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By Raymond E. Krauss

The McLaughlin Mine is based on a world class epithermal gold deposit located in the coastal thrust fault of northern California, about 1 12 air km (70 air miles) north of San Francisco. Owned and operated by Homestake Mining Co., the McLaughlin deposit contains about 18 Mt (20 million st) of gold ore at an average grade of 5.2 g/t (0.152 oz per st), or about 93 t (3 million oz). The area was identified as a gold target by Homestake in early 1978. Drilling confirmed it to be a commercial deposit by 1980. The mine was then planned, engineered, built and brought into production by March of 1985. The deposit was historically a part of the Knoxville District. It was mined for cinnabar, which was used to produce mercury for use in recovering gold and silver in the Mother Lode and Comstock districts. At that time, the mine was called the Manhatten and later the One Shot Mine. It was worked for more than 100 years, producing about 76,000 flasks of mercury without any awareness of the presence of economic concentrations of gold. By 1978, the site was largely disturbed and entirely unreclaimed.

Jan 1, 1990

By I. Fafoutis

Laboratory column studies were conducted in order to assess the effectiveness of slag and red mud reactive barriers for cleaning up leachates generated at mining and waste disposal sites and loaded with copper and manganese. Solutions containing the metals of concern were prepared by dissolving the required quantities of CuSO4?5H2O and MnSO4?H2O in distilled water so that Cu concentration was 100 ppm and Mn 20 ppm. Flow rates of 25 mL.h-1 for Cu solution and 75 mL.h-1 for Mn solution were used in order to simulate aquifer water velocities of 1 ft/d and 3 ft/d respectively. Solutions were pumped upflow, in Plexiglas laboratory columns filled with each reactive medium, using peristaltic pumps. Measurements of middle and outflow column pH, redox potential, conductivity and elements concentration were performed to provide information regarding removal mechanisms for both elements and exhaustion/inactivation rates for each reactive medium. Both reactive media showed fairly good removal efficiency over the period studied. Copper was mainly removed by precipitation and formation of Cu(OH)2 while removal of manganese was due to precipitation of Mn(OH2).

Jan 1, 2006

By Al Sylvester

The drill-and-shoot excavation of the two underground Pumphouses for the Metropolitan Sanitary District of Greater Chicago's Mainstream Pumping Station is described. The construction sequence involved the concurrent excavation and support of the two 19.2 m (63 feet) wide by 83.6 m (274 feet) long by 29.3 m (96 feet) high caverns. Excavation was interrupted after taking the 6.1 m (20 feet) high top heading in order to cast-in-place a 0.2 m (8 inch) thick by 19.2 m (63 feet) wide concrete arch. The remaining 23.3 m (76 feet) of rock was then excavated in benches below the concrete arch. PROJECT DESCRIPTION Twenty-four kilometers (15 miles) southwest of the city of Chicago, Peter Kiewit Sons' Co., in a joint venture with John F. Shea Co., and Kenny Construction Co., has successfully completed the construction of the Mainstream Pumping Station for the Metropolitan Sanitary District of Greater Chicago. The five year, 169 millon dollar project is a vital component in Chicago's Deep Tunnel and Reservoir Plan in that its function is to lift the sanitary/ storm sewage back up to grade from 107 m (350 feet) below ground, and pump it to the treatment facilities 8 km (5 miles) away.

Jan 1, 1985

By William M. PhD. Schafer

The net acid generation (NAG) pH method is an important analytical tool that supplements static and kinetic tests for assessment of the acid generation risk of rock samples. This method is useful because it is simple, rapid and cost-effective; it combines features of the static and kinetic tests; and it can be conducted at mine assay labs. The NAG pH test is particularly effective for operational testing programs used to classify, selectively handle, and route potentially acid-generating waste rock. The NAG pH procedure is based on a 24 hour oxidation of a pulverized rock sample with hydrogen peroxide and subsequent measurement of the sample's pH. If the NAG pH is below a critical value, determined empirically, then the sample has the potential to generate acid in the field. The critical NAG pH value is typically within the range of 3 to 4.5, but the exact relationship between NAG pH and potential acid generation should be determined individually for each mine site, based on comparison with results of acid base accounting, humidity cell tests, and mineralogical analyses. Calibration and use of the NAG test for predicting ARD risk at several mines are described in this paper.

Jan 1, 2000

By F. D. Mendes, A. H. Martins

The high copper grade in the Igarapé Bahia (Brazil) gold-copper ore restricts the direct application of the classical cyanidation process. Copper oxide and sulfide minerals react with cyanides in solution, causing high leach-reagent consumption, raising processing costs and decreasing gold recovery. According to studies, a feasible solution would be to pretreat the ore to remove copper minerals prior to cyanidation. The goal of this experimental work was to study the conditions for the removal of copper from the Igarapé Bahia gold-copper ore by sulfuric acid leaching, applying a statistical approach to the experimental design. By using the Plackett Burman method, it was possible to select the variables that exhibited the largest influence on copper extraction at the sulfuric acid leaching stage. These variables were leach solution temperature, stirring speed, sulfuric acid concentration in the leach solution and ore particle size. The individual effect of these variables and their interaction influences on the experimental response were analyzed by applying the replicated full-factorial design method. Finally, the selected variables were optimized by the ascending-path statistical method, which determined the best leach experimental conditions for maximum copper extraction. The optimized leaching conditions resulted in a copper extraction of 75.5%. Keywords: Copper, Gold, Extraction, Sulfuric leaching, Optimization

Jan 1, 2003

By J. M. Dean, R. L. Grayson, N. P. Reddy, Y. J. Wang

This 1988 survey provided a cross section of computer software use by the US coal industry. From 1250 mailed questionnaires, 171 responses were received, representing a 4.9% sampling of the 3496 US coal mines. Since the distribution of responses by regional stratum matched well with the distribution of mines by stratum, the survey was given statistical validity. A statistical description details the computer use by region, mining type, organizational size, the level of application within the organization, the type of software application used, the variety of computers on which the software was used and the percent of users within engineering, management and general applications categories. Overall, 63.5% of the respondents use computers at some level in their organizations. All of the mines producing more than 454 kt/a (500,000 stpy) used computers. However, for those producing more than 9 kt/a (10,000 stpy) but less than 91 kt/a (100,000stpy), only 44% used computers. Generally, the software applications were still data-processing oriented. The application sophistication grew with increasing mine size. Computer system models and configurations for different sized organizations are recommended based on the configurations used in the industry at the time of the survey.

Jan 1, 1994

By R. C. Oberth, C. F. Lee, E. M. Taylor

INTRODUCTION Underground siting of nuclear power stations is drawing increasing attention in various parts of the world. Scandinavian countries took the early lead in this field because of their experience in the design and construction of underground hydroelectric stations and industrial plants, and because they have near-surface rock formations which are ideally suited for hosting large underground caverns. The world's first underground nuclear facilities were built in Norway (Halden) and Sweden (Agesta) and were commissioned in 1959 and 1963 respectively. Figure 1 summarizes the main features of these and two other small-scale European facilities. (1-4) American utilities and regulators are also for a variety of reasons assessing the benefits and penalties of underground siting. A recent study by Sandia Laboratories (contracted by the Nuclear Regulatory Commission (NRC) focussed on identifying potential safety benefits of underground siting. (5) Although the study concluded that underground plants would have improved containment for some accidents, as well as better external protection, NRC, in assessing the overall benefits and penalties, decided not to impose mandatory underground siting for nuclear stations. In June 1976, the California Legislature enacted a law which directed the California Energy Commission (CEC) to examine the issues concerned with underground siting of

Jan 1, 1979

By Allan M. Johnson

Dewatering is a major operational cost at sane mines. Under certain conditions, costs associated with water disposal may continue beyond the productive life of the mine. For mines with mineralized waters, this is of special concern. Since 1974 experience has been gained from the examination of a number of closed underground metal mines that exhibited drainage problems. It was observed in certain cases, that had appropriate steps been taken prior to closure, that the resulting drainage problems could have been largely avoided. The pre-closure steps would have involved alteration to the "plumbing system" of the mines: i.e., the drifts and crosscuts interconnecting the workings of the mine. This could have best been accomplished by the placement of bulkheads and/or selective drifting. In addition to reconfirming that hindsight is 20-20, a lesson learned from these case studies shows that a relatively simple hydrologic evaluation prior to mine closure may avoid a troublesome and costly drainage problem.

Jan 1, 1983

By Robert E. Lovett

The truly educated man is better prepared to meet the challenge of the times. This challenge can be either beneficial or harmful depending upon one s orientation, Certainly man can no longer continue in the way of his father or even in the manner of his own previous experience as he seeks self-fulfillment, unless he is willing to sacrifice inner integrity--unless he is willing to compromise self-determination and self-expression. He must make a choice as society moves rapidly into high gear in the areas of automation and cybernetics. Industry, a unit of society, has a high stake in meeting this challenge, The better prepared and more mature its personnel, the better the end result as it attempts to meet the challenge. It therefore has a vital concern in proper training of such personnel, that their contribution will be of maximum quality. The specialized training required demands a broad liberal arts background which gives the individual a wider perspective upon which to base judgment. This greatly aids his development as he enters graduate school or goes directly into industry. In either case, his value to industry is enhanced. It would seem that the small liberal arts college provides the best environment for such a program, Consideration of several factors will, I hope, throw some light on the severity of the problem.

Jan 1, 1966

By A. S. Paschoa, A. W. Nóbrega

INTRODUCTION There are now over twenty years since the radiological characteristics of the brazilian regions of Araxá, Tapira and Barreiros, three locations adjacent to each other, in the state of Minas Gerais, Brazil, started being surveyed by investigators from the Instituto de Biofísica da Universidade Federal do Rio de Janeiro (IB/UFRJ), Pontifícia Universidade Católica do Rio de Janeiro (PUC/RJ), and New York University (NYU) (Roser and Cullen, 1958; Cullen et al, 1980). The importance of the Araxá apatite – Ca5,(P04)3(OH, F, Cl) - and pyrochlore - NaCaNB206F - for the production of large quantities of fertilizers and niobium was early recognized (Roser and Cullen, 1958). Interesting data have been gathered and published throughout the years on the contents of naturally occurring radionuclides in geologic materials, soils, grass, foods and waters of the Araxá region (Eisenbud, et al., 1964; Penna Franca, et al., 1965a, b; Roser et al., 1966; Penna Franca et al., 1970; Cullen, 1977; Penna Franca, 1977; Cullen and Paschoa, 1978; and Cullen et al., 1980). The radioactivity of the Araxá region is associated with mineral deposits of niobium rich pyrochlore and phosphate rich apatite. There are in this region mineral ores with 3 to 5% pyrochlore with 2 to 2.5% Th as Th02 and 50 to 150 ppm U308 in the matrix, while the apatite deposits contain up to 150 ppm U308 and a thorium concentration similar to that of the pyrochlore deposits (Paschoa and Palacios, 1981). As an indication of the high thorium content of the Araxá soils the 228Ra and 224Ra activity concentrations were reported to range from 10.6±0.2 to 62.4±0.7 pCi228Ra/g soil in 7 samples and 2.1±0.1 to 104±1 pCi224Ra/g soil in 19 samples (Cullen, et al., 1966). The uptake of radium isotopes by edible roots vegatables and fruits growing in the soils of the Araxá region can be illustrated by the data listed in Table I. The biological availability of natural radium isotopes in some segments of the Araxá soil allows a large variation in the 228Ra, 224Ra and 226Ra concentrations in vegetables and edible roots, as can be seen in Table I. This fact makes quite difficult a quantitative local assessment of the radiological implications of mining the Araxá mineral deposits of pyrochlore and apatite for production of niobium and phosphate fertilizers, respectively; since one cannot easily separate the naturally occurring from the technogically enhanced radionuclide contents of foods. The position of the city of Araxá inside the contour of the state of Minas Gerais appears in the upper part of Figure 1, which shows the outlined map of Brazil with the positions of the cities Brasilia and Rio de Janeiro also indicated. The lower part of Figure 1 is a representation of the Araxá region in an expanded scale, which indicates the locations of the pyrochlore and apatite deposits in relation to the city of Araxá, as well as the nearby hydrographic basins. The distance between the city of Araxá and the pyrochlore deposit is about 8 km, and between the pyrochlore and apatite deposits is 4 km. This paper deals tentatively with the radiological implications of the industrial operations taking place in the Araxá region for the exploration of the pyrochlore and apatite deposits. However, one must bear in mind, firstly, that the radiological implications of these industrial activities are by far too complex to be covered adequately by the limited amount of data to be presented in this paper, and secondly, that such implications cannot be considered of local character only. INDUSTRIAL OPERATIONS The commercial exploration of the Araxá deposits of pyrochlore and apatite started only few years ago, motivated by the increasing demand of niobium and phosphate fertilizers in Brazil and the world. As a consequence of the industrial operations in Araxá, a redistribution of the uranium, thorium, and radium originally present in the local deposits of pyrochlore and apatite started occurring in the seventies, with possible radiological implications for the Araxá region and its immediate surroundings, not to mention the destinations of the end products of such industrial operations. A literature review on the radioactivity associated with the extration industries of selected minerals was made by the USEPA (Bliss, 1978). The low level radioactive wastes of the industries for copper ore mining and rare metals processing have been object of particular attention (Fitzgerald, Jr., 1976; Eng, et al., 1979), but the short and long term implications of the radioactivity associated with the niobium industry were also subjects of concern (Knight and Makepeace, 1978). Recently, high 232Th and 226Ra concentrations in samples from the tin mining industry in West Malaysia were reported (Hu et al., 1981). A great deal of attention has been dedicated to the implications of the redistribution of radionuclides originally present in the mineral ores used by the phosphate fertilizer industry (Moore, 1967; Menzel, 1968; Spalding and Sackett, 1972; Eisenbud, 1973; Guimond and Windham, 1975; Guimond, 1976; Roessler,

Jan 1, 1981

By P. T. Bissert, T. J. Lutz, J. A. Yonkey, G. T. Homce

"Underground refuge alternatives (RAs) require an air source to supply breathable air to the occupants. This requires pressure relief valves (PRVs) to prevent unsafe pressures from building up within the RA. The Mine Safety and Health Administration (MSHA) mandates that PRVs prevent pressure from exceeding 1.25 kPa (0.18 psi or 5 in H2O), or as specified by the manufacturer, above mine atmospheric pressure when a fan or compressor is used for the air supply. Research to date by the National Institute for Occupational Safety and Health (NIOSH) suggests that the design and implementation of PRVs used in RAs has not yet had sufficient performance analysis or technical development. In response to this need, NIOSH tested a variety of PRVs using an instrumented test fixture consisting of data acquisition equipment, a centrifugal blower, ductwork, and various sensors to determine if subject PRVs meet the MSHA requirement. Relief pressures and flow characteristics including opening pressure and flow rate were measured for five different PRVs under a variety of conditions. Subject PRVs included two off-the-shelf modified check valves, two check valves used in MSHA-approved built-in-place (BIP) RAs, and a commercially available valve that was designed for a steel RA and is currently being used in some BIP RAs. The test results showed relief pressures ranging from 0.20 to 1.53 kPa (0.8 to 6.1 in H2O) and flow rates up to 19.3 m3/min (683 SCFM). INTRODUCTION The Mine Improvement and New Emergency Response Act of 2006 (MINER Act) was enacted in the wake of three mine explosions/fires that claimed 19 lives that year. Intended to help improve underground coal mine accident preparedness, the MINER Act includes provisions that target mine safety issues in areas such as emergency response planning, adoption of new technology, training and education, and mine safety standards enforcement [1]. Section 13 of the MINER Act specifically directed NIOSH to provide for research into the effectiveness and viability of refuge alternatives (RAs) for underground coal mines. This mandate culminated in the 2009 adoption of changes to 30 CFR mining health and safety regulations, requiring underground coal mines to provide mine emergency RAs and associated components, to provide a life-sustaining environment for persons trapped underground. Such RAs can be either self-contained mobile units or built-in-place (BIP) facilities. The regulatory changes also include provisions establishing requirements for Mine Safety and Health Administration (MSHA) approval of RAs and their components, and among these provisions are numerous criteria for providing a safe breathable atmosphere under positive pressure within the RAs. One specific criterion for maintaining a safe RA atmosphere requires the inclusion of an air pressure relief valve that will activate at a maximum of 1.25 kPa (0.18 psi or 5.0 in. H2O), or at a pressure above mine atmospheric pressure in the RA as specified by the manufacturer when the breathable air is supplied by a fan or compressor [2]."

Jan 1, 2017

By Gordon M. Pugh, David G. Rasmussen

INTRODUCTION Square-set timbering of stopes developed from stull support methods because veins too wide for stulling were being mined. In general, the void caused by the stoping of the ore is filled with a system of interlocking timbers. Timber framework supports the wall rock, the mining operations, and provides access. A timbered stoping method can be used in all widths of veins at any dip. The timbering can be normal and parallel to the planes of the walls or at angles to these planes. Irregularly shaped ore bodies can be worked by timbered methods. Pinching or swelling of the vein will not adversely affect the method. Timbered stoping is especially advanta¬geous where weak ground is encountered in the vein or the wall rock. The ground is unsupported only until timber sets are stood. These stopes can be filled with sand or waste when desirable. The customary method of developing a square-set timbered stope with haulage drifts above and below and timbered raises on each endline is shown in Fig. 1. The drifts are timbered the full stoping length. The raises have two compartments with the manway and timber slide in one compartment and the chute in the other. The drifts and the raises cannot be widely spaced as handling timbers is an important consideration. Stoping can begin immediately above the drift timber and continue in both directions and upward from the raise. Breasting down each blast round for only one timber set laterally is the common practice. The blasted ore falls to a lower floor where it is slushed or trammed to the chute. Drilling can proceed on the upper floor while broken ore is being removed from the stope. As shown in Fig. 2, square-set timbering may be used in cut-and-fill stopes to support the back and walls until fill is added. There are various ways of developing an ore block for timbered stoping. Fig. 3 depicts the situation for the main haulage in the vein with an intermediate drift separated from it by a sill pillar. The ore is slushed into the chute connecting the two drifts. The situation in Fig. 4 is identical to that in Fig. 3 except that no sill pillar is used. In Fig. 5, the haulage drift development is done in the footwall with crosscuts driven to intersect the ore body. The intermediate drift development is above the crosscuts with a minimal sill pillar. The main bottleneck in timbered stoping is in the timbering process. Drilling in the stope is generally held up while timbering is done. Two or three men are re¬quired to do the timbering and an additional one or two men are needed to transport and raise or lower the tim¬ber. Good organization is essential to timbering. Skill must be exercised in standing the timber to support the ground and still maintain good production. COSTS AND PRODUCTIVITIES Development and stoping costs are presented in Tables 1 through 7 for the situations in Figs. 3 and 5,

Jan 1, 1982

By B. Hornsby

At the Mount Isa mine, Mount Isa, Qld., Australia, sublevel open-stope mining is used for copper ore while both sublevel open-stope and cut-and-fill methods are used for the silver-lead-zinc ores. Production in 1979¬80 was 4 730 000 t (5,200,000 st) copper ore and 2 590 000 t (2,850,000 st) of lead ore. The deepest mine level currently is 960 m below the surface. GENERAL ORE BODY REQUIREMENTS AND LIMITATIONS Size, Shape, and Dip The mine is located in the valley of the Leichhardt River in Lower Proterozoic sediments of the Mount Isa group. The regional strike of the sediments is north¬south and they have a persistent westerly dip of about 1.1 rad (65°). In the mine area, the Mount Isa group comprises a sequence of alternating bands of dolomitic shales and siltstones some 3.2 km (2 miles) in width. It is bounded on the east by greenstones and quartzose sediments of the Eastern Creek volcanics, and on the west by the Mount Isa fault, west of which occur schists and other metamorphic rocks. The ore bodies as currently known at Mount Isa are restricted to the Urquhart shale, a formation of thinly bedded pyritic, dolomitic, and volcanic shales some 1070 m (3500 ft) thick. Towards the top of the Mount Isa group sediments, copper and silver-lead-zinc ore bod¬ies occur as contiguous but discrete entities and are mined and treated separately (see Figs. I and 2). Argentiferous galena, sphalerite, pyrite, and minor associated sulfides occur in distinct concordant bands throughout the Urquhart shales. Wherever these bands are grouped together in sufficient density they constitute silver-lead-zinc ore bodies with widths varying up to 36.6 m (120 ft). Other mineralized bands are common in intervening beds. Individual ore bodies persist for many hundreds of meters concordant with the strike and dip of the enclosing shales. Intersections of these beds with fold axes provide local zones of enrichment but otherwise the mineral content of the ore bodies varies only slightly throughout the extent of the dip and strike. Chalcopyrite is the only important primary copper mineral. It occurs in association with pyrite and pyrrhotite as disseminated flocks and as vein fillings throughout irregularly shaped zones of folded, brecciated, and re¬crystallized Urquhart shale. These zones, which are lo¬cally termed "silica-dolomite" bodies, are broadly transgressive to the shale bedding and confine all significant copper mineralization to the virtual exclusion of silver¬lead-zinc mineralization. In some areas, the downward percolation of acidic water through faults and shears has caused extensive leaching of the coarse-grained carbon¬ates to depths in excess of 610 m (2000 ft), but most of the silica-dolomite remains unleached and the ground is competent. The majority of lead ore being mined is north of the main shaft pillar (R62, U62) area. The major lead¬producing areas for many years have been the Black Star ore bodies (2 and 5 ore bodies) and the Racecourse ore

Jan 1, 1982

By H. Nematollahi

The comminution laws The grindability of the ores or minerals is an important factor that could not be deduced from their mineralogical characteristics (Testut, 1958). Many theories have been proposed to determine the amount of work required in a comminution operation as a function of the nature of material, size and shape of the minerals before and after of comminution. The most important laws are proposed by Rittinger, Kick and Bond. According to Rittinger (1867), the work is directly proportional to the new surfaces produced during the comminution. Kick (1885) believes that the work needed to produce similar modification is proportional to the volume or mass of the material. Bond, during his 25 years of experience and research, reached to the conclusion that on the average the energy required for a known comminution is between the Rittinger's and Kick's laws (Bond, 1952). According to Bond's Third Theory, the work input is proportional to the new crack tip length produced during the particle breakage, and equals the work represented by the product minus that represented by the feed. The work input is given by the following equation: [111W = 1 Owi( FP FF(1)] where W is the The energy input to the mill, (kWh/st); F is the Feed size based on 80% passed, (µm); P is the Product size based on 80% passed, (µm); and W; is the Work Index, (kWh/st) Methods to determine the Bond Work Index Various methods have been proposed by Bond to determine the Work Index. There are some problems with the Standard Bond Grindability Test: •Requiring a special mill. •Requiring a relatively large amount of sample. •Being relatively time consuming and tedious. [ ] During the recent years, numerous attempts have been made to install faster and easier methods to determine the Work Index. A complete description of these methods is presented by Yap et al. (1982). Determining the Bond Work Index by a new size ball mill During the recent years, researchers at the University of Tehran determined the Bond Work Index, using the Anaconda simplified methods by its Denver 305- x 127-mm (12 x 5-in.) laboratory wet ball mill. The equation used to calculate the Work Index for the above mill containing 16.12 kg (35.5 lbs) of steel balls is as follow: [1 _ 1-1W;=0.54x [P [)(2)] In addition, an attempt has been made to determine the Bond Work Index similar to standard Bond ball mill procedure but by a different ball mill, smaller and in consequent portable and less laborious than the Bond ball mill. Method description Just as the standard Bond grindability test, this method is a locked-cycle dry grinding and screening process that is carried out until steady state condition is reached. Test equipment The test is conducted in a special ball mill, called the New Size Ball Mill (NSBM). The mill is scaled down with a coefficient of two-thirds from the standard Bond ball mill. It measures 200 x 200 mm (8- x 8-in.) inside (instead of 300 x 300 mm or 12 x 12 in. in Bond ball mill). Just like the Bond

Jan 1, 1995

By William J. Douglas

Defining Productivity Productivity is a principal concern to all organizations - industrial, commercial, government, and academic. As a ratio of output to input, productivity measures the efficiency of an industrial process, much as thermodynamic efficiency measures the useful work obtained from the available energy consumed. However, there is one important difference. Whereas thermodynamic efficiency is a dimensionless a ratio of energies, productivity output and input are usually measured in different physical units. Nevertheless, the resulting ratio is a normalized expression for unit of output per unit of input to the process. In the early days of coal, mining was essentially a hand loading operation. There was little expenditure of alternative forms of energy within the process. Loading required expenditures of human energy on the order of 1.2 MJ/t (1,000 Btu per st). And if we accept the conventional value "you load 16 tons," the output to input ratio is 14.5 t (16 st) per manshift. In energy terms, it is on the order of 116 MJ/t (100,000 Btu per st) produced per labor Btu expended. However, the latter measure of efficiency was not meaningful in economic terms, while the 14.5 t (16 st) per manshift was significant. Since labor was the principal component of cost, it represented a direct relationship to the cost of production: [ ] Furthermore, when workers were paid directly on the basis of tons produced, the labor cost per ton was specified directly by this rate. With the introduction of mechanized loading, significant increases in productivity occurred, when measured on the basis of tons per manshift. Electric power consumed about 11.6-116 MJ/t (10,000-100,000 Btu per st). This makes the 29-GJ/t (25 million Btu per st) coal output/input ratio between 100 and 1,000. That is one or two orders of magnitude lower than hand loading. However, electric energy was quite inexpensive compared to labor, which made the mechanization economically efficient. The accepted productivity measure continued to be tons per manshift. This measure includes some of the effects of mechanization: namely, the additional manpower needed to maintain the machines and support the equipment that uses electrical energy. However, it does not consider the capital and operating costs that relate to mechanized equipment. As a result, the concept of tons per machine-shift has emerged as an accepted measure of shift productivity. The only appropriate measure that encorporates the productivity of men and machines is an economic one. The output is the tonnage per shift and the impact is the cost per shift. [ ] This is simply the inverse of the cost per ton. In addition, much flexibility is available in allo¬cating costs to the three categories. This adds a level of intangibility to the measure. The amount of information needed to obtain all of the required costs is appreciable compared to the simple matter of counting tons and workers. Furthermore, financial information relating to production costs is closely held by mining companies, so historical statistics on economic productivity are not publicly available. To extend the concept further, consider the value of the tonnage produced, to obtain a dimensionless ($/$) measure of economic productivity.

Jan 11, 1983

By J. D. Morgan

Introduction In 1987, the US economy continued to grow steadily, reaching an annual rate of $4.6 trillion in the last quarter. The value of domestically processed mineralbased materials rose slightly to $250 billion. The value of US metals rose sharply to more than $7 billion. Industrial minerals rose slightly to $18 billion recycled scrap was valued at $4 billion. Metal prices rose sharply toward year-end. A number of mining and metal companies experienced increased profitability, fostering more optimism about the future. Consumer demand strongly affects mining because the US economy is relatively saturated with long-lived products. Consumer, mortgage, and federal debt continue to rise. 244 million citizens already possess 170 million licensed motor vehicles and 100 million dwelling units. New car production fell 9% to 7.1 million units, but truck and bus production rose 9% to 3.8 million units. New housing starts fell 10% to 1.6 million units. Excess productive capacity exists not only in the US, but also in many other countries. Consequently, the US mineral industry is encountering stiff competition from others, as well as increasing competition from newer engi¬neered materials. Domestic production of plastics rose 9% to 25 Mt (27 million st) - on a volume basis, double all metals. Some 7% of petroleum goes to make petrochemicals including plastics. Imports of nonfuel mineral-based materials in 1987 were valued at $37 billion and exports at $24 billion. Imports supplied a significant proportion of total US consumption of several important mineral materials, including many classified as strategic and critical. In December, the Congress mandated that any major changes in stockpile goals be made only by law, and that the Department of Defense submit annually detailed stockpile supply/demand analyses. Concern about apartheid in South Africa continued, resulting in increasing interest about chromium, manganese, platinum-group metals, cobalt, vanadium, and gold. The National Critical Materials Council continued to monitor the US materials position. The Defense Production Act, authorizing priorities and allocations, supply expansions, voluntary agreements, and the National Defense Executive Reserve continues in effect through Sept. 30, 1989. Under the DPA, the US Bureau of Mines maintains the Emergency Minerals Administration. Further consultations were held with Canada to strengthen the North American defense industrial base. Coal production, 60% from open pits, rose 2% to 825 Mt (910 million st) valued at $21 billion. Nearly four-fifths was burned to generate 56% of US electricity. Exports included 42 Mt (51 million st) of metallurgical coal and 24 Mt (27 million st) of steam coal, with a total value of $3.3 billion. Domestic petroleum production fell 5% to 480 Mm' (3 billion bbl). Uranium mining, including recovery from phosphates, fell 4% to 5.9 kt (6500 st). Nonfuel minerals Major metals: Raw steel production - a major consumer of many minerals - rose 7% to 79 Mt (87 million st). Domestic iron ore production rose 11% to 44 Mt (48 million st), about 96% pelletized. Net imports, though, fell 8% to 11 Mt (10 million st). Raw steelmaking capacity fell 6% to 102 Mt (112 mil-

Jan 5, 1988

By Nicholas T. Esposito

An advanced coal preparation plant has been built at Homer City, Pennsylvania, by Pennsylvania Electric Company, a subsidiary of General Public Utilities Corporation, and New York State Electric and Gas Corporation, as an alternative to utilizing flue gas desulfurization technology to meet the Federal Environmental Protection Agency and the Pennsylvania Department of Environmental Resources air quality emission regulations of 4.0 lb S02/106BTU for the two (2) existing coal-fired generating station Units No. 1 and No. 2, and a 1.2 lb S02/106BTU for the new Unit No. 3. The coal preparation plant is designed to process 5,200,000 tons of run of the mine coal annually and has a design capability to process 1,200 tons per hour via two (2) equal capacity 600 tons per hour preparation circuits.- The plant is designed to produce multi-product coal streams consisting of a middling product of medium ash and medium sulphur content, which is environmentally compatible to support operation of the two (2) existing generating Units I and 2, and a deep cleaned, low ash, low sulphur coal product capable of environmentally supporting the ambient air quality requirements of the new Unit 3 generating facility. The waste product from the process consists of high ash, high sulphur reject material. The process has the acronym MCCS (Multi-Stream Coal Cleaning System).

Jan 1, 1982

By M. B. Mooiman

Cyanidation of gold and silver ores by conventional mining and milling techniques has been practiced for over a century. During the past decade, heap leaching has emerged as a viable process for treating certain gold and silver ores. (1) The rapid development of heap leaching for gold and silver ores is largely a result of lower capital and operating costs and faster start-up time than that offered by conventional mining and milling. In general, these features make heap leaching an ideal approach for exploiting either small or large low-grade disseminated deposits of gold and silver considered to be uneconomic by conventional methods. The development of heap leaching technology has evolved from the operations initiated in the western United States. The basic components of a typical heap leaching operation are depicted in Figure 1. Run-of-mine or crushed ore (usually 1 to 5 ppm gold) is delivered to specifically prepared impervious pads. Alkaline cyanide solution is applied to the surface of the heap and allowed to percolate through the heap (typically 10-30 ft high). Pregnant leach solution which drains from the heap is collected and stored in tanks of sufficient size or in collection reservoirs. Gold and silver are recovered from the pregnant solution and the barren solution is recirculated back to the heaps after reagent make-up.

Jan 1, 1983

By R. J. Andreini

Solvent extraction is widely used in hydrometallurgical processing of uranium for purification and upgrading leach solutions prior to recovery of metal values. Conventional solvent extraction processing utilizes mixer-settler units to achieve mixing of the aqueous and organic phases. Use of mixer-settlers permits continuous treatment of feed, but the processing rate is restricted by the time required for phase separation after mixing. Because of the high-shear type mixing used in a mixer settler a portion of the organic phase becomes mechanically entrained in the aqueous resulting in loss of extractant. For this reason application of mixer-settler units is often limited by the settling area required for phase separation, especially for systems where high volume throughputs are desirable or necessary. Several alternatives to mixer-settler operations involving the use of column extractors have been proposed. Packed columns (1-2), in which organic and aqueous phases are fed countercurrently, utilize packing materials similar to those used in gas absorption or distillation columns. Extraction columns utilizing rotating(3-5) or reciprocating elements(6-7) to achieve mixing have also been developed. Van Dijek(8) originated pulsed columns, in which mechanical or air pulsing of the phases enhances the mixing in the vessel. Each of the above column processes involve varying degrees of mechanical complexity which may lead to operational difficulties.

Jan 1, 1975

By Paul Basinski

The Northern Reese River Valley is in west-central Lander County approximately 31 miles north of Austin, Nevada in the north-central Basin and Range Province (Figure 1). Authigenic zeolites, which were previously undescribed in the literature, are voluminous in this small sedimentary basin. Uranium mineralization is also abundant in this study area. Until now, what we believe to be cause and effect have not been put together. X-ray diffraction, differential thermal analysis, and scanning electron microscopy reveal clinoptilolite, erionite, analcime, and minor chabazite to be present (Figures 2, 3). Assays show uranium to be present in thicknesses up to 0.7 meters at amounts up to 0.10% eU308. The sediments in the Northern Reese River Valley belong to the Mio-Pliocene Humboldt Formation equivalents. This formation consists largely of tuffacious lacustrine and fluviatile sedimentary rocks. Mudstone is the dominant lithology and intercalated thin zeolite strata (usually less than 0.6 meter thick) are present. Zeolites in the Northern Reese River Valley were diagenetically derived from rhyolitic glass deposited in a shallow, saline-alkaline lake under arid to semi-arid conditions. Clinoptilolite from the study area was K-Ar dated at approximately 4.7 + 0.5 million years which corresponds to Middle Pliocene age (Krueger and Basinski, in press). This age is further substantiated by Middle Pliocene mammalian fauna collected in the vicinity by Deffeyes (1).

Jan 1, 1979