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By J. W. Leonard

Introduction Gravity-based coal/mineral preparation plants must be operated to yield products of a quality satisfactory to existing markets. However, because of historic control problems, recovery is frequently sacrificed to achieve quality, resulting in losses of valuable product. Plant control has ranged from intuitive in-plant spot quality judgments made by various operators to gross methods involving such devices as density gauges, floats, grabsample on-the-spot sink/float tests, etc. Millions of tons of quality coal/minerals are lost to refuse each year, because of the historic lack of a continuous and dependable control system. The result is serious economic, as well as environmental, losses. While the economic losses are obvious, the less obvious environmental ones, in the case of coal, result from the misplacement of more ignitable quality fuel to refuse banks. Until recently, a control system capable of supplying a market-grade coal/mineral product, while continuously minimizing product losses to refuse, has been technologically unavailable. Coal/Mineral Washing Tracer System Performance Monitor (CMWTSPM) The first Coal/Mineral Washing Tracer System Performance Monitor (CMWTSPM) originated in the late 1970s as an innovative idea and ultimately resulted in Leonard Patent No. 4,345,994 issued on August 24, 1982. In a classic example of successful university basic research, the patent was followed by two US Department of Energy (DOE) merit awards for fundamental optimization research at the University of Kentucky, a number of publications, a successful applied research program (underwritten by SENTREX at Irvine, CA) and field tests at the Rochester and Pittsburgh Coal Company Keystone Mine near Indiana, PA. The system is now operational and is marketed by SENTREX as the SENTREX Performance Monitor. A diagram of the system is shown in Fig. 1. This system relies on metal detection as the basic tracing medium. Since it is capable of tracing particles as fine as 0.19-in., the system is ideal for coarse coal/ mineral cleaning processes. Basically, the CMWTSPM records the distribution of synthetic coal/mineral particles, of known size and specific gravity, between product and refuse output streams of coal/mineral washing, gravity-concentrating processes. For any given particle size, surface area and shape are constant. The particles are [ ] designed to find their way into the center of their respective inprocess specific gravity/size streamlines. The system will yield a complete partition curve to show the percentage of misplacement for any selected size/specific-gravity particle fraction, thereby providing a point-to-point insight into process failure. When used to evaluate operational processes, this full partition curve is far more diagnostic than the simplifying, derivative, single index number known as the Ep value. The Ep value is commonly used for convenience to represent symmetrical partition curves, but, if the actual partition curve is non-symmetrical, use of the Ep value can result in serious diagnostic error. While the Ep is useful in design and for rapid performance evaluation and process adjustment, the full partition curve is by far the more diagnostic. It will provide insight into the behavior of particulate flow, through non-symmetry, as a means to highlight potential systemic failures. Performance of the process is measured and improved by determining the extent of particle misplacement and by making timely adjustments to the unit to reduce the misplacement. Used in this manner, the CMWTSPM is not only a long needed processing control monitor, but it is also a very powerful diagnostic tool which, in the hands of skilled operators, has

Jan 1, 1993

By J. Lorosch

Improvement of current leaching technology was found necessary when processing ores which are more difficult to leach because they generate highly viscous, air-rejective pulps. Cyanidation of these pulps has to run at low oxygen concentrations if the conventional aeration technique with compressed air is used. Since the dissolution rate of precious metals mainly depends on the concentration of dissolved oxygen in the pulp [1, 4, 5], the kinetics of the gold extraction become slow in such cases, which in turn often leads to a significant decrease in the overall gold output within the conventional leaching time of up to 48 hours.

Jan 1, 1988

By M. Springett

Organization of teams for rapid and effective evaluation of international mining properties requires special considerations beyond those needed for domestic activities. Experience, technical ability, a sense of perspective, humor and self-discipline are vital characteristics to look for in the selection of individuals for forming an efficient and productive team.

Jan 1, 1994

By George P. Tateosian

Merchants perform a number of functions in the copper market. As a major distribution arm of the copper industry, they secure scrap and other copper bearing materials for processing into usable refined shapes. These are ultimately sold to fabricators. Merchants ' hedging and arbitrage activities help keep values in proper relationship from product to product or region to region. Through these switching and trading operations, they optimize the flow of copper from mine to consumer. And finally, merchants act as a repository for copper units during times of surplus and a stockpile from which to draw during tines of shortage.

Jan 1, 1979

By A. S. Moss, J. Linkous

Where difficult shaft sinking conditions exist, it may be appropriate to use a blind drilling technique. The success of the method is in part due to the presence of a drilling mud which fills the shaft void during excavation. The mud performs two important functions with respect to shaft stability: it reduces the influence of groundwater; and, due to the mud weight, gives a positive sup- port to the shaft walls. The application of the method is illustrated by a case history which traces the development of a shaft from the initial investigation to determine the shaft location, through the evaluation of wall stability and mud requirements, to the shaft sinking contract and actual conditions encountered.

Jan 1, 1986

By G. Ansong, P. K. Achireko

The authors present a new mineral price model, compare it with time series and naive models, and analyze the effects of the forecasting models on mineral project evaluation. Mineral commodity prices are volatile, which means that the results of evaluation tools that do not treat the stochasticity of metal prices rigorously may be misleading. But, in mine valuation, commodity price forecasts are required to assess the economic viability of a project. In this study, a new mineral forecasting method, called the MNDRVG-MFNN-RM model, which incorporates randomness, neural networks and regression models, is introduced. The MNDRVG-MFNN-RM model, a naive method and time series model were used to forecast gold prices for two successive years for the evaluation of a proposed open-pit mine. The MNDRVG-MFNN-RM model yielded the best results among the three methods. It produced the true optimum pit limits and an optimum pit value slightly less than the true optimum value. The main novelty of the methodology is the simulation and rigorous analysis of the randomness property associated with mineral prices to reduce the estimation and forecast errors, an important contribution to mineral venture evaluation, mine planning and design.

Jan 1, 2000

By John H. Duke

The success of most attempts to evaluate gold orebodies depends largely on the reliability and availability of representative sampling data and the accuracy of geological interpretation. An accurate prediction of the continuity of geology is paramount to a reliable prediction of gold reserves. Many of the problems encountered in gold mine evaluation and planning revolve around the difficulties in interpreting complex geology from sparse drilling data and the eagerness of mine financiers and promoters to start mining in order to derive an early cash flow. Following a program of sampling, geophysics, mapping and geological interpretation, a conceptual orebody model evolves in the minds of those working on the project. It is this model which is used typically in ore reserve computations and mine planning. Computer modelling techniques to represent and evaluate the conceptual model are now available. The main advantages of using computer modelling methods lie in being able to rapidly evaluate, modify and quantify the conceptual orebody model. Ore zones or domains can be recognised and defined both from geology and sampling results. Once these domains are defined as a series of boundaries, they may be modelled as two dimensional grid surfaces or as wire-framed three dimensional geometries, depending on the complexity of the orebody. It is the definition of these domains which provides the sound geological basis for reserves computation. To estimate reserves it is necessary to determine both volume of ore and grade of ore. The ore volume is calculated within each domain as defined by the confining surfaces or wire-frames. The ore

Jan 1, 1987

By R. N. Chakravorty, R. J. Kolada

Introduction Spontaneous combustion in coal mining is recognized as a major hazard in terms of safety and economics. A survey by Olaf (1979) revealed that 80% of coal mine fires were caused by spontaneous combustion. Modern mining methods demand a high capital investment. Closure of a working face may then result in a huge loss. Even a short production interruption can prove expensive. Spontaneous combustion may also produce lethal amounts of carbon monoxide, thus posing a serious threat to the health and safety of underground miners. The worldwide recession in the early 1980s resulted in a number of mine closures and production cutbacks. So large stockpiles at mine sites were common. Experience has shown that stockpile fires are difficult to extinguish. Critical factors influencing spontaneous combustion There is no simple method of predicting whether a particular mining method applied to a specific coal seam will result in spontaneous combustion. Under favorable conditions of heat accumulation, spontaneous combustion can occur with any type of coal. It is known that subbituminous coals are more susceptible compared to low volatility bituminous coals, and that a high ratio of exinite increases the risk. However, the inherent moisture content of the coal and the exposed surface area may be more significant. Actual mining and ventilation conditions also strongly influence susceptibility. In practice, the experience gained with the mining method applied to a particular type of coal seam must be carefully evaluated with respect to the factors responsible for spontaneous combustion. Feng, Chakravorty, and Cochrane (1973) summarized the critical factors influencing spontaneous combustion in coal mines (Table 1). Prevention methods and strategies Mine layout is the most important factor preventing spontaneous heating. Working districts should be designed so that a particular section can be isolated on short notice without affecting production in others. Sites for preparatory seals should be identified and marked during planning. With coal seams that are highly susceptible to spontaneous combustion, the retreat method of working is preferred. This is because the gob is not subjected to a large difference in ventilation pressure. Coal pillars should be designed to resist excessive crush. The panel system of working is preferred, particularly for mining coals susceptible to spontaneous combustion. The size of each panel is calculated based on the incubation period and the rate of extraction. Controlling air leakage is also important for controlling spontaneous combustion. This is usually achieved by minimizing ventilation pressure difference, proper siting of doors, and avoiding unnecessary stopping and starting of fans. Air leakage is also reduced by sealant coating, injection of cements in cracks and crevices, and by maintaining good gateside packs. Application of inhibitors to control spontaneous combustion met with limited success. Chamberlain and Hall (1973) concluded that borate solution or Montan powder sprayed in the gob area or infused into a low rank coal would reduce the possibility of spontaneous combustion. Early detection of heating Significant research is being conducted worldwide to develop methods for early detection of heating. Monitoring combustion products during the early stage of heating is the most suitable method for detecting spontaneous combustion. The major gaseous products resulting from low temperature oxidation of coal are carbon dioxide, carbon monoxide, and water vapor. In mining operations, carbon dioxide monitoring is considered unsuitable because there are sources other than spontaneous heating from which this gas may originate. Carbon monoxide, however, is a more specific product of combustion during low temperature oxidation of coal. Over the years,

Jan 10, 1988

By G. T. Adel

Hindered-bed separators are often used in the minerals processing industry to classify particles according to size and density. A new technology, known as the Eriez CrossFlow, was recently developed to overcome some of the limitations associated with hydraulic separators. The innovative feature of this unit is a novel feed presentation system that improves separation efficiency and capacity. In the present work, a detailed process engineering evaluation was conducted to determine the basis for the improved performance of this unit. The evaluation included controlled separation tests using well-characterized feeds, particle and liquid tracer experiments and mathematical modeling studies. Data obtained from this work show that the new separator is capable of maintaining good separation efficiencies at higher solid feed rates than traditional designs due to improved hydrodynamics in the separation zone. This paper reviews the operating principle of the Eriez CrossFlow separator, discusses the results of the tracer experiments and modeling studies and presents test data obtained from recent laboratory and plant trials. Key words: Size classification, CrossFlow separator, Hindered-bed separator, Hydraulic separator

Jan 1, 2003

By D. Altizer, E. Thompson, K. F. Unrug

Because of frequent sudden changes in the geologic composition of strata, the extrapolation of rock properties obtained from core samples to the surrounding areas can cause problems. To address this issue, a method of rapid strength testing in situ using a borehole penetrometer is being developed. This method, as opposed to conventional laboratory testing, does not require rock samples to be retrieved and handled/machined before testing. Rock strengths are determined di¬rectly on the drill-hole wall. The latest development is a borehole penetrometer that requires only a 38.1-mm- (1.5-in.-) diam hole. The small diameter of the penetrometer body allows for the drilling of test holes with production mine equipment such as a roof bolter. The new penetrometer allows for the possibility of a broad application in coal mines, as well as in hard rock mines and tunneling. The principles of the apparatus are described and are illustrated with examples of its applications.

Jan 1, 2002

By P. C. Cochrane, I. S. Clelland, S. H. E. Phillips

Geological and hydrological conditions in the strata overlying the Salado Formation vary considerably in the Carlsbad, NM, area. The first four shafts sunk at International Minerals and Chemical Corp. (IMC) property have been located in competent and essentially dry conditions, while other shafts on adjacent properties have had such adverse conditions that ground freezing has been chosen as the water and ground control technique for shaft sinking. At the location of the IMC No. 5 shaft there has been extensive erosion and salt dissolution in the Rustler Formation, leading to collapse of some zones of the strata. Both ground freezing and pregrouting were considered as alternative methods of stabilizing the extremely poor ground conditions and controlling the potentially very heavy water inflows. It was decided that pregrouting the shaft was feasible and would offer substantial cost and time saving over a ground freezing technique. This paper describes the pregrouting techniques used and illustrates the requirement for flexibility in a grouting program so that it can be modified to reflect any new or additional information obtained during the progress of the grouting.

Jan 1, 1987

By Peter Joralemon

Introduction The Sierra Nevada Foothill Gold Belt in California extends from Mariposa north for more than 420 km (200 miles). It includes the Grass Valley and Alleghany districts in the zone of Northern Mines and the famous Mother Lode to the south. The gold belt has produced more than 3.1 kt (100 million oz) of gold since its discovery in 1848. This remarkable production, at the present gold price, would be valued at more than $40 billion. The Law of Gambler's Ruin supposes that averages are based on systematic rather than random variations. It emphasizes the vast differences between finite and infinite probability. By applying this Law to this figure, it can be seen that the belt has produced an average of 15.5 t (500,000 oz) of gold per running mile. Many geologists believe, with some justification, that less than half the gold in this belt has been mined. Sixty per cent of the past production has come from lode deposits, the balance from Tertiary and Recent placer gravels. This paper will concern itself with the developing lode mines along the Sierra Nevada Foothill Gold Belt. As a further and final note regarding placer mining along this belt, Mark Twain suggested that placer miners, having lost their senses, had contributed liberally to the population of California's insane asylums. After a 40-year lull with little or no gold production, the lode mines of this famous belt are showing signs of renewed activity. Two open pit mines, the Sonora (Jamestown) and Carson Hill, are now in operation at substantial scales. Two others, the Goldenbell (Pine Tree-Josephine) and the Royal-Mountain King, are being readied for production on equally impressive scales. All are in the southern part of the Mother Lode. Exploration farther north, at Sutter Creek, Drytown, and Georgetown, is showing encouraging results in developing deeper lode deposits. This new activity has been sponsored to a large extent by junior Canadian mining and exploration companies. Most of the established American mining companies have looked the other way, not participating in this important development. One major reason for domestic disinterest in this opportunity is there is little chance for heap leachable open pit ore in this belt, excluding Carson Hill. And heap leaching has become fashionable with American mining companies today. Also, this great old gold belt must have been worked out, for why else is there so little activity here - Catch 22 logic. Another reason is that if a new deposit of size and grade similar to the mines in the past was found, high costs would preclude a profitable operation. And, finally, California environmentalists would not permit mining, even if a rich deposit were found. These may all be pefectly valid reasons not to explore for gold along this belt. But a look at the history of gold mining in California may suggest that the future for exploration and development of the gold resources in the Sierra Nevada Foothills can be greater than the past. It was during the Depression of the 1930s that this gold belt saw its maximum activity, with more than 3000 mines in operation. Some were father and son operations producing only a few tons of ore a day. Other mines employed hundreds of miners to hoist more than 900 t/d (1000 stpd). Some ores were of marginal grade. Others, like the Sixteen to

Jan 7, 1987

By Taneomi Harada

Mine drainage has high acidity and sometimes contains more than the allowable concentration of ionized iron. In such a case, mine drainage is neutralized with calcium carbonate and calcium hydroxide to separate precipitates, such as the iron hydroxide and gypsum generated. Currently, most of these precipitates are not utilized and are accumulated in tailing dams. As a result, the service life of the tailing dams is reduced. This becomes a matter of concern, since securing sites for such dams is difficult. A most effective means of solving this problem would be to promote utilization of these neutralized precipitates. This paper reports on the results of studies on neutralized precipitates produced at the old Matsuo Mine (Iwate Prefecture), which has the largest neutralization treatment facility in Japan. As a result of the studies, the following was proposed regarding application of neutralized precipitates. Utilization as ferrite: Mix ferrous hydroxide and ferric hydroxide in water to synthesize magnetite-like ferrite, to be used in the manufacture of magnetic markers for a mobility support system for blind pedestrians, or in producing magnetic fluids for sink-and-float separation of nonmagnetic metals and nonmetals. Utilization as hematite: Bake ferric hydroxide to produce hematite, thereby extracting metallic iron for paint pigment as well as for the manufacture of ironware by local industry. Production of aluminum sulfate: Precipitate aluminum ions from water and add sulfuric acid to produce aluminum sulfate.

Jan 1, 1995

By Matteo Cortinovis, Giuseppe Gelmi

"INTRODUCTIONEdilmac dei F.lli Maccabelli (hereinafter referred to as Edilmac) has recently developed a special civil engineering application using the Raise Boring technology with the assistance of Inrock MGS (Magnetic Guidance System). Applying the Paratrack Magnetic Guidance System coupled with a directional mud motor to the drill string allows a better accuracy compared to standard drilling, as showed in our tests. This is the first time the Paratrack System has been applied to the Raise Boring technology. RAISE BORING METHOD STATEMENT The Raise Boring technology was born in North America during the Sixties. In 1962, Ingersoll and Robbins were the first companies to produce Raise Boring Machines (RBM). The technology was first used in the underground mine industry, in order to bore ventilation shafts and passes through different levels, thus reducing the cost of haulage. The Raise Boring method is only feasible in stable rock conditions. The Raise Boring method consists of drilling a small diameter pilot hole that reaches a tunnel located at the bottom of the drilled hole. Once the pilot hole reaches the tunnel, a reamer head is installed at the end of the drill string and pulled up, creating the hole with the designed diameter (Figures 1 and 2). The main equipment, which is required to perform Raise Boring activities, is the following: •,An RBM; •,A tricone bit; •,Drilling rods; •,A reaming head; The standard mucking of the pilot hole is done with water or bentonite mud. For the last 30 years, Edilmac has developed a mucking process, which uses compressed air with the addition of foam or a small amount of water for dust control.Pilot hole tricone. The drilling of the pilot hole is usually performed with a tricone bit having a diameter between 11” (27.61 cm) and 15” (38.10 cm) (Figure 3). High strength rods. They generally have a diameter ranging from 10” (25.40 cm) to 12 ?” (32.70 cm) (Figure 4), depending on the length and the final diameter of the shaft."

Jan 1, 2016

By R. F. Kovar, R. N. Torbin

Foster-Miller has recently developed a new concept for a highly specialized shaft lining system. This innovative shaft lining system uses a continuous slip forming placement technique, lining the shaft from the bottom up such as in a raised bored shaft. Although this part is not unique, the concept is designed to use polyurethane foam instead of concrete for the liner material. Furthermore, the concept is designed to attain rates of advance of 30 m/h (98 fph). The polyurethane foam liner is designed to be thinner (100 mm or 4 in.) than a conventional concrete liner (300 mm or 12 in.). It will eliminate the high cost associated with the erection and operation of an on-site concrete batch plant. The system will be designed to operate remotely, requiring few personnel for its operation. This system (or parts of it) may be appropriate where fast construction speed is required or where a jointless liner is needed.

Jan 1, 1990

By B. Kendall

"ISSUES ASSOCIATED WITH HAND DRILLING/JACKLEGS In coal mines, hand held air, electric, and hydraulic powered drills are used along belt conveyors, in single entry development, in entries where there are obstructions, and in long wall recovering bolting. In hard rock mines pneumatically powered “jack leg” drills are typically used in narrow vein mining. Drilling and bolting in narrow confines has traditionally been performed with pneumatically or hydraulically powered hand-held drills or newer electrically powered hand held hammer due to their low cost, simplicity of operation, and extreme flexibility due to their small size. Mechanized equipment has typically been too large, too expensive, inefficient due to the confined space, and too restrictive due to lack of flexibility for use in narrow confines. Although the hand-held equipment is effective, it requires operator exposure to certain inherent hazardous conditions in use. These include falling rock from the roof, rib, and face; tripping hazards; bending twisting lifting hazards; high noise levels; and chemical fumes from the pneumatic exhaust. The operation of the hand held equipment can adversely affect the long-term health of the operator – continual jackleg operation frequently results in long term damage to hearing, shoulders, arm and wrist joints, and back injuries. This results in a reduction in life style for the operator and higher personnel turnover rates for the mining company. Hand held drills also typically have limited thrust and torque capability which limits their ability to push long resin bolts, inadequate torque to properly install resin bolts, or to properly torque mechanical or tensioned rebar bolts. Hand held drills do not offer any type of protection for the operator from roof or rib falls. They do not offer any means for handling roof or rib mesh. Since the operator stands on the ground the maximum safe drilling height without use of a ladder or “riding the drill” is limited to 8’ (2.44M)."

Jan 1, 2015

By Vi-Duong Dang

Lithium requirements in the next few decades for batteries and controlled thermonuclear fusion reactors (CTR) may exceed the availability of the current mineral and brine reserves. It is thus prudent to search for new reserves and resources to satisfy these and future lithium applications. The lithium content of the waters from the Smackover oil field. located in the Gulf Coast region of the United States, ranges from 100 to 500 mp/l and could represent a substantial new reserve. Experimental evidence described in the literature indicates that a specific chelating agent dipivaloylmethane (DPM), of the diketone type, has a specific selectivity toward lithium in the presence of other metal ions in aqueous solutions. Based in part on this unique property of dipivaloylmethane, a conceptual design of a full-size plant to extract lithium from the Smackover brine is presented in this paper. This study includes alternate flow-sheet development, design information on the major units of the process, energy requirements, and an economic analysis of a facility capable of producing 106 kg of lithium per year. The economics of three different process concepts depend primarily on the amount of water needing to be evaporated from the initial oil-field feed waters in concentrating the brine. The results, as a function of production rates, are indicated only in a general manner.

Jan 1, 1978

By M. J. McPherson, P. Mousset-Jones, J. Banik, F. Calizaya

Friction factors or coefficients of friction used to estimate the resistances of mine airways are, in the main, estimated from empirical measurements made in other airways considered to be of a similar geometry and type of lining. A somewhat more analytical approach, although still based on empiricism, is to estimate the ratio of the average height of the asperities to the hydraulic mean diameter of the airway (e/D ratio) and then to employ the Moody Chart or one of the equations that have long been established to represent the [coefficient of friction v Reynolds number curves] on that chart. Unfortunately, the Moody Chart and corresponding equations are based on pipes of uniformly distributed (sand grain) roughness whereas the asperities that exist on the surfaces of mine openings are frequently highly irregular both in their size and distribution. This is considered to be a major cause of discrepancies that have been found between coefficients of friction by the Moody Chart and those actually measured in mine airways. The work described in this paper examines an alternative method of estimating coefficients of friction for rough natural surfaces with uneven sizes and distribution of surface asperities. The technique utilizes the relatively recent developments in fractal analysis. A fractal dimension is determined from the topography of the surface. This has been correlated to coefficient of friction for a scale model of a mine airway. Further work is being carried out in actual mine airways. However, at this time, it appears promising that the fractal method may allow coefficient of friction to be predicted for given types of strata and method of roadway drivage.

Jan 1, 1993

By Gale F. Hoffnagle

INTRODUCTION On November 15, 1990, President Bush signed the Clean Air Act Amendments of 1990. These Amendments cover many aspects of air pollution control. The provisions which seek to control emissions of "air toxics" may, however, be the most far-reaching and will potentially have the greatest effect on American industry. The Administration has estimated that by the year 2005 industry will be spending $6.7 billion per year on air toxics control. Meanwhile, the Business Round Table has estimated that the price will be far higher, up to $62 billion per year, depending on how EPA and the States implement the program. BASIC REQUIREMENTS Any "major" source of emissions of 189 air toxics will be required to install "MACT." The translation of this statement requires some definitions: •MAJOR SOURCE - A facility (a contiguous property under single ownership and control) which has actual emissions of 10 tons or more per year of any single one of the air toxics or 25 tons per year of any combination of air toxics. •AIR TOXICS - Congress has provided a list of the 189 chemicals on this list. Those that may be important to the mining industry are shown on Table 1. This list can be changed by petition or by EPA. •MACT - Maximum Achievable Control Technology is to be defined by EPA for each industrial source category. EPA says there are about 400 categories. The Act defines MACT as: "the average emission limit achieved by the best performing 12% of the existing sources ... for categories with 30 sources or more" or, "the average emission limitation achieved by the best performing 5 sources in the category." TABLE 1 SELECTED AIR TOXICS FROM CLEAN AIR ACT LIST IMPORTANT TO MINING INDUSTRY Antimony Compounds Arsenic compounds (inorganic including arsenic)' Beryllium Compounds' Cadmium Compounds Chromium Compounds Colbalt Compounds Cyanide Compounds (dissociation compounds) Lead Compounds' Manganese Compounds Mercury Compounds' Fine Mineral Fibers Nickel Compounds Radionuclides (including radon)1 Selenium Compounds 1Previously listed under NESHAP 2The Administration may not list elemental lead as a hazardous air pollutant.

Jan 1, 1991

By Gordon V. lewis

The Penjom gold mine treats highly preg-robbing carbonaceous ore by using relatively inexpensive gravity and hydrometallurgical methods. The mine is a joint venture between Avocet Gold Limited, a subsidiary of Avocet Mining PLC, a U.K listed mining company with interests in gold and tungsten, and the Pahang State Development Corporation (PKNP) who receive a 2% royalty. The operating team at Penjom embarked on a programme of innovation during 1998 following a realisation that almost all of the primary ore in the gold deposit was highly carbonaceous in nature. Earlier attempts at desliming and leaching the deslimed product through a normal CIL circuit had failed, and through shear necessity, the team turned to new technologies which were considered most suited to the ore characteristics indicated from pre­feasibility testwork. Between April and September, 1998, the mine introduced three key processes, which combined represent the elements of "The Penjom Process". The gravity circuit was boosted to maximise the capture of leachable sulphide and free gold from the relatively carbon free cyclone underflow stream, kerosene and diesel blanking was introduced to treat the cyclone overflow and RIL (resin-in­leach) technology utilised to replace the existing CIL (carbon-in-leach) circuit. Further experimentation with selective resin in partnership with Mintek of South Africa yielded a significant improvement to the process during 1999. Minix­Dowex resin was introduced mid year to replace a non-gold selective resin, which had been used in a flotation/batch leaching circuit for about nine months. Lower carbon levels in the feed at that stage led to the abandonment of flotation and the introduction of continuous RIL, which has been adopted as the major chemical process at the Penjom gold mine since September, 1999. Given the proven performance of the circuit to date, this process may be considered as a low cost option for the treatment of highly carbonaceous ores, particularly those which are not refractory and contain a reasonable percentage of free gold.

Jan 1, 2000