Search Documents

By James Quigley

As the outcrop mines in the West developed into underground operations, systems of ground sup- port were gradually evolved. In the early coal mines there was little need for support except near the dirt line in portals, where stone masonry was common. Where the top was shaley or broken, native pine props with light cross bars and legs furnished enough support even in Utah's 25-ft coal seams. As depth of workings increased, roofs and backs of the same general nature as those near the surface became more and more unstable and required more and more support. Some coal airways show this tendency very clearly. From the surface down the same type of roof shows deterioration which an experienced eye can translate into a measure of depth under surface rather than change in rock characteristics. Rock bolts, developed by various companies and by the U. S. Bureau of Mines, have become an effective substitute for timber in sections of some metal and nonmetal mines formerly requiring excessive timber support, and further use of war surplus landing mats, chain link fencing, and a new punched channel developed by one of the steel companies has enabled other mines to operate deposits where costs of timber and lack of clearance for timber support would have prohibited mining. The block caving mines have made extensive use of reinforced concrete underground to achieve similar ends under difficult conditions. Steel sets are standard in many Bureau of Reclamation projects, although these are usually covered in with concrete to make the permanent structures the Bureau's reclamation projects require. But the use of steel in mining operations is limited and has been confined principally to the iron ore mines of Michigan, Wisconsin, and Minnesota. Some mines have installed used rail as posts, caps, and crossbars, but a rail section is not suited for load carrying, and used rails are generally brittle, having a tendency to fail without warning when overloaded.

Jan 7, 1959

By E. B. Thornhill

(San Francisco Meeting, September, 1915) IN this paper on the recovery of mercury as sulphide, from the residues from the amalgamation and cyanide treatment of high-grade ores and concentrates, I will not discuss the many reactions, chemical and other- Fig. 1. wise, that take place in the general process, but confine myself more particularly to the methods of recovering the mercury. I submit charts of two amalgamation-barrel charges, Figs. 1 and 2, which are self-explanatory. The flow sheet of the high-grade and the mercury extraction plants is shown in Fig. 3.

Jan 8, 1915

By C. J. Hicks

The labor policy of the Standard Oil Co. (New Jersey) is founded first of all on paying at least the prevailing scale of wages for similar work in the community; on the eight-hour day at the refinery, with time and one-half for overtime; one day's rest in seven; sanitary and up-to-date working conditions; just treatment assured each employee; opportunity for training and advancement; payment of accident benefits beyond the amount prescribed by the State compensation law; health supervision by a competent medical staff; payment of sickness benefits after one year's service; coöperation with employees in promoting thrift and better social and housing. conditions; and assurance of a generous annuity at the age of 65, guaranteed for life after 20 years of service. Most of these features have been a part of the company's policy for many years, but it is only during the past two years that the cooperation of employees in determining these matters has been definitely assured through industrial representation. Industrial representation, in the Standard Oil Co. (N. J.), is a principle rather than a procedure. It is built upon the belief that personal association of those interested in any problem leads to a mutual understanding and a fair decision as to what is right. Fully believing in this principle, representatives of employees and representatives of management evolved a simple plan, the basis of which is that it gives every individual employee representation at joint conferences on problems and fundamental principles affecting all those interested in the industry. It is based on cooperation, not antagonism; its operation makes perfectly clear both to management and to employees that their interests are identical, and not at variance with the interests of the stockholders, and that mutual understanding and cooperation insure progress and success for all. Furthermore, experience has definitely shown that representatives of the employees are not only alert for the employees' interests but are as keen as the representatives of the management in determining and insisting upon fairness to the employer. Though the plan has been in operation nearly two years, it is an experiment, in that, being based on a principle rather than on cut-and-

Jan 1, 1921

Robert Carl Sticht, member of the Institute since 1886, an American metallurgist of world-wide reputation, died in St. Margaret's Hospital, Launceston, Tasmania, on April 30, 1922, after an illness of eleven months, against which he fought with the highest courage and characteristic fortitude. The news of his passing came as a great shock to a host of his friends and former associates here, but on account of his long absence from the United States, exact biographical details have been heretofore lacking. Throughout Tasmania, the expressions of public sorrow were many and impressive, and the flags were flown at half-mast in Queenstown, Zeehan, and the entire Mt. Lyell district, in honor of the man who had won his place in the community as a great captain of industry and a man universally admired and loved. Sticht had been connected with the Mt. Lyell Mining & Railway Co. in Tasmania throughout its entire productive period. He had originally been induced to go to Tasmania through the good offices of the late Dr. E. D. Peters, then professor of metallurgy at Harvard University, who after personally examining the undeveloped Mt. Lyell properties, recommended Sticht as the best possible man to work out the complex metallurgical problem which that great orebody presented. Sticht had already made himself the leading authority on pyritic smelting, having taken up the idea as suggested and partly worked out by Lawrence Austin and carried it through to a certain degree of perfection in the case of limited tonnages of special ores. After studying the situation at Mt. Lyell, Sticht found the conditions there to be almost ideal for pyritic smelting, and he had the courage to adopt as the basis for a permanent, and eventually successful, solution of the metallurgical problem, a process that was then little more than a theoretically interesting possibility. The thorough studies and remarkable results attained at Mt. Lyell were published as chapters in Doctor Peters' various publications on the metallurgy of copper, Doctor Peters giving full credit to Sticht for their authorship. These chapters by Sticht practically constitute the: best literature of the art of pyritic smelting. The accuracy of observation,

Jan 1, 1923

Robert Carl Sticht, member of the Institute since 1886, an American metallurgist of world-wide reputation, died in St. Margaret's Hospital, Launceston, Tasmania, on April 30, 1922, after an illness of eleven months, against which he fought with the highest courage and characteristic fortitude. The news of his passing came as a great shock to a host of his friends and former associates here, but on account of his long absence from the United States, exact biographical details have been heretofore lacking. Throughout Tasmania, the expressions of public sorrow were many and impressive, and the flags were flown at half-mast in Queenstown, Zeehan, and the entire Mt. Lyell district, in honor of the man who had won his place in the community as a great captain of industry and a man universally admired and loved. Sticht had been connected with the Mt. Lyell Mining & Railway Co. in Tasmania throughout its entire productive period. He had originally been induced to go to Tasmania through the good offices of the late Dr. E. D. Peters, then professor of metallurgy at Harvard University, who after personally examining the undeveloped Mt. Lyell properties, recommended Sticht as the best possible man to work out the complex metallurgical problem which that great orebody presented. Sticht had already made himself the leading authority on pyritic smelting, having taken up the idea as suggested and partly worked out by Lawrence Austin and carried it through to a certain degree of perfection in the case of limited tonnages of special ores. After studying the situation at Mt. Lyell, Sticht found the conditions there to be almost ideal for pyritic smelting, and he had the courage to adopt as the basis for a permanent, and eventually successful, solution of the metallurgical problem, a process that was then little more than a theoretically interesting possibility. The thorough studies and remarkable results attained at Mt. Lyell were published as chapters in Doctor Peters' various publications on the metallurgy of copper, Doctor Peters giving full credit to Sticht for their authorship. These chapters by Sticht practically constitute the: best literature of the art of pyritic smelting. The accuracy of observation,

Jan 1, 1923

By Sheldon P. Wimpfen, Ralph H. Sweefser

FOR centuries the pumping of water has been one of the chief problems to be overcome by the persistent men who win the mineral wealth of the world. Profitable operations have often been forced to suspend activities as the mine penetrated well below the water table or when sudden rushes of water were encountered. To operate below the local water level requires continuous pumping equal in volume to the amount of water flow¬ing into the mine workings. Often the water to be removed exceeds the tonnage of valuable material produced. To be above local water level is a valuable asset. Modern mining practice permits nothing short of the extraction of the last pound of profitable ore from a mineral deposit. In the days before the development of mechanical and electrical power as we know it today. water in any quantity was a major

Jan 1, 1948

By Eckley B. Coxe

SINCE our last meeting, the Institute has lost, by the death of Mr. Gowen, one of its most distinguished members. I shall only attempt in this place to give a brief account of his many accomplishments and achievements; but our records would certainly be incomplete without a recognition of the important influence which he exerted upon the mining and metallurgical industries of this country, and a testimony to his private virtues of character. Although Mr. Gowen was best known as a great lawyer and as the head of a great railway corporation, he began his career, before he was of age, as the manager of a small anthracite blast-furnace at Shamokin, Northumberland County, Pennsylvania. He left this position, to engage on his own account in the mining of anthracite coal at Mt. Laffee, near Pottsville. This proved an unprofitable business, and, after the panic of 1857, he began the study of the law. As soon as he was admitted to the bar, he at once entered upon the active practice of his profession, and soon achieved an extraordinary success. In 1869 he was made President of the Philadelphia and Reading Railroad Company, and he afterwards organized the Pliladelphia and Reading Coal and Iron Company, the largest coalmining corporation in the world. He became a member of. this Institute during the first year after its organization, and remained a member until his death. He always took a deep interest in the work, and was prompt to co-operate by all means in his power in furthering the objects of the Institute. Mr. Gowen was one of the first to recognize the great importance to both miner and consumer, of the proper utilization of the small

Jan 1, 1890

By G. Reinberg, C. D. Clarke

Most underground mining operations are dependent on pumping installations to keep the mine unwatered. The reliability of such installations is obviously of paramount importance. The volume of water to be handled is often considerable, and the total head is relatively high. In these cases, both capital cost and operating expense of the pumping installations will become significant factors in overall mining costs. To insure reliability and to keep efficiencies, and hence operating costs, within acceptable limits it goes without saying that mechanical maintenance of a mine pumping installation must receive scrupulous attention at all times. Large mine pumping installations today almost invariably use multistage centrifugal pumps, since positive-displacement units would not be economically competitive except under very unusual conditions of small volume combined with extremely high heads. Centrifugal pump maintenance, under ideal circumstances, would be confined to parts subject to normal running water, i.e., bearing surfaces, stuffing box packing, and shaft sleeves. Under adverse conditions, however, metal may be lost from the wetted surfaces of a pump by erosive or corrosive action of the pumped fluid, and maintenance costs can easily attain enormous proportions.

Aug 1, 1956

By John V. Beall

When a mine has ore averaging 5% lead, 7% zinc, 0.60% copper, 1/4 oz gold, and 6 oz of silver, adequate reserves, power and water, easy access to market, and is situated in beautiful natural surroundings with the advantages of a big city within a few hours drive, there is little left to be desired. Such a mine is the Mayflower mine of the New Park Mining Co. situated 30 miles from Salt Lake City in the Wasatch Mountains near Keetley, Utah.

Jan 1, 1949

By James J. Wise

INTRODUCTION One basic design feature utilized in all caving and sublevel stoping techniques is the drawpoint. These draw- points may be located on sublevels when using sublevel caving methods, or may be located at the floor pillar when using block caving, sublevel stoping, or vertical crater retreat methods. How the drawpoint is designed and developed, how the ore is withdrawn from it, and how the ore is hauled to the shaft or portal encompasses the loading and hauling function. Historically, predominate loading and hauling equipment for caving and sublevel stoping has been scraper slushes, air powered overshot loaders, and rail mounted train haulage. All of this equipment has two common constraints. 1. The equipment locked into specific work sites and is not easily shifted to another work site. This constraint can often lead to low utilization and low productivity of the equipment. 2. The equipment is designed to work in the horizontal plane, which requires that the various horizontally-oriented working levels be connected by vertical raises. Vertical development by means of raises is not only increasingly expensive, but also is not well adapted to movement of large equipment into the s topes. In the last 20 years, two revolutionary labor saving concepts have become common in caving and sublevel stoping. 1. Long-hole drilling, which has mechanized the development of the drawpoint extraction structures as well as the actual stoping and undercutting. 2. Vertical access by means of trackless ramps between levels, and the consequent use of rubber-tired vehicles not only for loading and hauling ore, but also for the rapid movement of men, material, and equipment into the stopes. The introduction of trackless mining systems for loading and hauling has not been easy. Mine planners have had to re-orient their thinking to the larger operating space required by trackless equipment. Larger access drifts have necessitated reconsideration of mine layouts to insure proper ground support. Spiral ramp developments were often laid out on slopes steeper than the equipment could negotiate economically. Mine operators had to accept the added responsibility of roadway maintenance, water removal, increased ventilation, and more technical mechanical maintenance. As the mine operators enthusiastically embraced the superior productivity of trackless mining systems, they some- times disregarded opportunities to combine the older types of equipment with trackless vehicles to maximize productivity at lowest cost. In order to gain a proper perspective on this problem, it is necessary to review the various techniques of loading and hauling and to become more aware of the advantages or disadvantages that each system or combination contributes. LOADING Loading consists of two functions, (1) primary loading from a drawpoint and (2) secondary loading into long- haul system, a truck, train, or possibly a belt conveyor. Mine planners have four basic loading systems available to fit various operating conditions. These are, (1) gravity, (2) scrapers, (3) rail-mounted loaders, and (4) trackless loaders. Each system can produce optimum results under specific conditions. Gravity Loading Gravity loading is probably the oldest system in general use today.

Jan 1, 1981

By W. G. Matteson

THE origin of the salt domes of the Gulf coastal plain has been investigated by many of the most able geologists, but the problem cannot be said to have been satisfactorily solved. Since 1860, numerous theories have been presented, only to be discarded, at least in part, as more complete information revealed their fundamental weakness. Real progress toward solution dates from 1902, when Hill' advanced the theory of secondary deposition of the domal materials from saturated solutions of hot saline waters ascending from great depths under hydrostatic head along structural lines of weakness. Shortly thereafter, Harris,2 using Hill's hypothesis as a basis, explained the doming and pronounced uplift associated with these salt cores as the result of forces exerted by growing salt crystals. This was a marked advance over the ideas of Coste3 and Hager,4 since no. evidence of igneous intrusives, as they assumed to explain the uplifts, had been found associated with the domes. Harris5 developed his theory until it offered such apparently plausible explanations of so many details of dome phenomena that his hypothesis and conclusions received widespread acceptance, despite some serious objections, and today his theory, somewhat modified, is considered by many able investigators to be the best explanation of, the origin of these domes. The immense production of oil per acre, the recognition of the high lubricating quality of the oil, the development and recognition of the efficiency and advantages of oil-burning vessels, with the, subsequent

Jan 2, 1921

By Frank C. Roberts

Neglecting the hydrogen and hydrocarbons, 1 will assume the following analysis as a fair average composition, by weight, of the waste gases escaping from a coke-burning blast-furnace: CO2............17.25 CO,............25.25 N,.............57.50 100.00 The 25.25 CO requires for combustion 62.6 of air, or 11.398 of oxygen, necessitating the passage of 48.202 nitrogen into the products of combustion. The latter, therefore, have the following composition: CO2,,............ 56.9 N,............105.7 Tile total specific heats of these quantities of the respective gases are 12.31 and 25.79, giving for the combined product, 38.1 approximately. That is, the product of combustion will absorb 38.1

Jan 1, 1889

By William Vietti

WEST TEXAS and New Mexico has been overshadowed by the develop-ment in East Texas to such an extent that the area has been placed on a settled production basis by most of the operators. Considerable develop-ment work on both proven and unproven acreage remains to be carried on, but the incentive, a ready and profitable market, has been lacking. The main characteristics of the fields in this area are so well known that they are not described again in this paper, which thus resolves itself into a statistical review of the more important production features of the area. Proration has been in effect during the year and has been rigorously applied with the full cooperation of all producers. Proration in West Texas and New Mexico is based in the more pro-ductive fields on a potential and acreage distrbution of the allowance to the individual wells or acreage units. Potentials are determined generally by a short production test of from 1 to 4 hr.; and the hourly rate is multiplied by 24 to obtain the 24-hr. production or rated potential of the separate wells. The potential values thus set up have been questioned by many production men who are not willing to concede that the instantaneous (hourly) capacity of a well to produce is its potential capacity for a day with all other wells in the pool producing at their capacity. However, the potential of a well determined as above remains its chief rating as a measure of the permeability in place and as an indication of the possible reserve feeding that well. , The acreage factor has made it unnecessary to overdevelop properties in order to obtain an allowance proportionate to neighbors who are willing to drill an excessive number of wells on a piece of acreage in the hopes of a quick drainage and a corresponding profit. Proration has resulted in an orderly development of many of the pools in this area on the base as out-lined above, resulting in more reasonable spacing of wells and the more even withdrawal of oil and the ensuing expectation of high recoveries.

Jan 1, 1933

By C. C. Harris, A. Jowett, S. K. Ghosh

An equation derived from first-order kinetics and accounting for return from froth to pulp has correlated continuous flotation data. The concentration of floatable material in the pulp can be altered either by changing the feed concentration or the feed rate. The latter does not affect the flotation rate constant, the froth to pulp return constant, and the concentration of non-floatable material in both the pulp and concentrate. Both the return constant and the concentration of non-floatable material in the pulp are directly proportional to the feed concentration, while the concentration of non-floatable material in the concentrate is related to the feed concentration. The investigation of the froth flotation process by continuous test methods, previously used by Brown and smith,1 Jowett and Safvi2 and Jowett and West,3 is being continued. Recent tests, primarily concerned with flotation cell design, have yielded kinetic data suitable for testing an equation proposed by Arbiter and Harris4 which postulates that a flotation process is defined by two rate constants: 1) the rate constant for mass transfer from pulp to froth. Previous workers have regarded this as the flotation rate constant. 2) the rate constant for mass transfer from froth to pulp, which has previously been ignored. THEORY Under continuous flow conditions at the steady state in Fig. 1 the equation developed4 is Symbols are defined in Table I. The air-liquid ratio terms4 have been omitted, since they are substantially constant for a given set of conditions. Also, for a system operating at the steady state Vf and V, remain constant and Eq. 1 can be written: Cp/Cc=b'/a,+Qc/a' [2]

Jan 1, 1963

By Gilbert P. Moore

The production of petroleum in Argentina during 1932 was greater than in any preceding year. The total amount produced was 13,012,-756 bbl. This figure represents a decided increase in the production of oil in Argentina and can be attributed largely to the increased activities of the Royal Dutch operations at Kilometer 27 in the Comodoro Rivadavia district and those of the Standard Oil Co. of Argentina in the Salta region. Production from the Royal Dutch wells amounted to considerably more than 10,000 bbl. per day over quite a long period during the year. Of the 13,012,756 bbl. of oil produced during 1932, the Government Agency (Y. P. F.) was responsible for some 5,578,954 bbl., while 7,433,-802 bbl. were produced by private companies. Although in 1930 the Y. P. F. produced about 55 per cent of the total production and in 1930 50 per cent of the total, in 1932 its production had fallen to about 42 1/2 per cent of the total. This decrease in the proportion produced by the Y. P. F. was not due to a decrease in its production but to the decided increase in the production of private companies, particularly those two whose names are given above. One new discovery was recorded during the year. This was a well drilled by the Y. P. F. at Cacheuta in the province of Mendoza which came in pumping 80 bbl. of 15" gravity oil from a depth of 673 meters. This well was completed at approximately the same time that the provincial government of Mendoza granted a concession to the Y. P. F. and declared the whole province as a reserve in which no concessions may be granted for a period of 10 years. Under these conditions, the federally operated Y. P. F. will have no competition in the Cacheuta area from private companies such as they have in the other three fields of the republic. The Y. P. F. wildcat west of Comodoro Rivadavia at Pampa Maria Santissima on the Rio Senguerr was completed as a dry hole during 1932. This we11 was reported as a producer in 1930 by persons returning to this country from Argentina but it appears that they had been misinformed. The site of this test has been abandoned and a new location made north of the Rio Senguerr.

Jan 1, 1933

By M. W. Dumais, E. P. Abrahamson

In a paper by Abrahamson and Alexander concerning a series of correlations between electronic structure and property changes, it was hypothesized that each solute atom in a dilute solution had a characteristic volume of solvent atoms over which some form of electronic interaction occurred. From this description it is possible to picture the solute atoms as occurring in an ordered array for the most efficient arrangement. A recent review article2 has shown that some form of anomaly exists for a whole series of properties when dilute additions of tungsten are made to iron, of. Fig. 1. Any mechanism to fit one property must also be amenable to mechanisms for the other properties. The possibility of some structural change in this region appears to offer the best hope. The system chosen for investigation was the iron tungsten system. Zone-refined iron with zone-leveled tungsten additions were supplied by Materials Research Corp. as 3/8-in.-diam bars. Transmission electron microscopy was used to study the structure. One-quarter inch specimens of each alloy were cold-rolled to 10-mil sheets, cleaned, punched to electron-microscope specimen-holder size, and annealed in vacuum for 2 hr at 800°C and 2 hr at 700°C followed by a furnace cool. The specimens were attached to a platinum wire and the specimen edge and wire were painted prior to thinning in a solution of 10 pct perchloric acid in glacial acetic acid. It was believed that if ordering were present due to electronic interactions the polishing procedure chosen would provide a simultaneous combination of chemical attack and electropolishing to exhibit the ordered structure. The chemical attack would be expected to penetrate those areas equidistant from the tungsten atoms, while the electropolishing would serve to "plane off" the volumes where the chemical attack had taken place. If one of the ordered tungsten planes were parallel to the specimen face at the edge of the thinned hole, a plate or micalike structure would be expected. A typical result of this polishing is shown in Fig. 2. Here a series of plates can be seen lying one upon the other. In several other specimens the plates parallel to the electron beam have been observed, behaving like slices of bread in a loaf. These edge views coupled with moire patterns indicate that the minimum plate thickness is 37 to 42A. This is equivalent to a concentration of 455 at. ppm of W if a simple cubic superlat-tice exists, or one tungsten atom every twelve iron atoms on the ordered plane. It was further noted that the base iron exhibited no signs of platelike structure. As the concentrations increased above 100 at. ppm W the amount of plate material increased. Among the specimens investigated was that shown

Jan 1, 1967

By J. H. Schulman, M. H. Buckenham

R. W. Christy (Manager of Sales, Sanitary Engineering Equipment, Link-Belt Co.) and C.D. Rubert (Barrett, Haentjens & Co.) — Messrs. King and Schepman have presented an excellent paper which outlines the general practice in the design of thickener mechanisms. Lifting devices, controls, special applications and underflow pumping arrangements have been reviewed in detail. Pumping arrangements were illustrated which eliminate the need for an expensive tunnel beneath the thickener floor. Most of those illustrated have the common feature of a relatively long underflow suction line extending from the hopper floor to the pump located on the bridge at the periphery of the tank. The authors limit these arrangements to comparatively dilute or thin slurrys. It is implied that dense and coarse concentrates, which are difficult to pump, cannot be handled unless a tunnel is constructed. Fig. 1 shows an underflow pump arrangement which negates the need for a tunnel but which permits the operator to convey a heavy dense slurry. The pump is mounted directly on the fixed hoist platform and the impeller is located at the base of the steel center column. Priming water is not needed. The column

Jan 1, 1963

By A. P. Anderson, J. H. Jensen, W. E. Breckoff

Bromine is the intermediate member of the halogen family of elements between iodine, a solid, and chlorine, a gas. The name is derived from the Greek "bromos," meaning stench. Bromine is the only nonmetallic element that is liquid at room temperatures with a melting point of -7.2° C and a boiling point of 58.78º C. Reddish brown in color, it dissolves easily in water to yield a red solution. Bromine volatilizes at ordinary temperatures to a red vapor that is very irritating to the eyes, nose, and throat. Density of the liquid is 3.12 and gas weighs 7.59 gpl at standard conditions. As the element is highly active, it exists in nature only as bromide compounds. Bromine was discovered by Antoine Jerome Balard in seawater bitterns in 1826 and first prepared in quantity in 1860. Distribution Bromine is widely distributed in nature and compounds occur in solution in natural brines, in seawater, saline lakes, oil and gas well brines, and in evaporite chloride minerals. The concentration of bromine salts ranges from 60-65 ppm in seawater to several thousand ppm in oil well brines and saline lakes. The distribution of bromine in marine evaporite minerals and in the solutions from which they crystallized was determined many years ago by H. E. Boeke (1908). Theoretical aspects regarding the geochemistry of bromine have been published in numerous papers (Raup and Mite, 1969). Bromine occurs in solid solution in carnallite and sylvite associated in potash deposits; in halite in salt beds; salt in oil shales; and in trona deposits. Its presence is useful as a guide in geochemical exploration. The analysis of small amounts of bromides in the presence of large amounts of chlorides is discussed by W. Schwerdtner (1963). Manganese, iron, and iodine may interfere with the determination. Other analytical methods are discussed at length in the literature (Stenger and Atchison, 1964). Sources and Reserves The sources and reserves of bromine, given in Table 1, appear ample to meet present and foreseeable requirements in all producing countries. With the occurrence of bromine salts in seawater and other brines, the potential for bromine production is worldwide. It has been estimated that 99% of all commercially recoverable bromine is in the ocean. However, actual subterranean brines having a higher bromine content than seawater will continue to be the preferred sources of bromine for the foreseeable future. [ ]

Jan 1, 1983

By W. D. Johnston, T. P. Thayer

THE minerals that collectively are known as chromite form an isomorphous series of the general formula (Mg,Fe) 0. (Cr,Al,Fe) 203. So wide is the range in chemical composition in this group that chrome ore consisting entirely of the mineral chromite may range from less than 30 pct to more than 60 pct Cr203. The most comprehensive published data on the chemical com- position of chromite are by Stevens,62 who made complete analyses of 52 samples of chromite concentrate from many localities in North, Cen- [ ] tral, and South America. These samples were mechanically purified to remove associated silicates and might be regarded as the cleanest chromite that could be obtained by any mechanical milling process. Fig 1 shows the predominant zone of isomorphism, within the triangular prism of composition defined by the mineralogical end members of the series, wherein his analyzed samples fell.

Jan 1, 1949

By A. S. Richardson

AIR conditioning, or air cooling, for the improvement of ventilation in the Butte mines has come into increasing use during the past 10 years. In part, the methods practiced have been described in previous publications of the Institute, but some improvements on earlier methods have been made and a number of new features have been developed. This paper is presented as a record of progress made, and for the sake of completeness describes all general features of the work. The need for air conditioning in the ventilation of mines in the district arises from the fact that the temperature of the ground and mine water has shown a very great increase with increase in mining depth, and has now reached a maximum of slightly over 130ºF. The most difficult part of the ventilation problem is the maintenance of temperature and humidity of a satisfactory standard in the working places, especially on the lower levels. Although ordinary ventilation is adequate to maintain good conditions in most of the working places it is subject to a number of limitations at great depth. Most important among these limitations is that with increase in depth the air becomes heated before it reaches the working places, both by compression from increase in atmospheric pressure and by heat transferred to it from rock at high temperature, so that its capacity for lowering temperatures is greatly reduced before it reaches the operating zone. Increasing depth of mining also increases the distance traveled by the air in its passage through the mine, and this causes a corresponding increase in resistance to air flow, so that there is greater difficulty in maintaining even the same volume in circulation. Thus, in the face of a demand that the ventilating system have a very much greater capacity to remove heat from the mine, the tendency is for that capacity to diminish. The only evident alternatives were (I) the opening of additional air shafts to increase the volume of air in circulation, (2) an extension of the existing system that would be subject to the same limitations, or (3) the adoption of an entirely different method such as air cooling. Fortunately for an economic solution of the problem, the mean annual temperature of the surface atmosphere at Butte is about 40°F., with very low relative humidity in summer, so that there is unlimited natural cooling power at a temperature range adaptable to air-conditioning methods. METHODS Two similar methods of air conditioning are used, as necessitated by service requirements and dependent upon the equipment available. In one, which is the more important and has the greater cooling capacity, water is circulated in a closed circuit, and, alternately, first absorbs heat from warm mine air and then dissipates it in the surface atmosphere by cooling at a cooling tower. The second

Jan 1, 1941