GIFT OF Dean Frank E. Probert Sold by Book Department MINING AND SCIENTIFIC PRESS 42O MARKET STREET SAN FRANCISCO Catalogue of Technical Books on request .'r;' WORKS OF PROF. WALTER R. CRANE PUBLISHED BY JOHN WILEY & SONS Gold and Silver Comprising an Economic History of Mining in the United States, the Geographical and Geo- logical Occurrence of the Precious Metals, with their Mineralogical Associations, History and Description of Methods of Mining and Extrac- tion of Values, and a Detailed Discussion of the Production of Gold and Silver in the World and the United States. 8vo, x + 727 pages, illus- trated. Cloth, $5.00 net. Index of Mining Engineering Literature Comprising an Index of Mining, Metallurgical, Civil, Mechanical, Electrical, and Chemical Engi- neering Subjects as Related to Mining Engi- neering. 8vo, xii + 812 pages. Cloth, $4. 00 net. Morocco, $5.00 net. Ore Mining Methods Comprising descriptions of methods of support in extraction of ore, detailed descriptions of methods of stoping and mining in narrow and wide veins and bedded and massive deposits, in- cluding stull and square-set mining, filling and caving methods, open-cut work and a discussion of costs of stoping. 8vo, viii + 219 pages. CO full-page plates. Cloth, 3.00 net. ORE MINING METHODS COMPRISING DESCRIPTIONS OF METHODS OF SUPPORT IN EXTRAC- TION OF ORE, DETAILED DESCRIPTIONS OF METHODS OF STOPING AND MINING IN NARROW AND WIDE VEINS AND BEDDED AND MASSIVE DEPOSITS INCLUDING STULL AND SQUARE-SET MINING, FILLING AND CAVING METHODS, OPEN-CUT WORK AND A DISCUSSION OF COSTS OF STOPING BY WALTER R. CRANE, PH.D. DEAN OF THE SCHOOL OF MINES AND METALLURGY, AND PROFESSOR OF MINING, THE PENNSYLVANIA STATE COLLEGE FIRST EDITION FIRST THOUSAND NEW YORK JOHN WILEY & SONS LONDON : CHAPMAN & HALL, LIMITED IQIO GIFT OB 1 FMNK H COPYRIGHT 1910 BY WALTER R. CRANE Stanbopc ipress F. H. GILSON COMPANY BOSTON. U.S.A. cs PREFACE WHILE much has been written with regard to methods of mining ore and many excellent descriptions of the methods employed in the mines of the United States and abroad are to be found in the technical press, yet there is no work in which systematic and detailed descriptions of the various methods are to be found. With this thought in mind the writer has attempted to prepare a work on ore mining methods alone, which it is hoped may prove useful to both the student and the prac- tical man in acquiring a knowledge of ore mining and in comparing methods. That the work may be of the most service, the descriptions have been made brief and many illustrations employed to supplement them. Further, the application of each method has been specifically stated, together with the advantages and disadvantages of its use. The classification of methods followed is based upon size of deposit, rather than kind of mineral or metal and char- acter of deposit, which seems the simplest and most logical method of treatment. The idea has been to describe only those methods which have proven successful not only in one locality but several, and not to consider proposed methods nor those in the experimental stage. In order to verify descriptions and to study methods more in detail the writer has visited the mines in which practically iv PREFACE all of the methods described are employed; however, personal inspection has been confined to the mines of the United States. Special acknowledgment of suggestions and advice is due to Professors Henry S. Munroe and Edwin C. Holden, and the large number of mining men who have extended many courtesies to the writer while collecting the information upon which the work is based. WALTER R. CRANE. THE PENNSYLVANIA STATE COLLEGE SCHOOL OF MINES, Jan. i, 1910. CONTENTS CHAPTER I Support of Workings PAGE INTRODUCTION i METHODS or SUPPORT 6 PILLARS OF ORE OR WASTE; TIMBER AS MINE SUPPORT; PROPS; STULLS; CRIBS OR BULKHEADS; SQUARE-SETS; FILLINGS OF ORE OR WASTE; SUPPORT BY INDIRECT MEANS; RESUME PILLARS, PROPS OR POSTS, STULLS, CRIBS OR BULKHEADS, SQUARE-SETS, FILLING, CAVING 22 CHAPTER II Methods of Stoping and Handling Ore in Stopes METHODS OF STOPING 23 OVERHAND STOPING; UNDERHAND STOPING; COMBINED STOPING; BREAST STOPING; SIDE STOPING; LONG WALL STOPING; RESUING; RESUME OF STOP- ING OVERHAND STOPING, UNDERHAND STOPING, BREAST STOPING, OTHER METHODS OF STOPING 43 METHODS OF HANDLING ORE IN STOPES 45 CHAPTER III Mining in Narrow Veins and Bedded Deposits INTRODUCTION 55 MINING BEDDED DEPOSITS BY THE USE OF PROPS 56 IRON MINES OF THE BIRMINGHAM DISTRICT, ALABAMA 60 MINING MINERAL VEINS BY THE USE OF STULLS 60 TONOPAH MINE, TONOPAH, NEVADA; COMBINATION MINE, GOLDFIELD, NEVADA; HECLA MINE, BURKE, IDAHO 72 MINING MINERAL VEINS BY THE USE OF SQUARE-SETS 72 THE BUNKER HILL-SULLIVAN MINE, WARDNER, IDAHO 77 MINING MINERAL VEINS BY THE USE OF FILLING 77 THE ZARUMA MINE, ZARUMA, ECUADOR; THE ST. LAWRENCE MINE, BUTTE, MONTANA; THE BALTIC AND TRIMOUNTAIN MINES, MICHIGAN 89 MINING BEDDED DEPOSITS BY CAVING 89 MERCUR AND GOLDEN GATE MINES, MERCUR, UTAH 94 v vi CONTENTS CHAPTER IV Methods of Mining in Wide Veins and Masses PAGE INTRODUCTION 95 SHRINKAGE STOPING METHODS OF MINING 97 THE GOLD PRINCE MINE; ANIMAS FORKS, COLORADO; THE ALASKA-TREAD- WELL MINES, DOUGLAS ISLAND, ALASKA 104 SQUARE-SET METHODS OF MINING 104 THE MINES AT ROSSLAND, BRITISH COLUMBIA; THE QUEEN MINE, NEGAUNEE, MICHIGAN no FILLING METHODS no THE BROKEN HILL MINES, N. S. W.; THE HOMESTAKE MINE, LEAD, SOUTH DAKOTA 131 CAVING METHODS 132 IRON DEPOSITS OF THE LAKE SUPERIOR REGION; THE MINES OF BINGHAM CANYON, UTAH; THE DIAMOND MINES OF SOUTH AFRICA 155 CHAPTER V Open-cut Mining INTRODUCTION 156 SURFACE MINING BY HAND 158 SURFACE MINING BY SCRAPERS 163 OPEN-CUT MINING BY STEAM SHOVEL 166 THE MILLING METHOD 172 CHAPTER VI Cost of Stoping INTRODUCTION 183 DETAILED DISCUSSION OF COST OF STOPING 187 COST OF STOPING IN VARIOUS LOCALITIES , 193 THE COPPER MINES OF KEWEENAW POINT, MICHIGAN; THE CRIPPLE CREEK DISTRICT, COLORADO; THE ALASKA-TREAD WELL MINES, DOUGLAS ISLAND, ALASKA; THE LEAD-SILVER DISTRICT, COZUR D'ALENE, IDAHO; THE GOLD- FIELD CONSOLIDATED MINES COMPANY, GOLDFIELD, NEVADA; THE JOPLIN LEAD-ZINC DISTRICT, MISSOURI; THE WAR EAGLE MINE, BRITISH COLUMBIA 207 COST OF SUPPORT IN STOPES 207 LIST OF ILLUSTRATIONS FIGURE PAGE Frontispiece 1. Corduroy and Filling in the Comstock Mines 2 2. Use of Square-Sets and Filling n 3. Forms of Square-set Framing 14 4. Square-Sets in Large Stope 16 5. Overhand Stoping, 'Breaking-Through' . . . .' 26 6. Methods of Stoping and Handling Ore. A Composite Sketch 28 (Correction. Positions of 'toe' and 'heel' reversed.) 7. An 1 8-inch Stope in the Rand Mines, South Africa 30 8. Methods of Opening and Working Deposits by Underhand Stoping 33 9. Plan of Underhand Stoping Workings in Massive Deposit 35 10. Loading Cars by Chute, Mohawk Mine 47 11. Portion of Stope, showing Method of Handling Soft Ore .'. . 49 12. Use of Winged Stulls in Handling Ore 52 13. A Chinaman Chute as used in Australian Mines 54 14. Plan of Iron Mine, Birmingham District, Alabama 58 15. Application of Stulls to Moderately Wide Veins ' 61 16. Use of Stulls and Stull-Levels in Mining Moderately Wide Veins 65 17. Application of Stull-Sets to the Mining of Medium-sized Veins 69 18. Plan of Second Floor in Stull-set Method 71 19. Square-set Mining in Horizontal Floors 74 20. Square-set Mining in Inclined Floors 76 21. Overhand Stoping in Inclined Floors or Rill Stoping 79 22. Elevation and Plan of Stopes. Back-filling Method 82 23. Baltic and Trimountain Filling Method 86 24. Caving Method in Slightly Inclined Deposits 90 25. Plan of Caving Method in Mercur Mines, Utah 93 26. Longitudinal Section through Stope, showing Method of Working by Shrinkage Stoping 96 27. Vertical Section through Stope worked by Shrinkage Method 99 28. Plan of Stopes in the Alaska-Treadwell Mines 102 29. Longitudinal Section through Stopes in Alaska-Treadwell Mines 105 30. Square-Sets composed of Round Timbers 107 31. Square-set Mining in Massive Deposit 109 32. Square-set Mining in Broken Hill Mines, N. S. W in 33. Plan of Square-set Mining in Broken Hill Mines 114 34. Section through Lode. Broken Hill Mines, showing Open-stope Method ... 116 35. Plan of Pillar-and-Stope Method in Broken Hill Mines 118 vii viii LIST OF ILLUSTRATIONS FIGURE PAGE 36. Back-filling Method used in Homestake Mines 122 37. End View of Stope in Homestake Mine. Back-filling Method 124 38. Plan of Stopes of Back-filling Method, Homestake Mines 127 39. Longitudinal Section through Stopes in Homestake Mines. Back-filling Method 130 40. Section through Vein, showing Development in Top-slice Method 131 41. Plan and Longitudinal Section of Top-slice Method 134 42. Section through Lode, showing Method of Development in Sub-drift Method 137 43. Longitudinal Section and Plan of Sub-drift Method 140 44. Plan of Block of Bad Ground worked by Sub-drift Method 142 45. Longitudinal Section through Massive Deposit worked by Sub-drift Caving Method 144 46. Plan of Portion of Sub-Level, showing Method of Caving Ore by Raises . . . 147 47. Plan of Pipe and Method of Development (in Diamond Mines) 149 48. Vertical Section through Pipe, showing Method of Working by Galleries. . . 150 49. Section through Pipe, showing Method of Working by Caving 151 50. Elevations and Plans, showing Method of Opening up a Stope 153 51. Sketch, showing Plan of Stopes run together 154 52. Vertical Section, showing Stopes in Various Stages of Working 155 53. Mining Bank of Shale by Hand '. 159 54. Quarry, showing Bench before Blast 161 55. Quarry, showing Result of Blast 162 56. Stripping Coal by Scrapers 164 57. Section across Bingham Canyon, showing Beginning of Steam Shovel Work in Stripping Capping 167 58. Steam Shovel Mining in Soft Iron Ore of Birmingham District, Ala 170 59. Vertical Section through Massive Deposit of Iron Ore, showing Method of Development and Working by Milling Method 176 ORE MINING METHODS CHAPTER I SUPPORT OF WORKINGS INTRODUCTION METHODS of mining and support of workings are so closely related that the discussion of one necessitates a more or less detailed treatment of the other. It therefore seems eminently proper and even necessary to preface a work of this character with a brief discussion regarding the elements of support. A description of the elemental units of support, such as pillars, props, cribs, stulls and square- sets will not therefore be out of place in this connection. Further, the use of filling is considered, as it is rapidly becoming an important factor in the support of under- ground excavations; caving as a factor in support is also discussed. While no particular knowledge regarding methods of support other than may be found in the following pages is essential to a full and complete understanding of the con- tents of this work, yet a working knowledge of support of excavations will not come amiss, and such knowledge is assumed to be possessed by the intelligent reader of this work. 2 ORE MINING METHODS To the careful observer it is becoming more and more evident that timber cannot be relied upon to support mine workings as mining is, and must of necessity be, carried on to-day. With the constantly decreasing value of the mineral content of the ores of many mines and the opening up of enormous deposits of low-grade ores, the demand is becom- ing more urgent for decreased costs of working or extracting FIG. i. Corduroy and Filling in the Comstock Mines. the ores. Contemporaneously with this general trend of affairs has occurred a scarcity, in many localities, of a suit- able supply of timber at reasonable rates. The result has been, then, that with no other available material at hand that was cheaper, methods requiring a minimum amount of timber were resorted to, and as a further advancement filling and caving methods are rapidly coming into general use and are supplanting the older and more expensive methods where much timber is used. As the methods of SUPPORT OF WORKINGS 3 working mineral deposits have then yielded to the demands of economy, in like manner the old type of conservative mine superintendent is giving way to the ingenious, ener- getic and efficient modern mining engineer, whose slogan is " increased tonnage at decreased costs." Further, aside from the question of economy the mining engineer has long since learned that timber or any other similar form of support must be considered as temporary only when we come to maintaining openings at a depth of several thousand feet. To attempt to support a mountain by timber or even pillars of ore or rock is but to invite in the course of time disastrous caves with the possible resulting loss of life and property. The extremes gone to in an endeavor to hold back loose or swelling ground is well illustrated by the close-set cribbing or corduroy employed in the bonanza days on the Comstock Lode and still used there in isolated places. (See Fig. i.) The veritable forest of closely placed props to be seen in many of our metal mines, and the stulls of three or four feet in diameter em- ployed in the lower levels of the deep copper mines of Keweenaw Point, Michigan, all attest the ever-present and constantly growing need of a radical change in methods of procedure in supporting workings made for the economic extraction of mineral. While the application of rock-filling to the support of mine workings is by no means recent in the mines of the United States, yet its rapid extension to a majority of the metal mining districts, irrespective of the kind of metal mined, has taken place within the last ten years. By rock- 4 ORE MINING METHODS filling, as referred to above, is meant a filling of waste, the excavations receiving little or no other support except of the most temporary character. Filling in connection with square-sets has been used extensively in the mines of this country ever since its application to the mines of the Corn- stock Lode. Aside from the question of an available supply of suitable material for filling there are certain objections to its use, some of which are so serious as to preclude its employment except under prescribed and limiting conditions. Probably the principal disadvantages are shrinkage of the mass of filling and a tendency to become ' quick' and flow. The former action leads to movements which although gradual are nevertheless pronounced and may result in serious disarrangement of the workings, shafts, levels, etc., and may lead, under certain conditions, to the flooding of the workings. However, under normal conditions, these disadvantages may be insignificant compared with the benefits resulting from its use. The latter disadvantage while always present is accentuated only when the filling employed is mixed with a certain amount of earthy or clayey material and becomes charged or saturated with water. Further, the practice, often a necessity, of using the filling over and over again tends to render it less suitable for the work owing to the constantly increasing proportion of fine material produced by the attrition of the moving mass of filling, when drawn from one part of the workings to another, and the accumulation of gouge and muck left from the mining operations. SUPPORT OF WORKINGS 5 It is not, however, so much the seriousness of the dis- advantages as it is the lack of control of the actions leading thereto. It may be said without hesitation that, where conditions are favorable, such as a moderately strong ore supporting itself sufficiently well to permit introducing and spreading the filling without interference with temporary supports, together with a suitable filling and plenty of it readily available, the filling methods have proved and are proving amply adequate. When such general conditions do not prevail and suitable timber at reasonable rates is not available, some other method not dependent upon such factors must be resorted to. The caving methods might then well be employed. Caving is confined to ore bodies of considerable size, especially of horizontal extent, and to ores of a fairly uni- form mineral content, its application being gradually ex- tended to districts where other methods of mining have long been in use. Often where square-setting, with or without filling, was formerly exclusively employed, caving has now taken its place wholly or in part or a combination of the two is resorted to. Caving is usually employed only where other methods are inapplicable and inadequate. Its use means large-scale, continuous and rapid work, with a con- sequently large tonnage and small expense per ton. Caving is not synonymous with scant use of timber; on the contrary a large amount of timber may be required as when the sub-drift system is used, but as the timber is for temporary use only, being often of inferior quality and used in the rough, the expense may be considerably less than a 6 ORE MINING METHODS more permanent method of support where less timber is employed. What timber support is used serves mainly for protection to the miners who as parts of an intelligent system are directing and utilizing the tremendous force of the superimposed mass of loose and broken rock and ore which is slowly but irresistibly following the withdrawal of the ore downward. METHODS or SUPPORT The means of supporting mine workings may be outlined as follows: 1. Pillars of ore or waste rock. 2. Timbering, consisting of props, stulls, cribs and square- sets. 3. Fillings of ore or waste; the former temporary, the latter permanent. 4. Support by indirect means, i.e., by arching the work- ings and by caving methods, where the ore to be mined takes the load temporarily, being reenforced by timber. Pillars of Ore, or Waste Rock. Pillars were naturally first employed in the support of workings underground, and will always be used instead of artificial support except when their use means the permanent curtailment of the output of the mine, or when they are less stable and durable than other available supports. The chief objection to the use of pillars, aside from the loss of valuable mineral, is that it is difficult to ensure their proper formation and location. To secure the maximum benefit of supports of any kind requires that they should be SUPPORT OF WORKINGS 7 symmetrically and systematically placed, a thing that is next to impossible to obtain in the case of pillars underground. Either there will be ore occurring at the place where a pillar should logically come or some irregularity of or in the deposit will influence a change in location and result in a serious irregularity of the system adopted. In like manner the shape of the pillar may be changed; instead of a square or rectangular section with ends flaring slightly at both top and bottom, where connection is made with the hanging and foot walls, the sections are more usually roughly round or ellipti- cal, while the general appearance resembles an hourglass. The pernicious habit of gradually cutting away pillars to secure a few more tons of ore results in producing most grotesque shapes and an alarming condition of support. Pillars standing 12 to 15 feet high, in moderately inclined deposits, are not infrequently reduced from a diameter of 1 6 to 20 feet at the top and bottom to 4 and often 3 feet at the middle, and in certain observed instances to i foot diameter at the 'waist line.' Such pillars soon deteriorate under the enormous weight thrown upon them and show signs of distress by vertical cracks extending from top to bottom. The caved stopes of the upper levels of the large copper mines of the Lake Superior region bear witness to the fact that inefficient support in the shape of ill-formed pillars is both inadequate and futile. Pillars are named according to the position they occupy with respect to the stope; those at the top of the stope are known as 'arch' pillars, those next to the shaft are 'shaft' pillars, while those occupying various positions in 8 ORE MINING METHODS the stope are usually known as 'wall' pillars. A special form of wall pillar is the so-called ' dead-end,' a pillar ex- tending the whole height of the stope and spaced at inter- vals of about 200 feet along the stope. (See Fig. 6.) Timber as Mine Support. Timber well adapted to use in underground work is becoming somewhat scarce in many localities in the United States. Oak is excellent but is rarely used owing to its scarcity. On the Pacific coast the cone-bearing or coniferous trees are widely used. Of the thirty-six varieties found there the most important are: the Oregon pine, spruce, yellow pine, tamarack, sugar pine, pinion or bull pine, besides several varieties of fir and red- wood. In Washington and many of the Western states the Oregon pine is extensively used for both mine and surface work and is known in different localities by various names, such as, Douglas fir, Douglas spruce, yellow fir or red fir, while in the parlance of the lumbermen it is known as Oregon pine and Puget Sound pine. Yellow pine al- though of no great durability or strength is widely used. Fir is quite strong, as is pine also, the softer woods having the advantage over the harder in that they crush more readily, thus taking up the load more uniformly. Props or posts may be considered as the principal element in mine timbering, being employed in connection with nearly all forms of timbering under certain conditions. Props and posts may be round or square and are set normal to the roof and floor of the workings. They have their widest range of usefulness in flat or slightly inclined deposits and are there- fore especially applicable to bedded deposits. In order to SUPPORT OF WORKINGS increase the bearing surface caps are often provided, which consist of short lengths of plank placed between the ends of the props and roof or floor. Stulls while performing the same function as props and posts are used only in more or less highly inclined deposits, having their widest range of usefulness in narrow veins, say up to 15 feet in width. Stulls are, however, used in veins of 35 to 40 feet in width, and for inclinations up to 90, or the vertical. The application of stulls is considerably different from that of props owing to conditions brought about by change in dip of the deposit. Like the prop or post the stull often has a cap used with it, but it is placed at the upper end only, the lower end being set into a notch or ' hitch ' cut into the lower or foot wall of the vein and wedged tight. The object of the hitch is to prevent the timber slipping from its place. Further, stulls are not set normal to the walls of the vein but in such a position that their devia- tion from the normal, called 'angle of underlie,' is about one-fourth that of the angle of dip of the deposit, thus: Dip of Vein Angle of Underlie of Stull Dip of Vein Angle of Underlie of Stull 10 :> 40 10 20 5^ 50 I2j 30 7i 60 15 The reason for setting stulls at an angle with the walls instead of normal to them is to ensure against their becom- ing loose and falling out of place, which would surely result if they were set normal and a movement of the walls should 10 ORE MINING METHODS take place. When set at an angle any downward move- ment of the hanging wall serves only to set the stull more firmly in the hitch. Stulls are extensively employed at the foot of stopes in veins of steep or moderately steep inclinations and serve both as a protection to the levels and as a support for the ore or waste that is placed upon them. Stulls when covered with lagging may serve as platforms upon which drills may be mounted in the work of stoping. In steep veins, inter- mediate levels or floors may be formed at intervals of 15 or 20 feet, by rows of stulls, lagged and covered with ore or waste, the stoping of the ore extending horizontally and vertically from the level so formed until sufficient room is made for another row of stulls to be placed. Waste-covered stulls are usually designated as 'waste-stulls.' It is often necessary to reenforce stulls, which is usually done by placing several below the one to be reenforced. The auxiliary stulls may be placed directly below or grouped together forming the so-called 'battery of timbers' or stulls. Still another modification in the use of stulls is where they are used in conjunction with square-sets, long stulls often being employed in holding the square-sets in place when for certain reasons it is not considered necessary or desirable to fill the stope with sets. The stulls serve in reality as elongated caps in the system of square-sets. (See Fig. 2.) Props or struts and stulls are occasionally used together, especially when long stulls are necessary, the struts being set in between the stulls to hold them in place, thus steadying them and preventing buckling. SUPPORT OF WORKINGS II 12 ORE MINING METHODS Cribs or Bulkheads are usually composed of damaged timber, old ties, props and stulls, put together in pigsty fashion, two or more timbers being placed parallel one with the other and then bound together by other timbers laid across their ends and middle, which operation is continued until the roof or hanging wall is reached, when they are wedged fast. In order to make these constructions more stable they are often filled with waste. Cribs filled with waste, or otherwise, probably have their widest range of usefulness in the mining of coal, but are often employed in wide stopes where ordinary methods of support are inade- quate and where a certain amount of room for mining and handling the ore is available. Cribs in combination with filling, being built in the stopes during the extraction of the ore and then buried in filling when the stope is abandoned, give added strength and stability to the filling. Square-Sets have been very extensively employed in the metal mines of the United States and are still used to the exclusion of other methods in certain districts. While especially applicable to wide veins of moderately steep in- clinations, square-sets are often used in veins from 15 to 20 feet in width. In placing square-sets the usual practice is to begin at the bottom of a stope and lay long sill timbers which are regu- larly spaced by other timbers, thus covering the floor of the open stope with a system of timbers arranged in squares. Upon these timbers are erected other timbers which consist of posts, caps and girts or ties. The posts are placed up- right at the intersection of the sills and cross-pieces, and upon SUPPORT OF WORKINGS 13 the posts are placed caps, the ends of which rest on two adjacent posts in a direction transverse with the vein. The girts also rest upon the posts but run longitudinally with the vein. The caps and girts when in place form a new level or floor, and by successive additions of posts, caps and girts the timber support can be kept within easy reach of the walls or roof of the stope. In like manner by the addition of sills the sets can be extended indefinitely in either direction along the vein or deposit. A platform or staging as well as support is thus provided for any portion of the roof or sides of the stope. The stopes are then filled with a cellular mass of timbering perfectly matched together and symmet- rical in all directions. In order that the various members of the square-sets may fit together and be in perfect alinement, the posts standing vertically and the caps and girts lying horizontally, it is necessary that they be cut to gauge, and the ends formed so as to both hold the members in place and provide a perfectly fitting joint. Further, the ends of the different timbers are so cut that the largest cross-sectional area is opposed to the greatest pressure, as in the case of the caps which are placed normal to the walls. While there are a large number of different forms of joints suitable to framing both sawed and round timber, yet the details given in Fig. 3 illustrate very well two methods of framing that are widely used. Where the ground is particularly heavy, diagonal braces are placed in the sets and in line with the greatest pressure. The length of the posts varies largely with the locality, but as a rule the first set of posts, and in fact the posts at any ORE MINING METHODS SUPPORT OF WORKINGS 15 level, where hauling is done in cars, is sufficiently high to permit the passage of men. The usual length of posts is 6 to 8 feet in the clear, the caps and girts being about 5 to 6 and 4 to 6 feet respectively. As timber became more difficult to secure for the mines the first and most natural expedient was to modify the con- struction of the square-sets by using rough round instead of sawed timber and the employment of longer posts. Round timber while being somewhat more difficult to frame is con- siderably stronger than the sawed forms. Thus the result was decreased cost of framing and increased strength. Increased length of posts also decrease the cost of fram- ing, but there is a definite limit in this direction if strength and rigidity of support are desiderata. A further modifi- cation is the variation in size of the different members of the sets, the posts, caps and girts being of different cross- sectional dimension. A drift may be the starting point of square-set timbering, which is extended laterally and vertically therefrom. Experience has shown that it is not so much the depth with consequent increase in pressure as the strength and firmness of the walls that determines the usefulness and safety of square-sets as support for workings. This was demonstrated in the mines of the Comstock Lode, where the support of the upper workings was often fully as difficult as in other localities at greater depth. Further, there is a limit in height to which square-sets can be used, beyond which the timbers will crush under their own weight. The limit in the Homestake mines, South Dakota, ranges be- i6 ORE MINING METHODS SUPPORT OF WORKINGS 17 tween 80 and 90 feet. It is then evident that when square- sets are employed the height of the stopes should not exceed 100 feet. Use of square-sets in a gold mine is shown in Fig. 4. From the standpoint of economy the use of square-sets is hardly warrantable, although there are instances where owing to the occurrence of cheap timber it may prove to be the most economical method that can be employed. Fillings of Ore or Waste. Filling methods have been successfully employed for many years in the mines of this country and are rapidly being extended, especially the use of waste. The filling of underground excavations, as stopes, with ore is a method employed for reasons of utility and economy as well as support. Ore may be located and broken in the stopes but not drawn off, except as is found necessary to provide room for the operation of stoping. As there is an increase in volume of from 30 to 40 per cent in broken ore, it is evident that a certain amount must be drawn off after each round of shots to give space for sub- sequent work at the face. A large amount of ore may then remain in the mine, forming an 'ore reserve.' The advan- tages of such a system are: a large force of men may be employed in breaking ore; less danger from falls of rock owing to rapidity of working; reduced cost of breaking and handling ore; a more uniform output; and a more careful grading of ores resulting from not having to rush work in order to keep up with the required output. The work at the face is materially facilitated by this method of procedure, as the ore serves as a platform upon l8 ORE MINING METHODS which the drills are mounted, the height of which may be varied at will. The ore while stored in the s topes also serves as a support for the workings, reducing or eliminating the support that would otherwise be necessary. It is difficult to imagine a case where ore would be introduced into a mine or transferred to any part of it for support, owing to the extra cost involved, as well as the loss in fine ore resulting from attrition in handling. That ore is occasionally so used is due either to the fact that when so employed its grade is not considered sufficient at the time to warrant treatment, or the temporary need of support is so urgent that it is expedi- ent to resort to the use of even a fair grade of ore. The use of waste in the support of underground workings is now a well-established method, and its widespread appli- cation indicates how favorably it is looked upon by mining men. The employment of waste-filling depends to a large extent upon its source. There are three possible sources of waste, namely : that resulting from mining operations, being sorted from the ore or portions of the walls that have to be broken down in cutting out the ore; that obtained from special excavations made in the vein walls, usually the hang- ing-wall; and material from quarries or open-cuts on the surface and the waste products from concentrating works, such as tailings. The first source mentioned is the most important, as comparatively little labor is required in placing it properly in the excavation to be supported. This is particularly true in the case of veins where but a small part of the ore is valuable, the bulk of the vein-content being used as filling; also in certain cases where more waste is SUPPORT OF WORKINGS 19 required than can be obtained from sorting the ore, the additional amount being secured by blasting several feet off the walls. Much filling is now taken from the surface and by the use of waste chutes is conducted to any portion of the mine desired, being distributed by cars. Under- ground excavations opened especially to secure waste for filling are occasionally made, but it is a method of procedure which is liable to lead to disastrous results, as in starting caves, unless the ground is particularly strong. Support by Indirect Means. Indirect methods are re- sorted to wherever intelligent supervision is given to the work and where conditions are favorable. The natural arch formed by caving ground, or the so-called 'dome of equi- librium,' may be employed to advantage in the temporary support of underground excavations. By arching the roof it is often possible to maintain it without any support or with very temporary constructions. The character of the ground is the governing factor in this work, certain forma- tions not being sufficiently strong to stand even with short spans and high arches, while other specially strong forma- tions may be given exceedingly long spans and low arches. The wide stopes of the Homestake and Alaska-Treadwell mines illustrate remarkably well the application of the 'dome of equilibrium 7 to strong and stable formations. Caving may be employed as a supplementary method following some well-defined system, usually with timber supports, until its limit of applicability has been reached or exceeded. The weight of the unmined ore together with the mass of broken waste and timber lying above the ore is 20 ORE MINING METHODS temporarily supported by pillars of ore and timber. In the course of time the pillars begin to break up, and by care- fully and systematically removing the timber supports and attacking the pillars in such a manner as to assist the dis- integration, practically all of the ore remaining above the level worked may be drawn off with little or no danger to the laborers or the integrity of mine workings. The support of the caving ore and overlying caved material is of the most temporary character and really amounts to a well-defined and scientific control of the movement of the caving mass rather than its definite support. In order that the methods of support discussed above may be rendered still more comprehensive the following brief statements are made regarding their application and com- parative advantages and disadvantages. Pillars of mineral constitute the most natural form of support for underground workings. The advantages in their use are : the vein-content left in place is probably the strong- est possible support obtainable; support can be provided at any desired point; there is no expense attendant upon their use and no risk from fire. The disadvantages are : loss of mineral when formed in ore; a tendency to make them too small to save ore; also a like tendency and for similar reasons to place them irregularly or dispense with them altogether. Props or Posts can be used to advantage in a vertical or nearly vertical position only. Their chief advantage lies in the ease with which they can be placed and removed if desired. SUPPORT OF WORKINGS 21 Stulls have a very much wider range of application than posts, as they can be employed in veins ranging from an inclination of about 10 to the vertical. When properly placed they are not affected by slight movements of the walls and are therefore suitable for a great variety of conditions. They may be employed as supports of scaffoldings upon which drills are mounted, forming ' stull-levels ' and ' waste- stulls.' Cribs or Bulkheads owing to their width are more stable than posts or stulls, but to give the best results must be built practically vertical. They cannot be used to advan- tage except in horizontal or slightly inclined deposits or wide veins. While readily built they are difficult to take down, especially when filled with waste, and occupying considerable space encumber the workings, interfering with handling ore and supplies. Square-Sets like cribs must be built along horizontal and vertical lines and are therefore confined to compara- tively wide veins and massive deposits. They are expensive to frame and place and unless filled with waste soon buckle and crush, both under their own weight and that of the walls. However, for the support of large openings they have proved indispensable in the past, the ease with which extensions can be made in any direction being a most important factor in mining. Filling mine workings, especially with waste, is growing in favor owing to the facts that support can be placed quickly and readily; the waste of the mine can be disposed of at minimum expense, and cheap material can be trans- 22 ORE MINING METHODS f erred underground with little work; it can be used a num- ber of times, being drawn from one part of the mine to another; a good support uniformly distributed over the walls is obtained, and there is no fire risk. The disadvantages resulting from the use of filling are shrinkage of filling disturbing workings and a tendency for the filling to become quick and flow under pressure. Caving as an indirect method of support is applicable to large deposits only; requires continuous and rapid work; the loss of mineral may be considerable owing to the move- ment of the caving mass getting beyond control; and a large amount of timber is required with certain deposits. The advantages are: a large output at moderate cost; operations must begin near the surface; and the overlying rock must cave readily. CHAPTER II METHODS OF STOPING AND HANDLING ORE IN STOPES METHODS OF STOPING THE openings in metal mines from which ore is taken are called stopes and the methods employed in breaking down the ore are known as stoping. Stoping then constitutes the fundamental operation in the extraction of ore and must be well understood before a discussion of methods of mining is undertaken. Under certain conditions the methods of stoping constitute in themselves methods of mining and give the latter the name of the kind of stoping employed. The methods of stoping employed in the mines of the United States and, in fact, throughout the mining world may be outlined as follows: i. Overhand Stoping. .2. Underhand Stoping. 3. Breast Stoping. 4. Resuing. Other methods of stoping may result through combining overhand and underhand stoping, such as: 1. Combined or overhand-underhand stoping. 2. Side stoping, sometimes called breast stoping. 3. Longwall stoping or cutting-out stoping. 23 24 ORE MINING METHODS The direction of the working face with respect to the lines of development, as levels, raises and winzes, furnishes the basis for the above classification. The methods of stoping as outlined may then be defined as follows: Over- hand stoping is working up the dip and usually in a direc- tion diagonal to raises and winzes; underhand stoping is working down the dip also in a direction diagonal to raises and winzes; breast stoping may be either overhand or under- hand stoping applied to deposits of slight inclination and resembles breast work in coal mining; combined stoping is where both overhand and underhand stoping are carried on in the same working place or stope, the two lines of working faces extending diagonally up and down the stope from a common point in the center of the stope; side stoping is where the working face is parallel with the winzes; while longwall stoping has the working face parallel with the levels. These terms are, however, more or less elastic and may be employed differently in various districts and mines. The conditions influencing and controlling the choice of method of stoping are as follows: 1. Character of ore and its value. 2. Occurrence of valuable mineral. 3. Width of vein or deposit. 4. Dip and pitch of ore body. 5. Size and shape of ore bodies other than in veins. 6. Character and condition of wall-rocks. 7. Cost of timber for support. Of the conditions given above that of dip or inclination probably exerts the greatest influence on method of stoping, STOPING AND HANDLING ORE IN STOPES 25 being the principal factor in the choice between overhand and underhand methods. Wide veins or large deposits while often worked by overhand stoping may necessitate breast stoping wholly or in part. The character and occurrence of the valuable mineral while not necessarily influencing the method of attack may require modifications which are more or less radical. The character of wall-rock concerns the method of support mainly and therefore affects the general scheme of working rather than the method of attack or method of stoping. The handling of mineral in stopes varies widely with the method of stoping employed, and may even necessitate a change in method in order that the work may be facilitated and cheapened. The factors which influence the handling of mineral in stopes are, in order of importance, dip and width of vein and character and occurrence of mineral. Overhand Stoping. This method of stoping is probably more extensively employed than the other methods, being used in practically all kinds of metal mines where condi- tions are at all suitable. Overhand stoping is commonly employed in both narrow and wide veins, in moderately highly or highly inclined stratified deposits, and in massive deposits. The location of a body of ore having been determined by levels and raises or winzes driven through it, the work of cutting out the ore is begun by attacking it on one or both sides of a raise or winze, which connects the two levels and extends through the ore located at that point. (See Figs. 5 and 6.) 26 ORE MINING METHODS As there are several methods of procedure that are de- pendent upon the character and occurrence of the mineral in the vein, the determining conditions should now be stated. Where all of the vein matter is sufficiently valuable to mine FIG. 5. Overhand Sloping, 'Breaking-Through.' it may be broken down, transferred to the level below, loaded into cars and hauled away. There are cases, however, where it is not possible or advisable to dispose of the ore as rapidly as it is mined, although its preparation for with- drawal from the stopes is an important consideration. As ore when broken increases in bulk about 40 per cent it is evident that to provide working space for the miners at the STOPING AND HANDLING ORE IN STOPES 27 face a certain amount of the broken ore will have to be drawn off after a certain advance has been made. This is known as ' shrinkage ' stoping, while the ore remaining in the stope is called an 'ore reserve' and serves a useful purpose in regulating the output of the mine. On the other hand the bulk of the vein matter may be barren or so low-grade as to warrant only the least possible handling, in which case provision must be made for both the storage of the waste and the disposal of the valuable mineral. In either of the cases mentioned some provision must be made for the support of the ore or waste left in the stopes, if that is done. If all of the ore is removed from the stopes as rapidly as it is broken down, then supports for the main- tenance of walls and protection of levels is all that is neces- sary. Stope marked A-i, in Fig. 6, illustrates the first case mentioned, where the ore is drawn off as soon as broken down. Stopes B and B-i may be taken as representing the condition where ore is stored in the stopes, forming an ore reserve. Stope A may represent the condition existing in a precious-metal mine where the gold or silver occurs in small veins or stringers, the bulk of the vein-filling being barren or low-grade and is left in the stope. Stopes may be opened in two ways, namely, by beginning at a winze or raise, or by first driving a 'raise stope.' Raise stoping differs from driving raises mainly in width of passage or cut made, the usual width for a raise stope varying from 20 to 25 feet. From such a starting point the height of the drift may be increased by a 'cutting-out' stope, and con- sists in removing the vein-content in a more or less regular 28 ORE MINING METHODS O be G I STOPING AND HANDLING ORE IN STOPES 29 way, i.e., by cutting out a portion of definite width from the back of the drift. This is the usual method of procedure when a stope is started after the level has been run. When, however, drifting precedes breaking ore or stoping by but a few feet, 'drift stoping' is employed in enlarging the drift or level previous to the actual work of stoping, or cutting- out stoping. Drifting and stoping are then combined in one operation and consist in carrying a face about 25 feet high practically the full width of the vein. As each cutting-out stope is advanced, receding from the common starting point, and is followed by others at regular intervals, the working face of the stope assumes an inverted- stepped appearance as shown in stopes B and B-i, Fig. 6. The successive stope faces are then called 'back-stopes,' being numbered in order from the drift-stope upward (B, Fig. 6). The parts of the stope designated as 'toe' and 'heel' are shown in B-i. The usual practice in the mines of the United States is to carry the stopes up from the levels without leaving a row of pillars directly above them as shown in stope B-i. Wall pillars are, however, commonly left for support (see stope A-i), which is the usual practice in veins of moderate inclinations. In more highly inclined veins, unless of too great width, stulls and lagging with ore or waste-filling are employed. (See stopes A and B.) Overhand stoping is employed in veins varying in dip from a few degrees up to the vertical, but may be used more readily in veins of slighter inclination than underhand stoping. ORE MINING METHODS FIG. 7. An i8-inch Stope in the Rand Mines, South Africa. Underhand Sloping. In many respects underhand re- sembles overhand sloping, and may be said to be overhand sloping upside down, i.e., the work of breaking the ore is downward instead of upward. (See slopes C and B, Fig. 6.) The relation between the sloping face and the lines of devel- opment is also similar to that in overhand work. The Cornish system of underhand sloping consists in sinking a pit in the floor of a level and then beginning the work of removing the ore by working laterally therefrom. STOPING AND HANDLING ORE IN STOPES 31 This method has two serious disadvantages, namely: all the ore has to be shoveled out or raised by windlass, and the accumulation of water in the pit so formed will, if the mine is wet, necessitate pumping. Where a piece of ground of limited extent is known to contain valuable ore the Cornish system of stoping may be not only advisable but necessary. When, however, ore has been blocked out between levels and known to extend for some distance along the stope, the method employed in removing the ore should be undertaken on a larger scale and more systematically. Provision will have to be made also for handling the ore quickly and cheaply and for keeping the workings free from water. This can readily be accomplished by beginning stoping on the sides of a raise or winze connecting levels. Ore and water are both discharged through the connecting passage to the lower level, the former being loaded into cars while the latter is conducted by drains to the sumps located in the levels or at the foot of the shaft. (See left-hand portion of stope C.) Underhand stoping unlike overhand work is not applicable to deposits where only a small portion of the vein-content is valuable, for the very evident reason that there is no con- venient place to store the waste. Occasionally a line of stulls may be set in the stope, with a flooring of lagging, thus forming a staging upon which a limited quantity of waste may be thrown. The method is, however, applicable to both high- and low-grade deposits the whole or a large part of which is workable, also to massive deposits where the work of stoping is carried on in horizontal floors. Underhand stoping may be employed on quite a range of 32 ORE MINING METHODS dips, but is most successful in veins of 50 and up, due to the necessity of handling ore by gravity. Underhand stoping may be done in very small veins even as narrow as 18 inches. (See Fig. 7.) Both overhand and underhand stoping may begin next to the shaft, the width of shaft pillars, if employed, determining the beginning of the stopes. A winze ' or raise is driven connecting the levels, forming the shaft pillars and at the same time providing a point of attack in stoping. In over- hand work the stope is begun on the corner where the winze and level intersect, successive cuts increasing both the width and height of the stope. With underhand stoping, unless no arch pillars are left, the work of removing the ore can- not begin until a drift is run below the arch pillars, thus definitely determining their position and forming them. At the intersection of the drift and winze or raise the work of stoping may begin and extend downward until the level below is reached. The beginning of stoping next to the shaft is shown in stopes B and B-i for overhand stoping and in stopes C and C-i for underhand work. Underhand stoping is largely employed in massive de- posits and in slightly inclined bedded deposits of consider- able thickness. The opening of a stope may be accom- plished in one of two ways, namely : a shaft may be sunk to or near the deposit and a drift run into the ore body at a point as near the top as possible; or an ore body having been entered by an exploratory drift, any height of stope may be developed by running a raise to the top of the deposit. In the first case the stope may be increased in height by cutting STOPING AND HANDLING ORE IN STOPES 33 3 '3* o C/2 "S CM a Goldfield, Nevada. The lodes of the Mine, Goldfield, Go ldfield district consist of shattered and 2. Gold and Silver, fissured zones of silification. In the Com- 3. Veins or Zones. 4. Average thickness bination Mine the vein filling as well as the country-rock is altered dacite. Occasion- ally the silicified zones extend into the walls, making the width of the workable deposit rather indeterminate. The width of the silicified zones usually does not exceed 50 feet, while in the majority of cases 20 feet is a fair average. As a usual thing the ground is easy to support and wide stopes are often worked without fear of collapse. Referring to the section, Fig. 16, it is seen that the first level was formed at a depth of 80 feet, two drifts being driven in the deposit to the limits of the ore-shoot, one on either side of the lode. By cutting-out stoping, both of the stopes were increased in height and width until they ran together in the center of the lode and at the same time were extended to the walls of the lode. As soon as sufficient height of stope was secured to permit the running of cars, MINING IN NARROW VEINS AND BEDDED DEPOSITS 65 GLORY-HOLE I m^^^^^^S^A ' w^lMSif&SM^m < a Bi ^ rt !_ quartz bearing considerable quantities of 4. Maximum width finely disseminated pyrites, and bunches of galena and blende next to the hanging-wall. The wall-rock is diorite. The vein is faulted by an extensive fault-plane which lies within the vein and on the contact of foot- wall and vein-matter. Owing to the extensiveness of the movement, a very heavy gouge occurs which ranges be- tween 3 and 4 feet in thickness and is extremely weak and treacherous. The value of the ore is between $4 and $15 per ton. In developing the ore-body the levels are run in the foot- wall at a distance of some 20 feet from the vein, from which cross-cuts are driven every 65 feet, connecting the levels with the deposit. From the various points of attack pro- vided by the cross-cuts entering the ore-body stoping is 78 ORE MINING METHODS begun, being carried the full width of the vein and to a height of about 8 feet. (See Fig. 21.) Connection is made between the levels and the surface by means of a number of raises along the footwall through which waste rock is introduced into the stopes. Beginning at the raises the ore is cut out by overhand stoping, the ore being cleared away as rapidly as possible and hauled through the cross-cuts and levels to the main shaft. When the stopes have been carried as high as is considered safe, filling is thrown down the raises until the stopes are nearly filled; the work of stoping is then resumed, but to prevent the mixing of ore and waste rock, slabs of wood are placed upon the sloping sides of the filling. This operation is repeated, each slice being carried as far as is considered safe and then filling run in to support the walls and bring the footing for the drills sufficiently close to the working face. Further, temporary supports, as posts, may be set up between the face and the filling as occasion demands. The filling run in from above distributes itself evenly in the stopes without extra handling, and as the work of stoping is carried on from the slope of the filling the stope face must of necessity be maintained parallel with the slope of the fill- ing, which is practically that of the angle of repose of the waste rock, but slightly less owing to the miners working upon the filling. In the course of time the various stopes run together and at points midway between the raises, or at the intermediate cross-cuts. At these points cribbed chutes are begun and built upward as the work of stoping and filling proceeds. MINING IN NARROW VEINS AND BEDDED DEPOSITS 79 Cribbed man-ways are maintained through the center of the stopes to provide means of ingress and egress to and from the stopes. The method of filling employed at the Zaruma mines is applicable to moderately wide deposits of solid and firm ore 8o ORE MINING METHODS but not overly strong walls. The method is usually desig- nated as 'rill stoping.' The advantages of the method are: 1. Little timber is required. 2. Levels may be placed a considerable distance apart. 3. There is a minimum amount of handling of ore and waste-filling. 4. Filling can be carried close to the face, as it does not have to be distributed. 5. Ventilation is good. The disadvantages of the method are: 1. The inconvenience of working on a sloping bank of filling. 2. Loss of ore by mixing with waste. 3. Stoppage of all work in a stope while running in filling. 4. Little opportunity to sort ore in stopes. A variety of methods of mining is to be found in use in the copper mines of Butte, Montana, some of the more 1. St. Lawrence Mine, im P rtant f whkh are: the US6 f Stulls Butte, Mont. an( j lagging, with or without filling; 2. Copper Ore. 3. Vein. square-set timbering, with or without 4. .. without timbering, known as ' back-filling/ The width of the veins worked by this method varies from 8 to 50 feet and dip at fairly high angles, although that is not a requisite. The country rock is granite, which is usually fairly strong and solid, standing well. The vein- matter is quartz with pyrite and copper minerals. The deposits are developed by vertical shafts from which MINING IN NARROW VEINS AND BEDDED DEPOSITS 8 1 cross-cuts are driven to the veins at intervals of 200 feet, levels being run in the veins. Stopes may be opened directly off the levels, or pillars may be left immediately above the levels; in the former case the filling introduced into the stopes to support the walls is held in position by stulls set along the levels, while in the latter case a much more durable and satisfactory support for the filling is provided by the pillars. In either case the stopes are carried horizontally or the work of cutting out the ore is done by longwall stoping. (See Fig. 22.) Preparatory to stoping and before the stopes have been more than opened, waste chutes are formed in the foot-wall connecting both levels and stopes and are spaced 80 to 100 feet apart along the vein. Ore chutes and man-ways, built up from the levels, are carried upward along the foot-wall as the stopes increase in height, being strongly timbered. The ore chutes are usually placed at 2 5 -foot intervals, while the man- ways are 100 to 125 feet apart. It is customary to build two-compartment passages, an ore chute and a man-way when the two come together, which saves time and expense. Beginning at a raise or winze cut in the vein, stopes are worked laterally from it, being carried from 12 to 14 feet high and the full width of the vein. As rapidly as the broken ore can be cleared from the stope by shoveling it into the ore chutes, waste is run in, filling the stope to a depth of about 8 feet, being distributed by a limited amount of shoveling. Distribution of waste is done largely by cars running between waste chutes. The ore chutes are timbered up and kept above the level of the filling. A 82 ORE MINING METHODS I STORE -WHwaaa^ IT/ l FIG. 22. Elevation and Plan of Stopes. Back-filling Method. MINING IN NARROW VEINS AND BEDDED DEPOSITS 83 space of 4 to 6 feet is maintained between the filling and the back of the stope, which provides room for handling the waste in cars. As the filling is carried on back of the working face of the stope this particular method of han- dling it is known as 'back-filling/ and when employed in a mine the method of mining is commonly spoken of as the ' back-filling method/ Subsequent stoping is carried on in a manner similar to that of the initial work, the stopes being from 12 to 14 feet high, and the successive layers of filling placed are 8 feet thick. By this arrange- ment of parts the stopes where work is being done are 12 to 14 feet high, while the space between filling and stope-back is maintained at a fairly uniform height of 4 to 6 feet. The back-filling method is usually not employed except in strong or moderately firm ground, but occasionally ground is worked that is so weak that props must be used. Usually no attempt is made to draw the props prior to blasting, but they are pulled out of the broken ore as it is shoveled up. Comparatively few of the props are reused as supports for the back, but are employed in building chutes: In order to prevent loss of ore from mixing with the waste-filling during blasting a platform or mat of plank is placed on the filling. Planks or 'floor-boards 7 for this purpose are 2 by 8 to 12 inches and are cut in 8-foot lengths. Shoveling is materially facilitated by the use of such platforms, which are advanced with the stoping face. That there may not be an undue amount of shoveling of waste, the tracks upon which the cars carrying the filling operate are frequently shifted from 84 ORE MINING METHODS one wall to the other, the filling being run in to place rather than shoveled. Stopes may be completely worked out by this method, but it is the usual practice to leave an arch pillar of 12 to 1 6 feet thickness between the stopes and the levels. (See Fig. 22.) The back-filling method is applicable to high and moder- ately high dipping veins. The wall-rock and ore should be fairly strong and practically self-supporting, although the use of props is common. The advantages of the method are: 1. Under favorable conditions little or no timber is re- quired for support. 2. Levels are far apart, reducing the amount of develop- ment work. 3. The working face is always close enough for thorough inspection. 4. There is little danger of accidents. 5. Large outputs are possible. 6. Ore can be sorted and waste stowed in stopes. 7. Ventilation is good. The disadvantages of the method are: 1. Applicable only to veins having strong or fairly strong walls and ore. 2. Difficulty and expense of forming waste chutes. 3. Loss of ore remaining in pillars. 4. Considerable handling of ore and waste-filling. MINING IN NARROW VEINS AND BEDDED DEPOSITS 85 The method of mining employed in the copper mines of the Lake Superior region is overhand stoping with slight modifications in handling ore due to vary- j Baltic and Tri _ ing inclinations of lodes. The dip of the Mi^VMich* lodes ranges from 35 to 70 in the various c^^. Ore mines. In those lodes where the steeper 3. Vein. ,. ., , , ,, . , ^ r . 4. Width 24 to 36 ft. dips prevail and where the weight of the walls is consequently less, as in the mines of the Copper Range Consolidated, a comparatively new method of mining has recently been adopted, which is variously designated as the ' dry- wall' or the l rock- wall' and again simply as a ' filling system/ Copper occurs in the native state in the Lake Superior copper region, being found in both sedimentary and inter- stratified igneous rocks. The copper constitutes a cement which binds together and replaces the pebbles and boulders of porphyry conglomerate, or fills the amygdules especially in the upper portions of the interbedded massive rocks. In the Quincy, Franklin and Atlantic mines the lodes are amygdaloidal, i.e., are strongly altered diabase, parts of which are known as ash-beds. (See Fig. 23.) Stations are established in the shafts every 100 to 125 feet along the lodes from which levels are driven 8 feet high and the width of the lode wide. The level drifts are en- larged by cutting-out stoping, and from the rock broken down the larger pieces of waste are employed in building the pack or so-called dry-walls or rock-walls, which are 8 feet high. On these walls timbers are placed which reach from wall to wall, upon which in turn is laid a lagging of 86 ORE MINING METHODS and to operate them 50C profitably a large tonnage and low cost of mining is necessary. The ore-bodies are broad zones of impregnations in schists; they are quite irregular, varying from 30 to 500 feet in width, and usually stand vertically or nearly so. Owing to the great width of the deposits the stopes are run transversely, extending from foot- wall to hanging- wall, pillars being left between the respective stopes. Formerly it was customary to employ square-sets to support the walls, which combined with filling permitted the stopes to be worked to a height of 85 to 100 feet, the latter being more usual. It was found that square-sets if carried above 85 feet would often collapse under their own weight. With the exhaustion of the supply of suitable timber and the con- sequently increased cost, also owing to the gradually de- creasing value of ore, other and cheaper methods of working MINING IN WIDE VEINS AND MASSES 121 the ore-bodies were found to be necessary. While the general method of attack has not changed materially, radical changes in support have been made, the main idea apparently being to reduce the amount of timber employed. Timber is still used, but it is doubtful whether there are many other mines in the world in which so little timber is actually used per ton of ore extracted. This is rendered possible, however, only through the exceptionally strong and solid ore and wall-rocks. In many places the ore stands without support in low arched stopes of 60 to 80 feet in width. Following the use of square-sets and filling, a* system of back-filling was introduced, being first employed with con- siderable timbering in the form of timbered passages on the ground or stope-floor, but as the work is now carried on it would seem that the amount of timber used has been re- duced to a minimum. This has been rendered possible by a rearrangement of the drifts and cross-cuts through which the ore is withdrawn from the stopes. Descriptions of two of the more recent methods of min- ing are given below and will serve to illustrate the gradual change that is being made in these mines. In the first and earlier method levels are driven from 100 to 150 feet apart, depending largely upon the condition of the ground and the depth of the workings. The levels having been formed and connected by foot-wall and hang- ing-wall drifts and one or more intermediate drifts, the work of opening up the stope is begun. This is accomplished by carrying a working face outward and across the deposit from the drift on the foot- wall side. The stope is cut to a 122 ORE MINING METHODS e (D | In o O ffi .2 -s en g b/J MINING IN WIDE VEINS AND MASSES 123 width of 60 to 75 feet and to a height of about 10 feet, the work being done by breast stoping. Other stopes are begun along the line of the level drifts at intervals of 25 to 40 feet, the unworked portions serving as pillars between the rooms or stopes on either side. The stope having been cleared of broken ore, all lines of haulage that are to be maintained in the stope are carefully timbered and lagged. The pas- sages that are considered necessary for the proper handling of the ore are sideways and endways, the former being known as cross-cuts and the latter as drifts. The drift in the foot- wall side is timbered with a double row of sets. There were also one or more intermediate passages running transversely with the stope and connecting the cross-cuts. (See Figs. 36 and 37.) Back stoping is then begun, usually on the hanging-wall side, and carried lengthwise of the stope for a width of about 14 fet^t less than that of the first or level stope. By this method of procedure the cross-cuts are set into the pillars and protected by them from movements of ore in the stopes. No attempt is made to remove the ore as it is broken down, except to provide space for the miners above, the excess being drawn off from below along the line of the drifts and cross-cuts. As the height of the stopes increases it is necessary to provide passages for the men to and from them; this is accomplished by putting in raises, which are in line with the cross-cuts and like them are set into the pillars. These raises are timbered, and besides serving as man- ways assist in ventilating the stopes. With levels 100 feet I2 4 ORE MINING METHODS apart the stopes are carried to a height of 70 feet, at which point the roof is arched, giving an additional height of 15 feet, thus making the stopes 85 feet high and leaving an arch pillar 15 feet in thickness. With greater distance Fig. 37. End View of Stope in Homestake Mine, Back-filling Method. From Model in Engineering Office of Company. between levels, the height of the stopes is proportionally greater. Finally raises are put through the arch pillars at the highest point of the stope, thus establishing communi- cation with the level above. These raisers are subse- MINING IN WIDE VEINS AND MASSES 125 quently employed in introducing waste into the stopes for filling. The work of stoping having been completed, the ore may be withdrawn or left in the stope as a reserve supply that may be drawn upon as occasion demands. It is drawn out of the stope by breaking away the lagging on the side of the sets on the foot-wall side, thus permitting the ore to run into the drift, where it is shoveled into cars and sent to the shaft. In the course of time the foot-wall end of the stope is emptied of ore, and as the work con- tinues the shovelers leave the shelter of the timbered drifts and work in the open stope. When sufficient room has been cleared of ore the work of filling the stope is begun and continues at a safe distance behind the shovelers. It is customary, however, to cover the floor of the stope with old timber previous to placing the filling. As an extra precaution against accidents dams are often erected to check and hold back larger pieces of waste. (See D, Fig. 36.) The filling, as previously mentioned, is run into the stopes through the waste chutes formed in the arch pillars, and is similar in many respects to the back- filling method employed in the Butte mines. Drawing ore from the stopes is not confined to the drifts and inter- mediate passages, but may be carried on along the line of the cross-cuts. The ore having been completely drawn from the stope, the work of filling is continued until the curve of the arch is reached, when the filling is leveled preparatory to placing square-sets, which are employed in removing the arch pillars. 126 ORE MINING METHODS The arch pillars are removed by overhand stoping and square-setting, the work being done in sections running transversely with the stope. As the floor of the stope above is approached considerable care must be taken to prevent falls, but if the mat of timber has been properly placed there is not much danger, provided the roof is re- moved in small sections. As each section across the stope is cut out to the stope above and timbered, it is filled with waste, and work on another section is begun. It is ob- viously necessary to sacrifice the timber employed in re- moving the arch pillars, which is practically all that is lost, the parts of the sets employed in the drifts, cross-cuts and raises being used again and again until broken, when they are employed in making the timber mat. Owing to the weakening of pillars by under-cutting them for the cross-cuts and by the vertical cuts for raises, also for reasons of economy in the use of timber, a further change was considered necessary. The present method of mining, which has but recently been introduced, has had these objectionable features eliminated, and while it has not probably been in use sufficiently long to demonstrate com- pletely its success and adaptability under all conditions, it has so far proven amply adequate where its application seemed advisable. In this method the ore-body is divided into stopes and pillars, the former being 60 feet wide, the latter 42 feet, thus giving the pillars approximately ico-foot centers. Through the center of each pillar a drift 6 feet wide is run, from which cross-cuts are driven, one about midway MINING IN WIDE VEINS AND MASSES 127 V.;:(}:fiijj^'::; ; :-;:-:"<:'-o 0) \n'-'':.'-'i:, u 128 ORE MINING METHODS of the pillar and the others spaced at intervals of 30 feet on either side. Only one drift or driveway is maintained in the stopes, which is a timbered passage extending along the hanging-wall side, the main drive or level being driven in the foot-wall some distance from the deposit. (See Fig. 38.) Raises are put up as timbered passages in the stopes and at points opposite the cross-cut openings, but on one side of the pillars only. They are placed a few feet distant from the pillars, but standing wholly within the stopes, and are surrounded by broken ore. Stoping is carried on in a manner similar to that previously described for the earlier method employed. The levels are usually run 150 feet apart, making the arched stopes some 135 feet high. The arch pillars are removed by overhand stoping and square-sets. Ore is drawn from the stopes by shoveling from the cross-cuts and driveways connecting the drifts in the pil- lars. The stopes in this method of mining may be likened to huge ore pockets, the cross-cuts being chutes through which the ore is drawn off. Filling follows the withdrawal of the ore, beginning with the hanging-wall side, its introduc- tion into the stope being accomplished as described for the earlier method. It is the intention where possible to re- move the pillars after the ore has been drawn and the stopes filled. To accomplish this to the best advantage the sides of the pillars are laced for a height of 15 to 20 feet, beginning with the floor, which is done before filling the stope with broken ore and is carried upward as the stope increases in height. The lacing consists of 8 by 8 inch MINING IN WIDE VEINS AND MASSES 129 timbers placed vertically, to which slabs and planks are spiked. The lacing assists in holding back the waste-filling and prevents the mixing with the ore as it is broken in the work of stoping out the pillars. Where the stope extends above the lacing the waste may be held back temporarily by facing-boards and props. Square-sets may be employed in removing the pillars. (See Fig. 39.) Considerable ore may be lost in drawing the ore from the stoped pillars, especially during the latter part of the operation. The methods of mining employed in the Homestake mines, and as described above, are applicable to very large deposits of low-grade ore, both ore and wall-rock being hard and strong, permitting wide low-arched stopes to be worked with safety. The advantages of the methods, but with special refer- ence to the latter, are: 1. Levels may be placed a considerable distance apart. 2. Little timber is used. 3. Ore is broken at small cost. 4. Shovelers are well protected. 5. Filling is easily and cheaply placed. 6. Percentage extraction high. 7. Amount of development work small. 8. Large outputs are easily obtainable. The disadvantages of the methods are: 1. Applicable only to wide deposits standing nearly vertical. 2. The work must be carried along vertical lines. 130 ORE MINING METHODS C/2 MINING IN WIDE VEINS AND MASSES 3. As the ore breaks in large masses considerable hand work must be done in reducing to proper size to be loaded into cars. 4. The method requires considerable handling of ore. 5. The loss of ore in pillars is large unless they are ulti- mately removed 132 ORE MINING METHODS CAVING METHODS During the comparatively short time that iron ore has been mined in the Lake Superior region many changes in methods have been made, which con- 1. No Local Applica- tion dition of affairs has been brought about 2. Iron Ore. . ... 3. Massive Deposits largely by experience in mining under 4. width of Veins 40 vai> i us conditions, lack of suitable timber to so ft. anc | a d emanc i f or cheaper ore. There are, however, two methods of mining that have been em- ployed for many years, and while modified from time to time to meet certain conditions, they remain fundament- ally the same. These are the top-slice and sub-drift methods. No local application will be made in the descriptions of these methods, other than to state that they are applied equally well to wide veins and to masses covering considerable areas. Veins ranging in width from 40 to 80 and 100 feet and with dips of 60 to 80 may be readily worked by both methods. The development of the deposits is the same, except as to the work in the vein, consisting of inclined or vertical shafts sunk in the foot-walls of veins or in the firm ground some distance from masses of ore, levels being 50 to 75 feet apart. In the top-slice method, after the cross-cuts from the shaft have reached and been driven into the deposit, main levels intersecting them are run through the center of the ore-body, being connected at intervals of 100 feet by two compartment raises. These raises contain an ore chute and a timber chute and a man-way, the last two being the same, MINING IN WIDE VEINS AND MASSES 133 and are put up to barren or to caved ground as the case may be. Beginning at the top of a raise a drift is run parallel with the main level below and from both sides of the raise. (See Figs. 40 and 41.) If the work is carried on sys- tematically these drifts should meet other drifts similarly driven from adjoining raises, or encounter caved ground, the ore having been mined out. Cross-cuts are turned off at the ends of the drifts and the ore removed to the vein- walls. These drifts and cross-cuts must be carefully tim- bered, the sets often being given double posts. The ore is hauled to the chute in small cars and in some cases handled in wheelbarrows. The cross-cuts having been run to the walls, a mat of timber is placed on the floor, consisting of three long stringers laid near the foot of the posts of the sets and midway between them, upon which in turn are placed split lagging and slabs. This mat of timber sup- ports the caved material when a drift is run beneath it. To facilitate the work of placing the mat, the cross-cuts are driven in only one direction at a time, thus permitting the placing of the mat in the finished cross-cuts on one side of the drift. (See Plan of top-slice, Fig. 41.) The mat having been placed, the sets are blasted out, permitting the roof to cave close up to the ends of the pillars. Other cross-cuts are then opened up at the ends of the drifts adjacent to the caved ground, the same process of cutting out, timbering, placing mat and caving the ground being repeated. This is continued until the pillars are entirely removed, when the drift is of necessity closed and a new drift is opened up at the top of the raise as was previously 134 ORE MINING METHODS LONGITUDINAL ELEVATION TOP-SLICE Fig. 41. Plan and Longitudinal Section of Top-slice Method. MINING IN WIDE VEINS AND MASSES 135 done, and work on a new slice is begun. Timber is hoisted through the man-ways to the slicing drifts. The top-slice method is applicable to large bodies of cheap ore, which may be hard or moderately soft. If veins are worked they should have a dip not less than 60. The advantages of the method are: 1. Development is simple and quickly done. 2. Opportunity is afforded for sorting ore, as keeping Bessemer and non-Bessemer ores separate. , 3. Practically the complete extraction of ore is possible. 4. Ventilation is good. 5. Little danger of accidents from falls. 6. Cost of mining is low. The disadvantages of the method are: 1. Number of working places limited, thus limiting out- put. 2. Levels close together. 3. Considerable timber required. 4. Much handling of ore and timber. 5. Confined to deposits close to the surface. The sub-drift method, while employed in the same district and even in the same mines as the top-slice, differs radically from it both in methods of development and in working. The development of a wide lode which is to be worked by the sub-drift method is shown in Fig. 42. A main level is run in the deposit, near the foot-wall, connecting the points where the cross-cuts from the shaft enter the lode, from which drifts are driven at intervals of about 50 feet, 136 ORE MINING METHODS cross-cutting the lode. A second main level is then run along close to the hanging-wall and connected with the cross-cutting drifts. The ore on the levels is cut-up by means of the drifts and levels into blocks some 50 feet long and the full width of the lode. At 5o-foot intervals along the line of the main levels, raises are put up from which other drifts are driven, forming the so-called sub-drifts. Beginning at a lower level than is being worked, a raise is put up for a height of 6 or 8 feet and timbered, after which two drift sets are placed and lagged over, thus forming the starting point of sub-drifts which are driven in both directions, ultimately making connection with other drifts driven from adjoining raises. As soon as the ' subs ' are well started the raise is put up another 6 or 8 feet and a second set of subs is begun. The operation of putting up raises and driving subs is con- tinued until the raises break through into the level above and the subs have made connection with other subs. It is then evident that when all the subs and raises have been completed the ore between two adjoining levels is honey- combed by both horizontal and vertical passages and is ready for the last stage of the operation of extraction of the ore. Sub-drifting is, then, preliminary development work in the deposit itself, and is an intermediate operation between the opening of the deposit by shafts, cross-cuts, levels, etc., and the actual work of breaking down the ore. (See Fig. 43.) The height of the respective subs is the distance from the floor of one to that of another directly above it, and varies from 12 to 15 feet, depending largely upon the character and condition of the ore. MINING IN WIDE VEINS AND MASSES 137 CROSS-SECTION SUB-DRIFT Fig. 42. Section through Lode showing Method of Development in Sub-drift Method. 138 ORE MINING METHODS The work of sub-drifting is followed by the removal of ore from the pillars standing between the subs and the drifts, also that standing in the back above the level of the tops of the subs, and is commonly known as l stripping.' Consider that the work of stripping has reached the point shown in the longitudinal section, Fig. 43. By knocking down the supporting posts, as shown at the left of the first sub, the back of ore will fall and can be shoveled up and hauled away to the chutes. The settlement of the broken rock above is controlled by the mat of timbers which is constantly being added to by the timbers in the subs that are lost and broken. The method of cutting-out the pillars is shown in the plan, Fig. 43, as at the left where the stubs of pillars are being removed, the back standing on posts. As a sub cannot be worked beneath others not yet removed, it is necessary to either entirely remove the upper sub before beginning work on a lower one, or to carry on the stripping in descending order, each sub being carried some distance in advance of the one below. As soon as the stripping operation reaches a main level that level is abandoned and all communication with the subs below must be through the lower level. The usual practice is to have one level or lift (the block of ore between levels) in the process of stripping; the next lower sub- drifting, while the third lift below is being opened up by cross-cuts. The ore will also have to be run through the chutes from the upper to the lower sub. In order to facili- tate the handling of timber it is brought in from the upper MINING IN WIDE VEINS AND MASSES 139 level and lowered to the respective subs instead of being raised as in the top-slice method. Light but close timbering is the rule and by careful work the caving ground can be controlled with little or no danger of crushes and loss of ore. The work of mining by the sub-drift method as described is for comparatively hard and strong formations, but when soft and unstable formations are encountered, either the method will have to be modified to meet the special condi- tions or a change of method will be necessary. The method of working by sub-drifting as employed at the Susquehanna Mine at Hibbing, Minnesota, is shown in Fig. 44. On approaching the limits of the ore-bodies in this mine masses of clay and sand are encountered, which unless care- fully controlled will break into and fill the workings. A block of ore is shown, the opening up of which has developed the bad condition of the ground, which is under control by the employment of dams in the drifts and cross-cuts and even at the face where stripping is being done. Two sets of dams are shown, which were found necessary in order to hold back the clay and sand. The dams are built of one- inch pine boards strongly reenforced by backing strips and braces. The method of attacking the pillars is shown by the arrows. The back varies from 8 to 12 feet in thickness, and is caved by blasting out three sets at a time, thus bring- ing the cave to within one set of the working face. The timber used for sets in this mine is 8 to 10 inches in diameter, the floor being covered with rough pine boards upon which the sets stand. These boards render shoveling easy and 140 ORE MINING METHODS PLAN OF THIRD SUB-DRIFT Fig. 43. Longitudinal Section and Plan of Sub-drift Method. MINING IN WIDE VEINS AND MASSES 141 make a good mat in controlling the movement of broKen ground and waste ore. The sub-drift method of mining is applicable to both hard and moderately soft ores, preferably the former, but not to mixed ores as where Bessemer and non-Bessemer ores occur together. It is strictly large-scale work and may be applied to massive deposits or large lodes of cheap ore. The advantages of the method are: 1. Large outputs are possible owing to the large number of points of attack. 2. Cost of mining low. 3. The complete extraction of ore practically possible. The disadvantages of the method are: 1. Much timber is required. 2. Development work extensive and complicated. 3. Little or no opportunity afforded for sorting ore. 4. Considerable handling of ore and timber necessary. 5. Ventilation is poor. 6. Stripping operation rather dangerous. 7. Confined to deposits lying close to the surface. 8. Limited to comparatively hard ores. Of the various methods of mining in use in the Bingham Canyon mines, that employed by the Utah Copper Com- pany is both ingenious and efficient, if one Utah copper Co.'g can judge by the speed and facility with which cars are loaded and handled. 3* Sassfve Deposit. The caving method referred to above 4 ' Very Extensive - is employed at a point opposite the extensive steam 142 ORE MINING METHODS MINING IN WIDE VEINS AND MASSES 143 shovel workings. It is employed in working the porphyry ore, which averages 1.8 per cent copper. The extent of the deposit is stupendous, varying in thickness from 100 to 300 feet and reaching practically from center to center of the mountains on either side of the Canyon. It is, then, evident that there is practically an unlimited field for the develop- ment of a method of mining, which should, however, be extensive, systematic and economical in operation. The deposit is opened up by a tunnel which connects on the main level with a system of drifts and cross-cuts by means of which a certain area is subdivided into blocks averaging probably 50 to 75 feet square. This preliminary development work is essential, as it determines the lateral extent of the workings above, and facilitates handling ore. The same method of procedure is followed on each main level, of which there are only two in this mine, the levels being 200 feet apart. From the main levels, raises or chutes are put up 30 to 33 feet vertically, after which they are driven at an angle of 55 with the horizontal. These main raises or chutes usually extend to cap-rock, and often break through on the surface, providing good ventilation. At intervals of 30 to 35 feet, usually 33 feet, sub-levels or subs are opened from the sides of the raises, which are in turn connected by cross-cuts, forming roughly square pillars 50 to 75 feet in size. (See Figs. 45 and 46.) Branch raises or chutes are then driven at angles of 50 to 55 with the main raises, making connection with midway or inter- mediate points in the subs and cross-cuts, thus facilitating the handling of ore in the blocked-out ground. When all 144 ORE MINING METHODS SHOOTS JO HOnOUHl NOIJ.03S g a oi9-37 7,482.08 1,329.87 4,158.20 11,667.61 61,629.00 7,876.30 9,292.80 2,297.20 $0.185 0.076 o-379 0.048 0.403 0.023 0.023 0.091 0.023 0.004 0.013 0.035 0.186 0.024 0.028 0.007 $0.191 0.082 0.400 . 042 0.450 0.027 0.025 O.III 0.026 0.004 0.014 0.032 0.199 0.024 0.030 0.007 $0.165 0.063 o-339 0.058 0-379 0.021 0.021 0.087 0.017 0.006 O.OI2 0.025 o. 165 0.027 0.030 0.006 Miners Car-men Shovelers Power labor Repair labor Explosives Illuminants Lubricants. Iron and steel Miscellaneous supplies. . Timber and lagging. . . . Power supplies Wood Stable and stock Total $511,288.16 $1.548 $1 . 664 Nov. $1.421 May. Ore is not particularly hard to drill and blast. The comparatively high cost of timber as shown in the above table is due to the fact that square-set timbering is an important adjunct to the mining of the ore in this district. The high cost of labor, particularly for shovelers, is due to the necessity of freeing the stopes from ore and placing waste-filling. 200 ORE MINING METHODS The Goldfield Consolidated Mines Company, Goldfield, Nevada The costs of stoping during ten months of 1909 are given in the following tabulation: Cost per Ton. Labor $i . 24 Supplies o . 66 Power o . 03 Department o. 25 Construction o . 02 General . . o. 18 Total $2.38 Ore is a fair average for drilling and blasting. The first three items given are regular and legitimate cost for this kind of work; the last three are indeterminate, and while they may be composed wholly or in part of ex- penditures necessary for the proper carrying on of the work of stoping, yet their designation leaves this in doubt. The Joplin Lead-Zinc District, Missouri The cost of breaking ground in the Joplin district varies considerably owing to character of ground, which ranges from very hard to very soft. The usual conditions existing in the sheet ground in the vicinity of Joplin, Webb City, etc., permit the ore to be broken down at moderate cost. The following costs are representative of the district: COST OF STOPING 2OI COST OF STOPING IN 1901 2 machine men at $3.00 $6 . oo 2 machine helpers at $2.50 5 . oo 2 shovelers at $2.50 5 . oo i blacksmith at $2.50 2 . 50 i ground boss at $3.00 3 . oo Explosives 6 . oo Incidentals 3 . oo Total $30 . 50 Drilling and blasting fairly easy, although variable, owing to character of ground encountered. The $30.50 represents the expenditure for one day when 75 tons of ore are broken; the cost per ton was then about $0.40. Other more detailed costs of operations that go to make up the cost of breaking ground, also related cost data ex- pressed in cents per ton, are as follows: COST OF STOPING IN 1903 Cost of drilling, hand work $0.06800 Cost of drilling, machine work 0.05600 Cost of drill steel o . 00878 Cost of powder, caps and fuse o . 04050 Cost of oil for lamps o . 00080 Cost of timbering, soft ground o. 00045 Cost of pumping, mine pumps o . 00005 Cost of track o . 00009 Cost of shoveling o . 03900 Cost of labor underground o. 19890 Cost of hoisting o . 02860 Cost of tramming 0.02600 Cost of air compressor 0.00150 Total $0.46867 The cause of the variation of 7 cents per ton noted above is difficult to explain, but is slight when the factors influ- encing the costs are considered. The period during which 202 ORE MINING METHODS the figures from which the averages were calculated is a controlling factor if short, otherwise not. The War Eagle Mine, British Columbia The costs previously given are for mines located in the United States. The cost of stoping as given in the company's report of the War Eagle Mine for the year 1909 illustrates, even to better advantage than in the previous cases cited, the spread of costs, involving practically all operations having to do with the underground work. The following costs are figured on a ton basis: 1. Drilling $i-53 2. Tramming and shovelling o. 53 3. Timbering o . 29 4. Hoisting o . 13 5. Smithing o. 15 6. Ore sorting o.oi 7. General labor o . 30 8. Air 0.21 9. Candles and illuminating oil 0.03 10. Explosives 0.02 11. Drills and fittings. . . 0.25 12. Mine supplies 0.05 13. Lumber expense o . 04 14. Stable and teaming o . 03 15. Assaying o . 04 1 6. Surveying o . 05 17. Electric lighting 0.02 18. Salaries o . 03 19. Office expenses o. 18 20. General expenses 0.05 Total $3.95 Ore drills and blasts moderately well. In comparing this cost of stoping with others which have not been so extensively distributed it would be necessary COST OF STOPING 203 to eliminate a number of items, those chosen for actual use being i, 5, 8, 9, 10, n and 12. The items 2, 3, and 6 might very properly in this case be included, especially 3, as square- set timbering is employed. The item of drilling is probably labor of operating drills, while the air item indicates the cost of power. Drills, fitting and mine supplies consist of steel and other drill repairs. An examination of the above data brings out the fact that the larger the company, and consequently the operation, the more detailed are the working costs, which is not shown to particularly good advantage either owing to the com- bining of certain costs in this connection. By increasing the number of items in an operation and putting the collec- tion of the data upon which the costs are based in the hands of a sufficient number of competent men it is possible to secure fairly accurate results, but there is always danger of lax work being done, short cuts being taken and approxi- mations made, which if persisted in mean inaccurate and untrustworthy returns. Another cause of error, aside from poor organization of the data-collecting force and arising from the distribution of costs, is that often no account is taken of variations in work done by the factors involved. This can be illustrated by the one item of power, the cost of which is commonly distributed uniformly over all the machines of a kind, as machine drills in stoping. It is rarely the case that out of 100 or even 50 drills employed in stop- ing, all are being operated at the same time, i.e., continu- ously day after day. An ordinary piston drill is seldom running more than one-half the time that it is supposed to 204 ORE MINING METHODS be in operation. The advent of the air-hammer drill, which is now being largely employed in stoping operations, might be supposed to change these conditions, for- where used in similar work as the piston drill it is running the greater part of the time. It would seem that the consumption of air would be greater, and so it would were it not for the fact that the consumption of air is less, approximately one- half that of a piston drill. Where continuous operation is maintained under conditions such as permit the drilling of a greater footage than with piston drills, there would have to be a different unit of cost calculated if the two types of drills were operating in the same mine, which would lead to still further complication in the estimation of costs of power. Further, the power required for each drill varies considerably both with its period of service and the skill and experience of its operators, and to a less extent with its distance from the source of power, as in the use of air drills. In order, then, to show the correct cost of power for a drill employed in stoping it is necessary to know at least the number of drills that are in actual operation, which can only be determined by daily inspection. This requires a constant and often daily change of unit costs, which is somewhat confusing. A fair and uniform charge per drill-shift is probably preferable, which unit cost multiplied by the number of units will at once give the power cost desired. The cost per drill-shift for various styles of compres- sors and at different altitudes is given in the following table. COST OF STOPING 205 Cost per loco cu. ft. Free Air, Com- Cost per Drill- oViiff pressed. snitt. Maximum Total Style of Compressor. Capacity, cu. ft. Free Air per Cost per H.P. Sea Level. 5000 ft. alt. 10,000 ft alt. Sea Level. 5000 ft. alt. 10,000 ft. alt Minute. Hour. cents. cents. cents. cents. dols. dols. dols. Simple steam (non-condensing) 200 2.2 5-9 5-3 4.8 2.07 2. 22 2.40 Compound steam (non-condensing) 300 i-5 4.0 3-6 3-3 1.40 1.50 1.65 Simple steam (condensing). . . . 2500 I.O 2.7 2.4 2.2 -95 I .01 I. 10 Compound steam (condensing) .... 3000 0.8 2. 2 1.9 1.8 .76 .81 .88 Three-inch drill taken as standard. Eight-hour shift time of working. Cost of coal, $5.00 per ton. The cost will vary, of course, with the character of rock or ore drilled. The above figures were calculated from data collected from work done in granite. The compressors are all two-stage, intercooled. The differentiation between cost of various operations, rendering each account simple and complete in itself, would seem desirable. Tramming, hoisting, etc., might readily be placed under a class of operations separate from stoping, as handling ore outside the stope. In other words, charge to stoping just those operations that are confined to the stopes, thus localizing the operations and their costs. Sim- plicity, both with regard to the management of the work and the collection of data upon which costs are figured, is of probably the most importance, and this can be effected to good advantage by contract work, where the miner keeps his own accounts largely, or at least is sufficiently inter- ested to keep close check upon them. The operator, in 206 ORE MINING METHODS turn, checks off results as the output resulting from the miners' labor, and pays for work actually done. The con- tract work previously mentioned as in the case of the Wolverine Mine illustrates the point. The two general contract systems employed are: measure- ment of volume, as ' advance ' in drifting and volume of ore broken in stoping; and the hole-contract, i.e., the measure- ment of the number of feet of hole drilled. The following data show the saving effected by the employment of the contract system in place of the wage system in stoping as was done in the Center Star and War Eagle mines of Ross- land, British Columbia: Contract (hole) System, per Ton. Wage System, per Ton. $0 -1*6 f d Blasting O O2I $0.750 Explosives . O. IOO o. nc; Total $o. 477 $0.865 The advantage gained by the company was also a gain for the miner in that his daily wage was increased from $4 to $4.25, as against $3.50 under the wage system. The increased wage shows both a saving per ton in cost of stop- ing and an increased tonnage of ore broken, a natural result due to better pay, as previously indicated. It might be stated in this connection that the contract system, in which the miner is paid by the fathom or other unit of volume, has proven unsatisfactory in these mines owing to the difficulty of measuring exactly the volume of COST OF STOPING 207 ore broken in the very irregular stopes the pay-shoots being very irregular in outline. COST OF SUPPORT IN STOPES In certain kinds of work, as working slightly dipping deposits, square-set mining, etc., the cost of support may be a necessary and important part of the cost of breaking ore or stoping, being usually figured on the tonnage basis. A single case will suffice to show the cost per ton under average conditions, and for comparative purposes the cost under two different systems of working are given. The figures given below, prepared by Mr. B. C. Yates, are for the old square-set method and a more recent method now being largely employed in the Homestake mines of South Dakota. AMOUNT AND COST OF TIMBER, SQUARE-SET METHOD Name of Piece. Number of Pieces. Lineal Feet or Feet Board Measure. Cost of Material. Labor, Sawing and Framing. Total. Sill-floor posts 421 3,650 $474. 50 $06.83 $^7l . 33 Upper floor posts. . . Caps . 2,077 2,410 16,616 13, 2CC 2,160.08 1,723. 1C 477-71 506 10 2 6 37 -79 2 22O 2 ? Ties 2,261 12,43s 1,616. ex 474.81 2 OQI 36 Sills, 203 long, 382 short A 537 226 85 22 60 Lastjinsr 13,020 75 006 37QC -30 770 c -} 41 74. 83 Lagging strips Wedges 47 sill-floor chutes, complete 2,410 2.352 4,025 784 64.82 13-33 3ii 68 30.00 11.76 16 25 94.82 25.09 215 upper- floor bins, complete 786 22 37 QO 6* 1 -yo 824 12 Ladders 14 H7 I .QO 3 to 54O Labor placing tim- bers and chutes . . 4 74^ OO Breakage (10%) of lagging, 5% posts, caps and ties 7Q7 Q7 Totals $11 174. 47 $2 O57 08 $-18 770 (J2 208 ORE MINING METHODS AMOUNT AND COST OF TIMBER, HOMESTAKE METHOD Name of Piece. Number of Pieces. Lineal Feet or Feet Board Measure. Cost of Material. Labor, Sawing and Framing. Total. Sill-floor posts 421 3,6co $474.50 $96.83 $C7I.33 Caps 4.IO 2,2C.O 2Q3. JC 86 10 270 2C Ties ^Si 2,00? 272. 3C, 80 01 3C2 36 Sills, long 2O3 ^,-. y ^ 2,436 121. 80 12. 18 133 08 Sills, short 382 2,IOI IOC .OC IO.