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By G. Bloomsburg, R. E. Williams, S. D. Vincent

A modeling scheme is developed to simulate the hydrogeologic effects of mine design and development in unsaturated rock. Simulations are conducted using the UNSAT2 finite element computer program and hydrogeologic data from the site of a proposed mined-out waste repository at Yucca Mountain, NV. Results of the simulations are analyzed for: •variations in the direction of ground water flow and in the distribution of pressure head caused by the design of the mined out openings; and •mine design variables that affect the predicted rates of mine water inflow. Evaluating the hydrogeologic impacts of mine design and mine development in unsaturated rock is significant in several respects. Characterization of the preemplacement of wastes along the fastest path ground water flow system at the Yucca Mountain site has been a primary research effort. Ultimately, however, the degree to which waste isolation is achieved will depend largely on the post-mining hydrogeologic environment as altered by the mine design and on the radionuclide inventory and resulting heat effects of the repository. Therefore, an ongoing characterization of the proposed mined-out nuclear waste repository at Yucca Mountain, NV, is recommended. Modeling results indicate that: •mined out openings will affect the movement of ground water, both in rate and direction; •hydraulic effects of mine development depend on the hydrogeologic environment and on mine design geometry; •mine water inflow is possible in the unsaturated zone, even for mines developed in hydrogeologically homogeneous rocks; and •mine water inflow can occur at values of down ward flux that are appreciably less than the saturated hydraulic conductivity of the overlying rocks.

Jan 1, 1991

By Victor F. Hollister

Porphyry copper deposits can be categorized into three models for purposes of prospect evaluation: Breccia-pipe, modified Lowell and Guilbert, and diorite models. The modified Lowell and Guilbert model is normally associated with a quartz-bearing intrusive and a potassic, phyllic, argillic, and propylitic alteration sequence. Variations can occur in the alteration zones of this model that range from orthoclase-rich (Kalamazoo, Silver Bell, and Mineral Park) to ortho- clase-deficient (Petaquilla and Bougainville) potassic zones. The unifying features of the model are the presence of a phyllic zone and a quartz-bearing intrusion. The breccia-pipe model (Toquepala) is characterized by structure and alteration related to or controlled by breccia. Where tourmaline occurs in the breccia, the identity of the model is usually clear. However, if tourmaline is not commonly developed in the breccia (La Caridad), the deposit can be misidentified as to model. Porphyry copper deposits associated with quartz-deficient intrusives, whether these are calc-alkalic diorites or alkalic plutons, are characterized by alteration suites distinct from those of the modified Lowell and Guilbert model. These have been generalized as diorite model porphyry deposits. Because alteration and mineralogical development in diorite model deposits is distinct from that of the modified Lowell and Guilbert, ore guides and exploration tactics differ for the two models. The reprint that follows describing the three prospecting models summarizes their features. It is to be emphasized that these are models used in exploration for specific deposit types and are not genetic, tectonic, or geographic models. Porphyry copper deposits can be metamorphosed. Gibralter is an example of a Lowell and Guilbert model deposit that has undergone regional metamorphism.

Jan 1, 1991

By Michael W. Neill, O&apos

Drilling slurry has become an effective aid to the construction of drilled shafts in caving and/or waterbearing soils. Historically, drilling slurry made of bentonitic clay and water was first used in the US in water well drilling as early as 1889. In coastal Texas drilled shaft contractors began using slurry, often made of on-site clay mixed with potable water, in the years following World War II, on a relatively routine basis. This type of slurry was used to "process" boreholes, in which the borehole was drilled "in the dry" until water or unstable soil was encountered, after which water and on-site clay were introduced into the borehole and mixed in place with the auger or other drilling tool. Drilling then continued under a slurry consisting of the uncontrolled mixture of clay and water until the excavation had reached a relatively impermeable and cohesive material. At this point, a steel casing was dropped into the hole and sealed into the lower stratum of impermeable geomaterial (soil or rock). The slurry inside the casing was bailed or pumped out, drilling continued to plan depth in the dry, a reinforcing cage was set in the partially cased borehole, concrete was placed and the casing was withdrawn. Some soil-slurry was undoubtedly trapped between the casing and the borehole wall, but the quality of that slurry was usually of no concern, because engineers of the period usually viewed drilled shafts as nothing more than deeply buried footings. Any unejected slurry would only serve to lower side shearing resistance, not yet considered in design, but would have no effect on end bearing. In the 1960 's the effectiveness of soil-slurry came into question because it was often ineffective in maintaining borehole stability at marginal drilling sites and because the economy of using shaft resistance, in addition to end

Jan 1, 1991

By M. J. Adam

The U.S. Bureau of Mines is investigating the partitioning of selected complex minerals into simple phases using sulfidation reactions. Successful partitioning of complex mineralogy to simple phases may afford an opportunity to improve selective extraction of mineral constituents of economic value. The research has shown that complex minerals, such as chalcopyrite (CuFeS2) and pentlandite [(Fe,Ni)9Se]' may be partitioned to the simpler phases covellite (CuS) plus pyrite (FeS2) and vaesite (NiS2) plus pyrite (FeS2), respectively. Demonstrations of these reactions were verified through long-react ion-time (24 h or more) experiments, but basic rate investigations and modeling were not included in the previous research. This report describes research aimed at determining the rate at which the complex mineral CuFeS2 converts to the simple sulfides CuS plus FeS2. Small samples of CuFeS2 were blended with elemental S prior to thermal treating under an He atmosphere for time periods up to 4 h. Products from each treatment period were characterized using metallography, chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results of the investigation revealed a rapid conversion of CuFeS2 to CuS plus FeS2 early in thermal treatment periods. As the reaction occurred, a CuS rimming of particles was observed which separated the reacting species (CuFeS2 and S) and caused a considerable decrease in transformation rate.

Jan 1, 1991

By S. B. Castor

Although production generally satisfies demand for rare earths, new markets may make undeveloped resources, particularly those rich in yttrium, more interesting. A Precambrian carbonalite orebody at Mountain Pass, California, has been the world's largest rare earth producer. Minor rare earth production comes from titanium placer mining in Florida and uranium mining in Canada. Prior to operations at Mountain Pass, North American production was mostly from placer deposits that constitute large, low-grade rare earth resources. Newly discovered North American rare metal resources in peralkaline igneous rocks are potential yttrium producers. Most of these resources are in a continent-wide belt of anorogenic magmatic rocks approximately coeval with mineralization at Mountain Pass. Other untapped rare each resources in North America are generally light rare earth-dominated and small or of low grade.

Jan 1, 1991

By Alfred Jr. Petrick

Modelling of cash flows and calculation of net present value of rate of return over the expected life of a mine/processing unit continues to be the accepted basis for mineral investment decision-making. The computer and spreadsheet programs have greatly improved ability to perform sensitivity and risk analysis, hence our ability to deal with key analytical problems. These problems of cash flow analysis result from the necessity of forecasting an uncertain and risky future. Cash flow models begin with the critical assumption of a "design basis", then integrate all of the variables relevant to the investment decision including forecasts of price, cost, taxation, financial conditions, and company strategy. Alternate "scenarios" portray possible future outcome of the investment decision. The potential for straying from reality is enormous. The computer has eliminated the time consuming hand calculations from the cash flow analysis, but the analyst still struggles with the risk of trying to predict "how the project will really turn out".

Jan 1, 1991

By Mathew P. J

The CSIRO Division of Mineral and Process Engineering in Melbourne has been developing on-stream analysis sensors based on neutron and gamma radiation for better control of quality and process operations. This has resulted in the development of Ironscan, an on-stream analyser that measures the iron content of both lump and fine iron ore on conveyor belts. It can be mounted under existing conveyors with minimal modifications to the conveyor structure and can cope with steel cables in the belt. An interface gauge and an on-stream coal ash analyser have also been developed, both based on measurement of natural radioactivity. The interface gauge monitors the interface between liquor and mud in thickeners and washers, provided the natural radioactivity of the mud is sufficiently high to detect it above background. The natural-gamma ash gauge is a valuable addition to the Coalscan range of ash gauges. It is applicable to heavily laden coal conveyors or bins where the coal bed thickness exceeds 30 cm, and also to lightly laden conveyors, provided the coal is profiled on the conveyor.

Jan 1, 1991

By N. S. Dalal, V. Castranova, K. Van Dyke, V. Vallyathan, J. H. Kang

Previously we reported crushing or grinding crystalline silica results in silica-based free radicals on the particulate surface which can generate hydroxyl radicals in aqueous solution (1). Now we find that freshly ground silica is more cytotoxic to and a more potent activator of alveolar macrophages than similarly sized aged silica. Since the United States Department of Labor estimates that over 1.25 million American workers may be exposed to freshly ground crystalline silica arid nearly 60,000 may be at risk of developing some degree of silica-based occupational lung disease, then this is hardly a trivial problem. Occupations of concern include workers who come in contact with silica including miners of soft and hard minerals, stone quarry workers, glass workers and even millers who stone grind flour. Acute silicosis is manifested by inflammation, alveolar lipo-proteinosis, and the rapid development of respiratory disability that depending on the dose of silica can produce chronic silicosis which takes 20 - 40 years to develop. It is demonstrated by the appearance of concentric hyalinized nodular lesions and progressive development of dyspnea(3). Certainly the free radicals produced on the surface of freshly ground crystalline silica play a most important role in producing the acute and chronic symptoms of silicosis. When respirable-size freshly- ground silica (0.1 -- 5 microns in diameter) enters the deep alveolar spaces in the lung and contacts an aqueous environment, hydroxyl radical are generated and cellular damage is bound to occur. We have found that freshly ground silica can cause lipid peroxidation and lysis of erythrocytes(1). The objective of this investigation was to further elucidate the enhanced toxicity of freshly ground versus aged silica. It can be deduced from the data that not only is freshly ground silica more cytotoxic to alveolar macrophages but it is a more potent stimulant of these phagocytes. However the mere characterization of toxicity is not entirely helpful if there is not a useful means to detoxify the cause of the damage. We have identified an aqueously soluble substance that can be used in high dilution to detoxify the SiO(•) and Si(•) type of free radicals. This is the organosilane known as Prosil 28 (R). We have found that coating of the freshly ground silica can effectively reduce its toxicity. The importance of this observation is that such a coating could be used with water cooled drills. This may partially detoxify silica at the point of generation of the free radical, i.e., the generation of the fresh silica dust itself. Such a coating could be used in great dilution 1:103 or 1:104. The coating would be long lasting, inexpensive and should be non-toxic because of the great dilution.

Jan 1, 1991

By William S. Gardner

It is certainly an honor to have been invited to address the Deep Foundation's Annual Meeting on such a vast and weighty topic as "Present to Future Design Considerations of Deep Foundations." Acknowledging the enormity of this 30-minute assignment, I hope to at least scratch the surface of the topic deep enough to generate some thought and reflection. Design considerations, be they current or future, bring to mind a number of important subtopics which comprise the design process. As shown by Figure 1, a flow chart of this process describes, in general terms, the sequence of a deep foundation design.

Jan 1, 1991

By Terry R. Neumann

In 1989, the Bureau of Mines conducted a mineral resource investigation of the 52,350-acre Jersey Jack study area, located in the Clearwater Mountains of north-central Idaho. Twenty-eight mines and prospects were examined, and 483 rock, placer, and petrographic samples were collected during the field study. Two properties contain gold resources; mining company data show the Robinson Dike mine contains an estimated 940,000 tons of "drill proven and probable reserves" averaging 0.041 oz/ton gold, and the Bureau of Mines investigation showed the Blacksand placer mine contains an estimated 64,000 cubic yards of identified placer resources averaging $8.13 in gold per cubic yard. Sample analyses from other properties indicate that gold resources are likely to exist; however the low tonnage, narrow, fissure-vein type deposits would require mining by relatively high-cost underground methods and would be subeconomic at a gold price of $400/oz.

Jan 1, 1991

By Williams J. D

Magnetite has been used in coal processing for many years and it is likely that its use will continue well into the twenty first Century. While magnetite is only a minor cost component in coal processing, the use of processed magnetite in dense medium separation is essential to provide the split of quality coal products which the markets of today demand. The occurrence of magnetite in Australia is relatively abundant, but a combination of its iron content, magnetic properties, quality and proximity to the coal processing plants is essential to provide a low cost product for use in the Coal Industry. The demand for more splitting of coal in coal processing may require more grades of magnetite, particularly as a finer grade lower specific gravity medium to separate the finer quality low ash coals.

Jan 1, 1991

By B. J. Scheiner, D. A. Stanly, P. M. Brown

The Bureau of Mines has developed an equation that describes the dewatering of clay slurries with poly- ethylene oxide. This dewatering equation is: A[ ] = KC + b where n, k, and h are empirical constants and C is the concentration of polymer solution used for dewatering. The minimum amount of polymer required for dewatering, A, is determined by titration of the clay slurry with a polymer solution. In this report, the dewatering equation is applied to data obtained for a polyacrylamide dewatering sequence. Fundamental similarities between the dewatering properties of clays and the viscosity of polymer solutions were observed. These similarities were explained by correlating an equation describing polymer configuration in solution with the dewatering equation. This correlation showed that the amount of polymer required for dewatering and polymer solution viscosity are both the consequences of the frictional interaction of entangled polymer coils.

Jan 1, 1991

By Thomas E. P. Wechsler

The limiting factor for most pyro-metallurgical processes in secondary cop- per melting is the time required to heat and melt the product. American Combustion's proprietary PYRETRON variable £uel/air/oxygen combustion system improves the throughput of existing scrap melting and heating furnaces for copper and copper alloy production by increasing the rate of heat transfer from the flame to the product. The increased productivity and energy savings obtained from this technology can result in sizable reductions in operating costs for smelting operations.

Jan 1, 1991

By W. M. McKewan

This U.S. Bureau of Mines report discusses wire ropes used for hoisting in U.S. mines. The in-formation presented was extracted from a large body of data compiled by the U.S. Mine Safety and Health Administration (MSHA) using a data base management system (DMS). Further, these extracted data were then manipulated to provide tables of data that show the types and amount of wire rope used for hoisting. This report describes the different types of wire ropes and how a DMS can be used to manipulate MSHA's wire rope inventory data. The data indicate that more 1-1/4-in-diam ropes, 6x27 construction ropes, and right lang lay ropes are used in U.S. mines than ropes of any other diameter, construction, or lay type.

Jan 1, 1991

By David S. Holmes

An overview of existing biological technologies for the recovery of copper and uranium is presented. Engineering and biological challenges and opportunities in these areas. are discussed. New opportunities for the biooxidation of refractory gold ore are described. Techniques for the development of new strains of microorganisms. for commercial metal recovery applications are discussed with special reference to the genetic manipulation for bacterial strain improvement.

Jan 1, 1991

By G. Grant Smith

In situ bulk density of coal is a variable applied to various aspects of coal resource evaluation, such as compositing ply analyses of coal attributes that are expressed on a weight per cent basis, and determining tonnages from volume estimates. Its value is a function of composition and porosity of the in situ material. When densities of ash-free coal, ash and water are fixed, in situ bulk density of a coaly mix can be expressed as a function of proportionate weight of ash in the mix. Correlations between in situ bulk densities and weight per cent ash contents of coaly mixes have been estimated for four general rank classes of coal (low medium volatile bituminous, high volatile bituminous, subbituminous, and lignitic).

Jan 1, 1991

Over the past 15 years many world-class gold discoveries have been made in the region. Some deposits, such as Lihir and Porgera in P.N.G., have a contained gold resource that places them among the top dozen deposits ever found on a worldwide basis. Can we see any pattern to these discoveries, or are they the result of good luck or chance by geologists and prospectors who struck it rich? Whilst such discoveries were a feature of the gold rushes of the 1850s and the 1900s, the present boom is now scientifically based. This paper develops an argument that long-tent, multi-disciplinary exploration by experienced geoscience teams underlie the successes achieved. Dis- coveries nearly always reflect a combination of skills, drawn from the areas of geology, geochemistry, geophysics and remote sensing, and a team approach. They do not represent the chance finds of a prospector's pick or such as the Norseman discovery where the gold reef was first noted by the prospector when his horse fell over the outcrop. The following deposits provide major examples of exploration successes within the Australian-Pacific region, it is not an exhaustive list and I have noted other significant producers at the end of this paper. For the Australian mines listed and based on our estimates for 1990 gold production, they represent about 20 per cent of the Australian production total.

Jan 1, 1991

By Eric Pirard

"A mineralogical and trace element analysis was performed on the Küre historical slags in order to evaluate the possible recovery of copper and cobalt. Reflected light microscopy, electron microprobe and image analysis were combined to determine the Cu and Co distribution in the slag.The results indicate that 81% of the total cobalt is chemically combined in the fayalite whereas only 3.4% is in the mechanically entrapped sulphides. The remainder being in hercynite and wiistite. On the other hand, 95% of the total copper is in the sulphide phase.This kind of applied mineralogical investigation gives invaluable information when it is performed preliminary to metallurgical experiments.IntroductionThe recycling of metallurgical slags is a growing business. The operation is directed toward recovering base metals (Cu, Pb, Zn), and by-products (Floyd and Mackey, 1981).Two reasons are invoked to explain metallic losses in slags: (1) mechanical entrapment of matte globules in the silicate melt; and (2) chemically combined metals in the slag-forming phases. Obviously, a chemical analysis of the slag cannot distinguish between those two modes. Grinding and flotation of the liberated sulphides have often been used to evaluate the importance of mechanical entrapment (Mechev, 1970; Imris , 1982).Recent studies in applied mineralogy of pyrometallurgical products (Bérubé et al., 1987; Pignolet et al., 1986) have demonstrated the benefits of quantitative mineralogical analyses of slags. Optical microscopy together with electron microprobe and image analysis offers a powerful and easy way of quantifying the relative importance of mechanical and chemical losses."

Jan 1, 1991

Integrated chemical thermodynamic software and computerised databank systems have evolved over the last 15 years. The extent to which these systems have automated thermodynamic calculations relevant to extractive metallurgy is examined. The scope for further automation and the role of the expert consultant is discussed.

Jan 1, 1991

By Equivar J, Mirabal C, Pyper R

In 1984, work was started to determine the viability of heap leaching silver-containing waste dumps from Cerro Rico near Potosi - Bolivia, at an elevation of 4300 meters (14 100 ft.). The result today is an unusual heap leach utilizing fine crushing, grinding, and agglomeration to process 1000 tonnes per day of ore containing 200 g/tonne silver. The unique metallurgi- cal, economic, and political factors will be discussed which led to the decision to build a heap leach rather than a conventional agitation leach plant. Capital and operating costs will be given along with some of the uncommon process design and equipment problems encountered while developing the operation.

Jan 1, 1991