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By Frank R. Milliken, Robert Goodwin

In September 1937, the Ohio Copper Co. inaugurated the treatment of its copper-bearing mill tailings at Lark, Utah. These tailings had been accumulated during the regular operation of the Ohio Copper mine and mill over the period 1907 to 1919. Gravity concentration had been employed except for a comparatively short period in 1919, when flotation was used. The ore milled during that period assayed about I per cent Cu. The chief copper mineral, chalcocite, was disseminated in a shattered quartzite, mainly along fracture or cleavage planes. The quartzite gangue was extremely hard and grinding to liberation resulted in excessive sliming of the "sooty" chalcocite, with consequent high tailings losses. Recovery on the seven million tons treated was probably less than 60 per cent of the total copper content. As early as 1918, attempts had been made to sample the dump. In 1928, a complete sampling program was undertaken. The sampling consisted of seventy-four 5-in. post auger holes drilled to the full depth of the dump at regular intervals of 250 ft. Each 10-ft. portion thereof comprised a sample for analysis. Each sample was screened, rolled, divided into three parts, dried and assayed. The reject was retained for testing purposes. From the depth of the auger holes a contour map of the dump was plotted, Fig. I, which gives percentages of tonnage and copper content. The tonnage within the limit of the drill holes was estimated at about five million tons with an average content of 0.42 per cent Cu, 31 per cent of which (0.13 per cent) was acid-soluble. A screen analysis of the composite dump sample is shown in Table I. Flotation tests by several companies and individuals were then made, the results of which ranged from 62 to 74 per cent recovery. On the basis of these, a 200-ton pilot plant employing straight flotation was built and operated for a few months. Operation of this plant was unsuccessful, as no provision had been made to handle the copper-bearing solutions resulting from the water-soluble copper, a point that was overlooked in the laboratory test work. Attempts to decant the copper-bearing solution for precipitation in the usual manner ahead of flotation were not satisfactory because of low water recovery (owing to poor settling characteristics of the pulp) and contamination of the copper precipitate with unsettled slime. Low copper prices in 1931 necessitated the termination of testing. With the stimulus of higher copper prices in 1937, a review was made of metallurgical

Jan 1, 1943

By Robert Goodwin, Frank R. Milliken

In September 1937, the Ohio Copper Co. inaugurated the treatment of its copper-bearing mill tailings at Lark, Utah. These tailings had been accumulated during the regular operation of the Ohio Copper mine and mill over the period 1907 to 1919. Gravity concentration had been employed except for a comparatively short period in 1919, when flotation was used. The ore milled during that period assayed about I per cent Cu. The chief copper mineral, chalcocite, was disseminated in a shattered quartzite, mainly along fracture or cleavage planes. The quartzite gangue was extremely hard and grinding to liberation resulted in excessive sliming of the "sooty" chalcocite, with consequent high tailings losses. Recovery on the seven million tons treated was probably less than 60 per cent of the total copper content. As early as 1918, attempts had been made to sample the dump. In 1928, a complete sampling program was undertaken. The sampling consisted of seventy-four 5-in. post auger holes drilled to the full depth of the dump at regular intervals of 250 ft. Each 10-ft. portion thereof comprised a sample for analysis. Each sample was screened, rolled, divided into three parts, dried and assayed. The reject was retained for testing purposes. From the depth of the auger holes a contour map of the dump was plotted, Fig. I, which gives percentages of tonnage and copper content. The tonnage within the limit of the drill holes was estimated at about five million tons with an average content of 0.42 per cent Cu, 31 per cent of which (0.13 per cent) was acid-soluble. A screen analysis of the composite dump sample is shown in Table I. Flotation tests by several companies and individuals were then made, the results of which ranged from 62 to 74 per cent recovery. On the basis of these, a 200-ton pilot plant employing straight flotation was built and operated for a few months. Operation of this plant was unsuccessful, as no provision had been made to handle the copper-bearing solutions resulting from the water-soluble copper, a point that was overlooked in the laboratory test work. Attempts to decant the copper-bearing solution for precipitation in the usual manner ahead of flotation were not satisfactory because of low water recovery (owing to poor settling characteristics of the pulp) and contamination of the copper precipitate with unsettled slime. Low copper prices in 1931 necessitated the termination of testing. With the stimulus of higher copper prices in 1937, a review was made of metallurgical

Jan 1, 1943

By NEWTON C. MARSHALL

AS every school boy knows, the Andes mountain range forms the backbone of South America, extending the full length of the continent along its western edge and fairly close to the Pacific coast. But in Colombia these mountains are divided into three distinct ranges known as the Western, Central and Eastern ranges of the Andes. United at the southern end, they spread out like three fingers in a northerly direction across the Republic of Colombia. These great natural barriers have only in recent years been tarried by railroads or wagon roads, and they have had their effect upon the history of the country, both political and ethnological. Each of the three ranges dies out and dwindles away before reaching the boundary of Colombia on the Caribbean Sea. When I studied my geography as a youngster 1 used to think that the

Jan 1, 1935

By J. L. Bray

ACCELERATED programs, as discussed in this paper, refer to the year-around operation of a college or university with three sixteen-week or four twelve-week terms per year, with pauses between sufficient only to allow the administrative group to perform their functions. In most engineering schools, under such conditions, the conventional four-year course can be condensed to two years and eight months. These accelerated programs of study, which now exist in most of our technical institutions, were forced upon us under the influence of the outburst of wartime patriotism, perhaps one might go so far as to call it hysteria. Many of us felt and hoped that these programs were temporary expedients, but the cold hard threat of permanency now rears its head; consequently we should examine the merits and shortcomings of the new order, and evaluate its effect on our educational system, since it may persist in some form in the postwar years, because of the changing political and financial situation. Many engineering students are being educated in state supported institutions

Jan 1, 1944

Adams, John H., Pres. & Mgr., Alabama Lime & Stone Corpn., 1302-4-8 First Ave., Birmingham, Ala. '14 Adams, L. W., Otis Steel Co., Riverside Plant Cleveland, Ohio. '15 Adams, Leland D., Min. Engr., Mgr., Signal Mines Co., Goldbanks Quicksilver Co., 485 California St., San Francisco, Cal. '14 Adams, R. L., Min. Engr., Old Ben Coal Corpn., Mine 12 Christopher, III. `19 Adams, Robert M., Robert M. Adams Co 1201 Fidelity Bldg., Duluth, Minn. '20

Jan 1, 1925

By J. C. Swartz

Measurements of the effect of precipitation stresses on the solubility of cementite (Fe3C) precipitates in a iron are reported. Solubilities were determined from measurements of the Snoek relaxation due to interstitial carbon after quenching from various equilibrium treatments. Stress-free precipitates were obtained by a spheroidizing treatment of vacuum-melted Fe 0.06 wt pet C. Subsequent equilibration treatments were designed to suppress nucleation of other precipitates. The results for stress-free cementite give a heat of solution of 14.8 i 0.2 keal per mole and an entropy change of 1.1 i 0.2 eu in the temperature range 400" to 715°C. Comparison with previous data indicates that the heat of solution increases about 6 keal per mole as temperature increases from 700" to 1000°C. Data on self-stressed cementite in quench-aged specimens of Fe 0.013 wt pet C indicate 1) an apparent heat of solution of 12.1 i 0.4 keal per mole in the range 280" to 690°C, 2) a strain energy of- 1.1 keal per mole Fe3C accompanying precipitation at 280°C, and 3') a gradual decrease in the strain energy of precipitation with increasing equilibration temperature. In com-parison with 2 and 3 the strain energy calculated for an isotropic model is 1.7 keal per mole Fe3C. The lower values obtained from the experiment indicated substantial stress velaxation by dislocation motion. WHEN a supersaturated solution of carbon in a iron is aged at temperatures in the range 200o to 700oC, the carbon clusters by interstitial diffusion and forms cementite (Fe3C) precipitate particles. Unstressed cementite has a volume per iron atom 9 pet higher than that of a iron;' hence, cementite precipitate particles are usually under pressure from the iron matrix. The pressure would tend to increase the solubility of cementite in iron.' This report describes anelastic measurements of the solubilities of self-stressed and stress-free cementite in a iron. Previous determinations of the cementite solubility are summarized in Table I. The method of cementite formation for each reference was studied to ascertain the state of stress of the cementite. The results judged to be for stress-free and stressed cementite are distinguished in the table. In the next section an estimate of the stress effect is obtained which is clearly too small to account for the large difference between the previous results in parts A and B of the table. THEORETICAL Let AGO be the standard free-energy change of the reaction Fe3C (eem.) = 3Fe (a) + C (in a) [1] in the absence of stresses. Since cementite precipitates appear to be rather pure10 and the carbon is so dilute in the iron,8 the cementite and iron of Eq. [ I] for the stress-free case have essentially unit activities and the activity of carbon equals its atom fraction xoC Then the stress-free equilibrium is expressed by RT In XoC = -?GO 121 To first approximation the change in the chemical potential of carbon due to the precipitation stresses equals the elastic strain energy W accompanying precipitation of a mole of cementite.2 Hence, in the presence of the precipitation stresses the equilibrium is described by RT In x sq = -?G° + W [3] where xsC is the mole fraction of dissolved carbon in the stressed case. An approximate value of W can be obtained from analysis of the inclusion problem in elasticity theory. The inclusion is a small portion of the matrix phase which has suffered a transformation while still imbedded in the matrix. In the absence of the constraint of the matrix the transformation would be equivalent to a uniform dilational strain eT. Both the matrix (a) phase and inclusion (0) phase are assumed to be homogeneous, isotropic materials. When the a and 0 phases have the same elastic moduli, which is approximately true for iron and cementite,11 the total strain energy per mole ß is12 2µVß(eT)2(3 +4 µx)-I [4]

Jan 1, 1968

By AIME AIME

THE fall meeting at El Paso this year (Oct. 13¬15) will be of unusual interest due to the international atmosphere imparted by the many engineers from Mexico, who are making arrangements to attend this meeting. The meeting will be held jointly with the Western Division of the American Mining Congress. Cooperating in the program will be the representative society of Mexican engineers known as Centro National de Ingenieros of Mexico City, who are plan¬ning on sending many delegates and well known Mexican engineers to the convention. The cooperation of the West Texas Geological Society and the American Association of Petroleum Geologists has also been secured. Brent N. Rickard, manager of the El Paso Smelting Works of the American Smelting & Refining Co. at El Paso, Tex., is general chairman in charge of arrangements. He is receiving splendid cooperation from the Mining Department of the El Paso Chamber of Commerce and from the business people of El Paso, who feel highly honored in having these mining societies meet with them this year.

Jan 1, 1930

By Sherwin F. Kelly

THAT gold ores occur in Georgia is a fact apparently not widely known outside of that state, yet in the last hundred years nearly $18,000,000 worth of gold has been mined there. The discovery of gold-hearing quartz was made in 1823 on the "Forty Acre Lot" (which now belongs to the Columbia Mining Co.), in McDuffie County, and about seven years later the first stamp mill on record was erected near there. In recent years Georgia's gold production has dwindled to an insignificant figure. However, with the increase in gold price, interest in this district has been revived, so an electrical geophysical survey was undertaken to aid in discovering new quartz veins, on a part of the Forty Acre Lot, the adjoining Hamilton mine, and the nearby Woodall property.

Jan 1, 1934

By AIME AIME

THE 130th Meeting of the Institute was held in Birmingham on Oct. 13 to 15, with visits to other mines and districts before and after. The last visit of the Institute to Birmingham was made in 1888, thirty-six years ago, and vast development has been made in' the district since then. With proverbial southern hospitality compounding over this period of years the welcome given to the Institute was such that .it is difficult to express properly the gratification and appreciation of the visiting members and the officers of the Institute. The Birmingham News in an editorial said: Birmingham is duly appreciative of the presence of these gentlemen, not because they are all distinguished in their great services in the mining and metallurgical world, but for the further reason that our interests are very largely wrapped up in their deliberations. Birmingham is one of the great industrial centers of America. Their discussions are of vital concern to all of us.

Jan 1, 1924

By G. G. Griswold, B. S. Morrow

The copper-bearing ores concentrated at the Anaconda plant of the Anaconda Copper Mining Go. are principally a mixture of copper and iron sulfides associated in a gangue consisting of quartz, lightly altered granite and feldspars, with sphalerite and galena and more rarely barite and hubnerite as accessory minerals. The predominant sulfide is pyrite. The copper minerals present are: chalcocite, bornite (erubescite), enargite, chalcopyrite, covellite, tetrahedrite and some tennantite. Normal concentrator practice removes a slime prior to ball-mill grinding. The deslimed ore is ground to approximately 10 per cent plus 65 mesh for flotation. Two selective flotation circuits are used, one for deslimed ore and one for slime. Microscopic studies of concentrator products disclose such an interlocking of copper minerals with pyrite that any material increase in concentrate grade entails additional grinding unless recovery is sacrificed to a considerable extent. During the latter part of 1931 and the early part of 1932 the problem of producing a high-grade concentrate (40 per cent Cu) with at least no

Jan 1, 1935

By M. King Hubbert

DuRing the past summer the writer was asked by the Illinois State Geological Survey to make a study of some of its economic geological problems with regard to the applicability of geophysical methods of prospecting to their solution. The following four problems were suggested for investigation: (1) the fluorspar area of Southern Illinois, (2) oil structures in the south central part of the state, (3) the lead and zinc-bearing area of northwestern Illinois, and (4) the water supply and gravel deposits of the glacial drift. The prime requirements were to find a means of obtaining a maximum of useful information with a fairly modest outlay of expenditure for technical staff and equipment. The method of procedure adopted was that of making a preliminary study of each of the problems named by means of available office data and published reports with supplementary field reconnaissance where necessary. Preliminary Studies Fluorspar.—The fluorspar deposits of southern Illinois as shown by Weller,1 Bastin2 and others are of two main types: (1) vein deposits along steeply dipping normal fault planes, and (2) "blanket" deposits occurring practically horizontally along a certain sedimentary horizon. The vein deposits are composed mostly of calcite and fluorspar in sheetlike veins of thicknesses, where mined, ranging from about 2 to 12 ft. The surrounding topography is in a mature state of development with a relief of about 100 ft. or more. Any geophysical prospecting for this ore would have to depend either upon the physical properties of the ore and associated minerals or upon the properties of the geologic structure containing them. Fluorspar has a density of 3.18, which is somewhat greater than 2.7, that of calcite. Its

Jan 1, 1934

By C. D. King

The key to maximum production of ingots for the war effort is maximum production of pig iron. For any given furnace and ore, the most important single influence on blast-furnace production is the quality of the furnace coke. It is generally recognized that undoubtedly deterioration of Pittsburgh coking coals will be accelerated by the depletion of some of the better grades of coal; the extension of mine mechanization, with attendant degradation of coal quality; and the opening of new coal fields, some of which are known to be fairly high in sulphur. All of these factors, contributing as they do to higher ash and sulphur, and not infrequently to inferior quality of coke, made it desirable that an extensive study be undertaken to determine the effect of washing some coals that closely approximate the average chemical composition of coking coals to be expected in the future by the subsidiaries of the United States Steel Corporation in the Pittsburgh district. It was deemed advisable to study the improvement obtained by washing such coals and to determine the need for supplementing the existing coal washery at Clairton to assure continued maximum production of pig iron from presently available furnace stacks. The existence of the coal washer at Clairton made it possible to conduct tests on coals used in raw form and on similar coals after washing. This study covers an investigation of the quality of furnace coke as affected by washing coking coals, and is confined to the use of 100 per cent high-volatile Pittsburgh seam coals from Fayette and Greene Counties in the manufacture of furnace coke. It covers the improvement in chemical and physical properties as well as the degree of uniformity in coke obtained by washing these coals, and includes the effect on blast-furnace production and practice. The test period involved is four months; the plants, Clairton by-product coke plant, and the Carrie No. 1 and No. 2 blast furnaces at Rankin, Pa., Carnegie-Illinois Steel Corporation. Clairton By-product Coke Plant and Coal Washer The Clairton by-product coke plant carbonizes 30,800 net tons of coal daily in 22 batteries containing 1482 ovens. Three oven sizes are used, commonly known as wide, medium, and narrow types, recognizing the difference in oven width, These ovens also differ in height and length. The present coal washer has a daily capacity of approximately 14,000 tons, leaving 16,800 tans to be carbonized in raw form. Washed coal is used on all the narrow ovens and on three of the six batteries with ovens of medium width, raw coals being used on all the remaining ovens. The customary arrangement is

Jan 1, 1944

By C. D. King

The key to maximum production of ingots for the war effort is maximum production of pig iron. For any given furnace and ore, the most important single influence on blast-furnace production is the quality of the furnace coke. It is generally recognized that undoubtedly deterioration of Pittsburgh coking coals will be accelerated by the depletion of some of the better grades of coal; the extension of mine mechanization, with attendant degradation of coal quality; and the opening of new coal fields, some of which are known to be fairly high in sulphur. All of these factors, contributing as they do to higher ash and sulphur, and not infrequently to inferior quality of coke, made it desirable that an extensive study be undertaken to determine the effect of washing some coals that closely approximate the average chemical composition of coking coals to be expected in the future by the subsidiaries of the United States Steel Corporation in the Pittsburgh district. It was deemed advisable to study the improvement obtained by washing such coals and to determine the need for supplementing the existing coal washery at Clairton to assure continued maximum production of pig iron from presently available furnace stacks. The existence of the coal washer at Clairton made it possible to conduct tests on coals used in raw form and on similar coals after washing. This study covers an investigation of the quality of furnace coke as affected by washing coking coals, and is confined to the use of 100 per cent high-volatile Pittsburgh seam coals from Fayette and Greene Counties in the manufacture of furnace coke. It covers the improvement in chemical and physical properties as well as the degree of uniformity in coke obtained by washing these coals, and includes the effect on blast-furnace production and practice. The test period involved is four months; the plants, Clairton by-product coke plant, and the Carrie No. 1 and No. 2 blast furnaces at Rankin, Pa., Carnegie-Illinois Steel Corporation. Clairton By-product Coke Plant and Coal Washer The Clairton by-product coke plant carbonizes 30,800 net tons of coal daily in 22 batteries containing 1482 ovens. Three oven sizes are used, commonly known as wide, medium, and narrow types, recognizing the difference in oven width, These ovens also differ in height and length. The present coal washer has a daily capacity of approximately 14,000 tons, leaving 16,800 tans to be carbonized in raw form. Washed coal is used on all the narrow ovens and on three of the six batteries with ovens of medium width, raw coals being used on all the remaining ovens. The customary arrangement is

Jan 1, 1944

By Merlin H. Aylesworth

THE subject assigned to me is peculiarly appropriate to the anniversary of the birth of Abraham Lincoln. If we applied to our present problems the ideals and methods of the Great Emancipator, the future of American institutions would be so definitely assured that there would be little need to discuss the matter. The only inquiries would relate to the pace of progress, not to the possibility of progress. As a nation we have grown more and more to revere the memory of Lincoln, to honor his character, to extol his teachings and to eulogize his concepts of democracy. We rec-

Jan 1, 1940

By R. F. Burdyn

The inadequate use of centrifugation to economically recover solids from weighted drilling fluids reflects the need for better equipment and techniques for this putpose. Laboratory studies in the development of an improved separator are described in which an operating equation is derived and tested. Results show that the concentric cylinder geometry employed effectively separates bnrite from a suspension and that the operating equation provides a good approxinmtion for scale-up. INTRODUCTION Our current drilling technology frequently requires a high-density drilling fluid obtained by addition of barite. In the course of drilling, formation solids which are too fine to be removed either by screening or settling become suspended in the drilling fluid and gradually the volume of solids in the mud increases. The volume fraction of solids must be limited (if a satisfactory set of rheological parameters are to be maintained). A centrifugal separatorprovidesan economical way of accomplishing this. The barite recovery process can be considered as a separation of two solids. One, the light solids, composed of formation and added solids, has a specific gravity of 2.6 to 2.7; the other, barite, has a specific gravity of 4.2 to 4.3. This density difference, plus the fact that the average light-solids particle size is much smaller than the average barite particle size, permits separation by a centrifuge. In drilling fluids some of the coarse particles of the light-solids-range will settle faster than fine particles of the barite-particle range. As a result a complete separation of the two species is not possible. since the object of the process is not merely recovering the maximum amount of barite but includes as well removing the maximum amount of light solids, an optimum barite recovery efficiency exists. From a practical standpoint this optimum cannot be determined in the field for each drilling fluid system, and in practice the separation is less than optimum, with some sacrifice of barite. Drilling technology has included centrifugal separators for barite recovery for more than a decade. Results have been reported by a number of investigators indicating that the process is practical and economica1. l-4 The decision to use a centrifuge is based on economics in which direct cost savings and the indirect benefits in rig time derived from improvement of the drilling fluid are important factors. One would expect that centrifugal separation of barite from drilling fluids would significantly affect barite consumption; however, this is not the case. The Minerals Yearbook shows an annual domestic barite consumption in the drilling industry of nearly 1 million tons.5 By rough estimate there are perhaps 80 separators presently in field use. Assuming half of these in use at any one time, operating an average of four hours per day, at recovery rates averaging 3,000 Ib of barite per hour, total annual recovery is about 90,000 tons. This is less than 10 per cent of he total barite used. I conservatively estimate that barite consumption in drilling operations can be reduced by 30 per cent through greater utilization of centrifugal separators. To encourage more widespread acceptance of centrifugal separators in the drilling industry, improved equipment and techniques would be very desirable. The present paper, covering theory and results obtained from a laboratory model, is the first in a series on he development of an improved mud separator for field use. THE CONCENTRIC CYLINDER GEOMETRY AS A SEPARATING DEVICE Consider the geometry shown in Fig. 1, consisting of two concentric cylinders separated by an annular space. These are arranged so that the outer cylinder is fixed and the inner one can be rotated about its axis on shafts sealed against the ends of the outer cylinder. If the outer cylinder is fitted with openings at either end, the inner

Jan 1, 1966

By AIME AIME

Do you Possess, or Can you Obtain; and Will you Give, or Sell, to the Institute Library Early Volumes of the following Proceedings and Journals? American Chemical Society. American Foundrymen's Association. Australian Mining Standard. Chemical Society of London. Deutsche Chemische Gesellschaft. The Foundry. New Zealand Mines Record. Queensland Government Mining Journal. La Revue Universelle des Mines.

Jan 9, 1907

By Arthur Notman

TO present some idea of the magnitude of the gold-mining industry of Canada and the world, the records of 106 gold-mining companies currently paying dividends have been studied. Forty of these are in Canada, and 37 on the Rand in South Africa, these being all the straight gold-mining companies that paid dividends in the two areas in 1938. None of the base-metal companies that produce gold as a by- product, or even as a major fraction of the value of their total product, have beezl included. In addition, a group of 29 similar companies from Southern Rhodesia and the Gold Coast in Africa, India, Australia, Manchuria, Philippine Islands, the

Jan 1, 1939

By F. X. Meyer

THE United States Smelting Refining and Mining Company maintains an ore-purchasing department for procurement of custom tonnages of milling and smelting ores and concentrates for treatment at its Midvale plant. Arrangements with other companies provide for treatment of Company and custom zinc concentrates. Location of the Midvale plant in the heart of the Western mining country makes it possible to serve shippers from these nine producing states: Arizona, California, Colorado, Idaho, Montana, Nevada, Oregon, Utah, and Washington. Shipments from most of these states travel over main-line railroads, delivery being made at Midvale within a short time after billing of the shipment. Shipments varying in size from a few sacks to carloads can be handled at

Jan 1, 1948

By David R. Maneval, H. B. Charmbury

At the turn of the century, iron and coal were the keys to industrial prosperity. At that time, Pennsylvania was the leading mineral producer in the Country, producing 200,000,000 tons of coal in a typical post-World War I year. Close to 90% of the Nation's energy was generated by coal. Today, coal accounts for but 22% of the energy generated, leading to a drastic reduction in Pennsylvania coal output. In contrast with the post-World War I days, 1964 figures showed a drop in production to 93,846,480 net tons. This huge decrease has created a serious economic problem in a state so much dependent on the coal industry. Along with the reduction in coal production, employment has dropped considerably through these years (the number of miners alone has gone from 280,011 to 43,149), thus causing a heavy burden of supporting the unemployed on the taxpayers. As far back as 1939, coal operators and economists saw the problems on the horizon and the need for improvement. Realizing that research was a way to improve and stabilize the industry they demanded legislative action. The Legislature reciprocated with a small grant to The Pennsylvania State University with the provision that each State research dollar be backed with one from the industry. This initial grant laid the foundation for the further growth in coal research.

Jan 3, 1966

By Henry J. Sandri

The use of economic models for forecasting purposes is an inexact yet necessary tool for mineral decision making. One method not commonly used is cyclical analysis because of its "non-scientific approach". However, under certain circumstances a modified cyclical approach can provide useful insight to mining companies. The current paper discusses mineral modeling, the type of economic models and the use of cyclical forecasting for mining firms (not speculators) involved in precious metals.

Jan 1, 1984