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By M. E. Rossi

Reconciliation of long-term block model reserves and mine production frequently shows significant discrepancies. This reconciliation can be done comparing the long-term block model reserves against a grade control model (generally, a model based on blast holes or production data). in this paper called an FI factor for tonnages, grade, and ounces; and also it should be done comparing the grade control model to the mill feed (or loaded to heaps) tonnages, grades and ounces (called an F2 factor). The long-term model usually contains blocks with dimensions larger than the size of the selective mining unit (SMU) of the operation. The smoothing effect of an estimator such as kriging will generally result in a grade-tonnage curve that does not match the grade-tonnage curve of the SMU's to be recovered. This problem is partly to blame for the reconciliation discrepancies found. In addition, in-pit perfect selection is impossible. and therefore the grade-tonnage predictions based on blast holes also need to be assessed, considering both unplanned dilution and the errors of estimation of the grade control model. This paper will focus on using conditional simulations to assess the uncertainty of the predicted grade-tonnage curve in terms of minable reserves, and in the framework of long-term mine planning. Quantifying the uncertainty in no uncertain terms is done in conjunction with a popular pit optimizer, which will yield not one, but several possible minable reserves, and therefore a range of possible minable tonnages and grades per pit shell or scheduled phase. This is a step further from the usual sensitivity analyses that are performed for deposit evaluation or development planning. Specifically, this approach takes into account the volume-variance relationship, the selectivity of the mining operation, planned and unplanned dilution. and carries the local uncertainty implicit in grade estimation into the mine design and mine planning phases. The motivation for the approach is discussed through an example, as well as a description of the procedures and steps involved.

Jan 1, 1998

By Shane Yanagisawa

The Mineral Creek Diversion Project is at the Asarco Ray Mine Complex, about128 km (80 miles) east of Phoenix, Arizona. The new tunnel will intercept the waters of Mineral Creek about 2,134 m (7,000 ft) upstream from an existing tunnel. The 5.74 m(18.83 ft) hard rock TBM will break into the old tunnel about 2,162 m (7,090 ft) in from the old portal after mining 3,888 m (12,753 ft). The TBM will mine through a series of igneous and metamorphic formations including volcanic tuff, soft volcanic ash, massive diabase, fractured quartzite, and schist. The TBM will hole through into the existing 4.88 m (16 ft) dia. horseshoe tunnel where the TBM will be disassembled and removed from the tunnel.

Jan 1, 2001

By H. E. Rojas, G. T. Adel

The primary objective of most comminution operations is liberation; however, mill performance is generally quantified in terms of particle size. Only recently has the use of image analysis equipment made it possible to quantify mill performance on the basis of liberation. In this investigation, a series of tests were carried out to study the effect of mill operating parameters on the liberation of sphalerite from a sphalerite/dolomite ore. The parameters studied included mill rotational speed, mill loading and ball size. The results of this work appear to indicate that sphalerite liberation is improved under conditions that promote impact breakage, while dolomite breakage is enhanced under attrition conditions.

Jan 1, 1992

By D. Greene

The close integration of mine planning and mine operation continues to be the goal of mine operators. Depending upon the complexity, size and sophistication of the mine, limited success has been achieved in this area. Despite tremendous strides in the development of computer-aided mine planning, digital plans must usually be converted to error-prone paper maps and physical ground surveys for actual excavation and reclamation. However, advances in global positioning systems (GPSs), operator displays and mobile computers now enable equipment operators to work directly from on-board digital plans. A computer-aided earthmoving system (CAES) offers reduced survey costs, faster field transition time and improved excavation accuracy, coupled with faster, more informed decision making regarding key mining operations.

Jan 1, 2000

By J. R. Henke

Dewatering wells producing iron-rich water experience rapid declines in yield and drawdown due to the formation of ferric (Fe +) hydroxide deposits in well screen, pump intake and riser pipe. Precipitation is caused by a combination of dewatering-promoted iron oxidation and iron-oxidizing bacteria. Physical and chemical well rehabilitation techniques, as well as alternative well construction and well development techniques designed to minimize well clogging, were evaluated in this study. The addition of acid downhole feed systems to dewatering wells prone to iron encrustation can, in some cases, prolong their operational lives up to 500 percent that of unacidified wells.

Jan 1, 1989

By Mike L. Aziz, Keith D. Ferguson, Glenda Ferris

The Equity Silver mine has been a severe producer of Acid Rock Drainage (ARD) since 1982. The mine was closed in 1994 and a compacted clay cover installed, but ARD continues to be produced. Three permanent employees manage the collection and treatment system at the site. The site still poses a significant environmental risk to the environment and downstream users and requires a high level of diligence. Various stakeholders' perspectives of the risk posed by Equity, and what constitutes acceptable risk, will be examined in this paper from a company operation staff, corporate environmental manager and downstream environmentalist perspective.

Jan 1, 2000

By Donald J. Olson, Thomas J. Lutzenberger, John Ramage

The North Shore Inline Interceptor, Phase IA tunnel is a 8,550-meter (28,000-ft) interceptor tunnel currently being constructed by Traylor Bros./Frontier-Kemper, Joint Venture, using a 9.8-meter (32-ft - 4-in) diameter Robbins tunnel boring machine (TBM). This tunnel is being driven in Silurian age dolomite approximately 91.5 m (300 ft) below ground surface. Significant water inflows were encountered when the tunnel drive penetrated the thinly-bedded Waubakee Formation. Flow increases approaching 0.75 cu m per min per 30 m of tunnel (200 gpm per 100 ft) have occurred in this formation. After driving approximately 2,285 m (7,500 ft) of tunnel (200 m full face in the Waubakee Formation), total flows exceeded 12 cu m per min (3,200 gpm) with about 5.7 cu m per min (1,500 gpm) entering the tun¬nel from the 200 m (600 ft) of exposed Waubakee Formation. Additional water control measures consisting of increased pumping capacity, increased water treatment capacity, surface grouting ahead of the tunnel, grouting ahead of the tunnel face and panning to improve the working environment for installation of tunnel support, were implemented to deal with the large water inflows. Currently (January 24, 1989), 3,400 m (11,000 ft) of tunnel has been driven, total water inflows are in the range of 11.7 cu m per min (3,100 gpm) with only 6.8 cu m per min (1,800 gpm) inflow from about 1,220 m (4,000 ft) of tunnel driven full face through the Waubakee Formation.

Jan 1, 1989

By Charles H. Arnold, Timothy Fallara, David A. Day, Paul H. Marshall

The Upper Scioto West Interceptor Sewer (USWIS), Parts 1 and 2, consists of approximately 7,128 meters (23,385 ft) of 328 cm (129 in.) diameter tunnel. The project ex-tends from the City of Dublin to Griggs Dam in the City of Columbus. The majority of the tunnel was designed for excavation in rock by TBM. The remaining portions span pre-glaciation formed valleys in-filled with glacially-derived sediments. Tunnel construction in one of the glacial till filled sections includes excavation by drilling and controlled blasting. The other section will be constructed by ground consolidation followed by excavation by TBM. This paper describes the methods employed to mine the glacial till filled valleys.

Jan 1, 1997

By P. Huttagosol

The use of computer models to design ultimate pit limits during feasibility study and long range mine planning is becoming a significant practice in open pit mining. One of the problems in determining optimal ultimate pit limits using true optimization techniques has been they require a great deal of computer memory and execution time. In this paper, the maximum closure of a graph, which is a true optimizing model developed by Lerchs and Grossmann, is modified for solving ultimate pit limit problems. By using some properties of the original L&G graph algorithm, the tree configuration can be reduced to only connections between positive ore nodes. The modified algorithm is shown to require less memory and processing time while still yielding an optimal solution.

Jan 1, 1989

By R. A. Hodge

Over the past decade, there has been a significant increase in effort put to tracking progress toward sustainability. Many aspects of society are participating in this “movement” including mining. The drivers are diverse and include evolving ideas in business and public administration as well as concerns for human well-being, community robustness, environmental integrity, and overall social and ethical responsibility. The scale in question varies greatly from local to global. For the most part, there has been a pre-occupation with developing discrete measurable signals. This paper argues that the overwhelming focus on the quantitative is ill-advised and that a more effective approach is to bring together the best of both quantitative and qualitative. The mining industry in particular is well-placed to affect this shift and reap the associated benefits.

Jan 1, 2004

By Stephen H. Hall

INTRODUCTION At some point in the design and development stage of a mineral venture, the assay laboratory building, its interior layout, and major pieces of analytical equipment must be specified for construction or purchase. Even the most experienced chemist would have difficulty in proposing useful specifications without a good deal of investigation into the kinds of analytical tasks that the laboratory will be expected to address, the probable workload, and the operating time constraints. This chapter will provide a logical approach to laboratory design that starts with such an investigation. Specific examples throughout the chapter are drawn from the author's tenure as Chief Chemist at Barrick Mercur Gold Mines, Mercur, Utah, from 1982 to 1985. It is necessary to understand the nature of a modern production laboratory, and to recognize that its operations bear more resemblance to its parent processing plant than to a research, teaching, or custom analytical laboratory. The assay lab is a processing facility unto itself, where samples and reagents are the raw materials, and assay results are the final product. Its most efficient operating mode is as an assembly line, treating samples in a nearly continuous flow. Nevertheless , there are important differences between the lab and the process plant. The products - assays - are individually unknown quantities until they are "produced.' This can vastly complicate quality control compared to the process plant. Capital costs are general 1 y small compared to the plant, but the ratio of operating costs to capital costs for a laboratory is often very much higher than for the plant. This is due to the labor intensive nature of analytical work. For instance, during Fiscal Year 1984 at Barrick Mercur Gold Mines, labor costs for the laboratory staff represented about five percent of the total labor budget, while the laboratory building and equipment represented only about six-tenths of one percent of the original start-up capital. Failure to recognize both the similarities and differences between laboratory and plant operations is the foremost cause of difficulty encountered in designing a laboratory. The

Jan 1, 1986

By Henry H. Roos

NTRODUCTION In the mining industry, a "drill jumbo" is a drilling unit equipped with one or more rock drills and mounted on a mechanical conveyance. Jumbos range from single¬drill ring drills mounted on simple steel skids to sophisti¬cated multiple-drill units mounted on diesel engine powered carriers and equipped with automatic controls and sound-abatement cabs. Individual types of jumbos usually are designed for specific tasks such as fan drilling in sublevel caving operations. Some units, such as development jumbos, can be utilized for several functions in addition to their normal applications, e.g., for production drilling in room-and-pillar operations, stoping in cut-and-fill mining, etc. Mine operators can purchase individual components from manufacturers, assembling these components into a jumbo suitable for specific conditions. However, this requires that mine personnel have good engineering and mechanical abilities. Although manufacturers of jumbos maintain facilities for designing machines to meet con¬ditions created by new mining methods and unusual ap¬plications, the cost of the engineering and experimental work for new types of jumbos should be evaluated in terms of both costs and benefits; it may be advantageous to plan the mining operation so that existing and proven units can be utilized. GENERAL SELECTION CRITERIA Since the operating conditions vary in underground mines, the design of a jumbo must be selected to cope with the individual characteristics of the mine. The necessary considerations include access space into the working areas, grades expected to be encountered, radii of the curves, ambient temperatures, the characteristics of the rock, the acidity or alkalinity (pH rating) of the mine water, etc. Access to Mine Workings The mine workings must be accessible to the selected jumbo. Frequently, a jumbo must be disassembled at least partially to pass through the mine shafts. There¬fore, a bolted construction allowing disassembly into pieces of suitable size and weight is desirable in most applications. Type of Undercarriage Generally, a crawler-type undercarriage should not be used in trackless mines having acidic mine water. The acidic water causes an electrolytic action between the individual crawler parts and causes rapid corrosion and early failures. Propulsion A two-wheel drive on a pneumatic-tired jumbo is marginal for grades exceeding 12%. A four-wheel drive unit with good weight distribution is capable of operat¬ing on grades of up to 35%. At least 30% of the gross vehicle weight (GVW) should be carried on the steering axle; otherwise, the steering tires may not have sufficient traction on loose road surfaces and may "plow" instead of steer. To assure stable operation in mines with steep grades, the height of the center of gravity of the jumbo should be considered. It should not make the unit prone to rolling over on the steep grades that may be encoun¬tered. Turning Ability In confined working areas, a skid-steering or crawler unit has the best maneuverability. An articulated carrier is preferable when base-rotated parallel booms are being utilized. A rigid-frame jumbo with automotive steering is compact and economical, having lower maintenance requirements than the other two types. However, the turning radius of a rigid-frame unit is wider than either the skid-steering or articulated units, and this wider turning radius may be detrimental in mines with narrow drifts. JUMBO COMPONENTS Rail Undercarriages A mine with a rail-transportation system generally utilizes drill jumbos that are mounted on rail-type under¬carriages. With a light load and good weight distribu¬tion, this carrier may consist of a simple two-axle four-wheel platform onto which the boom-mounting brackets are attached. As the depth of the round and the penetration rates increase, the weight of the equip¬ment installed on the chassis also increases. The greatest problem with a heavy overhung load is balancing the carrier; a three-boom unit may require a substantial amount of counterweighting to maintain an acceptable 70% to 30% axle-load balance. Although lengthening the wheelbase helps balance the unit, a long wheelbase increases the turning radius, often creating problems on curves and sometimes requiring a swivel truck-type chassis. A good rule of thumb for a simple four-wheel undercarriage is to maintain a wheelbase length to track gage-width ratio that does not exceed 2.5 to 1.0. For a larger ratio, a swivel truck should be utilized. Swing-out outriggers or roof jacks help keep a jumbo in place during the drilling cycle. Usually, a rail-mounted jumbo is not self-propelled. Instead, it is maneuvered into place by a locomotive. Occasionally, several headings are being advanced in close proximity, and a self-propelled jumbo is con¬venient. In electrified mines, such a jumbo utilizes conventional battery-powered traction gear; in dieselized mines, hydrostatic drive components offer good flexi¬bility. The tractive power requirements of a typical rail jumbo may be calculated from the formula: HP = [(RR + GR) X Sl/[33,000 X Em X Eh]

Jan 1, 1982

By David Muir, Slobodanka Vukcevic

Gold is commonly associated with copper minerals, particu­larly in the more geologically recent rocks of Northern Australia, Chile and the Pacific Rim. Traditionally, oxidised copper-gold ores are selectively mined and processed for gold by cyanidation, ensuring that levels of reactive copper in the ore are kept low to minimise cyanide consumption; whilst sulphide copper-gold ores are floated and gold is ultimately recovered as the by-product from copper smelting and refining (La Brooy, 1992). Very few process­ing options exist for treating copper ores which cannot be selec­tively mined or floated, and for treating floation tailings which often contain significant gold (Muir et.al.,1989). The ammonia-cyanide leach system stands out as a unique method of selectively extracting gold without copper using economic levels of cyanide (1-2 kg/t NaCN) and ammonia (1-5 kg/t). Although first patented in 1904, it proved difficult to control and predict per formance with different ores. However, recent research and development in Western Australia by Ruane (1991), Hayes and Corrans (1992), La Brooy et.al.(1991), Muir et.al.(1993), Muir and La Brooy (1993), has led to an under­standing of the mechanism, and the commercialisation of the process at the Paris Dump (W.A.), Akjoujt (Mauritania), and in the Eastern Transvaal (Laxen,1994). Efforts are now underway to pilot and develop a tailings treatment plant at Telfer following successful laboratory trials. To date, process optimisation has relied on trial and error and large numbers of tests covering a range of conditions. Thus the results are specific to the ore. At Murdoch University, process optimisation is now focused on measuring and control­ ling Eh, pH, NH3 [Cu(II)], and Cu-CN species at the optimum levels identified from the recent mechanistic studies. In this way, the optimum composition required to process any ore should be readily established and maintained.

Jan 1, 1995

By J. J. Gusek

An 81 hectare (200 acre) tailings impoundment at a taconite operation in Wyoming that ceased operations in 1983 has been a source of blowing dust. The site qualified for reclamation under Wyoming's Abandoned Mine Land (AML) reclamation program. The ultimate reclamation construction included: incorporating commercially available organic amendments and fertilizers into a 300 mm (12 in) thick "cap" of a sterile clay loam cover material, lowering the water level in an adjacent flooded mine pit that was feeding uncontrolled seeps into the tailings basin, constructing a wide tailings pond spillway that allows flood control while minimizing seasonal water level fluctuations in the pond, and building rock berms and rock snow fences for wind erosion control and soil moisture preservation. Tree planting in the protective wind/snow shadows of rock berms and rock snow fences, and the plugging of a decant pipe are planned for future work.

Jan 1, 1998

The Bagdad mill, built in 1977, was de-signed for a mill capacity of 36,300 tpd. An ABC (Autogenous Mill-Ball Mill-Crusher) grinding circuit was chosen. The original mill contained three completely independent grinding circuits, each containing one 9.75 m diameter by 3.96 m long fixed speed autogenous mill, one 4.72 m diameter by 6.71 m long ball mill and one 2.13 m diameter short-head cone crusher. Total installed power per grinding circuit was 8,464 kw with 5,966 kw in the autogenous mill, 2,237 kw in the ball mill and 261 kw in the crusher. (See FIGURE I--Major Equipment Flow Diagram.) The autogenous mills were designed to be able to operate semi-autogenously but were never converted to SAG. As a result of this design, only about 4,100 kw of the designed power is utilized in the autogenous mills. The grinding circuits are closed with 2.44 m by 6.10 m double deck vibrating screens. Screen oversize is returned, by a series of conveyors, underneath the mill coarse ore stockpile to feed the crushers. Variable speed belts feed the crushers and control power draw. Crusher product reports directly to the tail end of the autogenous mill feed belt. (See FIGURE 2--Typical Crusher Feed and Product Size Distributions.) Tramp iron in the autogenous mill-crusher circuit is handled in a unique way. A magnetic sensor detects the metal. This closes a gate which directs the crusher feed onto a separate belt which bypasses the crusher and returns the material to the autogenous mill feed belt.

Jan 1, 1992

By Charles G. Frush

The function of the mine surveyor is to (a) provide a network of points of accurately known position, covering the entire mine property, (b) obtain the required data for the preparation of useful maps and sections! (c) provide position and directional control for the guidance of the operations, (d) measure the progress of the work, (e) measure the movement of rock masses, and (f) make miscellaneous surveys as needed. Mining properties range from the very small to the extremely large, and from those which involve only surface operations to those involving extensive underground workings. Active mines undergo constant change, necessitating continual updating of the surveys. The differences in the character of the deposits, the scale of mining and the mining methods result in large differences in the surveyor's activities and techniques, but many of the problems involved are common to most mines. The surface work of the mine surveyor is very similar to that, of the plane surveyor in that control points are established by triangulation, trilateration and traversing. Detail is taken by direct measurement, by stadia and by aerial photography. The equipment used, the techniques and the methods of processing the resulting data are likewise very similar. However, the underground work is quite different : A. The lines of sight frequently must be carried through constricted openings, often involving short lines of sight and awkward setups. B. The lighting often is poor, requiring illumination of the backsights and foresights, and the crosshairs. C. The ambient conditions often are difficult, involving falling water, high tem- peratures, poor visibi 'kv and heavy traffic through the area being suneyed. D. The surrounding rock map be unstable, resulting in movement or loss of the surveying stations, as well as hazard to the surveyors. E. The points to be measured often are difficult or impossible to reach. F. Steep vertical sights often are necessary, requiring the use of special equipment. G. Many working levels commonly are involved, requiring the transfer of position and orientation to each with a high level of precision. This section therefore will concentrate on surveying problems peculiar to the mine surveyor, chiefly underground work. 22.1-THE MINE COORDINATE SYSTEM A system of coordinates is essential for all permanent mining operations It is very desirable that all mining operations in a ,given area b~ tied into the same system, as this minimizes problems of boundaries and connections Whenever possible this system should be tied into and made part of the state or regional grid system. It is desirable to orient the coordinate grid on a true-north line and to position the origin of the coordinates so that all of the work will be in the "northeast" quadrant, making the north and east coordinates always positive. This can be done by subtracting suitable constant values from the north and east coordinates of the regional system The residual values are of more convenient magnitude and can be used as the local mine coordinates. If the long axis of the mineralization is not generally north-south or east-west.

Jan 1, 1973

By Dale R. Ralston, Roy E. Williams, Gerry V. Winter, George L. Bloomsburg

GENERAL STATEMENT Data frequently can be collected by several dif¬ferent methods. The method required for the nec¬essary precision for inflow prediction to mines should be selected and other methods avoided. Pre¬cision monitoring or measuring techniques fre¬quently require more time, expertise, and expense in their implementation that may not be justifiable. The temporal distribution of the data needs also may dictate the method used for data collection. Continuous recording devices may be required for time sensitive data whereas point measurements of other parameters may be adequate. Data needs will vary as the hydrologic investigation proceeds. In¬itial data needs may require only a qualitative col¬lection of data such as the areal distribution of precipitation. Subsequent data needs may require the measurement of ground water levels to the near¬est hundredth of a foot. Data requirements can be difficult to fulfill for ground water systems. This is particularly true for anisotropic, heterogeneous hydrostratigraphic units since the hydrogeologic parameters vary both ver¬tically and areally. Techniques exist for determining the storage characteristics of both unconfined and confined hydrostratigraphic units but these pro¬cedures require the installation of multiple wells in the same unit which may be impractical. Specific tests are discussed subsequently that permit the determination of vertical hydraulic conductivity. Data collected from field procedures or tests are generally preferred to laboratory derived data. This is especially true for hydrogeologic parameters such as hydraulic conductivity. SURFACE WATER SYSTEMS Precipitation Precipitation data can be collected from sources that maintain a historical record. The US Depart¬ment of Commerce, National Oceanic and Atmos¬pheric Administration (NOAA), maintains weather observation stations across the country. Such a sta¬tion frequently can be found near a proposed mine site but the type of weather data collected varies from station to station. Fortunately, precipitation data are collected ubiquitously. The data collected by NOAA can be purchased for the area of interest in the form of monthly and annual tabulations. Private weather stations constitute a second source of precipitation data. Existing data usually are analyzed by one of three methods. The station average method merely sums the depth of precipitation at each station and divides the sum by the number of stations as fol¬lows: [ ] where Pavg is the average precipitation (L), P, is the depth of precipitation at station i (L), and N is the total number of stations. This method is applicable where there are a relatively large number of stations uniformly distributed across the area (Hjelnfelt and Cassidy, 1975, pp. 71-72). The second method, called the Thiessen poly¬gon method, weights the precipitation at each sta¬tion in direct proportion to the area it represents without consideration of topography. The stations are plotted on a map and perpendicular bisectors are drawn on the lines connecting the stations. The polygons formed by these bisectors constitute the area that the precipitation for that station repre¬sents. The overall precipitation can be calculated with the following equation:

Jan 1, 1986

By R. D. Hendry, R. A. Pearce, Allyn J. Steward, Dennis C. Martin

This paper outlines the geotechnical exploration and design approach utilized for the Km 80 and Km 86 Tunnels on the British Columbia Railway Tumbler Ridge Branchline. Information from surface mapping, trenching and diamond drilling was used to prepare a rational support design using accepted rock mass classification systems. Four possible support types were developed and used as a basis for preparing a cost estimate and contract documents for the tunnels. A unit price contract was selected to provide flexibility and to enable rational selection of support based on actual ground conditions encountered during excavation. Although ground conditions along the tunnels are variable, the general geology and quantities of support installed were consistent with those estimated from the geotechnical investigation and design.

Jan 1, 1985

By Richard M. Crowell, John W. Shield, Todd J. Harvey

Facing lower gold prices, gold mine operators throughout the world are seeking ways to reduce costs for treating refractory sulfide ores. Many gold mines, currently producing oxide ores, have underlying refractory sulfide deposits and the operators could extend the mine life by processing these sulfides. Fortunately, oxidation technologies for refractory ores need not be complex nor costly. GeoBiotics, Inc. has developed heap biooxidation technologies (GEOCOAT™) for treatment of refractory gold ores and concentrates. GEOCOATTM uses simple low cost unit operations common to heap leaching of gold and copper ores. The cost effectiveness and flexibility of GEOCOAT™ heap biooxidation allows mining companies to expand operations to include refract01y ore. In addition, GEOCOAT™ can be utilized to supplement or replace existing oxidation processes such as roasting, autoclaving, or agitated tank biooxidation, and to treat a lower resource grade than is currently economic. The GEOCOAT™ technology involves coating sulfide concentrates onto sized support rocks and biooxidizing the sulfides in a heap configuration. After biooxidation the concentrate is stripped from the support rock, neutralized and leached in conventional cyanidation facilities. Ashanti Goldfields Company Ltd. (AGC) produces over 885,000 ounces of gold per year from oxide and refractory ores at its Obuasi operations in Ghana. Refractory flotation concentrates are treated in roasters and in the world's largest stirred tank biooxidation facility. In August 1998, AGC and GeoBiotics jointly constructed and operated a field demonstration heap of the GEOCOATTM process at the Obuasi operations. The heap contained I 082 tonnes of support rock and 125 tonnes of concentrate. The heap was approximately 19 meters square at the base and 3.8 meters high, and ran for 88 days after which the concentrate was reclaimed. Average gold recovery after biooxidation was 91.5% with a NaCN consumption of 8.6 kg/t. Baseline gold recovery by direct cyanidation of the concentrate was 53.8%.

Jan 1, 1999

By C. A. Young, R. G. Robins, E. J. Dahlgren

The formation of copper thio-complexes in sulfide solutions has been recognized for many years and the measured solubilities of certain copper sulfide minerals attributed to these complexes. Attempts to model this system have proposed either copper(I) or copper(II) thio-complexes, and these have been incorporated into computer programs for generating stability diagrams for the copper-sulfur-water system in order to delineate the region where the reductive dissolution of copper sulfide minerals is likely. In this paper it is proposed that the dissolution of copper from both ore bodies and sulfide tailings can be explained by the formation of the cupro-thio-complexes under anaerobic conditions. Stability diagrams are presented to depict the region and extent of the solubility.

Jan 1, 2001