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By R. Mensah-Biney

The loading characteristics of gold-tetrabromide species onto activated carbon have been evaluated using a completely mixed batch reactor system. The overall loading of gold onto carbon was rapid for the first hour but continued slowly without cessation as a result of reduction of gold. Conventional equilibrium considerations were therefore not applicable. Although loading continued slowly after several days, abnormally high loading capacity values of 10-12 meq/g carbon (650-800 kgAu/tonne) could be attained within 72 hours. The loading of gold-bromo species by activated carbon was by the mass transfer of [AuBr4l-onto the carbon surface where reduction to metallic gold took place. Elution of gold from the loaded carbon was feasible provided the carbon had not been loaded to too high capacity values. If loading is carried to high levels, complete elution becomes impractical and the gold may be recovered by ashing the carbon. For the high loading capacities observed, this option would appear to be cost effective. The effect of several variables on the loading capacity of the activated carbon is discussed.

Jan 1, 1992

By Ashis Bhattacherjee, Subrata Chatterjee, Michael T. Dewey, Christopher J. Bise

In order to continue the advancements made during the past two decades in the reduction of the severity of accidents and injuries in underground coal mining, closer attention will have to be paid to the increasing number of accidents resulting in disabling injuries and lost time. With the increased emphasis on safety training reflected in the Federal Mine Safety and Health Amendments Act of 1977 (Public Law 96-1641, and on MSHA's current focus on the application of Job Safety Analysis, it appears that the acquisition, evaluation, and application of accident and incident data will take on an even greater importance. To manage this large amount of information will require a significant commitment of time and attention on the part of mine training departments. A USBM-sponsored research project is currently being completed at Penn State which focuser on the development of a model training program for mining. The program is based on five distinct steps which represent the coupling of a needs assessment with the program implementation. The five steps are: 1) database analysis, 2) workplace observations, 3) identification of trainable problem areas, 4) a library of training resources, and 6) the implementation of the program. In each of these areas, the microcomputer has proven to be a valuable tool for collecting, analyzing, and presenting accident and incident information. This paper will detail the manner in which microcomputers have been fully integrated into the model training program. Examples of applications at existing mines will also be discussed.

Jan 1, 1992

By J. F. Fitzpatrick

This paper examines the cost elements associated with changes to gold mining practice over the last decade that result from the changes in environmental regulation and the heightened governmental and public awareness of environmental issues. The main experience base is Pegasus Gold Corporation's flagship mine, Zortman/Landusky, located in the Little Rocky Mountains of Phillips County, Montana. This operation was among the first mines that were permitted under the 1974 Montana Metal Mining Reclamation Act. In 1974, the Montana Metal Mine Reclamation Act was enacted, creating a permit system for metal and industrial mineral mines for the state of Montana. The act established the content of mine permit applications and defined parameters for the reclamation of mining disturbances. The Act can be viewed as implementing legislation for Article 9, Section 2, of Montana's Constitution, which provides that "all lands disturbed by the taking of natural resources shall be reclaimed." Pegasus Gold Corporation's Zortman/Landusky mine was among the first mines permitted under the new Act. In 1978, the initial permit applications were submitted for Zortman and Landusky, and a full Environmental Impact Statement was prepared by the Montana Department of State Lands; permits were issued in 1979. When opened later that year, the anticipated mine life for the combined Landusky and Zortman operations was approximately 18 years, based upon a proven and probable ore reserve of 43.2 million tons. Zortman/Landusky was the first large-scale heap leach gold mine in the United States. Its distinguishing feature was, and remains, a remarkably low ore grade, now .016 oz/ton. The ore is economic because it requires neither crushing nor agglomerating to leach effectively. Approximately two years after the initiation of the state's regulatory process, the Federal Land Policy Management Act (FLPMA) was enacted, establishing a mine regulatory framework for lands under the administration of the Bureau of Land Management.

Jan 1, 1992

By Jasinder S. Jaspal

The United States has very large coal reserves in seams that are less than 1065 mm (42 in.) thick. These reserves are often not mined because of the difficulty of working in low heights and, in most cases, the seams are beyond the technical or economical limits. It is estimated that the remaining reserves in 355 to 710 mm (14 to 28 in.) thick seams that are not faulted or intruded, dip less than 15° and under a cover of 610 m (2000 ft) or less are nearly 910 Gt (1 trillion st). This is a very large percentage of coal reserves in the United States (Unrug, 1985; DuCarme et al., 1990). The US Bureau of Mines is attempting to develop new techniques for mining 150 to 1065 mm (6 to 42 in.) thick coal seams. Research has focused on existing thin seam mining techniques, testing of small- and full-scale physical models of the Bureau's slot mining concept and computer modeling of the full-scale process. In 1986, only 21 % of the total US coal production came from -1065 mm (-42 in.) thick seams. Of that, 355 to 710 mm (14 to 28 in.) thick seams share of production was minimal, probably 5% or less (Mayercheck et al., 1990). This shows that the thin seams, particularly the seams 355 to 710 mm (14 to 28 in.) thick, have not been mined to the extent of the available reserves. Thin seam coal, generally, is of premium quality. As thicker seams are depleted, the mining of thin seams could become more important. Thus, there is a need to develop technology to mine these seams (J. Farinelli et al., 1987). A successfully applied technology could change reserve categorization. In the Appalachian Plateau there are 417 Gt (460 billion st) in 355 to 1065 mm (14 to 42 in.) seams. This represents nearly 9.2% of the US remaining reserves (Unrug, 1985). At depths of 152 m (500 ft) or less, the Appalachian Plateau has about 214 Gt (236 billion st) of reserves in 355 to 1065 mm (14 to 42 in.) thick seams. Other mining areas also have substantial coal reserves in this seam thickness category. Those, however, are not as attractive for mining as the Appalachian Plateau. In the past, most of the reserves of the Appalachian Plateau region were partially worked by contour and highwall auger mining. It is estimated that these mining systems had left some 40,230 km (25,000 miles) (Readers Digest, 1987) of unreclaimed highwalls. The Bureau recognized this situation. In FY1987, the agency initiated a research project to develop anew technology for mining thin seams of the Appalachian Plateau.

Jan 1, 1992

By W. J. Whiten

A rule-based control system was developed for a 7-foot Hydrocone crusher with automatic set regulation, based on operating data collected in the field. When implemented in a plant PLC, the system was found to behave as predicted. Benefits included a significant reduction in the frequency of control actions, the incidence of power overloads, and the standard deviation of feeder speed, whilst maintaining crusher performance.

Jan 1, 1992

By Jr. Smith

Industrial minerals are just other rocks, except for the unique characteristics that make them useful in an industrial process. There is not a ready market for this type mineral and one or more uses must be developed to sustain production. The name "olivine" is a generic term used to indicate a group of orthosilicate minerals in a solid solution series, with forsterite (Mg2SiO4) and fayalite (Fe2SiO4) as endpoints. Since neither is found alone in nature, the mineral is always a combination of the two. The commercial deposits are high in magnesium and on the high end of the melting scale in the series. The name comes from the olive-green color.

Jan 1, 1992

By C. L. Karr

Establishing suitable control of pH, a requirement in a number of mineral and chemical industries, poses a difficult problem because of inherent nonlinearities and frequently changing process dynamics. Researchers at the U.S. Bureau of Mines have developed a technique for effectively controlling such systems. This technique successfully combines the process control capabilities of fuzzy logic and the search capabilities of genetic algorithms. Fuzzy logic offers an effective mechanism for handling nonlinearities, while genetic algorithms can provide fuzzy logic controllers with real-time adaptive capabilities. This Bureau-developed technique is applied to a laboratory acid-base neutralization experiment. Nonlinearities in the laboratory system are associated with the logarithmic pH scale and the changing process dynamics are due to alterations in pH and buffering capacity input solutions. Results indicate fuzzy logic controllers augmented with genetic algorithms offer a powerful alternative to conventional process control techniques in such nonlinear, rapidly changing systems.

Jan 1, 1992

By Simon W. Houlding

This paper summarizes recent developments in computer modelling and estimation technology. Significant improvements in computational and modelling efficiencies have advanced technical computing to the stage where, for the first time, it can be realistically applied to short-term mine planning and production control. Real-time interactive grade estimation of complex shapes, volumes and grade distributions, based on immediate turn-around of production sample grades, is now possible. An added benefit is the ability to produce complete geostatistical estimates which include confidence limits. These can be incorporated into the decision making and risk assessment processes of production control. Why the need for new technology? What is wrong with the conventional methods which have sufficed for the last thirty years? The response is manyfold. They suffer from inefficient computational processes and conflicts with geostatistical theory. They are responsible for constricting the flow of information between the disciplines involved in the mine production process. Finally, it is illogical to approximate irregular geological and mining volumes with orthogonal sets of rectangular blocks. Geological materials do not occur in block formation; and mining methods which excavate rectangular blocks have yet to be developed. Other computer based technologies have evolved out of the dark ages of rectangular approximations and have successfully dealt with irregular three-dimensional geometries. It is time for computing in the mining industry to follow this example and take full advantage of available technology. To provide the necessary background, consider the basic requirements for successful implementation of technical computing within the mine production process.

Jan 1, 1992

By H. M. Conger

I'm really very pleased to be talking with you today about the environmental impacts of gold ore processing as part of this symposium on emerging process technologies for a cleaner environment. But before I talk about some of the newer developments that are coming, I would like to set the stage by reviewing some of the recent past. Over the last decade or so the U.S. gold mining industry has experienced remarkable growth, primarily in heap leaching operations, and not surprisingly there has been parallel growth of environmental regulations. At Homestake, we have had the excitement of bringing on-line a new mine embodying state-of-the-art technology and environmental planning, and during the same period the flagship of our company, the Homestake mine, has been brought into modern day compliance through the application of innovative environmental technology. This has been a learning process; in both cases we found that we had to develop new ways to meet our objectives. At our McLaughlin mine in California a major achievement was pioneering the use of pressure oxidation, or autoclaves, for refractory gold ores, and at the Homestake it was the development of a unique bio-treatment plant for wastewater. These projects were developed balancing operational goals, environmental concerns and costs, and I would submit that being cost-effective is our greatest challenge in the development of new, environmentally sound, process technology. In meeting that challenge, our job has not been made any easier by the myriad environmental laws and regulations that directly affect the design and operation of our facilities. Most of these constraints have evolved through the political process more or less independently, but in their application there often are over-lapping provisions. Adding to this complexity is the fact that action takes place in both state and federal arenas. As a result, state and federal roles sometimes become intertwined, and a good case in point is provided by various cyanide issues faced by gold producers. The vast majority of U.S. gold mining takes place in the so-called "mineral States," the western States that come under the Mining Law of 1872 as amended. This is the basic statute that provides for access and tenure to develop mineral resources on federal lands in those states. There is gold mining outside the defined mineral States, and there is also gold mining in the mineral States on private lands. Our own Homestake mine in South Dakota is one of the best examples of the latter category: located entirely on private land, it is nevertheless subject to at least 13 federal environmental statutes and some 29 federal regulatory requirements. There are also nine significant state statutory and regulatory requirements that apply. On federal lands in the mineral States there are numerous federal statutes and regulations which affect mining, over and above the current Mining Law. These, which are in addition to the laws applying to private land, include the National Environmental Protection Act and the Federal Land Policy and Management Act, among others. Still, those who advocate radical changes in the basic Mining Law would have us believe that sweeping environmental protection and reclamation provisions, not to mention new land use restrictions, are needed. Such changes could effectively prohibit mining on the federal public lands. Strict enforcement of our current Mining Law would have presented most of the abuses cited by the critics but if the Law is to be changed at all, I believe that, at a minimum, the principles of self-initiation and security of tenure embodied in the present statute should be maintained. These are critically important concepts, but there are other statutory and regulatory issues constantly before us as gold miners. Let me cite a few examples: Reauthorization of RCRA There are several bills being considered by Congress to amend the Resource Conservation and Recovery Act (RCRA) that have as their theme

Jan 1, 1992

By Jerry Motz, Gary Beerkircher

Through a joint development program between Bougainville Copper Ltd. and Nordberg, the MP1000 cone crusher was developed and tested during the period between 1982 and 1987. Following the successful prototype work, Bougainville Copper purchased an additional three units. A second prototype was installed at Codelco's El Teniente three-stage crushing installation in 1987. This unit has also completed its test period successfully. Three additional units have been sold, making a total of eight, to date. Two will be installed as secondary crushers in two separate large aggregate plants. The first unit installed in the United States was placed in operation at Vulcan Materials Company's plant in Manassas, Virginia in early May 1990. Another unit is being installed in Asarco's Ray Mines expansion. The Asarco installation will be a SAG MILL pebble crusher producing approximately 600 STPH of nominal 1/2" product. Application Objective The objective was to design a crusher that would fit on an existing 7' foundation with minimum modification and yet be capable of twice the production of a 7' cone crusher. In meeting this objective, the power rating was increased to 1000 HP, the maximum design crushing force was increased and the crusher was designed to operate at higher speeds than an equivalent size Symons cone crusher. The MP1000 was also designed to operate with a head throw that can be greater than the equivalent Symons design. Design The crusher design criteria involved the recognition of the crushing force increase required for the finer crushed products than

Jan 1, 1992

By W. J. Roberds

A formal and explicit yet cost-effective approach is proposed to ensure that decisions made during mine development are optimum (with respect to their ultimate consequences) as well as defensible. This risk management approach is based on probabilistic risk assessment and established decision analysis techniques, and appropriately considers the relationships among various mine development decisions, tradeoffs among consequences, the uncertainty in predicting consequences, and the benefits of flexibility to respond to changed conditions.

Jan 1, 1992

By N. B. Prenn

Many recent projects have been developed and mined based upon imaginary reserves. Imaginary or "geo-fantasy" reserves have cost many companies millions of dollars. The significant and varied technological advances in the mining arena have done little to curb reserve calculation problems. These advances may have served to increase the prevalence of reserve problems by putting more tools in the hands of personnel not properly trained or experienced in reserve estimation. This paper will discuss potential problems related to calculating reserves, which include: SAMPLING ERRORS -obtaining a representative sample. -Decay analysis of wet RC drilling -Bias introduced by sample preparation. -Assay bias; Coarse gold. -Specific gravity samples. GEOLOGICAL ERRORS -structural boundary definition. -Separation of high grade and low grade zones. -Incorrect continuity assumptions MODELING ERRORS -Too much influence of high grade samples. -Improper method of calculation. -Assumed range of influence. -Errors in the data. ENGINEERING ERRORS -Inaccurate assumptions. -Inadequate metallurgical testing. -Designed bottlenecks.

Jan 1, 1992

By D. Diggins

Experimental apparatus for the determination of powder wettability is described. The principle of the technique is based on the measurement of the equilibrium capillary pressure in a packed bed of particles. Both the macroscopic solid-solution-vapour contact angle, e, and the specific surface area, A(m2g-1), of the powder, can be obtained. Experiments on angular quartz particles have been performed. A wide range of situations have been covered: hydrophobic and hydrophobic particles wetted with water, a variety of organic liquids and solutions of surfactants. The results show that reliable and reproducible values for 0 and A for angular and relatively coarse powders can be obtained with the proposed equipment for advancing liquid fronts in the absence of soluble surfactants. In the latter case and for receding liquid fronts in general, only qualitative trends have been obtained.

Jan 1, 1992

By Roy Eric Lurie

Computer based signal processing techniques for obtaining empirical dynamic models from measured mill circuit data are discussed. This modelling is the first step towards designing a particle size control strategy. Experimental data from a computerized acquisition sys tern is examined and analysed, and a number of model identification procedures are applied. The resulting models are compared and a suitable model is selected, illustrating the benefits of computer tools for control system design.

Jan 1, 1992

By Matthew J. DeMarco, Anthony T. Iannacchione

Coal bumps have presented serious mining problems in the U.S. throughout the 20th Century. Fatalities and injuries have resulted when these destructive events occur at the working face. Persistent bump problems can result in abandonment of large reserves or lead to premature mine closure. Through the years, a1ternative techniques such as artificial supports, extraction sequencing, destressing, pillar design changes and specific pi1lar retreat practices have been successful1y imp1emented to mitigate coal mine bumps. Several techniques have evolved for room-and-pi1lar operations that control the way the roof rock breaks, regulating the manner in which stresses are redistributed in the mined section. Special mine layouts employed in longwall mines have also proved to be successful in safely redistributing or containing excessive loadings. However, with ever increasing production rates, greater overburdens and new mining systems, the need to evolve even more effective bump control designs will continue to challenge the U.S. coal mine industry.

Jan 1, 1992

By R. Kadeg, S. Pavlou

A methodology for developing and utilizing risk-based action levels for soils in site closures is discussed. The methodology is based on standard exposure pathway models which are consistent with current regulatory guidance on conducting risk assessment. A simple approach to evaluating the potential for contamination ground water from the projected criteria based on the Toxicity Characteristic Leachate Procedure (TCLP) is also presented.

Jan 1, 1992

By V. P. Keran, K. Leung

Two 32 foot x 14% foot, 6.4 MW autogenous mills have been installed in the Mount Isa Mines Copper Concentrator to replace the fine crushing plant, fine ore bin, rod mills and primary ball mills. This paper describes the reasons for the change, the rationale for the new circuit design and configuration, the design and scale-up processes used to size the mills, considerations for the installation of large mills inside an operating concentrator and some early operating data.

Jan 1, 1992

By S. Serata

Background Results of the above study in the August 1991 issue of Mining Engineering offer valuable lessons in the solution of cutter-roof problems. The original study plan was initiated by the discussion authors to solve the problems using the "stress control method" of mining (Serata 1976,1982; Serata, Carr and Martin, 1984; Serata and Gardner, 1986; Serata, Gardner and Preston, 1986; Serata, Gardner and Shrinivasan,1986; Serata and Kikuchi, 1986; Serata, Preston and Galagoda, 1987) However, the plan and the planner were changed to the arrangement reported in the paper. The change was considered reasonable at the time due to the mine engineers' uncertainties about the stress control method. Consequently, the basic principle of the study was shifted from the original stress control method to the method described in the paper, which will be called the "yield pillar method" for the purposes of this discussion. The paper convinces the reader that the yield pillar method fails to solve the cutter-roof problems. This doesn't mean that the stress control method also fails. Actually the contrary is true, as discussed below. Limitation of the yield pillar method The paper illustrates clearly how poorly the yield pillar method performs in solving the problem. The reason for this failure is the lack of the protective stress envelope needed to stabilize the cutter roof. Unfortunately, the protective envelope cannot be formed properly without utilizing the stress control method of mining. Changing the pillar size does not make much difference in the roof stability.

Jan 1, 1992

By Robert S. Ondrey, Robert A. Haney, David J. Atchison

The Mine Safety and Health Administration has conducted tests to determine the effectiveness of two methods for reducing diesel particulate emissions in underground coal mines. Both methods involved collection of the particulate material before being released into the environment. One method utilized a disposable pleated paper filter attached to the tail pipe; the other utilized a reusable wire mesh screen attached to the tail pipe. This paper describes the instrumentation and testing used to evaluate both control methods. Results of respirable dust and diesel particulate measurements made underground are presented and analyzed.

Jan 1, 1992

By D. E. Healy

In 1989 an Autogenous Grinding Task Force was formed to study potential autogenous grinding circuits to replace the existing semi-autogenous grinding at the National Steel Pellet Plant located in Keewatin, Minnesota. Pilot plant test work performed by the Hanna Research Center (HRC) indicated that fully autogenous grinding with pebble extraction and crushing could feasibly be incorporated into the existing circuits. In 1990, one of the existing ten grinding mills was converted for an in-plant test incorporating pebble crushing. The full scale test work conducted in 1990 and 1991 verified the pilot plant projections with primary mill throughputs from the fully autogenous circuit utilizing pebble crushing being greater than throughput of the existing SAG mill circuits.

Jan 1, 1992