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By Kerry M. Masson

Perhaps the hottest item on the agendas of most state legislators this year is the state budget. The main question: Where will all the dollars come from to finance health care programs, state jobs, unemployment compensation programs, and on and on? This is especially so since people are out of work, business bankruptcies are up, sales are down, and incoming revenues from some sources have decreased or dried up. A sure bet is that state taxes will be increased in some form or another. The mining industry could face increased income taxes, property taxes, severance taxes, or even a host of new taxes (if the state does not already have them) like a gross receipts tax, investment tax, or tax on revenues made outside state borders. That's bad news for an already depressed industry, even though increased taxes may be the least of the industry's worries in the current economic climate. While reopening existing mines and developing most new mineral projects depends primarily on higher commodity prices, new taxes still could pose long term concerns for mine project development. Just how mineral tax law impacts a project is not easy to figure. It involves a complex set of calculations based on interpretations of numerous federal, state, and local tax laws that change almost annually. At best, projections of tax effects for the life of a mine are educated guesses. At the same time, projections are necessary to evaluate the economic feasibility of a mineral project. At a recent Technology Transfer Seminar, the US Bureau of Mines introduced a computer software program designed to evaluate the feasibility of a mineral project and to determine the tax effects on the project's discounted cash flow rate of return (DCFROR). The program, called MINSIM, began in 1967 as a 200-statement FORTRAN II program for evaluating a hypothetical large-scale open-pit gold mine. This single-commodity oriented program employed discrete simulation techniques and a continuous DCFROR was used to measure the effect of changes in revenues and costs. Over the past 15 years, MINSIM has developed into a program 70 to 100 times larger than the original. Basically, it will analyze costs and parameters specific to an identified deposit, then determine the DCFROR. Or by using a specified DCFROR, it will determine the primary commodity price required to attain that specified rate of return. MINSIM, which is explained in detail in this article, is available from the Division of Minerals Availability, USBM free of charge. Written in FORTRAN IV, it comes on punch cards or magnetic tape and is compatible with most major computer systems. The MINSIM Program The main objective of any freeenterprise mining venture is to make a profit. To determine profitability of a given project, alternate methods of operating and financing must be evaluated. That is the purpose of MINSIM. While there are a number of methods of evaluating the economic profitability of a mining project, MINSIM uses the Discounted Cash Flow Rate of Return (DCFROR) method as its major criterion because DCFROR considers the time value of money and gives the truest measure of profitability. One disadvantage is that the calculations are deposit oriented. In other words, MINSIM analyzes only those costs and parameters specific to the deposit. It cannot be used to evaluate the overall corporate picture. The program is designed to simultaneously handle five different commodities and a leach operation for any type of mining project. For example, analysis of a coal project would include only one commodity-coal at the mine mouth. Analysis of a copper operation might include numerous commodities-from the raw material to the refined product. Input MINSIM considers capital investment-recoverable exploration, acquisition, and development costs; depreciable capital investments such as mine plant and equipment, mill plant and equipment, and infrastructure costs; all general and commodity specific operating costs; and the cost of alternate financing methods. The program has the capacity to incorporate different types of depletion allowances, numerous commodity-dependent severance taxes, variations of property taxes, and many methods for calculating state or provincial taxes. There are even many different ways to calculate federal and national taxes. The capacity to handle tax variations is generated from an internal subroutine in the program called the "open file." The user can reconstruct, customize, or evaluate any kind of tax desired. Outputs Given this kind of capacity for numerous input parameters, MINSIM is capable of the follow¬ing major outputs:

Jan 3, 1983

By J. Pang, S. Chander, A. Briceno

The mechanism of sulfur oxidation in pyrite is a function of the rate and driving force for oxidation. New evidence is presented to show that, at moderate potentials, a sulfur-rich hydrophobic layer is formed. Under ordinary conditions, the sulfur layer is covered with a layer of iron oxides, hydroxides, sulfate or oxy-sulfide ions. Pyrite is hydrophilic under these conditions. In the presence of iron-chelating agents or iron sequestering ions, an iron layer might not form. Under these conditions, the sulfur layer is exposed, and the pyrite might become hydrophobic. Stronger oxidizing conditions decompose the sulfur layer, thereby making the surface hydrophilic.

Jan 1, 1994

By J. D. McKendrick

Alaska's Arctic Slope lies between the Brooks Range and Beaufort Sea and is a region about the size of Nebraska. It has some of Alaska's richest hydrocarbon deposits. In addition to containing petroleum and natural gas. Much of the area west from the Colville River has low-sulfur coal deposits which are shallow enough for surface mining. Developing those resources will require a firm and realistic' commitment to protecting and rehabilitating the natural habitats. Balancing such a commitment with economic constraints in a practical sense requires knowledge of the environment and its associated biological components, i.e. the soil/water-plant-animal relationships.

Jan 1, 1988

By Patrick M. Hurley

The spreading-ridge, or accreting plate margin, is the primary conduit of metals delivered to the earth's surface. Isotope ratios of lead show primitive mantle values at these sites, indicating that this is true. We can use lead isotopes in any mineral deposit to indicate the degree to which the metal is "primitive" in the sense of having been uncontaminated with U-enriched crust or "crustal" in the sense that it has been cycling at the earth's surface since earlier times. The reason for this is that the upper continental crust has an enrichment in the ratio of U/Pb over that in the mantle, so that old continental leads have a larger radiogenic component. The primitive metals delivered to the surface at the spreading-ridge are transported on the oceanic plate until they reach a subduction zone. Here they become cycled in the "orogen". However, in this process the primitive metals are mixed with metals from the continent so that the average lead isotope ratios are between those in the mantle and the average upper continental crust. Subsequently a part of the metals in the orogen may become fixed in a new block of continent. However there are processes which continue to uplift and erode ancient continental regions so that there is a continuous feeding back of metals to the orogen. We have therefore a cycling of metals from the existing continental crust into the orogen where they are mixed with new contributions from the spreading ridge and mantle.

Jan 1, 1977

By Jack G. Pippenger

This report focuses on the procedures required to review, prepare specifications, bid, and purchase a fully integrated computer system for utilization by engineering personnel in all phases of mine engineering. The presentation is based on the experiences encountered in 1984 in procuring an engineering computer system at The North American Coal Corporation's Western Divi- sion. A two-phase report detailing the purchasing process and subsequent utilization of the engineering computer system will be given. Special detail is also provided on the final system hardware and software setup.

Jan 1, 1989

By D. J. Kennedy, W. G. Klinowski

Over the past few years the Cape Breton Coal Research Laboratory's staff designed, built, tested and proved the necessary hardware, software and methodology of tracer gas based surveying techniques applied in the field of mine ventilation. These methods are now used routinely in a variety of applications where traditional anemometric methods do not provide the required accuracies or cannot be effectively employed. Irregular or highly turbulent flows, leakages, geometrically complicated or highly obstructed airways are just a few examples where traditional anemometry can produce unacceptable errors in calculated ventilation parameters. Tracer gas based ventilation techniques have been used in many problematic situations where the standard ventilation methods are inadequate. One such problem, faced by many mine operators, is the emergency imposed by the ever present threat of a mine fire. An understanding of the propagation of smoke contaminants and the demonstrated integrity of appointed escape routes can save lives and property during a fire. That knowledge can be gained quickly and inexpensively by the application of tracer gas smoke simulation methods. The concept of controlled air recirculation has recently gained considerable attention in the mining industry. While mathematical models can be used to predict performance, the ultimate proof of a ventilation system's performance can best be provided by a tracer gas based simulation of contaminant levels. Fan performance tests and assessment of auxiliary ventilation systems are highly dependent on accurate definition of airflows; precise data can be easily obtained by tracer gas based volumetric surveys. This paper contains a brief description of the equipment and the methodology of tracer gas based ventilation techniques and presents typical examples of their use

Jan 1, 1991

By Robert D. Brown, Charles A. Sorrell

The decade of the 1980's saw "advanced materials" become a key factor among the industrialized nations, with the United States, Japan, and the European Economic Community being the major competitors. All three have identified communications technology, advanced materials, and biotechnology as the keys to future industrial leadership and the closing decade of the 20th Century is expected to be an era of rapid development and restructuring. The progress of EC'92, the effort to develop uniform standards and remove trade barriers in Europe; the determination of Japan to commercialize advanced structural ceramics, alloys, composites, and superconductors; and the emergence of less developed countries as major supplies of commodity materials pose enormous challenges to the position of the United States as an industrial and financial leader. A consensus is developing that the industries that are first to commercialize the large array of new structural materials and electronic, optical, and magnetic materials and devices will be those who determine the structure of national and world economics. Many technical, economic, legal, political, social, and cultural factors are important determinants in the race to commercialize new materials. Millions of words have been written about these factors and their interdependence; yet the sheer complexity of the problems, the rate at which changes are taking place, and the economic risks involved are so great that government policy makers and industrial decision makers find adequate understanding to be very difficult. Of the many factors involved in advanced materials, the Bureau of Mines has the statutory responsibility to provide information on where materials can be found and how they are mined, extracted, purified, combined, and recycled. It is obvious that minerals availability is essential to implementation of any new technology just as there can be no commodity metals industry if the ores are not available. Because "minerals availability" for commercialization of advanced materials and devices is more complex than for commodity materials and a new mix of materials and processes is emerging, the Information and Analysis Directorate of the Bureau of Mines is redirecting resources to provide reliable information for policy and decision making. The Office of Advanced Materials Coordination (OAMC) was established as a staff operation in July 1987 to assist the efforts of the divisions and branches. The key issues and problems were defined and the role of the Bureau was outlined (Sorrell, 1987, 1988). In February 1990, the functions of OAMC were transferred to the new Branch of Advanced Materials, a line organization parallel with the Branches of Ferrous, Nonferrous, and Industrial Minerals, and was given the responsibility for developing new methods to acquire, analyze, and disseminate information about new materials. The purpose of this paper is to provide definitions, a summary of major issues and problems, an overview of minerals and processing availability problems, and a perspective of the ways in which the mining and materials industries can help to ensure domestic availability of raw and processed materials.

Jan 1, 1990

By R. J. Pruett, J. Yuan

Kaolin clays from five different commercial deposits in Georgia were studied to understand the variations of zeta potential and related fundamental properties. The results suggest that higher negative zeta potential is related to exchangeable or soluble calcium ions in the clays.

Jan 1, 1999

By J. E. Gebhardt, D. King

Field-testing of a new on-stream X-ray fluorescence analyzer was conducted in a copper concentrator. The evaluation of copper tailings and concentrate streams indicated a statistically acceptable correlation with laboratory chemical analyses. The new equipment employs a “components off-the-shelf” approach to minimize capital cost and maintenance issues and to utilize the latest advancements in X-ray fluorescence detector technology and computer capability. A general description of the system is provided, and performance of the analyzer measuring copper (Cu), iron (Fe), and molybdenum (Mo) is presented.

Jan 1, 2003

By Milton F. Searl

Introduction The urgency of further development of our domestic energy resources becomes more apparent every day. The production capability of existing facilities, taken in the aggregate, declines perhaps 10% per year; imported energy is expensive if available at all; conservation helps reduce demand but eventually will reach a point of diminishing return; new energy sources are promising but past experience, as with nuclear power, teaches us lead times are long and success is not assured. To approach the energy future rationally, it is essential to have some idea of the size of the nation's remaining energy resources, their characteristics, and the degree of uncertainty involved in their estimates. Resources are, of course, only one end of a long chain leading to energy supply to the ultimate consumer. They are an essential element, however, and the only one not under society's control. Given that the resources and a national will to produce the energy exist, it is possible to convert the resources to supply in, generally, an environmentally reasonable manner. However, the process of developing supply takes time. Government must permit access to the resource, and remunerative prices and further evolution of technlogy are required. This paper does not deal with these essentials, but they must not be forgotten. This discussion is limited to coal, oil, natural gas and gas liquids, uranium, and oil shale. Other energy sources are discussed elsewhere in this issue. Crude Oil Conventional crude oil resources are of greatest concern today, given our dependence on imported oil and its rapidly rising price. Estimates of oil originally in place (OOIP) range from 619 billion bbl to 1,094 billion bbl, differing by almost a factor of two (Table 1). This is surprising because the U.S. is a mature petroleum province with over 120 billion bbl produced and over 400 billion bbl OOIP discovered. Differences in the estimates involve differences in the experience of the various estimators, the interpretation of present geologic information and historical statistics, the methodology, and probably the extent (i.e., water depths) for which offshore resources are included. The range shown for the estimate of a given estimator appears to be primarily due to geologic uncertainty. This uncertainty can be measured by taking the ratio of the low and of the high estimate to the expected estimate for that information source. The low estimates range from 0.85 to 0.87 of their respective values. The high estimates range from 1.18 to 1.27 of the expected values. In all cases the high estimate is further from the expected value than the low,

Jan 1, 1980

By Searl. Milton F.

Introduction The urgency of further development of our domestic energy resources becomes more apparent every day. The production capability of existing facilities, taken in the aggregate, declines perhaps 10% per year; imported energy is expensive if available at all; conservation helps reduce demand but eventually will reach a point of diminishing return; new energy sources are promising but past experience, as with nuclear power, teaches us lead times are long and success is not assured. To approach the energy future rationally, it is essential to have some idea of the size of the nation's remaining energy resources, their characteristics, and the degree of uncertainty involved in their estimates. Resources are, of course, only one end of a long chain leading to energy supply to the ultimate consumer. They are an essential element, however, and the only one not under society's control. Given that the resources and a national will to produce the energy exist, it is possible to convert the resources to supply in, generally, an environmentally reasonable manner. However, the process of developing supply takes time. Government must permit access to the resource, and remunerative prices and further evolution of technology are required. This paper does not deal with these essentials, but they must not be forgotten. This discussion is limited to coal, oil, natural gas and gas liquids, uranium, and oil shale. Other energy sources are discussed elsewhere in this issue. Crude Oil Conventional crude oil resources are of greatest concern today, given our dependence on imported oil and its rapidly rising price. Estimates of oil originally in place (OOIP) range from 619 billion bbl to 1,094 billion bbl, differing by almost a factor of two (Table 1). This is surprising because the U.S. is a mature petroleum province with over 120 billion bbl produced and over 400 billion bbl OOIP discovered. Differences in the estimates involve differences in the experience of the various estimators, the interpretation of present geologic information and historical statistics, the methodology, and probably the extent (i.e., water depths) for which offshore resources are included. The range shown for the estimate of a given estimator appears to be primarily due to geologic uncertainty. This uncertainty can be measured by taking the ratio of the low and of the high estimate to the expected estimate for that information source. The low estimates range from 0.85 to 0.87 of their respective values. The high estimates range from 1.18 to 1.27 of the expected values. In all cases the high estimate is further from the expected value than the low,

Jan 9, 1980

By Gerald H. Luttrell, Roe-Hoan Yoon

Flotation columns are becoming increasingly popular due to their ability to improve selectivity and to reduce operating costs. Unfortunately, these advantages are not often realized because of poor operating practices and difficulties associated with design and maintenance. This article provides guidelines for the operation and design of columns. The discussion will focus on designing proper wash water systems for improved selectivity, maximizing throughput by increasing the bubble surface area rate, and minimizing operating and maintenance costs. It is suggested that the design of the air sparging system is the most critical element in column flotation.

Jan 1, 1993

By G. H. Lewis, C. L. Krcil, N. S. Harding, D. E. Havekotte

INTRODUCTION Limestone injection work was completed in a 440-kW (1.5-million Btu per hour) pilot-scale combustor in preparation for a 50,000-kg/h (110,000-lb per hour) industrial steam boiler limestone injection test program. The main objectives were to: (1) identify the important variables that affect sulfur capture, (2) determine the maximum SO2 removal, and (3) determine the effect of limestone addition on furnace operability and heat transfer. A more detailed report is given by Lewis et al. (1985). The test program was divided into two phases. The objectives of Phase I were to determine the important variables that affect SO2 reduction and to investigate the effect of limestone addition on combustor operation and heat transfer surfaces. The objective of Phase II was to determine, using only the important variables identified during Phase I, the conditions that resulted in the greatest sulfur dioxide reduction. Phase I Test program Using one limestone, five variables were identified as having an effect on SO2 reduction. These are noted with their respective ranges: heat release rate [103 to 166 kW/m3 (10,000 to 16,000 Btu per hour-cu ft)], Ca/S molar ratio (0 to 3), flue gas oxygen concentration (3% to 5%), additive particle size [90% -150 µm (-100 mesh) and 90% -45 µm (-325 mesh)], and burner stoichiometry (SR = 0.75 and >1.15). A 2.3% sulfur northern West Virginia coal, pulverized to a nominal grind of 70% -75 µm (-200 mesh), was burned for the tests. The limestone used was obtained from a Maysville, KY, quarry and contained 51.75% (wt) CaO. An 11-run statistically designed program (plus three duplicates) was used to screen the five variables. The effect of limestone injection on the combustor heat transfer surfaces was determined by comparing the heat transfer rates through a slag panel and fouling probes during periods with and without limestone injection. Combustor operation was determined by noting any operating problems that occurred during the tests. Test procedure After furnace wall temperatures had stabilized at operating conditions, heat transfer surfaces (slag panel and fouling probes) and the convection section were blown clean, and a four-hour test was begun. The

Jan 1, 1987

By Haydn H. Murray

The three major catalyst markets that utilize industrial minerals as raw materials are petroleum refining, chemical processing, and emission control. Because of economic, competitive, and regulatory pressures, catalyst producers are pushed to develop products with improved performance to meet changing environmental standards. Also, refiners are demanding new families of cracking catalysts that will crack residual fuels. In 1987, worldwide cracking catalyst sales amounted to $457 million (Occelli, 1988a). Recently enacted federal and state laws to improve air quality have prompted strong growth for environmental catalysts, which in 1989 accounted for more than a third of the $1.9 billion catalyst market in the United States (Farrauto, Heck, and Speronello, 1992). A catalyst is a material that promotes or enhances a chemical reaction but does not itself enter into the reaction. One of the more important mineral groups used as catalysts is clays. The first recorded use of clay as a catalyst was its use in the dehydration of alcohol (Bondt et al., 1797). Clay minerals that are used as catalysts are kaolinite, halloysite, smectite, palygorskite, and sepiolite. Minerals used as catalysts, catalyst supports, or as a raw material to make zeolites are kaolinite, halloysite, sodium montmorillonite, calcium montmorillonite, hectorite, palygorskite, sepiolite, talc, calcined kaolinite, gibbsite, chlorite, and titanium dioxide.

Jan 1, 1994

By H. E. Epstein, B. K. Parekh, W. M. Goldberger

Comminution is the single most expensive operation in mineral processing. It consumes about 50% of the energy required for mineral extraction (Agar, 1976). Current comminution technology is both energy-intensive and inefficient. A novel noncontact comminution process concept was developed in this study, whereby selective lib¬eration of minerals from an ore could be potentially achieved. The process involves application of electric and ultrasonic energy to liberate minerals from gangue particles. Introduction The mineral industry is a large user of energy in the US. Energy usage is increasing as the grade of ores processed decreases. It is es¬timated that comminution of ores uses about 32 000 kWh (115 trillion kJ), or 2% of the electric power produced in the US (NMAB-365, 1981). Among other minerals, ce¬ment, iron, and copper processing plants are the largest users of en¬ergy in comminution. Very little of this energy used in conventional grinding (about 1%) is used to gen¬erate new surface. The remainder is wasted (Table 1). Thus, there are substantial energy-saving and economic incentives to improve the efficiency of crushing and grinding techniques for mineral recovery. With an energy efficiency of only 1%, it would seem possible to devise methods to significantly improve comminution technology. This requires that breakage force be applied only where needed, not indiscriminately as in a conven¬tional ball mill (NMAB-365, 1981). Can apparatus and methods be de¬ veloped for large-scale commer¬cial use that allow energy to be fo¬cused at intergranular bounda¬ries? If this can be done, mono¬mineral grains would remain in¬tact and the grinding action would be selective and substantially more efficient. The novel comminution process concept described in this paper uses a combination of electric and ultrasonic energy. This energy breaks the ore and selectively lib¬erates minerals. The process has also been termed a two-stage or electroacoustical comminution process (Goldberger, Epstein, and Parekh, 1982). The mineral grain boundary is usually the weakest area in an ore. By applying electri¬cal energy to the ore, the rock frac¬tures mostly at grain boundaries. At the same time, the electric shock creates secondary hairline fractures in the ore. Additional application of ultrasonic energy to this ore provides further break¬age. The concept was proven on a molybdenum porphyry ore but needs additional study. Technical Background There have been substantial im¬provements in milling machinery and grinding operations, but rela¬tively few attempts have been made to develop alternatives to conventional impact milling. Sev¬eral methods, however, have been investigated that relate to this study. In the early 1970s there was considerable interest in a size re¬duction method known as the Snyder Process (Cavanaugh, 1972). It involved charging coarse ore into a pressure chamber, pressur¬izing with a gas, and activating a quick-opening (15 msec ) dis¬charge valve that connected the chamber to a discharge duct. This allowed solids to fluidize and ac¬celerate, subjecting the material to a variety of impulse phenomena that caused the desired size reduction. Other nonimpact means of achieving breakage and selective size reduction have been de¬scribed in technical and patent literature. Kanellopoulos and Ball (1975) considered using heat to induce thermal stress in quartz¬ite. This would cause cracking and, thus, increase grinding efficiency. The use of electrical energy to induce thermal stress was studied by the General Elec¬tric Co., in cooperation with the Montana School of Mines, under a research grant from the Anaconda

Jan 9, 1984

By D. Papacharalampos

A combination of decision- theoretic and knowledge-based methods can be used to classify rock-types from satellite data both efficiently and accurately. An expert system utilizes knowledge-based rules, as a field geologist does, to produce results that make geological sense. Our expert system (GEMS), first processes background information from preexisting knowledge and develops a plan, then classifies individual pixels, and finally generalizes the results using geological rules and plots a map. The system is implemented on a microcomputer and is inexpensive enough to be a part of the standard equipment of any geologist who prepares reconnaissance maps.

Jan 1, 1986

By R. Hogg, P. Bunnaul

Sedimentation in highly, flocculated suspensions of fine particles, such as clays, occurs through individual settling units (flocs) that have very open structures and correspondingly low densities (typically less than 5% solids by volume). Such settling processes rapidly lead to the buildup of a bed of flocs that are essentially close-packed, with an inter-floc porosity of perhaps 50%. However, the overall solids content is no more than about 2% to 3% by volume. Consequently, the thickening process is dominated by the bed consolidation rather than by the simple settling of the individual flocs. Experimental measurements of sediment consolidation in flocculated clay suspensions indicate, for a given system, that consolidation rates are essentially determined by the solids concentration and can be evaluated using the classical Kynch treatment. However, these rates are strongly dependent on the physical, as well as the chemical, conditions of the flocculation process. Furthermore, the extent to which gravity consolidation proceeds depends on the total weight of the sediment (i.e., on the bed height and the solids concentration). The implications with respect to thickener operation and the requirements for the laboratory testing for thickener design are discussed.

Jan 1, 1993

By Y. Akin, M. S. Celik, T. Batar, F. Arslan

Despite its importance in various diverse industries, research on beneficiation strategies of boron minerals has not received enough attention. Boron minerals are primarily upgraded by wet processing methods. However, severe environmental constrains have accelerated the development of dry processing techniques such as calcination. Interestingly, the boron minerals colemanite, ulexite and borax undergo decrepitation, shrinkage and expansion, respectively, upon heat treatment. Each mineral then requires a different beneficiation scheme. In this study, laboratory and pilot-plant studies conducted in our laboratories on the calcination of boron minerals are briefly reviewed and their implications to commercial operations are discussed.

Jan 1, 1999

By Anthony Peach, Lok Home

Introduction Raise boring is the most accepted form of mechanized hard rock boring in the mining industry. It appeared logical to take this mechanization one step further by introducing computers. Atlas Copco Jarva has produced a series of raise boring models that use an integrated computer. The company decided to use electronics and computerization, not for marketing purposes, but to make its equipment more cost-effective. Basis of Cost-Effective Design From the manufacturer's standpoint, it is possible for the equipment owner to reduce the cost of putting in raises by: • Replacing existing components with less expensive components that produce the same results; • Replacing existing components with more expensive components that make the equipment more productive; • Mechanizing equipment to reduce associated labor costs; and • Combining the above. Analysis of a standard raise boring machine (RBM) system showed that little could be done with less expensive components. It appeared, however, that the RBM could be more productive by transmitting more horsepower through the expensive drill string, while being precisely controlled by computers. An RBM system includes a basic machine, drill pipe, accessories, reamer, and cutters. The approximate percentage cost of various components on a standard system capable of boring 300 m (985 ft) long and 3-m-diam (10-ft-diam) aises in medium to hard rock is shown in Table 1. Also shown is the increased cost above standard of the Jarva computerized machine, and the productivity of both. Increased Productivity Penetration is important during the reaming cycle for more productive raise boring. This is possible by increasing the cutter load with constant rpm or increasing the rpm with constant cutter load. To increase thrust and maintain rpm requires increased capacity in the cylinders, drive train, main thrust bearings, drill string, electrical motors, and power units. To increase rpm and maintain cutter load requires only increased capacity in the electrical motors and power units. This is possible because the torque requirement remains constant for a constant thrust load. Only the horsepower increases, proportional to rpm. Since cutter costs are a big factor in raise boring, changes in machine performance must be analyzed to assess the effect on cutter performance. With a standard or typical carbide cutter, as used on raise boring machines, the effects of increased thrust or rpm are shown in Table 2. The assumption is made that the base data is the current rpm and thrust range where the cutters are now operated. It is also assumed one variable is held constant while the other increases. The result of this comparison, approximately, is that a 50% penetration increase can be achieved with little or no increase in cutter cost if rpm is increased 50% and cutter load is maintained constant. A similar 50% penetration increase can be achieved with a 45% increase in cutter cost, if the cutter load is increased by 20% and maintained constant. From an equipment standpoint, it is significantly less expensive to increase rpm 50% than it is to in-

Jan 7, 1984

By J. G. Smith, L. P. Sheets

Introduction Potential applications that exploit the electrical properties of coal measure rocks include: (1) radar sensing of coal face, floor, and roof for automated mining operations; (2) underground wireless communications; and (3) sensing extent of subsidence, blasting operations, coal gasification bums, and moisture migrations. Impediments to exploitation of electrical properties include: (1) a lack of reliable electrical properties data for in situ conditions and (2) a lack of correlation data between electrical properties and other relevant physical properties. In this paper data are presented for electrical conductivity and permittivity for Appalachian and Illinois shales for a frequency range 2 x 10 to 2 x 10 Hz. These data are useful in establishing in situ electrical property variability, lower limits, and anisotropy. Electrical proper¬ties measurement and values for other coal measure rocks are discussed as well. Laboratory measurement For the frequency range investigated, a capacitance bridge and Q-meter were employed. These instruments are designed to yield bulk values of permittivity and conductivity. Disk samples of thickness 0.396 cm (0.156 in.) and diameter 2.54 cm (1 in.) were machined from cores obtained from the two coal basins. While both the capacitance bridge and the Q-meter must be balanced manually, the bridge has an analog-to-digital interface and an attached computer specifically designed to expedite data collection and interpretation. Sample holders are critical components in the measurement process. A Hartshom-Ward holder was employed with the bridge and a Marconi micrometer jig was used with the Q-meter. Neither commercial sample holder was designed to regulate ambient humidity conditions. Because water adsorbed on sample faces may cause errors approaching 100%, special enclosures were designed for both holders. Each enclosure contains a flush-mounted externally-manipulable carousel, an externally-manipulable rigid arm that can accomodate translational motion and three-dimensional rotation, a compartment for humidity regulating solids or liquids, and a humidity sensor. Each enclosure will accomodate several samples that can be manipulated within the enclosure without opening it. Experience gained during this research demonstrated that humidity regulation was necessary to obtain repeatable results. Grinding and polishing shale to a very thin thickness (about 0.4 mm) was shown to cause changes in electrical properties as well. These latter changes were attributed to alterations in the water content. Theoretical considerations A very comprehensive discussion of the electrical properties of sedimentary rocks is available in literature (Sen and Chew, 1983). These authors reviewed the work of others and proposed modifications to better explain the frequency dependent behavior of the permittivity and conductivity of rocks. A large portion of their article was devoted to explanations of large relative permittivities at low frequencies such as observed in this research. They noted that the electrical properties of formations containing shales and clays are the most difficult to explain. Sen and Chew noted the need for additional experimental data and further refinements in theory. Results Shales, limestones, and sandstones were examined for a single 150-m (492-ft) core from Pennsylvania and for a dark shale from a southern Illinois coal mine. Figures 1 and 2 illustrate the conductivities and relative permitivities for the southern Illinois dark shale at a single location. The differences in electrical properties clearly

Jan 1, 1987