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The Atlanta Mine is located in east central Nevada, in Lincoln County, 116 km (72 miles) south of Ely and 80 km (50 miles) northeast of the old mining town of Pioche. From this famous district, high-grade copper ore was mined and shipped to a smelter in Wales in the 1850s; an early day lead blast furnace was also in operation. The Standard Slag Company began operations in May 1975 on the well known Atlanta Mine, which was operated by Roy Hardy in the 1930s. The mill is currently processing 450 mtpd (500 stpd) of gold-silver bearing ore. Mining by open pit is in a brecciated zone occurring between limestone-dolomites on the foot wall and tertiary rhyolites on the hanging wall. The quartz breccia is considered among the most abrasive in the world - shovel teeth must be replaced every week. Stripping ratio is 3.9 to 1.0. Because of the hard abrasive ore, the crushing plant consists of four units: two jaw crushers in series, one Hydrocone, and one Gyradisc. Mine feed to the primary crusher is limited to 610 mm (24 in.) in size. The remaining crushers work in closed circuit with screens to produce a mill feed of 6 to 13 mm (0.25 and 0.50 in.). Hardness of the ore is demonstrated by the fact that the reversible liners of the primary jaw crusher had to be replaced in early 1978 after handling only 39,000 mt (44,000 st) at a cost of $0.095 per mt ($0.086 per st). Another example of the extreme abrasiveness of the breccia ore was the total cost per ton in 1977 for all wear parts in the comminution circuit, including screens and grinding media. This amounted to $2.84 per mt ($2.58 per st). The Atlanta grinding plant consists of three ball mills to grind the 7 mm (1 /4 in.) crushing plant product to 85 to 90% minus 150 microns (100 mesh). Feed rate to the primary Tricone mill is determined by maintaining a cyclone overflow at 28 to 38% solids, which controls the grind mentioned above. A mixture of 90 and 65 mm (3.5 and 2.5 in. ) balls are charged to this primary mill. Both the secondary mills are charged with 50 mm (2 in ) balls. Total ball consumption is 2 kg per mt (4 lb per st). All three ball mills use rubber liners. Primary mill cyclone underflows are fed to the secondary mills close circuited with the same cyclones.

Jan 1, 1981

By Luther B. Eames

J. V. N. DORR, New York, N. Y.-I have read Mr. Eames' excellent paper on this' subject with great interest, for besides being connected with the design and installation of the first modern countercurrent decantation plant, he was associated with me in the development of the thickener in the Black Hills some years earlier, and has now been operating the largest plant that has used this method of treatment. His, discussion, of the influence of different factors on the results obtained is quite thorough, but several features I think may not be apparent to the reader who has not studied the subject carefully. 1. Grade of Ore That Can Be Treated.-Mr. Eames has shown graphically that' the assay of all solutions increases directly as the grade of the ore treated. He has not emphasized, however, the fact that, as most operators prefer to keep the assay of pregnant solutions down below a certain figure in order to insure complete precipitation, an increase in ore value beyond a certain point means a proportional increase in solution precipitated and therefore not only an increase in the percentage of dissolved gold recovered, but an actual descrease in tailing loss. The importance of the influence of the percentage of moisture in the underflow on loss is made clear, and I. may add that unless it is quite evident that pulp can be safely settled to 50 per cent. solids, or more, it is usually advisable to use a continuous filter at the end of. a decantation plant to reduce losses in cyanide and gold. Dissolution in Thickeners.-The influence of a change of solution on silver dissolution has long been emphasized and most gold operators have. recognized the annoying way in which a gold ore after being agitated until nothing more can be dissolved will loosen up again when almost ready for the dump after the dissolved metal has been removed by decantation or filtration. Continuous decantation gives favorable conditions for this additional dissolution and a chance to recover most of what is thus dissolved. This is especially true if an extra tank is used in the series and barren solution added at the second tank from the end instead, of the first, as shown in Mr. Eames' Fig. 1. It can be calculated that the use of this tank will reduce the mechanical loss of cyanide by one-third and cut the gold loss as well; but the saving in gold or silver that may dissolve when the pulp is first diluted with weak solution may be as important.

Jan 4, 1917

By Howard I. Smith

THE mineral trona was discovered on Government land in 1938, about 18 miles west of the town of Green River, Wyo., in the core of the John Hay, Jr., well, a test well drilled for oil by the Mountain Fuel Supply Co. in sec. 2, T. 18 N., R. 11o W., sixth principal meridian. Although no oil or gas was reported, the drilling led to a discovery of great potential economic importance and exceptional scientific interest. Trona is a relatively rare mineral found at various places in playa deposits but not previously found at any great depth. It is composed of hydrous sodium carbonate and sodium bicarbonate (Na2CO3.NaHCO3.2H2O). Pure trona contains the equivalent of 70.35 per cent of sodium carbonate. Total sodium computed to carbonate times 1.42 equals the percentage of trona in the absence of other sodium carbonate minerals in the sample. ANALYSES Two short pieces of core sent to the author a few days after the completion of the Hay well were analyzed by R. C. Wells† and found to be exceptionally pure trona. A brief article on this discovery has already been published.1 Arrangements were then made through W. T. Nightengale‡ for the author to inspect and sample the core. The company log of the well included notations of sodium salt crystals from a depth of 1190 to 1820 ft. Not being able to identify all the minerals present, the author selected several specimens of the core for petrographic examinations and sampled the sections of trona for analysis. J. J. Fahey, of the Geological Survey, examined the specimens and reported most of the crystals to be a new anhydrous sodium carbonate and calcium carbonate mineral (Na2CO3.2CaCO3), which he named shortite,2 after Maxwell N. Short.* He analyzed the samples of trona, with the results shown in Table i. [ ] In addition to the 10 ft. I in. of trona in the first section, it is reasonable to assume that the 9 ft. 8 in. for which no core was available for sampling is either mostly trona or some other soluble salt, but it should not be included in calculating reserves. In the part of the core between 1590 ft. 3 in. and 1600 ft. 4 in. the material insoluble in cold water, amounting to about 5 per cent, was estimated petrographically to contain 70 per cent clay, 25 per cent shortite, and 5 per cent pyrite. ACCOMPANYING MINERALS Fahey later secured about 600 ft. of the core for a detailed examination and study

Jan 1, 1942

By Coopers &. Lybrand

INTRODUCTION From a tax viewpoint, United States mining companies are at a substantial disadvantage in the international mining area compared with companies in other major capital-exporting countries, according to a 1975 study by Coopers & Lybrand for the American Mining Congress. The study compared the relative tax position of a United States investor with investors from Belgium, Canada, France, Germany, Japan, the Netherlands, Switzerland, and the United Kingdom. The comparison was based on average rates of return realizable by investor companies on four mine-model investments in twelve capital-importing countries. The countries in which these investments were assumed to be made are varied in their tax systems so that a wide range of possibilities was included in the analyses. Each mine model was standard so that the rates of return for each investment by each investor were affected solely by the respective tax systems of the capital-exporting and capital-importing countries. UNITED STATES POSITION The study found that the United States competitive position, in terms of the average rate of return on an overall basis, ranked next to last among the nine capital-exporting countries in the study. Further, the United States overall rate of return is more than 20% below that of the country (Japan) with the highest overall rate of return. On an average return-on-equity basis, the United States' position among the nine investor countries, for each of the mine investments studied, was: copper, eighth; iron ore, sixth; nickel, fifth; manganese, a tie for last place. Figure 1 shows the overall results realized by each capital-exporting country on the basis of average return on equity. [ ] The frequency with which a given capital-exporting country attains the highest or next highest rate of return in a capital-importing country provides further insight and another basis for comparing the tax laws of the capital-exporting countries. Of the situations compared in the study, the United States never attained the highest rate of return, and reached the second and third highest rate of return in only two instances. The tables showing the frequencies of rankings are given in Table 1 for each of the four mine models. In summary, the United States mining company does not have a competitive advantage under the tax rules when competing for mineral concessions in other countries. The United States company, in fact, appears to be at a clear disadvantage. The study also considered the effect of the following recent tax proposals on United States investors in international mining ventures:

Jan 1, 1985

By James K. Stanley

IRON-COBALT alloys in the range of 35-50 pct cobalt are of interest in the electrical industry because they possess the highest magnetic saturation of any magnetic material known.1,2 The magnetic saturation induction of the 35 pct alloy is 24,200 gausses, compared to 21,600 for pure iron (Fig I). This difference is significant in electrical apparatus, where weight or space is at a premium. Saturation values higher than that for iron can be attained up to about 70 pct Co but economics restrict the use to as low a cobalt content as possible without sacrifice of saturation. Fig 2 shows the iron-cobalt equilibrium diagram. Up to the present time, two factors have retarded the use of iron-cobalt alloys in the electrical industry for magnetic purposes.† One is the high cost of cobalt ($1.50 per pound) and the other is the inherent brittleness of the binary iron-cobalt alloys. Straight iron-cobalt alloys up to 25 pct cobalt are ductile and easy to process to thin sheet or strip by conventional methods of hot and cold rolling, but the alloys containing higher percentages of cobalt, including those for which the saturation magnetization is a maximum (35 to 40 pct), are increasingly brittle with increasing cobalt, at least up to 50 pct, and are consequently difficult to process, either hot or cold. Work by White and Wah13 indicated that iron-cobalt alloys could be made ductile by alloying with vanadium, and after quenching the alloys (vanadium up to about 4 pct) were found to be cold rollable to very thin gauges. With this as a background, we resumed our work on these alloys with the objective of developing methods for economical commercial production of wide strip. For this purpose we have concentrated on the 35 pct alloy in order to obtain the highest possible saturation value. Experiments were carried out on many alloy additions to the iron-cobalt alloys and on the response of these compositions to heat treatments. This work finally culminated in a commercially producible iron-cobalt alloy which has been named Hiperco. * MATERIALS STUDIED AND PROCEDURE Binary alloys of iron and cobalt in the range of 35 pct cobalt are difficult to hot work (by forging or rolling) without such additions as C, Mn, Si, V, Cr, Mo, W or perhaps others. Another beneficial effect of such additions is that they in-crease to a greater or less extent the strangely low electrical resistivity of these alloys (about 10 microohms per cm3

Jan 1, 1947

By M. E. Wadsworth, I. B. Cutler, R. W. Bartlett

The oxidation kinetics of ZrC was studied between 450" and 580°C in oxygen pressures from 6.5 x 10-to 1 atm using a ther mogravimetric apparatus and sized powder samples. Two parallel rate controlling processes were observed. A surface reaction occurring at the ZrC-ZrO2 phase boundary accounted for most of the oxidation and had an activation enthalpy of 46 kcal per mole. The other process, believed to be diffusion of oxygen into the ZrC lattice partially replacing carbon, had an activation enthalpy of 53 kcal per mole. The enthalpy for chemisorption of O2 on ZrC was determined to be —13 kcal per mole. Water vapor in the presence of oxygen accelerated the surface reaction rate. THERE has been little reporting of formal rate studies or attempts to ascertain the mechanism of oxidation of carbides. MacDonald and Ransley1 studied the oxidation of titanium carbide which has the same structure as zirconium carbide, fcc. They observed an initial increase in rate with increasing temperature followed by a rapid decrease through a rate minimum and a subsequent second increase at higher temperatures. The discontinuity in the rate rise was attributed to a phase change in the oxide which changed the rate determining step from the surface reaction at the carbide-oxide interface to diffusion through the oxide layer. Samsonov and Golybera 2 studied titanium carbide and reported that during the initial period of oxidation a dense film of Tic-TiO was formed followed by the formation of less adhering layers of higher oxides. The purpose of this investigation was to study the kinetics of oxidation of zirconium carbide and to attempt to gain some knowledge of the mechanism by which oxidation occurs. EXPERIMENTAL PROCEDURE Measurement of the weight gain associated with the oxidation of ZrC was used to determine oxidation rates. The principal experimental parameters were surface area, temperature, and oxygen pressure. Although moderately sized crystals of ZrC can be grown by the Van Arkel method, the only commercially available ZrC is a powder. In using powders, the surface area must be controlled either by fabricating the powder into a sintered pellet with a measurable surface area, relatively fixed during oxidation, or by using sized unconsolidated powder and applying appropriate geometric considerations to the shape of the grains to correct for their diminishing surface areas as they oxidize. Both techniques involve some difficulties. pellets of binder-free zirconium carbide can be made by hot pressing, but it is difficult to obtain densities greater than 90 pct of

Jan 1, 1963

By Earl Hunner

IT is common knowledge that the iron orebodies of the Mesabi range lie nearly horizontal and are of trough or blanket-like types. These orebodies are from a few feet to several hundred feet thick and vary from a few acres in extent to the size of the largest one, at Hibbing, Minn., which is over 1 mile wide and 3 miles long. They are covered with sand, boulder and clay overburden and occasionally, shallow depths of ledge material, varying in total depth from about 20 to 200 ft. Large areas are not capped with overlying ledge material; the top of the ore lies directly underneath the surface material. Because of the comparatively great tonnage of ore, open-pit mining has made tremendous strides since the first open-pit ore was shipped from this range by the Merritt brothers, from the Mountain iron mine in October, 1892, and along with the great development of open-pit mining on the Mesabi range has gone a tremendous change in the character of equipment used.

Jan 1, 1930

By T. W. Lippert

CUBA fancies herself the "pearl of the Antilles" and, by many, Jamaica is called "blessed." But far to the southward lies what is seemingly the Caribbean's most glittering jewel, the sparsely-settled, Spanish-speaking United States of Venezuela, indeed blessed by nature to a lavish degree. Not a large country, Venezuela is leaping from the donkey to the airplane under the impact of its natural wonders. Angel Falls, dwarfing Niagara and seldom seen by man, is hidden in the cold, primitive and unexplored Guiana highlands along the southeast border. A few hundred miles northwest are the low and torrid coastal plains from which gush unlimited black-gold streams of oil. About midway are the Llanos-low-lying, savanna-type grasslands, beneath which large deposits of bauxite are as yet barely touched by the explorer's diamond drill. And jutting starkly upward 2000 ft from a surrounding expanse of savanna is a small mountain (see front cover), 11 miles long and 1 mile wide. It is, or was, La Parida.

Jan 2, 1950

By John T. Ryan

DEFINITE improvement in its accident fatality rate in the coal-mining industry was recorded during 1941, based on preliminary figures for the period from January through October. Total production during this ten-month period was approximately 91 percent of the total production in all of 1940. The ten-month accident rate for both bituminous and anthracite mining in 1941 was 2.15 killed per million tons of coal mined, compared with a rate of 2.66 for the full year of 1940. The bituminous rate decreased from 2.55 in 1940 to 1.99 in ten months of 1941, and the anthracite rate from 3.62 to 3.53 in similar periods. The decrease is more apparent for the bituminous branch of the industry, as the high figure in 1940 was due to seven major disasters which brought death to 276 men. The same number of major explosions during ten months of 1941 caused only 64 lives to be lost. The severity of the explosions has been lower this year but a definite need still exists for reduction in this type of accident.

Jan 1, 1942

By G. M. Ritcey

Sulphuric acid leaching has been up to the present, the most popular of the leaching routes. Oxide ores are usually leached with sulphuric acid directly by dump leaching, as practiced at the Bagdad or Bluebird Mines in Arizona, or by vat leaching as done at Inspiration Mining in Arizona. Upgrading of the low-grade oxide ores by dump leaching followed by cementation of the copper from solution by scrap iron has been replaced by the leaching-solvent extraction-electrowinning route which results in a high purity product at the mill site at reduced production costs compared to previous practice. High-grade oxide ores, vat leached with H2SO4, can contain, for example, 25 g Cu/l and 25 g H2S04/,l, or higher concentrations of both, and are presently fed directly to electrorefining plants. Advantages of coupling solvent extraction-electrowinning with the low cost dump leaching instead of using cementation, are as follows (1): a) the production of high purity electrolytic copper rather than cement copper;

Jan 1, 1978

By Philip D. Pearson

CALAND Ore Co.'s dredging program has reached the halfway mark. The goal is to remove more than 160 million cu yd of lake bottom material overlying the iron orebody in Falls Bay of Steep Rock Lake, Ont. Two large dredges were constructed to remove this overburden, a layer of soil about 90 pct varved clay some 400 ft thick. Moisture content of the clay is high-approximately at the liquid limit of the soil. A few years ago, searching for additional reserves of ore, Inland Steel Co. looked toward Canada and the newly developed Steep Rock iron range. To this end an option agreement was signed Dec. 30, 1949, between Steep Rock Mines Ltd. and Caland Ore Co. Ltd., a wholly owned subsidiary of Inland Steel. Several drilling programs were conducted between this date and Jan. 1, 1953, when a 99-year lease was signed covering an area of 1249 acres. This lease calls for ore production to begin in 1960, with full production of 3 million tons per year by 1969.

Jan 8, 1957

By T. S. Fuller

The work of D. J. McAdam, Jr.1,2 at the U. S. Naval Engineering Experiment Station, Annapolis, Md., on what has been called by him "corrosion-fatigue" has focussed the attention of the engineering profession in general, and of those interested especially in the study of corrosion in particular, on the importance of making tests which will indicate as nearly as possible what can be expected from a given material in service. Pitting is unquestionably the chief agent operating so tremendously to reduce fatigue limits, but in the light of previous work3, 4, 5, 6, 7, 8 it is fair to assume that absorbed hydrogen resulting from the action of the corroding medium upon steel may, under certain conditions, have a perceptible influence. The experiments described in this paper deal more precisely with stressless corrosion, or "prior-corrosion fatigue,"9 and have been carried out to test such an assumption, to segregate, if possible, the effect of pitting from that of absorbed hydrogen, and although very preliminary in nature they indicate results which are striking.

Jan 1, 1929

By T. S. Fuller

The work of D. J. McAdam, Jr.1,2 at the U. S. Naval Engineering Experiment Station, Annapolis, Md., on what has been called by him "corrosion-fatigue" has focussed the attention of the engineering profession in general, and of those interested especially in the study of corrosion in particular, on the importance of making tests which will indicate as nearly as possible what can be expected from a given material in service. Pitting is unquestionably the chief agent operating so tremendously to reduce fatigue limits, but in the light of previous work3, 4, 5, 6, 7, 8 it is fair to assume that absorbed hydrogen resulting from the action of the corroding medium upon steel may, under certain conditions, have a perceptible influence. The experiments described in this paper deal more precisely with stressless corrosion, or "prior-corrosion fatigue,"9 and have been carried out to test such an assumption, to segregate, if possible, the effect of pitting from that of absorbed hydrogen, and although very preliminary in nature they indicate results which are striking.

Jan 1, 1929

By W. A. Naismith, R. T. Pakalnis

The Umgal a section of the We1gedacht Exploration Company Ltd., a member of the Rand Mines Group, is situated near Utrecht in the province of Natal, South Africa. Two coal seams, the Alfred and Gus, are mined to fulfill commitments to both inland and export markets. To increase extraction in the high quality Alfred Seam, pillar extraction, known locally as stooping, was introduced to the mine in September, 1980. Mining is a conventional cut-drill -blast operation and takes place under a unique set of geological conditions viz. moderately thick seam at 3.5 m; rapidly varying cover from 25m to 120 m; an overburden containing competent sandstone and dolerite horizons. In order to improve the understanding of the manner in which the pillar and overburden interact during pillar extraction, a largely visual system of monitoring backed up by roof-floor convergence measurements was employed. Preliminary analysis of the observations suggests that roof collapse or goafing occurs in three phases but is only initiated once a critical amount of convergence has taken place.

Jan 1, 1983

By William J. Robinson

What is the cummulative rate of recovery of copper from a sulfide leach dump? The technical answers to this frequently asked question may vary from "I don't know" to "quite good" from people of the same company. Management also poses this question because it plays a vital role in planning future production. The answer is difficult because of the many variables between different operations such as physical construction of the dump, topography of the original site, characteristics of dump material, mineralization and water application. Each of these factors and others have a bearing on the rate of recovery. Anaconda's method of water distribution at Butte is unique in that each dump is drilled to allow physical injection of water into the dump. The injection holes are drilled vertically on 25 ft centers from the surface of the dump. Normally, the holes are drilled 40 ft deep and cased with 4-in. PVC perforated pipe. The pipe is perforated at one-foot intervals with four 1/2 in. diam holes at 90" spacing on the pipe circumference.

Jan 9, 1972

By Hsun Hu

C. G. Dunn (Geneva1 Electvic Reseavclz Labo,vatory)-Dr. Hu16 has obtained a number of rolling and annealing texture results that partly agree with those of Dunn17 and Dunn and Kohl8 for experiments of a similar nature. I would like to discuss some of the points of agreement as well as some of disagreement and then present some unpublished data as a contribution to the work on textures. Firstly, there is agreement on the components produced during a 70 pct cold-rolling reduction of a (110) [001 ] single crystal; there is agreement on the forma- tion of a (110) [001] recrystallization texture provided recrystallization occurs at 800°C or higher; and there is agreement on the formation of (120) [001] components provided recrystallization occurs below 600°C. There is some disagreement on the low-temperature recrystallization since I also obtained a substantial amount of a (110) [001] component while the author obtained only (120) [001] components. I also discussed the differences between low- and high-temperature recrystallization (which included further annealing changes in the samples on long

Jan 1, 1962

By Sidney A. Swensrud

This paper reviews the subject of gasoline margins, discusses some of the more current marketing problems, and gives some consideration to the main urges to marketing expansion, or overexpansion, in the oil industry. Margins In an earlier paper1, some comparisons were shown for the years 1929, 1930 and 1931, of the margin between the refinery cost of gasoline in Oklahoma, the market price in Oklahoma, and the average retail price in 50 representative cities of the United States. These figures indicated a small margin for the refiner in 1929 between his gasoline cost and the wholesale price, which, however, had turned into a loss by 1931. The margin between either refinery costs or wholesale prices and the retail price in the 50 cities showed a continuous decline during the three years. We have now worked out these figures on a similar basis for a longer period—from 1928 through 1936. The figures for refinery gasoline cost are slightly different from those in the earlier study, owing to the use of

Jan 1, 1937

By A. M. Gaudin, R. T. Hukki

PREVIOUS work on the principles of comminution has shown: (I) that the surface produced is proportional to work input (Rittinger law, 1a-3); (2) that there is regularity to the weight distribution of the fragments according to size.4-10 In this paper it is brought out that the surface on the fragments is distributed in definite and simple relation to size. The experimental work has involved: I. Construction of an apparatus capable of measuring the surface of mineral fragments independently of the chemical composition of the fragments and independently of the site of the surface; 2. Refining the methods available for measurement of particle size; 3. Designing and building a crusher capable of operating on very small quantities of mineral, if necessary on single crystals, and in such fashion as to minimize handling losses of material. Complete experiments have been carried out with massive quartz and individual quartz crystals. Partial experiments, lacking surface measurements, have been made with glass spheres, galena, sphalerite, fluorite, salt and coal.

Jan 1, 1944

By E. R. Parker, D. L. Martin

During the heat-treatment of silver specimens for tensile tests it was observed that the bars blistered and became brittle when heated in a hydrogen atmosphere. To check this unexpected result, a wide variety of commercial silvers were heated in hydrogen at 850°C. Only a few of the materials developed blisters, the most severe of which is the tube pictured in Fig. I. The microstructure of a cross section of the tube is shown in Fig. 2. The embrit-tlernent is extremely severe at the edge; the blisters result from the severe deformation of the surface material by large under- lying gas pockets. The effects resulting from hydrogen embrittlement of silver have been observed by numerous investigators over a long time l,2,3 although it was only recently that a clear explanation was offered.4 However, the damage resulting from hydrogen embrittlement has not been generally recognized; and it is of advantage to know more about this phe- 1 References are at the end of the paper.

Jan 1, 1943

By D. L. Martin, E. R. Parker

During the heat-treatment of silver specimens for tensile tests it was observed that the bars blistered and became brittle when heated in a hydrogen atmosphere. To check this unexpected result, a wide variety of commercial silvers were heated in hydrogen at 850°C. Only a few of the materials developed blisters, the most severe of which is the tube pictured in Fig. I. The microstructure of a cross section of the tube is shown in Fig. 2. The embrit-tlernent is extremely severe at the edge; the blisters result from the severe deformation of the surface material by large under- lying gas pockets. The effects resulting from hydrogen embrittlement of silver have been observed by numerous investigators over a long time l,2,3 although it was only recently that a clear explanation was offered.4 However, the damage resulting from hydrogen embrittlement has not been generally recognized; and it is of advantage to know more about this phe- 1 References are at the end of the paper.

Jan 1, 1943