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By E. A. Metz

It has been approximately four years since the International Agency for Research on Cancer (IARC) reclassified crystalline silica as a "group one" substance. Since then, crystalline silica has been considered a human carcinogen. Silicosis is a preventable disease, and several aggressive campaigns have been developed to increase awareness of silica-dust-related problems in the industrial environment. New analytical techniques are now being developed to determine quantitatively the amount of crystalline silica in materials. Yet, still much is to be learned about the surface properties of silica and the way in which the disease progresses into full-blown silicosis. This paper discusses the interaction of free radicals generated by the mineral particles and lung tissue. It is the cell injury and DNA damage that progresses to fibrogenesis. Freshly fractured surfaces of silica contain free radicals. These free radicals play an important role in the stimulation of the alveolar macrophage and the development of the inflammatory reactions leading to the fibrotic response caused by silica. Engineers, scientists and physicians need to discuss the mineralogy of silica and the technical issues concerning the development of silicosis.

Jan 1, 2000

By M Scoble, W S. Dunbar

This paper reviews methods for grade estimation in short-term mine planning for block caving. Two particular tools are used: Ordinary Kriging and Simple Kriging with moving averages. It is also considered the influence of draw characteristics on the grade estimation process. Reference is made to mine case study data and analysis. These demonstrate that operational grade estimation is not a trivial process. It must take into consideration: the grade variability (in terms of ore and dilution), sampling interval, geological and geotechnical characteristics, geometrical layout and draw characteristics. Significant improvements appear possible in short-term planning if variogram analysis, as well as kriging methodologies, are introduced into the operational grade estimation process.

Jan 1, 2000

By Lars Lövgren, Jörgen Jönsson

Heavy metals may be retained within deposits of sulfide minerals under oxidation and in the nearest recipients of drainage water by sorption to secondary iron precipitates. The extent of sorption is strongly influenced by solution pH and presence of complexing ligands, such as sulfate and natural organic acids. Desorption of metals and organidinorganic anions to recent secondary Fe precipitates, collected at the Kristineberg mine, Sweden, has been investigated under different geochemical conditions. Elemental composition and structural characterization (X-ray powder diffraction) indicate presence of schwertmannite. While metals such as Ni and Pb were fractionally desorbed from the precipitates under acidic conditions, oxyanions, e.g. arsenatdarsenite and sulfate were desorbed preferably under alkaline conditions. In a separate study the adsorption of NOM onto synthetic goethite was investigated. NOM adsorption showed a strong pH dependence, 95% was adsorbed at pH 3 and 40 % was adsorbed at pH 9. Addition of 2 mM of sulfate desorbed about 10 % of the adsorbed NOM.

Jan 1, 2000

By G. S. Hansford, C. J. N. Dempers, G. E. Searby, A. W. Breed, M. A. Jaffer

The bioleaching of sulfide minerals involves a ferric attack of the mineral with the role of the micro-organisms being the oxidation of the ferrous-iron back to the ferric form, and the oxidation of sulfur, either via thiosulfate or polysulfides, to sulfate. The kinetics of bacterial ferrous-iron oxidation and the chemical ferric leach kinetics of sulfide minerals can both be described as functions of the ferric/ferrous-iron ratio. The independently determined bacterial ferrous-iron oxidation and chemical ferric-iron leaching kinetics have been successfully used to predict continuous bioleaching operations.

Jan 1, 2000

By K Gilliland

The past decade has seen the widespread implementation of computerised real-time operational management systems in open pit mines. While these systems have made a significant impact on operational efficiency at a process level, surprisingly little work has gone into integrating these systems with other IT systems, including those used for tactical planning and enterprise resource planning. As a result of this gap in the information hierarchy, the goal of optimising an entire operation, or multiple operations, remains elusive. Implementation of computerised operational management systems in underground mines has been much slower. This is a significant, though often overlooked, reason why the productivity for underground mining is generally so much lower than for open pits. The historical reluctance to implement computerised operational management systems underground can in part be attributed to the underground environment, particularly the difficulty in establishing effective communications. Another factor retarding the implementation of systems underground has been the perception that the nature and scale of underground mining does not lend itself to computerised operational management. This perception can be challenged, not only by a process level examination of the underground mining, but also by a holistic examination of the entire industry. In recent years, the mining industry as a whole has destroyed rather than created wealth and underground mines are major culprits. The degree of value destruct has been more pronounced with underground mines, as the usual problem û low commodity prices û has been exacerbated by the harsh environment, low productivity and a æfog of warÆ no longer generally found in open pits. Faced with these realities, underground mines will have to adopt modern management tools or suffer extinction at the hands of an unsympathetic investment community. All is not gloom and doom, however. Technological advances have largely overcome the difficulties associated with the underground environment. As a result, there is a small, but growing, number of underground mines using computerised operational management systems to directly improve the bottom line. Much greater improvements can be realised if the industry takes advantage of the recent convergence in technology, to integrate process information with tactical and enterprise resource planning systems in order to provide a solid platform for all decision-making. This would result in the æeÆ mine. Given that the underground fraternity is essentially starting with a blank sheet, they have the opportunity to æsteal a marchÆ on open pit mines, who may be constrained by legacy systems. The benefits of the æeÆ mine are presented through a hypothetical case study that examines the shortfalls of the non-æeÆ mine. The paper ends by presenting a future vision for the æeÆ mine.

Jan 1, 2000

By Mostafa Benzaazoua, Bruno Bussière, Mukendi Kongolo

The desulphurization process has been proposed over the last few years for acid mine drainage control at certain mines, which generate low to medium grade sulphidic tailings (-3 to +25 wt% S). The environmental sulphur recovery, which means the sulphur to be floated to produce a non-acid generating final tailings, depends mainly on the intrinsic neutralizing potential of the tailings. However, in some cases the sulphur cleaning is complicated by other parameters which affect the flotation probability of the sulphide particles. In this study, a number of tests were conducted with a Hallimond tube and Denver Cell on both pure mineral and mine tailings. To develop a better understanding of the mechanisms of non-selective sulphide flotation, three types of approach were investigated in this work: (i) pure pyrite at progressive milling degrees, (ii) artificial mix of pyrite and quartz at different calibrated granulometry and (iii) same composition tailings with 26 % wt sulphur at progressive milling degrees. The effect of the granulometry on the sulphide flotation was demonstrated both. The results allow us to define a granulometry model, which can then be considered in the whole desulphurization modeling.

Jan 1, 2000

By Michael Amick, G. Swan, R. Hill, C. Pritchard

Falconbridge, a major base metal producer in the Sudbury Basin of Ontario, identified a need to find a safe and cost effective replacement for welded-wire mesh used to support loose ground during underground nickel mining. Falconbridge took a methodical approach to the concept of a spray-on liner as a screen replacement proving the strength characteristics of the liner as a safe, cost effective, and suitable method of supporting ground. Compact, hydraulic mixing and spraying equipment have been developed and are in use at the Fraser mine. The Tekflex material has been approved as a wire-mesh replacement and has been in use since November1998.

Jan 1, 2000

By H. J. Marais, P. C. van Aswegen

The Biological Oxidation (BlOX®) Process for the treatment of refractory gold ores was commercialized in 1988. During the last decade, the technology has developed into a mature, commercially viable process, with five additional operations commissioned, including operations at Sao Bento in Brazil, Harbour Lights and Wiluna in Australia, Ashanti in Ghana and Tamboraque in Peru. With ongoing development, the efficiency and cost effectiveness of the process have both improved, making it an attractive alternative to conventional refractory treatment processes such as roasting and pressure oxidation. The bacterial culture is robust and can withstand the normal fluctuations experienced on an operating plant. The plants are simple to operate, making it ideal for remote areas. The scale-up potential of the process has been proven, and it can be applied to large refractory ore bodies. The process is environmentally friendly. Neutralization of plant effluents produces precipitates that comply with the most stringent environmental regulations.

Jan 1, 2000

By Philip K. Chan

Batu Hijau is a new copper and gold mine located on the island of Sumbawa in the Republic of Indonesia. This paper details the design and construction of the Batu Hijau overland conveyor, one of the most challenging efforts of the project. The 1.8 m wide, 5.6 km long conveyor has a design capacity of over 10,000 mtph and carries primary crushed ore through the steep mountains of Sumbawa, which necessitated a 160 m vertical downhill section, a 75 m vertical uphill section, ten vertical curves and one horizontal curve.

Jan 1, 2000

By A Mulyadi, J Barber, R Golden

The Deep Ore Zone (DOZ) underground mine will be a 25 000 tpd mechanised block cave operation starting production in 2000. The ore handling system consists of a direct truck dumping 54 +74 gyratory crusher, which feeds into an ore bin. An apron feeder below the bin is used to load a conveyor belt. This paper describes the design, sequencing and methodology of the crusher station, ore bin and feeder chamber excavations. The Geotechnical investigation and analysis of the site are also discussed as well as the design, installation and quality control of the long-term ground support methods.

Jan 1, 2000

By L. P. James, W. W. Atkinson

Utah has produced about one billion troy oz. (31.7M tonnes) of silver, more than any U.S. state except Idaho. Several very high grade ore systems, now closed, occur within large polymetallic limestone-hosted districts related to plutonic complexes. These Utah mines fed several major lead smelters for nearly a century. Interaction of magmatic chloride-rich fluids with carbonate rocks localized significant bonanzas within these districts. A low sulfidation state was produced in the fluids by their passage through limestones. The Bingham porphyry mine has also yielded more byproduct silver than other porphyry copper-gold systems. Away from exposed intrusive rocks, some large silver-only systems occur in Mesozoic sandstone and in caldera-related veins in volcano sedimentary rocks. Thick permeable latest-Proterozoic basement meta quartzite sequences present beneath western Utah may have been important, as perhaps they were in the Coeur d’Alene district of Idaho, in providing chloride and silver-rich ore fluids. However, it is clear that specific Tertiary magmatic events played an essential role in the evolution of the Utah silver-rich metallogenic province. The largest silver districts in the state are genetically related to porphyritic plutonic rocks.

Jan 1, 2000

By A B. Christie

Known epithermal deposits in the Coromandel region belong to the low-sulphidation type, represented by three subtypes: (1) andesite-hosted epithermal Au-Ag, (2) rhyolite-hosted epithermal Au-Ag, and (3) andesite-hosted polymetallic veins. Paleo-depths for a range ofdeposits are estimated using various features including: paleo-surface indicators (e.g. sinters), hydrostatic pressures estimated from homogenisation temperature measurements on fluid inclusions, and alteration mineralogy. Paleo-depth estimates to the base of the ore zone for the rhyolite-hosted Coromandel deposits are in the range 200 to 500 m. Andesite-hosted Au-Ag deposits have more variable paleo-depths, and are deeper (up to 950 m) in those deposits with base metals at depth. The majority of Coromandel Au-Ag deposits have limited depth extents (<200 m) of economic grade mineralisation, although Waihi and Karangahake are notable exceptions with depth extents of 575 m and 700 m respectively. Limited depth extents of economic ore are a feature of epithermal systems worldwide and are commonly attributed to gold deposition from boiling fluids. Under hydrostatic conditions in epithermal/geothermal systems, boiling in an up-flowing hydrothermal fluid is controlled by the boiling point for depth (BPD) curve. From fluid inclusion studies of many low-sulphidation epithermal systems, deposition of electrum in economic concentrations appears to be confined to a temperature window of 260 to 180¦C. This means that for dilute, gas-poor fluids that follow the BPD curve, gold deposition is limited to a vertical depth zone of about 400 m, with its upper boundary at about 100 m below the ground surface. The greater depth extent at Waihi and Karangahake, can be explained by mixing of/a deep, hot (300¦C) fluid with cooler (c. 200¦C) heated ground waters. This has the effect of lowering the 260¦C isotherm by up to 300 m, thereby increasing the depth range of economic grade gold deposition within the 260 to 180¦Cwindow of electrum deposition.

Jan 1, 2000

By Dale Preece, Stephen Chung

The DMC-BLAST (Distinct Motion Code) has been developed for modeling bench blasting to one or two free faces such as choked blasting in surface gold operation and cast blasting in coal mining, respectively. This computer code has been used to assist the analysis of rock mass displacement after a blast was initiated in an orderly delay sequence. Applications of this feature can be found in the studies of dilution control in surface mining of gold as well as coal involving complex rock structures. Recently, DMC-BLAST has been modified to include a designated delay firing order coupled with variable rock strengths in the blasted media. This newly added feature allows the investigation of the effects of delay firing order on rock displacement in blasting a complex interbedded ore-waste structure. Examples of blasting a steeply dipping coal seams and bedded rock structure, especially in coal mining operations will be addressed and the comparison of efficiency in blasting in an up-dip as opposed to blasting in a down-dip direction will be discussed. Also covered in the paper is a new application of DMC-Blast to simulate a stope blasting underground. Simulations of blasting in a few selected types of timing/structure combinations will be presented in this paper.

Jan 1, 2000

By Eric C. Schwamberge, Clem A. Pelletier, Deborah L. Muggli, George W. Poling

The Pit Lake at Island Copper has evolved into a 3-layered meromictic system. Acid Rock Drainage (ARD) is collected and injected into the lake at 220 m depth via 2 diffuser systems. In situ dye studies were conducted during 2 differing hydrological regimes in order to determine the behavior of the ARD plume within the Pit Lake. Results indicated that when runoff from the waste dumps was low, the injected ARD remained within the bottom half of the intermediate layer of the Pit Lake, initially below depths of 90 m. However, when runoff from the waste dumps was high, the injected ARD at -220 m depth rose through the intermediate water column layer rapidly, but did not breach the top pycnocline at -10 m depth. Overall, the system is currently performing as a mixing bowl with a strong boundary or cap at the upper pycnocline. maintaining mixing below the 10 m depth water level.

Jan 1, 2000

By P Yß±ez, G Ferguson

The El Teniente mine produces more than 340 000 tonnes of fine copper per year from an industrial complex of underground mine, concentrator and smelter. Mass caving methods are employed to deliver approximately 95 000 tpd of ore to the mill, from a number of sectors underground, each sector being in effect a large-scale mine in its own right. This mining activity has faced challenges over the course of the last century such as:the capacity of the underground mine has been expanded to maintain and increase output of fine copper; the increasing size of the ore fragmentation forced to change the mining method to achieve the high productivity and profitability required in the business; and to modify the mining methods to continue mining at depth with safety. Fundamental activities in these mining methods, for the successful initiation of caving and subsequent draw, are:undercutting the base of the block or panel by blasting; and excavating of drawbells. The undercutting design evolves mainly on the height of the blasting to manage the change on ore fragmentation. The methodology move away from incorporating massive areas, typical of the block caving method, to a continuos blasting, typical of the panel caving method. Drawbell design changes on geometry, dimensions and sequence of excavation to deal with a corse ore fragmentation and the resolution of mining difficulties in the form of major rock bursts and collapses of production facilities. This paper focuses upon the evolution of the undercutting and drawbell design used at El Teniente mine and techniques under consideration to deal with future caving operations to provide the bulk of the daily production for the foreseeable future.

Jan 1, 2000

By J. M. Scharer, Bruce E. Halbert, Pettit. Carol M., Lysane Bolduc

The ratio of neutralization potential (NP) to acid production (AP) ratio is often employed for predicting acidic discharges from waste rock dumps. The available NP was evaluated in laboratory studies of limestone dissolution in simulated acidic mine water. The available neutralization potential strongly depended on the particle size. Using limestone particles of 114" (6.4 mm) or greater, less than 20% of the total neutralization potential was exhausted at the onset of acid conditions. Apparently, the dissolution of limestone became mass transfer limited. Under mass transfer limitations, the rate of pyrite oxidation may exceed the rate of neutralization by buffering minerals. The implications concerning the controls on limestone dissolution were examined using a geochemical predictive model for sulphide mineral oxidation in waste rock. The results have shown that in case of heterogeneous waste rock piles the NP/AP ratio is a reliable indicator for short-tam predictions only. Kinetic data on the depletion rate of the neutralizing minerals and geochemical modelling suggest that waste rock environments with NP/AP ratios as high as 5.0 may turn acidic in the long term.

Jan 1, 2000

By R. Sharon

Barrick Goldstrike Mines, Inc. Betze-Post open pit operations, located in northeastern Nevada, have experienced slope instability attributed to the presence of generally weak rock mass conditions, local adverse structural geology and perched groundwater. Ground movements are monitored with acombination of optical survey, extensometers, inclinometers, and time domain reflectometry (TDR).The slope monitoring system at Goldstrike includes two robotics theodolites, which provide real-time coverage for all highwall areas. Survey instruments are housed in specially designed climate controlled shelters in locations where all slopes can be observed. A “remote” computer housed with each theodolite collects data. The “base” computer, located in the mine offices, is used to access data from the remote computers via radio modem.

Jan 1, 2000

By Gabriel Esterhuizen

When designing pillars in coal and hard rock mines it is necessary to determine the strength of the rock mass forming the pillars. Empirical strength equations, based on rock mass classification techniques, assume that the rock mass is isotropic, this simplification may result in under estimation of pillar strength. Numerical model studies showed that the effect of jointing on pillar strength diminishes as the width to height ratio of a pillar increases. Therefore, the weakening effect of joints should not be equally applied to all pillars regardless of their width to height ratio. The paper presents equations that were developed from laboratory tests on jointed rock samples and numerical models to account for the effects of joint orientation, friction, frequency, and pillar width to height ratio on pillar strength. The equations were calibrated using field data of actual pillar performance in South African coal mines. The method was applied in two case studies in which the strength of jointed coal pillars was assessed and layouts were designed accordingly.

Jan 1, 2000

By T Kitajima, T Kawaguchi, T Nakamura

Carbothermic reduction of iron oxide is an attractive mechanism to produce metallic iron, since it can directly utilise coal as both reductant and fuel. To improve energy efficiency and productivity of the metallic iron production based on this mechanism, the combustion bed process packed with the composites of iron oxide and coal powder was experimentally evaluated. The process has a potential of high heat efficiency since it can automatically utilise the heat of reduced materials as that necessary to the subsequent reduction of the composite by a large heat exchange rate between the packed particles and gas flowed across the bed. However, it is hard to perfectly prevent the reoxidation of formed metallic iron in the bed. The present paper reports the effect of coal content, pellet size and so forth on the reduction/metallisation degrees of the samples after the reduction experiment. It also discusses the effect of pretreatment of the composite pellets using CaO bearing materials to suppress the reoxidation of formed metallic iron in the bed.

Jan 1, 2000

The paper reviews the results emanating from an experiment conducted in Bochum?Germany in which various international rope inspection authorities were requested to assess the conditions of a corroded rope sample as well as a rope sample containing internal fatigue breaks. Both samples were of the multi-layer low rotation construction.

Jan 1, 2000