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By Carl Lee

WITH the modern trend toward motor drive in coal mines, more careful forethought should be given to future layouts than has usually been done in the past. Both top and bottom equipment of future new mines is likely to differ radically from those of a decade ago. No one is able to predict very far ahead, but provisions can be made to allow for uncertainty. One thing stands out: the mine of the future will be laid out for long life compared to that of the small mine of the past, where an inexpensive top plant, simple equipment, a small timbered shaft, small cars, light rail, hand loading and mule haulage all contributed to a short economical life.

Jan 1, 1933

By G. S. Rice

IT is evident from Professor Louis' remarks that he holds a different opinion on certain phenomena connected with a specific type of surface subsidence from mining than is held by many engineers in the United States. The question which appears to be at issue is whether or not the line or plane of "draw" produced in ground movement resulting from extraction of pillars may, under certain conditions, be vertical or even inclined toward the workings rather than inclined for- ward over the unworked mineral, as it is universally agreed occurs in mining by the longwall advancing method. In discussing this case it is well to take the simplest condition, such as specified by Professor Louis, of a flat bed, whether it be coal, iron or other mineral, where the overburden is stratified rock and where there is no overlying quicksand. Professor Louis says in effect that his experience is that the ultimate angle of draw is always positive and inclined 5" to 15" from the perpendicular over the unwrought mineral. My experience under Illinois coal-mining conditions is that .'where longwall advancing is used the draw is always positive as Professor Louis describes it, but that in extracting of panels by withdrawal of pillars, the ground movement is manifested, after the first roof' beam break, by the forming of an unstable dome over the goave. Then subsequently, by the falling of individual slabs from the under side, the dome gets larger and higher until it breaks through to the surface of the rock., Up to this time, arch stresses buttress the rocks above the solid coal or mineral. When, however, after. the dome breaks through and the central hole - #enlarges so the arch is no longer sufficiently supported -the stratified rocks cantilever out .from over the solid unworked mineral and tend to break off in masses triangular in vertical cross-section, until the broken loose material, sliding down against the solid rock, .has such a thrust that it balances the tendency ,for the solid stratified rock to break away and slide toward the excavation.

Jan 1, 1929

By Paul Averitt

The U. S. Geological Survey has been actively engaged in work on coal for more than 50 years. During this long period we have released more than 300 publications containing information about coal and coal reserves, including details on the thickness, distribution, and quality of coal, and the structure and stratigraphy of the coal-bearing rocks. We have also cooperated with state surveys on many similar publications. For many areas these reports are the only reliable published data on our resources of coal. During the last several years we have substantially increased our activities above the wartime low. We now have field work in progress, or reports in preparation, on 13 detailed mapping projects distributed as follows: 1. Pennsylvania anthracite field 2. Casselman Basin, Md. 3. Leslie County, Ky. 4. Deep River field, N. C. 5. Coosa field, Ala. 6. Powder River field, Mont. 7. Spotted Horse field, Wyo. 8. Yampa field, Colo. 9. Paonia field, Colo. 10. Trinidad field, Colo. 11. Durango field, Colo. 12. Chaco River area, N. M. 13. Lewis and Thurston County fields, Wash. For two of these areas; the Paonia field, Colo., and the Coosa field, Ala., we have published recently preliminary reports, and final reports are in preparation. In addition, we are nearing completion of a coal reserve study of Montana, and are beginning similar studies in several other states, as part of a program of revising our estimate of national coal resources on the basis of presently available data. Factors Involved in Making Estimates Our responsibilities include detailed field mapping to secure information on areas of outcrop of coal beds, their range in thickness, nature of roof rock, amount of overburden, correlation of the beds, stratigraphy and structure of the coal-bearing rocks, and the preparation of coal reserve figures based on these data. The computation and estimation of resources of coal in the ground, like that of resources of other mineral commodities, involves consideration of many additional purely geological factors that can be appraised best through such regional studies. Regional variations in the thickness and texture of rocks overlying and underlying coal beds, for example, give evidence as to the probable position of the edges of the basin of coal deposition, or may aid in the delineation of sand-filled channels that sometimes cut out coal beds. It is apparent that the detailed field studies, in which data are gathered, are the basis for coal reserve studies, and in our present program these two phases of work are being carried on together. Previous Coal Reserve Estimates For many years we have been aware

Jan 1, 1950

By Jack Fox

It is some time since these columns have contained a report to the members on just what is doing in the Society of Mining Engineers. Accordingly, even though it is now a month and a half after the Annual Meeting in Denver, it seems that a report on what transpired at the SME Board Meeting there is in order. First off, I'd like to say that the Members of the Society of Mining Engineers can be justly proud of their representatives on the SME Board of Directors. Of 21 members and officers on the "Old" Board of Directors, 19 were present. President Brower Dellinger chaired the "Old" Board Meeting. Of the 21 members on the "New" Board of Directors, every single one was present. James Boyd, the outgoing AIME President, attended and expressed his appreciation of the support that the Society of Mining Engineers had given him during his year as President of AIME. Members Multiply Robert S. Shoemaker, Chairman of the SME Membership Committee, pointed out that based on figures available, the Society of Mining Engineers had a net gain of 523 members during 1969 while SPE had a 490 net gain and The Metallurgical Society a net loss of 159. This is probably the first time in the last 20 years that anyone has exceeded the SPE net gain in membership. While SME still has a way to go to surpass the Society of Petroleum Engineers in number of members, we did have, on December 1, 1969, 16,369 members. However, 419 were dropped at the end of that month leaving us with a net for the year of 15,950.

Jan 1, 1970

The following description is based on the film's narrative script: The film opens with a description of the terrain--tens of thousands of yearly snows compressed into glacial ice, stretching further than the eye can see. A single massive frozen cap--1 812 992 km2 (700 thou- sand sq miles) covering most of the land mass of the world's largest island, christened strangely enough--Greenland. Greenlanders comprise more than two-thirds of the 40 thousand Danish subjects who brave the elements in the Arctic Circle. Along the coastal fringe where the Gulf Stream sheds its last vestige of tropical warmth to temper Greenland summers, tiny villages survive In virtual isolation. Jagged fjords and creeping glaciers are barriers to conventional communication. There are no roads through the year-round ice. Yet, when there is wealth in the land, there are people to tame it, harnessing those unrelenting forces of nature if they can building and surviving in spite of them if they must. Near the tiny site of Marmorilik in west Greenland a gathering of men from places more benign came to challenge a sheer, frozen rock named Black Angel Mountain to tap a deposit of lead and zinc ore. As far back as the 19301s, surface investigation showed zinc and lead sulfides in the vicinity. In the mid-60's mountaineering geological examinations were made and deep-hole drilling, directed by Cominco Ltd., of Canada, confirmed the presence of an ore body, 600 m (2000 ft) above the fjord. These findings led to the formation In 1965 of Greenex A/S, a'Danish company with principal offices in Copenhagen. A utilization con- cession, with rigorous safety standards and environmental controls to

Jan 1, 1977

By P. Barnes

Exact accounts hare been kept of the cost of these chimneys, and it may he a matter of some possible interest. that the plans and details of cost should be laid before the Institute. The statement of cost herewith submitted does not give minute particulars of the weights or quantities of material used, although these are noted upon the company's books.

By S. E. Bretherton

This title introduces the subject I wish to describe to my fellow members, very few of whom, I 'hope, have ever had as much trouble with the smelting of ore containing much zinc, either in the lead blast furnace or the matting furnace, as circumstances have forced upon me: First, for several years in Leadville, Colo., after the sulphide ores containing zinc had been developed with greater depth and were sold to the intereats with which I was connected for smelt-ing in the blast furnace for the recovery of the lead, silver, and gold; then, in New Mexico and Arizona, where the principal source of ore supply for our custom smelter was from miners who sent most of their product in the form of concentrates, which we briquetted and smelted in the blast furnace, producing a matte containing copper, silver, and gold, for which we were paid; together with some zinc and lead, which was penalized if in excess of a maximum base set by the refinery to which we sold our copper matte; last, but not least, my experience in Shasta county, Gal., where for the sake of recovering $13 per ton value in copper, silver, and gold, I have smelted ore containing as high as 40 per cent. zinc (the last 18,951 tons smelted averaged 15 3/10 per cent. zinc) which we not only lost, but which it cost us money to lose. After such an experience, and knowing that, instead of being worth only $13 per ton, such 15 per cent. zinc ore should be worth about $30, including zinc at the present market value, the question of recovering the zinc in a profitable manner from such ore became very interesting to me. During several years' time I sent samples, of from 5 to 1,200 lb. each, to be tested by the different best-known zinc-recovery plants, and experimented with several processes proposed by others for the treatment of such ore, with but little encouragement, until I

Jan 1, 1914

Hermann A. Keller was born in Philadelphia, Pa., Mar. 23; 1860. He received a preliminary education at the gymnasium of Darmstadt, in Germany, and subsequently entered the University of Pennsylvania, graduating in 1881. After serving for a few months as an assistant instructor in mining and metallurgy at the University, he went to Leadville, Colo., where he became, at first, assayer and chemist, and in due time (1886) superintendent of the Arkansas Valley smelting works. In 1888, he was appointed metallurgist of the Globe works at Denver; in 1889, superintendent of the Philadelphia works at Pueblo; and in 1891, superintendent of the Parrot works at Butte, Mont., where he remained until 1896, in which year he was employed to reconstruct the smelting plant of the Mountain mines at Keswick, Cal. In 1897, he opened an office as consulting engineer in San Francisco; and from this time on enjoyed a wide practice both as metallurgical and as mining engineer. In the former capacity, Mr. Keller had already distinguished himself by the invention of the Keller mechanical roasting furnace employed at the Parrot works in Butte and the Germania works near Salt Lake. He was a frequent contributor to the technical journals, and he collaborated in the preparation of the chapter oil "Bessemerizing" in Dr. Peters's work, "Modern American Copper-Smelting." It is a curious coincidence that these two friends and collaborators died at almost the same time, Keller in Arizona and Peters in Massachusetts on the 16th and 17th of February respectively. The latter years of Mr. Keller's life were largely given to the examination and development of mines in all parts of the world-Alaska, Chile, Germany, etc. He finally established his professional headquarters in New York City. His death was caused by an underground locomotive accident at Clifton, Arizona, on Feb. 16, 1917.

Jan 5, 1917

By E. R. Russell, N. E. Richards

The current ejyiciency of aluminum cells was derived from the metal produced over a period of time and the theoretical faradaic yield. The difference in the actual amount of aluminum in the cathode at the beginning and end of the period must be determined. The weight of aluminum in the cathode was calculated from the dilution of an added quantity of impurity metal. Use of multiple indicator metals, copper, manganese, and titanium, demonstrated that the weight of aluminum in cells can be determined to within 1 pct with routine but careful chemical analyses. Over intervals of the order of 30 days, current efficiencies reliable to within 1 pct can be obtained. INVESTIGATIONS beginning with those of Pearson and waddington ,' through the most recent published work of Georgievskii,9-11 illustrate the direct relationship between the composition of the anode gas and the applicability of analysis of anode gases to the control of alumina reduction cells. McMinn12 noted the lack of an independent method for measuring cell production efficiency over the short term. There is no doubt that changes in the current efficiency are immediately reflected in the composition of anode gases. However, the accuracy of faradaic yields calculated from gas analyses depends upon the degree of interaction between primary anode gas and Carbon.6 A conventional industrial practice of obtaining long-term current efficiency for production units from mass balances and quantity of electricity is generally insensitive to the impact of planned control of any one or more of the influential reduction cell parameters such as temperature, alumina concentration, and mean interelectrode distance. Consequently, there is a real need in the aluminum industry for a procedure to obtain the absolute cell current efficiency over a short term—10 to 30 days—both for the calibration of values obtained from gas analysis6 and for evaluating the effect of controlling specific parameters in the reduction process. The amount of aluminum produced may be determined by considering the cathode pool as a reduction of an impurity metal in aluminum. Analyses over a period will show a decreasing concentration of the impurity due to the accumulation of aluminum solvent. The increase in aluminum inferred from analyses is the amount produced by the cell during the period. Combining weights of the cell aluminum in the cathode at the beginning and end of a specific period, weights of aluminum tapped and the quantity of electricity passed during the interval will yield the current efficiency. Smart,I3 Lange;4 Rempel,15 Beletskii and Mashovets,16 and winkhaus17 have used dilution techniques to determine aluminum inventory in alumina reduction cells. A technique for determining the weight of aluminum in production cells by addition of small amounts of copper to the aluminum cathode was described by smart.13 The precision in values of the aluminum reservoir through dilution of copper in the cathode ranged from about 1 to 3 pct depending upon the quantity of copper added in the range 0.2 to 0.01 wt pct, respectively. Because the method appears so direct and apparently simple, one would not anticipate difficulties in application to industrial cells. The objective of this study was to resolve this problem associated with the trace metal dilution technique for determining the amount of aluminum in a cell. The approach in evaluating trace metal dilution as a basic factor in determining the weight of aluminum in the cell reservoir, and the absolute current efficiency of the Hall-Heroult cell, was to dilute more than one trace metal in the aluminum cathode so that we could discriminate among complications arising from physical mixing, the possibility of separation of intermetallic compounds, loss of the added elements, and chemical detection. EXPERIMENTAL METHODS These experiments are not complex but require standardized procedures. The technique involves addition of the trace metals to the cathode, knowing when these metals are homogeneously distributed in the liquid cathode, timing of the sampling, employing accurate and precise analytical methods, using reliable procedures for monitoring the amount of electricity passed through the cell, and accurate weighing of aluminum removed from the cell during the particular period. More accurate results might be obtained if the increment in concentration of the added indicator metals were of the order of 0.1 to 0.2 wt pct. The method must be applicable to production units and, hence, the contamination of the aluminum minimized. For this reason, the concentration of trace metals in the cathode was kept below 0.07 wt pct and generally at 0.04 wt pct level. Trace quantities of copper, manganese, titanium, and silicon are already present in virgin aluminum and are suitable as additives from electrochemical and analytical points of view. Concentration of silicon is quite dependent upon the characteristics of the raw materials and was not used extensively in this work. Chemical Analyses. All instrumental analyses require calibration against an absolute technique such as a gravimetric, volumetric, or spectrophotometric method which represents the ultimate in sensitivity, precision, and accuracy. On review, the best methods for copper appeared to be optical absorption without

Jan 1, 1969

By Pierre de P. Ricketts

Having had occasion while in Europe during the past summer to visit some of the foreign mints and assay offices connected with the same, I thought a brief description of the general process of coining employed, and such items connected with assaying as were new, might prove interesting to the Institute. The principal foreign mints are: the Royal Mint, London; and the mints in Paris, Brussels, Utrecht, Berlin, Vienna, Copenhagen, St. Petersburg, Stockholm, Madrid, Milan, Rome, and Constantinople. My time only permitted my visiting a few of the principal and largest given in the list, and for a description of the remainder I am indebted to the kindness of Mr. James M. Napier, who in company with the deputy master, and chemist of the Royal Mint, made a complete inspection of all the European Mints in 1870.

By William L. Fink

Nickel is used as an alloying element in several complex commercial aluminum alloys, among which are found some very interesting properties, such as relatively high strength at elevated temperatures, relatively low coefficient of expansion, the absence of permanent growth, ability to take a good polish, and a bright, pleasing as-cast surface. For that reason the aluminum-nickel system was included in the list of binary aluminum systems that are being studied as a preparation for the investigation of more complex commercial alloys. This paper is the fifteenth of a series from the Research Laboratories of the Aluminum Company of America reporting the results of investigations of equilibrium relations in aluminum-base alloys of high purity. The aluminum-nickel equilibrium diagram from 0 to 18 per cent nickel was determined, using the purest material available. Previous Investigations The entire aluminum-nickel system was studied thermally and microscopically by Gwyer.1 At the aluminum end of the system he found the intermetallic compound NiA13. He found a eutectic at 6 per cent nickel with a melting point of 630" C. A slight thermal arrest, which he could not explain, was also noted in alloys from 2.5 per cent to 41.9 per cent nickel at 550" C. Bingham and Haughton,2 in a later investigation of alloys of aluminum with copper and nickel found the eutectic concentration of the binary aluminum-nickel system at about 5.3 per cent nickel. The melting point of the eutectic was about 633" C., or slightly higher than that found by Gwyer. Although the solid solubility of nickel in aluminum could not

Jan 1, 1934

By James T. Kemp

Some interesting and, to American eyes, rather unusual processes for refining impure aluminum derived from scraps were found by American and British investigators who went into Germany in 1945 for the Technical Industrial Intelligence Committee of the Joint Chiefs of Staff. What was found was recorded in a series of reports (see page ), many of which have been released for general reading. This paper gathers under one title and summarizes the German work in refining light metal scrap. Reference must be made to the original reports for greater detail. Basically, the occasion and stimulus for the German developments in treating light metal scrap were hard necessity. Germany needed the metal for a rapacious war industry. Adequate supplies of new aluminum from reduction works were not assured. Great quantities of airplane and other light metal war scraps were forecast. It was evident that the scrap metal would have to be reabsorbed by the producing industry and would have to be kept of good quality. The normal current production of manufacturing scrap was being and could be consumed as generated. It offered no technical problem. The mixed scraps, especially those arising from crashed and decommissioned airplanes, however, presented problems of another kind. Airplane Scrap The recovery of usable aluminum alloy from the mixed assemblies that made up the piles of airplane scrap was attacked in different ways by different groups and with differing degrees of success. Three procedures actually were used on a commercial scale, one was in pilot-plant stage and another had come to a halt in the laboratory a year before Germany collapsed. Four of these five processes actually involved "refining"; that is, some measure of purification of the metal after melting. Sorting and Separation on a Sloping Hearth The simplest procedure for utilizing airplane scrap involved no refining in the strict sense of the word. This was the practice adopted by two representative plants visited by the author, the Leipziger Leichtmetalle Werke, Rackwitz, Saxony, and the Vereinigte Leichtmetalle Werke, Hanover. These firms did essentially the same thing that was done in England but not with equal success, to judge by their shorter experience, the smaller tonnage handled and by the number and quality of alloys produced. The two German firms named rough-sorted scraps by their easily recognizable alloys, essentially by part and shape. They used hand labor to chop and hack and tear apart. The easily separated heavy metal and nonmetallic scraps were discarded as they were found. Steel and the higher-melting-point metal parts riveted to aluminum or built into

Jan 1, 1947

By James T. Kemp

Some interesting and, to American eyes, rather unusual processes for refining impure aluminum derived from scraps were found by American and British investigators who went into Germany in 1945 for the Technical Industrial Intelligence Committee of the Joint Chiefs of Staff. What was found was recorded in a series of reports (see page ), many of which have been released for general reading. This paper gathers under one title and summarizes the German work in refining light metal scrap. Reference must be made to the original reports for greater detail. Basically, the occasion and stimulus for the German developments in treating light metal scrap were hard necessity. Germany needed the metal for a rapacious war industry. Adequate supplies of new aluminum from reduction works were not assured. Great quantities of airplane and other light metal war scraps were forecast. It was evident that the scrap metal would have to be reabsorbed by the producing industry and would have to be kept of good quality. The normal current production of manufacturing scrap was being and could be consumed as generated. It offered no technical problem. The mixed scraps, especially those arising from crashed and decommissioned airplanes, however, presented problems of another kind. Airplane Scrap The recovery of usable aluminum alloy from the mixed assemblies that made up the piles of airplane scrap was attacked in different ways by different groups and with differing degrees of success. Three procedures actually were used on a commercial scale, one was in pilot-plant stage and another had come to a halt in the laboratory a year before Germany collapsed. Four of these five processes actually involved "refining"; that is, some measure of purification of the metal after melting. Sorting and Separation on a Sloping Hearth The simplest procedure for utilizing airplane scrap involved no refining in the strict sense of the word. This was the practice adopted by two representative plants visited by the author, the Leipziger Leichtmetalle Werke, Rackwitz, Saxony, and the Vereinigte Leichtmetalle Werke, Hanover. These firms did essentially the same thing that was done in England but not with equal success, to judge by their shorter experience, the smaller tonnage handled and by the number and quality of alloys produced. The two German firms named rough-sorted scraps by their easily recognizable alloys, essentially by part and shape. They used hand labor to chop and hack and tear apart. The easily separated heavy metal and nonmetallic scraps were discarded as they were found. Steel and the higher-melting-point metal parts riveted to aluminum or built into

Jan 1, 1947

By Homer Staley

THE casting alloy 88 copper, 10 tin, 2 zinc, commonly known in England as Admiralty metal and in this country as Government bronze, gun metal, or Naval Department composition G, has, at its best, many valuable properties. However, its physical properties are known to vary widely with slight changes in method of manufacture of the castings, such as slight variations in composition, variation in pouring temperature, kind of mold used, method of pouring and gating of molds, size and shape of castings, amount and kind of heat treatment., and so forth.1 The microstructure of castings made from this alloy is influenced by slight variations of composition, rate of cooling, and kind and length of heat treatment. This is best understood by reference to the equilibrium diagram. The part of the diagram in which we are interested and the effect of the thermal equilibrium relations on the physical properties of the alloy 88 copper, 10 tin, 2 zinc, have been discussed by Hoyt, Camp-bell, Primrose, and Rawdon.2 In Fig. 1 is given the equilibrium diagram of the copper-tin alloys. Briefly stated, the relations of composition and temperature changes are as follows. Compositions between A and a consist of but one constituent-the a bronze, which is a, solid solution of copper and tin, rich in copper. On cooling from the molten state these compositions gradually crystallize, at temperatures above 790°, into a mass of interwoven tree-like crystals or dendrites. The cores of the dendrites are rich in copper and the percentage of tin gradually increases as the surfaces are approached. As cooling progresses, after all the metal has crystallized, no further changes occur, in the crystals other than diffusion within the crys-

Jan 9, 1919

By David R. Mitchell

The mineral pyrite (or marcasite) occurs in coal beds as balls, lenses, veinlets and bands. Several million tons are wasted annually on the refuse dumps from coal mining and coal-preparation activities. Sporadic attempts have been made in the United States to recover this pyrite for manufacture of sulphuric acid but only a few plants have succeeded in recovering it on a commercial scale. Several chemical companies in the East became concerned about supplies of pyrite early in 1943, but by late summer of that year the situation had eased. If for no other reason than national security and self-sufficiency during wartime, methods of recovering pyrite from coal-mine refuse should be worked out and made available to coal-mine operators who are potential producers of pyrite. Eastern sulphuric-acid plants are particularly likely to have their sources of raw material blocked by war conditions, so that special studies to determine where supplies of pyrite can be obtained for these plants from inland sources are desirable. Davis's1 summarization of conditions during World War I gives the following facts: During those years, the shortage of pyrite became acute. Shipments of hand-picked pyrite were made from a number of coal mines in Illinois, Indiana, western Kentucky, Ohio and Pennsylvania. A mechanical concentrating plant for sepa- rating pyrite from picking-table refuse was built at Danville, Ill., and operated for several years, and a small pyrite-concen-trating plant treating washery refuse near Gillespie, Ill., operated for several months in 1918. The Consolidation Coal Co. of Fairmont, W. Va., constructed and operated a sulphuric-acid plant using pyrite recovered from coal-mine refuse. The U. S. Bureau of Mines during 1917-1919 made a comprehensive survey of pyrite-production possibilities from coal mines and estimated that there was a potential yearly production of 435.000 tons from Ohio and Pennsylvania and 928,000 tons from Kansas, Missouri, Iowa, Illinois, and Indiana mines. This estimate included only mines that could produce one per cent or more of their coal production as pyrite containing a minimum of 40 per cent sulphur. PyRite Production According to the Minerals Yearbook,2 approximately 660,000 long tons of pyrite was produced in the United States in 1941, with an average sulphur content of 42 per cent. The average value f.o.b. mines was $3.09 per long ton. Spanish pyrite, 48 per cent sulphur minimum, was quoted at 12 cents a unit c.i.f. U. S. ports, equal to $5.76 a ton for shipments of minimum sulphur content. Most of the pyrite produced in the United States is obtained as a by-product in the dressing of copper and zinc ores. Metal mines in the East making pyrite concentrate for the market or use in company-operated sulphuric-acid plants

Jan 1, 1944

By David R. Mitchell

The mineral pyrite (or marcasite) occurs in coal beds as balls, lenses, veinlets and bands. Several million tons are wasted annually on the refuse dumps from coal mining and coal-preparation activities. Sporadic attempts have been made in the United States to recover this pyrite for manufacture of sulphuric acid but only a few plants have succeeded in recovering it on a commercial scale. Several chemical companies in the East became concerned about supplies of pyrite early in 1943, but by late summer of that year the situation had eased. If for no other reason than national security and self-sufficiency during wartime, methods of recovering pyrite from coal-mine refuse should be worked out and made available to coal-mine operators who are potential producers of pyrite. Eastern sulphuric-acid plants are particularly likely to have their sources of raw material blocked by war conditions, so that special studies to determine where supplies of pyrite can be obtained for these plants from inland sources are desirable. Davis's1 summarization of conditions during World War I gives the following facts: During those years, the shortage of pyrite became acute. Shipments of hand-picked pyrite were made from a number of coal mines in Illinois, Indiana, western Kentucky, Ohio and Pennsylvania. A mechanical concentrating plant for sepa- rating pyrite from picking-table refuse was built at Danville, Ill., and operated for several years, and a small pyrite-concen-trating plant treating washery refuse near Gillespie, Ill., operated for several months in 1918. The Consolidation Coal Co. of Fairmont, W. Va., constructed and operated a sulphuric-acid plant using pyrite recovered from coal-mine refuse. The U. S. Bureau of Mines during 1917-1919 made a comprehensive survey of pyrite-production possibilities from coal mines and estimated that there was a potential yearly production of 435.000 tons from Ohio and Pennsylvania and 928,000 tons from Kansas, Missouri, Iowa, Illinois, and Indiana mines. This estimate included only mines that could produce one per cent or more of their coal production as pyrite containing a minimum of 40 per cent sulphur. PyRite Production According to the Minerals Yearbook,2 approximately 660,000 long tons of pyrite was produced in the United States in 1941, with an average sulphur content of 42 per cent. The average value f.o.b. mines was $3.09 per long ton. Spanish pyrite, 48 per cent sulphur minimum, was quoted at 12 cents a unit c.i.f. U. S. ports, equal to $5.76 a ton for shipments of minimum sulphur content. Most of the pyrite produced in the United States is obtained as a by-product in the dressing of copper and zinc ores. Metal mines in the East making pyrite concentrate for the market or use in company-operated sulphuric-acid plants

Jan 1, 1944

By C. W. Hoffman, W. R. Hinken

Probability sizing, a fairly recent development in the field of particle separation, is now under investigation to determine its value to the mining industry. The method employed is probability sizing through a vibrating network of decreasing screen openings. While probability sizing is not new, the possibility of using it for coarse, highly abrasive ores at high tonnage rates has only recently appeared to merit practical consideration. The advantages of probability sizing vs. conventional screening methods are: (1) reduced space requirements for a high capacity unit, (2) fewer moving parts, (3) more versatile product sizing selection, (4) reduced maintenance requirements, and (5) lower power consumption. Screening is a necessary part of virtually every crushing circuit. At some stage in the process, particle separation becomes a controlling factor in the operation. The basic type of screen in use today is the vibrating unit, which usually employs a mechanical vibrator of one type or another to obtain sizing and material transportation across the screen surface. The vibrating screen has its limitations and inherent problems. Operators must live with: (1) high maintenance — worn rods, screen cloth, spacers, cross members, chutes, etc., (2) low capacity in relation to floor space requirements, (3) extreme noise levels, (4) high power consumption, and (5) structural problems in the screens and supporting steelwork. All plant operators have become tolerant of these drawbacks through the years, and little innovation has been developed in screening. The vibrating screens in use today incorporate improved metals, more efficient power sources, better lubricants, and increased manufacturing skill, but the basic machine itself remains unchanged. Screening is a relatively small part of most plants' operating expenditures and gets relatively little attention from research and development. The HiProb sizer is a new approach to the problem of particle separation on a high tonnage basis. Developed by Dr. Fredrik Mogensen (president of Fred-rik Mogensen, A. B. of Djursholn, Sweden), this unit has found its primary acceptance in the sizing of wet or dry materials in the fine ranges. Climax has been working cooperatively with Mine and Smelter Supply Company, the United States licensee, on the adaptation of the sizer to obtain consistent recovery at a high tonnage rate on a — 3/8-in. separation. This was a new application for the sizer and opened up a whole new field of problems. Dr. Mogensen's machine utilizes the control of normal probability of falling particles and is designed to eliminate some of the undesirable features of vibrating screens mentioned earlier. The machine is light, compact, consumes less power than conventional screens and has a low noise level. PRINCIPLES Probability sizing is a process designed to allow solid particles to segregate with a high ratio of the materials reporting into their respective size fractions with a minimum amount of misplaced particles. Sizing is defined in this paper as segregation of dry solid particles into fractions of comparable sizes. Probability is usually estimated as the ratio of the number of ways an event might occur vs. the total number of allowable ways. The probability process described depends upon the fact that particles falling through a network will segregate across the sizing surface even though all openings are larger than the particles. The degree of segregation is dependent upon the particle size and the trajectory applied by the sizing network to each falling particle. Specifically, the process utilizes a maze made up of screen cloth to control the path of a particle in free fall as illustrated in Fig. 1. The usefulness of this probability sizing process is dependent upon the degree of efficiency of an effective maze. Primarily, a maze must be extremely flexible to meet the multi-faceted nature of solid particles and, at the same time, the degree of control must be reproducible so that a desired separation is predictable. Dr. Fredrik Mogensen has formulated a maze that is not only flexible and easily controlled, but, mote importantly, easily adaptable to a working machine.

Jan 1, 1970

By J. W. Snavely

THE high tension belt conveyor is introducing a new and tremendously expanded era of low cost bulk material handling. High tension belt conveyors are generally those installations involving very long centers, high lifts, or drops, in which the belts are stressed up to their maximum tension values, and further, where the belt construction provides tension capacity far beyond what is possible with conventional belt constructions. With these high tension installations, the magnitude of the forces involved demands careful refinement of accepted design practice in order to achieve optimum balance of all factors.

Jan 3, 1951

By H. B. Muller

Single stage autogenous grinding of run-of-mine ore was selected by Broken Hill South Ltd., parent Company of Cobar Mines Pty. Ltd. for the concentrator to treat 60,000 tons per four weekly period of copper and complex copper-lead-zinc sulphide ores from the C.S.A. Mine at Cobar, Australia. Ore is mined by mechanised horizontal cut-and-fill stoping and is prepared for grinding by crushing under- ground in a 60 in. x 48 in. jaw-crusher set at 5 in. closed side setting. The ore is reduced to 80% minus 76 microns in two parallel sections each of one 22 ft. dim. x 7 ft. long autogenous grinding mill, powered by a 1,250 H.P. motor, operating in closed circuit with a single stage 20 in. dim. cyclone. Broken Hill South's original concept of the concentrator required the maximum use of reliable instrumentation, centralised control, and the minimum of manning. To achieve this objective the control room, housing the process recorders, alarms, closed circuit television monitors and all the control equipment, overlooks the grinding and flotation sections, and the whole plant is serviced by a public address system. The grinding units and associated equipment are located in the open and are serviced with the aid of a mobile crane and a mobile hydraulically-operated liner lifting device.

Jan 1, 1970

By H. A. Sawin, C.M. Romanowitz

Placer dredging as we know it today, especially gold dredging, is an industry about 40 years old, dating from the beginning of this century, when a few mining men in California saw the possibilities in adapting earlier dredging methods to California placer fields in and immediately adjacent to streams. At first it was thought that dredges must be operated in existing stream beds, but experience soon pointed the way to dredging alluvial deposits of old stream beds, operating on landlocked dredging ponds. Within the first five or six years of modern dredging, experience was gained so rapidly that dredges to dig 60 ft. below water level were *designed and built. This depth was believed by many operators to be the maximum at which successful dredging could be carried on. Alluvial deposits of gold, suitable for dredging, were readily handled by equipment available and developed early in the industry's history. Much of the gravel was easily dug and if deposits were cemented, contained large boulders, or for some other reason could not be handled by a dredge, the ground was abandoned in favor of other deposits that could be handled easily. Many failures, adversely affecting the dredging industry, resulted from attempts at that time to extend the scope of placer dredging with equipment not suited to the formation being dredged. Dredging ground suited to early equipment was exhausted eventually, but many supposedly undredgeable alluvial fields containing gold in commercial quantities were found and became known to dredgemen. Improved equipment was needed to work deposits known to exist at great depths or associated with unusual obstructions. Operating companies looked to dredge manufacturers and metallurgists, particularly manganese-steel foundries, for improved designs and materials. Experience developed in California has spread throughout the world, and dredges of improved types have been adapted to the mining of platinum and tin as well as gold. Space will not permit a description of all the improvements in dredging since the early days, but a few of the recent developments are worthy of note, because they make possible the dredging of placer deposits of great depth, those having hard, irregular bedrock or containing large boulders in great quantities, and compacted or cemented gravel deposits. Deep Dredging At Hammonton, calif., yuba consolidated Gold Fields has, within= the past two years, built its dredge No. 20. The company has operated continuously in that field since 1904, digging successively at maximum depths of 60 ft., 80 ft., 112 ft., and now 124 ft. below water level. The first dredges were equipped with buckets of 6 and 7½-cu. ft. capacity; six dredges operating in the field today have 18-cu. ft. buckets, digging now 65 to 124 ft. below water level. Some ground near Hammonton has been dug for the third time, owing to the devel-

Jan 1, 1943