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By Philip W. Holland

The Bureau of Mines has developed a trace helium analyzer for deter-mining helium-4 in the parts-per-billion range. The instrument is used for analyzing pure gases, laboratory-prepared standards, and atmospher-ic samples. Accuracy at the 95-pct confidence level in the 50-to 20,000-ppb range is within ±2 ppb or ±0.4 pct, whichever is greater. The minimum detectable helium-4 concentration is calculated to be 5 ppb. The analyzer consists of a modified helium leak-detector mass spec-trometer, a laboratory-built sample inlet system, and a liquid-nitrogen-cooled charcoal trap. A programmable integrator and event-control module make automatic operation possible. The portability of the analyzer allows it to be used in the field.

Jan 1, 1984

Estimation of the semi-variogram is basic to the geostatistical processing of data. The most widely used arithmetic average estimator is here employed with various sampling patterns to calculate experimental semi-variograms in a deposit which is simulated to have a defined semi-variogram. Percentage differences between theoretical and experimental semi-variograms are reported.

Jan 1, 1984

By Claude Cunningham

Late in 1982 a fire began in the shallow, abandoned workings of the Uitkyk Colliery near Witbank, South Africa. Urgent measures had to be taken to quench the fire, before the surface caving it caused could put an important railroad connection out of action. This paper outlines the way in which the job was tackled.

Jan 1, 1984

By J. F. Abel, F. T. Lee

Subsidence is controlled by a complex com¬bination of mining and geologic factors. For example, a compilation of worldwide data shows that, as the percentage of shale in the overlying rock mass decreases and the amount of sandstone increases, the angle of draw (and the area affected by subsidence) decreases. Limestone in the over¬burden appears to cause a more than twofold decrease in the angle of draw compared to a like amount of sandstone. Increased amounts of sandstone were accompanied by a greater surface subsidence relative to the mining height. The total thickness of overburden did not appear to influence the subsidence magnitude above super-critical panels. The greater the thickness extracted, the smaller percentage of that thickness shows up at the surface as subsidence. The greater the percent of the seam extracted, the greater the subsidence reaching the surface. The maximum subsidence above room-and-pillar panels de¬pends on the pillar height and minimum width as well as the other factors listed.

Jan 1, 1984

By Joseph S. Coffman

To determine the availability of manganese for metallurgical purposes from selected world resources, the Bureau of Mines evaluated the potential production of contained manganese in concentrates based on the demonstrated resources of 23 foreign and 8 domestic mines and deposits in 9 market economy countries. All but 2 of the 23 foreign deposits are operating mines; none of the domestic deposits are in operation. The demonstrated resources of the mines and deposits used in this study represent an in situ ore resource of approximately 2.2 billion tons," containing 780 million tons of manganese with a total recoverable production potential of 514 million tons of contained manganese in concentrates. The analyses of mines and deposits in this study indicate that about 213 million tons of the contained manganese (41 pct) is potentially available at a January 1981 constant dollar long-run total cost of up to $1.50 per long ton unit (22.4 lb, or 10.15 kg contained Mn), approximately 428 million tons (83 pet) is potentially available at a cost of about $1.75 or less, and 491 million tons (95 pet) is available at less than $3.30. The remaining 23 million tons, which is potentially available at much higher costs (about $8 to $35 per unit), represents the U.S. deposits. On an annual basis, with a cost range of up to $1.75 per long ton unit, the availability from currently operating mines would last at least 80 years based on 1980 world production data. Total manganese production costs are estimated to comprise mining-8 pet, beneficiation-3 pet, transportation-26 pet, and smelting-63 pet.

Jan 1, 1984

Reduce well construction and operation costs associated with in situ leach mining while increasing mineral recovery. Approach To accommodate the size of centrifugal pumps presently in use, in situ leaching production wells are typically drilled to 6 inches in diameter, while monitor wells are drilled to measure 4 inches in diameter. However, in order to reduce the cost of drilling these larger diameter wells and to increase recovery, the Bureau has developed jet pumps which have smaller diameters than centrifugal pumps of the same capacity. This allows both production and monitor wells to be drilled smaller. Bureau estimates indicate that the cost of drilling a 3-inch-diameter production well at in situ leaching operations would be about 35 percent less than the cost of a 6-inch well. Similarly, the cost of drilling a 2-inch-diameter monitor well would be about 26 percent less than the cost of a 4-inch well. Such significant savings in the cost of drilling these wells would effect a substantial reduction in total capital cost. Use of the new jet pumps can also increase the percentage of recovery because less costly wells allow closer well spacings, improving the distribution of the leach solution. How the System Works After the borehole is cased, the new small-diameter jet pump, along with piping and accessories, is installed and connected to a centrifugal pumping unit on the surface. High-pressure water from the surface pump is forced through a nozzle into the venturi of the jet type pump injector. This jet action lifts the leach and mineral-bearing solution to the surface.

Jan 1, 1984

By Roger M. Nendick

The recovery of precious metals from heap leach solutions can be accomplished by two processes: 1. The Carbon Adsorption Process 2. The Merrill-Crowe Zinc Precipitation Process A brief review of the relative process economics is made. Each process presents certain design considerations that must be addressed during the evaluation and engineering design for the project. Discussion is presented on the design criteria for each process.

Jan 1, 1984

By A. Grenoble

The mining of seams in close proximity can greatly accentuate interaction problems. At distances of less than 110 feet vertically interaction can occur for both over and under mining. Research into ground control problems resulting from undermining a previously mined seam has been carried out using finite element and body-loaded photoelastic modeling methods in conjunction with numerous case studies. Analysis of field data was used to validate and expand the model results. Research findings demonstrate situations under which the worst ground control conditions can be expected to occur for a specified geologic environment, depth, innerburden spacing and mining geometry. Special emphasis has been placed on the effects of pillar load transfer on the lower seam in terms of pillar and floor stability and roof control. Roof and floor condition indexes are used to summarize structural and lithologic conditions in the affected seam. The effects of joint orientation and continuity are incorporated in the analysis and the research results have been compiled into a software package for application by the field engineer.

Jan 1, 1984

By Kot F. Unrug

When reading different studies discussing trends in coal mining, it appears that a substantial expansion of output by the year 2000 is predicted, even in the most pessimistic forecasts. Depletion of shallow, easy-to-mine deposits is only a matter of time, and the future average mining depth will increase. The proportion of slope to shaft mines operated during the next decades will change in favor of the shaft mines. Since an increasing amount of shafts in new nine developments seems to be inevitable, it appears appropriate to focus more attention on shaft design criteria. Some valuable papers have recently been published (1) that emphasize geotechnical aspects of shaft design. In the discussion that follows some other aspects of design criteria will be evaluated.

Jan 1, 1984

By Wittenberg J. C, Reid A. F

A method is described for the rapid and effective production of polished section mounts of ore and mineral particulates to the standards required for automated image analysis. This requires mounting without segregation of particles by mass or density, and it is also preferable to avoid having particles in contact so that they can be recognised as individuals. To achieve this, the particle samples are first split to an appropriate degree in a rotary riffle, and the sub-sample mechanically diluted and thoroughly mixed with an inert filler of the same size range as the particles. Just sufficient epoxy resin is added to make the mixture fluid. During setting, the ore particles are mechanically supported by the inert filler particles, thus maintaining the particles in a random three-dimensional distribution. A rapid two-stage grinding process, based on the successive use of 600 mesh silicon carbide and 1200 mesh (10 um) corundum on cast iron plates, is followed by three stages of mechanical diamond polishing on cloth laps. Hand polishing is entirely avoided, as is the use of papers.

Jan 1, 1984

By Z. J. Hladysz

The Hladysz Rock Tester was developed at the South Dakota School of Mines as a portable rock strength tester. The hand held device is placed against a rock surface and struck by a hammer. The impacted force causes a steel ball in the device nose piece to indent the rock and simultaneously indent a standard steel bar also contained in the nose piece. By comparing the two indented diameters the compressive strength of the rock can be calculated using laboratory determined correlation coefficients.

Jan 1, 1984

By David L. Pentz

This paper discusses exploration objectives and requirements for a nuclear repository in the U.S.A. The importance of designing the exploration program to meet the system performance objectives is emphasized and some examples of the extent of exploration required before the License Application for Construction Authorization is granted are also discussed.

Jan 1, 1984

By Charles Stahl

El presente texto describe la comercialización de la plata a corto y mediano plazo. El periodo de corto plazo se refiere a cualquier negociación dentro de un período de 5 minutos y tres semanas, mientras que la de mediano plazo, es la transacción que se produce entre dos y tres meses. Para la comercialización de metales es necesario la confianza y la paciencia como habildidad para el éxito de la negociacion, de forma que se tiene que comerciar con un equilbrio y sin excesos.

Jan 1, 1984

By T. M. Tharp

Attempts to analyze the stability of slopes, foundations and underground openings in discontinuously jointed rock have generally assumed full joint continuity or ignored the role of stress concentration at the tips of discontinuous joints. The most common approach in rock slopes is to consider a failure plane consisting of coplanar, but discontinuous joints separated by intact rock. The intact rock is assumed to fail in shear as a MohrCoulomb material and to contribute a strength component proportional to the fraction of the failure plane that is intact rock (Jennings, 1970). An alternative approach by Stimpson (1978) applies Lajtai's (1969) theory for shear strength of discontinuously jointed rock masses to slopes. Lajtai allows tensile failure in the intact rock of a composite surface. This theory yields lower shear strength than that of Jennings (1970) except in the presence of high normal compression, however it also fails to account for the stress concentration at the tip of a discontinuous joint. For a given slope geometry, stresses increase with slope height, but in both of these models rock mass strength is independent of size. A fracture mechanics analysis shows that particularly for small slopes, rock mass strength decreases with size.A continuous stepped failure surface produced by propagation of preexisting joints may develop at lower shear stress than pre¬dicted by the Jennings (1970) or Lajtai (1969) models. This fracture mechanics model applied to slopes in competent rock is more realistic in its assumed failure mechanism, and for large slopes more conservative than the Jennings (1970) or Lajtai models (1969).

Jan 1, 1984

By William G. Fischer

This paper attempts to close the gap between extensive rock testing with field measurements and the mine operator's need for safe mine layouts and alternatives. It was found that many of the variables that influence mine geometry and worker safety are relatively unimportant while others are critical. The development of empirical relationships which tie the critical variables to the "safe useful life" of a trona mine layout and observations made in 140 production areas where the variables were researched over a fifteen year period are discussed. The concepts presented may have applicability in mine design for other bedded deposits.

Jan 1, 1984

By T. P. Meloy

Economic constraints require that the optimum mineral processing circuit be chosen for a given ore and then the circuit be optimized. Meloy (1983) developed a general methodology for finding the best circuit for a given ore. This analysis, however, did not specify a way to optimize the best circuit once it has been found. To optimize a given circuit, it is necessary to find the optimum set points for each unit operation in the circuit. Developed in this paper is a simple, general equation which, when applied, defines the optimum separation set point for the maximum mineral grade. This general equation, Equation (4), applies not only to simple ores, but also to complex ores containing variable and locked particles. Currently, the optimum set point can be calculated only for heavy media and cyclone circuits, because they are the only unit operations for which the necessary data has been measured.

Jan 1, 1984

As partition curves are widely employed to characterize screening efficiency which, by definition, should include a time parameter, it is shown, perhaps for the first time, that time is already included in the partition curves and how. Laboratory and plant results are used to show how screening efficiency depends on feed composition, near-mesh and oversize material and screen motion, and how these factors may combine to give an erroneous result that two identically efficient screens are different and two screens of different efficiency are identical. Reasons are given which show why a renewed interest in screening would benefit not only screen engineers and operators but also those concerned in formulating standard specifications of screen analysis methods.

Jan 1, 1984

By Mark E. Emerson

Foreign and domestic companies find the mineral potential of this country's stern public lands, its capital markets, political stability, and "open-door" policy attractive for hard mineral exploration. Traditionally, exploration in the US has been geographically based and responsibility oriented at the district level. The 1970s brought a decentralized approach to exploration as major non-metal companies began to diversify into hard minerals. The emphasis was on capital intensive metal and energy projects involving bulk-tonnages. The recent economic downturn in metals has caused many of the new participants to withdraw from the mineral scene. The surviving companies have shifted their emphasis toward medium scale precious metal projects having high operating margins and rapid return on equity. Exploration expenditures in the United States are now principally focused on gold and silver to the exclusion of practically all other commodities. In the search for precious metals companies have scaled back their exploration efforts and have began to apply new approaches to target selection. The search is being assisted by rapidly evolving conceptual models. The change in orientation has led to numerous new discoveries. The finds are essentially "rediscoveries" that c,-re previously uneconomic. The majority are low-grade surface deposits that have involved low discovery costs and short lead times for development by low-cost mining and beneficiation methods. The emphasis on gold to the exclusion of all other commodities raises questions regarding the direction of exploration in the US for the rest of the 80s.

Jan 1, 1984

By D. E. Ranta, M. W. Ganster, A. D. Ward

An ore zoning technique developed by Climax geologists during the past forty years has been used to contour drill-hole assay values on cross-sections for fourteen porphyry molybdenum deposits in western North America, including the Climax and Henderson orebodies. Detailed geological studies of these large, complex deposits are essential in determining ore controls, which are the factors most critical to the zoning of MoS2 and to conceptualizing geologic model s. The technique provides a detailed representation of the size, shape, grade distribution, and geologic continuity of the individual deposits. It demands a disciplined approach and adheres to rigorous rules while maintaining flexibility for adaptation to widely varying geologic conditions. By defining the limits that guide and control manual, computer-assisted conventional, and geostatistical reserve estimates, it exerts a strong geologic influence on the estimation process. A combination of ore zoning and geostatistical analysis of molybdenum deposits produces a significantly more accurate, precise, and defendable geologic reserve estimate than other methods.

Jan 1, 1984

By O. K. Brown

U.S. Borax has two tailings disposal requirements which are uniquely different in many respects, but with the common goal to minimize the impact on the environment, utilize dependable technology and minimize the economic impact. The existing borax mine in the grid Mojave desert of Southern California has gone through a series of changes in tailings disposal practices in the 56 years of operations, The other tailings disposal requirement is a new molybdenum mine, presently in the feasibility phase, in the high precipitation setting of Southeast Alaska. II. Introduction U.S. Borax is faced with two tailings disposals situations, at diverse locations:

Jan 1, 1984