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By Richard W. Hutchinson, Christopher Osterman

Abstract -The Selebi-Phikwe deposits are hosted by amphibolite to granulite facies gneisses of the Limpopo belt. The sulfide orebodies are generally stratiform and conformable to the foliation of the wallrock gneiss. Sulfide remobilization has occurred during metamorphism and has produced discordant sulfide veins, called piercement structures, which project into the hanging wall and foot­ wall gneisses. These piercement structures are compositionally similar to the stratiform sulfides, consisting mainly of pyrrhotite, pentlandite and chalcopyrite. However, texturally the piercement sulfides are coarse grained and inclusion-free, whereas the stratiform sulfides are fine grained and packed with tectonically produced wallrock inclusions. The piercement structure sulfides and adjacent stratabound sulfides were sampled and analyzed for major base metals and PGE's for comparative purposes. Most of the piercement structures were enriched in Cu, Ag and Au, whereas they were generally depleted in Ni, Co, Fe and PGE's. Changing elemental associations were observed from the stratabound sulfides and along the length of the piercement structures. This and the degree of depletion or enrichment of various major and minor elements in the sulfide piercement structures may reflect the relative mobilities of metals under metamorphic conditions. The similarities between sulfide piercement structures and the footwall Cu-POE veins in some Sudbury deposits are reviewed.

Jan 1, 1994

By Anthony McDonald, Dominic Verhelst

"Hudson Bay Mining and Smelting Co. Ltd. (HBM&S) started up a zinc plant and smelter in late 1930, employing technology of that period. The zinc plant has since converted from a roast/leach operation to a two stage pressure leach operation to eliminate sulphur dioxide emissioms. The smelter, however, is still continuing with much of the original roaster/reverberatory furnace technology. This paper reviews the process flow of the copper smelter, with some comments on past and recent changes.Smelter FlowsheetPrior to July 1993, the HBM&S smelter operation consisted of seven areas, namely feed preparation, roasters, reverberatory furnace, converters, anode casting, fuming plant, and dust collection. A simplified smelter flowsheet is shown in Figure 1. The data for tonnage of materials moving through the circuit are presented in Tables I to 4, and are representative of the time period from July 1992 to June 1993. A change in the zinc plant technology in 1993 resulted in the elimination of a zinc-bearing sulphide leach residue from the smelter feed blend, thereby greatly reducing the zinc content of slag produced in the smelter. Consequently the fuming plant and ancillary equipment, such as the drying plant, were shut down. These areas will, however, be described. With the closure of the zinc fuming furnaces all the slag from the reverberatory furnace is now discarded to stockpile.The over-all smelter metal recoveries are 96% for Cu and rn.5010 for Au and Ag. Figures 2 and 4 indicate historical production numbers of copper, silver and gold, respectively. A review of the minor element distribution in the smelter can be found elsewhere."

Jan 1, 1994

By Gerhard W. Heinrich, Gerald V. Schroeder, Daniel A. Murphy, Daniel F. Suarez, Jamie B. Beauchamp

"Washwater 'Finger' sprays were installed and tested in the copper/nickel separation circuit at Strathcona Mill to improve flotation capacities and related metallurgical performances. The new spray design features submerged sideways introduction of wash water into the flotation froth through nozzles at the end of vertical pipes which are suspended from a header above the froth. This maximizes the effective cross sectional area of flotation vessels while maintaining effective froth cleaning and a desirably high density of the concentrate slurry. The plant tests gave increases of copper concentrate production rates of 17% to 20% for conventional cells and 16% to 20% in column flotation at target grades of 29% to 30% copper and of less than 0.5% nickel. Basic considerations and concepts of tests and evaluation procedures are described.IntroductionMeeting flotation concentrate grade targets at maximum production rates and recoveries is a challenge all too familiar to operators of base metal ore concentrators. Frothwashing is an option to improve grade/recovery performance by minimizing entrainment of impurities into the concentrate, which is commonly known since the sixties (Kaya & Laplante, 1989). It has been recommended for the flotation of sulphides and industrial minerals alike (Kaya & Laplante, 1989; Miller, 1969; Heinrich, 1989) and has found its ultimate application in flotation columns (Finch & Dobby, 1990). The washwater addition in a flotation column is most evenly distributed over the column's cross-sectional area thus ensuring almost complete displacement of feed water from the froth by a countercurrent washwater flow -provided, a positive bias is maintained. Therefore, flotation columns are ideal for cleaning flotation. However, there is usually less room for boosting the concentrate production capacity by increasing airflow or slurry level then with conventional cells because of the smaller cross-sectional area available."

Jan 1, 1994

By Z. T. Bieniawski

A major study was performed on determination of long term strength of coal strata directed to the design of coal pillars to ensure their stability beyond the life-time of a mine. Based on field investigations, numerical modeling and reliable data from 12 case histories, three aspects of time effect in the strength of coal strata were studied; (1) strength reduction based on the concept of volumetric strain estimate from in-situ tests, (2) strength reduction in terms of three failure criteria applicable to coal strata: original Hoek-Brown criterion, modified Hoek-Brown criterion, and Generalized criterion, and (3) long-term strength estimation as a function of coal strata quality RMR based on case studies. From these investigations, an integrated approach to long-term pillar stability is proposed, based on numerical modeling and empirical pillar strength formulation. The values of factors of safety for coal pillars are analyzed in terms of probability of failure and practical meaning for mine design purposes.

Jan 1, 1994

By J. S. Lewis

Beneficiation and physical and chemical processing of non-terrestrial materials will borrow strongly from terrestrial experience but will also involve the necessity of handling literally unEarthly feedstocks, reagents and environmental conditions. The present state of scientific and engineering understanding of the processing of non-terrestrial minerals, gases and hydrocarbons is reviewed, with the production of rocket propellants, life-support fluids, structural metals and refractories as the goal.

Jan 1, 1994

The basic principles of mineral valuation were recognised and propounded at the beginning of this century and have remained virtually unchanged since then. Valuation is seen as a two part process commencing with a technical examination of the mineral property followed by a manipulation of the results of the technical examination in order to determine the monetary value of the project. A thorough and competent technical examination was seen then and remains now as the essential but not sufficient foundation for reliable valuation. All authors stressed the need to maintain the integrity of the data base and to ensure adequate coverage of all relevant aspects. The monetary valuation process through most of the first half of this century was mainly based on the Hoskold two rate method, derived from the formulae for valuing annuities but modified to provide explicitly for recovery of capital. Though the basic principles of valuation have not changed significantly, the means of implementing the components of the technical examination, the styles of deposits being evaluated and the mechanisms of monetary valuation have changed dramatically. Despite all the technological improvements, however, mineral valuations are still as apt to vary from realised performance as at any time in the past. As well, mineral property valuations are now being extended to cover all assets of potential value, including valuation of exploration tenements with or without identified resources. Valuation of exploration tenements will continue to be one of the most difficult and contentious of valuation tasks.

Jan 1, 1994

By B. Moudgil, M. Bogan

A mathematical model, based on first-order kinetics, is derived to describe batch settling data. The model is used to predict the settling behavior of solid suspensions under different conditions. The potential benefits of this model to solid-liquid separation processes are discussed.

Jan 1, 1994

By A. Fawceit, B. C. Dyer

"The basis of the tomographic velocity imaging technique is briefly described and an application of the method to detect and image a cross-section through a chromite pod is presented. Using the chromite application as an example, the relative costs of tomographic data acquisition and processing are compared with those of diamond drilling to obtain similar resolution. A number of different tomographic survey configurations and the potential role of the method in surface and underground exploration are discussed.IntroductionThe technique of seismic tomography has been most widely applied in oil industry exploration, nuclear waste disposal, civil engineering site investigations and in the assessment of the condition of mass concrete structures. Although model studies had indicated that tomography would be a useful tool in mineral exploration, relatively few applications have been reported.Essentially the method relies on the determination of the speed with which sound travels through a region within a cross-section of the earth or large body. The speed of sound is determined by the physical characteristics of the medium through which it is passing. In geophysics the speed of sound is generally referred to as the seismic velocity. Due to variations in the formations of different rocks the seismic velocity will vary and so can be used to map geological boundaries"

Jan 1, 1994

Since 1969, a substantial number of geophysical methods have been applied in the search for porphyry copper and mesothermal type -sulpha-de deposits. These have assisted with geological mapping as well as the definition of various sulphide depos-its. The application of these methods at the Frieda-Nena deposits, Papua New Guinea, can be used as a case study for exploration in other parts of New Guinea.In 1993, Highlands Gold Limited carried out an intensive geophysical program over the Nena deposit. The methods employed included, CSAMT (controlled-source audio magneto-tellurics), airborne and ground elect-romagnetics, IP/resistivity and ground magnetics. The magnetic method was used as a regional mapping tool as well as a way of mapping alteration zones over both the Nena and Frieda River copper deposits. Electromagnetics, in part-icular FLAIRTEM, is a rapid reconn-aissance tool as well as a detailed mapping tool for the location of Nena-style massive sulphide deposits. IP/ resistivity is an expensive but most useful tool for mapping out Frieda porphyry copper style disseminated sulphides as well as Nena style deposits. It can be used to define drill targets in areas of difficult Access.a

Jan 1, 1994

By R. K. Mehta, S. K. Dhar, R. R. Mallepali

Introduction The incentives for developing a distributed form of the comminution model include: • for describing the heterogeneous comminution behavior of multiphase mineral systems (i.e. realistic ore bodies, such as complex sulfide ores consisting of chalcopyrite, galena, sphalerite, pyrite and siliceous minerals) and •for generating, for various locked and free particles, in situ, microscopic, breakage behavior such as the mode of fracture (intergranular vs. transgranular), the relative rates of breakage and the breakage distribution. However, the computational difficulty and the effort made in estimating a large number of parameters (Andrews and Mika, 1975; Wiegel, 1976; Herbst et al., 1985, 1988) do not justify the utility of this approach. Also, obtaining the results experimentally is very tedious and time consuming if using this approach. Although recent work in this area (Choi, Adel and Yoon, 1987; Mehta, Adel and Yoon, 1989, 1990) showed good results for liberated particles, the quality of the estimation and prediction was poor for locked particles. Attributing this to the complex breakage behavior of locked particles, it was concluded that additional constraints, and possibly modification in the breakage distribution functional form for locked particles, were necessary. However, further mathematical analysis revealed that the method previously used was in error. The purpose of this technical note is to present the correct solution methodology used in solving the general model equations of a multicomponent mineral system containing multiple classes of locked particles. Previous work and connection The general form of the comprehensive, distributed-component comminution model has been described as (Herbst et al., 1985) [d (m (0) -[ I - B ] S_ m(t) = A m(t) (1)] where [A] is the fundamental matrix/state companion matrix, commonly referred to, in the comminution literature, as the "mill matrix." Note that for a distributed-component comminution model, this is a full, general, real matrix, unlike a lower triangular matrix for a simple grinding model or a lumped-binary grinding model with one locked-particle class (Herbst et al., 1985, 1988). Also note that all of the underlined letters refer to matrices. Herbst et al. addressed the difficulty in arriving at a closed form of the analytical solution of Eq. (1) via similarity transformation [IT J inv (T)]]. This difficulty occurs for several reasons: •[A], as a general real matrix, may have complex eigenvalues and complex eigenvectors. •More importantly, there is no guarantee that a set of eigenvectors of [A] will turn out to be independent. An attempt was made to solve this problem by implementing a decomposition method. With this technique, the mill matrix was decomposed into a sum of lower and upper triangular matrices [(i.e., A = L + U)]. Then the solution was obtained using similarity transformation (Mehta, Adel and Yoon, 1989, 1990). [e(At) = e(L+U)t = e(Lt).e(Ut) _ [ TL Jt- (t) inv(T_L)] [-Tu Ju (t) inv(Tu)]] [But, unfortunately, e 1+U = e t . eu is true only for scalars and not for matrices (i.e., eL+u# eL- eU) unless they commute. In other words. eAt = e(L+u)t= ekt - eU' if LU = UL. Hence, this decomposition scheme must be replaced by a mathematically acceptable method known as the "splitting method"]

Jan 1, 1994

By Steven Wright

The extent and the rate of reduction of slags produced from the smelting of recycled lead batteries were investigated under laboratory conditions using graphite as reductant. Simultaneous reduction of PbO, Fe2O3, Sb2O3 and As2O3 occurred at temperatures of 1180 and 1200°C, with Sb and As reporting to the metal phase while the PbO content of the slag was above 2 wt%. Fuming of As from the metal occurred at lower concentrations of lead in the slag. Discard slags with low levels of As, Pb and Sb were produced. Arsenic levels were reduced to less than accurately measurable by ICP analysis, and Sb levels in the final slags were in the range of 0.1 to 0.2 wt%. The kinetic data obtained were analysed and compared with other measurements on lead oxide containing slags. The results showing a dependence of the reduction rate on the oxidation state and the basicity are consistent with other studies on well characterised industrial and. synthetic lead slags. These results indicate that when carbonaceous reductants are used, the rate of interfacial reactions play an important role in enabling the production of environmentally acceptable discard slags.

Jan 1, 1994

By PDF

Flotation columns are widely used in mineral processing and coal preparation industry today. Mathematical modeling of flotation columns has conventionally been done using axial dispersion or tank-in-series models. However, for design and scale up purposes these models are not adequate enough because they do not provide detailed information of the flow fields within the column. This paper presents a Two-Dimensional, Two-Phase. Fluid-dynamic Model and its numerical solutions for some cases encountered in column flotation. The MAC (Marker and Cell) method was employed to obtain the numerical solutions, and based on this method a computer code COLUMNFLOW was developed. The simulated flow field reveals the presence of a circulation flow structure in flotation columns, which could be one of the main reasons for mixing in column flotation. The effects of some parameters such as superficial gas and liquid velocities on the characteristics of the flow structure in flotation columns were also tested with the numerical model.

Jan 1, 1994

In mineral asset valuation the use of any valuation method requires the input of competent and independent technical professionals. A resource valuation must be as transparent as possible to allow others to assess the validity of their underlying assumptions. Materiality is a dominant factor in all valuations and a valuer should set out the basis for the subjective decisions made in this regard. Any valuation methodology must comply with the requirements of the law, practice notes and guidelines issued by the various relevant authorities and professional bodies. The valuation methodology chosen to value a mineral asset depends upon the amount of data available on that asset and the reliance that can be placed upon those data. Mineral assets generally fall into one of three broad categories, depending upon their state of development, ie whether they are at the exploration, development or operating stage. Naturally there are transition phases. Hence, there are ""Grass Roots"" Exploration Areas and Advanced Exploration Prospects; Pre-Development Projects and Developing Mines; and Operating Mines. The features of each of these mineral asset status categories are described, mainly in terms of the confidence in the contained identified Resources/ Reserves. The various subjective methodologies available for the valuation of ""Grass Roots"" Exploration Areas and Advanced Exploration Prospects -are specifically reviewed. The pitfalls in adopting a ""recipe"" approach are noted. It is the author's view that the Expected Value Method (based on the probability adjustment of the output of a Discounted Cash Flow/ Net Present Value model) has little application in the valuation of exploration mineral assets, so it is only briefly addressed. The methodologies reviewed are listed below. ò Multiple of Exploration Expenditure Method (expenditure based). ò Joint Venture Terms Method (expenditure based). ò Geoscience Rating Methods (eg Kilburn - area based). ò Comparable Market Value Method (real estate based). ò Rules of Thumb (eg $/Resource or production unit; % of in situ value). Some recent Prospectuses are used to provide examples of their misinterpretation and misapplication.

Jan 1, 1994

By W. Mark Hart

The current Automatic Data Acquisition system developed by some support manufacturers make it possible to monitor and record changes in leg pressure, DA RAM stroke in every shield and shearer position at any moment during mining operation. But how can these massive data (more than 1 MB for every 3 hrs for the current scanning option) be effectively used for improving production and maintenance management as well as providing better roof control at a longwall face? The research currently conducted jointly by WWU and Cyprus Amax Minerals at Emerald Mine and Twentymile Mine attempts to answer this question and make the data, especially leg pressure, more meaningful. A computer software package has been being developed to (1) determine mining cycles, cycle time, face advance rate, production rates, machinery delays, and production delays for each shift; (2) identify defective sensors, check valves, yield valves, by-passing leg and DA RAM cylinders, and other hydraulic and electrical abnormalities; (3) determine the roof weighting period; (4) evaluate the performance of the current shield support design - demand relationships; and (5) predict and overcome ensuing encroaching problems and roof conditions ahead of the face.

Jan 1, 1994

By Curtis G. Kremer, Jeffrey L. Brummert

Blue Circle Cement's Ravena, New York quarry mines approximately 6.7 million tons of limestone per year. Blasting occurs approximately twice a week on three separate benches. Shots average 60,000 tons but can range up to 140,000 tons. Ongoing scrutiny of the drilling and blasting program allows for maximum blast efficiency which results in lower overall mining and crushing costs. Close cooperation between management and explosives supplier assures Blue Circle Cement's objective, "To develop, implement, and continuously improve a measurable drilling and blasting system that will optimize the total mining and crushing costs while ensuring compliance to safety and maintaining or reducing the environmental impacts of blasting".

Jan 1, 1994

By P. Malozemoff

Discussion by P. Malozemoff I have no objection to using mathematics in the value appraisal of properties. The factor that is not emphasized in the paper is that very few important properties have a lifetime that reflects the initial ore reserves of the property divided by the rate of production adopted. In the majority of cases, major properties mine out several times the initial reserves. How much more will be mined out is not known, and only exceptionally gifted geologists can predict that additional reserves will be found. There is the further factor of metals price, which, over the long term, is not predictable. Another factor vitiating making calculations on initially established ore reserves is the speculative nature of exploration success. In my judgment, the life of a property, in addition to an established ore reserve, should include ample time for exploration to find additional reserves. The likelihood of additional reserves is based on the geological promise of the general area where the mine is established. This is especially important because of various risk factors associated with small orebodies, the economic life of which is about five to seven years. In underground mines, it is not economic to develop reserves beyond a certain depth, so the life of initially established reserves must be limited. In these cases, it is especially important to have a good geological understanding of the orebody and its continuity. To accommodate these concepts and present proof of economic soundness for a mining enterprise, a mathematical analysis should yield a life long enough to allow exploration and the development of additional reserves that would ensure a longer mine life and a more profitable result.

Jan 1, 1994

By Jiuhua Xu, Shuiku Jia, Weiren Sun

"The Jinqingding gold deposit, situated in the east Jiaodong Peninsula of Shandong province, is typical of the pyrite-quartz vein gold deposits in the Muping-Rushan gold belt of China. The gold deposit is controlled by a great NNE fracture zone and is composed of several lenticular orebodies within the fracture rone occurring in the Kunyushan granite massif. The Kunyushan granite massif was formed by the replacement of the Archean Jiaodong group.The main minerals associated with gold are pyrite, chalcopyrite, galena and sphalerite; the gangue minerals are dominated by quartz, sericite, microcline and calcite. The mineralizing event can be divided into four stages: (1) pyrite-quartz; (2) quartz-pyrite; (3) siderite-polymetallic sulfides; and (4) calcite-quartz. Gold occurs mainly as native gold and electrurn in stage I and stage II. There are some evident differences between pyrite from major stages of gold mineralization and that from minor stages; these include differences in crystal forms, size and composition of fluid inclusions.Wallrock alterations consist of sericitization, silicification, pyritization and potash-feldspar alteration. Five alteration zones can be distinguished from unaltered granite (zone 0) to vein lodes (zone IV). Au and Ag increase rapidly from zone 0 to rone IV, Cu increases continuously, while Pb and Zn increase slowly. R-type geological factor analysis indicates that the Au, Ag, Cu, Pb and Zn bear a close relationship to wallrock alteration."

Jan 1, 1994

One of the most challenging and ambitious dump rehabilitation projects in South Africa’s mining industry is being carried out at Greenside Colliery’s smoldering coal dump, which lies adjacent to the N 12 Johannesburg-Witbank highway. Greenside Colliery is the largest coal mine in the Gold Fields Group. It began operation in 1946, the year in which the burning dump had its origins. Today, Gold Fields plans to spend R16 million (about $USS8 million) to encapsulate the dump, bringing it into compliance with South Africa’s Mining Environmental Management Programme, according to Martin Hamer, engineering manager of the Greenside Colliery. The improved environmental management approach will result in reduced sulfur dioxide gas, smoke and dust emisson into the air and an enhanced aesthetic appearance of the dump from the N 12 highway. The objectives of the project are to place and compact coal discard to within the National Institute of Coal Research specifications in order to prevent spontaneous combustion, and to preserve as an asset the coal portion of the discard.

Jan 1, 1994

By H. Nematollahi

The comminution laws The grindability of the ores or minerals is an important factor that could not be deduced from their mineralogical characteristics (Testut, 1958). Many theories have been proposed to determine the amount of work required in a comminution operation as a function of the nature of material, size and shape of the minerals before and after of comminution. The most important laws are proposed by Rittinger, Kick and Bond. According to Rittinger (1867), the work is directly proportional to the new surfaces produced during the comminution. Kick (1885) believes that the work needed to produce similar modification is proportional to the volume or mass of the material. Bond, during his 25 years of experience and research, reached to the conclusion that on the average the energy required for a known comminution is between the Rittinger's and Kick's laws (Bond, 1952). According to Bond's Third Theory, the work input is proportional to the new crack tip length produced during the particle breakage, and equals the work represented by the product minus that represented by the feed.

Jan 1, 1994

The demand for gallium has increased significantly over the last few decades due to the expanding use of Ga compounds in the electronics industry. Because it is widely dispersed and rarely found naturally in concentrations greater than 0.1%, Ga is expensive (approximately US$500/kg) and difficult to produce in large quantities.   A previous study of metals in geothermal systems reported significant quantities of Ga present in the muds on the northeast margin of Lake Rotokawa, an acidic lake associated with a high-temperature geothermal field situated in the Taupo Volcanic Zone of New Zealand. Similar muds are present in many other geothermal fields in the zone, suggesting that geothermal muds could be a commercial source ofGa.

Jan 1, 1994