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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

By A. K. Mukhopadhyay, B. Sikdar, V. P. Arora

Introduction During the past several years, persistent concerns about an economic slowdown in India have tempered capital-expan¬sion plans. This has encouraged companies to find methods of increasing the capacity of existing production equipment. One of the more cost-effective methods of increasing produc¬tion capacity without major capital investment is to improve equipment maintenance to prevent needless machine down¬time. This can have a significant financial impact because of reduced maintenance costs and increased machine availabil¬ity. The maintenance program employs different techniques, but the analysis of the vibration behavior of machine compo¬nents to assess their condition was found to be the most accurate technique for monitoring various machine disorders. A dragline that handles overburden in open pit mines is one of the more capital-intensive pieces of production equip¬ment. It is imperative that the machine be run at its optimum capacity under the prevailing environmental conditions. Condition monitoring of the various components of the dragline through vibration analysis not only improves the machines availability but also ensures a long operation time free from sudden failure. This paper describes the application of vibration monitor¬ing and analysis techniques to assess the components of a W2000 dragline. The paper reveals that condition monitoring through vibration analysis can be as valuable in failure prevention as it is in failure analysis. Finally, the paper presents an approach to a knowledge-based expert system to the quick and correct diagnosis of mechanical faults in a dragline. Equipment A dragline is an intermittent-discharge-type excavator having a long boom at one end. Unlike other excavators, the bucket is not rigidly held by the frame structure. In favorable geomining conditions, the intensive operation of these exca¬vators is the least-expensive means of overburden removal. The basic working elements of this equipment are the hoist system, the crowd and retract system, the wing mechanism and the propel mechanism. The walking dragline is accepted as the most economical machine for stripping overburden at depths of up to 60 m (200 ft). They are electrically powered and the various motions are effected by individual drives. The Ward-Leonard system is used to provide the optimum flexibility in controlling different dc-drive motors. To mini¬mize the cost of mineral extraction, the largest such machine in India has a 24-m3 (850-cu ft) bucket with a boom length of 96 m (315 ft). Draglines are very costly, and considerable financial penal¬ties may arise from sudden stoppages due to component fail¬ures. Thus, operational reliability is of the greatest importance. Active measures are now being taken to minimize downtime by adopting condition-based maintenance techniques. Though a number of techniques come under this scheme, it has been observed that assessing the health of the dragline by measuring vibration is the best method of determining the dynamic behavior of its various rotating components to avoid any catastrophic failure. Based on criticality, the vibration-behav¬ior of the following components are studied: • motor-generator unit, • exciter unit, • hoist motor-gearbox unit, • hoist drum-gearbox unit, • drag motor-gearbox unit, • drag drum-gearbox unit and • swing motor unit The approach Increases in the vibration levels in different subsystems of the dragline were observed due to the presence of faults such as unbalance, misalignment, looseness and bad bearings. A vibration behavior study included the measurement of vibra¬tion level, trend analysis of time-domain vibration signals and vibration frequency analysis at bearing points of the components. A vibration meter, a vibration analyzer and a data collector are used. Vibration-level measurement. When the dragline was assembled and put into operation for the first time, vibration data were collected to generate baseline data for the equip¬ment (based on International Standard ISO 2372). After¬wards, the vibration levels were recorded regularly using a vibration meter. The measurements were taken at all bearing

Jan 1, 2000

By C G. Ferguson, S L. Makin

The Cawse nickel project is a new generation pressure acid leach (PAL), solvent extraction and electrowinning process used to produce LME grade nickel metal and cobalt sulphide concentrate containing 40 per cent cobalt by treating nickel and cobalt oxide ores from a lateritic ultramafic profile. The project is located 50 kilometres NW of Kalgoorlie in Western Australia. The commercial success of the Cawse nickel operation is dependent in part upon the ability of the principal ore type to be beneficiated. A simple process of rejecting lower grade material on the basis of particle size achieves this. The process is called upgrading and allows subgrade material to become commercial ore grade and also allows higher ore grades to be processed in the early parts of the operation. The success of the upgrade process is dependent upon the physical and chemical properties of the ore being processed and the nickel grade of the ore. The upgrade ore type represents >80 per cent of the Cawse nickel resource and is hosted mostly within a limonite unit, represented by goethitic clays in the upper saprolite zone. In the upgrade processing circuit the ore is crushed and slurried. It is then passed over a series of screens that remove all material over 0.5 mm. This ensures that coarse material is removed from the main ore stream. Upgrade is reliant on selectively rejecting lower grade or barren material, which can include silica, magnesite and relict saprock. To predict leach feedgrade, the grade control estimates the head grade and upgrade percentage for all ore delivered to the run of mine ore pad. To do this reverse circulation (RC) drill holes are logged for ore type, assayed for a range of elements and undergo simulated upgrade testwork. The percentage and grade of material rejected through the upgrade circuit has the most influence on upgrade per cent. This reject is determined by the physical properties of the rock mass and drum scrubber parameters. The correlation between nickel upgrade and reject can be established to predict upgrade from the known mass reject. Parcels of upgrade ore milled to date closely follow projected correlation trends. Upgrade circuit results have been excellent, with average nickel grades upgrading by 34 per cent, cobalt by 23 per cent, with 55 per cent mass passing.

Jan 1, 2000

By J. T. Gepford, K. A. Prisbrey, T. Scott, M. Spangler

Using neural networks for plant control is challenging. The objective was to show how to make a neural network effective, even with noise, lag times, and unmeasured disturbances in the plant. The procedure was to evaluate the neural network in a laboratory flotation vision system and in a plant refractory gold autoclave system. Although the resulting neural network easily conquered simple laboratory data, the noisy plant data was much more difficult, and adaptive linear models were equally effective. We concluded that the neural network needs support by combining it with other tools found in the best control packages.

Jan 1, 2000

By M. Josick Comarmond, Paul L. Brown, Greg P. Timms, A. Ian M. Ritchie, John W. Bennett

Geochemical kinetic models have only become available in recent years and their utilisation in the prediction of effluent chemistry from sulfidic waste rock piles is even more recent. The models used to date, however, have incorporated some questionable assumptions. This paper shows how geochemical, mineralogical and physical field data have been coupled to remove some ill-founded assumptions in the construction of a geochemical kinetic model. Further, the paper discusses a comparison between the observed effluent chemistry from a waste rock dump at the Rum Jungle copper/uranium mine in northern Australia with model predictions. In general, there is good agreement between the two, although an anomalous result is discussed.

Jan 1, 2000

By J B. Farrow

The AJ Parker Cooperative Research Centre for Hydrometallurgy carries out research on behalf of, and in collaboration with, the Australian mining industry. As might be expected, much of its research is directed towards improving the efficiency of alumina and gold processing plants. However, the Centre also carries out research of relevance to base and other metal producers. A key element in its work is the successful transfer of its technology to the companies with which it is working. In general, this is achieved in the following five steps:definition of the problem through discussions with the company commissioning the research; execution of the research; assessment of the research findings; testing of the research findings by pilot plant or on-site trials; and implementation of the results on the full-scale. This pattern is exemplified by the work carried out by the Centre to improve the performance of gravity thickeners which are used throughout the minerals industry for solid-liquid separation. The research has focussed mainly on ways to optimise the use of flocculants (long chain polymers) to enhance thickener performance. It has been shown that the way the flocculant is mixed with the slurry is of profound importance. Computational fluid dynamics modelling of the feedwell region of thickeners and laboratory and plant flocculation studies have been used to determine better ways to contact the flocculant with the feed slurry. Implementation of these and other findings on the full-scale confirmed that improvements in thickener performance were indeed possible. As a result of this AMIRA funded thickener technology work, there have been considerable savings to a number of Australian mineral processing companies, through improved operation, higher throughputs and flocculant savings.

Jan 1, 2000

By David J. Reddish

Longwall systems are inflexible in layout, intolerant of disruption and represent a substantial investment. It is therefore essential drat all understanding of the likely strata behaviour and support requirements is obtained prior to panel development. For many tears rock mechanics engineers have applied numerical modelling based kill finite element techniques to the design of the support and layout of underground excavations. Whilst such design methodology has worked well in civil engineering and hard rock situations, it has been less reliable when applied to excavation design in the soft rocks of the coal measures. This lack of reliability has been identified largely as being the result of the utilisation of unsatisfactory input data, This paper describes the results of an ongoing research programme at the University of Nottingham in which a novel rock mass rating system known as the UK Coal Mine Classification system was developed to enable the prediction of the strata properties that are required as input parameters for use in numerical modelling of the deformation of soft rocks around excavations such as roadways and longwall faces in coal mines. The paper describes the development of the system. the way in which classifications are applied to derive input data for numerical models and gives two case studies ill which deformations and stress re-distributions around coal mine excavations have been simulated by numerical modelling using the FLAC finite difference code.

Jan 1, 2000

By William R. Yernberg

The Fifth International Conference on acid rock drainage (ICARD 2000) was held May 21-24, 2000, in Denver, CO. The three-day conference consisted of about 150 oral presentations and poster sessions that described the state-of-the-art of acid-rock-drainage (ARD) science and technology. The conference also featured a trade show. It included representatives from consulting companies and government agencies with interests in ARD, as well as other environmental issues related to mining. The conference also included field trips to ARD treatment sites and short courses on acid rock drainage issues. ICARD 2000 was planned and promoted by the ICARD 2000 Organizing Committee and the Society for Mining, Metallurgy, and Exploration, Inc. (SME). Financial support was provided by Barrick Gold, BHP Copper, Homestake Mining, Noranda, Phelps Dodge, PlacerDome, the US Bureau of Land Management, the USEnvironmental Protection Agency and the US Geological Survey. Since the original ICARD was held in Roros, Norway, in 1988, knowledge has improved of the behavior of mine wastes as have methods of environmental mitigation. The ICARD 2000 presented the latest advancements in the field of acid drainage.

Jan 1, 2000

By R. C. Ford, J. Kelsey, S. A. Pierce, M. D. Ankeny

Evaluation of acid drainage risk from spent (leached) ore in arid climatic zones consists of two components: (1) whether residual and secondary minerals will release acid and metals when exposed to rainfall, and (2) whether ambient rainfall is likely to infiltrate, and eventually impact surface or ground water resources. The risk of acid drainage from spent ore at the El Abra on-off copper leach pad operation was evaluated using conventional geochemical methods and unsaturated flow models. Although geochemical testing indicated poor quality water would result from any seepage, unsaturated flow modeling demonstrated that infiltration and seepage were unlikely given the arid climatic conditions. Modeling further demonstrated that the residual moisture content of the spent ore when it is removed from the leach pad controls the risk of seepage. To further reduce the risk of seepage, operational controls were developed and implemented at the El Abra site.

Jan 1, 2000

By Mingchun Lu, Yunjin Yan

"This paper describes a new type of bell-less top installed on two relined blast furnaces at Tianjin Iron Works and another new-built at Echeng Steel Works in China. A compact installation was presented for existing furnace top innovation with the least reformation of existing top structure. A water cooling and sealing gearbox used for driving the chute discards completely the traditional idea about necessity of continuous supply of cooling gas for the gearbox. A multiring spreader and its dozens of selectable charging patterns enables an operator to achieve optimal burden distribution easily under the condition of a minimum investment of control equipment. Some useful conclusions have been made through a small-size model and a full-scale model tests. The excellent characteristics and the superiority of the new top have been fully proved at both works.IntroductionIt is known that there are some advantages with the bell-less top of a blast furnace: suitable for furnace to operate at high top pressure, capable of realizing optimal burden distribution, less investment and maintenance costs, etc. But why do most of blast furnaces in the world still remain using conventional bell top. One of the concerns is that current bell-less tops still have some shortcomings:1) The height of a current bell-less top might be lower than three or four-bell top or two-bell plus valve seal top, but still much higher than an ordinary two-bell top.2) The gearbox for driving the rotating chute is positioned onto the lip of the furnace. It is subject to attack by crude hot bf gas. Continuously pumping cooling gas (pressurized nitrogen or clean bf gas) into the gearbox is indispensable to withstand such a harsh working environment. Therefore, a plant furnished with blower8 and its ancillaries has to be built, It involves a large sum of investment and much expense in its annual running costs.3) Although the current bell-less charging device as a means of controlling burden distribution possesses a wide range of freedom, it is difficult to realize optimal burden distribution. There are some large blast furnaces realized better burden distribution, but sophisticated control means is indispensable so that the investment of control means is much higher."

Jan 1, 2000

The Sto Tomas II orebody of Philex Mining Corporation is a porphyry copper deposit located at Padcal, Tuba, Benguet, Philippines. It was mined through open pit method for the first two years starting 1958 and subsequently through underground method using the Block Cave System. The slusher type of draw was employed at the upper levels of the orebody from mid-year of 1959 up to 1994 and then shifted to LHD as the ore became more competent at the lower levels. Application of rock mechanics played a vital role during the conceptualisation of the LHD method of draw, the first of its kind in the Philippines. Rock mechanics is a combined responsibility of the geology and the mine engineering staffs, with the geology providing the vital information to the mine engineering to include in the mine planning the following:the general geology of the orebody; the ground characterisation through rockmass classification; determination of the cavability of the ore column (this includes our experience on airblasts which occurred during the early stage of our last slusher blocks); undercutting sequence; fragmentation of the rockmass in the ore column; drawzone spacing; proper draw control procedure; lay-out of openings; and the design of ground supports based on the rockmass condition. For the proper interpretation of the rockmass that would cater to the diverse mining situations, Philex adopted the modified geomechanics rockmass classification (Mining Rockmass Rating, MRMR) as this system is recognised and used by most of the block cave mine worldwide. This paper aims to discuss and present the role of rock mechanics in the analysis and determination of geomechanical issues encountered in Philex mechanised block cave operation.

Jan 1, 2000