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By D S. Clarke, K B. Sporli

Structure is an important control in the localisation of gold mineralisation in epithermal systems. There has been, however, only limited investigation of the structural elements involved; such a study is currently directed at the gold deposits of the Coromandel Volcanic Zone (CVZ). Here, mineralised veining and brecciation ranges up to tens of metres in thickness. Dips of veins are mostly steep, but not vertical, and there is a significant number of low angle veins. The structural control of epithermal deposits may be considered on four scales. At the mega-tectonic scale, pre-volcanism fault patterns mostly relate to separation of the New Zealand micro-continent from Gondwana. The major structural controls on mineralisation at this scale, however, are associated with the volcanic arc processes responsible for the CVZ. Post-mineralisation faulting are linked to the Hauraki Rift and the Colville Ridge-Havre Trough system. Regional scale faults controlling the distribution of gold deposits are the product of these tectonic events; much of the faulting may relate to rifting and calderas, but further work is required to demonstrate this. Detailed study is also needed on vein systems at the prospect scale to validate models of brittle deformation responsible for such systems. Evidence that a variety of structural mechanisms dominated in different deposits is found at the vein scale, with Coromandel gold deposits being classified according to their different styles of vein-fill texture.

Jan 1, 1990

By M. Craig Miller

As the trend continues in the U. S. toward inceased capital investment in longwall mining equipment and wider panels. the risk also increases for gotential financial and production loses due to undetected geologic anomalies. This paper describes how RIM Sm (Radio Imaging Method) is utilized in conjunction with more traditional exploration and interpretive methods to delineate fluvial channels. displacement faults and poor roof conditions in a Southeastern Ohio coal mine

Jan 1, 1990

By Samuel B. Romberger

During the formation of most epithermal precious metal deposits geochemical changes can be characterized by the introduction of large amounts of silica, minor amounts of sulfur, and trace quantities of gold, silver, and other metals. During the same process, large amounts of alkalis and alkaline earth elements, such as sodium and calcium, and sometimes aluminum are removed from the rocks. In deposits hosted by carbonate sedimentary rocks large amounts of carbonate may be removed before or during the silicification process. Small amounts of iron may be introduced by the mineralizing solutions, however, in most epithermal deposits this may be a relatively immobile component and is locally derived. The results of these changes are deposits consisting of up to 90 to 95 percent silica as quartz veins, breccias, silicified host rocks, and jasperoids containing a few percent sulfides, mostly pyrite, and a few parts per million gold and silver. Other minerals commonly but not always present are barite, arsenic, antimony, or mercury sulfides, and tellurides. Often gold shows a spatial, and therefore an apparent genetic, relationship to pyrite in primary ores. Alteration and gangue assemblages sometimes include sericite and/or adularia, and parts of the deposits may contain alunite and/or clay minerals. Even though the value of these deposits usually lies in their gold content, silver is usually present in larger quantities than gold (Romberger, 1990). Based on these general characteristics observed in a large number of epithermal deposits, together with processes occurring in active geothermal areas to which they are often genetically linked (Henley, 1985), a model is proposed whereby deposition occurs along a subhorizontal zone separating environments of contrasting chemistries. The upper environment is characterized by oxygenated acid waters and the deeper environment by a reducing near neutral aqueous system. The model describes the chemical changes occurring as a result of mixing and/or boiling within this zone. It builds upon the physical models proposed by Romberger (1988a) for disseminated gold deposits and Bonham (1988; 1989) for volcanic rockhosted deposits.

Jan 1, 1990

By Kenneth N. Pike

The need to comply with environmental regulations and increase production has resulted in modifications to the East Penn blast furnace operation. Changes made include furnace design modifications, closed loop water cooling with heat recovery, automated weighing and charging, automated tuyere punching, ammonia scrubbing of tail gases and improved metal and slag handling to minimize environmental impact. These changes have resulted in a marked increase in yearly production and compliance with many of the air, water and solid waste regulations.

Jan 1, 1990

By Thomas M. Barczak

The U.s. Bureau of Mines is conducting research to optimize the utilization and design of mine roof support systems. This report describes methods to evaluate resultant loading on longwall shields, defined as external resultant vertical and horizontal force acting on the canopy and base. Four models are considered: two rigid-body models, an elastic model, and a numerical model. The rigid-body models equate measured internal shield forces to unknown external resultant shield forces (loads) through rigid-body analysis of static equilibrium requirements. The elastic model develops a solution to shield mechanics by evaluation of the load-displacement relationship and stiffness characteristics of the support structure. The numerical model is a two-dimensional finite-element representation of a shield structure. Model determination of resultant shield loading is compared to controlled loading of a shield in the Bureau's mine roof simulator. Parameters investigated are shield height, canopy contact configuration, canopy and base horizontal constrainment, and boundary conditions imposed by vertical and horizontal shield displacements. It is concluded that rigid-body models are most applicable to in situ measurement of shield loading. Applications requirements and potential error sources are discussed.

Jan 1, 1990

By Gary A. Wickham

In the zinc industry, this past decade has seen both prosperity and depression. Significant changes have occurred throughout the world in mining, smelting, refining, and marketing. This paper will review many of the industrywide changes of recent years and the potential impact for 1990s. In addition to an historical review of supply and demand are discussion of technology considerations for zinc and zinc based products, effects of geographical shifting of markets, and projections for the 1990s.

Jan 1, 1990

By Paula N. Wilson, W. T. Parry

Carbonaceous and metalliferous black shales occur in close proximity to Mercur-type gold deposits in the southern Oquirrh Mountains, Utah. These shale units, the Manning Canyon shale and the Long Trail shale, have undergone regional hydrothermal alteration. Hydrothermal solutions oxidized organic matter and pyrite, replaced shale by hydrothermal phyllosilicates and silica, and replaced fossils by phyllosilicates. The shales are depleted in organic carbon, calcium carbonate, alkali and alkaline earth metals, and enriched in aluminum and hydrogen. Hydrothermal veins containing illite, chlorite, pyrophyllite, kaolinite, Fe-oxides, and sulfides are present throughout the study area.The illite in veins is an ammonium illite that contains up to 2 % NH4 and is correspondingly depleted in K. Correlations among Au, As, Hg, TI, Sc, and rare earth elements indicate that hydrothermal fluids responsible for formation of ammonium illite were gold bearing. K/Ar ages of illite veins and illite-rich, clay-size separates of altered shales indicate hydrothermal activity occurred in the time range 193 to 122 Ma. Several ages from clay-size separates within the Mercur district cluster near 160 Ma. These ages are coeval with thrust faulting recognized to the north and west.

Jan 1, 1990

A nuclear technique utilising the gamma-ray resonance scattering process is used at Isa Mine for the determination of copper in drill core and bulk mineral samples. The Copper Bulk Analyser (CBA) provides quick and accurate non-destructive copper analysis of drill core at costs two to three times cheaper than conventional chemical techniques.The almost immediate availability of sample results enhances the efficiency of the mine geologist in the duties of grade control, design of diamond drilling programmes, and input to planning. The unit has proven to be a reliable and accurate production tool requiring a minimum of technical support.

Jan 1, 1990

By M. G. Hester

The inadequacy of traditional geostatistical methods for estimating some precious metals deposits has become apparent in the last few years. New methods or estimation such as Indicator, Probability and Multigaussian Kriging are difficult to understand and apply. Case studies using a new method of variogram calculation proposed by Srivastava show the method valuable for variogram estimation in precious metal deposits. Some simple, sometimes unorthodox. estimation methods that have proved useful in Some situations are presented.

Jan 1, 1990

By B. N. Church, A. R. Pettipas

"The second vertical derivative method of processing aeromagnetic data from low level helicopter surveys yields results correiatable with the known geology and may be utilized to indicate possible targets for future exploration in the Silver Queen and Equity Silver mines areas, near Houston in central British Columbia . The principal zones of alteration associated with mineralization, known from detailed mapping, are further delineated and extended in a way not possible by a cursory examination of the original magnetic data.IntroductionThe second derivative method of processing aeromagnetic data is a long established procedure used to enhance the short wavelength content of the magnetic fields. Some recent exam pies of the use of the second derivative technique have been published by Chandler (p. 385), Sun Yunsheng et al. (p. 424) and Yarger (p. 223) in Hinze, 1985. According to theory, the ""second vertical derivative"" is closely related to the rate of curvature of magnetic (or gravity) fields and is particularly useful in resolving and sharpening local anomalies. The contours on second derivative maps may coincide with important features such as lithological boundaries, faults and mineralized zones.In the Houston area, central British Columbia, aeromagnetic data supplied by local mining companies provide a ready base for analyses. Examples are data sets for the Silver Queen and Equity Silver mines centred 35 km and 34 km south and southeast, respectively, from Houston (Fig. 1), (Cochrane, 1970 and Church, 1985)."

Jan 1, 1990

By Chen L. Lin, Luis R. M. Bittencourt, Jan D. Miller

Recently research efforts have been made to obtain a high-purity gibbsite concentrate, suitable for first-class alumina refractories, from a Brazilian bauxite ore containing gibbsite (50%), quartz (35%),and kaolinite (15%). Detailed polished-section microprobe analysis was used to describe the liberation characteristics of the ore. Experimental results suggest that the kaolinite liberation characteristics can be described by King's liberation model and that only about 11% of the kaolinite is expected to be liberated at a particle size of 75 µ. Bench-scale experiments for the flotation of gibbsite/kaolinite from quartz using alkyl sulfates as collectors were particularly successful at pH 2, and under appropriate conditions a concentrate containing 93.0% A1 0 (calcined basis) was obtained 2 3 at a gibbsite recovery of about 96%. Subsequently, the more difficult separation of kaolinite from gibbsite was accomplished by kaolinite flotation from the alumina concentrate with a quaternary ammonium salt at pH 6 to produce a high-purity gibbsite product, 97.4% A12O3 (calcined basis), at an overall gibbsite recovery from the bauxite flotation feed of about 90%.

Jan 1, 1990

By K. V. Viswanathan, P. Sornasundaran, S. E. El-Mofty

Dolomite is found to undergo preferential dissolution in aqueous solutions and this is found to be strongly dependent on the solid to liquid ratio (SIL). Electrokinetic studies done under the sump conditions revealed that the mineral surface charge is also affected markedly by the solid content in the suspension. Conditioning of the dolomite at low SIL ratios for short time intervals showed preferential dissolution of calcium leading to a magnesium-enriched dolomite surface. At higher SIL ratios and longer conditioning times, calcium depletion from the solution and a calcium-enriched dolomite surface resulted. The results are discussed in terms of surface precipitation and/or bulk precipitation and surface conversion of dolomite to the calcium-enriched phase (calcium carbonate and/or magnesian calcites).

Jan 1, 1990

By D. M. Wyslouzil

The fundamentals of dissolving silver and silver minerals are discussed in the following sections: 1) Basic chemical reactions in the silver system 2) Leaching of pure silver minerals 3) Leaching of silver-bearing ores 4) Description of processes The basic chemical reactions of silver are an important guide to the mineral processor or the extractive metallurgist, particularly for systems in which complex formations are balanced against solubilities. The competition of other cations for free ligands can shift the equilibrium to the detriment of silver. Solubilities of pure silver minerals in specific solvents may not be a good indication of the solubility of silver minerals in ores. The abundance of silver minerals which usually appear in a typical ore precludes the selection of a single method that would result in the best extraction of silver from all minerals in the ore. Frequently, the recovery of silver from host minerals requires a destructive pretreatment such as intensive leaching, oxidation with or without elevated temperature and oxygen pressure, or roasting. The transformation of the host or the silver minerals does not always result in a leachable species? and this requires additional treatment before the precious metal can be recovered.

Jan 1, 1990

By Roger L. Williams

The Zinc Corporation of America Monaca smelter continues to use the St. Joe-developed electrothermic process for producing zinc metal and zinc oxide. As we enter the 1990s, the electrothermic process flexibility permits treatment of larger quantities? and lower-grade zinc-bearing recycle materials. A new sinter plant having one large sinter machine will increase sinter feed production required to meet our capacity target of 150,000 tons per year.

Jan 1, 1990

By K. S. Izbakhanov

The Chimkent Lead Plant was constructed in 1934 and since that time has undergone many revisions. In 1975 the slag fuming operation was changed from pulverized coal to natural gas fuel. In 1981 the slag fuming furnace water jacket system was converted to evaporative cooling with high pressure steam production. The impact of these changes and the method of their application are described.

Jan 1, 1990

The nickel operations at Kambalda consist of mining thin massive to disseminated Ni sulphide orebodies from 10 individual mines of variable grade.Daily sampling involves visual estimation of the grade of working faces based on geological parameters. This system of grade estimation is used as a guide for daily grade control only.Nickel metal allocation is based on an external sampling system. As all ore sources are blended at the primary crusher, only one calculated mill head grade is available. Therefore all sources are sampled prior to crushing. This system historically consisted of mechanically grab sampling ore from trucks as they passed over a weighbridge on arrival at the concentrator. Currently the system involves diverting one out of every ten trucks to its mine sample stockpile, which is crushed through the primary, secondary and tertiary crushing system fortnightly. The individual mine grades are re-combined to create a total sample grade. This is reconciled against the calculated mill head grade. The reconciliation factor is applied uniformly to all individual mine sample grades to calculate mill reconciled mine grades.

Jan 1, 1990

By D. C. Carter, J. P. Anderle

"Exploration drilling of evaporite sequences in eastern Canada has undergone significant changes in equipment, techniques and philosophy since the early 1970s. The result has been the recovery of full-size cores from properly conditioned and stabilized holes, high quality open hole geophysical logs, and high quality metallurgical samples. The majority of modifications have resulted from the necessity to preserve the integrity of the evaporite deposit, and thus ensure the potential development, combined with the need for cost-effective high quality information. This is particularly evident in the priority placed on the development of non-erosive drilling fluids, casing and cementing procedures. The results are applicable to diamond drilling exploration of evaporite deposits anywhere in the world.IntroductionThe majority of current technical and scientific literature and expertise available on such subjects as drilling fluids or cementing procedures is applicable to large diameter, deep (several thousand metres) oil-field type drilling . The differences between oil-field drilling and wire-line core diamond-drilling are dramatic: large diameter, deep holes drilled with a low rpm tricone bit using large volumes of fluid pumped through a large annulus versus small diameter, shallow (less than 600 m) holes drilled with a high rpm diamond-set core bit using small volumes of fluid pumped through a small annulus. Exploration drilling of evaporite sequences in eastern Canada in the early I970s was conducted using oil-field equipment and techniques to complete holes of moderate (1000 m to 1500 m) depth . The prohibitive cost of these operations has necessitated that subsequent exploration drilling employs modified diamond-drilling equipment and techniques developed as part of a transition away from oilfield methodology. The result has been full size core, recovery approaching 1000/0 and the ability to run open hole geophysical logs; a combination of factors enhancing the collection of high quality information (Carter, I989a)."

Jan 1, 1990

By J. M. Goris

The U.S. Bureau of Mines is conducting research on cable bolt ground supports to assess their material and support properties, to provide design criteria for using cable bolt supports as roof control systems under various types of underground mining conditions, and to provide a mathematical model of cable bolt support systems. Part 1 describes laboratory studies of the support properties of cable bolts made of conventional steel cables and provides recommendations on such topics as the use of thick grouts, selection of breather tubes, and reduction of water bleeding in cement-based grouts. The studies evaluated both single and double cables; effects of different embedment lengths, water-cement ratios, and grout curing temperatures on support strength; effects of use or nonuse of breather tubes; pumpability and water-bleeding properties of grouts; and the strength properties of sand-cement grouts. Part 2 will cover the strength characteristics of birdcage cable bolt supports, epoxy-coated cables, and cables with steel buttons attached.

Jan 1, 1990

By William Petruk

Mineralogical and image analysis studies have been performed on four volcanogenic base metal ores that contain 0.01 to 4.5 wt% Pb to determine the behaviour of galena during mineral processing. The galena in these ores is fine grained and is poorly liberated in both the primacy and regrind mill discharges. Consequently, low grade Pb concentrates are produced to obtain relatively high Pb recoveries. The Pb concentrates contain many impurities including high amounts of pyrite and sphalerite, and small amount of CU-, As-, Ag-, Bi-, and Se-sulfides. These impurities need to be rejected from the Pb bullion during smelting. The galena commonly contains up to 1 wt% Ag in solid solution with an average of 600 to 1460 ppu for the deposits studied to date. The Ag in galena accounts for up to 65% of the Ag in some ores.

Jan 1, 1990

By M. S. Prasad

This paper presents the process methods of beneficiating various copper-cobalt and copper-zinc ores mined by Gecamines in Zaire. Geology and mineralization of both sedimentary and vein type deposits are described with special emphasis on the production of oxide, dolomitic and sulfide concentrates. Description of different types of concentrators and their treatment methods are discussed for the production of sulfide, oxide and dolomitic concentrates. Production of concentrates, their consumption and stocks are briefly reviewed. Modernization of the concentrators with substantial investments on grinding, classification, flotation methods and tailings treatments are also discussed to improve the metallurgical efficiency of the concentrators with a view to improve the production of concentrates both qualitatively and quantitatively.

Jan 1, 1990