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By P. W. George, G. A. Hellstrand

In 1915, H. A. Guess, Vice President of American Smelting & Refining Co., in charge of its Mining Department, learned that the Anglo-Newfoundland Development Co., Ltd., a pulpwood and paper-mill enterprise, had found upon its large concession in Newfoundland, and had opened up by shaft to the third level and some drifting, a lenticular orebody indicating about 100,000 tons, as an extremely fine-grained sulfide ore, averaging about 0.05 oz. Au, 4 oz. Ag, 1.5 per cent Cu, 10 per cent Pb, 18 per cent Zn; and that having sent parcels of this ore to Minerals Separation, Ltd., and various other metallurgical testing concerns without obtaining any success in commercial separations thereof, had discontinued work thereon and let the workings fill. Mr. Guess wrote to the general manager of that company and obtained a few hundred pounds of the typical ore, which he sent to his company's metallurgical testing laboratory at Flat River, Mo., outlining various flotation tests desired thereon, in an endeavor to obtain separation into a commercial lead concentrate and a zinc concentrate. But the art of flotation had not then progressed far enough to treat such ore, the galena and zinc blende being so fine grained that grinding to about 300 mesh was required to release the mineral particles in their gangue. Mr. Guess had flotation and other tests continued upon this ore from time to time with whatever new reagents and flotation devices were evolved as time went on, and finally, in 1925, he succeeded in effecting in his company's testing plant, then at Wallace, Idaho, separations into lead concentrates and zinc concentrates of satisfactory commercial grade. Mr. Guess then proceeded to unwater, examine and sample the property and made with the owners a partnership operating agreement upon the mine itself and a considerable area surrounding it, and in the early summer of 1926 began to prospect for additional orebodies, utilizing for such prospecting geophysical methods under the direction of Hans Lundberg, methods which up to that time had been little used in mining in the western hemisphere. This geophysical work found two large flat-lying orebodies of a type precisely similar to the smaller body of the original discovery. The larger orebody, some 3500 ft. west of the original

Jan 1, 1935

University of Alabama University, Alabama Mining and Metallurgical Society JOSEPH CHARLES MEAD, President WAYNE G. BRIGGS, Secretary J. R. CUDWORTH, Faculty Sponsor RICHARD L. BOWRON, Counselor University of Arizona Tucson, Arizona Miners' Society W. JAMES THOMAS, President LAMONT WEST, Secretary J. B. CUNNINGHAM, Faculty Sponsor B. R. HATCHER, Counselor

Jan 1, 1938

By Frederick C. Hull

THE grain size of a metal or alloy is one of the most important factors determining its properties. In steels, for example, grain size affects hardenability, toughness and machinability; in brasses, grain size is related to hardness and deep-drawing quality. In the field of heat-resistant alloys, grain size has a marked effect on ductility, creep and endurance strength. In order to determine these effects, as well as to control the properties of materials, many accurate and rapid measurements of grain size must be made. This paper presents a new and improved method for the estimation of grain size. USUAL METHODS of EVALUATING GRAIN SIZE A frequently used method of estimating grain size is that of comparing the image of a polished and etched specimen on the ground-glass screen of a metallographic microscope with standard grain-size charts. Several types of standards are available for use with different classes of microstructures. Geometric Grids.-The Metals Handbook1 has a series of hexagonal grids ranging in size from ASTM No. I to 8. Idealized Grain Networks.-Idealized grain-boundary networks for ASTM grain sizes I to 8 are included in the American Society for Testing Materials Tentative Standard E19-39T. Standard Micrographs.- The Metals Handbook and ASTM Tentative Standard EI9-39T contain micrographs of hypoeutectoid and hypereutectoid steels ranging in grain size from No. I to 8. The grain size of annealed brass (diam¬eter of the average grain in millimeters) is obtained by comparison with 10 micrographs of varying grain size in ASTM Tentative Standard Es-39T. A handicap to accurate evaluation of grain size by this method is the fact that it is difficult to compare photographs in a dimly lighted room with the image on the ground-glass screen, or, if the general illumination is increased so that the printed standards may be clearly seen, the contrast of the image of the unknown is decreased. It is easier to estimate grain size by comparing a micrograph of the unknown with the grain-size standards. However, photographing every specimen on which the grain size is desired is too costly in time and materials to be practicable. For hardened steels, the Shepherd or Jernkontoret fracture grain-size standards are very accurate and useful, but this method obviously cannot be applied to ductile alloys such as brass, stainless steels and austenitic heat-resistant alloys. Jeffries' method for grain-size measurements consists of counting the number

Jan 1, 1947

By Roy Thomas

SOON after the Waelz plant for the fire concentration of low-grade zinc ores was put into operation in the early part of 1929 at Katowice, it was found that the conveyor equipment for transporting the hot residue from the furnace dust chambers was inadequate. Hand tram-ming with water cooling was used for a time, but that method was injurious to the workmen as well as costly. The problem was to find some practical mechanical means of conveying flue dust at temperatures of from 450° to 600° C. as it was drawn from the dust chambers. After considerable preliminary investigation it was decided to install pneu-matic equipment for conveying the hot materials to a central mixing plant, where it would be mixed with slime and from which it would be returned to the furnace feed hoppers. The first pneumatic equipment was installed in 1930, and has been in successful operation since that time. The pneumatic method of transportation has shown a considerable saving in operating costs over the former methods of dust handling and a decided improvement in working and hygienic conditions at the plant, through the elimination of the dust hazard. Additional pneumatic equipment was installed in 1933 for conveying the furnace fume from the baghouses to the roaster plant. At the same time pick-up lines were provided for collecting the cleanings from the vertical and horizontal cooling pipes that are between the furnace dust chambers and the baghouses. The latter installation has practically eliminated a dusty and costly hand-tramming operation.

Jan 1, 1939

By Merrill, Charles White

MOST extraordinary of the technical developments in placer gold mining during the last five years has been the rise of the dragline dredge, by which is meant a floating washing plant for auriferous gravel, fed by a dragline excavator. The idea originated in the fall of 1933, when Horace Onyett constructed a floating washing plant to which gravel was delivered by a dragline excavator standing on dry land. Onyett's operation near Oroville, Calif., and another started by H. F. England later on Wyandotte Creek, Butte County, Calif., yielded '75 oz. of fine gold before the end of 1933. Although the first operation was abandoned shortly as un- profitable, the dragline-dredge method of gold recovery soon began to expand at a boom rate. As a matter of interest, the Onyett operation was taken over later by Lord and Bishop, who are re- ported to have succeeded in making it the first financially successful drag- line dredge. In California alone drag- line dredges produced $3,294,970 worth of gold in 1937, and the pros-

Jan 1, 1938

By T. S. Lovering

The Moffat tunnel passes through the continental divide about 50 miles west of Denver, Colo., on the Denver & Salt Lake R. R.: It is 16 ft. wide, 24 ft. high, and 32,383 ft. long, a distance of a little more than 6 miles. The advantages accruing from its construction may be briefly summarized as follows: The tunnel eliminates 27 miles of grade averaging more than 3.5 per cent. and actually running well over 4 per cent. in many places, and changes the steepest grade from 4.5 to 2 per cent. It reduced the peak of the railroad from 11,660 to 9249 ft. which enables one engine to pull four times as much freight as it could before the tunnel was built. If the Denver & Salt Lake R. R. completes its line, this road will shorten the distance between Denver and Salt Lake City by 200 miles and will have no steeper grades than the lines now connecting the two cities. The proposal to drive the tunnel through the divide dates back about 25 years and D. H. Moffat, who was the leading spirit in the organization of the Denver & Salt Lake R. R. spent much of his time and energy in efforts to raise money for the tunnel that bears his name. He was unsuccessful and died before the work was started. In 1920 an effort was made to obtain state legislation favoring a bond issue to finance three important railroad tunnels in Colorado but the measure was defeated, largely through the efforts of the citizens of the region near Pueblo. A few years later devastating floods caused the Pueblo voters to seek relief from the state and at this time they withdrew their objection to the tunnel bond issue. As a result, a $6,720,000 bond was issued to finance the Moffat tunnel. Construction bids were so high that the work was finally allotted on a scheme analogous to a cost-plus basis. The contract was awarded to Hitchcock and Tinckler, who are paid a fee of $140,000 for driving the tunnel. All bills are paid by the Moffat Tunnel Commission. The contract was let Sept. 19, 1923, and Hitchcock and Tinckler agreed to complete the work by July 19, 1927. In the event of finishing before this date they were to be given a bonus of $1000 a day and

Jan 1, 1928

By Edward Pesout

THE McGill smelter started operations in the year 1907. The smelter furnaces were fired with run-of-mine coal on grates until April 1911, when oil firing was introduced. Oil firing continued until April 1918, when the initial coal-pulverizing plant was started.1 EARLY PULVERIZING PLANT Various alterations were made to that plant during its operation, one of the more important being in connection with the system for delivering pulverized coal. In order to minimize coal-dust explosions and fires, the return portion of the main delivery line was eliminated in the year 1928. Thereafter coal-dust explosions and fires were greatly reduced. Pulverized coal was prepared at this plant primarily for the reverberatory furnaces, but for several years it was also delivered to the converting plant, roasters and power-plant boilers by a system of auxiliary fans and delivery lines. During the period March 29 to April 8, 1929, one reverberatory furnace was fired with pulverized coal produced by an Aero, type J, unit coal pulverizer with a rated capacity of 5 tons per hour. This machine actually pulverized its rated capacity but the product was too coarse. After certain regulations, a finer product was obtained but the pulverizer capacity decreased and this resulted in insufficient coal for efficient furnace operation. Table I gives a comparison of the average screen analyses of the pulverized-coal products from the impact-type unit pulverizer and the regular coal-plant installation. [ ] It was definitely proved that this size and type of unit pulverizer could not furnish sufficient coal of proper fineness to give smelting results comparable to that obtained with the regular coal-pulverizing plant. The coal from this unit pulverizer was so coarse that it did not ignite or burn properly and thus did not produce the proper heat for efficient smelting. During the latter part of 1929 and the early part of 1930, experimental work was conducted with a 7-ft. 0-in. by 48-in. Hardinge conical ball-mill coal-grinding unit, which was installed alongside a furnace in the reverberatory building. Results obtained from the test run indicated that this unit would furnish sufficient coal of proper fineness for good smelting.

Jan 1, 1945

Jan 1, 1885

By P. K. Weimer

Coinpletely integrated thin-film circuits inco?,porating more than 1000 active and passive elements have been fabricated reproducibly in the laboratory by evaporation of- all components. A 180-stage modified shift register comprising 540 CdSe TFT's, 360 resistovs, and 180 capacitors was deposited upon a glass substrate during one pump-down of the vacuum systeitl. Experimental units have been operated for more than 5000 hr at temperatures uP to 85°C without failure of any slages. The present pupper reviews the charvactevistics of evaporated thin-film transistors (TFT's) and discusses their application to integrnted circuils. INTEGRATED circuits most widely used today are based upon silicon technology, with the circuits formed on the surface of a block of single-crystal silicon1 or on a block of sapphire 2,3 upon which a thin layer of silicon has been deposited. Transistor patterns and interconnections are defined by photographic procedures using photoresist masking. Large groups of transistors are produced in batches which undergo many processing steps, some of which are carried out at elevated temperatures. Passive elements are formed by treatment of the semiconductor surface or are deposited by evaporation alongside the active elements. The size and complexity of the circuits are limited by defects in the devices and by the size of the available single-crystal chips. Capacitative coupling to the semiconducting substrate may also limit useful size and frequency response of the circuits. An alternative approach to integrated circuits is based upon the deposition by evaporation of all circuit components upon a noncrystalline, insulating substrate such as glass.4 Thin-film field-effect transistors,1'6 known as TFT's, can be deposited in large arrays on glass or plastic substrates at the same time the associated passive elements are being deposited. Although still in the research stage the all-evaporated approach is expected to offer certain advantages for many applications. In particular, the use of thin films upon a noncrystalline substrate offers the prospect of producing complex, large-area circuits not now feasible with single-crystal silicon. Important applications of this type include memory arrays for computers and imaging devices for television. The ease with which the evaporated TFT's can be deposited may permit continuous, automated production methods not possible with high-temperature batch processing. Recent advances7'8 in the fabrication of thin-film transistors have led to greatly improved reproduci-bility and life of the TFT's. Experimental circuits having over 1000 active and passive elements deposited upon a common glass substrate are currently being produced in the laboratory. The present paper reviews recent progress in the development of the TFT and in its application to integrated circuits. I) DESCRIPTION OF THE THIN-FILM FIELD-EFFECT TRANSISTOR The TFT is a field-effect transistor of the type having the control gate separated from the semiconductor by a thin insulating spacer. Although its operation resembles that of the silicon MOS transistorg its construction is based entirely on thin-film techniques. Fig. 1 shows a cross-sectional view of an evaporated TFT deposited upon a glass substrate compared with a silicon MOS transistor deposited upon single-crystal sapphire.3 The semiconductor in the TFT is a poly crystal line layer, of a material which can be readily evaporated, such as cadmium sulfide, cadmium selenide,l0 or tellurium." Silicon monoxide layers have usually served as the gate insulator, but other oxides, sulfides, and fluorides may be used. Film thicknesses range from a few hundred to a few thousand angstroms. The source, drain, and gate electrodes in the TFT are of metal. Qpical source-drain gap dimensions are 0.0003 x 0.030 in., with a gate strip whose width slightly overlaps the source and drain. The source and drain electrodes should make low impedance contacts to the semiconductor. With cadmium sulfide films, gold is a satisfactory material for underlying electrodes, while aluminum is preferable for overlying electrodes.12 Considerable variation in design of the TFT is permissible, with the electrodes being

Jan 1, 1967

By Charles W. Merrill

WHETHER the valuable components in a mineral deposit can be mined and separated from the worthless matrix, processed, and marketed depends not only upon the natural factors and the physical and chemical techniques, but also upon many extrinsic factors relevant to the economics of the business of exploring, developing, and producing minerals. To meet a need for proper coverage of this specialized field of economics, the Mineral Economics Div. of the AIME has developed a plan for assembling a volume setting forth important factors affecting mineral enterprises other than those that lend themselves to solution through science or technology. The program has been considered by the Institute's Directors and they have approved it, subject to a decision of the Mineral Economics Div. to carry it out.*

Jan 8, 1954

By G. W. Josephson

Since the earliest years of recorded history the durability and protective qualities of asphalt and tar have been known and utilized. The mummies of early Egyptian kings were coated with asphaltic materials, and asphalt mastics were common in Babylon. However, according to various authorities, it was not until 1780 that the first forerunner of present-day composition roofing was discovered,l and the large-scale expansion of the industry has taken place since 1900. Historical Background Development was stimulated by the growing popularity of manufactured gas. The by-product tars from these operations accumulated in large waste piles that had no commercial value and were a source of annoyance and expense to the gas companies. These tars were offered at very attractive terms to anyone who would take them away, and the infant "composition" roofing industry benefited accordingly. At first the process consisted simply of dipping sheets of burlap or other fabric in a tank of molten tar or asphalt. The long strip of roofing was rolled up for convenient handling, and the early experimenters soon found that it was necessary to dust the surface of their new "roll roofing" with some kind of material that would prevent the tarred surfaces from sticking together. Any finely divided, low- priced local material like sand or fine gravel served this purpose and from its application the roofing-granule industry grew. As time went on other characteristics of a properly applied mineral surfacing were recognized. As with wooden shingles, tar and asphalt can be ignited by flying embers from near-by fires. It was found that by increasing the largest particle size to the maximum that could be successfully embedded, and by properly controlling the amount of smaller fractions retained in the grade so as to cover the asphalt completely a high degree of resistance to fire was attained. Needless to say, in this early period asphaltic roofing needed such selling points to gain acceptance in a field dominated by wood, slate, and tile. When asphalt is protected from the sun's rays it is extremely durable, but when exposed to sunlight its surface is comparatively rapidly decomposed. Completely covering asphalt roofing with mineral surfacing protects the asphalt and adds materially to the life of the roof—conservatively, 500 per cent. Slate Graftules In the production of split slate shingles a large quantity of waste slate is accumulated, as 60 to go per cent of the rock quarried is discarded. This waste was a continuing burden on the industry. Some was marketed as ground slate flour for filler in paint and linoleum, and there is a record that as early as 1906 two carloads of coarse screenings from slate flour were marketed as granules for surfacing roofing. This new field appeared to the slate Pro-

Jan 1, 1948

By G. W. Josephson

Since the earliest years of recorded history the durability and protective qualities of asphalt and tar have been known and utilized. The mummies of early Egyptian kings were coated with asphaltic materials, and asphalt mastics were common in Babylon. However, according to various authorities, it was not until 1780 that the first forerunner of present-day composition roofing was discovered,l and the large-scale expansion of the industry has taken place since 1900. Historical Background Development was stimulated by the growing popularity of manufactured gas. The by-product tars from these operations accumulated in large waste piles that had no commercial value and were a source of annoyance and expense to the gas companies. These tars were offered at very attractive terms to anyone who would take them away, and the infant "composition" roofing industry benefited accordingly. At first the process consisted simply of dipping sheets of burlap or other fabric in a tank of molten tar or asphalt. The long strip of roofing was rolled up for convenient handling, and the early experimenters soon found that it was necessary to dust the surface of their new "roll roofing" with some kind of material that would prevent the tarred surfaces from sticking together. Any finely divided, low- priced local material like sand or fine gravel served this purpose and from its application the roofing-granule industry grew. As time went on other characteristics of a properly applied mineral surfacing were recognized. As with wooden shingles, tar and asphalt can be ignited by flying embers from near-by fires. It was found that by increasing the largest particle size to the maximum that could be successfully embedded, and by properly controlling the amount of smaller fractions retained in the grade so as to cover the asphalt completely a high degree of resistance to fire was attained. Needless to say, in this early period asphaltic roofing needed such selling points to gain acceptance in a field dominated by wood, slate, and tile. When asphalt is protected from the sun's rays it is extremely durable, but when exposed to sunlight its surface is comparatively rapidly decomposed. Completely covering asphalt roofing with mineral surfacing protects the asphalt and adds materially to the life of the roof—conservatively, 500 per cent. Slate Graftules In the production of split slate shingles a large quantity of waste slate is accumulated, as 60 to go per cent of the rock quarried is discarded. This waste was a continuing burden on the industry. Some was marketed as ground slate flour for filler in paint and linoleum, and there is a record that as early as 1906 two carloads of coarse screenings from slate flour were marketed as granules for surfacing roofing. This new field appeared to the slate Pro-

Jan 1, 1948

By D. B. Barker, D. C. Holloway, J. F. Cardenas-Garcia

Tround International Inc. is currently developing a hard rock drill that uses a salvo of three frangible projectiles to prefracture the rock ahead of a conventional tri-cone bit. This paper reports on a series of experiments conducted for Tround to study the fragmentation enhancement possible through the use of an optimally timed and spaced salvo of projectiles. In this study the complex three-dimensional problem was simplified to a two dimensional salvo impact problem in a transparent brittle plate of glass. The use of high speed photography and dynamic photoelasticity was then used to study the development of the impact damage zone and the various interactions of the stress waves.

Jan 1, 1982

By Barry K. McMahon

The fundamental problem in rock mechanics is accounting for the discontinuous and anisotropic nature of the jointed rock mass. It is this problem that makes rock mechanics distinct from the mechanics of steel, glass, or concrete. Existing mathematical models explain much of the behavior of rock cores in the laboratory but, in civil engineering at least, the rocks that matter are the ones that are already broken. On the other hand, the basically descriptive methods now used in engineering geology do not lend themselves easily to mathematical analysis. A set of indices of geological properties related to the strength and deformation characteristics of jointed rock is needed. Like the index properties used in soil mechanics these will probably not have precise mathematical meaning, but once correlations are established with large scale tests they can form a basis for the transfer of test results, obtained in one area under one set of conditions, to the prediction of rock behavior in another area under another set of conditions. Indices of rock properties are even more important in rock mechanics than in soil mechanics as the cost of testing is much higher. To be useful, these indices must be easily and quickly measured and give reproducible results when measurements are made by different people. In this paper the word "joint" means all naturally occurring rock fractures with less than 3 in. of clay or other soft coating material. EXISTING INDICES OF ROCK PROPERTIES A comprehensive review of indices of rock properties for intact rock is given by Deere and Miller.' They provide charts ". . . for estimating the strength or modulus properties for intact rock from the numerical indices obtained by either the Schmidt hammer, the Shore Scleroscope,

Jan 1, 1968

By D. W. Kestner

Recent developments and trends in the state of the art as being commercially applied to the pelletizing and sintering of metallic ores, concentrates and reverts will be reviewed. Both ferrous and non-ferrous materials will be covered. The influence of environmental considerations on the decision to build, the process selection, and design of the plants will be discussed. Use of coal in iron ore pellet induration will also be reviewed as the availability and price structure of oil and gas becomes a consideration to the plant operators.

Jan 1, 1980

By John A. Dunn

Continued increase in electric power requirements for mining, brought on by higher capacity mining machines and total mechanization, emphasizes the importance of proper power system design and planning. How effective a mine operates to produce quality coal at low cost depends to a great extent on how well its power system is planned and how well it is maintained. To be planned well it must be adequate to serve all the needs of the mine, it should be safe, there should be a margin for expansion, and it should be easily maintained. In planning a power system for mining coal it is helpful to establish a reliable base for estimating loads. Since most mines are served electric power by utility, power bills for similar mine loads are useful in setting up a base for estimates.

Jan 12, 1964

By W. F. de Lange, M. I. Brittan

A mathematical model of the Western Holdings gold concentrator in South Africa was generated by multiple regression analysis of routine plant operating data. Interpretation of the computer results and application of the model indicated that significant economic improvement in gold recovery could be realized by relatively minor modifications to the circuit. The modifications made are described and the economic benefits resulting from the increased gold production are assessed. Comparison, of the projections of the mathematical model with actual plant performance is illustrated.

Jan 1, 1976

Jan 1, 1967

By J. L. Bruce

For a number of years, from an economic standpoint, the ventilation of the Colorado mine of the Davis-Daly Copper Co. has been a difficult problem. The development through the main hoisting shaft was pursued for a number of years and to a depth of about 2500 ft.( 762 m.)before large bodies of good commercial ore were opened up. This lack of early success in exploration restricted expenditures for ventilation, with the result that the present orebodies were opened up at a depth of 2500 ft., and in country rock f relatively high temperature, without adequate means f supplying the development faces and the stopes with cool or fresh air of low humidity and suitable velocity. During the progress of development, two or three connections were made at higher levels with the workings of adjoining operations, but these were of a makeshift and unsatisfactory character and afforded no means for carrying downcast air from the surface, in anything approaching a direct course, to the working faces. During the latter part of 1917, arrangements were made with. the Anaconda Copper Mining Co., whereby, during the year 1918 and the early part f the year 1919, a crosscut was driven eastwards on the 2500-ft. level of the Colorado shaft and connection was made by means f an up-raise of approximately 200 ft. to a crosscut driven westwards from the 2800-ft. level of the Belmont mine, this crosscut at the top of the raise being driven at Davis-Daly expense by the Anaconda Copper Mining Co. This connection, in conjunction with a No. 11 Sirocco fan installed near the Colorado shaft, provided the Colorado mine with a maximum of approximately 30,000 cu. ft. per min. of relatively fresh air, most of which came in a fairly direct route from the downcast Belmont shaft through the No. 11 fan to the 2500-ft. level stopes. After passing through these stopes and the stopes of overlying levels, it passed through the main crosscuts on higher levels back to the Colorado shaft, which provided the upcast for this current of air. The improvement

Jan 9, 1921

By Gerald M. Friedman

CONVENTIONAL usage defines emery as a natural aggregate of corundum and magnetite. Because emery bodies contain abundant spinel two types are recognized, spinel-bearing and spinel- free. Watson and Steiger1 introduced the name spinellite for emery in which spinel is a major constituuent, but this term has not been generally adopted. Spinel emery grades locally into spinel magnetite rocks with or without accessory corundum. Even this variety has been used commercially in the past. The term emery therefore applies to natural aggregates composed of corundum and magnetite; corundum, magnetite, and spinel; and spinel and magnetite.

Jan 7, 1957