697-h/images/fig_28.png diff --git a/26697-h/images/fig_29.png b/26697-h/images/fig_29.png Binary files differnew file mode 100644 index 0000000..1e50522 --- /dev/null +++ b/26697-h/images/fig_29.png diff --git a/26697-h/images/fig_30.png b/26697-h/images/fig_30.png Binary files differnew file mode 100644 index 0000000..b0518c4 --- /dev/null +++ b/26697-h/images/fig_30.png diff --git a/26697-h/images/fig_31.png b/26697-h/images/fig_31.png Binary files differnew file mode 100644 index 0000000..1d36ab6 --- /dev/null +++ b/26697-h/images/fig_31.png diff --git a/26697-h/images/fig_32.png b/26697-h/images/fig_32.png Binary files differnew file mode 100644 index 0000000..a5eaf1a --- /dev/null +++ b/26697-h/images/fig_32.png diff --git a/26697-h/images/fig_33.png b/26697-h/images/fig_33.png Binary files differnew file mode 100644 index 0000000..f1f5caa --- /dev/null +++ b/26697-h/images/fig_33.png diff --git a/26697-h/images/fig_34.png b/26697-h/images/fig_34.png Binary files differnew file mode 100644 index 0000000..a9bb7e3 --- /dev/null +++ b/26697-h/images/fig_34.png diff --git a/26697-h/images/fig_35.png b/26697-h/images/fig_35.png Binary files differnew file mode 100644 index 0000000..bf454fd --- /dev/null +++ b/26697-h/images/fig_35.png diff --git a/26697-h/images/fig_36.png b/26697-h/images/fig_36.png Binary files differnew file mode 100644 index 0000000..face42a --- /dev/null +++ b/26697-h/images/fig_36.png diff --git a/26697-h/images/fig_37.png b/26697-h/images/fig_37.png Binary files differnew file mode 100644 index 0000000..1aa1194 --- /dev/null +++ b/26697-h/images/fig_37.png diff --git a/26697-h/images/fig_38.png b/26697-h/images/fig_38.png Binary files differnew file mode 100644 index 0000000..8feb96c --- /dev/null +++ b/26697-h/images/fig_38.png diff --git a/26697-h/images/fig_39.png b/26697-h/images/fig_39.png Binary files differnew file mode 100644 index 0000000..dc48f22 --- /dev/null +++ b/26697-h/images/fig_39.png diff --git a/26697-h/images/fig_40.png b/26697-h/images/fig_40.png Binary files differnew file mode 100644 index 0000000..3c572d2 --- /dev/null +++ b/26697-h/images/fig_40.png diff --git a/26697-h/images/fig_41.png b/26697-h/images/fig_41.png Binary files differnew file mode 100644 index 0000000..8f13a54 --- /dev/null +++ b/26697-h/images/fig_41.png diff --git a/26697-h/images/fig_42.png b/26697-h/images/fig_42.png Binary files differnew file mode 100644 index 0000000..9d8223f --- /dev/null +++ b/26697-h/images/fig_42.png diff --git a/26697-h/images/fig_43.png b/26697-h/images/fig_43.png Binary files differnew file mode 100644 index 0000000..eef34b7 --- /dev/null +++ b/26697-h/images/fig_43.png diff --git a/26697-h/images/fig_44.png b/26697-h/images/fig_44.png Binary files differnew file mode 100644 index 0000000..7d7caee --- /dev/null +++ b/26697-h/images/fig_44.png diff --git a/26697-h/images/fig_45.png b/26697-h/images/fig_45.png Binary files differnew file mode 100644 index 0000000..d5974d0 --- /dev/null +++ b/26697-h/images/fig_45.png diff --git a/26697.txt b/26697.txt new file mode 100644 index 0000000..d846a88 --- /dev/null +++ b/26697.txt @@ -0,0 +1,7552 @@ +The Project Gutenberg EBook of Principles of Mining, by Herbert C. Hoover + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Principles of Mining + Valuation, Organization and Administration + +Author: Herbert C. Hoover + +Release Date: September 24, 2008 [EBook #26697] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK PRINCIPLES OF MINING *** + + + + +Produced by Robert J. Hall + + + + +PRINCIPLES OF MINING + ++--------------------------------------------------------------+ +| Published by the | +| McGraw-Hill Book Company | +| New York | +| | +| Successors to the Book Departments of the | +| McGraw Publishing Company Hill Publishing Company | +| | +| Publishers of Books for | +| Electrical World The Engineering and Mining Journal | +| Engineering Record Power and The Engineer | +| Electric Railway Journal American Machinist | +| Metallurgical and Chemical Engineering | ++--------------------------------------------------------------+ + + + + +PRINCIPLES OF MINING + +VALUATION, ORGANIZATION AND ADMINISTRATION + +COPPER, GOLD, LEAD, SILVER, TIN AND ZINC + + +BY + +HERBERT C. HOOVER + +_Member American Institute of Mining Engineers, Mining and Metallurgical +Society of America, Societe des Ingenieurs Civils de France, Fellow +Royal Geographical Society, etc._ + +First Edition + +_FOURTH THOUSAND_ + +McGRAW-HILL BOOK COMPANY + +239 WEST 39TH STREET, NEW YORK + +BOUVERIE STREET, LONDON, E.C. + +1909 + + + + +PREFACE. + +This volume is a condensation of a series of lectures delivered +in part at Stanford and in part at Columbia Universities. It is +intended neither for those wholly ignorant of mining, nor for those +long experienced in the profession. + +The bulk of the material presented is the common heritage of the +profession, and if any one may think there is insufficient reference +to previous writers, let him endeavor to find to whom the origin +of our methods should be credited. The science has grown by small +contributions of experience since, or before, those unnamed Egyptian +engineers, whose works prove their knowledge of many fundamentals +of mine engineering six thousand eight hundred years ago. If I +have contributed one sentence to the accumulated knowledge of a +thousand generations of engineers, or have thrown one new ray of +light on the work, I shall have done my share. + +I therefore must acknowledge my obligations to all those who have +gone before, to all that has been written that I have read, to +those engineers with whom I have been associated for many years, +and in particular to many friends for kindly reply to inquiry upon +points herein discussed. + + + + +CONTENTS. + +CHAPTER 1. + +Valuation of Copper, Gold, Lead, Silver, Tin, and Zinc Lode Mines + +Determination of average metal content; sampling, assay plans, +calculations of averages, percentage of errors in estimate from +sampling. + +CHAPTER II. + +Mine Valuation (_Continued_) + +Calculation of quantities of ore, and classification of ore in sight. + +CHAPTER III. + +Mine Valuation (_Continued_) + +Prospective value. Extension in depth; origin and structural character +of the deposit; secondary enrichment; development in neighboring +mines; depth of exhaustion. + +CHAPTER IV. + +Mine Valuation (_Continued_) + +Recoverable percentage of the gross assay value; price of metals; +cost of production. + +CHAPTER V. + +Mine Valuation (_Continued_) + +Redemption or amortization of capital and interest. + +CHAPTER VI. + +Mine Valuation (_Concluded_) + +Valuation of mines with little or no ore in sight; valuations on +second-hand data; general conduct of examinations; reports. + +CHAPTER VII. + +Development of Mines + +Entry to the mine; tunnels; vertical, inclined, and combined shafts; +location and number of shafts. + +CHAPTER VIII. + +Development of Mines (_Continued_) + +Shape and size of shafts; speed of sinking; tunnels. + +CHAPTER IX. + +Development of Mines (_Concluded_) + +Subsidiary development: stations; crosscuts; levels; interval between +levels; protection of levels; winzes and rises. Development in the +prospecting stage; drilling. + +CHAPTER X. + +Stoping + +Methods of ore-breaking; underhand stopes; overhand stopes; combined +stope. Valuing ore in course of breaking. + +CHAPTER XI. + +Methods of Supporting Excavation + +Timbering; filling with waste; filling with broken ore; pillars +of ore; artificial pillars; caving system. + +CHAPTER XII. + +Mechanical Equipment + +Conditions bearing on mine equipment; winding appliances; haulage +equipment in shafts; lateral underground transport; transport in +stopes. + +CHAPTER XIII. + +Mechanical Equipment (_Continued_) + +Drainage: controlling factors; volume and head of water; flexibility; +reliability; power conditions; mechanical efficiency; capital outlay. +Systems of drainage,--steam pumps, compressed-air pumps, electrical +pumps, rod-driven pumps, bailing; comparative value of various +systems. + +CHAPTER XIV. + +Mechanical Equipment (_Concluded_) + +Machine drilling: power transmission; compressed air _vs._ electricity; +air drills; machine _vs._ hand drilling. Workshops. Improvement in +equipment. + +CHAPTER XV. + +Ratio of Output to the Mine + +Determination of possible maximum; limiting factors; cost of equipment; +life of the mine; mechanical inefficiency of patchwork plant; +overproduction of base metal; security of investment. + +CHAPTER XVI. + +Administration + +Labor efficiency; skill; intelligence; application coordination; +contract work; labor unions; real basis of wages. + +CHAPTER XVII. + +Administration (_Continued_) + +Accounts and technical data and reports; working costs; division +of expenditure; inherent limitations in accuracy of working costs; +working cost sheets. General technical data; labor, supplies, power, +surveys, sampling, and assaying. + +CHAPTER XVIII. + +Administration (_Concluded_) + +Administrative reports. + +CHAPTER XIX. + +The Amount of Risk in Mining Investments + +Risk in valuation of mines; in mines as compared with other commercial +enterprises. + +CHAPTER XX. + +The Character, Training, and Obligations of the Mining Engineering +Profession + +Index + + + + +PRINCIPLES OF MINING. + +CHAPTER I. + +Valuation of Copper, Gold, Lead, Silver, Tin, and Zinc Lode Mines. + +DETERMINATION OF AVERAGE METAL CONTENT; SAMPLING, ASSAY PLANS, +CALCULATIONS OF AVERAGES, PERCENTAGE OF ERRORS IN ESTIMATE FROM +SAMPLING. + +The following discussion is limited to _in situ_ deposits of copper, +gold, lead, silver, tin, and zinc. The valuation of alluvial deposits, +iron, coal, and other mines is each a special science to itself and +cannot be adequately discussed in common with the type of deposits +mentioned above. + +The value of a metal mine of the order under discussion depends +upon:-- + +_a_. The profit that may be won from ore exposed; +_b_. The prospective profit to be derived from extension of the + ore beyond exposures; +_c_. The effect of a higher or lower price of metal (except in + gold mines); +_d_. The efficiency of the management during realization. + +The first may be termed the positive value, and can be approximately +determined by sampling or test-treatment runs. The second and the +third may be termed the speculative values, and are largely a matter +of judgment based on geological evidence and the industrial outlook. +The fourth is a question of development, equipment, and engineering +method adapted to the prospects of the enterprise, together with +capable executive control of these works. + +It should be stated at the outset that it is utterly impossible to +accurately value any mine, owing to the many speculative factors +involved. The best that can be done is to state that the value +lies between certain limits, and that various stages above the +minimum given represent various degrees of risk. Further, it would +be but stating truisms to those engaged in valuing mines to repeat +that, because of the limited life of every mine, valuation of such +investments cannot be based upon the principle of simple interest; +nor that any investment is justified without a consideration of +the management to ensue. Yet the ignorance of these essentials +is so prevalent among the public that they warrant repetition on +every available occasion. + +To such an extent is the realization of profits indicated from +the other factors dependent upon the subsequent management of the +enterprise that the author considers a review of underground engineering +and administration from an economic point of view an essential to +any essay upon the subject. While the metallurgical treatment of +ores is an essential factor in mine economics, it is considered that +a detailed discussion of the myriad of processes under hypothetic +conditions would lead too far afield. Therefore the discussion is +largely limited to underground and administrative matters. + +The valuation of mines arises not only from their change of ownership, +but from the necessity in sound administration for a knowledge +of some of the fundamentals of valuation, such as ore reserves +and average values, that managerial and financial policy may be +guided aright. Also with the growth of corporate ownership there +is a demand from owners and stockholders for periodic information +as to the intrinsic condition of their properties. + +The growth of a body of speculators and investors in mining stocks +and securities who desire professional guidance which cannot be based +upon first-hand data is creating further demand on the engineer. +Opinions in these cases must be formed on casual visits or second-hand +information, and a knowledge of men and things generally. Despite +the feeling of some engineers that the latter employment is not +properly based professionally, it is an expanding phase of engineers' +work, and must be taken seriously. Although it lacks satisfactory +foundation for accurate judgment, yet the engineer can, and should, +give his experience to it when the call comes, out of interest +to the industry as a whole. Not only can he in a measure protect +the lamb, by insistence on no investment without the provision of +properly organized data and sound administration for his client, but +he can do much to direct the industry from gambling into industrial +lines. + +An examination of the factors which arise on the valuation of mines +involves a wide range of subjects. For purposes of this discussion +they may be divided into the following heads:-- + +1. _Determination of Average Metal Contents of the Ore._ +2. _Determination of Quantities of Ore._ +3. _Prospective Value._ +4. _Recoverable Percentage of Gross Value._ +5. _Price of Metals._ +6. _Cost of Production._ +7. _Redemption or Amortization of Capital and Interest._ +8. _Valuation of Mines without Ore in Sight._ +9. _General Conduct of Examination and Reports._ + +DETERMINATION OF AVERAGE METAL CONTENTS OF THE ORE. + +Three means of determination of the average metal content of standing +ore are in use--Previous Yield, Test-treatment Runs, and Sampling. + +PREVIOUS YIELD.--There are certain types of ore where the previous +yield from known space becomes the essential basis of determination +of quantity and metal contents of ore standing and of the future +probabilities. Where metals occur like plums in a pudding, sampling +becomes difficult and unreliable, and where experience has proved +a sort of regularity of recurrence of these plums, dependence must +necessarily be placed on past records, for if their reliability is +to be questioned, resort must be had to extensive test-treatment +runs. The Lake Superior copper mines and the Missouri lead and zinc +mines are of this type of deposit. On the other sorts of deposits +the previous yield is often put forward as of important bearing +on the value of the ore standing, but such yield, unless it can +be _authentically_ connected with blocks of ore remaining, is not +necessarily a criterion of their contents. Except in the cases +mentioned, and as a check on other methods of determination, it +has little place in final conclusions. + +TEST PARCELS.--Treatment on a considerable scale of sufficiently +regulated parcels, although theoretically the ideal method, is, +however, not often within the realm of things practical. In examination +on behalf of intending purchasers, the time, expense, or opportunity +to fraud are usually prohibitive, even where the plant and facilities +for such work exist. Even in cases where the engineer in management +of producing mines is desirous of determining the value of standing +ore, with the exception of deposits of the type mentioned above, +it is ordinarily done by actual sampling, because separate mining +and treatment of test lots is generally inconvenient and expensive. +As a result, the determination of the value of standing ore is, +in the great majority of cases, done by sampling and assaying. + +SAMPLING.--The whole theory of sampling is based on the distribution +of metals through the ore-body with more or less regularity, so +that if small portions, that is samples, be taken from a sufficient +number of points, their average will represent fairly closely the +unit value of the ore. If the ore is of the extreme type of irregular +metal distribution mentioned under "previous yield," then sampling +has no place. + +How frequently samples must be taken, the manner of taking them, +and the quantity that constitutes a fair sample, are matters that +vary with each mine. So much depends upon the proper performance +of this task that it is in fact the most critical feature of mine +examination. Ten samples properly taken are more valuable than +five hundred slovenly ones, like grab samples, for such a number +of bad ones would of a surety lead to wholly wrong conclusions. +Given a good sampling and a proper assay plan, the valuation of a +mine is two-thirds accomplished. It should be an inflexible principle +in examinations for purchase that every sample must be taken under +the personal supervision of the examining engineer or his trusted +assistants. Aside from throwing open the doors to fraud, the average +workman will not carry out the work in a proper manner, unless +under constant supervision, because of his lack of appreciation of +the issues involved. Sampling is hard, uncongenial, manual labor. +It requires a deal of conscientiousness to take enough samples and +to take them thoroughly. The engineer does not exist who, upon +completion of this task, considers that he has got too many, and +most wish that they had taken more. + +The accuracy of sampling as a method of determining the value of +standing ore is a factor of the number of samples taken. The average, +for example, of separate samples from each square inch would be +more accurate than those from each alternate square inch. However, +the accumulated knowledge and experience as to the distribution +of metals through ore has determined approximately the manner of +taking such samples, and the least number which will still by the +law of averages secure a degree of accuracy commensurate with the +other factors of estimation. + +As metals are distributed through ore-bodies of fissure origin +with most regularity on lines parallel to the strike and dip, an +equal portion of ore from every point along cross-sections at right +angles to the strike will represent fairly well the average values +for a certain distance along the strike either side of these +cross-sections. In massive deposits, sample sections are taken +in all directions. The intervals at which sample sections must +be cut is obviously dependent upon the general character of the +deposit. If the values are well distributed, a longer interval +may be employed than in one subject to marked fluctuations. As +a general rule, five feet is the distance most accepted. This, +in cases of regular distribution of values, may be stretched to +ten feet, or in reverse may be diminished to two or three feet. + +The width of ore which may be included for one sample is dependent +not only upon the width of the deposit, but also upon its character. +Where the ore is wider than the necessary stoping width, the sample +should be regulated so as to show the possible locus of values. +The metal contents may be, and often are, particularly in deposits +of the impregnation or replacement type, greater along some streak +in the ore-body, and this difference may be such as to make it +desirable to stope only a portion of the total thickness. For deposits +narrower than the necessary stoping width the full breadth of ore +should be included in one sample, because usually the whole of +the deposit will require to be broken. + +In order that a payable section may not possibly be diluted with +material unnecessary to mine, if the deposit is over four feet and +under eight feet, the distance across the vein or lode is usually +divided into two samples. If still wider, each is confined to a +span of about four feet, not only for the reason given above, but +because the more numerous the samples, the greater the accuracy. +Thus, in a deposit twenty feet wide it may be taken as a good guide +that a test section across the ore-body should be divided into +five parts. + +As to the physical details of sample taking, every engineer has +his own methods and safeguards against fraud and error. In a large +organization of which the writer had for some years the direction, +and where sampling of mines was constantly in progress on an extensive +scale, not only in contemplation of purchase, but where it was also +systematically conducted in operating mines for working data, he +adopted the above general lines and required the following details. + +A fresh face of ore is first broken and then a trench cut about +five inches wide and two inches deep. This trench is cut with a +hammer and moil, or, where compressed air is available and the +rock hard, a small air-drill of the hammer type is used. The spoil +from the trench forms the sample, and it is broken down upon a +large canvas cloth. Afterwards it is crushed so that all pieces +will pass a half-inch screen, mixed and quartered, thus reducing the +weight to half. Whether it is again crushed and quartered depends +upon what the conditions are as to assaying. If convenient to assay +office, as on a going mine, the whole of the crushing and quartering +work can be done at that office, where there are usually suitable +mechanical appliances. If the samples must be taken a long distance, +the bulk for transport can be reduced by finer breaking and repeated +quartering, until there remain only a few ounces. + +PRECAUTIONS AGAINST FRAUD.--Much has been written about the precautions +to be taken against fraud in cases of valuations for purchase. The +best safeguards are an alert eye and a strong right arm. However, +certain small details help. A large leather bag, arranged to lock +after the order of a mail sack, into which samples can be put +underground and which is never unfastened except by responsible +men, not only aids security but relieves the mind. A few samples +of country rock form a good check, and notes as to the probable +value of the ore, from inspection when sampling, are useful. A +great help in examination is to have the assays or analyses done +coincidentally with the sampling. A doubt can then always be settled +by resampling at once, and much knowledge can be gained which may +relieve so exhaustive a program as might be necessary were results +not known until after leaving the mine. + +ASSAY OF SAMPLES.--Two assays, or as the case may be, analyses, +are usually made of every sample and their average taken. In the +case of erratic differences a third determination is necessary. + +ASSAY PLANS.--An assay plan is a plan of the workings, with the +location, assay value, and width of the sample entered upon it. In +a mine with a narrow vein or ore-body, a longitudinal section is +sufficient base for such entries, but with a greater width than one +sample span it is desirable to make preliminary plans of separate +levels, winzes, etc., and to average the value of the whole payable +widths on such plans before entry upon a longitudinal section. Such +a longitudinal section will, through the indicated distribution +of values, show the shape of the ore-body--a step necessary in +estimating quantities and of the most fundamental importance in +estimating the probabilities of ore extension beyond the range of +the openings. The final assay plan should show the average value +of the several blocks of ore, and it is from these averages that +estimates of quantities must be made up. + +CALCULATIONS OF AVERAGES.--The first step in arriving at average +values is to reduce erratic high assays to the general tenor of +other adjacent samples. This point has been disputed at some length, +more often by promoters than by engineers, but the custom is very +generally and rightly adopted. Erratically high samples may indicate +presence of undue metal in the assay attributable to unconscious +salting, for if the value be confined to a few large particles +they may find their way through all the quartering into the assay. +Or the sample may actually indicate rich spots of ore; but in any +event experience teaches that no dependence can be put upon regular +recurrence of such abnormally rich spots. As will be discussed +under percentage of error in sampling, samples usually indicate +higher than the true value, even where erratic assays have been +eliminated. There are cases of profitable mines where the values +were all in spots, and an assay plan would show 80% of the assays +_nil_, yet these pockets were so rich as to give value to the whole. +Pocket mines, as stated before, are beyond valuation by sampling, +and aside from the previous yield recourse must be had to actual +treatment runs on every block of ore separately. + +After reduction of erratic assays, a preliminary study of the runs of +value or shapes of the ore-bodies is necessary before any calculation +of averages. A preliminary delineation of the boundaries of the +payable areas on the assay plan will indicate the sections of the +mine which are unpayable, and from which therefore samples can +be rightly excluded in arriving at an average of the payable ore +(Fig. 1). In a general way, only the ore which must be mined need +be included in averaging. + +The calculation of the average assay value of standing ore from +samples is one which seems to require some statement of elementals. +Although it may seem primitive, it can do no harm to recall that if +a dump of two tons of ore assaying twenty ounces per ton be added +to a dump of five tons averaging one ounce per ton, the result has +not an average assay of twenty-one ounces divided by the number of +dumps. Likewise one sample over a width of two feet, assaying twenty +ounces per ton, if averaged with another sample over a width of five +feet, assaying one ounce, is no more twenty-one ounces divided by +two samples than in the case of the two dumps. If common sense were +not sufficient demonstration of this, it can be shown algebraically. +Were samples equidistant from each other, and were they of equal +width, the average value would be the simple arithmetical mean of +the assays. But this is seldom the case. The number of instances, +not only in practice but also in technical literature, where the +fundamental distinction between an arithmetical and a geometrical +mean is lost sight of is amazing. + +To arrive at the average value of samples, it is necessary, in +effect, to reduce them to the actual quantity of the metal and volume +of ore represented by each. The method of calculation therefore +is one which gives every sample an importance depending upon the +metal content of the volume of ore it represents. + +The volume of ore appertaining to any given sample can be considered +as a prismoid, the dimensions of which may be stated as follows:-- + + _W_ = Width in feet of ore sampled. + _L_ = Length in feet of ore represented by the sample. + _D_ = Depth into the block to which values are assumed to penetrate. + +We may also let:-- + + _C_ = The number of cubic feet per ton of ore. + _V_ = Assay value of the sample. + +Then _WLD_/C_ = tonnage of the prismoid.* + _V WLD_/C_ = total metal contents. + +[Footnote *: Strictly, the prismoidal formula should be used, but +it complicates the study unduly, and for practical purposes the +above may be taken as the volume.] + +The average value of a number of samples is the total metal contents +of their respective prismoids, divided by the total tonnage of +these prismoids. If we let _W_, _W_1, _V_, _V_1 etc., represent +different samples, we have:-- + +_V(_WLD_/_C_) + _V_1 (_W_1 _L_1 _D_1/_C_) + _V_2 (_W_2 _L_2 _D_2/_C_) +--------------------------------------------------------------------- + _WLD_/_C_ + _W_1 _L_1 _D_1/_C_ + _W_2 _L_2 _D_2/_C_ += average value. + +This may be reduced to:-- + +(_VWLD_) + (_V_1 _W_1 _L_1 _D_1) + (_V_2 _W_2 _L_2 _D_2,), etc. +--------------------------------------------------------------- + (_WLD_) + (_W_1 _L_1 _D_1) + (_W_2 _L_2 _D_2), etc. + +As a matter of fact, samples actually represent the value of +the outer shell of the block of ore only, and the continuity of +the same values through the block is a geological assumption. +From the outer shell, all the values can be taken to penetrate +equal distances into the block, and therefore _D_, _D_1, _D_2 +may be considered as equal and the equation becomes:-- + +(_VWL_) + (_V_1 _W_1 _L_1) + (_V_2 _W_2 _L_2), etc. +--------------------------------------------------- + (_WL_) + (_W_1 _L_1) + (_W_2 _L_2), etc. + +The length of the prismoid base _L_ for any given sample will be +a distance equal to one-half the sum of the distances to the two +adjacent samples. As a matter of practice, samples are usually taken +at regular intervals, and the lengths _L_, _L_1, _L_2 becoming thus +equal can in such case be eliminated, and the equation becomes:-- + +(_VW_) + (_V_1 _W_1) + (_V_2 _W_2), etc. +---------------------------------------- + _W_ + _W_1 + _W_2 , etc. + +The name "assay foot" or "foot value" has been given to the relation +_VW_, that is, the assay value multiplied by the width sampled.[*] +It is by this method that all samples must be averaged. The same +relation obviously can be evolved by using an inch instead of a +foot, and in narrow veins the assay inch is generally used. + +[Footnote *: An error will be found in this method unless the two +end samples be halved, but in a long run of samples this may be +disregarded.] + +Where the payable cross-section is divided into more than one sample, +the different samples in the section must be averaged by the above +formula, before being combined with the adjacent section. Where +the width sampled is narrower than the necessary stoping width, +and where the waste cannot be broken separately, the sample value +must be diluted to a stoping width. To dilute narrow samples to +a stoping width, a blank value over the extra width which it is +necessary to include must be averaged with the sample from the +ore on the above formula. Cases arise where, although a certain +width of waste must be broken with the ore, it subsequently can +be partially sorted out. Practically nothing but experience on +the deposit itself will determine how far this will restore the +value of the ore to the average of the payable seam. In any event, +no sorting can eliminate all such waste; and it is necessary to +calculate the value on the breaking width, and then deduct from +the gross tonnage to be broken a percentage from sorting. There +is always an allowance to be made in sorting for a loss of good +ore with the discards. + +PERCENTAGE OF ERROR IN ESTIMATES FROM SAMPLING.--It must be remembered +that the whole theory of estimation by sampling is founded upon +certain assumptions as to evenness of continuity and transition +in value and volume. It is but a basis for an estimate, and an +estimate is not a statement of fact. It cannot therefore be too +forcibly repeated that an estimate is inherently but an approximation, +take what care one may in its founding. While it is possible to +refine mathematical calculation of averages to almost any nicety, +beyond certain essentials it adds nothing to accuracy and is often +misleading. + +It is desirable to consider where errors are most likely to creep +in, assuming that all fundamental data are both accurately taken +and considered. Sampling of ore _in situ_ in general has a tendency +to give higher average value than the actual reduction of the ore +will show. On three West Australian gold mines, in records covering +a period of over two years, where sampling was most exhaustive as +a daily regime of the mines, the values indicated by sampling were +12% higher than the mill yield plus the contents of the residues. +On the Witwatersrand gold mines, the actual extractable value is +generally considered to be about 78 to 80% of the average shown +by sampling, while the mill extractions are on average about 90 +to 92% of the head value coming to the mill. In other words, there +is a constant discrepancy of about 10 to 12% between the estimated +value as indicated by mine samples, and the actual value as shown +by yield plus the residues. At Broken Hill, on three lead mines, +the yield is about 12% less than sampling would indicate. This +constancy of error in one direction has not been so generally +acknowledged as would be desirable, and it must be allowed for +in calculating final results. The causes of the exaggeration seem +to be:-- + +_First_, inability to stope a mine to such fine limitations of +width, or exclusion of unpayable patches, as would appear practicable +when sampling, that is by the inclusion when mining of a certain +amount of barren rock. Even in deposits of about normal stoping +width, it is impossible to prevent the breaking of a certain amount +of waste, even if the ore occurrence is regularly confined by walls. + +If the mine be of the impregnation type, such as those at Goldfield, +or Kalgoorlie, with values like plums in a pudding, and the stopes +themselves directed more by assays than by any physical differences +in the ore, the discrepancy becomes very much increased. In mines +where the range of values is narrower than the normal stoping width, +some wall rock must be broken. Although it is customary to allow for +this in calculating the average value from samples, the allowance +seldom seems enough. In mines where the ore is broken on to the +top of stopes filled with waste, there is some loss underground +through mixture with the filling. + +_Second_, the metal content of ores, especially when in the form of +sulphides, is usually more friable than the matrix, and in actual +breaking of samples an undue proportion of friable material usually +creeps in. This is true more in lead, copper, and zinc, than in +gold ores. On several gold mines, however, tests on accumulated +samples for their sulphide percentage showed a distinctly greater +ratio than the tenor of the ore itself in the mill. As the gold is +usually associated with the sulphides, the samples showed higher +values than the mill. + +In general, some considerable factor of safety must be allowed +after arriving at calculated average of samples,--how much it is +difficult to say, but, in any event, not less than 10%. + + + + +CHAPTER II. + +Mine Valuation (_Continued_). + +CALCULATION OF QUANTITIES OF ORE, AND CLASSIFICATION OF ORE IN SIGHT. + +As mines are opened by levels, rises, etc., through the ore, an +extension of these workings has the effect of dividing it into +"blocks." The obvious procedure in determining tonnages is to calculate +the volume and value of each block separately. Under the law of +averages, the multiplicity of these blocks tends in proportion +to their number to compensate the percentage of error which might +arise in the sampling or estimating of any particular one. The +shapes of these blocks, on longitudinal section, are often not +regular geometrical figures. As a matter of practice, however, they +can be subdivided into such figures that the total will approximate +the whole with sufficient closeness for calculations of their areas. + +The average width of the ore in any particular block is the arithmetical +mean of the width of the sample sections in it,[*] if the samples be +an equal distance apart. If they are not equidistant, the average +width is the sum of the areas between samples, divided by the total +length sampled. The cubic foot contents of a particular block is +obviously the width multiplied by the area of its longitudinal +section. + +[Footnote *: This is not strictly true unless the sum of the widths +of the two end-sections be divided by two and the result incorporated +in calculating the means. In a long series that error is of little +importance.] + +The ratio of cubic feet to tons depends on the specific gravity +of the ore, its porosity, and moisture. The variability of ores +throughout the mine in all these particulars renders any method +of calculation simply an approximation in the end. The factors +which must remain unknown necessarily lead the engineer to the +provision of a margin of safety, which makes mathematical refinement +and algebraic formulae ridiculous. + +There are in general three methods of determination of the specific +volume of ores:-- + +_First_, by finding the true specific gravity of a sufficient number +of representative specimens; this, however, would not account for +the larger voids in the ore-body and in any event, to be anything +like accurate, would be as expensive as sampling and is therefore +of little more than academic interest. + +_Second_, by determining the weight of quantities broken from measured +spaces. This also would require several tests from different portions +of the mine, and, in examinations, is usually inconvenient and +difficult. Yet it is necessary in cases of unusual materials, such +as leached gossans, and it is desirable to have it done sooner +or later in going mines, as a check. + +_Third_, by an approximation based upon a calculation from the +specific gravities of the predominant minerals in the ore. Ores +are a mixture of many minerals; the proportions vary through the +same ore-body. Despite this, a few partial analyses, which are +usually available from assays of samples and metallurgical tests, +and a general inspection as to the compactness of the ore, give a +fairly reliable basis for approximation, especially if a reasonable +discount be allowed for safety. In such discount must be reflected +regard for the porosity of the ore, and the margin of safety necessary +may vary from 10 to 25%. If the ore is of unusual character, as +in leached deposits, as said before, resort must be had to the +second method. + +The following table of the weights per cubic foot and the number +of cubic feet per ton of some of the principal ore-forming minerals +and gangue rocks will be useful for approximating the weight of +a cubic foot of ore by the third method. Weights are in pounds +avoirdupois, and two thousand pounds are reckoned to the ton. + +============================================ + | | Number of + | Weight per | Cubic Feet + | Cubic Foot | per Ton of + | | 2000 lb. +------------------|------------|------------ +Antimony | 417.50 | 4.79 + Sulphide | 285.00 | 7.01 +Arsenical Pyrites | 371.87 | 5.37 +Barium Sulphate | 278.12 | 7.19 +Calcium: | | + Fluorite | 198.75 | 10.06 + Gypsum | 145.62 | 13.73 + Calcite | 169.37 | 11.80 +Copper | 552.50 | 3.62 + Calcopyrite | 262.50 | 7.61 + Bornite | 321.87 | 6.21 + Malachite | 247.50 | 8.04 + Azurite | 237.50 | 8.42 + Chrysocolla | 132.50 | 15.09 +Iron (Cast) | 450.00 | 4.44 + Magnetite | 315.62 | 6.33 + Hematite | 306.25 | 6.53 + Limonite | 237.50 | 8.42 + Pyrite | 312.50 | 6.40 + Carbonate | 240.62 | 8.31 +Lead | 710.62 | 2.81 + Galena | 468.75 | 4.27 + Carbonate | 406.87 | 4.81 +Manganese Oxide | 268.75 | 6.18 + Rhodonite | 221.25 | 9.04 +Magnesite | 187.50 | 10.66 + Dolomite | 178.12 | 11.23 +Quartz | 165.62 | 12.07 +Quicksilver | 849.75 | 2.35 + Cinnabar | 531.25 | 3.76 + Sulphur | 127.12 | 15.74 +Tin | 459.00 | 4.35 + Oxide | 418.75 | 4.77 +Zinc | 437.50 | 4.57 + Blende | 253.12 | 7.90 + Carbonate | 273.12 | 7.32 + Silicate | 215.62 | 9.28 +Andesite | 165.62 | 12.07 +Granite | 162.62 | 12.30 +Diabase | 181.25 | 11.03 +Diorite | 171.87 | 11.63 +Slates | 165.62 | 12.07 +Sandstones | 162.50 | 12.30 +Rhyolite | 156.25 | 12.80 +============================================ + +The specific gravity of any particular mineral has a considerable +range, and a medium has been taken. The possible error is +inconsequential for the purpose of these calculations. + +For example, a representative gold ore may contain in the main +96% quartz, and 4% iron pyrite, and the weight of the ore may be +deduced as follows:-- + + Quartz, 96% x 12.07 = 11.58 + Iron Pyrite, 4% x 6.40 = .25 + ----- + 11.83 cubic feet per ton. + +Most engineers, to compensate porosity, would allow twelve to thirteen +cubic feet per ton. + +CLASSIFICATION OF ORE IN SIGHT. + +The risk in estimates of the average value of standing ore is dependent +largely upon how far values disclosed by sampling are assumed to +penetrate beyond the tested face, and this depends upon the geological +character of the deposit. From theoretical grounds and experience, +it is known that such values will have some extension, and the +assumption of any given distance is a calculation of risk. The +multiplication of development openings results in an increase of +sampling points available and lessens the hazards. The frequency +of such openings varies in different portions of every mine, and +thus there are inequalities of risk. It is therefore customary in +giving estimates of standing ore to classify the ore according +to the degree of risk assumed, either by stating the number of +sides exposed or by other phrases. Much discussion and ink have +been devoted to trying to define what risk may be taken in such +matters, that is in reality how far values may be assumed to penetrate +into the unbroken ore. Still more has been consumed in attempts +to coin terms and make classifications which will indicate what +ratio of hazard has been taken in stating quantities and values. + +The old terms "ore in sight" and "profit in sight" have been of +late years subject to much malediction on the part of engineers +because these expressions have been so badly abused by the charlatans +of mining in attempts to cover the flights of their imaginations. A +large part of Volume X of the "Institution of Mining and Metallurgy" +has been devoted to heaping infamy on these terms, yet not only +have they preserved their places in professional nomenclature, +but nothing has been found to supersede them. + +Some general term is required in daily practice to cover the whole +field of visible ore, and if the phrase "ore in sight" be defined, +it will be easier to teach the laymen its proper use than to abolish +it. In fact, the substitutes are becoming abused as much as the +originals ever were. All convincing expressions will be misused +by somebody. + +The legitimate direction of reform has been to divide the general +term of "ore in sight" into classes, and give them names which will +indicate the variable amount of risk of continuity in different parts +of the mine. As the frequency of sample points, and consequently the +risk of continuity, will depend upon the detail with which the mine +is cut into blocks by the development openings, and upon the number +of sides of such blocks which are accessible, most classifications +of the degree of risk of continuity have been defined in terms of +the number of sides exposed in the blocks. Many phrases have been +coined to express such classifications; those most currently used +are the following:-- + +Positive Ore \ Ore exposed on four sides in blocks of a size +Ore Developed / variously prescribed. +Ore Blocked Out Ore exposed on three sides within reasonable + distance of each other. +Probable Ore \ +Ore Developing / Ore exposed on two sides. + +Possible Ore \ The whole or a part of the ore below the +Ore Expectant / lowest level or beyond the range of vision. + +No two of these parallel expressions mean quite the same thing; +each more or less overlies into another class, and in fact none +of them is based upon a logical footing for such a classification. +For example, values can be assumed to penetrate some distance from +every sampled face, even if it be only ten feet, so that ore exposed +on one side will show some "positive" or "developed" ore which, on +the lines laid down above, might be "probable" or even "possible" +ore. Likewise, ore may be "fully developed" or "blocked out" so far +as it is necessary for stoping purposes with modern wide intervals +between levels, and still be in blocks too large to warrant an +assumption of continuity of values to their centers (Fig. 1). As +to the third class of "possible" ore, it conveys an impression +of tangibility to a nebulous hazard, and should never be used in +connection with positive tonnages. This part of the mine's value +comes under extension of the deposit a long distance beyond openings, +which is a speculation and cannot be defined in absolute tons without +exhaustive explanation of the risks attached, in which case any +phrase intended to shorten description is likely to be misleading. + +[Illustration: Fig. 1.--Longitudinal section of a mine, showing +classification of the exposed ore. Scale, 400 feet = 1 inch.] + +Therefore empirical expressions in terms of development openings +cannot be made to cover a geologic factor such as the distribution +of metals through a rock mass. The only logical basis of ore +classification for estimation purposes is one which is founded +on the chances of the values penetrating from the surface of the +exposures for each particular mine. Ore that may be calculated +upon to a certainty is that which, taking into consideration the +character of the deposit, can be said to be so sufficiently surrounded +by sampled faces that the distance into the mass to which values +are assumed to extend is reduced to a minimum risk. Ore so far +removed from the sampled face as to leave some doubt, yet affording +great reason for expectation of continuity, is "probable" ore. +The third class of ore mentioned, which is that depending upon +extension of the deposit and in which, as said above, there is great +risk, should be treated separately as the speculative value of the +mine. Some expressions are desirable for these classifications, and +the writer's own preference is for the following, with a definition +based upon the controlling factor itself. + +They are:-- + +Proved Ore Ore where there is practically no risk of + failure of continuity. + +Probable Ore Ore where there is some risk, yet warrantable + justification for assumption of continuity. + +Prospective Ore Ore which cannot be included in the above + classes, nor definitely known or stated in + any terms of tonnage. + +What extent of openings, and therefore of sample faces, is required +for the ore to be called "proved" varies naturally with the type +of deposit,--in fact with each mine. In a general way, a fair rule +in gold quartz veins below influence of secondary alteration is +that no point in the block shall be over fifty feet from the points +sampled. In limestone or andesite replacements, as by gold or lead +or copper, the radius must be less. In defined lead and copper +lodes, or in large lenticular bodies such as the Tennessee copper +mines, the radius may often be considerably greater,--say one hundred +feet. In gold deposits of such extraordinary regularity of values +as the Witwatersrand bankets, it can well be two hundred or two +hundred and fifty feet. + +"Probable ore" should be ore which entails continuity of values +through a greater distance than the above, and such distance must +depend upon the collateral evidence from the character of the deposit, +the position of openings, etc. + +Ore beyond the range of the "probable" zone is dependent upon the +extension of the deposit beyond the realm of development and will +be discussed separately. + +Although the expression "ore in sight" may be deprecated, owing to +its abuse, some general term to cover both "positive" and "probable" +ore is desirable; and where a general term is required, it is the +intention herein to hold to the phrase "ore in sight" under the +limitations specified. + + + + +CHAPTER III. + +Mine Valuation (_Continued_). + +PROSPECTIVE VALUE.[*] EXTENSION IN DEPTH; ORIGIN AND STRUCTURAL +CHARACTER OF THE DEPOSIT; SECONDARY ENRICHMENT; DEVELOPMENT IN +NEIGHBORING MINES; DEPTH OF EXHAUSTION. + +[Footnote *: The term "extension in depth" is preferred by many +to the phrase "prospective value." The former is not entirely +satisfactory, as it has a more specific than general application. +It is, however, a current miner's phrase, and is more expressive. +In this discussion "extension in depth" is used synonymously, and +it may be taken to include not alone the downward prolongation of +the ore below workings, but also the occasional cases of lateral +extension beyond the range of development work. The commonest instance +is continuance below the bottom level. In any event, to the majority +of cases of different extension the same reasoning applies.] + +It is a knotty problem to value the extension of a deposit beyond +a short distance from the last opening. A short distance beyond +it is "proved ore," and for a further short distance is "probable +ore." Mines are very seldom priced at a sum so moderate as that +represented by the profit to be won from the ore in sight, and what +value should be assigned to this unknown portion of the deposit +admits of no certainty. No engineer can approach the prospective +value of a mine with optimism, yet the mining industry would be +non-existent to-day were it approached with pessimism. Any value +assessed must be a matter of judgment, and this judgment based on +geological evidence. Geology is not a mathematical science, and +to attach a money equivalence to forecasts based on such evidence +is the most difficult task set for the mining engineer. It is here +that his view of geology must differ from that of his financially +more irresponsible brother in the science. The geologist, contributing +to human knowledge in general, finds his most valuable field in the +examination of mines largely exhausted. The engineer's most valuable +work arises from his ability to anticipate in the youth of the mine +the symptoms of its old age. The work of our geologic friends is, +however, the very foundation on which we lay our forecasts. + +Geologists have, as the result of long observation, propounded for +us certain hypotheses which, while still hypotheses, have proved +to account so widely for our underground experience that no engineer +can afford to lose sight of them. Although there is a lack of safety +in fixed theories as to ore deposition, and although such conclusions +cannot be translated into feet and metal value, they are nevertheless +useful weights on the scale where probabilities are to be weighed. + +A method in vogue with many engineers is, where the bottom level +is good, to assume the value of the extension in depth as a sum +proportioned to the profit in sight, and thus evade the use of +geological evidence. The addition of various percentages to the +profit in sight has been used by engineers, and proposed in technical +publications, as varying from 25 to 50%. That is, they roughly +assess the extension in depth to be worth one-fifth to one-third +of the whole value of an equipped mine. While experience may have +sometimes demonstrated this to be a practical method, it certainly +has little foundation in either science or logic, and the writer's +experience is that such estimates are untrue in practice. The quantity +of ore which may be in sight is largely the result of managerial +policy. A small mill on a large mine, under rapid development, +will result in extensive ore-reserves, while a large mill eating +away rapidly on the same mine under the same scale of development +would leave small reserves. On the above scheme of valuation the +extension in depth would be worth very different sums, even when the +deepest level might be at the same horizon in both cases. Moreover, +no mine starts at the surface with a large amount of ore in sight. +Yet as a general rule this is the period when its extension is most +valuable, for when the deposit is exhausted to 2000 feet, it is +not likely to have such extension in depth as when opened one hundred +feet, no matter what the ore-reserves may be. Further, such bases +of valuation fail to take into account the widely varying geologic +character of different mines, and they disregard any collateral +evidence either of continuity from neighboring development, or from +experience in the district. Logically, the prospective value can +be simply a factor of how _far_ the ore in the individual mine +may be expected to extend, and not a factor of the remnant of ore +that may still be unworked above the lowest level. + +An estimation of the chances of this extension should be based +solely on the local factors which bear on such extension, and these +are almost wholly dependent upon the character of the deposit. +These various geological factors from a mining engineer's point +of view are:-- + +1. The origin and structural character of the ore-deposit. +2. The position of openings in relation to secondary alteration. +3. The size of the deposit. +4. The depth to which the mine has already been exhausted. +5. The general experience of the district for continuity and + the development of adjoining mines. + +THE ORIGIN AND STRUCTURAL CHARACTER OF THE DEPOSIT.--In a general +way, the ore-deposits of the order under discussion originate primarily +through the deposition of metals from gases or solutions circulating +along avenues in the earth's crust.[*] The original source of metals +is a matter of great disagreement, and does not much concern the +miner. To him, however, the origin and character of the avenue +of circulation, the enclosing rock, the influence of the rocks +on the solution, and of the solutions on the rocks, have a great +bearing on the probable continuity of the volume and value of the +ore. + +[Footnote *: The class of magmatic segregations is omitted, as +not being of sufficiently frequent occurrence in payable mines to +warrant troubling with it here.] + +All ore-deposits vary in value and, in the miner's view, only those +portions above the pay limit are ore-bodies, or ore-shoots. The +localization of values into such pay areas in an ore-deposit are +apparently influenced by: + +1. The distribution of the open spaces created by structural + movement, fissuring, or folding as at Bendigo. +2. The intersection of other fractures which, by mingling of + solutions from different sources, provided precipitating + conditions, as shown by enrichments at cross-veins. +3. The influence of the enclosing rocks by:-- + (a) Their solubility, and therefore susceptibility to replacement. + (b) Their influence as a precipitating agent on solutions. + (c) Their influence as a source of metal itself. + (d) Their texture, in its influence on the character of + the fracture. In homogeneous rocks the tendency + is to open clean-cut fissures; in friable + rocks, zones of brecciation; in slates or schistose + rocks, linked lenticular open spaces;--these + influences exhibiting themselves in miner's terms + respectively in "well-defined fissure veins," + "lodes," and "lenses." + (e) The physical character of the rock mass and the + dynamic forces brought to bear upon it. This + is a difficult study into the physics of stress in + cases of fracturing, but its local application has + not been without results of an important order. +4. Secondary alteration near the surface, more fully discussed + later. + +It is evident enough that the whole structure of the deposit is +a necessary study, and even a digest of the subject is not to be +compressed into a few paragraphs. + +From the point of view of continuity of values, ore-deposits may +be roughly divided into three classes. They are:-- + +1. Deposits of the infiltration type in porous beds, such as + Lake Superior copper conglomerates and African gold bankets. +2. Deposits of the fissure vein type, such as California quartz veins. +3. Replacement or impregnation deposits on the lines of fissuring + or otherwise. + +In a general way, the uniformity of conditions of deposition in +the first class has resulted in the most satisfactory continuity of +ore and of its metal contents. In the second, depending much upon +the profundity of the earth movements involved, there is laterally +and vertically a reasonable basis for expectation of continuity +but through much less distance than in the first class. + +The third class of deposits exhibits widely different phenomena +as to continuity and no generalization is of any value. In gold +deposits of this type in West Australia, Colorado, and Nevada, +continuity far beyond a sampled face must be received with the +greatest skepticism. Much the same may be said of most copper +replacements in limestone. On the other hand the most phenomenal +regularity of values have been shown in certain Utah and Arizona +copper mines, the result of secondary infiltration in porphyritic +gangues. The Mississippi Valley lead and zinc deposits, while irregular +in detail, show remarkable continuity by way of reoccurrence over +wide areas. The estimation of the prospective value of mines where +continuity of production is dependent on reoccurrence of ore-bodies +somewhat proportional to the area, such as these Mississippi deposits +or to some extent as in Cobalt silver veins, is an interesting +study, but one that offers little field for generalization. + +THE POSITION OF THE OPENINGS IN RELATION TO SECONDARY ALTERATION.--The +profound alteration of the upper section of ore-deposits by oxidation +due to the action of descending surface waters, and their associated +chemical agencies, has been generally recognized for a great many +years. Only recently, however, has it been appreciated that this +secondary alteration extends into the sulphide zone as well. The +bearing of the secondary alteration, both in the oxidized and upper +sulphide zones, is of the most sweeping economic character. In +considering extension of values in depth, it demands the most rigorous +investigation. Not only does the metallurgical character of the ores +change with oxidation, but the complex reactions due to descending +surface waters cause leaching and a migration of metals from one +horizon to another lower down, and also in many cases a redistribution +of their sequence in the upper zones of the deposit. + +The effect of these agencies has been so great in many cases as +to entirely alter the character of the mine and extension in depth +has necessitated a complete reequipment. For instance, the Mt. +Morgan gold mine, Queensland, has now become a copper mine; the +copper mines at Butte were formerly silver mines; Leadville has +become largely a zinc producer instead of lead. + +From this alteration aspect ore-deposits may be considered to have +four horizons:-- + +1. The zone near the outcrop, where the dominating feature + is oxidation and leaching of the soluble minerals. +2. A lower horizon, still in the zone of oxidation, where the + predominant feature is the deposition of metals as native, + oxides, and carbonates. +3. The upper horizon of the sulphide zone, where the special + feature is the enrichment due to secondary deposition + as sulphides. +4. The region below these zones of secondary alteration, where + the deposit is in its primary state. + +These zones are seldom sharply defined, nor are they always all +in evidence. How far they are in evidence will depend, among other +things, upon the amount and rapidity of erosion, the structure and +mineralogical character of the deposit, and upon the enclosing +rock. + +If erosion is extremely rapid, as in cold, wet climates, and rough +topography, or as in the case of glaciation of the Lake copper +deposits, denudation follows close on the heels of alteration, +and the surface is so rapidly removed that we may have the primary +ore practically at the surface. Flat, arid regions present the +other extreme, for denudation is much slower, and conditions are +most perfect for deep penetration of oxidizing agencies, and the +consequent alteration and concentration of the metals. + +The migration of metals from the top of the oxidized zone leaves +but a barren cap for erosion. The consequent effect of denudation +that lags behind alteration is to raise slowly the concentrated +metals toward the surface, and thus subject them to renewed attack +and repeated migration. In this manner we can account for the enormous +concentration of values in the lower oxidized and upper sulphide +zones overlying very lean sulphides in depth. + +Some minerals are more freely soluble and more readily precipitated +than others. From this cause there is in complex metal deposits a +rearrangement of horizontal sequence, in addition to enrichment at +certain horizons and impoverishment at others. The whole subject +is one of too great complexity for adequate consideration in this +discussion. No engineer is properly equipped to give judgment on +extension in depth without a thorough grasp of the great principles +laid down by Van Hise, Emmons, Lindgren, Weed, and others. We may, +however, briefly examine some of the theoretical effects of such +alteration. + +Zinc, iron, and lead sulphides are a common primary combination. +These metals are rendered soluble from their usual primary forms +by oxidizing agencies, in the order given. They reprecipitate as +sulphides in the reverse sequence. The result is the leaching of +zinc and iron readily in the oxidized zone, thus differentially +enriching the lead which lags behind, and a further extension of +the lead horizon is provided by the early precipitation of such +lead as does migrate. Therefore, the lead often predominates in +the second and the upper portion of the third zone, with the zinc +and iron below. Although the action of all surface waters is toward +oxidation and carbonation of these metals, the carbonate development +of oxidized zones is more marked when the enclosing rocks are +calcareous. + +In copper-iron deposits, the comparatively easy decomposition and +solubility and precipitation of the copper and some iron salts +generally result in more extensive impoverishment of these metals +near the surface, and more predominant enrichment at a lower horizon +than is the case with any other metals. The barren "iron hat" at the +first zone, the carbonates and oxides at the second, the enrichment +with secondary copper sulphides at the top of the third, and the +occurrence of secondary copper-iron sulphides below, are often +most clearly defined. In the easy recognition of the secondary +copper sulphides, chalcocite, bornite, etc., the engineer finds a +finger-post on the road to extension in depth; and the directions +upon this post are not to be disregarded. The number of copper +deposits enriched from unpayability in the first zone to a profitable +character in the next two, and unpayability again in the fourth, +is legion. + +Silver occurs most abundantly in combination with either lead, +copper, iron, or gold. As it resists oxidation and solution more +strenuously than copper and iron, its tendency when in combination +with them is to lag behind in migration. There is thus a differential +enrichment of silver in the upper two zones, due to the reduction +in specific gravity of the ore by the removal of associated metals. +Silver does migrate somewhat, however, and as it precipitates more +readily than copper, lead, zinc, or iron, its tendency when in +combination with them is towards enrichment above the horizons of +enrichment of these metals. When it is in combination with lead +and zinc, its very ready precipitation from solution by the galena +leaves it in combination more predominantly with the lead. The +secondary enrichment of silver deposits at the top of the sulphide +zone is sometimes a most pronounced feature, and it seems to be +the explanation of the origin of many "bonanzas." + +In gold deposits, the greater resistance to solubility of this +metal than most of the others, renders the phenomena of migration to +depth less marked. Further than this, migration is often interfered +with by the more impervious quartz matrix of many gold deposits. +Where gold is associated with large quantities of base metals, +however, the leaching of the latter in the oxidized zone leaves the +ore differentially richer, and as gold is also slightly soluble, +in such cases the migration of the base metals does carry some of +the gold. In the instance especially of impregnation or replacement +deposits, where the matrix is easily permeable, the upper sulphide +zone is distinctly richer than lower down, and this enrichment is +accompanied by a considerable increase in sulphides and tellurides. +The predominant characteristic of alteration in gold deposits is, +however, enrichment in the oxidized zone with the maximum values +near the surface. The reasons for this appear to be that gold in its +resistance to oxidation and wholesale migration gives opportunities +to a sort of combined mechanical and chemical enrichment. + +In dry climates, especially, the gentleness of erosion allows of +more thorough decomposition of the outcroppings, and a mechanical +separation of the gold from the detritus. It remains on or near +the deposit, ready to be carried below, mechanically or otherwise. +In wet climates this is less pronounced, for erosion bears away +the croppings before such an extensive decomposition and freeing +of the gold particles. The West Australian gold fields present an +especially prominent example of this type of superficial enrichment. +During the last fifteen years nearly eight hundred companies have +been formed for working mines in this region. Although from four +hundred of these high-grade ore has been produced, some thirty-three +only have ever paid dividends. The great majority have been unpayable +below oxidation,--a distance of one or two hundred feet. The writer's +unvarying experience with gold is that it is richer in the oxidized +zone than at any point below. While cases do occur of gold deposits +richer in the upper sulphide zone than below, even the upper sulphides +are usually poorer than the oxidized region. In quartz veins +preeminently, evidence of enrichment in the third zone is likely +to be practically absent. + +Tin ores present an anomaly among the base metals under discussion, +in that the primary form of this metal in most workable deposits +is an oxide. Tin in this form is most difficult of solution from +ground agencies, as witness the great alluvial deposits, often of +considerable geologic age. In consequence the phenomena of migration +and enrichment are almost wholly absent, except such as are due +to mechanical penetration of tin from surface decomposition of +the matrix akin to that described in gold deposits. + +In general, three or four essential facts from secondary alteration +must be kept in view when prognosticating extensions. + + Oxidation usually alters treatment problems, and oxidized ore + of the same grade as sulphides can often be treated more cheaply. + This is not universal. Low-grade ores of lead, copper, and zinc + may be treatable by concentration when in the form of sulphides, + and may be valueless when oxidized, even though of the same grade. + + Copper ores generally show violent enrichment at the base of the + oxidized, and at the top of the sulphide zone. + + Lead-zinc ores show lead enrichment and zinc impoverishment in + the oxidized zone but have usually less pronounced enrichment + below water level than copper. The rearrangement of the metals + by the deeper migration of the zinc, also renders them + metallurgically of less value with depth. + + Silver deposits are often differentially enriched in the oxidized + zone, and at times tend to concentrate in the upper sulphide zone. + + Gold deposits usually decrease in value from the surface through + the whole of the three alteration zones. + +SIZE OF DEPOSITS.--The proverb of a relation between extension +in depth and size of ore-bodies expresses one of the oldest of +miners' beliefs. It has some basis in experience, especially in +fissure veins, but has little foundation in theory and is applicable +over but limited areas and under limited conditions. + +From a structural view, the depth of fissuring is likely to be more +or less in proportion to its length and breadth and therefore the +volume of vein filling with depth is likely to be proportional to +length and width of the fissure. As to the distribution of values, +if we eliminate the influence of changing wall rocks, or other +precipitating agencies which often cause the values to arrange +themselves in "floors," and of secondary alteration, there may be +some reason to assume distribution of values of an extent equal +vertically to that displayed horizontally. There is, as said, more +reason in experience for this assumption than in theory. A study +of the shape of a great many ore-shoots in mines of fissure type +indicates that when the ore-shoots or ore-bodies are approaching +vertical exhaustion they do not end abruptly, but gradually shorten +and decrease in value, their bottom boundaries being more often +wedge-shaped than even lenticular. If this could be taken as the usual +occurrence, it would be possible (eliminating the evident exceptions +mentioned above) to state roughly that the minimum extension of an +ore-body or ore-shoot in depth below any given horizon would be +a distance represented by a radius equal to one-half its length. By +length is not meant necessarily the length of a horizontal section, +but of one at right angles to the downward axis. + +On these grounds, which have been reenforced by much experience among +miners, the probabilities of extension are somewhat in proportion +to the length and width of each ore-body. For instance, in the A +mine, with an ore-shoot 1000 feet long and 10 feet wide, on its +bottom level, the minimum extension under this hypothesis would +be a wedge-shaped ore-body with its deepest point 500 feet below +the lowest level, or a minimum of say 200,000 tons. Similarly, +the B mine with five ore-bodies, each 300 hundred feet long and +10 feet wide, exposed on its lowest level, would have a minimum of +five wedges 100 feet deep at their deepest points, or say 50,000 +tons. This is not proposed as a formula giving the total amount of +extension in depth, but as a sort of yardstick which has experience +behind it. This experience applies in a much less degree to deposits +originating from impregnation along lines of fissuring and not at +all to replacements. + +DEVELOPMENT IN NEIGHBORING MINES.--Mines of a district are usually +found under the same geological conditions, and show somewhat the same +habits as to extension in depth or laterally, and especially similar +conduct of ore-bodies and ore-shoots. As a practical criterion, one +of the most intimate guides is the actual development in adjoining +mines. For instance, in Kalgoorlie, the Great Boulder mine is (March, +1908) working the extension of Ivanhoe lodes at points 500 feet +below the lowest level in the Ivanhoe; likewise, the Block 10 lead +mine at Broken Hill is working the Central ore-body on the Central +boundary some 350 feet below the Central workings. Such facts as +these must have a bearing on assessing the downward extension. + +DEPTH OF EXHAUSTION.--All mines become completely exhausted at +some point in depth. Therefore the actual distance to which ore +can be expected to extend below the lowest level grows less with +every deeper working horizon. The really superficial character of +ore-deposits, even outside of the region of secondary enrichment +is becoming every year better recognized. The prospector's idea +that "she gets richer deeper down," may have some basis near the +surface in some metals, but it is not an idea which prevails in +the minds of engineers who have to work in depth. The writer, with +some others, prepared a list of several hundred dividend-paying +metal mines of all sorts, extending over North and South America, +Australasia, England, and Africa. Notes were made as far as possible +of the depths at which values gave out, and also at which dividends +ceased. Although by no means a complete census, the list indicated +that not 6% of mines (outside banket) that have yielded profits, +ever made them from ore won below 2000 feet. Of mines that paid +dividends, 80% did not show profitable value below 1500 feet, and +a sad majority died above 500. Failures at short depths may be +blamed upon secondary enrichment, but the majority that reached +below this influence also gave out. The geological reason for such +general unseemly conduct is not so evident. + +CONCLUSION.--As a practical problem, the assessment of prospective +value is usually a case of "cut and try." The portion of the capital +to be invested, which depends upon extension, will require so many +tons of ore of the same value as that indicated by the standing +ore, in order to justify the price. To produce this tonnage at +the continued average size of the ore-bodies will require their +extension in depth so many feet--or the discovery of new ore-bodies +of a certain size. The five geological weights mentioned above +may then be put into the scale and a basis of judgment reached. + + + + +CHAPTER IV. + +Mine Valuation (_Continued_). + +RECOVERABLE PERCENTAGE OF THE GROSS ASSAY VALUE; PRICE OF METALS; +COST OF PRODUCTION. + +The method of treatment for the ore must be known before a mine +can be valued, because a knowledge of the recoverable percentage +is as important as that of the gross value of the ore itself. The +recoverable percentage is usually a factor of working costs. Practically +every ore can be treated and all the metal contents recovered, but +the real problem is to know the method and percentage of recovery +which will yield the most remunerative result, if any. This limit to +profitable recovery regulates the amount of metal which should be +lost, and the amount of metal which consequently must be deducted +from the gross value before the real net value of the ore can be +calculated. Here, as everywhere else in mining, a compromise has to +be made with nature, and we take what we can get--profitably. For +instance, a copper ore may be smelted and a 99% recovery obtained. +Under certain conditions this might be done at a loss, while the +same ore might be concentrated before smelting and yield a profit +with a 70% recovery. An additional 20% might be obtained by roasting +and leaching the residues from concentration, but this would probably +result in an expenditure far greater than the value of the 20% +recovered. If the ore is not already under treatment on the mine, +or exactly similar ore is not under treatment elsewhere, with known +results, the method must be determined experimentally, either by +the examining engineer or by a special metallurgist. + +Where partially treated products, such as concentrates, are to be +sold, not only will there be further losses, but deductions will +be made by the smelter for deleterious metals and other charges. +All of these factors must be found out,--and a few sample smelting +returns from a similar ore are useful. + +To cover the whole field of metallurgy and discuss what might apply, +and how it might apply, under a hundred supposititious conditions +would be too great a digression from the subject in hand. It is +enough to call attention here to the fact that the residues from +every treatment carry some metal, and that this loss has to be +deducted from the gross value of the ore in any calculations of +net values. + +PRICE OF METALS. + +Unfortunately for the mining engineer, not only has he to weigh +the amount of risk inherent in calculations involved in the mine +itself, but also that due to fluctuations in the value of metals. +If the ore is shipped to custom works, he has to contemplate also +variations in freights and smelting charges. Gold from the mine +valuer's point of view has no fluctuations. It alone among the +earth's products gives no concern as to the market price. The price +to be taken for all other metals has to be decided before the mine +can be valued. This introduces a further speculation and, as in +all calculations of probabilities, amounts to an estimate of the +amount of risk. In a free market the law of supply and demand governs +the value of metals as it does that of all other commodities. So +far, except for tariff walls and smelting rings, there is a free +market in the metals under discussion. + +The demand for metals varies with the unequal fluctuations of the +industrial tides. The sea of commercial activity is subject to +heavy storms, and the mine valuer is compelled to serve as weather +prophet on this ocean of trouble. High prices, which are the result +of industrial booms, bring about overproduction, and the collapse of +these begets a shrinkage of demand, wherein consequently the tide +of price turns back. In mining for metals each pound is produced +actually at a different cost. In case of an oversupply of base metals +the price will fall until it has reached a point where a portion of +the production is no longer profitable, and the equilibrium is +established through decline in output. However, in the backward +swing, due to lingering overproduction, prices usually fall lower +than the cost of producing even a much-diminished supply. There is +at this point what we may call the "basic" price, that at which +production is insufficient and the price rises again. The basic +price which is due to this undue backward swing is no more the +real price of the metal to be contemplated over so long a term +of years than is the highest price. At how much above the basic +price of depressed times the product can be safely expected to +find a market is the real question. Few mines can be bought or +valued at this basic price. An indication of what this is can be +gained from a study of fluctuations over a long term of years. + +It is common to hear the average price over an extended period +considered the "normal" price, but this basis for value is one which +must be used with discretion, for it is not the whole question when +mining. The "normal" price is the average price over a long term. +The lives of mines, and especially ore in sight, may not necessarily +enjoy the period of this "normal" price. The engineer must balance +his judgments by the immediate outlook of the industrial weather. +When lead was falling steadily in December, 1907, no engineer would +accept the price of that date, although it was then below "normal"; +his product might go to market even lower yet. + +It is desirable to ascertain what the basic and normal prices are, +for between them lies safety. Since 1884 there have been three cycles +of commercial expansion and contraction. If the average prices +are taken for these three cycles separately (1885-95), 1895-1902, +1902-08) it will be seen that there has been a steady advance in +prices. For the succeeding cycles lead on the London Exchange,[*] +the freest of the world's markets was L12 12_s._ 4_d._, L13 3_s._ +7_d._, and L17 7_s._ 0_d._ respectively; zinc, L17 14_s._ 10_d._, +L19 3_s._ 8_d._, and L23 3_s._ 0_d._; and standard copper, L48 16_s._ +0_d._, L59 10_s._ 0_d._, and L65 7_s._ 0_d._ It seems, therefore, +that a higher standard of prices can be assumed as the basic and +normal than would be indicated if the general average of, say, +twenty years were taken. During this period, the world's gold output +has nearly quadrupled, and, whether the quantitative theory of +gold be accepted or not, it cannot be denied that there has been +a steady increase in the price of commodities. In all base-metal +mining it is well to remember that the production of these metals +is liable to great stimulus at times from the discovery of new +deposits or new processes of recovery from hitherto unprofitable +ores. It is therefore for this reason hazardous in the extreme +to prophesy what prices will be far in the future, even when the +industrial weather is clear. But some basis must be arrived at, +and from the available outlook it would seem that the following +metal prices are justifiable for some time to come, provided the +present tariff schedules are maintained in the United States: + +[Footnote *: All London prices are based on the long ton of 2,240 +lbs. Much confusion exists in the copper trade as to the classification +of the metal. New York prices are quoted in electrolytic and "Lake"; +London's in "Standard." "Standard" has now become practically an +arbitrary term peculiar to London, for the great bulk of copper +dealt in is "electrolytic" valued considerably over "Standard."] + +========================================================================== + | Lead | Spelter | Copper | Tin | Silver + |------------|----------|----------|----------|--------------- + |London| N.Y.|Lon.| N.Y.|Lon.| N.Y.|Lon.| N.Y.| Lon. | N.Y. + | Ton |Pound|Ton |Pound|Ton |Pound|Ton |Pound|Per oz.|Per oz. +------------|------|-----|----|-----|----|-----|----|-----|-------|------- +Basic Price | L11. |$.035|L17 |$.040|L52 |$.115|L100|$.220| 22_d._|$.44 +Normal Price| 13.5| .043| 21 | .050| 65 | .140| 130| .290| 26 | .52 +========================================================================== + +In these figures the writer has not followed strict averages, but +has taken the general outlook combined with the previous records. +The likelihood of higher prices for lead is more encouraging than +for any other metal, as no new deposits of importance have come +forward for years, and the old mines are reaching considerable +depths. Nor does the frenzied prospecting of the world's surface +during the past ten years appear to forecast any very disturbing +developments. The zinc future is not so bright, for metallurgy +has done wonders in providing methods of saving the zinc formerly +discarded from lead ores, and enormous supplies will come forward +when required. The tin outlook is encouraging, for the supply from +a mining point of view seems unlikely to more than keep pace with +the world's needs. In copper the demand is growing prodigiously, +but the supplies of copper ores and the number of copper mines +that are ready to produce whenever normal prices recur was never +so great as to-day. One very hopeful fact can be deduced for the +comfort of the base metal mining industry as a whole. If the growth +of demand continues through the next thirty years in the ratio of +the past three decades, the annual demand for copper will be over +3,000,000 tons, of lead over 1,800,000 tons, of spelter 2,800,000 +tons, of tin 250,000 tons. Where such stupendous amounts of these +metals are to come from at the present range of prices, and even +with reduced costs of production, is far beyond any apparent source +of supply. The outlook for silver prices is in the long run not +bright. As the major portion of the silver produced is a bye product +from base metals, any increase in the latter will increase the +silver production despite very much lower prices for the precious +metal. In the meantime the gradual conversion of all nations to +the gold standard seems a matter of certainty. Further, silver +may yet be abandoned as a subsidiary coinage inasmuch as it has +now but a token value in gold standard countries if denuded of +sentiment. + +COST OF PRODUCTION. + +It is hardly necessary to argue the relative importance of the +determination of the cost of production and the determination of +the recoverable contents of the ore. Obviously, the aim of mine +valuation is to know the profits to be won, and the profit is the +value of the metal won, less the cost of production. + +The cost of production embraces development, mining, treatment, +management. Further than this, it is often contended that, as the +capital expended in purchase and equipment must be redeemed within +the life of the mine, this item should also be included in production +costs. It is true that mills, smelters, shafts, and all the +paraphernalia of a mine are of virtually negligible value when it +is exhausted; and that all mines are exhausted sometime and every +ton taken out contributes to that exhaustion; and that every ton of +ore must bear its contribution to the return of the investment, +as well as profit upon it. Therefore it may well be said that the +redemption of the capital and its interest should be considered +in costs per ton. The difficulty in dealing with the subject from +the point of view of production cost arises from the fact that, +except possibly in the case of banket gold and some conglomerate +copper mines, the life of a metal mine is unknown beyond the time +required to exhaust the ore reserves. The visible life at the time +of purchase or equipment may be only three or four years, yet the +average equipment has a longer life than this, and the anticipation +for every mine is also for longer duration than the bare ore in sight. +For clarity of conclusions in mine valuation the most advisable +course is to determine the profit in sight irrespective of capital +redemption in the first instance. The questions of capital redemption, +purchase price, or equipment cost can then be weighed against the +margin of profit. One phase of redemption will be further discussed +under "Amortization of Capital" and "Ratio of Output to the Mine." + +The cost of production depends upon many things, such as the cost of +labor, supplies, the size of the ore-body, the treatment necessary, +the volume of output, etc.; and to discuss them all would lead +into a wilderness of supposititious cases. If the mine is a going +concern, from which reliable data can be obtained, the problem is +much simplified. If it is virgin, the experience of other mines +in the same region is the next resource; where no such data can be +had, the engineer must fall back upon the experience with mines +still farther afield. Use is sometimes made of the "comparison ton" +in calculating costs upon mines where data of actual experience +are not available. As costs will depend in the main upon items +mentioned above, if the known costs of a going mine elsewhere be +taken as a basis, and subtractions and additions made for more +unfavorable or favorable effect of the differences in the above +items, a fairly close result can be approximated. + +Mine examinations are very often inspired by the belief that extended +operations or new metallurgical applications to the mine will expand +the profits. In such cases the paramount questions are the reduction +of costs by better plant, larger outputs, new processes, or alteration +of metallurgical basis and better methods. If every item of previous +expenditure be gone over and considered, together with the equipment, +and method by which it was obtained, the possible savings can be +fairly well deduced, and justification for any particular line +of action determined. One view of this subject will be further +discussed under "Ratio of Output to the Mine." The conditions which +govern the working costs are on every mine so special to itself, +that no amount of advice is very useful. Volumes of advice have +been published on the subject, but in the main their burden is +not to underestimate. + +In considering the working costs of base-metal mines, much depends +upon the opportunity for treatment in customs works, smelters, +etc. Such treatment means a saving of a large portion of equipment +cost, and therefore of the capital to be invested and subsequently +recovered. The economics of home treatment must be weighed against +the sum which would need to be set aside for redemption of the +plant, and unless there is a very distinct advantage to be had by +the former, no risks should be taken. More engineers go wrong by +the erection of treatment works where other treatment facilities +are available, than do so by continued shipping. There are many +mines where the cost of equipment could never be returned, and +which would be valueless unless the ore could be shipped. Another +phase of foreign treatment arises from the necessity or advantage +of a mixture of ores,--the opportunity of such mixtures often gives +the public smelter an advantage in treatment with which treatment +on the mine could never compete. + +Fluctuation in the price of base metals is a factor so much to be +taken into consideration, that it is desirable in estimating mine +values to reduce the working costs to a basis of a "per unit" of +finished metal. This method has the great advantage of indicating +so simply the involved risks of changing prices that whoso runs +may read. Where one metal predominates over the other to such an +extent as to form the "backbone" of the value of the mine, the +value of the subsidiary metals is often deducted from the cost of +the principal metal, in order to indicate more plainly the varying +value of the mine with the fluctuating prices of the predominant +metal. For example, it is usual to state that the cost of copper +production from a given ore will be so many cents per pound, or so +many pounds sterling per ton. Knowing the total metal extractable +from the ore in sight, the profits at given prices of metal can +be readily deduced. The point at which such calculation departs +from the "per-ton-of-ore" unto the per-unit-cost-of-metal basis, +usually lies at the point in ore dressing where it is ready for the +smelter. To take a simple case of a lead ore averaging 20%: this +is to be first concentrated and the lead reduced to a concentrate +averaging 70% and showing a recovery of 75% of the total metal +content. The cost per ton of development, mining, concentration, +management, is to this point say $4 per ton of original crude ore. +The smelter buys the concentrate for 95% of the value of the metal, +less the smelting charge of $15 per ton, or there is a working +cost of a similar sum by home equipment. In this case 4.66 tons of +ore are required to produce one ton of concentrates, and therefore +each ton of concentrates costs $18.64. This amount, added to the +smelting charge, gives a total of $33.64 for the creation of 70% +of one ton of finished lead, or equal to 2.40 cents per pound which +can be compared with the market price less 5%. If the ore were +to contain 20 ounces of silver per ton, of which 15 ounces were +recovered into the leady concentrates, and the smelter price for +the silver were 50 cents per ounce, then the $7.50 thus recovered +would be subtracted from $33.64, making the apparent cost of the +lead 1.86 cents per pound. + + + + +CHAPTER V. + +Mine Valuation (_Continued_). + +REDEMPTION OR AMORTIZATION OF CAPITAL AND INTEREST. + +It is desirable to state in some detail the theory of amortization +before consideration of its application in mine valuation. + +As every mine has a limited life, the capital invested in it must +be redeemed during the life of the mine. It is not sufficient that +there be a bare profit over working costs. In this particular, +mines differ wholly from many other types of investment, such as +railways. In the latter, if proper appropriation is made for +maintenance, the total income to the investor can be considered as +interest or profit; but in mines, a portion of the annual income +must be considered as a return of capital. Therefore, before the +yield on a mine investment can be determined, a portion of the +annual earnings must be set aside in such a manner that when the +mine is exhausted the original investment will have been restored. +If we consider the date due for the return of the capital as the time +when the mine is exhausted, we may consider the annual instalments +as payments before the due date, and they can be put out at compound +interest until the time for restoration arrives. If they be invested +in safe securities at the usual rate of about 4%, the addition of +this amount of compound interest will assist in the repayment of +the capital at the due date, so that the annual contributions to +a sinking fund need not themselves aggregate the total capital to +be restored, but may be smaller by the deficiency which will be +made up by their interest earnings. Such a system of redemption +of capital is called "Amortization." + +Obviously it is not sufficient for the mine investor that his capital +shall have been restored, but there is required an excess earning +over and above the necessities of this annual funding of capital. +What rate of excess return the mine must yield is a matter of the +risks in the venture and the demands of the investor. Mining business +is one where 7% above provision for capital return is an absolute +minimum demanded by the risks inherent in mines, even where the +profit in sight gives warranty to the return of capital. Where +the profit in sight (which is the only real guarantee in mine +investment) is below the price of the investment, the annual return +should increase in proportion. There are thus two distinct directions +in which interest must be computed,--first, the internal influence +of interest in the amortization of the capital, and second, the +percentage return upon the whole investment after providing for +capital return. + +There are many limitations to the introduction of such refinements +as interest calculations in mine valuation. It is a subject not +easy to discuss with finality, for not only is the term of years +unknown, but, of more importance, there are many factors of a highly +speculative order to be considered in valuing. It may be said that +a certain life is known in any case from the profit in sight, and +that in calculating this profit a deduction should be made from +the gross profit for loss of interest on it pending recovery. This +is true, but as mines are seldom dealt with on the basis of profit +in sight alone, and as the purchase price includes usually some +proportion for extension in depth, an unknown factor is introduced +which outweighs the known quantities. Therefore the application of +the culminative effect of interest accumulations is much dependent +upon the sort of mine under consideration. In most cases of uncertain +continuity in depth it introduces a mathematical refinement not +warranted by the speculative elements. For instance, in a mine +where the whole value is dependent upon extension of the deposit +beyond openings, and where an expected return of at least 50% per +annum is required to warrant the risk, such refinement would be +absurd. On the other hand, in a Witwatersrand gold mine, in gold +and tin gravels, or in massive copper mines such as Bingham and +Lake Superior, where at least some sort of life can be approximated, +it becomes a most vital element in valuation. + +In general it may be said that the lower the total annual return +expected upon the capital invested, the greater does the amount +demanded for amortization become in proportion to this total income, +and therefore the greater need of its introduction in calculations. +Especially is this so where the cost of equipment is large +proportionately to the annual return. Further, it may be said that +such calculations are of decreasing use with increasing proportion of +speculative elements in the price of the mine. The risk of extension in +depth, of the price of metal, etc., may so outweigh the comparatively +minor factors here introduced as to render them useless of attention. + +In the practical conduct of mines or mining companies, sinking +funds for amortization of capital are never established. In the +vast majority of mines of the class under discussion, the ultimate +duration of life is unknown, and therefore there is no basis upon +which to formulate such a definite financial policy even were it +desired. Were it possible to arrive at the annual sum to be set +aside, the stockholders of the mining type would prefer to do their +own reinvestment. The purpose of these calculations does not lie +in the application of amortization to administrative finance. It +is nevertheless one of the touchstones in the valuation of certain +mines or mining investments. That is, by a sort of inversion such +calculations can be made to serve as a means to expose the amount +of risk,--to furnish a yardstick for measuring the amount of risk +in the very speculations of extension in depth and price of metals +which attach to a mine. Given the annual income being received, +or expected, the problem can be formulated into the determination +of how many years it must be continued in order to amortize the +investment and pay a given rate of profit. A certain length of +life is evident from the ore in sight, which may be called the +life in sight. If the term of years required to redeem the capital +and pay an interest upon it is greater than the life in sight, +then this extended life must come from extension in depth, or ore +from other direction, or increased price of metals. If we then take +the volume and profit on the ore as disclosed we can calculate the +number of feet the deposit must extend in depth, or additional tonnage +that must be obtained of the same grade, or the different prices of +metal that must be secured, in order to satisfy the demanded term +of years. These demands in actual measure of ore or feet or higher +price can then be weighed against the geological and industrial +probabilities. + +The following tables and examples may be of assistance in these +calculations. + +Table 1. To apply this table, the amount of annual income or dividend +and the term of years it will last must be known or estimated factors. +It is then possible to determine the _present_ value of this annual +income after providing for amortization and interest on the investment +at various rates given, by multiplying the annual income by the +factor set out. + +A simple illustration would be that of a mine earning a profit of +$200,000 annually, and having a total of 1,000,000 tons in sight, +yielding a profit of $2 a ton, or a total profit in sight of $2,000,000, +thus recoverable in ten years. On a basis of a 7% return on the +investment and amortization of capital (Table I), the factor is +6.52 x $200,000 = $1,304,000 as the present value of the gross +profits exposed. That is, this sum of $1,304,000, if paid for the +mine, would be repaid out of the profit in sight, together with +7% interest if the annual payments into sinking fund earn 4%. + +TABLE I. + +Present Value of an Annual Dividend Over -- Years at --% and Replacing +Capital by Reinvestment of an Annual Sum at 4%. + +======================================================= + Years | 5% | 6% | 7% | 8% | 9% | 10% +-------|-------|-------|-------|-------|-------|------- + 1 | .95 | .94 | .93 | .92 | .92 | .91 + 2 | 1.85 | 1.82 | 1.78 | 1.75 | 1.72 | 1.69 + 3 | 2.70 | 2.63 | 2.56 | 2.50 | 2.44 | 2.38 + 4 | 3.50 | 3.38 | 3.27 | 3.17 | 3.07 | 2.98 + 5 | 4.26 | 4.09 | 3.93 | 3.78 | 3.64 | 3.51 + 6 | 4.98 | 4.74 | 4.53 | 4.33 | 4.15 | 3.99 + 7 | 5.66 | 5.36 | 5.09 | 4.84 | 4.62 | 4.41 + 8 | 6.31 | 5.93 | 5.60 | 5.30 | 5.04 | 4.79 + 9 | 6.92 | 6.47 | 6.08 | 5.73 | 5.42 | 5.14 + 10 | 7.50 | 6.98 | 6.52 | 6.12 | 5.77 | 5.45 + | | | | | | + 11 | 8.05 | 7.45 | 6.94 | 6.49 | 6.09 | 5.74 + 12 | 8.58 | 7.90 | 7.32 | 6.82 | 6.39 | 6.00 + 13 | 9.08 | 8.32 | 7.68 | 7.13 | 6.66 | 6.24 + 14 | 9.55 | 8.72 | 8.02 | 7.42 | 6.91 | 6.46 + 15 | 10.00 | 9.09 | 8.34 | 7.79 | 7.14 | 6.67 + 16 | 10.43 | 9.45 | 8.63 | 7.95 | 7.36 | 6.86 + 17 | 10.85 | 9.78 | 8.91 | 8.18 | 7.56 | 7.03 + 18 | 11.24 | 10.10 | 9.17 | 8.40 | 7.75 | 7.19 + 19 | 11.61 | 10.40 | 9.42 | 8.61 | 7.93 | 7.34 + 20 | 11.96 | 10.68 | 9.65 | 8.80 | 8.09 | 7.49 + | | | | | | + 21 | 12.30 | 10.95 | 9.87 | 8.99 | 8.24 | 7.62 + 22 | 12.62 | 11.21 | 10.08 | 9.16 | 8.39 | 7.74 + 23 | 12.93 | 11.45 | 10.28 | 9.32 | 8.52 | 7.85 + 24 | 13.23 | 11.68 | 10.46 | 9.47 | 8.65 | 7.96 + 25 | 13.51 | 11.90 | 10.64 | 9.61 | 8.77 | 8.06 + 26 | 13.78 | 12.11 | 10.80 | 9.75 | 8.88 | 8.16 + 27 | 14.04 | 12.31 | 10.96 | 9.88 | 8.99 | 8.25 + 28 | 14.28 | 12.50 | 11.11 | 10.00 | 9.09 | 8.33 + 29 | 14.52 | 12.68 | 11.25 | 10.11 | 9.18 | 8.41 + 30 | 14.74 | 12.85 | 11.38 | 10.22 | 9.27 | 8.49 + | | | | | | + 31 | 14.96 | 13.01 | 11.51 | 10.32 | 9.36 | 8.56 + 32 | 15.16 | 13.17 | 11.63 | 10.42 | 9.44 | 8.62 + 33 | 15.36 | 13.31 | 11.75 | 10.51 | 9.51 | 8.69 + 34 | 15.55 | 13.46 | 11.86 | 10.60 | 9.59 | 8.75 + 35 | 15.73 | 13.59 | 11.96 | 10.67 | 9.65 | 8.80 + 36 | 15.90 | 13.72 | 12.06 | 10.76 | 9.72 | 8.86 + 37 | 16.07 | 13.84 | 12.16 | 10.84 | 9.78 | 8.91 + 38 | 16.22 | 13.96 | 12.25 | 10.91 | 9.84 | 8.96 + 39 | 16.38 | 14.07 | 12.34 | 10.98 | 9.89 | 9.00 + 40 | 16.52 | 14.18 | 12.42 | 11.05 | 9.95 | 9.05 +======================================================= +Condensed from Inwood's Tables. + +Table II is practically a compound discount table. That is, by +it can be determined the present value of a fixed sum payable at +the end of a given term of years, interest being discounted at +various given rates. Its use may be illustrated by continuing the +example preceding. + +TABLE II. + +Present Value of $1, or L1, payable in -- Years, Interest taken +at --%. + +=================================== +Years | 4% | 5% | 6% | 7% +------|------|------|------|------- + 1 | .961 | .952 | .943 | .934 + 2 | .924 | .907 | .890 | .873 + 3 | .889 | .864 | .840 | .816 + 4 | .854 | .823 | .792 | .763 + 5 | .821 | .783 | .747 | .713 + 6 | .790 | .746 | .705 | .666 + 7 | .760 | .711 | .665 | .623 + 8 | .731 | .677 | .627 | .582 + 9 | .702 | .645 | .592 | .544 + 10 | .675 | .614 | .558 | .508 + | | | | + 11 | .649 | .585 | .527 | .475 + 12 | .625 | .557 | .497 | .444 + 13 | .600 | .530 | .469 | .415 + 14 | .577 | .505 | .442 | .388 + 15 | .555 | .481 | .417 | .362 + 16 | .534 | .458 | .394 | .339 + 17 | .513 | .436 | .371 | .316 + 18 | .494 | .415 | .350 | .296 + 19 | .475 | .396 | .330 | .276 + 20 | .456 | .377 | .311 | .258 + | | | | + 21 | .439 | .359 | .294 | .241 + 22 | .422 | .342 | .277 | .266 + 23 | .406 | .325 | .262 | .211 + 24 | .390 | .310 | .247 | .197 + 25 | .375 | .295 | .233 | .184 + 26 | .361 | .281 | .220 | .172 + 27 | .347 | .268 | .207 | .161 + 28 | .333 | .255 | .196 | .150 + 29 | .321 | .243 | .184 | .140 + 30 | .308 | .231 | .174 | .131 + | | | | + 31 | .296 | .220 | .164 | .123 + 32 | .285 | .210 | .155 | .115 + 33 | .274 | .200 | .146 | .107 + 34 | .263 | .190 | .138 | .100 + 35 | .253 | .181 | .130 | .094 + 36 | .244 | .172 | .123 | .087 + 37 | .234 | .164 | .116 | .082 + 38 | .225 | .156 | .109 | .076 + 39 | .216 | .149 | .103 | .071 + 40 | .208 | .142 | .097 | .067 +=================================== +Condensed from Inwood's Tables. + +If such a mine is not equipped, and it is assumed that $200,000 +are required to equip the mine, and that two years are required +for this equipment, the value of the ore in sight is still less, +because of the further loss of interest in delay and the cost of +equipment. In this case the present value of $1,304,000 in two +years, interest at 7%, the factor is .87 X 1,304,000 = $1,134,480. +From this comes off the cost of equipment, or $200,000, leaving +$934,480 as the present value of the profit in sight. A further +refinement could be added by calculating the interest chargeable +against the $200,000 equipment cost up to the time of production. + +TABLE III. +=========================================================================== + Annual | Number of years of life required to yield--% interest, and in + Rate of | addition to furnish annual instalments which, if reinvested at +Dividend.| 4% will return the original investment at the end of the period. +---------|----------------------------------------------------------------- + % | 5% | 6% | 7% | 8% | 9% | 10% + | | | | | | + 6 | 41.0 | | | | | + 7 | 28.0 | 41.0 | | | | + 8 | 21.6 | 28.0 | 41.0 | | | + 9 | 17.7 | 21.6 | 28.0 | 41.0 | | + 10 | 15.0 | 17.7 | 21.6 | 28.0 | 41.0 | + | | | | | | + 11 | 13.0 | 15.0 | 17.7 | 21.6 | 28.0 | 41.0 + 12 | 11.5 | 13.0 | 15.0 | 17.7 | 21.6 | 28.0 + 13 | 10.3 | 11.5 | 13.0 | 15.0 | 17.7 | 21.6 + 14 | 9.4 | 10.3 | 11.5 | 13.0 | 15.0 | 17.7 + 15 | 8.6 | 9.4 | 10.3 | 11.5 | 13.0 | 15.0 + | | | | | | + 16 | 7.9 | 8.6 | 9.4 | 10.3 | 11.5 | 13.0 + 17 | 7.3 | 7.9 | 8.6 | 9.4 | 10.3 | 11.5 + 18 | 6.8 | 7.3 | 7.9 | 8.6 | 9.4 | 10.3 + 19 | 6.4 | 6.8 | 7.3 | 7.9 | 8.6 | 9.4 + 20 | 6.0 | 6.4 | 6.8 | 7.3 | 7.9 | 8.6 + | | | | | | + 21 | 5.7 | 6.0 | 6.4 | 6.8 | 7.3 | 7.9 + 22 | 5.4 | 5.7 | 6.0 | 6.4 | 6.8 | 7.3 + 23 | 5.1 | 5.4 | 5.7 | 6.0 | 6.4 | 6.8 + 24 | 4.9 | 5.1 | 5.4 | 5.7 | 6.0 | 6.4 + 25 | 4.7 | 4.9 | 5.1 | 5.4 | 5.7 | 6.0 + | | | | | | + 26 | 4.5 | 4.7 | 4.9 | 5.1 | 5.4 | 5.7 + 27 | 4.3 | 4.5 | 4.7 | 4.9 | 5.1 | 5.4 + 28 | 4.1 | 4.3 | 4.5 | 4.7 | 4.9 | 5.1 + 29 | 3.9 | 4.1 | 4.3 | 4.5 | 4.7 | 4.9 + 30 | 3.8 | 3.9 | 4.1 | 4.3 | 4.5 | 4.7 +=========================================================================== + +Table III. This table is calculated by inversion of the factors +in Table I, and is the most useful of all such tables, as it is +a direct calculation of the number of years that a given rate of +income on the investment must continue in order to amortize the +capital (the annual sinking fund being placed at compound interest +at 4%) and to repay various rates of interest on the investment. The +application of this method in testing the value of dividend-paying +shares is very helpful, especially in weighing the risks involved in +the portion of the purchase or investment unsecured by the profit +in sight. Given the annual percentage income on the investment from +the dividends of the mine (or on a non-producing mine assuming a +given rate of production and profit from the factors exposed), by +reference to the table the number of years can be seen in which +this percentage must continue in order to amortize the investment +and pay various rates of interest on it. As said before, the ore +in sight at a given rate of exhaustion can be reduced to terms of +life in sight. This certain period deducted from the total term +of years required gives the life which must be provided by further +discovery of ore, and this can be reduced to tons or feet of extension +of given ore-bodies and a tangible position arrived at. The test +can be applied in this manner to the various prices which must +be realized from the base metal in sight to warrant the price. + +Taking the last example and assuming that the mine is equipped, +and that the price is $2,000,000, the yearly return on the price is +10%. If it is desired besides amortizing or redeeming the capital to +secure a return of 7% on the investment, it will be seen by reference +to the table that there will be required a life of 21.6 years. As the +life visible in the ore in sight is ten years, then the extensions +in depth must produce ore for 11.6 years longer--1,160,000 tons. If +the ore-body is 1,000 feet long and 13 feet wide, it will furnish +of gold ore 1,000 tons per foot of depth; hence the ore-body must +extend 1,160 feet deeper to justify the price. Mines are seldom so +simple a proposition as this example. There are usually probabilities +of other ore; and in the case of base metal, then variability of price +and other elements must be counted. However, once the extension +in depth which is necessary is determined for various assumptions +of metal value, there is something tangible to consider and to +weigh with the five geological weights set out in Chapter III. + +The example given can be expanded to indicate not only the importance +of interest and redemption in the long extension in depth required, +but a matter discussed from another point of view under "Ratio of +Output." If the plant on this mine were doubled and the earnings +increased to 20% ($400,000 per annum) (disregarding the reduction +in working expenses that must follow expansion of equipment), it +will be found that the life required to repay the purchase +money,--$2,000,000,--and 7% interest upon it, is about 6.8 years. + +As at this increased rate of production there is in the ore in +sight a life of five years, the extension in depth must be depended +upon for 1.8 years, or only 360,000 tons,--that is, 360 feet of +extension. Similarly, the present value of the ore in sight is +$268,000 greater if the mine be given double the equipment, for +thus the idle money locked in the ore is brought into the interest +market at an earlier date. Against this increased profit must be +weighed the increased cost of equipment. The value of low grade +mines, especially, is very much a factor of the volume of output +contemplated. + + + + +CHAPTER VI. + +Mine Valuation (_Concluded_). + +VALUATION OF MINES WITH LITTLE OR NO ORE IN SIGHT; VALUATIONS ON +SECOND-HAND DATA; GENERAL CONDUCT OF EXAMINATIONS; REPORTS. + +A large number of examinations arise upon prospecting ventures +or partially developed mines where the value is almost wholly +prospective. The risks in such enterprises amount to the possible loss +of the whole investment, and the possible returns must consequently +be commensurate. Such business is therefore necessarily highly +speculative, but not unjustifiable, as the whole history of the +industry attests; but this makes the matter no easier for the mine +valuer. Many devices of financial procedure assist in the limitation +of the sum risked, and offer a middle course to the investor between +purchase of a wholly prospective value and the loss of a possible +opportunity to profit by it. The usual form is an option to buy the +property after a period which permits a certain amount of development +work by the purchaser before final decision as to purchase. + +Aside from young mines such enterprises often arise from the possibility +of lateral extension of the ore-deposit outside the boundaries of +the property of original discovery (Fig. 3), in which cases there +is often no visible ore within the property under consideration +upon which to found opinion. In regions where vertical side lines +obtain, there is always the possibility of a "deep level" in inclined +deposits. Therefore the ground surrounding known deposits has a +certain speculative value, upon which engineers are often called to +pass judgment. Except in such unusual occurrences as South African +bankets, or Lake Superior coppers, prospecting for deep level of +extension is also a highly speculative phase of mining. + +The whole basis of opinion in both classes of ventures must be +the few geological weights,--the geology of the property and the +district, the development of surrounding mines, etc. In any event, +there is a very great percentage of risk, and the profit to be gained +by success must be, proportionally to the expenditure involved, +very large. It is no case for calculating amortization and other +refinements. It is one where several hundreds or thousands of per +cent hoped for on the investment is the only justification. + +OPINIONS AND VALUATIONS UPON SECOND-HAND DATA. + +Some one may come forward and deprecate the bare suggestion of an +engineer's offering an opinion when he cannot have proper first-hand +data. But in these days we have to deal with conditions as well as +theories of professional ethics. The growing ownership of mines +by companies, that is by corporations composed of many individuals, +and with their stocks often dealt in on the public exchanges, has +resulted in holders whose interest is not large enough to warrant +their undertaking the cost of exhaustive examinations. The system +has produced an increasing class of mining speculators and investors +who are finding and supplying the enormous sums required to work +our mines,--sums beyond the reach of the old-class single-handed +mining men. Every year the mining investors of the new order are +coming more and more to the engineer for advice, and they should +be encouraged, because such counsel can be given within limits, +and these limits tend to place the industry upon a sounder footing +of ownership. As was said before, the lamb can be in a measure +protected. The engineer's interest is to protect him, so that the +industry which concerns his own life-work may be in honorable repute, +and that capital may be readily forthcoming for its expansion. +Moreover, by constant advice to the investor as to what constitutes +a properly presented and managed project, the arrangement of such +proper presentation and management will tend to become an _a priori_ +function of the promoter. + +Sometimes the engineer can make a short visit to the mine for data +purposes,--more often he cannot. In the former case, he can resolve +for himself an approximation upon all the factors bearing on value, +except the quality of the ore. For this, aside from inspection of +the ore itself, a look at the plans is usually enlightening. A +longitudinal section of the mine showing a continuous shortening of +the stopes with each succeeding level carries its own interpretation. +In the main, the current record of past production and estimates +of the management as to ore-reserves, etc., can be accepted in +ratio to the confidence that can be placed in the men who present +them. It then becomes a case of judgment of men and things, and +here no rule applies. + +Advice must often be given upon data alone, without inspection +of the mine. Most mining data present internal evidence as to +credibility. The untrustworthy and inexperienced betray themselves +in their every written production. Assuming the reliability of data, +the methods already discussed for weighing the ultimate value of +the property can be applied. It would be possible to cite hundreds +of examples of valuation based upon second-hand data. Three will, +however, sufficiently illustrate. First, the R mine at Johannesburg. +With the regularity of this deposit, the development done, and +a study of the workings on the neighboring mines and in deeper +ground, it is a not unfair assumption that the reefs will maintain +size and value throughout the area. The management is sound, and +all the data are given in the best manner. The life of the mine +is estimated at six years, with some probabilities of further ore +from low-grade sections. The annual earnings available for dividends +are at the rate of about L450,000 per annum. The capital is L440,000 +in L1 shares. By reference to the table on page 46 it will be seen +that the present value of L450,000 spread over six years to return +capital at the end of that period, and give 7% dividends in the +meantime, is 4.53 x L450,000 = L2,036,500 / 440,000 = L4 12_s_. +7_d_. per share. So that this mine, on the assumption of continuity +of values, will pay about 7% and return the price. Seven per cent +is, however, not deemed an adequate return for the risks of labor +troubles, faults, dykes, or poor patches. On a 9% basis, the mine +is worth about L4 4_s_. per share. + +Second, the G mine in Nevada. It has a capital of $10,000,000 in +$1 shares, standing in the market at 50 cents each. The reserves +are 250,000 tons, yielding a profit for yearly division of $7 per +ton. It has an annual capacity of about 100,000 tons, or $700,000 +net profit, equal to 14% on the market value. In order to repay +the capital value of $5,000,000 and 8% per annum, it will need +a life of (Table III) 13 years, of which 2-1/2 are visible. The +size of the ore-bodies indicates a yield of about 1,100 tons per +foot of depth. At an exhaustion rate of 100,000 tons per annum, +the mine would need to extend to a depth of over a thousand feet +below the present bottom. There is always a possibility of finding +parallel bodies or larger volumes in depth, but it would be a sanguine +engineer indeed who would recommend the stock, even though it pays +an apparent 14%. + +Third, the B mine, with a capital of $10,000,000 in 2,000,000 shares +of $5 each. The promoters state that the mine is in the slopes of +the Andes in Peru; that there are 6,000,000 tons of "ore blocked +out"; that two assays by the assayers of the Bank of England average +9% copper; that the copper can be produced at five cents per pound; +that there is thus a profit of $10,000,000 in sight. The evidences +are wholly incompetent. It is a gamble on statements of persons +who have not the remotest idea of sound mining. + +GENERAL CONDUCT OF EXAMINATION. + +Complete and exhaustive examination, entailing extensive sampling, +assaying, and metallurgical tests, is very expensive and requires +time. An unfavorable report usually means to the employer absolute +loss of the engineer's fee and expenses. It becomes then the initial +duty of the latter to determine at once, by the general conditions +surrounding the property, how far the expenditure for exhaustive +examination is warranted. There is usually named a money valuation +for the property, and thus a peg is afforded upon which to hang +conclusions. Very often collateral factors with a preliminary sampling, +or indeed no sampling at all, will determine the whole business. +In fact, it is becoming very common to send younger engineers to +report as to whether exhaustive examination by more expensive men +is justified. + +In the course of such preliminary inspection, the ore-bodies may +prove to be too small to insure adequate yield on the price, even +assuming continuity in depth and represented value. They may be +so difficult to mine as to make costs prohibitive, or they may +show strong signs of "petering out." The ore may present visible +metallurgical difficulties which make it unprofitable in any event. +A gold ore may contain copper or arsenic, so as to debar cyanidation, +where this process is the only hope of sufficiently moderate costs. +A lead ore may be an amorphous compound with zinc, and successful +concentration or smelting without great penalties may be precluded. +A copper ore may carry a great excess of silica and be at the same +time unconcentratable, and there may be no base mineral supply +available for smelting mixture. The mine may be so small or so +isolated that the cost of equipment will never be justified. Some +of these conditions may be determined as unsurmountable, assuming +a given value for the ore, and may warrant the rejection of the +mine at the price set. + +It is a disagreeable thing to have a disappointed promoter heap +vituperation on an engineer's head because he did not make an exhaustive +examination. Although it is generally desirable to do some sampling +to give assurance to both purchaser and vendor of conscientiousness, +a little courage of conviction, when this is rightly and adequately +grounded, usually brings its own reward. + +Supposing, however, that conditions are right and that the mine is +worth the price, subject to confirmation of values, the determination +of these cannot be undertaken unless time and money are available +for the work. As was said, a sampling campaign is expensive, and +takes time, and no engineer has the moral right to undertake an +examination unless both facilities are afforded. Curtailment is +unjust, both to himself and to his employer. + +How much time and outlay are required to properly sample a mine +is obviously a question of its size, and the character of its ore. +An engineer and one principal assistant can conduct two sampling +parties. In hard rock it may be impossible to take more than five +samples a day for each party. But, in average ore, ten samples for +each is reasonable work. As the number of samples is dependent +upon the footage of openings on the deposit, a rough approximation +can be made in advance, and a general idea obtained as to the time +required. This period must be insisted upon. + +REPORTS. + +Reports are to be read by the layman, and their first qualities +should be simplicity of terms and definiteness of conclusions. +Reports are usually too long, rather than too short. The essential +facts governing the value of a mine can be expressed on one sheet +of paper. It is always desirable, however, that the groundwork data +and the manner of their determination should be set out with such +detail that any other engineer could come to the same conclusion +if he accepted the facts as accurately determined. In regard to the +detailed form of reports, the writer's own preference is for a single +page summarizing the main factors, and an assay plan, reduced to a +longitudinal section where possible. Then there should be added, +for purposes of record and for submission to other engineers, a +set of appendices going into some details as to the history of +the mine, its geology, development, equipment, metallurgy, and +management. A list of samples should be given with their location, +and the tonnages and values of each separate block. A presentation +should be made of the probabilities of extension in depth, together +with recommendations for working the mine. + +GENERAL SUMMARY. + +The bed-rock value which attaches to a mine is the profit to be +won from proved ore and in which the price of metal is calculated +at some figure between "basic" and "normal." This we may call the +"_A_" value. Beyond this there is the speculative value of the +mine. If the value of the "probable" ore be represented by _X_, +the value of extension of the ore by _Y_, and a higher price for +metal than the price above assumed represented by _Z_, then if +the mine be efficiently managed the value of the mine is _A_ + +_X_ + _Y_ + _Z_. What actual amounts should be attached to _X, +Y, Z_ is a matter of judgment. There is no prescription for good +judgment. Good judgment rests upon a proper balancing of evidence. +The amount of risk in _X, Y, Z_ is purely a question of how much +these factors are required to represent in money,--in effect, how +much more ore must be found, or how many feet the ore must extend +in depth; or in convertible terms, what life in years the mine +must have, or how high the price of metal must be. In forming an +opinion whether these requirements will be realized, _X, Y, Z_ +must be balanced in a scale whose measuring standards are the five +geological weights and the general industrial outlook. The wise +engineer will put before his clients the scale, the weights, and +the conclusion arrived at. The shrewd investor will require to +know these of his adviser. + + + + +CHAPTER VII. + +Development of Mines. + +ENTRY TO THE MINE; TUNNELS; VERTICAL, INCLINED, AND COMBINED SHAFTS; +LOCATION AND NUMBER OF SHAFTS. + +Development is conducted for two purposes: first, to search for +ore; and second, to open avenues for its extraction. Although both +objects are always more or less in view, the first predominates +in the early life of mines, the prospecting stage, and the second +in its later life, the producing stage. It is proposed to discuss +development designed to embrace extended production purposes first, +because development during the prospecting stage is governed by +the same principles, but is tempered by the greater degree of +uncertainty as to the future of the mine, and is, therefore, of +a more temporary character. + +ENTRY TO THE MINE. + +There are four methods of entry: by tunnel, vertical shaft, inclined +shaft, or by a combination of the last two, that is, by a shaft +initially vertical then turned to an incline. Combined shafts are +largely a development of the past few years to meet "deep level" +conditions, and have been rendered possible only by skip-winding. The +angle in such shafts (Fig. 2) is now generally made on a parabolic +curve, and the speed of winding is then less diminished by the +bend. + +The engineering problems which present themselves under "entry" +may be divided into those of:-- + + 1. Method. + 2. Location. + 3. Shape and size. + +The resolution of these questions depends upon the:-- + + a. Degree of dip of the deposit. + b. Output of ore to be provided for. + c. Depth at which the deposit is to be attacked. + d. Boundaries of the property. + e. Surface topography. + f. Cost. + g. Operating efficiency. + h. Prospects of the mine. + +[Illustration: Fig. 2.--Showing arrangement of the bend in combined +shafts.] + +From the point of view of entrance, the cooeperation of a majority +of these factors permits the division of mines into certain broad +classes. The type of works demanded for moderate depths (say vertically +2,500 to 3,000 feet) is very different from that required for great +depths. To reach great depths, the size of shafts must greatly +expand, to provide for extended ventilation, pumping, and winding +necessities. Moreover inclined shafts of a degree of flatness possible +for moderate depths become too long to be used economically from +the surface. The vast majority of metal-mining shafts fall into +the first class, those of moderate depths. Yet, as time goes on +and ore-deposits are exhausted to lower planes, problems of depth +will become more common. One thing, however, cannot be too much +emphasized, especially on mines to be worked from the outcrop, and +that is, that no engineer is warranted, owing to the speculation +incidental to extension in depth, in initiating early in the mine's +career shafts of such size or equipment as would be available for +great depths. Moreover, the proper location of a shaft so as to +work economically extension of the ore-bodies is a matter of no +certainty, and therefore shafts of speculative mines are tentative +in any event. + +Another line of division from an engineering view is brought about +by a combination of three of the factors mentioned. This is the +classification into "outcrop" and "deep-level" mines. The former +are those founded upon ore-deposits to be worked from or close +to the surface. The latter are mines based upon the extension in +depth of ore-bodies from outcrop mines. Such projects are not so +common in America, where the law in most districts gives the outcrop +owner the right to follow ore beyond his side-lines, as in countries +where the boundaries are vertical on all sides. They do, however, +arise not alone in the few American sections where the side-lines +are vertical boundaries, but in other parts owing to the pitch of +ore-bodies through the end lines (Fig. 3). More especially do such +problems arise in America in effect, where the ingress questions +have to be revised for mines worked out in the upper levels (Fig. +7). + +[Illustration: Fig. 3.--Longitudinal section showing "deep level" +project arising from dip of ore-body through end-line.] + +If from a standpoint of entrance questions, mines are first classified +into those whose works are contemplated for moderate depths, and those +in which work is contemplated for great depth, further clarity in +discussion can be gained by subdivision into the possible cases arising +out of the factors of location, dip, topography, and boundaries. + +MINES OF MODERATE DEPTHS. + +Case I. Deposits where topographic conditions permit the + alternatives of shaft or tunnel. +Case II. Vertical or horizontal deposits, the only practical + means of attaining which is by a vertical shaft. +Case III. Inclined deposits to be worked from near the surface. + There are in such instances the alternatives of either + a vertical or an inclined shaft. +Case IV. Inclined deposits which must be attacked in depth, + that is, deep-level projects. There are the alternatives + of a compound shaft or of a vertical shaft, and + in some cases of an incline from the surface. + +MINES TO GREAT DEPTHS. + +Case V. Vertical or horizontal deposits, the only way of reaching + which is by a vertical shaft. +Case VI. Inclined deposits. In such cases the alternatives are + a vertical or a compound shaft. + +CASE I.--Although for logical arrangement tunnel entry has been +given first place, to save repetition it is proposed to consider +it later. With few exceptions, tunnels are a temporary expedient +in the mine, which must sooner or later be opened by a shaft. + +CASE II. VERTICAL OR HORIZONTAL DEPOSITS.--These require no discussion +as to manner of entry. There is no justifiable alternative to a +vertical shaft (Fig. 4). + +[Illustration: Fig. 4.--Cross-sections showing entry to vertical +or horizontal deposits. Case II.] + +[Illustration: Fig. 5.--Cross-section showing alternative shafts +to inclined deposit to be worked from surface. Case III.] + +CASE III. INCLINED DEPOSITS WHICH ARE INTENDED TO BE WORKED FROM +THE OUTCROP, OR FROM NEAR IT (Fig. 5).--The choice of inclined or +vertical shaft is dependent upon relative cost of construction, +subsequent operation, and the useful life of the shaft, and these +matters are largely governed by the degree of dip. Assuming a shaft +of the same size in either alternative, the comparative cost per +foot of sinking is dependent largely on the breaking facilities +of the rock under the different directions of attack. In this, +the angles of the bedding or joint planes to the direction of the +shaft outweigh other factors. The shaft which takes the greatest +advantage of such lines of breaking weakness will be the cheapest +per foot to sink. In South African experience, where inclined shafts +are sunk parallel to the bedding planes of hard quartzites, the cost +per foot appears to be in favor of the incline. On the other hand, +sinking shafts across tight schists seems to be more advantageous +than parallel to the bedding planes, and inclines following the +dip cost more per foot than vertical shafts. + +An inclined shaft requires more footage to reach a given point +of depth, and therefore it would entail a greater total expense +than a vertical shaft, assuming they cost the same per foot. The +excess amount will be represented by the extra length, and this +will depend upon the flatness of the dip. With vertical shafts, +however, crosscuts to the deposit are necessary. In a comparative +view, therefore, the cost of the crosscuts must be included with +that of the vertical shaft, as they would be almost wholly saved +in an incline following near the ore. + +The factor of useful life for the shaft enters in deciding as to +the advisability of vertical shafts on inclined deposits, from the +fact that at some depth one of two alternatives has to be chosen. +The vertical shaft, when it reaches a point below the deposit where +the crosscuts are too long (_C_, Fig. 5), either becomes useless, +or must be turned on an incline at the intersection with the ore +(_B_). The first alternative means ultimately a complete loss of +the shaft for working purposes. The latter has the disadvantage +that the bend interferes slightly with haulage. + +The following table will indicate an hypothetical extreme case,--not +infrequently met. In it a vertical shaft 1,500 feet in depth is taken +as cutting the deposit at the depth of 750 feet, the most favored +position so far as aggregate length of crosscuts is concerned. The +cost of crosscutting is taken at $20 per foot and that of sinking +the vertical shaft at $75 per foot. The incline is assumed for two +cases at $75 and $100 per foot respectively. The stoping height +upon the ore between levels is counted at 125 feet. + + Dip of | Depth of | Length of |No. of Crosscuts| Total Length +Deposit from | Vertical | Incline | Required from | of Crosscuts, + Horizontal | Shaft | Required | V Shaft | Feet +-------------|-------------|-------------|----------------|--------------- + 80 deg. | 1,500 | 1,522 | 11 | 859 + 70 deg. | 1,500 | 1,595 | 12 | 1,911 + 60 deg. | 1,500 | 1,732 | 13 | 3,247 + 50 deg. | 1,500 | 1,058 | 15 | 5,389 + 40 deg. | 1,500 | 2,334 | 18 | 8,038 + 30 deg. | 1,500 | 3,000 | 23 | 16,237 +========================================================================== + Cost of |Cost Vertical| Total Cost | Cost of Incline|Cost of Incline +Crosscuts $20| Shaft $75 | of Vertical | $75 per Foot | $100 per Foot + per Foot | per Foot |and Crosscuts| | +-------------|-------------|-------------|----------------|--------------- + $17,180 | $112,500 | $129,680 | $114,150 | $152,200 + 38,220 | 112,500 | 150,720 | 118,625 | 159,500 + 64,940 | 112,500 | 177,440 | 129,900 | 172,230 + 107,780 | 112,500 | 220,280 | 114,850 | 195,800 + 178,760 | 112,500 | 291,260 | 175,050 | 233,400 + 324,740 | 112,500 | 437,240 | 225,000 | 300,000 + +From the above examples it will be seen that the cost of crosscuts +put at ordinary level intervals rapidly outruns the extra expense +of increased length of inclines. If, however, the conditions are +such that crosscuts from a vertical shaft are not necessary at so +frequent intervals, then in proportion to the decrease the advantages +sway to the vertical shaft. Most situations wherein the crosscuts +can be avoided arise in mines worked out in the upper levels and +fall under Case IV, that of deep-level projects. + +There can be no doubt that vertical shafts are cheaper to operate +than inclines: the length of haul from a given depth is less; much +higher rope speed is possible, and thus the haulage hours are less +for the same output; the wear and tear on ropes, tracks, or guides +is not so great, and pumping is more economical where the Cornish +order of pump is used. On the other hand, with a vertical shaft +must be included the cost of operating crosscuts. On mines where +the volume of ore does not warrant mechanical haulage, the cost of +tramming through the extra distance involved is an expense which +outweighs any extra operating outlay in the inclined shaft itself. +Even with mechanical haulage in crosscuts, it is doubtful if there +is anything in favor of the vertical shaft on this score. + +[Illustration: Fig. 6.--Cross-section showing auxiliary vertical +outlet.] + +In deposits of very flat dips, under 30 deg., the case arises where +the length of incline is so great that the saving on haulage through +direct lift warrants a vertical shaft as an auxiliary outlet in +addition to the incline (Fig. 6). In such a combination the crosscut +question is eliminated. The mine is worked above and below the +intersection by incline, and the vertical shaft becomes simply a +more economical exit and an alternative to secure increased output. +The North Star mine at Grass Valley is an illustration in point. Such +a positive instance borders again on Case IV, deep-level projects. + +In conclusion, it is the writer's belief that where mines are to +be worked from near the surface, coincidentally with sinking, and +where, therefore, crosscuts from a vertical shaft would need to be +installed frequently, inclines are warranted in all dips under 75 deg. +and over 30 deg. Beyond 75 deg. the best alternative is often +undeterminable. In the range under 30 deg. and over 15 deg., although +inclines are primarily necessary for actual delivery of ore from levels, +they can often be justifiably supplemented by a vertical shaft as a +relief to a long haul. In dips of less than 15 deg., as in those over +75 deg., the advantages again trend strongly in favor of the vertical +shaft. There arise, however, in mountainous countries, topographic +conditions such as the dip of deposits into the mountain, which preclude +any alternative on an incline at any angled dip. + +CASE IV. INCLINED DEPOSITS WHICH MUST BE ATTACKED IN DEPTH (Fig. +7).--There are two principal conditions in which such properties +exist: first, mines being operated, or having been previously worked, +whose method of entry must be revised; second, those whose ore-bodies +to be attacked do not outcrop within the property. + +The first situation may occur in mines of inadequate shaft capacity +or wrong location; in mines abandoned and resurrected; in mines +where a vertical shaft has reached its limit of useful extensions, +having passed the place of economical crosscutting; or in mines in +flat deposits with inclines whose haul has become too long to be +economical. Three alternatives present themselves in such cases: a +new incline from the surface (_A B F_, Fig. 7), or a vertical shaft +combined with incline extension (_C D F_), or a simple vertical +shaft (_H G_). A comparison can be first made between the simple +incline and the combined shaft. The construction of an incline from +the surface to the ore-body will be more costly than a combined +shaft, for until the horizon of the ore is reached (at _D_) no +crosscuts are required in the vertical section, while the incline +must be of greater length to reach the same horizon. The case arises, +however, where inclines can be sunk through old stopes, and thus +more cheaply constructed than vertical shafts through solid rock; +and also the case of mountainous topographic conditions mentioned +above. + +[Illustration: Fig. 7.--Cross-section of inclined deposit which +must be attacked in depth.] + +From an operating point of view, the bend in combined shafts (at +_D_) gives rise to a good deal of wear and tear on ropes and gear. +The possible speed of winding through a combined shaft is, however, +greater than a simple incline, for although haulage speed through +the incline section (_D F_) and around the bend of the combined +shaft is about the same as throughout a simple incline (_A F_), the +speed can be accelerated in the vertical portion (_D C_) above that +feasible did the incline extend to the surface. There is therefore an +advantage in this regard in the combined shaft. The net advantages +of the combined over the inclined shaft depend on the comparative +length of the two alternative routes from the intersection (_D_) +to the surface. Certainly it is not advisable to sink a combined +shaft to cut a deposit at 300 feet in depth if a simple incline +can be had to the surface. On the other hand, a combined shaft +cutting the deposit at 1,000 feet will be more advisable than a +simple incline 2,000 feet long to reach the same point. The matter +is one for direct calculation in each special case. In general, there +are few instances of really deep-level projects where a complete +incline from the surface is warranted. + +In most situations of this sort, and in all of the second type +(where the outcrop is outside the property), actual choice usually +lies between combined shafts (_C D F_) and entire vertical shafts (_H +G_). The difference between a combined shaft and a direct vertical +shaft can be reduced to a comparison of the combined shaft below +the point of intersection (_D_) with that portion of a vertical +shaft which would cover the same horizon. The question then becomes +identical with that of inclined _versus_ verticals, as stated in Case +III, with the offsetting disadvantage of the bend in the combined +shaft. If it is desired to reach production at the earliest date, +the lower section of a simple vertical shaft must have crosscuts +to reach the ore lying above the horizon of its intersection (_E_). +If production does not press, the ore above the intersection (_EB_) +can be worked by rises from the horizon of intersection (_E_). +In the use of rises, however, there follow the difficulties of +ventilation and lowering the ore down to the shaft, which brings +expenses to much the same thing as operating through crosscuts. + +The advantages of combined over simple vertical shafts are earlier +production, saving of either rises or crosscuts, and the ultimate +utility of the shaft to any depth. The disadvantages are the cost +of the extra length of the inclined section, slower winding, and +greater wear and tear within the inclined section and especially +around the bend. All these factors are of variable import, depending +upon the dip. On very steep dips,--over 70 deg.,--the net result is in +favor of the simple vertical shaft. On other dips it is in favor +of the combined shaft. + +CASES V AND VI. MINES TO BE WORKED TO GREAT DEPTHS,--OVER 3,000 +FEET.--In Case V, with vertical or horizontal deposits, there is +obviously no desirable alternative to vertical shafts. + +In Case VI, with inclined deposits, there are the alternatives +of a combined or of a simple vertical shaft. A vertical shaft in +locations (_H_, Fig. 7) such as would not necessitate extension in +depth by an incline, would, as in Case IV, compel either crosscuts +to the ore or inclines up from the horizon of intersection (_E_). +Apart from delay in coming to production and the consequent loss of +interest on capital, the ventilation problems with this arrangement +would be appalling. Moreover, the combined shaft, entering the deposit +near its shallowest point, offers the possibility of a separate +haulage system on the inclined and on the vertical sections, and +such separate haulage is usually advisable at great depths. In +such instances, the output to be handled is large, for no mine of +small output is likely to be contemplated at such depth. Several +moderate-sized inclines from the horizon of intersection have been +suggested (_EF_, _DG_, _CH_, Fig. 8) to feed a large primary shaft +(_AB_), which thus becomes the trunk road. This program would cheapen +lateral haulage underground, as mechanical traction can be used +in the main level, (_EC_), and horizontal haulage costs can be +reduced on the lower levels. Moreover, separate winding engines +on the two sections increase the capacity, for the effect is that +of two trains instead of one running on a single track. + +SHAFT LOCATION.--Although the prime purpose in locating a shaft +is obviously to gain access to the largest volume of ore within +the shortest haulage distance, other conditions also enter, such +as the character of the surface and the rock to be intersected, +the time involved before reaching production, and capital cost. +As shafts must bear two relations to a deposit,--one as to the +dip and the other as to the strike,--they may be considered from +these aspects. Vertical shafts must be on the hanging-wall side +of the outcrop if the deposit dips at all. In any event, the shaft +should be far enough away to be out of the reach of creeps. An +inclined shaft may be sunk either on the vein, in which case a +pillar of ore must be left to support the shaft; or, instead, it +may be sunk a short distance in the footwall, and where necessary +the excavation above can be supported by filling. Following the +ore has the advantage of prospecting in sinking, and in many cases +the softness of the ground in the region of the vein warrants this +procedure. It has, however, the disadvantage that a pillar of ore +is locked up until the shaft is ready for abandonment. Moreover, as +veins or lodes are seldom of even dip, an inclined shaft, to have +value as a prospecting opening, or to take advantage of breaking +possibilities in the lode, will usually be crooked, and an incline +irregular in detail adds greatly to the cost of winding and maintenance. +These twin disadvantages usually warrant a straight incline in the +footwall. Inclines are not necessarily of the same dip throughout, +but for reasonably economical haulage change of angle must take +place gradually. + +[Illustration: Fig. 8.--Longitudinal section showing shaft arrangement +proposed for very deep inclined deposits.] + +In the case of deep-level projects on inclined deposits, demanding +combined or vertical shafts, the first desideratum is to locate +the vertical section as far from the outcrop as possible, and thus +secure the most ore above the horizon of intersection. This, however, +as stated before, would involve the cost of crosscuts or rises and +would cause delay in production, together with the accumulation +of capital charges. How important the increment of interest on +capital may become during the period of opening the mine may be +demonstrated by a concrete case. For instance, the capital of a +company or the cost of the property is, say, $1,000,000, and where +opening the mine for production requires four years, the aggregate +sum of accumulated compound interest at 5% (and most operators +want more from a mining investment) would be $216,000. Under such +circumstances, if a year or two can be saved in getting to production +by entering the property at a higher horizon, the difference in +accumulated interest will more than repay the infinitesimal extra +cost of winding through a combined shaft of somewhat increased +length in the inclined section. + +The unknown character of the ore in depth is always a sound reason +for reaching it as quickly and as cheaply as possible. In result, +such shafts are usually best located when the vertical section +enters the upper portion of the deposit. + +The objective in location with regard to the strike of the ore-bodies +is obviously to have an equal length of lateral ore-haul in every +direction from the shaft. It is easier to specify than to achieve +this, for in all speculative deposits ore-shoots are found to pursue +curious vagaries as they go down. Ore-bodies do not reoccur with +the same locus as in the upper levels, and generally the chances +to go wrong are more numerous than those to go right. + +NUMBER OF SHAFTS.--The problem of whether the mine is to be opened +by one or by two shafts of course influences location. In metal +mines under Cases II and III (outcrop properties) the ore output +requirements are seldom beyond the capacity of one shaft. Ventilation +and escape-ways are usually easily managed through the old stopes. +Under such circumstances, the conditions warranting a second shaft +are the length of underground haul and isolation of ore-bodies or +veins. Lateral haulage underground is necessarily disintegrated by +the various levels, and usually has to be done by hand. By shortening +this distance of tramming and by consolidation of the material +from all levels at the surface, where mechanical haulage can be +installed, a second shaft is often justified. There is therefore +an economic limitation to the radius of a single shaft, regardless +of the ability of the shaft to handle the total output. + +Other questions also often arise which are of equal importance +to haulage costs. Separate ore-shoots or ore-bodies or parallel +deposits necessitate, if worked from one shaft, constant levels +through unpayable ground and extra haul as well, or ore-bodies may +dip away from the original shaft along the strike of the deposit +and a long haulage through dead levels must follow. For instance, +levels and crosscuts cost roughly one-quarter as much per foot as +shafts. Therefore four levels in barren ground, to reach a parallel +vein or isolated ore-body 1,000 feet away, would pay for a shaft +1,000 feet deep. At a depth of 1,000 feet, at least six levels +might be necessary. The tramming of ore by hand through such a +distance would cost about double the amount to hoist it through +a shaft and transport it mechanically to the dressing plant at +surface. The aggregate cost and operation of barren levels therefore +soon pays for a second shaft. If two or more shafts are in question, +they must obviously be set so as to best divide the work. + +Under Cases IV, V, and VI,--that is, deep-level projects,--ventilation +and escape become most important considerations. Even where the +volume of ore is within the capacity of a single shaft, another +usually becomes a necessity for these reasons. Their location is +affected not only by the locus of the ore, but, as said, by the time +required to reach it. Where two shafts are to be sunk to inclined +deposits, it is usual to set one so as to intersect the deposit at +a lower point than the other. Production can be started from the +shallower, before the second is entirely ready. The ore above the +horizon of intersection of the deeper shaft is thus accessible from +the shallower shaft, and the difficulty of long rises or crosscuts +from that deepest shaft does not arise. + + + + +CHAPTER VIII. + +Development of Mines (_Continued_). + +SHAPE AND SIZE OF SHAFTS; SPEED OF SINKING; TUNNELS. + +SHAPE OF SHAFTS.--Shafts may be round or rectangular.[*] Round +vertical shafts are largely applied to coal-mines, and some engineers +have advocated their usefulness to the mining of the metals under +discussion. Their great advantages lie in their structural strength, +in the large amount of free space for ventilation, and in the fact +that if walled with stone, brick, concrete, or steel, they can be +made water-tight so as to prevent inflow from water-bearing strata, +even when under great pressure. The round walled shafts have a longer +life than timbered shafts. All these advantages pertain much more to +mining coal or iron than metals, for unsound, wet ground is often +the accompaniment of coal-measures, and seldom troubles metal-mines. +Ventilation requirements are also much greater in coal-mines. From +a metal-miner's standpoint, round shafts are comparatively much +more expensive than the rectangular timbered type.[**] For a larger +area must be excavated for the same useful space, and if support +is needed, satisfactory walling, which of necessity must be brick, +stone, concrete, or steel, cannot be cheaply accomplished under +the conditions prevailing in most metal regions. Although such +shafts would have a longer life, the duration of timbered shafts +is sufficient for most metal mines. It follows that, as timber +is the cheapest and all things considered the most advantageous +means of shaft support for the comparatively temporary character +of metal mines, to get the strains applied to the timbers in the +best manner, and to use the minimum amount of it consistent with +security, and to lose the least working space, the shaft must be +constructed on rectangular lines. + +[Footnote *: Octagonal shafts were sunk in Mexico in former times. +At each face of the octagon was a whim run by mules, and hauling +leather buckets.] + +[Footnote **: The economic situation is rapidly arising in a number +of localities that steel beams can be usefully used instead of +timber. The same arguments apply to this type of support that apply +to timber.] + +The variations in timbered shaft design arise from the possible +arrangement of compartments. Many combinations can be imagined, +of which Figures 9, 10, 11, 12, 13, and 14 are examples. + +[Illustration: FIG. 9. FIG. 10. FIG. 11. FIG. 12. FIG. 13. FIG. +14.] + +The arrangement of compartments shown in Figures 9, 10, 11, and +13 gives the greatest strength. It permits timbering to the best +advantage, and avoids the danger underground involved in crossing +one compartment to reach another. It is therefore generally adopted. +Any other arrangement would obviously be impossible in inclined +or combined shafts. + +SIZE OF SHAFTS.--In considering the size of shafts to be installed, +many factors are involved. They are in the main:-- + + _a_. Amount of ore to be handled. + _b_. Winding plant. + _c_. Vehicle of transport. + _d_. Depth. + _e_. Number of men to be worked underground. + _f_. Amount of water. + _g_. Ventilation. + _h_. Character of the ground. + _i_. Capital outlay. + _j_. Operating expense. + +It is not to be assumed that these factors have been stated in +the order of relative importance. More or less emphasis will be +attached to particular factors by different engineers, and under +different circumstances. It is not possible to suggest any arbitrary +standard for calculating their relative weight, and they are so +interdependent as to preclude separate discussion. The usual result +is a compromise between the demands of all. + +Certain factors, however, dictate a minimum position, which may +be considered as a datum from which to start consideration. + +_First_, a winding engine, in order to work with any economy, must +be balanced, that is, a descending empty skip or cage must assist +in pulling up a loaded one. Therefore, except in mines of very +small output, at least two compartments must be made for hoisting +purposes. Water has to be pumped from most mines, escape-ways are +necessary, together with room for wires and air-pipes, so that at +least one more compartment must be provided for these objects. +We have thus three compartments as a sound minimum for any shaft +where more than trivial output is required. + +_Second_, there is a certain minimum size of shaft excavation below +which there is very little economy in actual rock-breaking.[*] +In too confined a space, holes cannot be placed to advantage for +the blast, men cannot get round expeditiously, and spoil cannot be +handled readily. The writer's own experience leads him to believe +that, in so far as rock-breaking is concerned, to sink a shaft +fourteen to sixteen feet long by six to seven feet wide outside +the timbers, is as cheap as to drive any smaller size within the +realm of consideration, and is more rapid. This size of excavation +permits of three compartments, each about four to five feet inside +the timbers. + +[Footnote *: Notes on the cost of shafts in various regions which +have been personally collected show a remarkable decrease in the +cost per cubic foot of material excavated with increased size of +shaft. Variations in skill, in economic conditions, and in method +of accounting make data regarding different shafts of doubtful +value, but the following are of interest:-- + +In Australia, eight shafts between 10 and 11 feet long by 4 to +5 feet wide cost an average of $1.20 per cubic foot of material +excavated. Six shafts 13 to 14 feet long by 4 to 5 feet wide cost +an average of $0.95 per cubic foot; seven shafts 14 to 16 feet +long and 5 to 7 feet wide cost an average of $0.82 per cubic foot. +In South Africa, eleven shafts 18 to 19 feet long by 7 to 8 feet +wide cost an average of $0.82 per cubic foot; five shafts 21 to +25 feet long by 8 feet wide, cost $0.74; and seven shafts 28 feet +by 8 feet cost $0.60 per cubic foot.] + +The cost of timber, it is true, is a factor of the size of shaft, +but the labor of timbering does not increase in the same ratio. +In any event, the cost of timber is only about 15% of the actual +shaft cost, even in localities of extremely high prices. + +_Third_, three reasons are rapidly making the self-dumping skip +the almost universal shaft-vehicle, instead of the old cage for +cars. First, there is a great economy in labor for loading into +and discharging from a shaft; second, there is more rapid despatch +and discharge and therefore a larger number of possible trips; +third, shaft-haulage is then independent of delays in arrival of +cars at stations, while tramming can be done at any time and +shaft-haulage can be concentrated into certain hours. Cages to +carry mine cars and handle the same load as a skip must either +be big enough to take two cars, which compels a much larger shaft +than is necessary with skips, or they must be double-decked, which +renders loading arrangements underground costly to install and +expensive to work. For all these reasons, cages can be justified only +on metal mines of such small tonnage that time is no consideration +and where the saving of men is not to be effected. In compartments +of the minimum size mentioned above (four to five feet either way) +a skip with a capacity of from two to five tons can be installed, +although from two to three tons is the present rule. Lighter loads +than this involve more trips, and thus less hourly capacity, and, +on the other hand, heavier loads require more costly engines. This +matter is further discussed under "Haulage Appliances." + +We have therefore as the economic minimum a shaft of three compartments +(Fig. 9), each four to five feet square. When the maximum tonnage +is wanted from such a shaft at the least operating cost, it should +be equipped with loading bins and skips. + +The output capacity of shafts of this size and equipment will depend +in a major degree upon the engine employed, and in a less degree +upon the hauling depth. The reason why depth is a subsidiary factor +is that the rapidity with which a load can be drawn is not wholly a +factor of depth. The time consumed in hoisting is partially expended +in loading, in acceleration and retardation of the engine, and in +discharge of the load. These factors are constant for any depth, +and extra distance is therefore accomplished at full speed of the +engine. + +Vertical shafts will, other things being equal, have greater capacity +than inclines, as winding will be much faster and length of haul less +for same depth. Since engines have, however, a great tractive ability +on inclines, by an increase in the size of skip it is usually possible +partially to equalize matters. Therefore the size of inclines for +the same output need not differ materially from vertical shafts. + +The maximum capacity of a shaft whose equipment is of the character +and size given above, will, as stated, decrease somewhat with extension +in depth of the haulage horizon. At 500 feet, such a shaft if vertical +could produce 70 to 80 tons per hour comfortably with an engine +whose winding speed was 700 feet per minute. As men and material +other than ore have to be handled in and out of the mine, and +shaft-sinking has to be attended to, the winding engine cannot +be employed all the time on ore. Twelve hours of actual daily +ore-winding are all that can be expected without auxiliary help. +This represents a capacity from such a depth of 800 to 1,000 tons +per day. A similar shaft, under ordinary working conditions, with +an engine speed of 2,000 feet per minute, should from, say, 3,000 +feet have a capacity of about 400 to 600 tons daily. + +It is desirable to inquire at what stages the size of shaft should +logically be enlarged in order to attain greater capacity. A +considerable measure of increase can be obtained by relieving the +main hoisting engine of all or part of its collateral duties. Where +the pumping machinery is not elaborate, it is often possible to +get a small single winding compartment into the gangway without +materially increasing the size of the shaft if the haulage compartments +be made somewhat narrower (Fig. 10). Such a compartment would be +operated by an auxiliary engine for sinking, handling tools and +material, and assisting in handling men. If this arrangement can +be effected, the productive time of the main engine can be expanded +to about twenty hours with an addition of about two-thirds to the +output. + +Where the exigencies of pump and gangway require more than two +and one-half feet of shaft length, the next stage of expansion +becomes four full-sized compartments (Fig. 11). By thus enlarging the +auxiliary winding space, some assistance may be given to ore-haulage +in case of necessity. The mine whose output demands such haulage +provisions can usually stand another foot of width to the shaft, +so that the dimensions come to about 21 feet to 22 feet by 7 feet +to 8 feet outside the timbers. Such a shaft, with three- to four-ton +skips and an appropriate engine, will handle up to 250 tons per +hour from a depth of 1,000 feet. + +The next logical step in advance is the shaft of five compartments +with four full-sized haulage ways (Fig. 13), each of greater size +than in the above instance. In this case, the auxiliary engine +becomes a balanced one, and can be employed part of the time upon +ore-haulage. Such a shaft will be about 26 feet to 28 feet long +by 8 feet wide outside the timbers, when provision is made for +one gangway. The capacity of such shafts can be up to 4,000 tons a +day, depending on the depth and engine. When very large quantities +of water are to be dealt with and rod-driven pumps to be used, +two pumping compartments are sometimes necessary, but other forms +of pumps do not require more than one compartment,--an additional +reason for their use. + +For depths greater than 3,000 feet, other factors come into play. +Ventilation questions become of more import. The mechanical problems +on engines and ropes become involved, and their sum-effect is to +demand much increased size and a greater number of compartments. +The shafts at Johannesburg intended as outlets for workings 5,000 +feet deep are as much as 46 feet by 9 feet outside timbers. + +It is not purposed to go into details as to sinking methods or +timbering. While important matters, they would unduly prolong this +discussion. Besides, a multitude of treatises exist on these subjects +and cover all the minutiae of such work. + +SPEED OF SINKING.--Mines may be divided into two cases,--those +being developed only, and those being operated as well as developed. +In the former, the entrance into production is usually dependent +upon the speed at which the shaft is sunk. Until the mine is earning +profits, there is a loss of interest on the capital involved, which, +in ninety-nine instances out of a hundred, warrants any reasonable +extra expenditure to induce more rapid progress. In the case of +mines in operation, the volume of ore available to treatment or +valuation is generally dependent to a great degree upon the rapidity +of the extension of workings in depth. It will be demonstrated +later that, both from a financial and a technical standpoint, the +maximum development is the right one and that unremitting extension +in depth is not only justifiable but necessary. + +Speed under special conditions or over short periods has a more +romantic than practical interest, outside of its value as a stimulant +to emulation. The thing that counts is the speed which can be maintained +over the year. Rapidity of sinking depends mainly on:-- + +_a_. Whether the shaft is or is not in use for operating the + mine. +_b_. The breaking character of the rock. +_c_. The amount of water. + +The delays incident to general carrying of ore and men are such that +the use of the main haulage engine for shaft-sinking is practically +impossible, except on mines with small tonnage output. Even with a +separate winch or auxiliary winding-engine, delays are unavoidable +in a working shaft, especially as it usually has more water to contend +with than one not in use for operating the mine. The writer's own +impression is that an average of 40 feet per month is the maximum +possibility for year in and out sinking under such conditions. In +fact, few going mines manage more than 400 feet a year. In cases +of clean shaft-sinking, where every energy is bent to speed, 150 +feet per month have been averaged for many months. Special cases +have occurred where as much as 213 feet have been achieved in a +single month. With ordinary conditions, 1,200 feet in a year is +very good work. Rock awkward to break, and water especially, lowers +the rate of progress very materially. Further reference to speed +will be found in the chapter on "Drilling Methods." + +TUNNEL ENTRY.--The alternative of entry to a mine by tunnel is +usually not a question of topography altogether, but, like everything +else in mining science, has to be tempered to meet the capital +available and the expenditure warranted by the value showing. + +In the initial prospecting of a mine, tunnels are occasionally +overdone by prospectors. Often more would be proved by a few inclines. +As the pioneer has to rely upon his right arm for hoisting and +drainage, the tunnel offers great temptations, even when it is +long and gains but little depth. At a more advanced stage of +development, the saving of capital outlay on hoisting and pumping +equipment, at a time when capital is costly to secure, is often +sufficient justification for a tunnel entry. But at the stage where +the future working of ore below a tunnel-level must be contemplated, +other factors enter. For ore below tunnel-level a shaft becomes +necessary, and in cases where a tunnel enters a few hundred feet +below the outcrop the shaft should very often extend to the surface, +because internal shafts, winding from tunnel-level, require large +excavations to make room for the transfer of ore and for winding +gear. The latter must be operated by transmitted power, either +that of steam, water, electricity, or air. Where power has to be +generated on the mine, the saving by the use of direct steam, generated +at the winding gear, is very considerable. Moreover, the cost of +haulage through a shaft for the extra distance from tunnel-level +to the surface is often less than the cost of transferring the +ore and removing it through the tunnel. The load once on the +winding-engine, the consumption of power is small for the extra +distance, and the saving of labor is of consequence. On the other +hand, where drainage problems arise, they usually outweigh all +other considerations, for whatever the horizon entered by tunnel, +the distance from that level to the surface means a saving of +water-pumpage against so much head. The accumulation of such constant +expense justifies a proportioned capital outlay. In other words, +the saving of this extra pumping will annually redeem the cost of +a certain amount of tunnel, even though it be used for drainage +only. + +In order to emphasize the rapidity with which such a saving of +constant expense will justify capital outlay, one may tabulate the +result of calculations showing the length of tunnel warranted with +various hypothetical factors of quantity of water and height of lift +eliminated from pumping. In these computations, power is taken at +the low rate of $60 per horsepower-year, the cost of tunneling at +an average figure of $20 per foot, and the time on the basis of +a ten-year life for the mine. + +Feet of Tunnel Paid for in 10 Years with Under-mentioned Conditions. + +============================================================= + Feet of | 100,000 | 200,000 | 300,000 | 500,000 |1,000,000 +Water Lift | Gallons | Gallons | Gallons | Gallons | Gallons + Avoided |per Diem |per Diem |per Diem |per Diem |per Diem +-----------|---------|---------|---------|---------|--------- + 100 | 600 | 1,200 | 1,800 | 3,000 | 6,000 + 200 | 1,200 | 2,400 | 3,600 | 6,000 | 12,000 + 300 | 1,800 | 3,600 | 5,400 | 9,000 | 18,000 + 500 | 3,000 | 6,000 | 9,000 | 15,000 | 30,000 + 1,000 | 6,000 | 12,000 | 18,000 | 30,000 | 60,000 +============================================================= + +The size of tunnels where ore-extraction is involved depends upon +the daily tonnage output required, and the length of haul. The +smallest size that can be economically driven and managed is about +6-1/2 feet by 6 feet inside the timbers. Such a tunnel, with single +track for a length of 1,000 feet, with one turn-out, permits handling +up to 500 tons a day with men and animals. If the distance be longer +or the tonnage greater, a double track is required, which necessitates +a tunnel at least 8 feet wide by 6-1/2 feet to 7 feet high, inside +the timbers. + +There are tunnel projects of a much more impressive order than those +designed to operate upper levels of mines; that is, long crosscut +tunnels designed to drain and operate mines at very considerable +depths, such as the Sutro tunnel at Virginia City. The advantage +of these tunnels is very great, especially for drainage, and they +must be constructed of large size and equipped with appliances +for mechanical haulage. + + + + +CHAPTER IX. + +Development of Mines (_Concluded_). + +SUBSIDIARY DEVELOPMENT;--STATIONS; CROSSCUTS; LEVELS; INTERVAL +BETWEEN LEVELS; PROTECTION OF LEVELS; WINZES AND RISES. DEVELOPMENT +IN THE PROSPECTING STAGE; DRILLING. + +SUBSIDIARY DEVELOPMENT. + +Stations, crosscuts, levels, winzes, and rises follow after the +initial entry. They are all expensive, and the least number that +will answer is the main desideratum. + +STATIONS.--As stations are the outlets of the levels to the shaft, +their size and construction is a factor of the volume and character +of the work at the levels which they are to serve. If no timber +is to be handled, and little ore, and this on cages, the stations +need be no larger than a good sized crosscut. Where timber is to +be let down, they must be ten to fifteen feet higher than the floor +of the crosscut. Where loading into skips is to be provided for, +bins must be cut underneath and sufficient room be provided to +shift the mine cars comfortably. Such bins are built of from 50 to +500 tons' capacity in order to contain some reserve for hoisting +purposes, and in many cases separate bins must be provided on opposite +sides of the shaft for ore and waste. It is a strong argument in +favor of skips, that with this means of haulage storage capacity +at the stations is possible, and the hoisting may then go on +independently of trucking and, as said before, there are no idle +men at the stations. + +[Illustration: Fig. 15.--Cross-section of station arrangement for +skip-haulage in vertical shaft.] + +[Illustration: Fig. 16.--Cross-section of station arrangement for +skip-haulage in vertical shaft.] + +It is always desirable to concentrate the haulage to the least +number of levels, for many reasons. Among them is that, where haulage +is confined to few levels, storage-bins are not required at every +station. Figures 15, 16, 17, and 18 illustrate various arrangements +of loading bins. + +CROSSCUTS.--Crosscuts are for two purposes, for roadway connection +of levels to the shaft or to other levels, and for prospecting +purposes. The number of crosscuts for roadways can sometimes be +decreased by making the connections with the shaft at every second +or even every third level, thus not only saving in the construction +cost of crosscuts and stations, but also in the expenses of scattered +tramming. The matter becomes especially worth considering where +the quantity of ore that can thus be accumulated warrants mule +or mechanical haulage. This subject will be referred to later on. + +[Illustration: Fig. 17.--Arrangement of loading chutes in vertical +shaft.] + +On the second purpose of crosscuts,--that of prospecting,--one +observation merits emphasis. This is, that the tendency of ore-fissures +to be formed in parallels warrants more systematic crosscutting +into the country rock than is done in many mines. + +[Illustration: Fig. 18.--Cross-section of station arrangement for +skip-haulage in inclined shaft.] + +LEVELS. + +The word "level" is another example of miners' adaptations in +nomenclature. Its use in the sense of tunnels driven in the direction +of the strike of the deposit has better, but less used, synonyms in +the words "drifts" or "drives." The term "level" is used by miners +in two senses, in that it is sometimes applied to all openings on one +horizon, crosscuts included. Levels are for three purposes,--for a +stoping base; for prospecting the deposit; and for roadways. As a +prospecting and a stoping base it is desirable that the level should +be driven on the deposit; as a roadway, that it should constitute +the shortest distance between two points and be in the soundest +ground. On narrow, erratic deposits the levels usually must serve +all three purposes at once; but in wider and more regular deposits +levels are often driven separately for roadways from the level +which forms the stoping base and prospecting datum. + +There was a time when mines were worked by driving the level on ore +and enlarging it top and bottom as far as the ground would stand, +then driving the next level 15 to 20 feet below, and repeating the +operation. This interval gradually expanded, but for some reason +100 feet was for years assumed to be the proper distance between +levels. Scattered over every mining camp on earth are thousands +of mines opened on this empirical figure, without consideration +of the reasons for it or for any other distance. + +The governing factors in determining the vertical interval between +levels are the following:-- + + _a_. The regularity of the deposit. + _b_. The effect of the method of excavation of winzes and rises. + _c_. The dip and the method of stoping. + +REGULARITY OF THE DEPOSIT.--From a prospecting point of view the +more levels the better, and the interval therefore must be determined +somewhat by the character of the deposit. In erratic deposits there +is less risk of missing ore with frequent levels, but it does not +follow that every level need be a through roadway to the shaft or +even a stoping base. In such deposits, intermediate levels for +prospecting alone are better than complete levels, each a roadway. +Nor is it essential, even where frequent levels are required for +a stoping base, that each should be a main haulage outlet to the +shaft. In some mines every third level is used as a main roadway, +the ore being poured from the intermediate ones down to the haulage +line. Thus tramming and shaft work, as stated before, can be +concentrated. + +EFFECT OF METHOD OF EXCAVATING WINZES AND RISES.--With hand drilling +and hoisting, winzes beyond a limited depth become very costly to +pull spoil out of, and rises too high become difficult to ventilate, +so that there is in such cases a limit to the interval desirable +between levels, but these difficulties largely disappear where +air-winches and air-drills are used. + +THE DIP AND METHOD OF STOPING.--The method of stoping is largely +dependent upon the dip, and indirectly thus affects level intervals. +In dips under that at which material will "flow" in the stopes--about +45 deg. to 50 deg.--the interval is greatly dependent on the method of +stope-transport. Where ore is to be shoveled from stopes to the +roadway, the levels must be comparatively close together. Where +deposits are very flat, under 20 deg., and walls fairly sound, it is +often possible to use a sort of long wall system of stoping and to +lay tracks in the stopes with self-acting inclines to the levels. +In such instances, the interval can be expanded to 250 or even 400 +feet. In dips between 20 deg. and 45 deg., tracks are not often possible, +and either shoveling or "bumping troughs"[*] are the only help +to transport. With shoveling, intervals of 100 feet[**] are most +common, and with troughs the distance can be expanded up to 150 +or 175 feet. + +[Footnote *: Page 136.] + +[Footnote **: Intervals given are measured on the dip.] + +In dips of over 40 deg. to 50 deg., depending on the smoothness of the +foot wall, the distance can again be increased, as stope-transport is +greatly simplified, since the stope materials fall out by gravity. +In timbered stopes, in dips over about 45 deg., intervals of 150 to +200 feet are possible. In filled stopes intervals of over 150 feet +present difficulties in the maintenance of ore-passes, for the wear +and tear of longer use often breaks the timbers. In shrinkage-stopes, +where no passes are to be maintained and few winzes put through, the +interval is sometimes raised to 250 feet. The subject is further +discussed under "Stoping." + +Another factor bearing on level intervals is the needed insurance +of sufficient points of stoping attack to keep up a certain output. +This must particularly influence the manager whose mine has but +little ore in reserve. + +[Illustration: Fig. 19.] + +PROTECTION OF LEVELS.--Until recent years, timbering and occasional +walling was the only method for the support of the roof, and for +forming a platform for a stoping base. Where the rock requires no +support sublevels can be used as a stoping base, and timbering +for such purpose avoided altogether (Figs. 38, 39, 42). In such +cases the main roadway can then be driven on straight lines, either +in the walls or in the ore, and used entirely for haulage. The +subheading for a stoping base is driven far enough above or below +the roadway (depending on whether overhand or underhand stoping +is to be used) to leave a supporting pillar which is penetrated +by short passes for ore. In overhand stopes, the ore is broken +directly on the floor of an upper sublevel; and in underhand stopes, +broken directly from the bottom of the sublevel. The method entails +leaving a pillar of ore which can be recovered only with difficulty +in mines where stope-support is necessary. The question of its +adoption is then largely one of the comparative cost of timbering, +the extra cost of the sublevel, and the net value of the ore left. +In bad swelling veins, or badly crushing walls, where constant +repair to timbers would be necessary, the use of a sublevel is a +most useful alternative. It is especially useful with stopes to +be left open or worked by shrinkage-stoping methods. + +If the haulage level, however, is to be the stoping base, some +protection to the roadway must be provided. There are three systems +in use,--by wood stulls or sets (Figs. 19, 30, 43), by dry-walling +with timber caps (Fig. 35), and in some localities by steel sets. +Stulls are put up in various ways, and, as their use entails the +least difficulty in taking the ore out from beneath the level, +they are much favored, but are applicable only in comparatively +narrow deposits. + +WINZES AND RISES. + +These two kinds of openings for connecting two horizons in a mine +differ only in their manner of construction. A winze is sunk underhand, +while a rise is put up overhand. When the connection between levels +is completed, a miner standing at the bottom usually refers to +the opening as a rise, and when he goes to the top he calls it +a winze. This confusion in terms makes it advisable to refer to +all such completed openings as winzes, regardless of how they are +constructed. + +In actual work, even disregarding water, it costs on the average +about 30% less to raise than to sink such openings, for obviously +the spoil runs out or is assisted by gravity in one case, and in +the other has to be shoveled and hauled up. Moreover, it is easier +to follow the ore in a rise than in a winze. It usually happens, +however, that in order to gain time both things are done, and for +prospecting purposes sinking is necessary. + +The number of winzes required depends upon the method of stoping +adopted, and is mentioned under "Stoping." After stoping, the number +necessary to be maintained open depends upon the necessities of +ventilation, of escape, and of passageways for material to be used +below. Where stopes are to be filled with waste, more winzes must +be kept open than when other methods are used, and these winzes +must be in sufficient alignment to permit the continuous flow of +material down past the various levels. In order that the winzes +should deliver timber and filling to the most advantageous points, +they should, in dipping ore-bodies, be as far as possible on the +hanging wall side. + +DEVELOPMENT IN THE EARLY PROSPECTING STAGE. + +The prime objects in the prospecting stage are to expose the ore +and to learn regarding the ore-bodies something of their size, their +value, metallurgical character, location, dip, strike, etc.,--so much +at least as may be necessary to determine the works most suitable +for their extraction or values warranting purchase. In outcrop mines +there is one rule, and that is "follow the ore." Small temporary +inclines following the deposit, even though they are eventually +useless; are nine times out of ten justified. + +In prospecting deep-level projects, it is usually necessary to +layout work which can be subsequently used in operating the mine, +because the depth involves works of such considerable scale, even +for prospecting, that the initial outlay does not warrant any +anticipation of revision. Such works have to be located and designed +after a study of the general geology as disclosed in adjoining mines. +Practically the only method of supplementing such information is +by the use of churn- and diamond-drills. + +DRILLING.--Churn-drills are applicable only to comparatively shallow +deposits of large volume. They have an advantage over the diamond +drill in exposing a larger section and in their application to +loose material; but inability to determine the exact horizon of +the spoil does not lend them to narrow deposits, and in any event +results are likely to be misleading from the finely ground state of +the spoil. They are, however, of very great value for preliminary +prospecting to shallow horizons. + +Two facts in diamond-drilling have to be borne in mind: the indication +of values is liable to be misleading, and the deflection of the drill +is likely to carry it far away from its anticipated destination. +A diamond-drill secures a small section which is sufficiently large +to reveal the geology, but the values disclosed in metal mines must +be accepted with reservations. The core amounts to but a little +sample out of possibly large amounts of ore, which is always of +variable character, and the core is most unlikely to represent +the average of the deposit. Two diamond-drill holes on the Oroya +Brownhill mine both passed through the ore-body. One apparently +disclosed unpayable values, the other seemingly showed ore forty +feet in width assaying $80 per ton. Neither was right. On the other +hand, the predetermination of the location of the ore-body justified +expenditure. A recent experiment at Johannesburg of placing a copper +wedge in the hole at a point above the ore-body and deflecting +the drill on reintroducing it, was successful in giving a second +section of the ore at small expense. + +The deflection of diamond-drill holes from the starting angle is +almost universal. It often amounts to a considerable wandering +from the intended course. The amount of such deflection varies +with no seeming rule, but it is probable that it is especially +affected by the angle at which stratification or lamination planes +are inclined to the direction of the hole. A hole has been known +to wander in a depth of 1,500 feet more than 500 feet from the +point intended. Various instruments have been devised for surveying +deep holes, and they should be brought into use before works are +laid out on the basis of diamond-drill results, although none of +the inventions are entirely satisfactory. + + + + +CHAPTER X. + +Stoping. + +METHODS OF ORE-BREAKING; UNDERHAND STOPES; OVERHAND STOPES; COMBINED +STOPE. VALUING ORE IN COURSE OF BREAKING. + +There is a great deal of confusion in the application of the word +"stoping." It is used not only specifically to mean the actual +ore-breaking, but also in a general sense to indicate all the operations +of ore-breaking, support of excavations, and transportation between +levels. It is used further as a noun to designate the hole left +when the ore is taken out. Worse still, it is impossible to adhere +to miners' terms without employing it in every sense, trusting +to luck and the context to make the meaning clear. + +The conditions which govern the method of stoping are in the main:-- + + _a_. The dip. + _b_. The width of the deposit. + _c_. The character of the walls. + _d_. The cost of materials. + _e_. The character of the ore. + +Every mine, and sometimes every stope in a mine, is a problem special +to itself. Any general consideration must therefore be simply an +inquiry into the broad principles which govern the adaptability of +special methods. A logical arrangement of discussion is difficult, +if not wholly impossible, because the factors are partially +interdependent and of varying importance. + +For discussion the subject may be divided into: + + 1. Methods of ore-breaking. + 2. Methods of supporting excavation. + 3. Methods of transport in stopes. + +METHODS OF ORE-BREAKING. + +The manner of actual ore-breaking is to drill and blast off slices +from the block of ground under attack. As rock obviously breaks +easiest when two sides are free, that is, when corners can be broken +off, the detail of management for blasts is therefore to set the holes +so as to preserve a corner for the next cut; and as a consequence +the face of the stope shapes into a series of benches (Fig. +22),--inverted benches in the case of overhand stopes (Figs. 20, +21). The size of these benches will in a large measure depend on +the depth of the holes. In wide stopes with machine-drills they +vary from 7 to 10 feet; in narrow stopes with hand-holes, from +two to three feet. + +[Illustration: Fig. 20.] + +The position of the men in relation to the working face gives rise +to the usual primary classification of the methods of stoping. +They are:-- + + 1. Underhand stopes, + 2. Overhand stopes, + 3. Combined stopes. + +These terms originated from the direction of the drill-holes, but +this is no longer a logical basis of distinction, for underhand +holes in overhand stopes,--as in rill-stoping,--are used entirely +in some mines (Fig. 21). + +[Illustration: Fig. 21.] + +UNDERHAND STOPES.--Underhand stopes are those in which the ore +is broken downward from the levels. Inasmuch as this method has +the advantage of allowing the miner to strike his blows downward +and to stand upon the ore when at work, it was almost universal +before the invention of powder; and was applied more generally +before the invention of machine-drills than since. It is never +rightly introduced unless the stope is worked back from winzes +through which the ore broken can be let down to the level below, +as shown in Figures 22 and 23. + +[Illustration: Fig. 22.] + +This system can be advantageously applied only in the rare cases +in which the walls require little or no support, and where very +little or no waste requiring separation is broken with the ore +in the stopes. To support the walls in bad ground in underhand +stopes would be far more costly than with overhand stopes, for +square-set timbering would be most difficult to introduce, and +to support the walls with waste and stulls would be even more +troublesome. Any waste broken must needs be thrown up to the level +above or be stored upon specially built stages--again a costly +proceeding. + +A further drawback lies in the fact that the broken ore follows +down the face of the stope, and must be shoveled off each bench. +It thus all arrives at a single point,--the winze,--and must be +drawn from a single ore-pass into the level. This usually results +not only in more shoveling but in a congestion at the passes not +present in overhand stoping, for with that method several chutes +are available for discharging ore into the levels. Where the walls +require no support and no selection is desired in the stopes, the +advantage of the men standing on the solid ore to work, and of +having all down holes and therefore drilled wet, gives this method +a distinct place. In using this system, in order to protect the +men, a pillar is often left under the level by driving a sublevel, +the pillar being easily recoverable later. The method of sublevels +is of advantage largely in avoiding the timbering of levels. + +[Illustration: Fig. 23.--Longitudinal section of an underhand stope.] + +OVERHAND STOPES.--By far the greatest bulk of ore is broken overhand, +that is broken upward from one level to the next above. There are +two general forms which such stopes are given,--"horizontal" and +"rill." + +[Illustration: Fig. 24.--Horizontal-cut overhand stope--longitudinal +section.] + +The horizontal "flat-back" or "long-wall" stope, as it is variously +called, shown in Figure 24, is operated by breaking the ore in slices +parallel with the levels. In rill-stoping the ore is cut back from +the winzes in such a way that a pyramid-shaped room is created, +with its apex in the winze and its base at the level (Figs. 25 and +26). Horizontal or flat-backed stopes can be applied to almost any +dip, while "rill-stoping" finds its most advantageous application +where the dip is such that the ore will "run," or where it can be +made to "run" with a little help. The particular application of +the two systems is dependent not only on the dip but on the method +of supporting the excavation and the ore. With rill-stoping, it is +possible to cut the breaking benches back horizontally from the +winzes (Fig. 25), or to stagger the cuts in such a manner as to +take the slices in a descending angle (Figs. 21 and 26). + +[Illustration: Fig. 25.--Rill-cut overhand stope--longitudinal section.] + +In the "rill" method of incline cuts, all the drill-holes are "down" +holes (Fig. 21), and can be drilled wet, while in horizontal cuts +or flat-backed stopes, at least part of the holes must be "uppers" +(Fig. 20). Aside from the easier and cheaper drilling and setting +up of machines with this kind of "cut," there is no drill dust,--a +great desideratum in these days of miners' phthisis. A further +advantage in the "rill" cut arises in cases where horizontal jointing +planes run through the ore of a sort from which unduly large masses +break away in "flat-back" stopes. By the descending cut of the +"rill" method these calamities can be in a measure avoided. In +cases of dips over 40 deg. the greatest advantage in "rill" stoping +arises from the possibility of pouring filling or timber into the +stope from above with less handling, because the ore and material +will run down the sides of the pyramid (Figs. 32 and 34). Thus +not only is there less shoveling required, but fewer ore-passes +and a less number of preliminary winzes are necessary, and a wider +level interval is possible. This matter will be gone into more +fully later. + +[Illustration: Fig. 26.--Rill-cut overhand stope-longitudinal section.] + +COMBINED STOPES.--A combined stope is made by the coincident working +of the underhand and "rill" method (Fig. 27). This order of stope +has the same limitations in general as the underhand kind. For +flat veins with strong walls, it has a great superiority in that +the stope is carried back more or less parallel with the winzes, +and thus broken ore after blasting lies in a line on the gradient +of the stope. It is, therefore, conveniently placed for mechanical +stope haulage. A further advantage is gained in that winzes may +be placed long distances apart, and that men are not required, +either when at work or passing to and from it, to be ever far from +the face, and they are thus in the safest ground, so that timber +and filling protection which may be otherwise necessary is not +required. This method is largely used in South Africa. + +[Illustration: Fig. 27.--Longitudinal section of a combined stope.] + +MINIMUM WIDTH OF STOPES.--The minimum stoping width which can be +consistently broken with hand-holes is about 30 inches, and this +only where there is considerable dip to the ore. This space is +so narrow that it is of doubtful advantage in any case, and 40 +inches is more common in narrow mines, especially where worked +with white men. Where machine-drills are used about 4 feet is the +minimum width feasible. + +RESUING.--In very narrow veins where a certain amount of wall-rock +must be broken to give working space, it pays under some circumstances +to advance the stope into the wall-rock ahead of the ore, thus +stripping the ore and enabling it to be broken separately. This +permits of cleaner selection of the ore; but it is a problem to +be worked out in each case, as to whether rough sorting of some +waste in the stopes, or further sorting at surface with inevitable +treatment of some waste rock, is more economical than separate +stoping cuts and inevitably wider stopes. + +VALUING ORE IN COURSE OF BREAKING.--There are many ores whose payability +can be determined by inspection, but there are many of which it cannot. +Continuous assaying is in the latter cases absolutely necessary +to avoid the treatment of valueless material. In such instances, +sampling after each stoping-cut is essential, the unprofitable ore +being broken down and used as waste. Where values fade into the +walls, as in impregnation deposits, the width of stopes depends +upon the limit of payability. In these cases, drill-holes are put +into the walls and the drillings assayed. If the ore is found +profitable, the holes are blasted out. The gauge of what is profitable +in such situations is not dependent simply upon the average total +working costs of the mine, for ore in that position can be said to +cost nothing for development work and administration; moreover, +it is usually more cheaply broken than the average breaking cost, +men and machines being already on the spot. + + + + +CHAPTER XI. + +Methods of Supporting Excavation. + +TIMBERING; FILLING WITH WASTE; FILLING WITH BROKEN ORE; PILLARS +OF ORE; ARTIFICIAL PILLARS; CAVING SYSTEM. + +Most stopes require support to be given to the walls and often to +the ore itself. Where they do require support there are five principal +methods of accomplishing it. The application of any particular method +depends upon the dip, width of ore-body, character of the ore and +walls, and cost of materials. The various systems are by:-- + + 1. Timbering. + 2. Filling with waste. + 3. Filling with broken ore subsequently withdrawn. + 4. Pillars of ore. + 5. Artificial pillars built of timbers and waste. + 6. Caving. + +TIMBERING.--At one time timbering was the almost universal means of +support in such excavations, but gradually various methods for the +economical application of waste and ore itself have come forward, +until timbering is fast becoming a secondary device. Aside from +economy in working without it, the dangers of creeps, or crushing, +and of fires are sufficient incentives to do away with wood as +far as possible. + +There are three principal systems of timber support to excavations,--by +stulls, square-sets, and cribs. + +Stulls are serviceable only where the deposit is so narrow that +the opening can be bridged by single timbers between wall and wall +(Figs. 28 and 43). This system can be applied to any dip and is most +useful in narrow deposits where the walls are not too heavy. Stulls +in inclined deposits are usually set at a slightly higher angle than +that perpendicular to the walls, in order that the vertical pressure +of the hanging wall will serve to tighten them in position. The +"stull" system can, in inclined deposits, be further strengthened by +building waste pillars against them, in which case the arrangement +merges into the system of artificial pillars. + +[Illustration: Fig. 28.--Longitudinal section of stull-supported +stope.] + +[Illustration: Fig. 29.--Longitudinal section showing square-set +timbering.] + +[Illustration: Fig. 30.--Square-set timbering on inclined ore-body. +Showing ultimate strain on timbers.] + +Square-sets (Figs. 29 and 30), that is, trusses built in the opening +as the ore is removed, are applicable to almost any dip or width +of ore, but generally are applied only in deposits too wide, or to +rock too heavy, for stulls. Such trusses are usually constructed on +vertical and horizontal lines, and while during actual ore-breaking +the strains are partially vertical, ultimately, however, when the +weight of the walls begins to be felt, these strains, except in +vertical deposits, come at an angle to lines of strength in the +trusses, and therefore timber constructions of this type present +little ultimate resistance (Fig. 30). Square-set timbers are sometimes +set to present the maximum resistance to the direction of strain, +but the difficulties of placing them in position and variations in +the direction of strain on various parts of the stope do not often +commend the method. As a general rule square-sets on horizontal +lines answer well enough for the period of actual ore-breaking. The +crushing or creeps is usually some time later; and if the crushing +may damage the whole mine, their use is fraught with danger. +Reenforcement by building in waste is often resorted to. When done +fully, it is difficult to see the utility of the enclosed timber, +for entire waste-filling would in most cases be cheaper and equally +efficient. + +[Illustration: Fig. 31.--"Cribs."] + +There is always, with wood constructions, as said before, the very +pertinent danger of subsequent crushing and of subsidence in after +years, and the great risk of fires. Both these disasters have cost +Comstock and Broken Hill mines, directly or indirectly, millions of +dollars, and the outlay on timber and repairs one way or another +would have paid for the filling system ten times over. There are +cases where, by virtue of the cheapness of timber, "square-setting" +is the most economical method. Again, there are instances where the +ore lies in such a manner--particularly in limestone replacements--as +to preclude other means of support. These cases are being yearly +more and more evaded by the ingenuity of engineers in charge. The +author believes it soon will be recognized that the situation is +rare indeed where complete square-setting is necessarily without an +economical alternative. An objection is sometimes raised to filling +in favor of timber, in that if it become desirable to restope the +walls for low-grade ore left behind, such stopes could only be +entered by drawing the filling, with consequent danger of total +collapse. Such a contingency can be provided for in large ore-bodies +by installing an outer shell of sets of timber around the periphery +of the stope and filling the inside with waste. If the crushing +possibilities are too great for this method then, the subsequent +recovery of ore is hopeless in any event. In narrow ore-bodies +with crushing walls recovery of ore once left behind is not often +possible. + +The third sort of timber constructions are cribs, a "log-house" sort +of structure usually filled with waste, and more fully discussed +under artificial pillars (Fig. 31). The further comparative merits +of timbering with other methods will be analyzed as the different +systems are described. + +FILLING WITH WASTE.--The system of filling stope-excavations completely +with waste in alternating progress with ore-breaking is of wide +and increasingly general application (Figs. 32, 33, 34, 35). + +Although a certain amount of waste is ordinarily available in the +stopes themselves, or from development work in the mine, such a +supply must usually be supplemented from other directions. Treatment +residues afford the easiest and cheapest handled material. Quarried +rock ranks next, and in default of any other easy supply, materials +from crosscuts driven into the stope-walls are sometimes resorted +to. + +In working the system to the best advantage, the winzes through +the block of ore under attack are kept in alignment with similar +openings above, in order that filling may be poured through the +mine from the surface or any intermediate point. Winzes to be used +for filling should be put on the hanging-wall side of the area to +be filled, for the filling poured down will then reach the foot-wall +side of the stopes with a minimum of handling. In some instances, +one special winze is arranged for passing all filling from the +surface to a level above the principal stoping operations; and +it is then distributed along the levels into the winzes, and thus +to the operating stopes, by belt-conveyors. + +[Illustration: Fig. 32.--Longitudinal section. Rill stope filled +with waste.] + +[Illustration: Fig. 33.--Longitudinal section. Horizontal stope +filled with waste.] + +[Illustration: Fig. 34.--Longitudinal section. Waste-filled stope +with dry-walling of levels and passes.] + +In this system of stope support the ore is broken at intervals +alternating with filling. If there is danger of much loss from +mixing broken ore and filling, "sollars" of boards or poles are +laid on the waste. If the ore is very rich, old canvas or cowhides +are sometimes put under the boards. Before the filling interval, +the ore passes are built close to the face above previous filling +and their tops covered temporarily to prevent their being filled +with running waste. If the walls are bad, the filling is kept close +to the face. If the unbroken ore requires support, short stulls +set on the waste (as in Fig. 39) are usually sufficient until the +next cut is taken off, when the timber can be recovered. If stulls +are insufficient, cribs or bulkheads (Fig. 31) are also used and +often buried in the filling. + +[Illustration: Fig. 35.--Cross-section of Fig. 34 on line _A-B_.] + +Both flat-backed and rill-stope methods of breaking are employed in +conjunction with filled stopes. The advantages of the rill-stopes +are so patent as to make it difficult to understand why they are +not universally adopted when the dip permits their use at all. In +rill-stopes (Figs. 32 and 34) the waste flows to its destination +with a minimum of handling. Winzes and ore-passes are not required +with the same frequency as in horizontal breaking, and the broken +ore always lies on the slope towards the passes and is therefore +also easier to shovel. In flat-backed stopes (Fig. 33) winzes must +be put in every 50 feet or so, while in rill-stopes they can be +double this distance apart. The system is applicable by modification +to almost any width of ore. It finds its most economical field +where the dip of the stope floor is over 45 deg., when waste and ore, +with the help of the "rill," will flow to their destination. For +dips from under about 45 deg. to about 30 deg. or 35 deg., where the +waste and ore will not "flow" easily, shoveling can be helped by the +use of the "rill" system and often evaded altogether, if flow be +assisted by a sheet-iron trough described in the discussion of +stope transport. Further saving in shoveling can be gained in this +method, by giving a steeper pitch to the filling winzes and to the +ore-passes, by starting them from crosscuts in the wall, and by +carrying them at greater angles than the pitch of the ore (Fig. +36). These artifices combined have worked out most economically +on several mines within the writer's experience, with the dip as +flat as 30 deg. For very flat dips, where filling is to be employed, +rill-stoping has no advantage over flat-backed cuts, and in such +cases it is often advisable to assist stope transport by temporary +tracks and cars which obviously could not be worked on the tortuous +contour of a rill-stope, so that for dips under 30 deg. advantage lies +with "flat-backed" ore-breaking. + +[Illustration: Fig. 36.--Cross-section showing method of steepening +winzes and ore passes.] + +On very wide ore-bodies where the support of the standing ore itself +becomes a great problem, the filling system can be applied by combining +it with square-setting. In this case the stopes are carried in +panels laid out transversally to the strike as wide as the standing +strength of the ore permits. On both sides of each panel a fence +of lagged square-sets is carried up and the area between is filled +with waste. The panels are stoped out alternately. The application +of this method at Broken Hill will be described later. (See pages +120 and Figs. 41 and 42.) The same type of wide ore-body can be +managed also on the filling system by the use of frequent "bulkheads" +to support the ore (Fig. 31). + +Compared with timbering methods, filling has the great advantage +of more effective support to the mine, less danger of creeps, and +absolute freedom from the peril of fire. The relative expense of +the two systems is determined by the cost of materials and labor. +Two extreme cases illustrate the result of these economic factors +with sufficient clearness. It is stated that the cost of timbering +stopes on the Le Roi Mine by square-sets is about 21 cents per +ton of ore excavated. In the Ivanhoe mine of West Australia the +cost of filling stopes with tailings is about 22 cents per ton +of ore excavated. At the former mine the average cost of timber +is under $10 per M board-measure, while at the latter its price +would be $50 per M board-measure; although labor is about of the +same efficiency and wage, the cost in the Ivanhoe by square-setting +would be about 65 cents per ton of ore broken. In the Le Roi, on the +other hand, no residues are available for filling. To quarry rock +or drive crosscuts into the walls might make this system cost 65 +cents per ton of ore broken if applied to that mine. The comparative +value of the filling method with other systems will be discussed +later. + +FILLING WITH BROKEN ORE SUBSEQUENTLY WITHDRAWN.--This order of support +is called by various names, the favorite being "shrinkage-stoping." +The method is to break the ore on to the roof of the level, and by +thus filling the stope with broken ore, provide temporary support +to the walls and furnish standing floor upon which to work in making +the next cut (Figs. 37, 38, and 39.) As broken material occupies 30 +to 40% more space than rock _in situ_, in order to provide working +space at the face, the broken ore must be drawn from along the level +after each cut. When the area attacked is completely broken through +from level to level, the stope will be full of loose broken ore, +which is then entirely drawn off. + +A block to be attacked by this method requires preliminary winzes +only at the extremities of the stope,--for entry and for ventilation. +Where it is desired to maintain the winzes after stoping, they +must either be strongly timbered and lagged on the stope side, +be driven in the walls, or be protected by a pillar of ore (Fig. +37). The settling ore and the crushing after the stope is empty +make it difficult to maintain timbered winzes. + +[Illustration: Fig. 37.--Longitudinal section of stope filled with +broken ore.] + +Where it can be done without danger to the mine, the empty stopes +are allowed to cave. If such crushing would be dangerous, either +the walls must be held up by pillars of unbroken ore, as in the +Alaska Treadwell, where large "rib" pillars are left, or the open +spaces must be filled with waste. Filling the empty stope is usually +done by opening frequent passes along the base of the filled stope +above, and allowing the material of the upper stope to flood the +lower one. This program continued upwards through the mine allows +the whole filling of the mine to descend gradually and thus requires +replenishment only into the top. The old stopes in the less critical +and usually exhausted territory nearer the surface are sometimes +left without replenishing their filling. + +The weight of broken ore standing at such a high angle as to settle +rapidly is very considerable upon the level; moreover, at the moment +when the stope is entirely drawn off, the pressure of the walls +as well is likely to be very great. The roadways in this system +therefore require more than usual protection. Three methods are +used: (_a_) timbering; (_b_) driving a sublevel in the ore above +the main roadway as a stoping-base, thus leaving a pillar of ore +over the roadway (Fig. 39); (_c_) by dry-walling the levels, as in +the Baltic mine, Michigan (Figs. 34 and 35). By the use of sublevels +the main roadways are sometimes driven in the walls (Fig. 38) and in +many cases all timbering is saved. To recover pillars left below +sublevels is a rather difficult task, especially if the old stope +above is caved or filled. The use of pillars in substitution for +timber, if the pillars are to be lost, is simply a matter of economics +as to whether the lost ore would repay the cost of other devices. + +[Illustration: Fig. 38.--Cross-section of "shrinkage" stope.] + +Frequent ore-chutes through the level timbers, or from the sublevels, +are necessary to prevent lodgment of broken ore between such passes, +because it is usually too dangerous for men to enter the emptying +stope to shovel out the lodged remnants. Where the ore-body is +wide, and in order that there may be no lodgment of ore, the timbers +over the level are set so as to form a trough along the level; +or where pillars are left, they are made "A"-shaped between the +chutes, as indicated in Figure 37. + +[Illustration: Fig. 39.--Cross-section of "shrinkage" stope.] + +The method of breaking the ore in conjunction with this means of +support in comparatively narrow deposits can be on the rill, in order +to have the advantage of down holes. Usually, however, flat-back +or horizontal cuts are desirable, as in such an arrangement it +is less troublesome to regulate the drawing of the ore so as to +provide proper head room. Where stopes are wide, ore is sometimes +cut arch-shaped from wall to wall to assure its standing. Where +this method of support is not of avail, short, sharply tapering +stulls are put in from the broken ore to the face (Fig. 39). When +the cut above these stulls is taken out, they are pulled up and +are used again. + +This method of stoping is only applicable when:-- + +1. The deposit dips over 60 deg., and thus broken material will freely +settle downward to be drawn off from the bottom. + +2. The ore is consistently payable in character. No selection can be +done in breaking, as all material broken must be drawn off together. + +3. The hanging wall is strong, and will not crush or spall off waste +into the ore. + +4. The ore-body is regular in size, else loose ore will lodge on +the foot wall. Stopes opened in this manner when partially empty +are too dangerous for men to enter for shoveling out remnants. + +The advantages of this system over others, where it is applicable, +are:-- + +(_a_) A greater distance between levels can be operated and few +winzes and rises are necessary, thus a great saving of development +work can be effected. A stope 800 to 1000 feet long can be operated +with a winze at either end and with levels 200 or 220 feet apart. + +(_b_) There is no shoveling in the stopes at all. + +(_c_) No timber is required. As compared with timbering by stulling, +it will apply to stopes too wide and walls too heavy for this method. +Moreover, little staging is required for working the face, since +ore can be drawn from below in such a manner as to allow just the +right head room. + +(_d_) Compared to the system of filling with waste, coincidentally +with breaking (second method), it saves altogether in some cases +the cost of filling. In any event, it saves the cost of ore-passes, +of shoveling into them, and of the detailed distribution of the +filling. + +Compared with other methods, the system has the following disadvantages, +that: + +_A_. The ore requires to be broken in the stopes to a degree of +fineness which will prevent blocking of the chutes at the level. +When pieces too large reach the chutes, nothing will open them but +blasting,--to the damage of timbers and chutes. Some large rocks +are always liable to be buried in the course of ore-breaking. + +_B_. Practically no such perfection of walls exists, but some spalling +of waste into the ore will take place. A crushing of the walls +would soon mean the loss of large amounts of ore. + +_C_. There is no possibility of regulating the mixture of grade +of ore by varying the working points. It is months after the ore +is broken before it can reach the levels. + +_D_. The breaking of 60% more ore than immediate treatment demands +results in the investment of a considerable sum of money. An equilibrium +is ultimately established in a mine worked on this system when a +certain number of stopes full of completely broken ore are available +for entire withdrawal, and there is no further accumulation. But, +in any event, a considerable amount of broken ore must be held in +reserve. In one mine worked on this plan, with which the writer +has had experience, the annual production is about 250,000 tons +and the broken ore represents an investment which, at 5%, means +an annual loss of interest amounting to 7 cents per ton of ore +treated. + +_E_. A mine once started on the system is most difficult to alter, +owing to the lack of frequent winzes or passes. Especially is this +so if the only alternative is filling, for an alteration to the +system of filling coincident with breaking finds the mine short +of filling winzes. As the conditions of walls and ore often alter +with depth, change of system may be necessary and the situation +may become very embarrassing. + +_F_. The restoping of the walls for lower-grade ore at a later +period is impossible, for the walls of the stope will be crushed, +or, if filled with waste, will usually crush when it is drawn off +to send to a lower stope. + +The system has much to recommend it where conditions are favorable. +Like all other alternative methods of mining, it requires the most +careful study in the light of the special conditions involved. In many +mines it can be used for some stopes where not adaptable generally. +It often solves the problem of blind ore-bodies, for they can by +this means be frequently worked with an opening underneath only. +Thus the cost of driving a roadway overhead is avoided, which would +be required if timber or coincident filling were the alternatives. +In such cases ventilation can be managed without an opening above, +by so directing the current of air that it will rise through a +winze from the level below, flow along the stope and into the level +again at the further end of the stope through another winze. + +[Illustration: Fig. 40.--Longitudinal section. Ore-pillar support +in narrow stopes.] + +SUPPORT BY PILLARS OF ORE.--As a method of mining metals of the +sort under discussion, the use of ore-pillars except in conjunction +with some other means of support has no general application. To +use them without assistance implies walls sufficiently strong to +hold between pillars; to leave them permanently anywhere implies +that the ore abandoned would not repay the labor and the material +of a substitute. There are cases of large, very low-grade mines +where to abandon one-half the ore as pillars is more profitable +than total extraction, but the margin of payability in such ore must +be very, very narrow. Unpayable spots are always left as pillars, +for obvious reasons. Permanent ore-pillars as an adjunct to other +methods of support are in use. Such are the rib-pillars in the +Alaska Treadwell, the form of which is indicated by the upward +extension of the pillars adjacent to the winzes, shown in Figure +37. Always a careful balance must be cast as to the value of the ore +left, and as to the cost of a substitute, because every ore-pillar +can be removed at some outlay. Temporary pillars are not unusual, +particularly to protect roadways and shafts. They are, when left +for these purposes, removed ultimately, usually by beginning at +the farther end and working back to the final exit. + +[Illustration: Fig. 41.--Horizontal plan at levels of Broken Hill. +Method of alternate stopes and ore-pillars.] + +[Illustration: Fig. 42.--Longitudinal section of Figure 41.] + +A form of temporary ore-pillars in very wide deposits is made use +of in conjunction with both filling and timbering (Figs. 37, 39, +40). In the use of temporary pillars for ore-bodies 100 to 250 +feet wide at Broken Hill, stopes are carried up at right angles +to the strike, each fifty feet wide and clear across the ore-body +(Figs. 41 and 42). A solid pillar of the same width is left in the +first instance between adjacent stopes, and the initial series of +stopes are walled with one square-set on the sides as the stope is +broken upward. The room between these two lines of sets is filled +with waste alternating with ore-breaking in the usual filling method. +When the ore from the first group of alternate stopes (_ABC_, Fig. +42) is completely removed, the pillars are stoped out and replaced +with waste. The square-sets of the first set of stopes thus become +the boundaries of the second set. Entry and ventilation are obtained +through these lines of square-sets, and the ore is passed out of +the stopes through them. + +[Illustration: Fig. 43.--Cross-section of stull support with waste +reenforcement.] + +ARTIFICIAL PILLARS.--This system also implies a roof so strong +as not to demand continuous support. Artificial pillars are built +in many different ways. The method most current in fairly narrow +deposits is to reenforce stulls by packing waste above them (Figs. +43 and 44). Not only is it thus possible to economize in stulls by +using the waste which accumulates underground, but the principle +applies also to cases where the stulls alone are not sufficient +support, and yet where complete filling or square-setting is +unnecessary. When the conditions are propitious for this method, it +has the comparative advantage over timber systems of saving timber, +and over filling systems of saving imported filling. Moreover, +these constructions being pillar-shaped (Fig. 44), the intervals +between them provide outlets for broken ore, and specially built +passes are unnecessary. The method has two disadvantages as against +the square-set or filling process, in that more staging must be +provided from which to work, and in stopes over six feet the erection +of machine-drill columns is tedious and costly in time and wages. + +[Illustration: Fig. 44.--Longitudinal section of stull and waste +pillars.] + +In wide deposits of markedly flat, irregular ore-bodies, where a +definite system is difficult and where timber is expensive, cribs +of cord-wood or logs filled with waste after the order shown in +Figure 31, often make fairly sound pillars. They will not last +indefinitely and are best adapted to the temporary support of the +ore-roof pending filling. The increased difficulty in setting up +machine drills in such stopes adds to the breaking costs,--often +enough to warrant another method of support. + +[Illustration: Fig. 45.--Sublevel caving system.] + +CAVING SYSTEMS.--This method, with variations, has been applied +to large iron deposits, to the Kimberley diamond mines, to some +copper mines, but in general it has little application to the metal +mines under consideration, as few ore-bodies are of sufficiently +large horizontal area. The system is dependent upon a large area of +loose or "heavy" ground pressing directly on the ore with weight, +such that if the ore be cut into pillars, these will crush. The +details of the system vary, but in general the _modus operandi_ +is to prepare roadways through the ore, and from the roadways to +put rises, from which sublevels are driven close under the floating +mass of waste and ore,--sometimes called the "matte" (Fig. 45). +The pillars between these sublevels are then cut away until the +weight above crushes them down. When all the crushed ore which +can be safely reached is extracted, retreat is made and another +series of subopenings is then driven close under the "matte." The +pillar is reduced until it crushes and the operation is repeated. +Eventually the bottom strata of the "matte" become largely ore, +and a sort of equilibrium is reached when there is not much loss +in this direction. "Top slicing" is a variation of the above method +by carrying a horizontal stope from the rises immediately under the +matte, supporting the floating material with timber. At Kimberley +the system is varied in that galleries are run out to the edge of +the diamond-iferous area and enlarged until the pillar between +crushes. + +In the caving methods, between 40 and 50% of the ore is removed +by the preliminary openings, and as they are all headings of some +sort, the average cost per ton of this particular ore is higher +than by ordinary stoping methods. On the other hand, the remaining +50 to 60% of the ore costs nothing to break, and the average cost +is often remarkably low. As said, the system implies bodies of large +horizontal area. They must start near enough to the surface that +the whole superincumbent mass may cave and give crushing weight, +or the immediately overhanging roof must easily cave. All of these +are conditions not often met with in mines of the character under +review. + + + + +CHAPTER XII. + +Mechanical Equipment. + +CONDITIONS BEARING ON MINE EQUIPMENT; WINDING APPLIANCES; HAULAGE +EQUIPMENT IN SHAFTS; LATERAL UNDERGROUND TRANSPORT; TRANSPORT IN +STOPES. + +There is no type of mechanical engineering which presents such +complexities in determination of the best equipment as does that of +mining. Not only does the economic side dominate over pure mechanics, +but machines must be installed and operated under difficulties which +arise from the most exceptional and conflicting conditions, none of +which can be entirely satisfied. Compromise between capital outlay, +operating efficiency, and conflicting demands is the key-note of +the work. + +These compromises are brought about by influences which lie outside +the questions of mechanics of individual machines, and are mainly +as follows:-- + + 1. Continuous change in horizon of operations. + 2. Uncertain life of the enterprise. + 3. Care and preservation of human life. + 4. Unequal adaptability of power transmission mediums. + 5. Origin of power. + +_First._--The depth to be served and the volume of ore and water +to be handled, are not only unknown at the initial equipment, but +they are bound to change continuously in quantity, location, and +horizon with the extension of the workings. + +_Second._--From the mine manager's point of view, which must embrace +that of the mechanical engineer, further difficulty presents itself +because the life of the enterprise is usually unknown, and therefore +a manifest necessity arises for an economic balance of capital +outlay and of operating efficiency commensurate with the prospects +of the mine. Moreover, the initial capital is often limited, and +makeshifts for this reason alone must be provided. In net result, +no mineral deposit of speculative ultimate volume of ore warrants +an initial equipment of the sort that will meet every eventuality, +or of the kind that will give even the maximum efficiency which +a free choice of mining machinery could obtain. + +_Third._--In the design and selection of mining machines, the safety +of human life, the preservation of the health of workmen under +conditions of limited space and ventilation, together with reliability +and convenience in installing and working large mechanical tools, +all dominate mechanical efficiency. For example, compressed-air +transmission of power best meets the requirements of drilling, +yet the mechanical losses in the generation, the transmission, +and the application of compressed air probably total, from first +to last, 70 to 85%. + +_Fourth._--All machines, except those for shaft haulage, must be +operated by power transmitted from the surface, as obviously power +generation underground is impossible. The conversion of power into +a transmission medium and its transmission are, at the outset, +bound to be the occasions of loss. Not only are the various forms +of transmission by steam, electricity, compressed air, or rods, of +different efficiency, but no one system lends itself to universal +or economical application to all kinds of mining machines. Therefore +it is not uncommon to find three or four different media of power +transmission employed on the same mine. To illustrate: from the +point of view of safety, reliability, control, and in most cases +economy as well, we may say that direct steam is the best motive +force for winding-engines; that for mechanical efficiency and +reliability, rods constitute the best media of power transmission +to pumps; that, considering ventilation and convenience, compressed +air affords the best medium for drills. Yet there are other conditions +as to character of the work, volume of water or ore, and the origin +of power which must in special instances modify each and every one +of these generalizations. For example, although pumping water with +compressed air is mechanically the most inefficient of devices, +it often becomes the most advantageous, because compressed air may +be of necessity laid on for other purposes, and the extra power +required to operate a small pump may be thus most cheaply provided. + +_Fifth._--Further limitations and modifications arise out of the +origin of power, for the sources of power have an intimate bearing on +the type of machine and media of transmission. This very circumstance +often compels giving away efficiency and convenience in some machines +to gain more in others. This is evident enough if the principal +origins of power generation be examined. They are in the main as +follows:-- + +_a_. Water-power available at the mine. +_b_. Water-power available at a less distance than three + or four miles. +_c_. Water-power available some miles away, thus necessitating + electrical transmission (or purchased electrical power). +_d_. Steam-power to be generated at the mine. +_e_. Gas-power to be generated at the mine. + +_a_. With water-power at the mine, winding engines can be operated +by direct hydraulic application with a gain in economy over direct +steam, although with the sacrifice of control and reliability. Rods +for pumps can be driven directly with water, but this superiority +in working economy means, as discussed later, a loss of flexibility +and increased total outlay over other forms of transmission to pumps. +As compressed air must be transmitted for drills, the compressor +would be operated direct from water-wheels, but with less control +in regularity of pressure delivery. + +_b_. With water-power a short distance from the mine, it would +normally be transmitted either by compressed air or by electricity. +Compressed-air transmission would better satisfy winding and drilling +requirements, but would show a great comparative loss in efficiency +over electricity when applied to pumping. Despite the latter drawback, +air transmission is a method growing in favor, especially in view +of the advance made in effecting compression by falling water. + +_c_. In the situation of transmission too far for using compressed +air, there is no alternative but electricity. In these cases, direct +electric winding is done, but under such disadvantages that it +requires a comparatively very cheap power to take precedence over +a subsidiary steam plant for this purpose. Electric air-compressors +work under the material disadvantage of constant speed on a variable +load, but this installation is also a question of economics. The +pumping service is well performed by direct electrical pumps. + +_d_. In this instance, winding and air-compression are well accomplished +by direct steam applications; but pumping is beset with wholly +undesirable alternatives, among which it is difficult to choose. + +_e_. With internal combustion engines, gasoline (petrol) motors +have more of a position in experimental than in systematic mining, +for their application to winding and pumping and drilling is fraught +with many losses. The engine must be under constant motion, and +that, too, with variable loads. Where power from producer gas is +used, there is a greater possibility of installing large equipments, +and it is generally applied to the winding and lesser units by +conversion into compressed air or electricity as an intermediate +stage. + +One thing becomes certain from these examples cited, that the right +installation for any particular portion of the mine's equipment cannot +be determined without reference to all the others. The whole system +of power generation for surface work, as well as the transmission +underground, must be formulated with regard to furnishing the best +total result from all the complicated primary and secondary motors, +even at the sacrifice of some members. + +Each mine is a unique problem, and while it would be easy to sketch +an ideal plant, there is no mine within the writer's knowledge +upon which the ideal would, under the many variable conditions, +be the most economical of installation or the most efficient of +operation. The dominant feature of the task is an endeavor to find +a compromise between efficiency and capital outlay. The result is +a series of choices between unsatisfying alternatives, a number of +which are usually found to have been wrong upon further extension +of the mine in depth. + +In a general way, it may be stated that where power is generated +on the mine, economy in labor of handling fuel, driving engines, +generation and condensing steam where steam is used, demand a +consolidated power plant for the whole mine equipment. The principal +motors should be driven direct by steam or gas, with power distribution +by electricity to all outlying surface motors and sometimes to +underground motors, and also to some underground motors by compressed +air. + +Much progress has been made in the past few years in the perfection +of larger mining tools. Inherently many of our devices are of a +wasteful character, not only on account of the need of special +forms of transmission, but because they are required to operate +under greatly varying loads. As an outcome of transmission losses +and of providing capacity to cope with heavy peak loads, their +efficiency on the basis of actual foot-pounds of work accomplished +is very low. + +The adoption of electric transmission in mine work, while in certain +phases beneficial, has not decreased the perplexity which arises +from many added alternatives, none of which are as yet a complete or +desirable answer to any mine problem. When a satisfactory electric +drill is invented, and a method is evolved of applying electricity +to winding-engines that will not involve such abnormal losses due +to high peak load then we will have a solution to our most difficult +mechanical problems, and electricity will deserve the universal +blessing which it has received in other branches of mechanical +engineering. + +It is not intended to discuss mine equipment problems from the +machinery standpoint,--there are thousands of different devices,--but +from the point of view of the mine administrator who finds in the +manufactory the various machines which are applicable, and whose +work then becomes that of choosing, arranging, and operating these +tools. + +The principal mechanical questions of a mine may be examined under +the following heads:-- + + 1. Shaft haulage. + 2. Lateral underground transport. + 3. Drainage. + 4. Rock drilling. + 5. Workshops. + 6. Improvements in equipment. + +SHAFT HAULAGE. + +WINDING APPLIANCES.--No device has yet been found to displace the +single load pulled up the shaft by winding a rope on a drum. Of +driving mechanisms for drum motors the alternatives are the +steam-engine, the electrical motor, and infrequently water-power +or gas engines. + +All these have to cope with one condition which, on the basis of +work accomplished, gives them a very low mechanical efficiency. +This difficulty is that the load is intermittent, and it must be +started and accelerated at the point of maximum weight, and from +that moment the power required diminishes to less than nothing +at the end of the haul. A large number of devices are in use to +equalize partially the inequalities of the load at different stages +of the lift. The main lines of progress in this direction have +been:-- + +_a_. The handling of two cages or skips with one engine + or motor, the descending skip partially balancing + the ascending one. +_b_. The use of tail-ropes or balance weights to compensate + the increasing weight of the descending rope. +_c_. The use of skips instead of cages, thus permitting of + a greater percentage of paying load. +_d_. The direct coupling of the motor to the drum shaft. +_e_. The cone-shaped construction of drums,--this latter + being now largely displaced by the use of the tail-rope. + +The first and third of these are absolutely essential for anything +like economy and speed; the others are refinements depending on +the work to be accomplished and the capital available. + +Steam winding-engines require large cylinders to start the load, +but when once started the requisite power is much reduced and the +load is too small for steam economy. The throttling of the engine +for controlling speed and reversing the engine at periodic stoppages +militates against the maximum expansion and condensation of the +steam and further increases the steam consumption. In result, the +best of direct compound condensing engines consume from 60 to 100 +pounds of steam per horse-power hour, against a possible efficiency +of such an engine working under constant load of less than 16 pounds +of steam per horse-power hour. + +It is only within very recent years that electrical motors have +been applied to winding. Even yet, all things considered, this +application is of doubtful value except in localities of extremely +cheap electrical power. The constant speed of alternating current +motors at once places them at a disadvantage for this work of high +peak and intermittent loads. While continuous-current motors can +be made to partially overcome this drawback, such a current, where +power is purchased or transmitted a long distance, is available +only by conversion, which further increases the losses. However, +schemes of electrical winding are in course of development which +bid fair, by a sort of storage of power in heavy fly-wheels or +storage batteries after the peak load, to reduce the total power +consumption; but the very high first cost so far prevents their +very general adoption for metal mining. + +Winding-engines driven by direct water- or gas-power are of too rare +application to warrant much discussion. Gasoline driven hoists have a +distinct place in prospecting and early-stage mining, especially in +desert countries where transport and fuel conditions are onerous, +for both the machines and their fuel are easy of transport. As direct +gas-engines entail constant motion of the engine at the power demand +of the peak load, they are hopeless in mechanical efficiency. + +Like all other motors in mining, the size and arrangement of the +motor and drum are dependent upon the duty which they will be called +upon to perform. This is primarily dependent upon the depth to be +hoisted from, the volume of the ore, and the size of the load. +For shallow depths and tonnages up to, say, 200 tons daily, geared +engines have a place on account of their low capital cost. Where +great rope speed is not essential they are fully as economical as +direct-coupled engines. With great depths and greater capacities, +speed becomes a momentous factor, and direct-coupled engines are +necessary. Where the depth exceeds 3,000 feet, another element +enters which has given rise to much debate and experiment; that +is, the great increase of starting load due to the increased length +and size of ropes and the drum space required to hold it. So far +the most advantageous device seems to be the Whiting hoist, a +combination of double drums and tail rope. + +On mines worked from near the surface, where depth is gained by +the gradual exhaustion of the ore, the only prudent course is to +put in a new hoist periodically, when the demand for increased +winding speed and power warrants. The lack of economy in winding +machines is greatly augmented if they are much over-sized for the +duty. An engine installed to handle a given tonnage to a depth of +3,000 feet will have operated with more loss during the years the +mine is progressing from the surface to that depth than several +intermediate-sized engines would have cost. On most mines the +uncertainty of extension in depth would hardly warrant such a +preliminary equipment. More mines are equipped with over-sized +than with under-sized engines. For shafts on going metal mines +where the future is speculative, an engine will suffice whose size +provides for an extension in depth of 1,000 feet beyond that reached +at the time of its installation. The cost of the engine will depend +more largely upon the winding speed desired than upon any other +one factor. The proper speed to be arranged is obviously dependent +upon the depth of the haulage, for it is useless to have an engine +able to wind 3,000 feet a minute on a shaft 500 feet deep, since it +could never even get under way; and besides, the relative operating +loss, as said, would be enormous. + +HAULAGE EQUIPMENT IN THE SHAFT.--Originally, material was hoisted +through shafts in buckets. Then came the cage for transporting mine +cars, and in more recent years the "skip" has been developed. The +aggrandized bucket or "kibble" of the Cornishman has practically +disappeared, but the cage still remains in many mines. The advantages +of the skip over the cage are many. Some of them are:-- + + _a_. It permits 25 to 40% greater load of material in + proportion to the dead weight of the vehicle. + _b_. The load can be confined within a smaller horizontal + space, thus the area of the shaft need not be so great + for large tonnages. + _c_. Loading and discharging are more rapid, and the latter + is automatic, thus permitting more trips per hour and + requiring less labor. + _d_. Skips must be loaded from bins underground, and by + providing in the bins storage capacity, shaft haulage is + rendered independent of the lateral transport in the + mine, and there are no delays to the engine awaiting + loads. The result is that ore-winding can be concentrated + into fewer hours, and indirect economies in labor + and power are thus effected. + _e_. Skips save the time of the men engaged in the lateral + haulage, as they have no delay waiting for the winding + engine. + +Loads equivalent to those from skips are obtained in some mines +by double-decked cages; but, aside from waste weight of the cage, +this arrangement necessitates either stopping the engine to load the +lower deck, or a double-deck loading station. Double-deck loading +stations are as costly to install and more expensive to work than +skip-loading station ore-bins. Cages are also constructed large +enough to take as many as four trucks on one deck. This entails a +shaft compartment double the size required for skips of the same +capacity, and thus enormously increases shaft cost without gaining +anything. + +Altogether the advantages of the skip are so certain and so important +that it is difficult to see the justification for the cage under +but a few conditions. These conditions are those which surround +mines of small output where rapidity of haulage is no object, where +the cost of station-bins can thus be evaded, and the convenience +of the cage for the men can still be preserved. The easy change +of the skip to the cage for hauling men removes the last objection +on larger mines. There occurs also the situation in which ore is +broken under contract at so much per truck, and where it is desirable +to inspect the contents of the truck when discharging it, but even +this objection to the skip can be obviated by contracting on a +cubic-foot basis. + +Skips are constructed to carry loads of from two to seven tons, +the general tendency being toward larger loads every year. One +of the most feasible lines of improvement in winding is in the +direction of larger loads and less speed, for in this way the sum +total of dead weight of the vehicle and rope to the tonnage of +ore hauled will be decreased, and the efficiency of the engine +will be increased by a less high peak demand, because of this less +proportion of dead weight and the less need of high acceleration. + +LATERAL UNDERGROUND TRANSPORT. + +Inasmuch as the majority of metal mines dip at considerable angles, +the useful life of a roadway in a metal mine is very short because +particular horizons of ore are soon exhausted. Therefore any method +of transport has to be calculated upon a very quick redemption of +the capital laid out. Furthermore, a roadway is limited in its +daily traffic to the product of the stopes which it serves. + +MEN AND ANIMALS.--Some means of transport must be provided, and +the basic equipment is light tracks with push-cars, in capacity +from half a ton to a ton. The latter load is, however, too heavy +to be pushed by one man. As but one car can be pushed at a time, +hand-trucking is both slow and expensive. At average American or +Australian wages, the cost works out between 25 and 35 cents a +ton per mile. An improvement of growing import where hand-trucking +is necessary is the overhead mono-rail instead of the track. + +If the supply to any particular roadway is such as to fully employ +horses or mules, the number of cars per trip can be increased up +to seven or eight. In this case the expense, including wages of +the men and wear, tear, and care of mules, will work out roughly +at from 7 to 10 cents per ton mile. Manifestly, if the ore-supply +to a particular roadway is insufficient to keep a mule busy, the +economy soon runs off. + +MECHANICAL HAULAGE.--Mechanical haulage is seldom applicable to +metal mines, for most metal deposits dip at considerable angles, +and therefore, unlike most coal-mines, the horizon of haulage must +frequently change, and there are no main arteries along which haulage +continues through the life of the mine. Any mechanical system entails +a good deal of expense for installation, and the useful life of +any particular roadway, as above said, is very short. Moreover, +the crooked roadways of most metal mines present difficulties of +negotiation not to be overlooked. In order to use such systems it +is necessary to condense the haulage to as few roadways as possible. +Where the tonnage on one level is not sufficient to warrant other +than men or animals, it sometimes pays (if the dip is steep enough) +to dump everything through winzes from one to two levels to a main +road below where mechanical equipment can be advantageously provided. +The cost of shaft-winding the extra depth is inconsiderable compared +to other factors, for the extra vertical distance of haulage can +be done at a cost of one or two cents per ton mile. Moreover, from +such an arrangement follows the concentration of shaft-bins, and of +shaft labor, and winding is accomplished without so much shifting +as to horizon, all of which economies equalize the extra distance +of the lift. + +There are three principal methods of mechanical transport in use:-- + + 1. Cable-ways. + 2. Compressed-air locomotives. + 3. Electrical haulage. + +Cable-ways or endless ropes are expensive to install, and to work +to the best advantage require double tracks and fairly straight +roads. While they are economical in operation and work with little +danger to operatives, the limitations mentioned preclude them from +adoption in metal mines, except in very special circumstances such +as main crosscuts or adit tunnels, where the haulage is straight +and concentrated from many sources of supply. + +Compressed-air locomotives are somewhat heavy and cumbersome, and +therefore require well-built tracks with heavy rails, but they +have very great advantages for metal mine work. They need but a +single track and are of low initial cost where compressed air is +already a requirement of the mine. No subsidiary line equipment is +needed, and thus they are free to traverse any road in the mine and +can be readily shifted from one level to another. Their mechanical +efficiency is not so low in the long run as might appear from the +low efficiency of pneumatic machines generally, for by storage of +compressed air at the charging station a more even rate of energy +consumption is possible than in the constant cable and electrical +power supply which must be equal to the maximum demand, while the +air-plant consumes but the average demand. + +Electrical haulage has the advantage of a much more compact locomotive +and the drawback of more expensive track equipment, due to the +necessity of transmission wire, etc. It has the further disadvantages +of uselessness outside the equipped haulage way and of the dangers +of the live wire in low and often wet tunnels. + +In general, compressed-air locomotives possess many attractions +for metal mine work, where air is in use in any event and where +any mechanical system is at all justified. Any of the mechanical +systems where tonnage is sufficient in quantity to justify their +employment will handle material for from 1.5 to 4 cents per ton +mile. + +TRACKS.--Tracks for hand, mule, or rope haulage are usually built +with from 12- to 16-pound rails, but when compressed-air or electrical +locomotives are to be used, less than 24-pound rails are impossible. +As to tracks in general, it may be said that careful laying out +with even grades and gentle curves repays itself many times over in +their subsequent operation. Further care in repair and lubrication +of cars will often make a difference of 75% in the track resistance. + +TRANSPORT IN STOPES.--Owing to the even shorter life of individual +stopes than levels, the actual transport of ore or waste in them is +often a function of the aboriginal shovel plus gravity. As shoveling +is the most costly system of transport known, any means of stoping +that decreases the need for it has merit. Shrinkage-stoping eliminates +it altogether. In the other methods, gravity helps in proportion to +the steepness of the dip. When the underlie becomes too flat for +the ore to "run," transport can sometimes be helped by pitching +the ore-passes at a steeper angle than the dip (Fig. 36). In some +cases of flat deposits, crosscuts into the walls, or even levels +under the ore-body, are justifiable. The more numerous the ore-passes, +the less the lateral shoveling, but as passes cost money for +construction and for repair, there is a nice economic balance in +their frequency. + +Mechanical haulage in stopes has been tried and finds a field under +some conditions. In dips under 25 deg. and possessing fairly sound +hanging-wall, where long-wall or flat-back cuts are employed, temporary +tracks can often be laid in the stopes and the ore run in cars to +the main passes. In such cases, the tracks are pushed up close +to the face after each cut. Further self-acting inclines to lower +cars to the levels can sometimes be installed to advantage. This +arrangement also permits greater intervals between levels and less +number of ore-passes. For dips between 25 deg. and 50 deg. where the mine +is worked without stope support or with occasional pillars, a very +useful contrivance is the sheet-iron trough--about eighteen inches +wide and six inches deep--made in sections ten or twelve feet long +and readily bolted together. In dips 35 deg. to 50 deg. this trough, laid +on the foot-wall, gives a sufficiently smooth surface for the ore +to run upon. When the dip is flat, the trough, if hung from plugs +in the hanging-wall, may be swung backward and forward. The use of +this "bumping-trough" saves much shoveling. For handling filling +or ore in flat runs it deserves wider adoption. It is, of course, +inapplicable in passes as a "bumping-trough," but can be fixed to +give smooth surface. In flat mines it permits a wider interval +between levels and therefore saves development work. The life of +this contrivance is short when used in open stopes, owing to the +dangers of bombardment from blasting. + +In dips steeper than 50 deg. much of the shoveling into passes can be +saved by rill-stoping, as described on page 100. Where flat-backed +stopes are used in wide ore-bodies with filling, temporary tracks +laid on the filling to the ore-passes are useful, for they permit +wider intervals between passes. + +In that underground engineer's paradise, the Witwatersrand, where +the stopes require neither timber nor filling, the long, moderately +pitched openings lend themselves particularly to the swinging iron +troughs, and even endless wire ropes have been found advantageous +in certain cases. + +Where the roof is heavy and close support is required, and where +the deposits are very irregular in shape and dip, there is little +hope of mechanical assistance in stope transport. + + + + +CHAPTER XIII. + +Mechanical Equipment. (_Continued_). + +DRAINAGE: CONTROLLING FACTORS; VOLUME AND HEAD OF WATER; FLEXIBILITY; +RELIABILITY; POWER CONDITIONS; MECHANICAL EFFICIENCY; CAPITAL OUTLAY. +SYSTEMS OF DRAINAGE,--STEAM PUMPS, COMPRESSED-AIR PUMPS, ELECTRICAL +PUMPS, ROD-DRIVEN PUMPS, BAILING; COMPARATIVE VALUE OF VARIOUS +SYSTEMS. + +With the exception of drainage tunnels--more fully described in +Chapter VIII--all drainage must be mechanical. As the bulk of mine +water usually lies near the surface, saving in pumping can sometimes +be effected by leaving a complete pillar of ore under some of the +upper levels. In many deposits, however, the ore has too many channels +to render this of much avail. + +There are six factors which enter into a determination of mechanical +drainage systems for metal mines:-- + + 1. Volume and head of water. + 2. Flexibility to fluctuation in volume and head. + 3. Reliability. + 4. Capital cost. + 5. The general power conditions. + 6. Mechanical efficiency. + +In the drainage appliances, more than in any other feature of the +equipment, must mechanical efficiency be subordinated to the other +issues. + +FLEXIBILITY.--Flexibility in plant is necessary because volume and +head of water are fluctuating factors. In wet regions the volume +of water usually increases for a certain distance with the extension +of openings in depth. In dry climates it generally decreases with the +downward extension of the workings after a certain depth. Moreover, +as depth progresses, the water follows the openings more or less +and must be pumped against an ever greater head. In most cases +the volume varies with the seasons. What increase will occur, from +what horizon it must be lifted, and what the fluctuations in volume +are likely to be, are all unknown at the time of installation. If +a pumping system were to be laid out for a new mine, which would +peradventure meet every possible contingency, the capital outlay would +be enormous, and the operating efficiency would be very low during +the long period in which it would be working below its capacity. The +question of flexibility does not arise so prominently in coal-mines, +for the more or less flat deposits give a fixed factor of depth. +The flow is also more steady, and the volume can be in a measure +approximated from general experience. + +RELIABILITY.--The factor of reliability was at one time of more +importance than in these days of high-class manufacture of many +different pumping systems. Practically speaking, the only insurance +from flooding in any event lies in the provision of a relief system +of some sort,--duplicate pumps, or the simplest and most usual +thing, bailing tanks. Only Cornish and compressed-air pumps will +work with any security when drowned, and electrical pumps are easily +ruined. + +GENERAL POWER CONDITIONS.--The question of pumping installation +is much dependent upon the power installation and other power +requirements of the mine. For instance, where electrical power is +purchased or generated by water-power, then electrical pumps have +every advantage. Or where a large number of subsidiary motors can be +economically driven from one central steam- or gas-driven electrical +generation plant, they again have a strong call,--especially if +the amount of water to be handled is moderate. Where the water +is of limited volume and compressed-air plant a necessity for the +mine, then air-driven pumps may be the most advantageous, etc. + +MECHANICAL EFFICIENCY.--The mechanical efficiency of drainage machinery +is very largely a question of method of power application. The +actual pump can be built to almost the same efficiency for any +power application, and with the exception of the limited field +of bailing with tanks, mechanical drainage is a matter of pumps. +All pumps must be set below their load, barring a few possible +feet of suction lift, and they are therefore perforce underground, +and in consequence all power must be transmitted from the surface. +Transmission itself means loss of power varying from 10 to 60%, +depending upon the medium used. It is therefore the choice of +transmission medium that largely governs the mechanical efficiency. + +SYSTEMS OF DRAINAGE.--The ideal pumping system for metal mines +would be one which could be built in units and could be expanded +or contracted unit by unit with the fluctuation in volume; which +could also be easily moved to meet the differences of lifts; and +in which each independent unit could be of the highest mechanical +efficiency and would require but little space for erection. Such +an ideal is unobtainable among any of the appliances with which +the writer is familiar. + +The wide variations in the origin of power, in the form of transmission, +and in the method of final application, and the many combinations +of these factors, meet the demands for flexibility, efficiency, +capital cost, and reliability in various degrees depending upon +the environment of the mine. Power nowadays is generated primarily +with steam, water, and gas. These origins admit the transmission of +power to the pumps by direct steam, compressed air, electricity, +rods, or hydraulic columns. + +DIRECT STEAM-PUMPS.--Direct steam has the disadvantage of radiated +heat in the workings, of loss by the radiation, and, worse still, +of the impracticability of placing and operating a highly efficient +steam-engine underground. It is all but impossible to derive benefit +from the vacuum, as any form of surface condenser here is impossible, +and there can be no return of the hot soft water to the boilers. + +Steam-pumps fall into two classes, rotary and direct-acting; the former +have the great advantage of permitting the use of steam expansively +and affording some field for effective use of condensation, but +they are more costly, require much room, and are not fool-proof. +The direct-acting pumps have all the advantage of compactness and +the disadvantage of being the most inefficient of pumping machines +used in mining. Taking the steam consumption of a good surface +steam plant at 15 pounds per horse-power hour, the efficiency of +rotary pumps with well-insulated pipes is probably not over 50%, +and of direct-acting pumps from 40% down to 10%. + +The advantage of all steam-pumps lies in the low capital outlay,--hence +their convenient application to experimental mining and temporary +pumping requirements. For final equipment they afford a great deal +of flexibility, for if properly constructed they can be, with slight +alteration, moved from one horizon to another without loss of relative +efficiency. Thus the system can be rearranged for an increased +volume of water, by decreasing the lift and increasing the number +of pumps from different horizons. + +COMPRESSED-AIR PUMPS.--Compressed-air transmission has an application +similar to direct steam, but it is of still lower mechanical efficiency, +because of the great loss in compression. It has the superiority +of not heating the workings, and there is no difficulty as to the +disposal of the exhaust, as with steam. Moreover, such pumps will +work when drowned. Compressed air has a distinct place for minor +pumping units, especially those removed from the shaft, for they +can be run as an adjunct to the air-drill system of the mine, and +by this arrangement much capital outlay may be saved. The cost of +the extra power consumed by such an arrangement is less than the +average cost of compressed-air power, because many of the compressor +charges have to be paid anyway. When compressed air is water-generated, +they have a field for permanent installations. The efficiency of +even rotary air-driven pumps, based on power delivered into a good +compressor, is probably not over 25%. + +ELECTRICAL PUMPS.--Electrical pumps have somewhat less flexibility +than steam- or air-driven apparatus, in that the speed of the pumps can +be varied only within small limits. They have the same great advantage +in the easy reorganization of the system to altered conditions of +water-flow. Electricity, when steam-generated, has the handicap +of the losses of two conversions, the actual pump efficiency being +about 60% in well-constructed plants; the efficiency is therefore +greater than direct steam or compressed air. Where the mine is +operated with water-power, purchased electric current, or where +there is an installation of electrical generating plant by steam or +gas for other purposes, electrically driven pumps take precedence +over all others on account of their combined moderate capital outlay, +great flexibility, and reasonable efficiency. + +In late years, direct-coupled, electric-driven centrifugal pumps +have entered the mining field, but their efficiency, despite makers' +claims, is low. While they show comparatively good results on low +lifts the slip increases with the lift. In heads over 200 feet +their efficiency is probably not 30% of the power delivered to the +electrical generator. Their chief attractions are small capital +cost and the compact size which admits of easy installation. + +ROD-DRIVEN PUMPS.--Pumps of the Cornish type in vertical shafts, +if operated to full load and if driven by modern engines, have +an efficiency much higher than any other sort of installation, +and records of 85 to 90% are not unusual. The highest efficiency +in these pumps yet obtained has been by driving the pump with rope +transmission from a high-speed triple expansion engine, and in +this plant an actual consumption of only 17 pounds of steam per +horse-power hour for actual water lifted has been accomplished. + +To provide, however, for increase of flow and change of horizon, +rod-driven pumps must be so overpowered at the earlier stage of +the mine that they operate with great loss. Of all pumping systems +they are the most expensive to provide. They have no place in crooked +openings and only work in inclines with many disadvantages. + +In general their lack of flexibility is fast putting them out of +the metal miner's purview. Where the pumping depth and volume of +water are approximately known, as is often the case in coal mines, +this, the father of all pumps, still holds its own. + +HYDRAULIC PUMPS.--Hydraulic pumps, in which a column of water is +used as the transmission fluid from a surface pump to a corresponding +pump underground has had some adoption in coal mines, but little +in metal mines. They have a certain amount of flexibility but low +efficiency, and are not likely to have much field against electrical +pumps. + +BAILING.--Bailing deserves to be mentioned among drainage methods, +for under certain conditions it is a most useful system, and at +all times a mine should be equipped with tanks against accident +to the pumps. Where the amount of water is limited,--up to, say, +50,000 gallons daily,--and where the ore output of the mine permits +the use of the winding-engine for part of the time on water haulage, +there is in the method an almost total saving of capital outlay. +Inasmuch as the winding-engine, even when the ore haulage is finished +for the day, must be under steam for handling men in emergencies, +and as the labor of stokers, engine-drivers, shaft-men, etc., is +therefore necessary, the cost of power consumed by bailing is not +great, despite the low efficiency of winding-engines. + +COMPARISON OF VARIOUS SYSTEMS.--If it is assumed that flexibility, +reliability, mechanical efficiency, and capital cost can each be +divided into four figures of relative importance,--_A_, _B_, _C_, +and _D_, with _A_ representing the most desirable result,--it is +possible to indicate roughly the comparative values of various +pumping systems. It is not pretended that the four degrees are of +equal import. In all cases the factor of general power conditions +on the mine may alter the relative positions. + +==================================================================== + |Direct|Compressed| |Steam-| | + |Steam | Air |Electricity|Driven|Hydraulic|Bailing + |Pumps | | | Rods | Columns | Tanks +-------------|------|----------|-----------|------|---------|------- +Flexibility. | _A_ | _A_ | _B_ | _D_ | _B_ | _A_ +Reliability. | _B_ | _B_ | _B_ | _A_ | _D_ | _A_ +Mechanical | | | | | | + Efficiency.| _C_ | _D_ | _B_ | _A_ | _C_ | _D_ +Capital Cost | _A_ | _B_ | _B_ | _D_ | _D_ | -- +==================================================================== + +As each mine has its special environment, it is impossible to formulate +any final conclusion on a subject so involved. The attempt would lead +to a discussion of a thousand supposititious cases and hypothetical +remedies. Further, the description alone of pumping machines would +fill volumes, and the subject will never be exhausted. The engineer +confronted with pumping problems must marshal all the alternatives, +count his money, and apply the tests of flexibility, reliability, +efficiency, and cost, choose the system of least disadvantages, +and finally deprecate the whole affair, for it is but a parasite +growth on the mine. + + + + +CHAPTER XIV. + +Mechanical Equipment (_Concluded_). + +MACHINE DRILLING: POWER TRANSMISSION; COMPRESSED AIR _VS_. ELECTRICITY; +AIR DRILLS; MACHINE _VS_. HAND DRILLING. WORK-SHOPS. IMPROVEMENT +IN EQUIPMENT. + +For over two hundred years from the introduction of drill-holes +for blasting by Caspar Weindel in Hungary, to the invention of +the first practicable steam percussion drill by J. J. Crouch of +Philadelphia, in 1849, all drilling was done by hand. Since Crouch's +time a host of mechanical drills to be actuated by all sorts of +power have come forward, and even yet the machine-drill has not +reached a stage of development where it can displace hand-work +under all conditions. Steam-power was never adapted to underground +work, and a serviceable drill for this purpose was not found until +compressed air for transmission was demonstrated by Dommeiller +on the Mt. Cenis tunnel in 1861. + +The ideal requirements for a drill combine:-- + + a. Power transmission adapted to underground conditions. + b. Lightness. + c. Simplicity of construction. + d. Strength. + e. Rapidity and strength of blow. + f. Ease of erection. + g. Reliability. + h. Mechanical efficiency. + i. Low capital cost. + +No drill invented yet fills all these requirements, and all are +a compromise on some point. + +POWER TRANSMISSION; COMPRESSED AIR _vs_. ELECTRICITY.--The only +transmissions adapted to underground drill-work are compressed +air and electricity, and as yet an electric-driven drill has not +been produced which meets as many of the requirements of the metal +miner as do compressed-air drills. The latter, up to date, have +superiority in simplicity, lightness, ease of erection, reliability, +and strength over electric machines. Air has another advantage in +that it affords some assistance to ventilation, but it has the +disadvantage of remarkably low mechanical efficiency. The actual +work performed by the standard 3-3/4-inch air-drill probably does +not amount to over two or three horse-power against from fifteen to +eighteen horse-power delivered into the compressor, or mechanical +efficiency of less than 25%. As electrical power can be delivered to +the drill with much less loss than compressed air, the field for a +more economical drill on this line is wide enough to create eventually +the proper tool to apply it. The most satisfactory electric drill +produced has been the Temple drill, which is really an air-drill +driven by a small electrically-driven compressor placed near the +drill itself. But even this has considerable deficiencies in mining +work; the difficulties of setting up, especially for stoping work, +and the more cumbersome apparatus to remove before blasting are +serious drawbacks. It has deficiencies in reliability and greater +complication of machinery than direct air. + +AIR-COMPRESSION.--The method of air-compression so long accomplished +only by power-driven pistons has now an alternative in some situations +by the use of falling water. This latter system is a development +of the last twelve years, and, due to the low initial outlay and +extremely low operating costs, bids fair in those regions where +water head is available not only to displace the machine compressor, +but also to extend the application of compressed air to mine motors +generally, and to stay in some environments the encroachment of +electricity into the compressed-air field. Installations of this +sort in the West Kootenay, B.C., and at the Victoria copper mine, +Michigan, are giving results worthy of careful attention. + +Mechanical air-compressors are steam-, water-, electrical-, and +gas-driven, the alternative obviously depending on the source and +cost of power. Electrical- and gas- and water-driven compressors +work under the disadvantage of constant speed motors and respond +little to the variation in load, a partial remedy for which lies +in enlarged air-storage capacity. Inasmuch as compressed air, so +far as our knowledge goes at present, must be provided for drills, +it forms a convenient transmission of power to various motors +underground, such as small pumps, winches, or locomotives. As stated +in discussing those machines, it is not primarily a transmission +of even moderate mechanical efficiency for such purposes; but as +against the installation and operation of independent transmission, +such as steam or electricity, the economic advantage often compensates +the technical losses. Where such motors are fixed, as in pumps +and winches, a considerable gain in efficiency can be obtained by +reheating. + +It is not proposed to enter a discussion of mechanical details of +air-compression, more than to call attention to the most common +delinquency in the installation of such plants. This deficiency +lies in insufficient compression capacity for the needs of the +mine and consequent effective operation of drills, for with under +75 pounds pressure the drills decrease remarkably in rapidity of +stroke and force of the blow. The consequent decrease in actual +accomplishment is far beyond the ratio that might be expected on +the basis of mere difference of pressure. Another form of the same +chronic ill lies in insufficient air-storage capacity to provide +for maintenance of pressure against moments when all drills or +motors in the mine synchronize in heavy demand for air, and thus +lower the pressure at certain periods. + +AIR-DRILLS.--Air-drills are from a mechanical point of view broadly +of two types,--the first, in which the drill is the piston extension; +and the second, a more recent development for mining work, in which +the piston acts as a hammer striking the head of the drill. From an +economic point of view drills may be divided into three classes. +First, heavy drills, weighing from 150 to 400 pounds, which require +two men for their operation; second, "baby" drills of the piston type, +weighing from 110 to 150 pounds, requiring one man with occasional +assistance in setting up; and third, very light drills almost wholly +of the hammer type. This type is built in two forms: a heavier +type for mounting on columns, weighing about 80 pounds; and a type +after the order of the pneumatic riveter, weighing as low as 20 +pounds and worked without mounting. + +The weight and consequent mobility of a drill, aside from labor +questions, have a marked effect on costs, for the lighter the drill +the less difficulty and delay in erection, and consequent less +loss of time and less tendency to drill holes from one radius, +regardless of pointing to take best advantage of breaking planes. +Moreover, smaller diameter and shorter holes consume less explosives +per foot advanced or per ton broken. The best results in tonnage +broken and explosive consumed, if measured by the foot of drill-hole +necessary, can be accomplished from hand-drilling and the lighter +the machine drill, assuming equal reliability, the nearer it +approximates these advantages. + +The blow, and therefore size and depth of hole and rapidity of +drilling, are somewhat dependent upon the size of cylinders and +length of stroke, and therefore the heavier types are better adapted +to hard ground and to the deep holes of some development points. +Their advantages over the other classes lie chiefly in this ability +to bore exceedingly hard material and in the greater speed of advance +possible in development work; but except for these two special +purposes they are not as economical per foot advanced or per ton +of ore broken as the lighter drills. + +The second class, where men can be induced to work them one man per +drill, saves in labor and gains in mobility. Many tests show great +economy of the "baby" type of piston drills in average ground over +the heavier machines for stoping and for most lateral development. +All piston types are somewhat cumbersome and the heavier types +require at least four feet of head room. The "baby" type can be +operated in less space than this, but for narrow stopes they do +not lend themselves with the same facility as the third class. + +The third class of drills is still in process of development, but +it bids fair to displace much of the occupation of the piston types +of drill. Aside from being a one-man drill, by its mobility it +will apparently largely reproduce the advantage of hand-drilling +in ability to place short holes from the most advantageous angles +and for use in narrow places. As compared with other drills it +bids fair to require less time for setting up and removal and for +change of bits; to destroy less steel by breakages; to dull the +bits less rapidly per foot of hole; to be more economical of power; +to require much less skill in operation, for judgment is less called +upon in delivering speed; and to evade difficulties of fissured +ground, etc. And finally the cost is only one-half, initially and +for spares. Its disadvantage so far is a lack of reliability due to +lightness of construction, but this is very rapidly being overcome. +This type, however, is limited in depth of hole possible, for, +from lack of positive reverse movement, there is a tendency for +the spoil to pack around the bit, and as a result about four feet +seems the limit. + +The performance of a machine-drill under show conditions may be +anything up to ten or twelve feet of hole per hour on rock such +as compact granite; but in underground work a large proportion of +the time is lost in picking down loose ore, setting up machines, +removal for blasting, clearing away spoil, making adjustments, +etc. The amount of lost time is often dependent upon the width of +stope or shaft and the method of stoping. Situations which require +long drill columns or special scaffolds greatly accentuate the loss +of time. Further, the difficulties in setting up reflect indirectly +on efficiency to a greater extent in that a larger proportion of +holes are drilled from one radius and thus less adapted to the +best breaking results than where the drill can easily be reset from +various angles. + +The usual duty of a heavy drill per eight-hour shift using two men +is from 20 to 40 feet of hole, depending upon the rock, facilities +for setting up, etc., etc.[*] The lighter drills have a less average +duty, averaging from 15 to 25 feet per shift. + +[Footnote *: Over the year 1907 in twenty-eight mines compiled +from Alaska to Australia, an average of 23.5 feet was drilled per +eight-hour shift by machines larger than three-inch cylinder.] + +MACHINE _vs_. HAND-DRILLING.--The advantages of hand-drilling over +machine-drilling lie, first, in the total saving of power, the +absence of capital cost, repairs, depreciation, etc., on power, +compresser and drill plant; second, the time required for setting +up machine-drills does not warrant frequent blasts, so that a number +of holes on one radius are a necessity, and therefore machine-holes +generally cannot be pointed to such advantage as hand-holes. Hand-holes +can be set to any angle, and by thus frequent blasting yield greater +tonnage per foot of hole. Third, a large number of comparative +statistics from American, South African, and Australian mines show +a saving of about 25% in explosives for the same tonnage or foot +of advance by hand-holes over medium and heavy drill-holes. + +The duty of a skilled white man, single-handed, in rock such as +is usually met below the zone of oxidation, is from 5 to 7 feet +per shift, depending on the rock and the man. Two men hand-drilling +will therefore do from 1/4 to 2/3 of the same footage of holes +that can be done by two men with a heavy machine-drill, and two +men hand-drilling will do from 1/5 to 1/2 the footage of two men +with two light drills. + +The saving in labor of from 75 to 33% by machine-drilling may or +may not be made up by the other costs involved in machine-work. +The comparative value of machine- and hand-drilling is not subject +to sweeping generalization. A large amount of data from various +parts of the world, with skilled white men, shows machine-work +to cost from half as much per ton or foot advanced as hand-work +to 25% more than handwork, depending on the situation, type of +drill, etc. In a general way hand-work can more nearly compete +with heavy machines than light ones. The situations where hand-work +can compete with even light machines are in very narrow stopes where +drills cannot be pointed to advantage, and where the increased +working space necessary for machine drills results in breaking more +waste. Further, hand-drilling can often compete with machine-work +in wide stopes where long columns or platforms must be used and +therefore there is much delay in taking down, reerection, etc. + +Many other factors enter into a comparison, however, for +machine-drilling produces a greater number of deeper holes and +permits larger blasts and therefore more rapid progress. In driving +levels under average conditions monthly footage is from two to +three times as great with heavy machines as by hand-drilling, and +by lighter machines a somewhat less proportion of greater speed. +The greater speed obtained in development work, the greater tonnage +obtained per man in stoping, with consequent reduction in the number +of men employed, and in reduction of superintendence and general +charges are indirect advantages for machine-drilling not to be +overlooked. + +The results obtained in South Africa by hand-drilling in shafts, +and its very general adoption there, seem to indicate that better +speed and more economical work can be obtained in that way in very +large shafts than by machine-drilling. How far special reasons +there apply to smaller shafts or labor conditions elsewhere have +yet to be demonstrated. In large-dimension shafts demanding a large +number of machines, the handling of long machine bars and machines +generally results in a great loss of time. The large charges in +deep holes break the walls very irregularly; misfires cause more +delay; timbering is more difficult in the face of heavy blasting +charges; and the larger amount of spoil broken at one time delays +renewed drilling, and altogether the advantages seem to lie with +hand-drilling in shafts of large horizontal section. + +The rapid development of special drills for particular conditions +has eliminated the advantage of hand-work in many situations during +the past ten years, and the invention of the hammer type of drill +bids fair to render hand-drilling a thing of the past. One +generalization is possible, and that is, if drills are run on 40-50 +pounds' pressure they are no economy over hand-drilling. + +WORKSHOPS. + +In addition to the ordinary blacksmithy, which is a necessity, +the modern tendency has been to elaborate the shops on mines to +cover machine-work, pattern-making and foundry-work, in order that +delays may be minimized by quick repairs. To provide, however, +for such contingencies a staff of men must be kept larger than +the demand of average requirements. The result is an effort to +provide jobs or to do work extravagantly or unnecessarily well. +In general, it is an easy spot for fungi to start growing on the +administration, and if custom repair shops are available at all, +mine shops can be easily overdone. + +A number of machines are now in use for sharpening drills. +Machine-sharpening is much cheaper than hand-work, although the drills +thus sharpened are rather less efficient owing to the difficulty of +tempering them to the same nicety; however, the net results are +in favor of the machines. + +IMPROVEMENT IN EQUIPMENT. + +Not only is every mine a progressive industry until the bottom +gives out, but the technology of the industry is always progressing, +so that the manager is almost daily confronted with improvements +which could be made in his equipment that would result in decreasing +expenses or increasing metal recovery. There is one test to the +advisability of such alterations: How long will it take to recover +the capital outlay from the savings effected? and over and above +this recovery of capital there must be some very considerable gain. +The life of mines is at least secured over the period exposed in +the ore-reserves, and if the proposed alteration will show its +recovery and profit in that period, then it is certainly justified. +If it takes longer than this on the average speculative ore-deposit, +it is a gamble on finding further ore. As a matter of practical +policy it will be found that an improvement in equipment which +requires more than three or four years to redeem itself out of +saving, is usually a mechanical or metallurgical refinement the +indulgence in which is very doubtful. + + + + +CHAPTER XV. + +Ratio of Output to the Mine. + +DETERMINATION OF THE POSSIBLE MAXIMUM; LIMITING FACTORS; COST OF +EQUIPMENT; LIFE OF THE MINE; MECHANICAL INEFFICIENCY OF PATCHWORK +PLANT; OVERPRODUCTION OF BASE METAL; SECURITY OF INVESTMENT. + +The output obtainable from a given mine is obviously dependent +not only on the size of the deposit, but also on the equipment +provided,--in which equipment means the whole working appliances, +surface and underground. + +A rough and ready idea of output possibilities of inclined deposits +can be secured by calculating the tonnage available per foot of +depth from the horizontal cross-section of the ore-bodies exposed +and assuming an annual depth of exhaustion, or in horizontal deposits +from an assumption of a given area of exhaustion. Few mines, at the +time of initial equipment, are developed to an extent from which +their possibilities in production are evident, for wise finance +usually leads to the erection of some equipment and production before +development has been advanced to a point that warrants a large or +final installation. Moreover, even were the full possibilities of +the mine known, the limitations of finance usually necessitate a +less plant to start with than is finally contemplated. Therefore +output and equipment are usually growing possibilities during the +early life of a mine. + +There is no better instance in mine engineering where pure theory +must give way to practical necessities of finance than in the +determination of the size of equipment and therefore output. Moreover, +where finance even is no obstruction, there are other limitations +of a very practical order which must dominate the question of the +size of plant giving the greatest technical economy. It is, however, +useful to state the theoretical considerations in determining the +ultimate volume of output and therefore the size of equipments, +for the theory will serve to illuminate the practical limitations. +The discussion will also again demonstrate that all engineering +is a series of compromises with natural and economic forces. + +OUTPUT GIVING LEAST PRODUCTION COST.--As one of the most important +objectives is to work the ore at the least cost per ton, it is +not difficult to demonstrate that the minimum working costs can +be obtained only by the most intensive production. To prove this, +it need only be remembered that the working expenses of a mine +are of two sorts: one is a factor of the tonnage handled, such as +stoping and ore-dressing; the other is wholly or partially dependent +upon time. A large number of items are of this last order. Pumping +and head-office expenses are almost entirely charges independent +of the tonnage handled. Superintendence and staff salaries and +the like are in a large proportion dependent upon time. Many other +elements of expense, such as the number of engine-drivers, etc., do +not increase proportionately to increase in tonnage. These charges, +or the part of them dependent upon time apart from tonnage, may be +termed the "fixed charges." + +There is another fixed charge more obscure yet no less certain. +Ore standing in a mine is like money in a bank drawing no interest, +and this item of interest may be considered a "fixed charge," for +if the ore were realized earlier, this loss could be partially +saved. This subject is further referred to under "Amortization." + +If, therefore, the time required to exhaust the mine be prolonged +by the failure to maintain the maximum output, the total cost of +working it will be greater by the fixed charges over such an increased +period. Conversely, by equipping on a larger scale, the mine will +be exhausted more quickly, a saving in total cost can be made, and +the ultimate profit can be increased by an amount corresponding +to the time saved from the ravages of fixed charges. In fine, the +working costs may be reduced by larger operations, and therefore +the value of the mine increased. + +The problem in practice usually takes the form of the relative +superiority of more or of fewer units of plant, and it can be considered +in more detail if the production be supposed to consist of units +averaging say 100 tons per day each. The advantage of more units +over less will be that the extra ones can be produced free of fixed +charges, for these are an expense already involved in the lesser +units. This extra production will also enjoy the interest which +can be earned over the period of its earlier production. Moreover, +operations on a larger scale result in various minor economies +throughout the whole production, not entirely included in the type +of expenditure mentioned as "fixed charges." We may call these +various advantages the "saving of fixed charges" due to larger-scale +operations. The saving of fixed charges amounts to very considerable +sums. In general the items of working cost alone, mentioned above, +which do not increase proportionately to the tonnage, aggregate +from 10 to 25% of the total costs. Where much pumping is involved, +the percentage will become even greater. + +The question of the value of the mine as affected by the volume +of output becomes very prominent in low-grade mines, where, if +equipped for output on too small a scale, no profits at all could +be earned, and a sufficient production is absolutely imperative +for any gain. There are many mines in every country which with +one-third of their present rate of production would lose money. +That is, the fixed charges, if spread over small output, would be +so great per ton that the profit would be extinguished by them. + +In the theoretical view, therefore, it would appear clear that +the greatest ultimate profit from a mine can be secured only by +ore extraction under the highest pressure. As a corollary to this +it follows that development must proceed with the maximum speed. +Further, it follows that the present value of a mine is at least +partially a factor of the volume of output contemplated. + +FACTORS LIMITING THE OUTPUT. + +Although the above argument can be academically defended, there +are, as said at the start, practical limitations to the maximum +intensity of production, arising out of many other considerations +to which weight must be given. In the main, there are five principal +limitations:-- + + 1. Cost of equipment. + 2. Life of the mine. + 3. Mechanical inefficiency of patchwork plant. + 4. Overproduction of base metal. + 5. Security of investment. + +COST OF EQUIPMENT.--The "saving of fixed charges" can only be obtained +by larger equipment, which represents an investment. Mining works, +shafts, machinery, treatment plants, and all the paraphernalia cost +large sums of money. They become either worn out or practically +valueless through the exhaustion of the mines. Even surface machinery +when in good condition will seldom realize more than one-tenth of its +expense if useless at its original site. All mines are ephemeral; +therefore virtually the entire capital outlay of such works must +be redeemed during the life of the mine, and the interest on it +must also be recovered. + +The certain life, with the exception of banket and a few other +types of deposit, is that shown by the ore in sight, plus something +for extension of the deposit beyond exposures. So, against the +"savings" to be made, must be set the cost of obtaining them, for +obviously it is of no use investing a dollar to save a total of +ninety cents. The economies by increased production are, however, +of such an important character that the cost of almost any number +of added units (within the ability of the mine to supply them) +can be redeemed from these savings in a few years. For instance, +in a Californian gold mine where the working expenses are $3 and +the fixed charges are at the low rate of 30 cents per ton, one +unit of increased production would show a saving of over $10,000 +per annum from the saving of fixed charges. In about three years +this sum would repay the cost of the additional treatment equipment. +If further shaft capacity were required, the period would be much +extended. On a Western copper mine, where the costs are $8 and the +fixed charges are 80 cents per ton, one unit of increased production +would effect a saving of the fixed charges equal to the cost of +the extra unit in about three years. That is, the total sum would +amount to $80,000, or enough to provide almost any type of mechanical +equipment for such additional tonnage. + +The first result of vigorous development is to increase the ore in +sight,--the visible life of the mine. When such visible life has +been so lengthened that the period in which the "saving of fixed +charges" will equal the amount involved in expansion of equipment, +then from the standpoint of this limitation only is the added +installation justified. The equipment if expanded on this practice +will grow upon the heels of rapid development until the maximum +production from the mine is reached, and a kind of equilibrium +establishes itself. + +Conversely, this argument leads to the conclusion that, regardless +of other considerations, an equipment, and therefore output, should +not be expanded beyond the redemption by way of "saving from fixed +charges" of the visible or certain life of the mine. In those mines, +such as at the Witwatersrand, where there is a fairly sound assurance +of definite life, it is possible to calculate at once the size of +plant which by saving of "fixed charges" will be eventually the +most economical, but even here the other limitations step in to +vitiate such policy of management,--chiefly the limitation through +security of investment. + +LIFE OF THE MINE.--If carried to its logical extreme, the above +program means a most rapid exhaustion of the mine. The maximum output +will depend eventually upon the rapidity with which development +work may be extended. As levels and other subsidiary development +openings can be prepared in inclined deposits much more quickly +than the shaft can be sunk, the critical point is the shaft-sinking. +As a shaft may by exertion be deepened at least 400 feet a year on +a going mine, the provision of an equipment to eat up the ore-body +at this rate of sinking means very early exhaustion indeed. In +fact, had such a theory of production been put into practice by +our forefathers, the mining profession might find difficulty in +obtaining employment to-day. Such rapid exhaustion would mean a +depletion of the mineral resources of the state at a pace which +would be alarming. + +MECHANICAL INEFFICIENCY OF PATCHWORK PLANT.--Mine equipments on +speculative mines (the vast majority) are often enough patchwork, +for they usually grow from small beginnings; but any scheme of +expansion based upon the above doctrine would need to be modified +to the extent that additions could be in units large in ratio to +previous installations, or their patchwork character would be still +further accentuated. It would be impossible to maintain mechanical +efficiency under detail expansion. + +OVERPRODUCTION OF BASE METAL.--Were this intensity of production of +general application to base metal mines it would flood the markets, +and, by an overproduction of metal depress prices to a point where +the advantages of such large-scale operations would quickly vanish. +The theoretical solution in this situation would be, if metals +fell below normal prices, let the output be reduced, or let the +products be stored until the price recovers. From a practical point +of view either alternative is a policy difficult to face. + +In the first case, reduction of output means an increase of working +expenses by the spread of fixed charges over less tonnage, and +this in the face of reduced metal prices. It may be contended, +however, that a falling metal market is usually the accompaniment +of a drop in all commodities, wherefore working costs can be reduced +somewhat in such times of depression, thereby partially compensating +the other elements making for increased costs. Falls in commodities +are also the accompaniment of hard times. Consideration of one's +workpeople and the wholesale slaughter of dividends to the then +needy stockholders, resulting from a policy of reduced production, +are usually sufficient deterrents to diminished output. + +The second alternative, that of storing metal, means equally a +loss of dividends by the investment of a large sum in unrealized +products, and the interest on this sum. The detriment to the market +of large amounts of unsold metal renders such a course not without +further disadvantages. + +SECURITY OF INVESTMENT.--Another point of view antagonistic to +such wholesale intensity of production, and one worthy of careful +consideration, is that of the investor in mines. The root-value of +mining stocks is, or should be, the profit in sight. If the policy +of greatest economy in production costs be followed as outlined +above, the economic limit of ore-reserves gives an apparently very +short life, for the ore in sight will never represent a life beyond +the time required to justify more plant. Thus the "economic limit +of ore in reserve" will be a store equivalencing a period during +which additional equipment can be redeemed from the "saving of +fixed charges," or three or four years, usually. + +The investor has the right to say that he wants the guarantee of +longer life to his investment,--he will in effect pay insurance for +it by a loss of some ultimate profit. That this view, contradictory +to the economics of the case, is not simply academic, can be observed +by any one who studies what mines are in best repute on any stock +exchange. All engineers must wish to have the industry under them +in high repute. The writer knows of several mines paying 20% on +their stocks which yet stand lower in price on account of short +ore-reserves than mines paying less annual returns. The speculator, +who is an element not to be wholly disregarded, wishes a rise in +his mining stock, and if development proceeds at a pace in advance +of production, he will gain a legitimate rise through the increase +in ore-reserves. + +The investor's and speculator's idea of the desirability of a proved +long life readily supports the technical policy of high-pressure +development work, but not of expansion of production, for they +desire an increasing ore-reserve. Even the metal operator who is +afraid of overproduction does not object to increased ore-reserves. +On the point of maximum intensity of development work in a mine all +views coincide. The mining engineer, if he takes a Machiavellian +view, must agree with the investor and the metal dealer, for the +engineer is a "fixed charge" the continuance of which is important +to his daily needs. + +The net result of all these limitations is therefore an invariable +compromise upon some output below the possible maximum. The initial +output to be contemplated is obviously one upon which the working +costs will be low enough to show a margin of profit. The medium +between these two extremes is determinable by a consideration of +the limitations set out,--and the cash available. When the volume +of output is once determined, it must be considered as a factor +in valuation, as discussed under "Amortization." + + + + +CHAPTER XVI. + +Administration. + +LABOR EFFICIENCY; SKILL; INTELLIGENCE; APPLICATION COORDINATION; +CONTRACT WORK; LABOR UNIONS; REAL BASIS OF WAGES. + +The realization from a mine of the profits estimated from the other +factors in the case is in the end dependent upon the management. +Good mine management is based upon three elementals: first, sound +engineering; second, proper coordination and efficiency of every human +unit; third, economy in the purchase and consumption of supplies. + +The previous chapters have been devoted to a more or less extended +exposition of economic engineering. While the second and third +requirements are equally important, they range in many ways out of +the engineering and into the human field. For this latter reason +no complete manual will ever be published upon "How to become a +Good Mine Manager." + +It is purposed, however, to analyze some features of these second +and third fundamentals, especially in their interdependent phases, +and next to consider the subject of mine statistics, for the latter +are truly the microscopes through which the competence of the +administration must be examined. + +The human units in mine organization can be divided into officers +and men. The choice of mine officers is the assembling of specialized +brains. Their control, stimulation, and inspiration is the main work +of the administrative head. Success in the selection and control of +staff is the index of executive ability. There are no mathematical, +mechanical, or chemical formulas for dealing with the human mind +or human energies. + +LABOR.--The whole question of handling labor can be reduced to +the one term "efficiency." Not only does the actual labor outlay +represent from 60 to 70% of the total underground expenses, but +the capacity or incapacity of its units is responsible for wider +fluctuations in production costs than the bare predominance in +expenditure might indicate. The remaining expense is for supplies, +such as dynamite, timber, steel, power, etc., and the economical +application of these materials by the workman has the widest bearing +upon their consumption. + +Efficiency of the mass is the resultant of that of each individual +under a direction which coordinates effectively all units. The +lack of effectiveness in one individual diminishes the returns +not simply from that man alone; it lowers the results from numbers +of men associated with the weak member through the delaying and +clogging of their work, and of the machines operated by them. +Coordination of work is a necessary factor of final efficiency. This +is a matter of organization and administration. The most zealous +stoping-gang in the world if associated with half the proper number +of truckers must fail to get the desired result. + +Efficiency in the single man is the product of three factors,--skill, +intelligence, and application. A great proportion of underground +work in a mine is of a type which can be performed after a fashion +by absolutely unskilled and even unintelligent men, as witness the +breaking-in of savages of low average mentality, like the South +African Kaffirs. Although most duties can be performed by this +crudest order of labor, skill and intelligence can be applied to +it with such economic results as to compensate for the difference +in wage. The reason for this is that the last fifty years have seen +a substitution of labor-saving machines for muscle. Such machines +displace hundreds of raw laborers. Not only do they initially cost +large sums, but they require large expenditure for power and up-keep. +These fixed charges against the machine demand that it shall be +worked at its maximum. For interest, power, and up-keep go on in +any event, and the saving on crude labor displaced is not so great +but that it quickly disappears if the machine is run under its +capacity. To get its greatest efficiency, a high degree of skill +and intelligence is required. Nor are skill and intelligence alone +applicable to labor-saving devices themselves, because drilling and +blasting rock and executing other works underground are matters +in which experience and judgment in the individual workman count +to the highest degree. + +How far skill affects production costs has had a thorough demonstration +in West Australia. For a time after the opening of those mines +only a small proportion of experienced men were obtainable. During +this period the rock broken per man employed underground did not +exceed the rate of 300 tons a year. In the large mines it has now, +after some eight years, attained 600 to 700 tons. + +How far intelligence is a factor indispensable to skill can be well +illustrated by a comparison of the results obtained from working +labor of a low mental order, such as Asiatics and negroes, with those +achieved by American or Australian miners. In a general way, it may +be stated with confidence that the white miners above mentioned +can, under the same physical conditions, and with from five to ten +times the wage, produce the same economic result,--that is, an +equal or lower cost per unit of production. Much observation and +experience in working Asiatics and negroes as well as Americans +and Australians in mines, leads the writer to the conclusion that, +averaging actual results, one white man equals from two to three +of the colored races, even in the simplest forms of mine work such +as shoveling or tramming. In the most highly skilled branches, +such as mechanics, the average ratio is as one to seven, or in +extreme cases even eleven. The question is not entirely a comparison +of bare efficiency individually; it is one of the sum total of +results. In mining work the lower races require a greatly increased +amount of direction, and this excess of supervisors consists of +men not in themselves directly productive. There is always, too, +a waste of supplies, more accidents, and more ground to be kept +open for accommodating increased staff, and the maintenance of +these openings must be paid for. There is an added expense for +handling larger numbers in and out of the mine, and the lower +intelligence reacts in many ways in lack of coordination and inability +to take initiative. Taking all divisions of labor together, the +ratio of efficiency as measured in amount of output works out from +four to five colored men as the equivalent of one white man of the +class stated. The ratio of costs, for reasons already mentioned, +and in other than quantity relation, figures still more in favor +of the higher intelligence. + +The following comparisons, which like all mine statistics must +necessarily be accepted with reservation because of some dissimilarity +of economic surroundings, are yet on sufficiently common ground +to demonstrate the main issue,--that is, the bearing of inherent +intelligence in the workmen and their consequent skill. Four groups +of gold mines have been taken, from India, West Australia, South +Africa, and Western America. All of those chosen are of the same +stoping width, 4 to 5 feet. All are working in depth and with every +labor-saving device available. All dip at about the same angle and +are therefore in much the same position as to handling rock. The +other conditions are against the white-manned mines and in favor of +the colored. That is, the Indian mines have water-generated electric +power and South Africa has cheaper fuel than either the American or +Australian examples. In both the white-manned groups, the stopes +are supported, while in the others no support is required. + +======================================================================= + | Tons of | Average |Tons | + | Material | Number of Men | per |Cost per + Group of Mines | Excavated | Employed | Man | Ton of + |over Period|---------------| per |Material + |Compiled[5]|Colored| White |Annum| Broken +----------------------------|-----------|-------|-------|-----|-------- +Four Kolar mines[1] | 963,950 | 13,611| 302 | 69.3| $3.85 +Six Australian mines[2] | 1,027,718 | -- | 1,534 |669.9| 2.47 +Three Witwatersrand mines[3]| 2,962,640 | 13,560| 1,595 |195.5| 2.68 +Five American mines[4] | 1,089,500 | -- | 1,524 |713.3| 1.92 +======================================================================= + +[Footnote 1: Indian wages average about 20 cents per day.] + +[Footnote 2: White men's wages average about $3 per day.] + +[Footnote 3: About two-fifths of the colored workers were negroes, +and three-fifths Chinamen. Negroes average about 60 cents, and +Chinamen about 45 cents per day, including keep.] + +[Footnote 4: Wages about $3.50. Tunnel entry in two mines.] + +[Footnote 5: Includes rock broken in development work. + +In the case of the specified African mines, the white labor is +employed almost wholly in positions of actual or semi-superintendence, +such as one white man in charge of two or three drills. + +In the Indian case, in addition to the white men who are wholly +in superintendence, there were of the natives enumerated some 1000 +in positions of semi-superintendence, as contractors or headmen, +working-gangers, etc.] + +One issue arises out of these facts, and that is that no engineer +or investor in valuing mines is justified in anticipating lower +costs in regions where cheap labor exists. + +In supplement to sheer skill and intelligence, efficiency can be +gained only by the application of the man himself. A few months ago +a mine in California changed managers. The new head reduced the number +employed one-third without impairing the amount of work accomplished. +This was not the result of higher skill or intelligence in the men, +but in the manager. Better application and coordination were secured +from the working force. Inspiration to increase of exertion is +created less by "driving" than by recognition of individual effort, +in larger pay, and by extending justifiable hope of promotion. A +great factor in the proficiency of the mine manager is his ability +to create an _esprit-de-corps_ through the whole staff, down to +the last tool boy. Friendly interest in the welfare of the men +and stimulation by competitions between various works and groups +all contribute to this end. + +CONTRACT WORK.--The advantage both to employer and employed of +piece work over wage needs no argument. In a general way, contract +work honorably carried out puts a premium upon individual effort, +and thus makes for efficiency. There are some portions of mine +work which cannot be contracted, but the development, stoping, +and trucking can be largely managed in this way, and these items +cover 65 to 75% of the total labor expenditure underground. + +In development there are two ways of basing contracts,--the first +on the footage of holes drilled, and the second on the footage +of heading advanced. In contract-stoping there are four methods +depending on the feet of hole drilled, on tonnage, on cubic space, +and on square area broken. + +All these systems have their rightful application, conditioned upon +the class of labor and character of the deposit. + +In the "hole" system, the holes are "pointed" by some mine official +and are blasted by a special crew. The miner therefore has little +interest in the result of the breaking. If he is a skilled white +man, the hours which he has wherein to contemplate the face usually +enable him to place holes to better advantage than the occasional +visiting foreman. With colored labor, the lack of intelligence in +placing holes and blasting usually justifies contracts per "foot +drilled." Then the holes are pointed and blasted by superintending +men. + +On development work with the foot-hole system, unless two working +faces can be provided for each contracting party, they are likely +to lose time through having finished their round of holes before the +end of the shift. As blasting must be done outside the contractor's +shifts, it means that one shift per day must be set aside for the +purpose. Therefore not nearly such progress can be made as where +working the face with three shifts. For these reasons, the "hole" +system is not so advantageous in development as the "foot of advance" +basis. + +In stoping, the "hole" system has not only a wider, but a sounder +application. In large ore-bodies where there are waste inclusions, +it has one superiority over any system of excavation measurement, +namely, that the miner has no interest in breaking waste into the +ore. + +The plan of contracting stopes by the ton has the disadvantage +that either the ore produced by each contractor must be weighed +separately, or truckers must be trusted to count correctly, and to +see that the cars are full. Moreover, trucks must be inspected for +waste,--a thing hard to do underground. So great are these detailed +difficulties that many mines are sending cars to the surface in +cages when they should be equipped for bin-loading and self-dumping +skips. + +The method of contracting by the cubic foot of excavation saves +all necessity for determining the weight of the output of each +contractor. Moreover, he has no object in mixing waste with the ore, +barring the breaking of the walls. This system therefore requires +the least superintendence, permits the modern type of hoisting, +and therefore leaves little justification for the survival of the +tonnage basis. + +Where veins are narrow, stoping under contract by the square foot +or fathom measured parallel to the walls has an advantage. The miner +has no object then in breaking wall-rock, and the thoroughness of +the ore-extraction is easily determined by inspection. + +BONUS SYSTEMS.--By giving cash bonuses for special accomplishment, +much the same results can be obtained in some departments as by +contracting. A bonus per foot of heading gained above a minimum, +or an excess of trucks trammed beyond a minimum, or prizes for +the largest amount done during the week or month in special works +or in different shifts,--all these have a useful application in +creating efficiency. A high level of results once established is +easily maintained. + +LABOR UNIONS.--There is another phase of the labor question which +must be considered and that is the general relations of employer +and employed. In these days of largely corporate proprietorship, +the owners of mines are guided in their relations with labor by +engineers occupying executive positions. On them falls the +responsibility in such matters, and the engineer becomes thus a +buffer between labor and capital. As corporations have grown, so +likewise have the labor unions. In general, they are normal and +proper antidotes for unlimited capitalistic organization. + +Labor unions usually pass through two phases. First, the inertia +of the unorganized labor is too often stirred only by demagogic +means. After organization through these and other agencies, the +lack of balance in the leaders often makes for injustice in demands, +and for violence to obtain them and disregard of agreements entered +upon. As time goes on, men become educated in regard to the rights +of their employers, and to the reflection of these rights in ultimate +benefit to labor itself. Then the men, as well as the intelligent +employer, endeavor to safeguard both interests. When this stage +arrives, violence disappears in favor of negotiation on economic +principles, and the unions achieve their greatest real gains. Given +a union with leaders who can control the members, and who are disposed +to approach differences in a business spirit, there are few sounder +positions for the employer, for agreements honorably carried out +dismiss the constant harassments of possible strikes. Such unions +exist in dozens of trades in this country, and they are entitled to +greater recognition. The time when the employer could ride roughshod +over his labor is disappearing with the doctrine of "_laissez faire_," +on which it was founded. The sooner the fact is recognized, the +better for the employer. The sooner some miners' unions develop +from the first into the second stage, the more speedily will their +organizations secure general respect and influence.[*] + +[Footnote *: Some years of experience with compulsory arbitration +in Australia and New Zealand are convincing that although the law +there has many defects, still it is a step in the right direction, +and the result has been of almost unmixed good to both sides. One +of its minor, yet really great, benefits has been a considerable +extinction of the parasite who lives by creating violence.] + +The crying need of labor unions, and of some employers as well, +is education on a fundamental of economics too long disregarded +by all classes and especially by the academic economist. When the +latter abandon the theory that wages are the result of supply and +demand, and recognize that in these days of international flow of +labor, commodities and capital, the real controlling factor in +wages is efficiency, then such an educational campaign may become +possible. Then will the employer and employee find a common ground +on which each can benefit. There lives no engineer who has not +seen insensate dispute as to wages where the real difficulty was +inefficiency. No administrator begrudges a division with his men +of the increased profit arising from increased efficiency. But +every administrator begrudges the wage level demanded by labor +unions whose policy is decreased efficiency in the false belief +that they are providing for more labor. + + + + +CHAPTER XVII. + +Administration (_Continued_). + +ACCOUNTS AND TECHNICAL DATA AND REPORTS; WORKING COSTS; DIVISION +OF EXPENDITURE; INHERENT LIMITATIONS IN ACCURACY OF WORKING COSTS; +WORKING COST SHEETS. GENERAL TECHNICAL DATA; LABOR, SUPPLIES, POWER, +SURVEYS, SAMPLING, AND ASSAYING. + +First and foremost, mine accounts are for guidance in the distribution +of expenditure and in the collection of revenue; secondly, they +are to determine the financial progress of the enterprise, its +profit or loss; and thirdly, they are to furnish statistical data to +assist the management in its interminable battle to reduce expenses +and increase revenue, and to enable the owner to determine the +efficiency of his administrators. Bookkeeping _per se_ is no part +of this discussion. The fundamental purpose of that art is to cover +the first two objects, and, as such, does not differ from its +application to other commercial concerns. + +In addition to these accounting matters there is a further type +of administrative report of equal importance--that is the periodic +statements as to the physical condition of the property, the results +of exploration in the mine, and the condition of the equipment. + +ACCOUNTS. + +The special features of mine accounting reports which are a development +to meet the needs of this particular business are the determination +of working costs, and the final presentation of these data in a +form available for comparative purposes. + +The subject may be discussed under:-- + + 1. Classes of mine expenditure. + 2. Working costs. + 3. The dissection of expenditures departmentally. + 4. Inherent limitations in the accuracy of working costs. + 5. Working cost sheets. + +In a wide view, mine expenditures fall into three classes, which +maybe termed the "fixed charges," "proportional charges," and "suspense +charges" or "capital expenditure." "Fixed charges" are those which, +like pumping and superintendence, depend upon time rather than +tonnage and material handled. They are expenditures that would not +decrease relatively to output. "Proportional charges" are those +which, like ore-breaking, stoping, supporting stopes, and tramming, +are a direct coefficient of the ore extracted. "Suspense charges" are +those which are an indirect factor of the cost of the ore produced, +such as equipment and development. These expenditures are preliminary +to output, and they thus represent a storage of expense to be charged +off when the ore is won. This outlay is often called "capital +expenditure." Such a term, though in common use, is not strictly +correct, for the capital value vanishes when the ore is extracted, +but in conformity with current usage the term "capital expenditure" +will be adopted. + +Except for the purpose of special inquiry, such as outlined under +the chapter on "Ratio of Output," "fixed charges" are not customarily +a special division in accounts. In a general way, such expenditures, +combined with the "proportional charges," are called "revenue +expenditure," as distinguished from the capital, or "suspense," +expenditures. In other words, "revenue" expenditures are those +involved in the daily turnover of the business and resulting in +immediate returns. The inherent difference in character of revenue +and capital expenditures is responsible for most of the difficulties +in the determination of working costs, and most of the discussion +on the subject. + +WORKING COSTS.--"Working costs" are a division of expenditure for +some unit,--the foot of opening, ton of ore, a pound of metal, +cubic yard or fathom of material excavated, or some other measure. +The costs per unit are usually deduced for each month and each +year. They are generally determined for each of the different +departments of the mine or special works separately. Further, the +various sorts of expenditure in these departments are likewise +segregated. + +In metal mining the ton is the universal unit of distribution for +administrative purpose, although the pound of metal is often used +to indicate final financial results. The object of determination of +"working costs" is fundamentally for comparative purposes. Together +with other technical data, they are the nerves of the administration, +for by comparison of detailed and aggregate results with other mines +and internally in the same mine, over various periods and between +different works, a most valuable check on efficiency is possible. +Further, there is one collateral value in all statistical data not +to be overlooked, which is that the knowledge of its existence +induces in the subordinate staff both solicitude and emulation. + +The fact must not be lost sight of, however, that the wide variations +in physical and economic environment are so likely to vitiate +conclusions from comparisons of statistics from two mines or from +two detailed works on the same mine, or even from two different +months on the same work, that the greatest care and discrimination +are demanded in their application. Moreover, the inherent difficulties +in segregating and dividing the accounts which underlie such data, +render it most desirable to offer some warning regarding the limits +to which segregation and division may be carried to advantage. + +As working costs are primarily for comparisons, in order that they +may have value for this purpose they must include only such items +of expenditure as will regularly recur. If this limitation were more +generally recognized, a good deal of dispute and polemics on the +subject might be saved. For this reason it is quite impossible that +all the expenditure on the mine should be charged into working costs, +particularly some items that arise through "capital expenditure." + +THE DISSECTION OF EXPENDITURES DEPARTMENTALLY.--The final division +in the dissection of the mine expenditure is in the main:-- + + /(1) General Expenses. / Ore-breaking. \ + | | Supporting Stopes. | Various +_Revenue._< (2) Ore Extraction. < Trucking Ore. | expenditures + | \ Hoisting. | for labor, + \(3) Pumping. | supplies, power, + / Shaft-sinking. | repairs, etc., + | Station-cutting. > worked out per + | Crosscutting. | ton or foot + /(4) Development. < Driving. | advanced +_Capital | | Rising. | over each + or < | Winzes. | department. +Suspense._ | \ Diamond Drilling. / + | + | (5) Construction and \ Various Works. + \ Equipment. / + +The detailed dissection of expenditures in these various departments +with view to determine amount of various sorts of expenditure over +the department, or over some special work in that department, is +full of unsolvable complications. The allocation of the direct +expenditure of labor and supplies applied to the above divisions or +special departments in them, is easily accomplished, but beyond this +point two sorts of difficulties immediately arise and offer infinite +field for opinion and method. The first of these difficulties arises +from supplementary departments on the mine, such as "power," "repairs +and maintenance," "sampling and assaying." These departments must +be "spread" over the divisions outlined above, for such charges +are in part or whole a portion of the expense of these divisions. +Further, all of these "spread" departments are applied to surface +as well as to underground works, and must be divided not only over +the above departments but also over the surface departments,--not +under discussion here. The common method is to distribute "power" on +a basis of an approximation of the amount used in each department; +to distribute "repairs and maintenance," either on a basis of shop +returns, or a distribution over all departments on the basis of +the labor employed in those departments, on the theory that such +repairs arise in this proportion; to distribute sampling and assaying +over the actual points to which they relate at the average cost +per sample or assay. + +"General expenses," that is, superintendence, etc., are often not +included in the final departments as above, but are sometimes "spread" +in an attempt to charge a proportion of superintendence to each +particular work. As, however, such "spreading" must take place +on the basis of the relative expenditure in each department, the +result is of little value, for such a basis does not truly represent +the proportion of general superintendence, etc., devoted to each +department. If they are distributed over all departments, capital +as well as revenue, on the basis of total expenditure, they inflate +the "capital expenditure" departments against a day of reckoning when +these charges come to be distributed over working costs. Although it +may be contended that the capital departments also require supervision, +such a practice is a favorite device for showing apparently low +working costs in the revenue departments. The most courageous way +is not to distribute general expenses at all, but to charge them +separately and directly to revenue accounts and thus wholly into +working costs. + +The second problem is to reduce the "suspense" or capital charges +to a final cost per ton, and this is no simple matter. Development +expenditures bear a relation to the tonnage developed and not to +that extracted in any particular period. If it is desired to preserve +any value for comparative purposes in the mining costs, such outlay +must be charged out on the basis of the tonnage developed, and such +portion of the ore as is extracted must be written off at this +rate; otherwise one month may see double the amount of development +in progress which another records, and the underground costs would +be swelled or diminished thereby in a way to ruin their comparative +value from month to month. The ore developed cannot be satisfactorily +determined at short intervals, but it can be known at least annually, +and a price may be deduced as to its cost per ton. In many mines +a figure is arrived at by estimating ore-reserves at the end of +the year, and this figure is used during the succeeding year as a +"redemption of development" and as such charged to working costs, +and thus into revenue account in proportion to the tonnage extracted. +This matter is further elaborated in some mines, in that winzes +and rises are written off at one rate, levels and crosscuts at +another, and shafts at one still lower, on the theory that they +lost their usefulness in this progression as the ore is extracted. +This course, however, is a refinement hardly warranted. + +Plant and equipment constitute another "suspense" account even +harder to charge up logically to tonnage costs, for it is in many +items dependent upon the life of the mine, which is an unknown +factor. Most managers debit repairs and maintenance directly to +the revenue account and leave the reduction of the construction +outlay to an annual depreciation on the final balance sheet, on the +theory that the plant is maintained out of costs to its original +value. This subject will be discussed further on. + +INHERENT LIMITATIONS IN ACCURACY OF WORKING COSTS.--There are three +types of such limitations which arise in the determination of costs +and render too detailed dissection of such costs hopeless of accuracy +and of little value for comparative purposes. They are, first, the +difficulty of determining all of even direct expenditure on any +particular crosscut, stope, haulage, etc.; second, the leveling effect +of distributing the "spread" expenditures, such as power, repairs, +etc.; and third, the difficulties arising out of the borderland +of various departments. + +Of the first of these limitations the instance may be cited that +foremen and timekeepers can indicate very closely the destination of +labor expense, and also that of some of the large items of supply, +such as timber and explosives, but the distribution of minor supplies, +such as candles, drills, picks, and shovels, is impossible of accurate +knowledge without an expense wholly unwarranted by the information +gained. To determine at a particular crosscut the exact amount of +steel, and of tools consumed, and the cost of sharpening them, +would entail their separate and special delivery to the same place +of attack and a final weighing-up to learn the consumption. + +Of the second sort of limitations, the effect of "spread" expenditure, +the instance may be given that the repairs and maintenance are done by +many men at work on timbers, tracks, machinery, etc. It is hopeless +to try and tell how much of their work should be charged specifically +to detailed points. In the distribution of power may be taken the +instance of air-drills. Although the work upon which the drill is +employed can be known, the power required for compression usually +comes from a common power-plant, so that the portion of power debited +to the air compressor is an approximation. The assumption of an +equal consumption of air by all drills is a further approximation. +In practice, therefore, many expenses are distributed on the theory +that they arise in proportion to the labor employed, or the machines +used in the various departments. The net result is to level down +expensive points and level up inexpensive ones. + +The third sort of limitation of accounting difficulty referred +to, arises in determining into which department are actually to be +allocated the charges which lie in the borderland between various +primary classes of expenditure. For instance, in ore won from +development,--in some months three times as much development may +be in ore as in other months. If the total expense of development +work which yields ore be charged to stoping account, and if cost +be worked out on the total tonnage of ore hoisted, then the stoping +cost deduced will be erratic, and the true figures will be obscured. +On the other hand, if all development is charged to 'capital account' +and the stoping cost worked out on all ore hoisted, it will include +a fluctuating amount of ore not actually paid for by the revenue +departments or charged into costs. This fluctuation either way +vitiates the whole comparative value of the stoping costs. In the +following system a compromise is reached by crediting "development" +with an amount representing the ore won from development at the +average cost of stoping, and by charging this amount into "stoping." +A number of such questions arise where the proper division is simply +a matter of opinion. + +The result of all these limitations is that a point in detail is +quickly reached where no further dissection of expenditure is justified, +since it becomes merely an approximation. The writer's own impression +is that without an unwarrantable number of accountants, no manager +can tell with any accuracy the cost of any particular stope, or +of any particular development heading. Therefore, aside from some +large items, such detailed statistics, if given, are to be taken +with great reserve. + +WORKING COST SHEETS.--There are an infinite number of forms of +working cost sheets, practically every manager having a system of +his own. To be of greatest value, such sheets should show on their +face the method by which the "spread" departments are handled, and +how revenue and suspense departments are segregated. When too much +detail is presented, it is but a waste of accounting and consequent +expense. Where to draw the line in this regard is, however, a matter +of great difficulty. No cost sheet is entirely satisfactory. The +appended sheet is in use at a number of mines. It is no more perfect +than many others. It will be noticed that the effect of this system +is to throw the general expenses into the revenue expenditures, +and as little as possible into the "suspense" account. + +GENERAL TECHNICAL DATA. + +For the purposes of efficient management, the information gathered +under this head is of equal, if not superior, importance to that +under "working costs." Such data fall generally under the following +heads:-- + +LABOR.--Returns of the shifts worked in the various departments +for each day and for the month; worked out on a monthly basis of +footage progress, tonnage produced or tons handled per man; also +where possible the footage of holes drilled, worked out per man +and per machine. + +SUPPLIES.--Daily returns of supplies used; the principal items +worked out monthly in quantity per foot of progress, or per ton +of ore produced. + +POWER.--Fuel, lubricant, etc., consumed in steam production, worked +out into units of steam produced, and this production allocated to +the various engines. Where electrical power is used, the consumption +of the various motors is set out. + +SURVEYS.--The need of accurate plans requires no discussion. Aside +from these, the survey-office furnishes the returns of development +footage, measurements under contracts, and the like. + +SAMPLING AND ASSAYING.--Mine sampling and assaying fall under two +heads,--the determination of the value of standing ore, and of +products from the mine. The sampling and assaying on a going mine +call for the same care and method as in cases of valuation of the +mine for purchase,--the details of which have been presented under +"Mine Valuation,"--for through it, guidance must not only be had to +the value of the mine and for reports to owners, but the detailed +development and ore extraction depend on an absolute knowledge of +where the values lie. + + + + +CHAPTER XVIII. + +ADMINISTRATION (_Concluded_). + +ADMINISTRATIVE REPORTS. + +In addition to financial returns showing the monthly receipts, +expenditures, and working costs, there must be in proper administration +periodic reports from the officers of the mine to the owners or +directors as to the physical progress of the enterprise. Such reports +must embrace details of ore extraction, metal contents, treatment +recoveries, construction of equipment, and the results of underground +development. The value of mines is so much affected by the monthly +or even daily result of exploration that reports of such work are +needed very frequently,--weekly or even daily if critical work is +in progress. These reports must show the width, length, and value +of the ore disclosed. + +The tangible result of development work is the tonnage and grade +of ore opened up. How often this stock-taking should take place +is much dependent upon the character of the ore. The result of +exploration in irregular ore-bodies often does not, over short +periods, show anything tangible in definite measurable tonnage, +but at least annually the ore reserve can be estimated. + +In mines owned by companies, the question arises almost daily as +to how much of and how often the above information should be placed +before stockholders (and therefore the public) by the directors. In +a general way, any company whose shares are offered on the stock +exchange is indirectly inviting the public to become partners in the +business, and these partners are entitled to all the information +which affects the value of their property and are entitled to it +promptly. Moreover, mining is a business where competition is so +obscure and so much a matter of indifference, that suppression +of important facts in documents for public circulation has no +justification. On the other hand, both the technical progress of +the industry and its position in public esteem demand the fullest +disclosure and greatest care in preparation of reports. Most +stockholders' ignorance of mining technology and of details of +their particular mine demands a great deal of care and discretion +in the preparation of these public reports that they may not be +misled. Development results may mean little or much, depending +upon the location of the work done in relation to the ore-bodies, +etc., and this should be clearly set forth. + +The best opportunity of clear, well-balanced statements lies in +the preparation of the annual report and accounts. Such reports +are of three parts:-- + +1. The "profit and loss" account, or the "revenue account." +2. The balance sheet; that is, the assets and liabilities + statement. +3. The reports of the directors, manager, and consulting + engineer. + +The first two items are largely matters of bookkeeping. They or +the report should show the working costs per ton for the year. +What must be here included in costs is easier of determination +than in the detailed monthly cost sheets of the administration; +for at the annual review, it is not difficult to assess the amount +chargeable to development. Equipment expenditure, however, presents +an annual difficulty, for, as said, the distribution of this item +is a factor of the life of the mine, and that is unknown. If such +a plant has been paid for out of the earnings, there is no object +in carrying it on the company's books as an asset, and most +well-conducted companies write it off at once. On the other hand, +where the plant is paid for out of capital provided for the purpose, +even to write off depreciation means that a corresponding sum of +cash must be held in the company's treasury in order to balance +the accounts,--in other words, depreciation in such an instance +becomes a return of capital. The question then is one of policy +in the company's finance, and in neither case is it a matter which +can be brought into working costs and leave them any value for +comparative purposes. Indeed, the true cost of working the ore +from any mine can only be told when the mine is exhausted; then +the dividends can be subtracted from the capital sunk and metal +sold, and the difference divided over the total tonnage produced. + +The third section of the report affords wide scope for the best +efforts of the administration. This portion of the report falls +into three divisions: (_a_) the construction and equipment work +of the year, (_b_) the ore extraction and treatment, and (_c_) +the results of development work. + +The first requires a statement of the plant constructed, its object +and accomplishment; the second a disclosure of tonnage produced, +values, metallurgical and mechanical efficiency. The third is of +the utmost importance to the stockholder, and is the one most often +disregarded and obscured. Upon this hinges the value of the property. +There is no reason why, with plans and simplicity of terms, such +reports cannot be presented in a manner from which the novice can +judge of the intrinsic position of the property. A statement of +the tonnage of ore-reserves and their value, or of the number of +years' supply of the current output, together with details of ore +disclosed in development work, and the working costs, give the +ground data upon which any stockholder who takes interest in his +investment may judge for himself. Failure to provide such data +will some day be understood by the investing public as a _prima +facie_ index of either incapacity or villainy. By the insistence of +the many engineers in administration of mines upon the publication +of such data, and by the insistence of other engineers upon such +data for their clients before investment, and by the exposure of +the delinquents in the press, a more practicable "protection of +investors" can be reached than by years of academic discussion. + + + + +CHAPTER XIX. + +The Amount of Risk in Mining Investments. + +RISK IN VALUATION OF MINES; IN MINES AS COMPARED WITH OTHER COMMERCIAL +ENTERPRISES. + +From the constant reiteration of the risks and difficulties involved +in every step of mining enterprise from the valuation of the mine +to its administration as a going concern, the impression may be +gained that the whole business is one great gamble; in other words, +that the point whereat certainties stop and conjecture steps in +is so vital as to render the whole highly speculative. + +Far from denying that mining is, in comparison with better-class +government bonds, a speculative type of investment, it is desirable +to avow and emphasize the fact. But it is none the less well to +inquire what degree of hazard enters in and how it compares with +that in other forms of industrial enterprise. + +Mining business, from an investment view, is of two sorts,--prospecting +ventures and developed mines; that is, mines where little or no ore is +exposed, and mines where a definite quantity of ore is measurable or can +be reasonably anticipated. The great hazards and likewise the Aladdin +caves of mining are mainly confined to the first class. Although all +mines must pass through the prospecting stage, the great industry +of metal production is based on developed mines, and it is these +which should come into the purview of the non-professional investor. +The first class should be reserved invariably for speculators, and +a speculator may be defined as one who hazards all to gain much. +It is with mining as an investment, however, that this discussion +is concerned. + +RISK IN VALUATION OF MINES.--Assuming a competent collection of +data and efficient management of the property, the risks in valuing +are from step to step:-- + +1. The risk of continuity in metal contents beyond sample + faces. +2. The risk of continuity in volume through the blocks + estimated. +3. The risk of successful metallurgical treatment. +4. The risk of metal prices, in all but gold. +5. The risk of properly estimating costs. +6. The risk of extension of the ore beyond exposures. +7. The risk of management. + +As to the continuity of values and volumes through the estimated +area, the experience of hundreds of engineers in hundreds of mines +has shown that when the estimates are based on properly secured +data for "proved ore," here at least there is absolutely no hazard. +Metallurgical treatment, if determined by past experience on the +ore itself, carries no chance; and where determined by experiment, +the risk is eliminated if the work be sufficiently exhaustive. The +risk of metal price is simply a question of how conservative a +figure is used in estimating. It can be eliminated if a price low +enough be taken. Risk of extension in depth or beyond exposures +cannot be avoided. It can be reduced in proportion to the distance +assumed. Obviously, if no extension is counted, there is nothing +chanced. The risk of proper appreciation of costs is negligible where +experience in the district exists. Otherwise, it can be eliminated +if a sufficiently large allowance is taken. The risk of failure to +secure good management can be eliminated if proved men are chosen. + +There is, therefore, a basic value to every mine. The "proved" +ore taken on known metallurgical grounds, under known conditions +of costs on minimum prices of metals, has a value as certain as +that of money in one's own vault. This is the value previously +referred to as the "_A_" value. If the price (and interest on it +pending recovery) falls within this amount, there is no question +that the mine is worth the price. What the risk is in mining is +simply what amount the price of the investment demands shall be +won from extension of the deposit beyond known exposures, or what +higher price of metal must be realized than that calculated in +the "_A_" value. The demands on this _X, Y_ portion of the mine +can be converted into tons of ore, life of production, or higher +prices, and these can be weighed with the geological weights and +the industrial outlook. + +MINES COMPARED TO OTHER COMMERCIAL ENTERPRISES.--The profits from +a mining venture over and above the bed-rock value _A_, that is, +the return to be derived from more extensive ore-recovery and a +higher price of metal, may be compared to the value included in +other forms of commercial enterprise for "good-will." Such forms of +enterprise are valued on a basis of the amount which will replace +the net assets plus (or minus) an amount for "good-will," that is, +the earning capacity. This good-will is a speculation of varying +risk depending on the character of the enterprise. For natural +monopolies, like some railways and waterworks, the risk is less +and for shoe factories more. Even natural monopolies are subject +to the risks of antagonistic legislation and industrial storms. +But, eliminating this class of enterprise, the speculative value +of a good-will involves a greater risk than prospective value in +mines, if properly measured; because the dangers of competition +and industrial storms do not enter to such a degree, nor is the +future so dependent upon the human genius of the founder or manager. +Mining has reached such a stage of development as a science that +management proceeds upon comparatively well-known lines. It is +subject to known checks through the opportunity of comparisons +by which efficiency can be determined in a manner more open for +the investor to learn than in any other form of industry. While +in mining an estimate of a certain minimum of extension in depth, +as indicated by collateral factors, may occasionally fall short, +it will, in nine cases out of ten, be exceeded. If investment in +mines be spread over ten cases, similarly valued as to minimum of +extension, the risk has been virtually eliminated. The industry, +if reduced to the above basis for financial guidance, is a more +profitable business and is one of less hazards than competitive +forms of commercial enterprises. + +In view of what has been said before, it may be unnecessary to refer +again to the subject, but the constant reiteration by wiseacres +that the weak point in mining investments lies in their short life +and possible loss of capital, warrants a repetition that the _A, +B, C_ of proper investment in mines is to be assured, by the "_A_" +value, of a return of the whole or major portion of the capital. +The risk of interest and profit may be deferred to the _X, Y_ value, +and in such case it is on a plane with "good-will." It should be said +at once to that class who want large returns on investment without +investigation as to merits, or assurance as to the management of the +business, that there is no field in this world for the employment +of their money at over 4%. + +Unfortunately for the reputation of the mining industry, and metal +mines especially, the business is often not conducted or valued on +lines which have been outlined in these chapters. There is often +the desire to sell stocks beyond their value. There is always the +possibility that extension in depth will reveal a glorious Eldorado. +It occasionally does, and the report echoes round the world for years, +together with tributes to the great judgment of the exploiters. The +volume of sound allures undue numbers of the venturesome, untrained, +and ill-advised public to the business, together with a mob of +camp-followers whose objective is to exploit the ignorant by preying +on their gambling instincts. Thus a considerable section of metal +mining industry is in the hands of these classes, and a cloud of +disrepute hangs ever in the horizon. + +There has been a great educational campaign in progress during the +past few years through the technical training of men for conduct +of the industry, by the example of reputable companies in regularly +publishing the essential facts upon which the value of their mines +is based, and through understandable nontechnical discussion in +and by some sections of the financial and general press. The real +investor is being educated to distinguish between reputable concerns +and the counters of gamesters. Moreover, yearly, men of technical +knowledge are taking a stronger and more influential part in mining +finance and in the direction of mining and exploration companies. +The net result of these forces will be to put mining on a better +plane. + + + + +CHAPTER XX. + +The Character, Training, and Obligations of the Mining Engineering +Profession. + +In a discussion of some problems of metal mining from the point +of view of the direction of mining operations it may not be amiss +to discuss the character of the mining engineering profession in +its bearings on training and practice, and its relations to the +public. + +The most dominant characteristic of the mining engineering profession +is the vast preponderance of the commercial over the technical in +the daily work of the engineer. For years a gradual evolution has +been in progress altering the larger demands on this branch of the +engineering profession from advisory to executive work. The mining +engineer is no longer the technician who concocts reports and blue +prints. It is demanded of him that he devise the finance, construct +and manage the works which he advises. The demands of such executive +work are largely commercial; although the commercial experience +and executive ability thus become one pier in the foundation of +training, the bridge no less requires two piers, and the second +is based on technical knowledge. Far from being deprecated, these +commercial phases cannot be too strongly emphasized. On the other +hand, I am far from contending that our vocation is a business +rather than a profession. + +For many years after the dawn of modern engineering, the members +of our profession were men who rose through the ranks of workmen, +and as a result, we are to this day in the public mind a sort of +superior artisan, for to many the engine-driver is equally an engineer +with the designer of the engine, yet their real relation is but as +the hand to the brain. At a later period the recruits entered by +apprenticeship to those men who had established their intellectual +superiority to their fellow-workers. These men were nearly always +employed in an advisory way--subjective to the executive head. + +During the last few decades, the advance of science and the complication +of industry have demanded a wholly broader basis of scientific and +general training for its leaders. Executive heads are demanded who +have technical training. This has resulted in the establishment of +special technical colleges, and compelled a place for engineering +in the great universities. The high intelligence demanded by the +vocation itself, and the revolution in training caused by the +strengthening of its foundations in general education, has finally, +beyond all question, raised the work of application of science to +industry to the dignity of a profession on a par with the law, +medicine, and science. It demands of its members equally high mental +attainments,--and a more rigorous training and experience. Despite +all this, industry is conducted for commercial purposes, and leaves +no room for the haughty intellectual superiority assumed by some +professions over business callings. + +There is now demanded of the mining specialist a wide knowledge +of certain branches of civil, mechanical, electrical, and chemical +engineering, geology, economics, the humanities, and what not; and +in addition to all this, engineering sense, executive ability, +business experience, and financial insight. Engineering sense is +that fine blend of honesty, ingenuity, and intuition which is a +mental endowment apart from knowledge and experience. Its possession +is the test of the real engineer. It distinguishes engineering as +a profession from engineering as a trade. It is this sense that +elevates the possessor to the profession which is, of all others, +the most difficult and the most comprehensive. Financial insight can +only come by experience in the commercial world. Likewise must come +the experience in technical work which gives balance to theoretical +training. Executive ability is that capacity to coordinate and command +the best results from other men,--it is a natural endowment. which +can be cultivated only in actual use. + +The practice of mine engineering being so large a mixture of business, +it follows that the whole of the training of this profession cannot +be had in schools and universities. The commercial and executive +side of the work cannot be taught; it must be absorbed by actual +participation in the industry. Nor is it impossible to rise to +great eminence in the profession without university training, as +witness some of our greatest engineers. The university can do much; +it can give a broad basis of knowledge and mental training, and can +inculcate moral feeling, which entitles men to lead their fellows. It +can teach the technical fundamentals of the multifold sciences which +the engineer should know and must apply. But after the university +must come a schooling in men and things equally thorough and more +arduous. + +In this predominating demand for commercial qualifications over +the technical ones, the mining profession has differentiated to +a great degree from its brother engineering branches. That this +is true will be most apparent if we examine the course through +which engineering projects march, and the demands of each stage +on their road to completion. + +The life of all engineering projects in a general way may be divided +into five phases:[*]-- + +[Footnote *: These phases do not necessarily proceed step by step. +For an expanding works especially, all of them may be in process +at the same time, but if each item be considered to itself, this +is the usual progress, or should be when properly engineered.] + + 1. Determination of the value of the project. + 2. Determination of the method of attack. + 3. The detailed delineation of method, means, and tools. + 4. The execution of the works. + 5. The operation of the completed works. + +These various stages of the resolution of an engineering project +require in each more or less of every quality of intellect, training, +and character. At the different stages, certain of these qualities +are in predominant demand: in the first stage, financial insight; +in the second, "engineering sense"; in the third, training and +experience; in the fourth and fifth, executive ability. + +A certain amount of compass over the project during the whole +five stages is required by all branches of the engineering +profession,--harbor, canal, railway, waterworks, bridge, mechanical, +electrical, etc.; but in none of them so completely and in such +constant combination is this demanded as in mining. + +The determination of the commercial value of projects is a greater +section of the mining engineer's occupation than of the other +engineering branches. Mines are operated only to earn immediate +profits. No question of public utility enters, so that all mining +projects have by this necessity to be from the first weighed from +a profit point of view alone. The determination of this question +is one which demands such an amount of technical knowledge and +experience that those who are not experts cannot enter the +field,--therefore the service of the engineer is always demanded in +their satisfactory solution. Moreover, unlike most other engineering +projects, mines have a faculty of changing owners several times +during their career, so that every one has to survive a periodic +revaluation. From the other branches of engineering, the electrical +engineer is the most often called upon to weigh the probabilities +of financial success of the enterprise, but usually his presence +in this capacity is called upon only at the initial stage, for +electrical enterprises seldom change hands. The mechanical and +chemical branches are usually called upon for purely technical +service on the demand of the operator, who decides the financial +problems for himself, or upon works forming but units in undertakings +where the opinion on the financial advisability is compassed by some +other branch of the engineering profession. The other engineering +branches, even less often, are called in for financial advice, +and in those branches involving works of public utility the +profit-and-loss phase scarcely enters at all. + +Given that the project has been determined upon, and that the enterprise +has entered upon the second stage, that of determination of method of +attack, the immediate commercial result limits the mining engineer's +every plan and design to a greater degree than it does the other +engineering specialists. The question of capital and profit dogs +his every footstep, for all mines are ephemeral; the life of any +given mine is short. Metal mines have indeed the shortest lives of +any. While some exceptional ones may produce through one generation, +under the stress of modern methods a much larger proportion extend +only over a decade or two. But of more pertinent force is the fact +that as the certain life of a metal mine can be positively known in +most cases but a short period beyond the actual time required to +exhaust the ore in sight, not even a decade of life to the enterprise +is available for the estimates of the mining engineer. Mining works +are of no value when the mine is exhausted; the capital invested +must be recovered in very short periods, and therefore all mining +works must be of the most temporary character that will answer. +The mining engineer cannot erect a works that will last as long as +possible; it is to last as long as the mine only, and, in laying +it out, forefront in his mind must be the question, Can its cost +be redeemed in the period of use of which I am certain it will +find employment? If not, will some cheaper device, which gives +less efficiency, do? The harbor engineer, the railway engineer, +the mechanical engineer, build as solidly as they can, for the +demand for the work will exist till after their materials are worn +out, however soundly they construct. + +Our engineer cousins can, in a greater degree by study and +investigation, marshal in advance the factors with which they have +to deal. The mining engineer's works, on the other hand, depend at +all times on many elements which, from the nature of things, must +remain unknown. No mine is laid bare to study and resolve in advance. +We have to deal with conditions buried in the earth. Especially in +metal mines we cannot know, when our works are initiated, what +the size, mineralization, or surroundings of the ore-bodies will +be. We must plunge into them and learn,--and repent. Not only is +the useful life of our mining works indeterminate, but the very +character of them is uncertain in advance. All our works must be in +a way doubly tentative, for they are subject to constant alterations +as they proceed. + +Not only does this apply to our initial plans, but to our daily +amendment of them as we proceed into the unknown. Mining engineering +is, therefore, never ended with the initial determination of a method. +It is called upon daily to replan and reconceive, coincidentally with +the daily progress of the constructions and operation. Weary with +disappointment in his wisest conception, many a mining engineer +looks jealously upon his happier engineering cousin, who, when he +designs a bridge, can know its size, its strains, and its cost, +and can wash his hands of it finally when the contractor steps +in to its construction. And, above all, it is no concern of his +whether it will pay. Did he start to build a bridge over a water, +the width or depth or bottom of which he could not know in advance, +and require to get its cost back in ten years, with a profit, his +would be a task of similar harassments. + +As said before, it is becoming more general every year to employ +the mining engineer as the executive head in the operation of mining +engineering projects, that is, in the fourth and fifth stages of +the enterprise. He is becoming the foreman, manager, and president +of the company, or as it may be contended by some, the executive +head is coming to have technical qualifications. Either way, in +no branch of enterprise founded on engineering is the operative +head of necessity so much a technical director. Not only is this +caused by the necessity of executive knowledge before valuations +can be properly done, but the incorporation of the executive work +with the technical has been brought about by several other forces. +We have a type of works which, by reason of the new conditions +and constant revisions which arise from pushing into the unknown +coincidentally with operating, demands an intimate continuous daily +employment of engineering sense and design through the whole history +of the enterprise. These works are of themselves of a character +which requires a constant vigilant eye on financial outcome. The +advances in metallurgy, and the decreased cost of production by +larger capacities, require yearly larger, more complicated, and +more costly plants. Thus, larger and larger capitals are required, +and enterprise is passing from the hands of the individual to the +financially stronger corporation. This altered position as to the +works and finance has made keener demands, both technically and in +an administrative way, for the highly trained man. In the early +stages of American mining, with the moderate demand on capital and +the simpler forms of engineering involved, mining was largely a +matter of individual enterprise and ownership. These owners were +men to whom experience had brought some of the needful technical +qualifications. They usually held the reins of business management +in their own hands and employed the engineer subjectively, when +they employed him at all. They were also, as a rule, distinguished +by their contempt for university-trained engineers. + +The gradually increasing employment of the engineer as combined +executive and technical head, was largely of American development. +Many English and European mines still maintain the two separate +bureaus, the technical and the financial. Such organization is open +to much objection from the point of view of the owner's interests, +and still more from that of the engineer. In such an organization the +latter is always subordinate to the financial control,--hence the +least paid and least respected. When two bureaus exist, the technical +lacks that balance of commercial purpose which it should have. The +ambition of the theoretical engineer, divorced from commercial +result, is complete technical nicety of works and low production +costs without the regard for capital outlay which the commercial +experience and temporary character of mining constructions demand. +On the other hand, the purely financial bureau usually begrudges +the capital outlay which sound engineering may warrant. The result +is an administration that is not comparable to the single head with +both qualifications and an even balance in both spheres. In America, +we still have a relic of this form of administration in the consulting +mining engineer, but barring his functions as a valuer of mines, he +is disappearing in connection with the industry, in favor of the +manager, or the president of the company, who has administrative +control. The mining engineer's field of employment is therefore not +only wider by this general inclusion of administrative work, but +one of more responsibility. While he must conduct all five phases +of engineering projects coincidentally, the other branches of the +profession are more or less confined to one phase or another. They +can draw sharper limitations of their engagements or specialization +and confine themselves to more purely technical work. The civil +engineer may construct railway or harbor works; the mechanical +engineer may design and build engines; the naval architect may +build ships; but given that he designed to do the work in the most +effectual manner, it is no concern of his whether they subsequently +earn dividends. He does not have to operate them, to find the income, +to feed the mill, or sell the product. The profit and loss does +not hound his footsteps after his construction is complete. + +Although it is desirable to emphasize the commercial side of the +practice of the mining engineer's profession, there are other sides +of no less moment. There is the right of every red-blooded man to +be assured that his work will be a daily satisfaction to himself; +that it is a work which is contributing to the welfare and advance +of his country; and that it will build for him a position of dignity +and consequence among his fellows. + +There are the moral and public obligations upon the profession. +There are to-day the demands upon the engineers which are the demands +upon their positions as leaders of a great industry. In an industry +that lends itself so much to speculation and chicanery, there is the +duty of every engineer to diminish the opportunity of the vulture +so far as is possible. Where he can enter these lists has been +suggested in the previous pages. Further than to the "investor" +in mines, he has a duty to his brothers in the profession. In no +profession does competition enter so obscurely, nor in no other +are men of a profession thrown into such terms of intimacy in +professional work. From these causes there has arisen a freedom of +disclosure of technical results and a comradery of members greater +than that in any other profession. No profession is so subject to +the capriciousness of fortune, and he whose position is assured +to-day is not assured to-morrow unless it be coupled with a +consideration of those members not so fortunate. Especially is +there an obligation to the younger members that they may have +opportunity of training and a right start in the work. + +The very essence of the profession is that it calls upon its members +to direct men. They are the officers in the great industrial army. +From the nature of things, metal mines do not, like our cities and +settlements, lie in those regions covered deep in rich soils. Our +mines must be found in the mountains and deserts where rocks are +exposed to search. Thus they lie away from the centers of comfort +and culture,--they are the outposts of civilization. The engineer +is an officer on outpost duty, and in these places he is the camp +leader. By his position as a leader in the community he has a +chieftainship that carries a responsibility besides mere mine +management. His is the responsibility of example in fair dealing +and good government in the community. + +In but few of its greatest works does the personality of its real +creator reach the ears of the world; the real engineer does not +advertise himself. But the engineering profession generally rises +yearly in dignity and importance as the rest of the world learns +more of where the real brains of industrial progress are. The time +will come when people will ask, not who paid for a thing, but who +built it. + +To the engineer falls the work of creating from the dry bones of +scientific fact the living body of industry. It is he whose intellect +and direction bring to the world the comforts and necessities of +daily need. Unlike the doctor, his is not the constant struggle +to save the weak. Unlike the soldier, destruction is not his prime +function. Unlike the lawyer, quarrels are not his daily bread. +Engineering is the profession of creation and of construction, of +stimulation of human effort and accomplishment. + + + + +INDEX. + +Accounts. +Administration. +Administrative reports. +Air-compression. + -drills. +Alteration, secondary. +Alternative shafts to inclined deposit. +Amortization of capital and interest. +Animals for underground transport. +Annual demand for base metals. + report. +Artificial pillars. +Assay foot. + inch. + of samples. + plans. +Assaying. +A value of mine. +Averages, calculation. + +Bailing. +Balance sheet. +Basic price. + value of mine. +Benches. +Bend in combined shafts. +Bins. +Blocked-out ore. +Blocks. +Bonanzas, origin. +Bonus systems, of work. +Breaking ore. +Broken Hill, levels. + ore-pillars. +Bumping-trough. + +Cable-ways. +Cages. +Calculation of averages. + of quantities of ore. +Capital expenditure. +Caving systems. +Churn-drills. +Chutes, loading, in vertical shaft. +Classification of ore in sight. +Combined shaft. + stopes. +Commercial value of projects, determination. +Compartments for shaft. +Compressed-air locomotives. + -air pumps. + _vs_. electricity for drills. +Content, average metal, determining. + metal, differences. +Contract work. +Copper, annual demand. + deposits. + ores, enrichment. +Cost of entry into mine. + of equipment. + production. + per foot of sinking. + working. +Cribs. +Crosscuts. +Cross-section of inclined deposit which must be attacked in depth. + showing auxiliary vertical outlet. +Crouch, J. J. +Cubic feet per ton of ore. + foot contents of block. + +Deep-level mines. +Demand for metals. +Departmental dissection of expenditures. +Deposits, _in situ_. + ore, classes. + regularity. + size. + structure. +Depth of exhaustion. +Determination of average metal contents of ore. +Development in early prospecting stage. + in neighboring mines. + of mines. +Diamond-drilling. +Diluting narrow samples to a stoping width. +Dip. +Direct-acting steam-pumps. +Distribution of values. +Dividend, annual, present value. +Dommeiler. +Down holes. +Drainage. + comparison of different systems. + systems. +Drifts. +Drill, requirements. +Drilling. +Drives. +Dry walling with timber caps. + +Efficiency, factors of. + of mass. +Electrical haulage. + pumps. +Electricity for drills. +Engine, size for winding appliances. +Engineer, mining, as executive. +Engineering projects, phases of. +Enrichment. + at cross-veins. +Entry, to mine. + to vertical or horizontal deposits. +Equipment, cost. + improvements. + mechanical. +Erosion. +Error, percentage in estimates from sampling. +Escape. +Examination of mining property. +Excavation, supporting. +Exhaustion, depth. +Expenditures, departmental dissection. + mine. +Extension in depth. + +Factor of safety in calculating averages of samples. +Filling. + system combined with square-setting. + with broken ore subsequently withdrawn. + waste. +Fissure veins. +Fissuring. + depth. +Fixed charges. +Flat-back stope. +Flexibility in drainage system. +Floors. +Folding. +Foot-drilled system of contract work. + -hole system of contract work. + of advance system of contract work. + value. +Fraud, precautions against in sampling. + +General expenses. +Gold deposits. + deposits, alteration. + enrichment. + +Hammer type of drill. +Hand-drilling. + -trucking. +Haulage, electrical. + equipment in shaft. + mechanical. +Hole system of contract work. +Horizons of ore-deposits. +Horizontal deposits, entry. + stope. + filled with waste. +Hydraulic pumps. + +Impregnation deposits. +Inch, assay. +Inclined deposits to be worked from outcrop or near it. + deposits which must be attacked in depth. + shaft. +Inclines. + capacity. +Infiltration type of deposits. +Intelligence as factor of skill. +Interest calculations in mine valuation. +Intervals, level. +Inwood's tables. +Iron hat. + leaching. +Ivanhoe mine, West Australia. + +Kibble. + +Labor, general technical data. + handling. + unions. +Lateral underground transport. +Le Roi mine. +Lead, annual demand. + deposits. + enriching. + prices, 1884-1908. + -zinc ores, enrichment. +Lenses. +Levels. + intervals. + of Broken Hill. + protection. +Life, in sight. + of mine. +Locomotives, compressed-air. +Lode mines, valuation. +Lodes. +Long-wall stope. + +Machine-drill, performance. + drilling. + _vs_. hand-drilling. +Management, mine. +Matte. +Mechanical efficiency of drainage machinery. + equipment. +Men for underground transport. +Metal content, determining. + contents, differences. + demand for. + mine, value. + price. +Mines compared to other commercial enterprises. + equipment. + expenditures. +Mines--_continued._ + life of. + metal, value of. + of moderate depths. + to be worked to great depths. + valuation. +Mining engineering profession. +Mt. Cenis tunnel. +Morgan gold mine. + +Normal price. + +Obligations of engineering profession. +Openings, position in relation to secondary alteration. +Ore, average width in block. + blocked-out. + -bodies. + shapes. + -breaking, methods. + calculation of quantities of. + -chutes in shrinkage-stoping. + -deposits, classes. + determination of average metal contents. + developed. + developing. + expectant. + in sight. + sight, classification. + -pillars. + support in narrow stopes. + -shoots. + weight of a cubic foot. + width for one sample. +Origin of deposit. +Outcrop mines. +Output, factors limiting. + giving least production cost. + maximum, determination. +Overhand stapes. +Overproduction of base metal. +Oxidation. + +Patchwork plant, mechanical inefficiency of. +Pay areas, formation. +Pillars, artificial. +Positive ore. + value of metal mine. +Possible ore. +Power conditions. + general technical data. + sources. + transmission. +Preliminary inspection. +Previous yield. +Price of metals. +Probable ore. +Producing stage of mine. +Production, cost. +Profit and loss account. + factors determining. + in sight. +Proportional charges. +Prospecting stage of mine. +Prospective ore. + value. +Protection of levels. +Proved ore. +Pumping systems. +Pumps, compressed-air. + electrical. + hydraulic. + rod-driven. + +Ratio of output to mine. +Recoverable percentage of gross assay value. +Recovery of ore. +Rectangular shaft. +Redemption of capital and interest. +Reduction of output. +Regularity of deposit. +Reliability of drainage system. +Replacement. +Reports. + administrative. +Resuing. +Revenue account. +Rill-cut overhand stope. + method of incline cuts. + -stopes. + filled with waste. + -stoping. +Rises. +Risk in mining investments. + in valuation of mines. +Roadways, protecting in shrinkage-stoping. +Rod-driven pumps. +Rotary steam-pumps. +Round vertical shafts. +Runs of value. + test-treatment. + +Safety, factor of, in calculating averages of samples. +Sample, assay of. + average value. + narrow, diluting to a stoping width. + sections. + taking, physical details. + manner of taking. +Sampling. + accuracy. + percentage of error in estimates from. + precautions against fraud. +Saving of fixed charges. +Secondary alteration. + enrichment. +Security of investment. +Self-dumping skip. +Sets. +Shafts. + arrangement for very deep inclined shafts. + compartments. + different depths. + haulage. + location. + number. + output capacity. + shape. + size. +Shrinkage-stope. + -stoping. + advantages. + disadvantages. + when applicable. +Silver deposits. + deposits, enrichment. + prices. +Sinking, speed. +Size of deposit. +Skill, effect on production cost. +Skips. + balanced. + haulage in vertical shaft. +Sollars. +Solubility of minerals. +Specific volume of ores. +Speculative values of metal mine. + value of mine. +Spelter, annual demand. +Square-set. + -set timbering. +Stations. + arrangement for skip haulage in vertical shaft. +Steam-pumps, direct. +Steepening winzes and ore passes. +Stope filled with broken ore. + minimum width. +Stoping. + contract systems. +Storing metal. +Structural character of deposit. +Structure of deposit. +Stull and waste pillars. + support with waste reenforcement. + -supported stope. +Stulls. + wood. +Subheading. +Sublevel caving system. +Subsidiary development. +Superficial enrichment. +Supplies, general technical data. +Support by pillars of ore. +Supporting excavation. +Surveys. +Suspense charges. + +Test parcels. + sections. + -treatment runs. +Timber, cost. +Timbered shaft design. +Timbering. +Tin, annual demand. + deposits. + ore, migration and enrichment. +Tools. +Top slicing. +Tracks. +Transport in stopes. +Tunnel entry. + feet paid for in 10 years. + size. + +Underhand stopes. +Uppers. + +Valuation, mine. + of lode mines. + mines, risk in. + mines with little or no ore in sight. + on second-hand data. +Value, average, of samples. + discrepancy between estimated and actual. + distribution. + of extension in depth, estimating. + positive, of metal mine. + present, of an annual dividend. + of $1 or L1, payable in -- years. + runs of. + speculative, of metal mine. +Valuing ore in course of breaking. +Ventilation. +Vertical deposits, entry. + interval between levels. + shafts. + capacity. +Volume, specific, of ores. + +Waste-filled stope. +Water-power. +Weight per cubic foot of ore. +Weindel, Caspar. +Whiting hoist. +Width of ore for one sample. +Winding appliances. +Winzes. + in shrinkage-stoping. + to be used for filling. +Working cost. + inherent limitations in accuracy of. + sheets. +Workshops. + +Yield, previous. +Years of life required to yield --% interest. + +Zinc deposits. + leaching. + + + + + + +End of Project Gutenberg's Principles of Mining, by Herbert C. Hoover + +*** END OF THIS PROJECT GUTENBERG EBOOK PRINCIPLES OF MINING *** + +***** This file should be named 26697.txt or 26697.zip ***** +This and all associated files of various formats will be found in: + https://www.gutenberg.org/2/6/6/9/26697/ + +Produced by Robert J. Hall + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +https://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH F3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, is critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at https://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +https://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at https://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit https://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including including checks, online payments and credit card +donations. To donate, please visit: https://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart was the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + https://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. diff --git a/26697.zip b/26697.zip Binary files differnew file mode 100644 index 0000000..2326dc3 --- /dev/null +++ b/26697.zip diff --git a/LICENSE.txt b/LICENSE.txt new file mode 100644 index 0000000..6312041 --- /dev/null +++ b/LICENSE.txt @@ -0,0 +1,11 @@ +This eBook, including all associated images, markup, improvements, +metadata, and any other content or labor, has been confirmed to be +in the PUBLIC DOMAIN IN THE UNITED STATES. + +Procedures for determining public domain status are described in +the "Copyright How-To" at https://www.gutenberg.org. + +No investigation has been made concerning possible copyrights in +jurisdictions other than the United States. Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..dba8806 --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #26697 (https://www.gutenberg.org/ebooks/26697) |
