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By P. D. Pack, E. H. Skinner

During design of a 550-foot rectangular shaft in alluvium, lateral support within the excavation was an anticipated construction problem. Actual experience showed that the nearly 9 x 14 foot excavation required no lateral support. A strain measurement program con- current with construction and for a 9-month period following completion of the shaft detected only minor strains. Shaft design included consideration of available geological information. Site exploration included a 754-foot drill hole, cored at selected intervals, and a suite of geophysical well logs. Generalized physical properties of the alluvium were developed from laboratory core testing. An elasto-plastic, finite element computer program (DAHLKE) developed by the Spokane Mining Research Center U.S. Bureau of Mines, has been recently used to analyze the behavior of the alluvium around the shaft. Analysis showed that yielding first develops in the shaft corners and progressively expands into the wall zones around the shaft as loading increases. Gradual growth of a plastic zone progressed outward from the excavation boundary at increasing loads but had limited extent and was surrounded at all stress levels by an infinite elastic zone. This design review, aided by computer analysis, confirmed that the shaft would have been considered theoretically stable as designed.

Jan 1, 1977

By Nopadon Mantajit, Dallas W. Davis, Somsak Potisat, Prasert Kumalachan

For centuries Thailand has been a significant, though primarily unofficial, producer of gold. Panning has been the traditional way of making a living for innumerable villagers during the December to May dry season following the harvest. During this period groups can be seen working the streams, rivers, fields and dry valleys at as many as 90 localities in 28 provinces. Attesting to their efforts are the five and a half ton solid gold Buddha at Wat Trimit and much of the gold jewelry sold in Bangkok. This traditional panning will continue, and probably become more extensive, in harmony with commercial endeavors using modern technology suitable for extraction of gold from types of deposits for which gravity separation would give very low recoveries. Several such deposits have been discovered in the course of geochemical and geological surveys conducted by the Royal Thai Department of Mineral Resources with the object of contributing to early interpretation of the results of a country-wide airborne survey.

Jan 1, 1987

By S. K. Das Gupta

The rock laterite was first discovered and described in the State of Kerala, India in 1800 A.D. by Francis Buchanan. It had been used here, and elsewhere in India, for many centuries as a building stone, but in Buchanan's time it was not known that some of these laterites were highly aluminous and could be processed to produce alumina. After World War I India started searching for bauxite reserves with a minimum grade of at least 50% A12O3. By 1960, it was estimated that India had a potential reserve of 245 million tonnes of bauxite, about 10% of which was in the "Proved" category. Subsequent geological exploration now reveals that India has an overall resource of more than 2 billion tonnes of aluminium ore, not all of it bauxite, as defined by earlier geologists. In this paper, the geology, resources and distribution of bauxite and aluminium ore throughout India are described. The generalised stratigraphy, typical laterite and bauxite profiles and summary of the resource position are shown in the attached Tables 1 to 8. It is generally agreed that a tropical to sub-tropical climate, intermittent wet and dry season, good permeability of country rock and suitable drainage, as well as physiographic and ground water conditions are important in the development of bauxite.

Jan 1, 1984

As mentioned in chapter 8, one of the objectives of the budget is to provide a mechanism for ongoing measurement and control of the production operation. The budget shows expected performance. Actual results are compared to this benchmark to evaluate past performance and to direct future activities. The variances between budgeted and actual results identify specific activities that did not perform as expected (whether negatively or positively). Managers who use variance analysis are essentially applying a management- by-exception philosophy. Individual organizations will determine variances that reflect their own processes and managerial interests, but these variances all follow the approach outlined here. Firms will also vary in the extent to which variances are reported. Some firms use a few variance measures for the overall production organization whereas others calculate variances for individual departments or even individual work areas. As mentioned in chapter 5, it is important to distinguish between controllable and noncontrollable costs when using budgets for control and evaluation.

Jan 1, 1999

By John A. Ames

Limestone for portland cement must be beneficiated to produce uniform raw material for the kiln. Careful quarrying and selective recovery are factors in this process, but the chief aspects of beneficiation are "in plant" processes, such as crushing and screening, washing, grinding, flotation, and heavy-media separation. Numerous technical and economic problems exist. Detailed studies of the limestone deposit and the stone itself are required for intelligent beneficiation. As used in this paper, beneficiation is defined as the improving of limestone composition so as to produce an economically usable raw material A limestone deposit is defined as a mass of limestone which can be recovered, by quarrying or mining, for sale or for use in a commercially profitable operation. The stone may require elaborate processing, or it may qualify with little or none. Obviously, the "commercially profitable" qualification may change as the economy changes. Potentially commercial deposits may be of much better quality than actually developed deposits, and yet may be denied development for various economic reasons.

Jan 1, 1966

By T. D. Barkand

A recent coal mine elevator accident resulted in serious injuries to four passengers. The miners struck the ceiling of the elevator car as it collided into the overhead structure at an estimated speed four times faster than normal. In response to mine hoisting accidents, safety authorities have required additional protective devices on new and existing mine hoists and elevators. This paper examines supplemental safety circuits and new devices designed to provide ascending car overspeed protection on mine hoists and elevators. These devices provide needed protection that eliminates the hazard or significantly reduces the potential of a mine hoisting accident.

Jan 1, 1995

By D. Dolinar, T. P. Mucho

Horizontal stresses are caused by global platetectonic forces. During 1995 alone they were largely responsible for the closing of two longwall mines in the United States. This paper presents six case histories from Pennsylvania, West Virginia, Kentucky and Alabama. In each case, a mine encountered roof falls or difficult ground conditions at the headgate caused by horizontal-stress concentrations. The problems are detailed, and the control measures adopted are described. In most cases, nearby longwall panels without stress concentrations were trouble free. The paper also discusses detailed measurements that were made at two adjacent Pennsylvania longwalls. One headgate was oriented to avoid a horizontal-stress concentration, and the other was not. Eliminating the stress concentration dramatically reduced roof support loads and roof deformation. The paper concludes that proper panel orientation and sequence is the key to maintaining headgate ground control. The optimum orientation is not parallel to the maximum horizontal stress, as previously thought, but rather it is 20o in the stress shadow of the gob. Other stress-control techniques, including artificial support, are briefly discussed

Jan 1, 1999

By G. Bryant, P. Ziemkiewicz

Acid mine drainage (AMD) from both abandoned surface and underground mines is a serious problem. The flow of water and changes in quality over time from abandoned mines is important in determining remediation strategies. Acid mine drainage from surface mines is estimated to last for 10-20 years, while estimates of acid drainage from underground mines vary from 10- 100s of years. Fifteen underground mine discharges in West Virginia were studied to compare water quality changes between 1968 and 1999 to see if our data are consistent with other studies. Each of the discharges were categorized into one of three groups: undisturbed since 1968, affected by surface mining since 1968, and reclaimed. Comparing water quality between 1968 and 1999, the discharges in the undisturbed category showed a 35 to 95% improvement in acid concentration and a 40 to 99% reduction in iron concentration. The discharges affected by surface mining showed the most dramatic improvement. For acidity, iron, and aluminum, the percent improvements were all above 44%, and in most cases in the 70 to 99% range. In the reclaimed category, one of the four discharges declined in water quality. Discharge 82 showed a 76% increase in acidity, and iron and aluminum concentrations worsened by 58 and 96%. However, discharges 15 and 74 improved in water quality with a 94% acid load improvement and a 95% iron load improvement at both sites.

Jan 1, 2000

By Edgar O. McAlister

Associated with cordilleran intrusives of intemediate to acidic composition, gold/silver ores are generally found in the intruded host rocks which are adjacent to these intrusives. Generally precious metal deposits lie further from the intrusives than allied base metal deposits. For vented intrusives, the associated volcanics may constitute the intruded rock and form the host for precious metal accumulation. Potential field methods, particularly magnetics, can help to define unseen boundaries of intrusive systems and thus can point to generalized prospecting targets. Other clues arise from the intrusive system type, its emplacement fracturing, the host rock type and local magnetic changes caused by mineralization processes.

Jan 1, 1984

By B. W. Cavender

Capital investments are made for a variety of reasons, ranging from providing incremental capacity at existing operations to developing and implementing new technologies intended to radically improve a company's capabilities. These projects generate very different business opportunities and create value in distinctive ways. For incremental improvements, the capital budgeting process assures at least a loose fit between short-term goals and readily available resources. However, the criteria used to evaluate capital projects often prevent a company from committing to more aggressive goals, which lie beyond the firm's current abilities or resources. Such projects may not have clearly identifiable future cash flows, and the degree of interaction with other projects and the nature of the risk incurred may be difficult to estimate. Additionally, by focusing only on quantifiable benefits, the budgeting process often fails to recognize "soft" improvements such as increased operating flexibility or new knowledge generated by such projects. By rejecting these projects, the capital budgeting process may actually harm the company's future competitive position.

Jan 1, 1999

By William E. Foreman

Editor's Note: For purposes of uniformity throughout this book, Coal Preparation, 5th Edition, the editors have advocated the use of the U.S.A. Sieve Series of testing sieves (see Table 6-2) as the testing sieves of modem choice. The adoption and use of the U.S.A. Sieve Series and its forerunner, the Tyler Standard Screen Scale, has for over seventy-five years introduced uniformity into reports; has simplified the comparison of results; and has provided control for operation of modem coal preparation circuits. While a full explanation of the differences, and more importantly the similarities of these two measuring systems cannot be stated here, it is felt that a brief clarification of terms is in order. The difference between the U.S.A. Sieve Series and the Tyler Standard Screen Scale Sieve Series is the identification method. Tyler Screen Scale sieves are identified by mesh designation with the width of opening varying by the square root of two, or 1.414 times the width of opening in the previous sieve. The U.S.A. Sieves are identified by openings in millimeters or microns and also arbitrary numbers which do not necessarily mean the mesh count; this series uses width of opening variations in the order of approximately the ratio of the fourth root of two, or 1.189. Tyler Standard Screen Scale and U.S.A. Sieves can be used interchangeably, and to avoid confusion the nameplate of all Tyler Screen Scale sieves show the U.S.A. Number, while all U.S.A. Sieves show Tyler Screen Scale mesh equivalent numbers on the nameplate. INTRODUCTION Sizing is the process of separating mixed mineral particles into groups of particles all of the same size, or into groups in which all particles range between definite maximum and minimum sizes. This chapter applies the modem mechanical screen and the liquid-solid cyclone (hydrocyclone) to the process of sizing solid particles as applied to coal preparation. Screening is a mechanical process that separates particles by size. Modem coal preparation is made possible by efficient sizing. Sizing of coal is defined in terms of the opening through which an individual particle will or will not pass, or as two openings, the larger of which passes the particle and the smaller of which retains the particle. Screening accomplishes sizing by passing coal of a wide range of sizes through a series of screens, each of a decreasing size. The individual screen discharges are then directed into different screen products for subsequent sale or processing. Screening in modem preparation plants is done for the following reasons: 1. Removal of fine coal before a size reduction step. 2. Size separation of the coal into a coarse and fine fraction for sized products or for processing in coarse and fine coal circuits. 3. Recovery of heavy media from heavy media coal cleaning circuits.

Jan 1, 1991

By Bernard L. Cohen

INTRODUCTION The most serious occupational radiation episode in U.S. history was the exposure of uranium miners to radon daughters in the 1945-1968 time period. Although the maximum permissible dose at that time was 12 WLM (working level months) per year, average exposures were several times that figure, and ten times higher exposures were not uncommon. Starting in the early 1960s, mounting epidemiological evidence appeared for an excess incidence of lung cancer among these miners; up to 1974, there was an excess of 134 cases (159 observed vs 25 expected) among the 4000 in the group under study (NAS-1980). When this excess became apparent, the Federal Government took jurisdiction, greatly tightened enforcement, and in 1969 lowered the maximum permissible exposure to 4 WLM per year. These standards were met largely by a great improvement in ventilation. As a result of these measures, average miner exposures were reduced 5-fold from 1965 to 1968 and by another factor of 3 by 1970. In 1978, the 4 WLM/year maximum permissible exposure was exceeded by only 37 of 7500 underground miners, for only 16 wars it exceeded by more than 25%, and for only 8 was it exceeded by 502 (AIF-1980). The average exposures to the various groups are listed in Table 1. We see that the average exposure for all miners was 1.03 WLM, and for those who worked essentially full time underground it was 1.45 WLM. For purpose of later discussion, it will be convenient to choose a single value for average exposures. In view of the fact that employment situations and job categories are bound to vary over a lifetime of work, we take this to be 1.3 WLM/year. The purpose of this paper is not to dwell on history, but rather to address the question of whether or not this present situation is satisfactory. This question was considered recently by a study group under the auspices of National Institue of Occupational Safety and Health (NIOSH-1980) and it answered the question in the negative, concluding that the maximum permissible exposure should be substantially reduced. However, their arguments were incomplete and were lacking in perspective. The principal thrust of this paper is to provide some of the material overlooked. RISK TO URANIUM MINERS FROM RADON EXPOSURE In order to quantify the risk to uranium miners under present working conditions, it is first necessary to estimate the risk of lung cancer per WLM of exposure. The most straightforward way of doing this is to use the data on the group of uranium miners under study. These are listed in Table 2 for 8 exposure ranges and for the total group (NAS-1980). If all data are given equal weight, the risk is seen to be 3.5 x 10-6 per year per WLM. Much can be said in favor of using this value for the risk as dose independent; it is within one standard deviation (SD) of the observations in 5 of the 8 dose categories (as expected from the definition of SD), and within 2 SD for all 8, and for the three cases differing from the mean by more than one SD, two are above and one is below. However, the uranium miner exposures in the present situation will be far below those covered in Table 2, so it is worth considering the possibility that the risk differs from this at low doses. From the last column of Table 2 we see that the experience from all exposures below 600 WLM indicates a risk higher than the mean for the entire group by more than two standard deviations (the value 600 WLM in this comparison was deliberately chosen to maximize this deviation; for exposures below 360 WLM and 840 WLM, the excess is only 1.0 and 1.6 standard deviations respectively). In view of this tendency for the risk to be higher at lower dose, we will take the risk to be 5.0 x 10-6 per year per WLM in what we will refer to as model A. This risk estimate is based entirely on exposures much [higher] than those that will be experienced by

Jan 1, 1981

By Ned M. Smith

The Mississippian Salem Limestone, from which dimension stone is quarried in Indiana, is principally a calcarenitic rock formed of fossil bryozoans, echinoderms, and specimens of Endothyra. Numerical associations of the fossils, binding materials, oölitically coated fossils, and voids were determined by counting points on the surfaces of 278 thin sections of the limestone. Median sizes, coefficients of sorting, and skewness numbers were computed from measurements made of constituents in these thin sections. Many other samples and numerous exposures of the Salem and contiguous parts of adjacent formations also were studied. The organisms that furnished the skeletal material for formation of the Salem Limestone were chiefly gregarious and communal. Salem rocks are formed of nearly whole skeletons, of dismembered or slightly damaged skeletons, and of skeletons thoroughly ground up, because currents in the Salem sea varied in their ability to move and damage these materials. Locally the sediments are of uniform grain size because of sorting by currents and because related organisms grew to similar sizes. Rocks of the formation contain different proportions of the fauna both because the animals lived in these proportions and because their skeletons were mixed together by currents. The proportional relationships between members of the fauna were constant locally and for short periods of time. Study and mapping of the faunal associations, numbers of oölitically coated fossils, bedding structures, and size parameters enables geologists to suggest sedimentologic histories and sequences in areas of various sizes. Interpretations based upon such areal studies are necessary for evaluation of the dimension-stone potential within the Salem Limestone.

Jan 1, 1966

By John McMorran

An open pit mine design system should have the characteristics of being flexible, versatile, and simple. All of these characteristics are necessary for producing a dynamic mine design. In other words, a design that can be improved, updated, and implemented. Flexibility is an important characteristic due to changing times. For example, the effects of a changing economy, increased knowledge of the mineral deposit, or improvements in mining technology can result in a considerable, if not a complete change in the long range mining plans. Since the short range mining plans are based on the long range mining plans, they will-also be effected. Also, it is very important to validate the information used in the design or the design itself. This means the system should have the flexibility of being able, not only to detect, but to correct errors. Versatility is another important characteristic of a mine design system due to the wide range of situations that may appear. First, a design system must be able to handle both long and short term planning. This is necessary because of the variability in the definition of a time range. Second, a design system must be able to handle different types of deposits. Special emphasis must be placed on this issue, because many deposits, if not the majority, do not fit predefined categories such as bedded, massive, or roll-front, etc . . . Furthermore, the true test of the versatility of a design system is not only the ability to create an ultimate design but also to schedule sequences for this design. Thus, the versatility of being capable to design with a variety of time ranges, variety of deposit types, and scheduling are all important characteristics of the design system.

Jan 1, 1982

By David R. Kalasky

One of the primary areas of computer application in mine ventilation has been the analysis of mine ventilation networks. A variety of network analyzers that are aimed toward the solution of flows in a given network has been developed. These programs typically use the Hardy Cross or other iterative algorithm for solution of any network, even those that are complex. The computer software has become more efficient and sophisticated over time and has thus been widely adopted for ventilation network analysis. One of the shortcomings of these programs is that they have been developed with the idea of analyzing the ventilation requirements at a single point in the lifetime of a mine. This provides the ventilation engineer with an important tool for analysis but falls somewhat short of providing a convenient means to economically com- pare alternative methods for ventilating a mine. The program described in this paper provides such a tool. The principal concepts that were necessary for the completion of a computer program that analyzes ventilation alternatives is the capability of efficiently determining the ventilation requirements at a variety of times during the lifetime of the ventilation system and some method of analyzing the costs of the alternatives on a realistic comparative basis. To accomplish this task, the authors began using Penn State's mine ventilation simulator designated as PSU/MVS, Didyk et al. (1977a, 1977b) and added the necessary additional software to accommodate the need for multi-period, time-dependent analysis of the net- work. The software was then tested on a coal mine ventilation problem with a 23-year life. The problem points out the value of such a program for ventilation analysis.

Jan 1, 1986

By J. A. Herbst, Z. Rogovin

In order to develop more accurate procedures for scale-up and design of semi-autogenous grinding mills through detailed mathematical models, a better understanding of the charge motion and rocklball segregation is needed. To achieve this a 0.61 m (2.0 ft) diam by 0.305m (1 .0ft) length plexiglas mill was constructed as a scale model of a commercial SAG mill. Rock motion in the rotating mill was simulated using various sizes of ceramic balls. Quantitative measurements of dynamic angle of repose, water and slurry motion, holdup and size segregation of the charge were taken. In addition, a video presentation (available to the public) was prepared to elucidate charge and water motion at various mill speeds, charge volumes, rocksize distribution, and flow rates.

Jan 1, 1990

By P. T. Kane, O&apos

Capital and energy are the dominant cost factors in nickel production from laterites. Since the 1973 energy crisis, pyrometallurgical developments have been oriented towards lower cost sources of energy and higher grade ores and hydrometallurgy towards higher recoveries and greater flexibility in types of ores treated. Energy recuperation offers some potential, but at a price. 'The lower energy acid leaching process is indicated to have the greatest potential, particularly with its inherently high cobalt recovery.

Jan 1, 1979

By G. W. Luxbacher

Coal mine infrastructure is rarely designed solely on the basis of ventilating the underground workings. Instead the optimization of a mining sequence, the minimization of coal quality variation, reduction of coal losses by adapting to property boundaries and geologic structure (seam inclination, roof conditions, coal thickness, etc.) or other similar considerations have formed the objective for mine plant design and layout. Infrastructure development may also reflect a desire to maximize production early in the life of the mine or to permit flexibility in mining according to market conditions. Requirements for coal mine ventilation, established by the 1969 Coal Mine Health and Safety Act, have mandated changes in the traditional concepts of mine plant design in the United States. Mines, in operation prior to the passage of the Act have experienced severe limitations when attempting to adapt the existing mine infrastructure to meet the requirements of the law. In addition the increased quantities of air required, velocity limitations on trolley haulage and belt lines, the establishment of separate intake escapeways and gob area ventilation have com- pounded the inherent complexity in planning mine ventilation systems. Past practices in mine ventilation planning and design are no longer adequate. Given the complexity of today's ventilation systems, effective planning and design approaches are required. As such, the interrelationship between the overall coal mine plant design and ventilation system design is examined. An approach to ventilation system design constrained by global considerations of mine plant design, is presented. The proposed approach is, however, applicable to the design of new mine ventilation systems as well as to the modification of existing systems.

Jan 1, 1980

By R. S. Rickard, B. Ball

INTRODUCTION Pyrite responds to the flotation reagents normally used in sulfide flotation systems. For example, it is well known that xanthates are good collectors for pyrite, and cyanide, sulfide and hydroxides are depressants. The particular response of pyrite to these and other reagents is used to advantage in several areas. By careful control of depressant and collector additions, pyrite can be separated from other sulfides by flotation. This is of obvious importance in base metal sulfide flotation where pyrite depression is often required to produce a marketable grade concentrate. Flotation of pyrite has long been employed in gold ore processing, and it appears that pyrite flotation from coal may become important in the future (1). It is probably a direct consequence of this relative ease of separation, plus the low economic value of pyrite, that detailed investigations on the chemistry of its flotation and depression are relatively limited. Gaudin (2,3,4) and others, in the mid-1950's published data on the flotation of pyrite, but detailed or consistent mechanisms were lacking. In 1955, Sutherland and Wark's book (5) was published, in which a large amount of empirical information, especially earlier work of Wark and Cox, was presented. More recently, in 1968, significant contributions have been made by Fuerstenau et al. (6,7) and Majima and Takeda (El. These papers introduced electrochemical explanations of the effects observed with xanthate and cyanide ions.

Jan 1, 1976

By William A. Vogely, Robert T. Deacon, Walter J. Mead

Oil and gas together are the most important energy sources consumed in the United States. In 1983, 67% of total energy consumption was represented by these two resources (43% was oil and 25% natural gas), while coal accounted for only 23% of U.S. energy use. All other sources (hydroelectric, nuclear, geothermal, wood and other waste products) accounted for only 10% (U.S. Department of Energy, 1983, p. 1). In this chapter we address the issue of regulation in the oil and natural gas sectors of the U.S. energy industry. In addition, we analyze the cartel characteristics of the Organization of Petroleum Exporting Countries (OPEC). If OPEC is an effective cartel, then U.S. oil as well as substitute energy prices, production, and consumption will be affected by cartel action. Further, as the nation learned in the 1970s, major changes in oil prices produced major disturbances in other sectors of the U.S. and world economies. Consequently, it is important to determine whether the roughly ten-fold increase in nominal prices that occurred in the 1970s was the result of cartel action, the result of normal economic forces adjusting to the fact that the world was running out of cheap oil, or some combination of the two. Furthermore, the presence of OPEC- associated oil price increases is related to regulations that were imposed on the energy sector during the decade of the 70s. THE RATIONALE FOR GOVERNMENT INTERVENTION Economists have traditionally judged the state of an economy to be efficient if it is impossible to improve the welfare of any one member of society without harming someone else. Any economy that satisfies this condition is said to be Pareto efficient, after the Italian economist Vilfredo Pareto who first gave rigorous attention to such questions (see Chapter 4.10). It is easy to see why an economy that fails to satisfy this condition could not be efficient; by definition, it would be possible to alter the allocation of resources in a way that improves everyone's welfare.' Much of the appeal of this weak efficiency criterion is that it avoids comparisons of levels of well being among different individuals. The cost of such generality, however, is that in any given economic system a wide array of different Pareto efficient states will typically be attainable. In the simple Robinson Cursoe economy of the undergraduate textbook, for example, efficiency could just as easily be attained in the case where most of the island's resources are owned by Friday as in the case where they are under Crusoe's control. However, the distribution of welfare among the two inhabitants would obviously be quite different in the two situations. Such equity issues cannot be settled on objective or scientific grounds. To decide which distribution of welfare is socially "best" an explicit value judgment is needed. It is useful to keep in mind the preceding distinction between efficiency and equity issues when analyzing the role of government in a market economy. Decentralized market processes will not necessarily result in a distribution of welfare that society considers just. For this reason a potential role for government lies in the redistribution of income among individuals. In some circumstances, however, market pro-

Jan 1, 1985