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By W. R. Crane

The support of roof in mines is dependent largely on the character of the top rock and its occurrence. The formations overlying the orebed in the Birmingham district are sandstone and slate. The sandstone occurs in beds of sufficient thickness to constitute important elements in the system of support; the slate is relatively strong but is thinly stratified. The alternating beds of sandstone and slate furnish an excellent combination in that the former are strong and the latter are impervious; however, their continuity is broken by jointing or slip planes. The thickness, and consequent weight of the overlying formations, is important in so far as the size and arrangement of pillars are concerned but may be relatively unimportant, temporarily at least, as a factor in the support of the roof. The position of the respective beds of sandstone and slate, their relative thickness, and their inherent weakness because of the occurrence of faults and folds, may exert a predominating influence on their support in place, which is affected only in part by the weight of the cover. The only mine in this district that operates under a cover of approximately 2000 ft. (1900 ft.) is the Shannon so-called "twin slope," situated 14,000 ft. southeast of the portal of the No. 7 mine of the Tennessee Coal, Iron, & Railroad Co. The conditions in this mine indicate what may be expected in other mines when the same depth is attained; in fact, the effect of pressure is shown in several mines that have not reached two-thirds of that depth. It is evident, then, that conditions affecting the support of roof will not improve but rather will become more difficult with the extension of the mines into the valley under a constantly increasing weight of cover. Further, the difficulties will probably be augmented by the occurrence of faults and other disturbed ground, the presence and position of which at present are largely unknown.

Jan 1, 1925

Jan 1, 1910

"The 100,000 volt sub-station at Butte is located near the center of the district in which the power is distributed. The sub-station building is 150 feet by 50 feet in plan and 50 feet high. It is a brick walled, steel framed structure with concrete floors and roof.There are installed at present four banks of single-phase transformers, rated at 3,600 k-w. per bank and connected in delta on both high and low tension sides. They step the voltage down from 102,000 to 2,500, at which voltage it is distributed to customers. The transformers are installed in fireproof compartments, entirely shut off from the rest of the building by brick walls and opening only out of doors. The transformers are mounted on wheels and can readily be run out onto a flat car, which stands on a track running parallel with the building in front of the row of transformer compartments. This arrangement furnishes a convenient method of handling the transformers, both at the time of installation and afterward, in case it is necessary to make repairs."

Jan 1, 1913

By J. Kitagawa

INTRGDUCTION The Paragsha concentrator is the largest of Cerro de Pasco Corporation's base metal beneficiation plants operating in Peru. At present, this plant is treating an average of [ ]

Jan 1, 1970

By J. P. Zannaras

If we assume that testing of the model started at time t1, that time t2 was the instant at which the elastic limit of the material was passed at the points of the maximum stress, and that at time t3 the failure of the model was completed as shown in the typical photograph (Fig. I), then actually the photograph shows the final results of what took place between time t2 and t3. By the principle of similitude all conclusions drawn from the behavior of the model were applicable and valid for actual mine roofs up to the time t2 after time t2 motions and friction came into play during the destruction of the model. The events between t2 and t3 and the photograph itself are not representative of the events expected in an actual mine roof unless corrections imposed by the principle of similitude are made. It can therefore be stated that all conclusions and observations of the author from the photographs are applicable only to his small-scale experiments and not to actual mine roofs. Without investigation of the true stresses or the combined maximum stress induced in the beds it has been assumed by the author that failure occurred solely due to bending stress caused by loading of the beds. (The author states that D was taken to be the theoretical strain given by elementary beam theory.) Fig. 1 shows that the beds were clamped together. This clamping was necessary to prevent slipping of the beds due to the horizontal shear. However, this clamping caused an uncontrolled and undertermined com-pressive stress S at the end of the beds, and this com-pressive stress caused a true tensile stress ?S (? PoiS-son ratio). This true tensile stress combined with the tensile stress produced at the end of the beds due to loading (fixed beam uniformly loaded), and the horizontal shear which is maximum at the end appears to be the most probable maximum stress produced in the beds. It is therefore evident that the author in performing this experiment has introduced stresses in the model not existing or dissimilar to actual mine roofs, and therefore his conclusions may be applicable to his small-scale experiments but inapplicable to actual mine roofs. Louis A. Panek (author's reply)—The discusser's difficulty is related to mechanics of materials rather than similitude. The effect of time did not enter into the tests in any way, being simply excluded from consideration in this study, because all quantitative results entering into the design equations are based on measured (between time t1 and time t2) bending strains that are well below the breaking strain (i.e., in the elastic range) for the model material. Time does not become a significant factor until the rock stress reaches 80 to 90 pct of the breaking stress." The objective of this investigation was not to predict that bolted roof will fail after time t, but was instead to develop a safe roof, that is, roof in which the bending strain is much less than (say less than 50 pct of) the breaking strain. The models tested to failure had no direct bearing on the design equations. Although for some rocks time may influence the magnitude of stress or strain at which fracture occurs, breaking stress or breaking strain values were not employed for any purpose in this investigation. Tests to failure were made only to obtain additional evidence regarding the behavior of the bolted laminae' as evinced by the locations of the cracks. As stated in the last paragraph of the paper, if one wishes to predict the time or stress conditions for which the roof will fail, additional information is required. The reason for clamping the laminae is to make them behave liked clamped beams, which closely approximate the clamped-plate condition of the actual mine roof beds (Ref. 5, p. 1; Ref. 6). The writer has previously demonstrated that the bending stresses induced by centrifugal loading in a clamped model beam are in agreement with those predicted by theory;' hence clamping has no significant effect on the bending ,trains measured during a test. Moreover, actual ,in, roof beds are likewise subject to a clamping effect due to weight of superincumbent strata carried by the pillars or ribs on each side of the opening. It is emphasized that this study was restricted to evaluating only the reinforcing effect produced by the bolts. Procedures employed in the experiments and in the data analysis were such as to deliberately exclude the effects of other factors. The objections offered are therefore invalid,

Jan 1, 1957

By H. I. Altshuler

THE mines operated by the Compañia de Real del Monte y Pachuca, Pachuca, Mexico, are in two districts, the Pachuca, and Real del Monte. The principal area of mineralization is within a rectangle roughly 10 miles from east to west and 6 miles from north to south. It contains a number of veins from 2 to 20 ft. wide, which are exploited by this mining company. The scattered position of the producing mines led to the construction of two mills between 1906 and 1908; the Loreto mill, in Pachuca, averaged 2600 tons daily, and the Guerrero mill, in Real del Monte, milled 1270 tons daily. On Feb. 1, 1929, the management decided to enlarge the Loreto mill to take the combined tonnage of both mills at that time. This economic measure required the centralization of ore delivery, which would also afford a material saving in the cost of ore transport. The centralization would give the company the following advantages over the former system of operation: 1. Beneficiation at a single mill, closer to source of materials and supplies than the abandoned- Guerrero mill. The refinery is, also in the Loreto patio. 2. Ore delivery to surface at one point (San Juan Pachuca shaft) instead of at four. 3. Elimination of aerial tramways. To show what would be required to effect this centralization, it is necessary to describe the means by which the ore was delivered to the two mills, prior to centralization. The heart of the Real del Monte district is roughly four miles from that of the Pachuca section. The producing mines in these two districts were: Pachuca district: Santa Ana mine Camelia group

Jan 1, 1934

By A. F. Taggart

This paper describes the result of a series of experiments run in the laboratory of the School of Mines, Columbia University, during the winter of 1927-28. It shows that the several operating adjustments of a pneumatic table produce effects in the action of a given coal that may be grouped into two classes, viz.: stroke length, speed and rocker-arm angle, which affect longitudinal travel; air supply and table slope (transverse and longitudinal), which determine transverse travel. The magnitude of the effect of the different adjustments varies. Some of the adjustments affect stratification of the bed, both as respects size and specific gravity of the bed components, as well as direction of travel. Operation of a pneumatic table is fundamentally different from that of a wet table in that the former exerts, through the air supplied, a force on the particles upward away from the deck which is lacking on the wet table while, on the other hand, it lacks the positive control over cross travel that is supplied by the wash and feed water. Apparatus The pneumatic table used is shown in Fig. 1. Deck A is 20 by 12 in. and consists of nainsook supported on slats that register with the riffles. Fig. 2 is a photomicrograph of the nainsook used. It shows that the cotton threads average about 0.13 mm. dia. and the apertures about 0.17 mm. The deck carries 12 riffles consisting of wooden strips, 3/16 in. wide and 1/4 in. high, laid parallel to the feed side of the table. The riffles terminate along a line starting on the feed side at a point 11 in, from the mechanism end and running to the corner formed by the coal side and slate end. Taper starts from a line that runs parallel to their terminal line through the junction of the upper riffle with the mechanism end. The height at the terminal line is about 1/32 in. The deck with its supporting slats is carried on a framework consisting of rails A, sloping end rails B, and adjustable metal strips C, which latter permit variation in transverse slope. This frame is enclosed at the edges by means of heavy canvas, indicated in the sketch by wavy lines, which makes a flexible conduit between the deck and the stationary air chamber,

Jan 1, 1930

By John Van N. Dorr

Introduction.................... 212 The DoRR Classifier.........212 History................ 212 Description................... 215 Regulation of Products............. 216 Cost of Operation.............216 Power...........216 Capacity..............216 Uses.................217 The Dorr Thickener.............219 History...........292 Description.............. 221 Speed............ 222 Power......,....223 Repairs.............,... 223 Labor................. 224 Capacity................ 224 Density of Underflow............... 224 Uses.........,.......226 Continuous Counter-Current Decantation....... 227 Concentration..............227 Industrial Uses................228 Acid-Proof Thickeners.......... 228 The Dorr Tray Thickener........... 229 Description.................. 229 Capacity................. 231 The Dorr Agitator................. 232 History................... 232 Description................... 233 Speed.................... 234 Power.................... 234 Renewals................... 235 Efficiency................... 236 Selective Agitation................ 236 Conclusion................... 237

Jan 1, 1915

By Leonard C. Grimshaw

Diffusion of carbon from gases into iron has been the object of much research, because of its long recognized importance in carburizing processes, but the direct diffusion of carbon from steel into iron has received relatively little attention. Because of the increasing use of clad metals in industry, direct diffusion from steel into iron is becoming of practical importance. Therefore, the object of this investigation was to study the diffusion of carbon from several different kinds of steel directly into relatively pure iron, realizing that elements in the steels other than carbon might influence the rate of carbon diffusion. The previous work on diffusion of carbon into iron has been considerable, and includes many reports in foreign languages. This work has recently been well reviewed by Mehll and Krynitsky12 and the reader is referred to their excellent bibliographies. Methods of Study There are two main methods by which the direct diffusion of carbon from steel into iron may be studied. In one method, steel is first decar-burized in part, and diffusion of carbon then allowed to take place from the steel into the decarburized steel. This method is open to two serious objections: (1) the decarburized steel is not iron, but contains elements such as manganese, silicon, chromium or tungsten, which may be an essential part of the steel under study, and which may seriously influence the diffusion of carbon into the decarburized area; (2) there is from the start of diffusion an unknown carbon-concentration gradient between the steel and the decarburized area. Another method, which possesses neither of these disadvantages, is to study diffusion from steel into a thick plating of electrolytic iron. Herc the chief difficulty is to secure an electrolytic deposit of iron upon steel without introducing an oxide film at the interface that will interfere with diffusion. The author is able to deposit iron upon any kind of steel without introducing an oxide film at the interface, so that diffusion of elements from the steel into the iron is free to proceed unhindered.

Jan 1, 1938

By Leonard C. Grimshaw

Diffusion of carbon from gases into iron has been the object of much research, because of its long recognized importance in carburizing processes, but the direct diffusion of carbon from steel into iron has received relatively little attention. Because of the increasing use of clad metals in industry, direct diffusion from steel into iron is becoming of practical importance. Therefore, the object of this investigation was to study the diffusion of carbon from several different kinds of steel directly into relatively pure iron, realizing that elements in the steels other than carbon might influence the rate of carbon diffusion. The previous work on diffusion of carbon into iron has been considerable, and includes many reports in foreign languages. This work has recently been well reviewed by Mehll and Krynitsky12 and the reader is referred to their excellent bibliographies. Methods of Study There are two main methods by which the direct diffusion of carbon from steel into iron may be studied. In one method, steel is first decar-burized in part, and diffusion of carbon then allowed to take place from the steel into the decarburized steel. This method is open to two serious objections: (1) the decarburized steel is not iron, but contains elements such as manganese, silicon, chromium or tungsten, which may be an essential part of the steel under study, and which may seriously influence the diffusion of carbon into the decarburized area; (2) there is from the start of diffusion an unknown carbon-concentration gradient between the steel and the decarburized area. Another method, which possesses neither of these disadvantages, is to study diffusion from steel into a thick plating of electrolytic iron. Herc the chief difficulty is to secure an electrolytic deposit of iron upon steel without introducing an oxide film at the interface that will interfere with diffusion. The author is able to deposit iron upon any kind of steel without introducing an oxide film at the interface, so that diffusion of elements from the steel into the iron is free to proceed unhindered.

Jan 1, 1938

Featured at the 1977 SME-AIME Fall Meeting in St. Louis is a Lead-Zinc Update, organized to complement the 1970 AIME World Symposium on Mining and Metallurgy of Lead and Zinc, also held in St. Louis. The 21 papers comprising the Update are to be presented during four technical sessions at the Fall Meeting; in addition, the papers have been collected in a bound book available at meeting time.

Jan 9, 1977

By Stephen Birch

THE Chitina mining district of Alaska is located at the headwaters of the Chitina and Copper Rivers. At present, the only producing min-ing properties are the mines of the Kennecott Copper Corpn. and the Mother Lode Coalition Co., which are situated 196 miles from Cordova the port of entry. The first claims, later acquired by the Kennecott Mines Co. and afterwards transferred to the Kennecott Copper Corpn., were discovered in 1900. The Copper River & Northwestern Ry., which connects the mines with tide water at Cordova, was completed in the spring of 1911. Contemporary with the construction of the railroad, aerial tram equipment was brought to the mines by pack train and a tramway, 3 miles, long, connecting Bonanza mine with the proposed railroad terminal, was finished, enabling shipments of high-grade ore to be made immediately on the completion of the railroad. A mill to treat the lower grade ore was begun the same year. The Kennecott company's holdings consist of 111 mineral claims. The Mother Lode Coalition Mines Co., which is controlled by the Kennecott Copper Corpn., owns 73 claims adjoining the Kennecott holdings. All data on operations and geology refer equally well to the Mother Lode property.

Jan 1, 1924

By A. M. Johnson, M. M. Singh

The mechanism of failure under a drill bit is still improperly understood in spite of several investigations of the subject. Generally, the cratering process under static loading conditions is considered to be similar to that achieved dynamically by impact. This paper attempts to indicate that, although the sequence of fracturing in the two cases appear to be identical, at least some dissimilarities exist. For example, the width-to-depth ratios of the craters vary to some extent, and the amount of energy consumed per unit of volume of craters is unequal for the two different loading conditions. Prevalent rock penetration processes are dominated by methods utilizing mechanical attack on rock. It is, therefore, generally accepted that a better comprehension of the mechanism of rock failure under a wedge would prove beneficial towards improving present drilling techniques. Several attempts have been made in recent years to explain how craters are formed under a drill bit, but the mechanism of failure beneath a bit is still improperly understood. 1-11 Most investigators, to date, have inferred the sequence of events occurring during crater formation from analyses of force-time diagrams,1"6 from theoretical considerations,7 or from a study of the configurations of final craters.8-l0 These analyses have led to the presentation of widely divergent models for rock failure beneath a drill bit, ranging from brittle to viscoelastic. The cratering process under dynamic loading commonly is regarded as being similar to that obtained under gradually applied, or 'static', loads. But the effect of rate of loading on the action of a bit is still disputed. Some investigators11-12 maintain that there should be no such effects, whereas others have demonstrated experimentally that these exist.13-17' The purpose of the investigation reported in this paper was to examine petrographically the damage done to rock under the action of a chisel-shaped wedge, both with 'static' and dynamic loading, and to determine if rate-of-loading effects could be detected. Significant quantitative differences in crater volumes and depths were found to exist for a given consumption of energy. On the basis of this data, an attempt was made to indicate some of the rheological properties that a proposed model should possess. All the work reported herein was conducted at atmospheric pressures. EXPERIMENTAL APPARATUS AND PROCEDURE Two types of rocks were employed for most of the experiments reported in this paper, viz. Bedford (Indiana) limestone and Vermont marble. The mechanical properties of these rocks are given in Appendix A. Actually two types of Vermont marble were used, but since no marked difference could be discerned between the two varieties (as seen in Fig. 10) the data was used collectively for the analysis. Stronger rocks were not employed owing to difficulty in generation of observable craters without damage to the equipment. Six-in. diam cores were drilled from the rock samples and embedded in 8-in, diam steel pipe with 3/8-in. wall thickness, using hydrostone to fill the annulus between the core and the pipe. This procedure was adopted to confine the rock specimen so that fractures would not propagate to the edges of the cores. This goal was achieved satisfactorily for these tests because no cracks were observed to extend into the medium surrounding the rock, even when craters were formed only 1 in. from the rock core periphery. Three to four craters were formed on a core face, because the rock damage from any one crater generally did not appear to extend into the others. Whenever, interference between damaged areas around adjacent craters was suspected, the data was rejected for purposes of the analysis. The limestone and marble samples were tested with a 60-degree, wedge-shaped bit, 1 5/8-in. in length, made of tool steel. The bit shank had two SR-4 type electrical resistance strain gages, mounted axially, to record the force-time history during the loading operation. The static indentation tests were conducted using a 50-ton capacity press fitted with an adapter for drill bit attachment. See Fig. 1. The force exerted by the bit at any instant was measured with strain gages affixed to the bit shank. An aluminum cantilever, with two SR-4 strain gages mounted near its clamped end, was employed to measure bit displacement. Both sets of gages were included in Wheatstone bridge circuits,

Jan 1, 1968

By George W. Hezzelwood

THE Balatoc mine, one of the Haussermann group,† is on the Island of Luzon, the largest of the Philippine group, about 260 km north of Manila, and 12 km from the city of Baguio The Baguio district is the most important gold-mining area of the Philippines, with 14 producing mines in 1939, milling 2,358,804 tons of ore, yielding [P]40,881,048, approximately 55 per cent of the total Philippine production of [P]74,131,216 PRODUCTION HISTORY The Balatoc mine began production In January 1929 with a 150-ton cyanide mill Increases in mill capacity have taken place as follows March, 1932, to 330 tons June, 1933, to 470 tons December, 1933, to ;15 tons July, 1934, to 700 tons December, 1934, to loon tons May, 193, to 1200 tons October, 1938, to 1300 tolls April, 1939, to 2000 tons January, 1941, to 2T50 tons Production during the period of expansion has steadily increased in total value in spite of the fact that grade of ore milled has dropped-from $31 06 in 1929 to $5 78 in1940 Annual reports give production as shown in Table I, the average value, being based on gold at the old price of $20 67 per ounce [ ] GEOLOGY The ore occurs in quartz-calcite veins that vary in width from narrow stringers to mineralized zones 40 to 30 ft wide Wall rocks consist largely of diorites, with some andesite, and a fragmental breccia called locally the "Balatoc plug " Texture of the ore varies widely in the different vents-from a soft, highly altered, gouge material filled with quartz fragments through a soft, unaltered quartz-calcite to a hard, massive quartz ore Three major vein systems have been extensively developed, and smaller amounts of work have been done on several others These veins strike east-west to N 60°, clipping south from 50° to 90°, and are essentially tension breaks between a series of faults or shears striking N 30°E to N 30°E and clipping southeast from 50° to 90° The shear veins and tension veins probably formed more or less simultaneously,

Jan 1, 1942

By Elmer W., Pehrson

NOT much serious consideration was liven to the military aspects of raw materials before World War 1. Following the outbreak of war in Europe in 1914, however. this situation was promptly changed. Disruption of allied shipping and German submarine warfare soon cut off a substantial part of the material the United Staten was accustomed to receiving from overseas. At the same time, raw material requirements rose rapidly as the tempo of industrial preparedness was stepped up in anticipation of war. By April 1917, when we entered the war, serious shortages threatened and consideralde attention was being given to our "deficcient" raw materials. The term "war mineral," began to appear after we became active combatants. But there is no evidence that "strategics" and "critical." as now used, had entered the lexicon of our raw materials experts during the last war nor were there apparently any officially recog¬nized list or definitions of what con¬stituted war materials. According to G. A. Roush in his book, `'Strategic Mineral Supplies," C. K. Leith, while serving as mineral advisor to the War Industries Board. compiled the first unofficial list of deficient minerals in 1917.

Jan 1, 1944

By L. W. Saperstein, W. W. Kaufman

Stimulated by the hearing protection clauses in the 1969 Coal Mine Health and Safety Law, attempts were made to determine what safety hazards, in terms of warning signal discrimination, are attendant upon the wearing of hearing protectors. Warning signals of dangerous roof conditions were collected and analyzed from 11 different coal mines in four different coal seams. Primarily, signals of audible level emanating from roof, floor, or coal were recorded. The interpretations of these signals were seen to be very dependent upon coincident visual and tactile signals. Acoustic character of such signals is shown to be dependent upon the spectral energy distribution of the pulses. Roof talk signals generally have broad-band spectra concentrated below 5 kHz. Reverberation times of acoustic pulses are generally less than 0.5 sec in duration. Indications have developed which link the coal mine entry dimensions with the nature of noises recorded there. Related experiments suggest that roof talk can be discriminated from background noise equally well when wearing protection as when not. This conclusion is only appropriate when noise levels warrant the wearing of protection. When quiet, the wearing of protection somewhat reduces discriminatory ability.

Jan 1, 1976

By J. P. Zannaras

If we assume that testing of the model started at time C, that time t2 was the instant at which the elastic limit of the material was passed at the points of the maximum stress, and that at time t3 the failure of the model was completed as shown in the typical photograph (Fig. 1), then actually the photograph shows the final results of what took place between time t2 and t3. By the principle of similitude all conclusions drawn from the behavior of the model were applicable and valid for actual mine roofs up to the time t, after time t, motions and friction came into play during the destruction of the model. The events between t2 and t3 and the photograph itself are not representative of the events expected in an actual mine roof unless corrections imposed by the principle of similitude are made.

Dec 1, 1956

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Jan 1, 1938

The International Mining Convention held in Nelson, B; C., May 17 , to 19, was attended by nearly 500 delegates, of whom about 100 were from Spokane, 150 from the Slocan district, and the others from different points in Canada and the United States. Arrangements were in charge of the Nelson, Slocan and Eastern British Columbia Mining Men's Club, under the direction of Secretary Fred A. Starkey, assisted by the City of Nelson, Associated Boards of Trade of Eastern British Columbia and Nelson Board of Trade. The Columbia Section of the American Institute of Mining Engineers; cooperating with the Western Branch of the Canadian Mining Institute, provided the technical program, under the management of Secretary E. Jacobs, of Victoria, and Secretary L. K. Armstrong, of Spokane. Three technical sessions were held, at which the following were read: Difficulties of the Electrolytic Zinc Process, by Thomas French. Sketch of the Geology and Ore Deposits of Nelson and Kootenay Region, by Arthur Lake's. Advantages of Local Organization of National Societies, by W. H. Linney. Review of Kootenay Mining, by Bruce White. Milling of Partially Oxidized Ores, by S. S. Fowler.

Jan 7, 1917

By Ellison C. Means

Many Virginia furnaces are troubled with a small percentage of zinc in their stock, this element being present, although the chemist may have failed to report it, either in the ore or in the limestone.

Jan 1, 1889