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By Alfred Saulniers

El presente texto describe los cuatro mitos sobre las empresas públicas en Latinoamérica. El primer mito refiere al concepto de empresa como algo definido, donde hay una sola definición"correcta" del término puesto que se usaron diferentes enfoques (administrativo y jurídico) y por ende, se crean problemas en la evaluación del comportamiento de empresas públicas. El segundo mito señala que la empresa pública en Latinoamérica es un fenómeno post- depresión -en tanto es el resultado de la depresión de la segunda guerra mundial y estas se limitaron a generar una infraestructura mínima de apoyo a explotadores de la riqueza agrícola de la región. El tercer mito muestra que las empresas públicas son parásitos paraestatales, cuya función primordial es engullir subsidios de las aarcas públicas. El error estriba en el concepto errado del término subsidio y donde se aplica a una situación de dependencia perpetua impueta a la empresa. El último mito señala que las empresas públicas son inferiores a las empresas privadas debido a la clasificación por la naturaleza de su propiedad.

Jan 1, 1986

Underground testing was carried out by Ingersoll-Rand, Inc., under contract to the Bureau of Mines to determine the effectiveness of a machine-mounted scrubber system for ventilating the face during an extended advance. A continuous miner equipped with an integral flooded-bed dust scrubber system was instrumented with methanometers and Real-time Aerosol Monitor (RAM) dust monitors. Methane and respirable dust data were collected at brattice setbacks of 7.5 m (current operating distance), 10.5 m, and 15 m (blowing ventilation) during production shifts. Results showed that a suitable machine-mounted scrubber system can adequately ventilate the face at brattice setbacks up to 15 m. No deterioration in ventilation performance was observed as brattice setbacks were increased from 7.5 m to 15 m. The scrubber system effectively controlled face methane levels at large setbacks, though respirable dust levels increased as much as 33 pct at the operator's cab at setbacks greater than 7.5 m.

Jan 1, 1986

By John C. Edwards

The Bureau of Mines developed a mathematical model to predict the oxygen requirements for a miner evacuating a mine. The model accounts for variations in the miner's escape speed with mine airway height, and for the empirically determined expressions for the weight-specific oxygen uptake rate for upright walking, stooped walking (duck-walking), and crawling. A Fortran computer program that is user oriented was prepared based upon the model's constitutive equations. Specific instructions for utilizing the program, as well as applications to miner evacuation from a mine, are presented.

Jan 1, 1986

By Donald E. Stump

Subsidence from underground coal mining alters surface water discharge and availability. The magnitude and areal extent of these impacts are dependent on many factors, including the amount of subsidence, topography, geology, climate, surface water - ground water interactions, and fractures in the overburden. These alterations may have positive and/or negative impacts. One of the most significant surface water impacts occurred in July 1957 near West Pittston, Pennsylvania. Subsidence in the Knox Mine under the Coxton Yards of the Lehigh Valley Railroad allowed pan of the discharge in the Susquehanna River to flow into the mine and create a crater 200 feet in diameter and 300 feet deep. Fourteen railroad gondola cars fell into the hole which was eventually filled with rock, sand, and gravel. Other surface water impacts from subsidence may include the loss of water to the ground water system, the gaining of water from the ground water system, the creation of flooded subsidence troughs, the increasing of impoundment storage capacity, the relocation of water sources (springs), and the alteration of surface drainage patterns.

Jan 1, 1986

A Master of Applied Science degree course in Mining Geomechanics commenced in 1983 at The University of New South Wales, taught by extern- al (correspondence) studies. The course is aimed at graduates employed in the mining indust- ry, and especially people involved in geomechan- ics projects on a routine basis in remote locations. This kind of course is unique in Australia and is one of only two correspondence programmes available at this University. The author designed the course and nursed it through the early years, and was Director until 1986. The paper describes the teaching and assess- ment methods and also discusses aspects of admin- istration and coordination of such a course. It is concluded that an important need of the mining industry is being catered for and it appears that similar correspondence course for- mats would also be useful in other areas of the minerals industry.

Jan 1, 1986

By A. K. Sinha

Inspite of the growing demands worldwide, thermal coal must compete in the market both in price and quality. The design and performance efficiency of coal preparation plants is thus crucial to the survival and profitability of a coal industry. While the coal recovery influences the cost of production, the quality produced by a preparation plant determines the selling price. Several coal preparation plant simulation models have been developed in recent years to help Improve the performance of coal preparation plants. A research project was recently conducted at Southern Illinois University to evaluate the practical applicability of such a model. The results of this study are presented and discussed.

Jan 1, 1986

By D. Suarez

The work of engineers responsible for the design and performance of mine facilities is often challenged by economic and practical constraints in the field. Problems have developed in implementing design criteria dictated by persons or agencies not familiar with the dynamic nature of mine engineering. Regional and site-specific conditions frequently require changes to standard designs, or the use of a completely innovative approach, which is not provided for in the regulations. The implementation of engineering design, therefore, usually requires a hard-sell approach to management and regulatory agencies that allows for a happy-medium to all parties concerned. Flexibility on the part of the regulatory agencies is needed to solve operational and environmental problems with sound engineering. Typical hydrologic issues which will be discussed fall in the following general categories: ? Design criteria for sizing water control structures (i.e., culverts, diversion and sedimentation ponds, ditches, etc.) ? Implementation (construction and operation) difficulties ? Regulatory compliance ? Reclamation planning with hydrologic considerations ? Protection of groundwater resources

Jan 1, 1986

The paper considers the factors that will control the importance and the nature of R & D required by the Australian mineral industry over the next decade. The process required to determine the appropriate priorities for research and how it must be managed is described. The work of the Australian Mineral Industries Research Association is used to illustrate this process.

Jan 1, 1986

By Robert Semrad, J. Colin Anderson

INTRODUCTION Sulphur is a mineral which accounts for 0.05% of the earth's crust and may be found either in its elemental state or as a compound. References to sulphur production and consumption are found in early antiquity and international trade of sulphur from volcanic deposits in Sicily began in the 1880's. The supply of sulphur consists of two components: the first is production, and the second is inventory. HISTORICAL SUPPLY Production World sulphur production in 1984 was approximately 53.5 million metric tons, compared to the 1970 level of 42 million metric tons. Of this 11.5 million metric tons production increase, brimstone accounted for close to 90%. Production distribution in 1984 was 62% brimstone, 21% pyrites and 17% other forms, while in 1970 it was 55%, 28% and 17%, respectively. Brimstone Production is derived either from mining operations (Frasch, underground melting and native refined) or as a by-product from hydrocarbons. World production in 1984 exceeded 33 million metric tons, up approximately 10 million metric tons from the 1970 level. This increase was uniformly distributed throughout the world as shown in Table A.

Jan 1, 1986

By R. W. Hughes, R. Koopmans

This paper investigates the effect of varying stress levels on the determination of deformation moduli and examines the sensitivity of the borehole dilatometer in measuring rock mass scale features and its ability to represent rock mass characteristics. Cubical blocks of sandstone, limestone and granite were tested in the laboratory under triaxial stress conditions. Field programs were conducted in both granite and sandstone rock masses surrounding underground openings. The dilatometer's zone of influence was determined by conducting tests within an instrumented concrete cylinder and by performing a finite element analysis. Laboratory and field results suggest that the deformation modulus of a rock mass can be substantially affected by the stress field and that the borehole dilatometer is sensitive enough to profile deformation moduli as dictated by the in situ rock mass characteristics.

Jan 1, 1986

By S. R. Stine

The Cyprus Thompson Creek Mine is located at 2,286m (7500 feet) elevation in the Central Idaho mountains, 61.16 kilometers (38 miles) southwest of Challis, Idaho off State Highway 75. The Thompson Creek molybdenum deposit lies near the eastern border of the late Cretaceous Idaho Batholith within a complexly deformed sequence of Paleozoic sedimentary rocks. Molybdenum mineralization is contained in a composite biotite granodiorite-quartz monzonite stock considered to be genetically related to the Idaho Batholith intrusive event. The ore is being mined by open pit methods and delivered to the concentrator stockpile with an overland conveyor belt system. The concentrator is designed as a 22,680 metric tons (25,000 ton) per day plant at an average head grade of 0.1% Molybdenum.

Jan 1, 1986

The paper describes the geology, structure, stress, gas and strata geomechanical properties for Leichhardt Colliery and their reactions to mining.

Jan 1, 1986

By E. P. Chen

This investigation involves the development of a two-dimensional continuum model for the description of jointed media. Specific application of the model developed here is for the potential geological disposal of radioactive waste in the layered sequence of fractured volcanic tuffs under Yucca Mountain, Nevada. This is currently being considered by the Nevada Nuclear Waste Storage Investigations Project, administered by the Nevada Operations Office of the U. S. Department of Energy. The work is a direct extension of the previous constitutive model by Thomas (1982) based on the work of Morland (1974). The main feature of Thomas's model includes two parts: a continuum approximation based on average discontinuous displacements across jointing planes within a representative elementary volume, and a material constitutive description based on linear elastic matrix material behavior and nonlinear normal and shear joint behavior between jointing planes. The mathematical descriptions by Morland based on strain partitioning among matrix material and joint sets allow multiple joint sets to be included in the model. However, the initial effort by Thomas to implement Morland's mathematical model included only a single set of joints. To make the material model reflect more realistically the field characteristics, the current work extended Thomas's model to include orthogonal sets of joints. The nonlinear elastic normal joint behavior is retained in the present model. Joint shear response was treated as linear elastic in the shear stress versus shear displacement relationship prior to attaining the stress level governed by the Coulomb friction criterion. Beyond this critical stress value, a horizontal line is assumed in the work of Thomas for the shear stress versus slip displacement relationship such that the shear stress remains constant while the slip displacement increases. Motivated by experimental observation, the current work generalized the shear response to allow a line with finite slope to govern the slip behavior beyond the critical stress level. The inclusion of an orthogonal joint set led to a fourth order algebraic equation for the calculation of stress increments as compared with a second order equation obtained by Thomas. The nonlinear elastic normal joint behavior provides criteria which allow the selection of the root that yields result consistent with the loading condition of the problem. The addition of one more set of joints provides the potential to more completely study the interaction of various parameters representing the characteristics of jointed media behavior. Material responses to various loading conditions based on the present constitutive model have been obtained. These results and their comparisons to single joint set results are presented. Formulation of the Continuum Model The inclusion of an orthogonal joint set led to a fourth order algebraic equation for the calculation of stress increments as compared with a second order equation obtained by Thomas. The nonlinear elastic normal joint behavior provides criteria which allow the selection of the root that yields result consistent with the loading condition of the problem. The addition of one more set of joints provides the potential to more completely study the interaction of various parameters representing the characteristics of jointed media behavior. Material responses to various loading conditions based on the present constitutive model have been obtained. These results and their comparisons to single joint set results are presented. Let us focus our attention on the set with normal n first. Let the jump dilation displacement and jump slip dasplacement associated with the [ ]

Jan 1, 1986

By Christopher J. Bise

INTRODUCTION A mine's power system represents the driving force behind all of the extraction and auxiliary operations, because the production and transportation of mined material and the operation of equipment, such as fans and pumps, are all dependent upon a power source. Once, compressed air was the primary power source in mining; today, however, electrical power dominates. This chapter reviews the basic theories of com- pressed-air and electrical power and provides several examples of applications in mine power systems. COMPRESSED-AIR POWER General Compressed air has been, and should continue to be, an important source of power in mining operations. It has been used as a means of blasting coal in conventional mining and is widely used to operate stopers, mucking machines, and other air tools in both coal and hard-rock mines. Such applications demonstrate the suitability of compressed air for applications requiring linear motion, but it is also utilized for its reliability and safety. A compressed-air system is composed of a compressor, a receiver, a distribution network, and the air-operated machines. A compressor takes in air at normal atmospheric pressure (free air) and compresses it to a higher discharge pressure. The discharge pressure must be high enough to overcome the friction in the distribution system of pipes and hoses and deliver the compressed air to the machines at the pressure recommended by the manufacturer. The most common type of compressor used in mines is the reciprocating compressor in which the air is compressed by a piston in a cylinder. An air receiver is a container or storage tank that is located in the distribution system between the compressor and the machines. It stores compressed air, when the full capacity of the compressor is not being used, and gives a more steady flow of air to the machines. The distribution network consists of pipes, Oalves, elbows, tees, and hoses that transmit the compressed air from the receiver to the machines in the mine. It is essential that the distribution system be designed with the proper sizes and lengths of pipe, hose, and other components to keep pressure losses well within allowable limits. The air-operated machines consist primarily of drifters, stopers, pluggers (sinkers), slushers, and several other pieces of equipment. Compressor Operation Every compressor is made up of one or more basic elements; a single element, or a group of elements in parallel, comprises a single-stage compressor. Many compression problems involve conditions beyond the practical capability of a single compression stage. Too great a compression ratio (absolute discharge pressure divided by absolute intake pressure) may cause excessive discharge temperatures or other design problems. It, therefore, may become necessary to combine elements or groups of elements in series to form a multi- stage unit, in which there will be two or more steps of compression. The number of stages commonly used in reciprocating compressors is as follows: Pressure Number of stages 0- 150 pig 1 80- 500 psig 2 500-2500 psig 3 2500-5000 psig 4 When pressure is referred to as pounds per square inch gage (psig), it means the pressure (in pounds per square inch) above barometric pressure as measured by a gage. The sum of barometric pressure and gage pressure is the absolute pressure (in pounds per square inch). The gas is frequently cooled between stages to reduce the temperature and volume entering the subsequent stages, thereby reducing the work required for compression. The basic reciprocating compression element is a single cylinder compressing on only one side of the piston (single-acting). A unit compressing on both sides of the piston (double-acting) consists of two basic single-acting elements operating in parallel in one casing. The reciprocating compressor uses automatic spring-loaded valves that open only when the proper differential pressure exists across the valves. Intake valves open when the pressure in the cylinder is slightly below the intake pressure. Discharge valves open when the pressure in the cylinder is slightly above the discharge pressure. In Fig. 1, Diagram A shows the basic element with the cylinder filled with air at atmospheric pressure. On the corresponding theoretical pressure-volume

Jan 1, 1986

By Carmine Nappi

This article examines some important trends in East-West trade in non-fuel mineral products, in particular the recent decline in Eastern bloc exports of such products. It relates this decline to an improvement in Soviet terms of trade; a deterioration of geological and locational conditions in Soviet mineral production; an increased integration of the CMEA-countries based on a regional pooling of resources; and a surge in demand for mineral commodities in Eastern countries coupled with a slowdown in Western economic growth. Finally, it evaluates to what extent these determinants may evolve in a different direction during the eighties and thus foster East-West mineral trade. Eastern1 bloc trade in mineral products is a subject of perennial interest in the West. When exports increase, there is much talk of the dangers of dependence on the East for critical fuels and materials. When imports increase, talk turns to the danger of Soviet dependence on Western supplies. A common fear is that the USSR may not only seek to meet its own resource needs but also deny the access of Western countries to these resources. This paper, like three other recent additions to the lite5ature on Soviet foreign trade of commodities2, tries to put matters in clearer and cooler perspective. The first section evaluates the structure of East-West mineral trade and tries to identify some important trends of recent years. The second section relies on supply and demand factors, as well on the Comecon connection (the intra-Council for Mutual Economic Assistance mineral cooperation) to explain why there has been a reversal in the mineral trade trend since the end of the seventies. The last section evaluates the factors which could stimulate East-West mineral trade in the future.

Jan 1, 1986

The U.S. economy continued to expand during 1986, although at the slowest pace since 1982 when the current business expansion began. Real gross national product (GNP) grew about 2.6%, slightly below 1985 growth but significantly below that of 1984. The continuing expansion was fueled pre-dominantly by rising personal consumption expenditures as well as growing Government purchases of goods and services. Fixed investment, although positive, failed to grow at the rate of the overall economy. The trade deficit, which increased more than 30% over the record 1985 level, continued to depress economic growth despite significant declines in the price of petroleum and the value of the dollar. On a more positive note, domestic employment continued to grow--increasing over 2 million from the 1985 level--and inflation and interest rates declined. The unemployment rate dropped slightly to 7.0%. Of direct importance to the mineral-producing industries, expenditures for consumer and producer durables as well as investment in residential construction each grew faster than the overall economy, but investment in nonresidential structures fell more than 10% from the 1985 level. The level of real capital spending declined about 3% in 1986, following strong gains in 1985 and in 1984. Capital expenditures for new plant and equipment bottomed out in the second quarter and expanded in the third and fourth quarters. The decline in the first half of the year was partially attributed to uncertainty arising from the then-proposed tax bill. Also, there was little impetus for corporations to invest in new capacity since factories were operating at less than 80% of capacity during most of the year, in part because of continued competition from imports.

Jan 1, 1986

By Priscilla P. Nelson, Francis L. C. Fong

Introduction Fracture mechanics is the study of the behavior of cracks and their modes of propagation. During cracking, energy is consumed in creating new surface area. The more energy a material absorbs, the higher is its fracture resistance. This fracture energy is provided either by work done externally, by the release of elastic strain energy within the cracked body, or by a combination of these two effects. Fracture resistance is measured in terms of either the stress intensity factor, K, or the energy release rate (also referred to as crack driving force), G. For linearly elastic materials, these two quantities are related by the following equation: [ ] where [u] is Poisson's ratio and E is the modulus of elasticity. Both K and G are direct functions of the applied force and the crack length. The process of rock cutting with full-face tunnel boring machines (TBMs) involves the indentation of a rock surface by rolling disc tools. Excavation occurs as fractures, extending from the locus of chip indentation, propagate between concentric disc grooves and liberate rock chips from the intact rock face. Since disc cutting is achieved by a fracture process, it is logical to anticipate that differences in cuttability of a variety of rocks should be related to the variation of fracture material properties among the rocks. Such a relation has been demonstrated between the performance of full-face TBMs and the critical crack driving force for excavation in relatively high strength, brittle, low porosity, isotropic rock (Nelson et al., 1985). The objective of this paper is to report on the results of a continued investigation of the relationship between fracture material properties and the effectiveness of disc cutting. Additional reliable data on full-face TBM performance is difficult to obtain, so that the results of disc linear cutter tests performed by the Transport and Road Research Laboratory (TRRL) (U.K.) are utilized in this study. Fracture Material Property Evaluation If a crack tip is subjected to a perfectly plain strain condition, many materials will behave in a brittle manner, and the material resistance to fracture is constant during crack growth. This resistance is referred to as the plain strain fracture toughness, believed to be a material property. The standard testing procedure for this parameter is given in the American Society for Testing and Materials (ASTM) test designation E399. To ensure plain strain conditions, acceptable specimen geometries are specified. Unless these geometric specifications are adhered to, the measured fracture resistance is regarded as the apparent fracture toughness, and a subscript Q is used, as [ ]. The methodology adopted by ASTM E399 is within the framework of Linear Elastic Fracture Mechanics (LEFM). This approach assumes that material resistance against cracking is developed instantaneously, without initial stable or subcritical crack extension. Prior to crack advancement in rock, however, much of the crack driving energy is absorbed in a localized volume in front of the crack tip, referred to as the plasticity or microcracking zone. This capability for energy absorption substantially increases material resistance, and a crack may be arrested unless an increased crack driving force is applied. The LEFM or plain strain assumptions would underestimate the actual fracture resistance of such a material. Such a conservative approximation may be desirable in the design of structures against fatigue or brittle failure. In mining or tunneling, however, an underestimation of crack resistance can lead to the selection of underrated excavation equipment and a decrease in production efficiency. The development of fracture resistance in rock is best described by the material resistance curve, or R-curve, which is a plot of fracture resistance as a function of crack extension. Typically, peak resistance is only reached after a finite amount of subcritical crack growth. The

Jan 1, 1986

Pressures are foreseen for departments of metallurgy to make. radical changes in their undergraduate curricula. The curricula need to be made more attractive to high'school students in -order to increase the number of enrolled students. The distinctive character of extractive metallurgy needs to be emphasised to resist encroachment by chemical engineering. There should be content relevant to each of the professional functions and, particularly, to' society's broad expectations of metallurgists. Content, teaching methods, etc. need to be acceptable to women, mature-age -students, Aboriginals, and other groups, as well as young white males. Learning experiences should be negotiable by the students in response to the advent of learning packages delivered via personal computers. All of these needs could be satisfied by a radical change. in attitudes and objectives during the design; implementation and evaluation stages of . a new type of curriculum, using a wide range of problem-based learning experiences..

Jan 1, 1986

Increase the recycling of critical and strategic materials by simplifying the indentification and segregation of scrap. Background Because the United States is dl-most totally dependent on imports of such critical metals as chromium, cobalt and nickel, Bureau of Mines research has been directed towards conserving these metals by increasing the recycling of the complex scrap materials that contain them. Experienced scrap sorters, using the traditional techniques of object recognition, spark tests, chemical spot tests, color, apparent density, and magnetic properties, can adequately sort a wide variety of alloy groups. However, the complex nature of new materials entering the scrap market has made sorting both more difficult and more important. Some new alloys contain so many components that separation by discrete alloys becomes a prerequisite for effective recycling. The Bureau has completed Investigations on two methods for rapidly sorting complex scrap mixtures. One method uses a combination of two low-cost instruments. The other uses a single sorting instrument. Both approaches are reported.

Jan 1, 1986

By V. A. Evans

The preparation of a paper reporting fluorspar economics in the United States at one point in time could have been somewhat complicated be- cause of the number of producers, both large and small, that derived production from different locations throughout the Western U. S. and the Southern Illinois and Western Kentucky fluorspar districts . Companies such as Allied Chemical and William- son Mining operated in the Jamestown district of Colorado. In Walden and Salida, Colorado, the Colorado Fluorspar Company operated mines and mills.

Jan 1, 1986