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By J. J. Antony

The Cactus Gold Mine is a joint venture comprised of Middle Buttes Partners Ltd. (CoCa Mines, Inc.--operator, T. Congdon and W. Carey) and Compass Mining, Inc. The project includes 2.4 sq. miles of contiguous mining claims and leases in the Mojave Mining District, Kern County, California, approximately B5 miles northeast of Los Angeles. The property is readily accessible year round by all-weather roads and is within 6 miles of the main line of the Southern Pacific Railway.

Jan 1, 1988

Potassic alteration domains of greenstone belt lode gold deposits are characterized by systematic partitioning between different groups of incompatible elements, such that Al, Ga, Th, U, Ti and V are decoupled from K, Rb, Ba, Cs and Tl. The former group of elements have concentrations and interelement ratios in alteration domains which reflect host rock control, implying approximately isochemical behaviour. In contrast, K, Rb, and Ba are strongly coenriched, and linearly correlated over th4ee orders of magnitude in abundance, where K/Rb = 260, and K/Ba = 40: K/Cs (-10 ) and K/T1 (-2x10 ) are also correlated, though more weakly. Lithium abundances, and Rb/Sr ratios are erratic in altered rocks. These interelement trends, collectively, are present in deposits variously hosted by ultramafic, mafic, or felsic volcanic rocks, and sediments or granitoids.

Jan 1, 1988

By Kenneth J. Miller

Froth flotation is one of the most actively pursued research and development areas in the coal preparation industry today. Many new types of flotation machines and processes are being developed and compared in an effort to handle the increased quantity of coal fines produced by finer grinding for greater liberation of ash- forming and sulfur-bearing mineral matter. Of the many new machines and processes under development for deep cleaning ultrafine coals, it is quite likely that many will not reach industrial use in the near future; in fact, it is quite likely that some never will. Therefore, it is the objective of this paper to select and describe a few of the new flotation machines and processes that appear to have reached a level of development that would suggest their eventual use on an industrial scale. It is probable, and doubtless will be argued, that some of the selections given in this paper should not have been included, while others should have, but the reader must understand that the author is restricted by the information available. And because most of the information available comes from those who are developing the equipment and/ or processes, it is often confusing and conflicting. Thus with a somewhat moderated plan, the author proposes to point out some in- congruities in the literature in the hope that such information might promote more independent study and perhaps explain the abundant promise versus the scant use of the new equipment and processes described.

Jan 1, 1988

By Gene E. McClelland

4.1 INTRODUCTION Metallurgical testing is required on any ore, waste or tailing material before amenability to heap leaching treatment can be accurately determined. The amount of testing necessary to determine and optimize heap leach amenability and conditions for any feed material is determined by the ore type, grade, size of deposit, and the overall financial commitment a particular company is willing to make. It is very easy to either "under-test" or "over-test" a particular deposit or feed material. A good heap leach testing program will provide the necessary design information without "bogging" down in too much detail. The three basic stages of ore testing include: • Preliminary--bottle roll tests and small column percolation leach tests; • Detailed--larger column tests, different feed sizes, and feed size optimization; and • Pilot-Scale--Column or field heap. The following subchapters describe the stages of heap leach testing necessary to put a viable property into production. 4.2 PRELIMINARY METALLURGICAL TESTING The two types of preliminary tests that can be undertaken include bottle roll or cyanide agitation tests and small column leach tests. Each of these is described below, along with information about what the test results provide in terms of furthering knowledge of ore qualities. 4.2.1 Bottle Roll Tests The first step in a heap leach testing program is preliminary bottle roll tests at a relatively coarse feed size to determine the ore's leachability. Bottle roll tests are usually conducted on reverse circulation drill cuttings samples (= 1/4 inch (6 mm) in size). Bottle roll tests provide initial information about precious metal recovery, recovery rate, and reagent requirements. The recovery results are to be considered maximums because attrition grinding creates fines and liberates recoverable values that would not be liberated from the material during a static leach. Bottle roll tests can be conducted on up to 25 lb (11 kg) ore charges of up to two inches (50 mm) in size. However, the coarser the feed the more attrition grinding occurs during rolling.

Jan 1, 1988

By M. L. Clark

Advances in the recovery of gold from heap leaching are being made daily, but of all the systems vital to the maximum recovery of gold from a leach pile, none is more important than the methods used to construct the pile in preparation for the leaching operation. The technology described in this paper illustrates the latest systems developed to minimize compaction in the pile during its construction and reduce the cost of placement of ore on the pile. The Florida Canyon Mine of Pegasus is evaluated in detail to show reasons for its high degree of success to date.

Jan 1, 1988

By Jr. Cook

Panned stream-sediment,geochemistry-based gold exploration in those parts of the southeastern Piedmont proximal to the Fall Line must take into account potential contamination from basal fluvial gravels of the Coastal Plain. Anomalies attributable to the incorporation of placer gold of Coastal Plain origin into modern Piedmont drainages have been identified in portions of Lee, Macon, and Tallapoosa counties, Alabama, and Baldwin and Hancock counties, Georgia. Identification of such multicyclic anomalies must be based on knowledge of the local maximum Cretaceous transgression, paleotopography, modern and paleofluvial system dynamics, and fineness trends and Au-Ag zoning in gold grains.

Jan 1, 1988

By Sii Smith-Gruner

Blasthole drilling by todays standards is not a mature operation. In most mining appli¬cations, the blasthole drill rig is the least understood piece of machinery. Draglines, mining shovels, and haulage trucks may have more charisma, but the entire mining process starts with the drilling of blastholes to facilitate removal of the overburden and/or the primary material being mined. There are two (2) principal drilling methods them being rotary and percussion. In certain situations, percussion drilling is the most practical method, but for most applications, rotary drilling using the rotary tricone bit is the common and accepted drilling technique. While the drilling rig is on the surface and quite visible to everyone, it is really the object at the end of the drill pipe, the tricone bit, that is doing the work and drilling the hole. The rig supplies power to the bit and air to clean the hole. In addition, it must be capable of providing certain other functions and should be properly outfitted to adequately support the rotary tricone bit.

Jan 1, 1988

By S. K. Kawatra

It has been observed in some mineral processing plants that grinding circuit efficiency varies seasonally, such as in some plants which are located in the northern U. S. and Canada and undergo large seasonal temperature changes, with the grinding circuit efficiency different between summer and winter. This indicates that the temperature of grinding circuit slurry has a noticeable effect on grinding performance. The effect has rarely been studied. To this end, an investigation to examine the effects of changing temperature on efficiency and determination of the mechanism responsible has been carried out. Plant investigations and laboratory experiments have been conducted in order to study hydrocyclones. It was demonstrated that under otherwise constant operating conditions, the d50(c), size decreased linearly with increasing temperature, while the shape of the reduced efficiency curve remained constant. This effect was determined to be due to changes in slurry viscosity with temperature.

Jan 1, 1988

By S. Budirsky

J.B. Gwiazda's article deals with an interesting problem that has not been studied thoroughly up to now. Gwiazda has proposed a technical solution that eliminates horizontal load imposed by the supports on the roof. That load is due to a discrepancy between the trajectories of the canopy and the overlying strata. It is true that the improved lemniscate guidance system proposed by Gwiazda could eliminate the horizontal load but, on the other hand, it would represent a higher cost of the supports, and it would complicate the already complicated mechanism of powered supports. That is why we must be convinced that the proposed improvement is actually needed. From that point of view, the following questions should be elucidated. As shown in Fig. 1, the point O travels along the curve a, which produces horizontal load on the roof in the direction of the coal face. As stated by Gwiazda, "such a high load is capable of destroying the roof above the support, causing rock debris to be scattered around the face." The results of our measurements carried out in coal mines of the Czechoslovak part of the Upper Silesian Coal Basin show that the convergence in the modern type of powered supports does not exceed several millimeters (not more than 10) per hour. Similar conclusions were drawn from field measurements performed in the Polish part of the Upper Silesian Coal Basin (see S. Romanowicz and H. Szopka in Proceedings, Scientific and Technical Symposium Simmex '85, Katowice, Poland, pp. 73 -83). The small vertical closure of the supports also induces a small horizontal displacement of the canopy. In addition to this, the transmission of forces between the roof and the canopy is influenced by the layer of debris on it, i.e., the canopy slides without imposing a greater horizontal load on the roof. This was deduced from field measurements of Voest-Alpine F 4/4600 powered supports equipped with rams instead of the common front lemniscate links (denoted as 1 in Fig. 5). In these supports, the pressurizing of the space of piston rod (la in Fig. 5) causes the rams to close, which induces horizontal load on the roof in a direction toward the coal face. After the setting of a support unit, the pressure in the piston rod space was found to drop, frequently to zero, because the small horizontal sliding between the canopy and the debris or inside the debris caused the horizontal reaction from the roof to fall to zero, although the debris were pressurized by vertical setting load. As a consequence, there was no horizontal load imposed by the canopy on the roof. A rise of the horizontal load was recorded only after the passage of the shearer and during lowering of the adjacent units. Thorough information on the results of the afore- mentioned field measurement is given in the paper, "Analysis of the performance of shield powered supports installed in a thick seam," published in Mechanizacja i automatyzacja gornictwa, 1982, No. 12, pp. 38-46. An English translation of the paper is available from the author. We have deduced from our observations that horizontal load imposed by the canopy on the roof in the direction toward the coal face is useful for roof control because it limits the displacement of the immediate roof toward the gob particularly during the rise working. We came to the conclusion that horizontal load on the roof toward the coal face should be induced on purpose. Could Mr. Gwiazda prove with the results of field measurements his contrary opinion? Has the small horizontal displacement of the canopy toward the face actually had an adverse effect on the roof? As shown in Fig. 2, during the setting of a support unit, the canopy imposes a horizontal load on the roof in the direction of the gob. In this case, I share Gwiazda's opinion that the horizontal load could have an adverse effect on the roof. Nevertheless, two important circumstances were neglected - the horizontal compliance of the supports and the interaction of adjacent units. The question of the compliance was analyzed precisely by I. Krumnacker in Gluckauf -Forschungshefle, 1984, NO. 5, pp. 219-223. He found that due to the clearance between the hinge pins and the eyes of the sheild and due to the elasticity of the steel structure,

Jan 1, 1988

By M. Girardeau, J. Blondin, M. Nomine

It is well known that surface moisture and fine content have a strong influence on coal handle- ability. It is known as well that these two criteria are not sufficient to classify coals. It seems that certain types of coals are intrinsically difficult to handle, the reason being still not well understood. For these coals, moisture and fine content are aggravating factors and have to be strictly controlled in order to avoid handling problems (sticking, arching in hoppers.. .). CERCHAR has undertaken research aimed at identifying the role of intrinsic characteristics of coal with regard to handling properties. Two of them have been identified as particularly relevant : the clay content and the "colloidal particle" content. Two simple tests commonly used for soils characterisation, but never used so far for coal, have been applied to characterise a wide range of coals. The derived classification has been compared with an empirical classification based on dry screening tests. DRY SCREENING EXPERIMENTS Dry screening at a relatively low screen aperture (e.g. 6 mm) may be considered as a good tool for assessing the handleability of wet fine coals. Difficult to handle coals always lead to rapid plugging of the screen whilst easy to handle coals can be screened without difficulties. A wide range of coals has been selected with various ash, moisture and fine content. Their characteristics are given in table 1. The experimental set-up consists of a 2 t.p.h vibrating screen equipped with two automatic re- cording balances collecting respectively oversize and undersize material. Provided that the feeding rate is accurately controlled, good reproducibility in the percentage passing as a function of time is obtained. Figure 1 gives examples of different types of relations that were obtained. - LMC coal exhibits a behaviour that is characteristic of easy to handle coals : % passing remains constant in the course of the screening operation. - B coal behaves slightly differently. One observe first a rapid decrease in the flow passing through the screen and then a stabilization. Hand- ling properties can be considered as intermediately - The curve relative to LHB coal is characteristic of a very difficult to handle coal that blinds the screen almost immediately. It is necessary to point out the fact that the classification derived from screening experiments is a global one, including not only intrinsic factors but also external factors such as fines and moisture content. The role of surface moisture is in particular very important and variations in this parameter may upset the empirical classification

Jan 1, 1988

By E. Forssberg, T. Nordquist

Introduction In this technical note, pilot-scale tests with two types of gravity concentrators, the Knelson separator (Anon., 1983; Forssberg and Johansson, 1984) and the Mark VIIA Reichert spiral concentrator (Balderson, 1982; Forssberg and Johansson, 1984), are described. The experimental work was concentrated on the relatively untried Knelson separator. The materials tested have different concentration characteristics: one was an artificial ore with excellent liberation characteristics and with a wide difference in density between valuable and gangue minerals; the others include a spiral concentrate containing gold from the gravity circuit of Boliden, Sweden, an old scheelite tailing from Yxsjöberg, Sweden, and an auriferous ore, containing gold, that had not been crushed to full liberation. The latter three materials contained other heavy minerals, e.g. pyrite, that can interfere with concentration. Knelson separator The Knelson separator is a compact centrifugal separator with an active fluidized bed to capture heavy minerals. A centrifugal force equal to or exceeding 50 times the force of gravity acts on the particles. The strong centrifugal force traps the heavier particles in a series of rings located in the concentrator while gangue particles are flushed out (Fig. 1). The particular separator used in the tests has a 15-cm (6-in.) diam bowl and can process between ~70 and ~250 kg/h.

Jan 1, 1988

By Omar A. Muhtadi

8.1 INTRODUCTION Several methods currently exist by which gold may be recovered from a pregnant leach liquor. Two of these methods are discussed in this chapter, the Merrill-Crowe (zinc cementation) process and the carbon adsorption process. These two methods represent the most frequently used techniques for gold extraction and are, -in fact, used almost exclusively in U.S. heap leaching operations. Because of the efficiency and ease of use of these two methods, it is extremely likely they will continue to be quite prevalent within the gold mining industry in years to come. The remainder of this chapter includes information on the history of the two processes, descriptions of the actual processes, criteria to consider in selecting a recovery process, and commercial design and construction considerations for both of the gold recovery methods. As with other chapters in this book, some fairly technical information is presented for the benefit of those readers needing a greater level of detail. However, the overall intent of the chapter is to provide an overview of the processes likely to be used in gold extraction, thus giving the reader a firm basis for more technical research into the topic, should this be needed. 8.1.1 History of Zinc Cementation During the late 18901s, zinc cementation was introduced for the precipitation of gold and silver from cyanide solutions. This occurred at about the same time as the introduction of the cyanidation process, the history of which is recapped in Chapter 1. The initial cementation process involved introduction of a gold-bearing cyanide solution onto a bed of zinc shavings. It proved to be quite inefficient because the reaction rate was very slow. The zinc quickly became "passive", inhibiting further gold deposition. Shortly after this first introduction, zinc precipitation was improved by adding a lead salt (usually lead nitrate) to the zinc. This allowed a zinc-lead couple to form on the surface of the shavings, eliminating passivation of zinc surfaces and thereby allowing continued deposition of gold. Further improvements were shortly forthcoming. The first of these involved the use of zinc dust rather than zinc shavings. This provided a much

Jan 1, 1988

By V. Roze, M. E. A. Robertson, C. J. Sharland

Current Techniques - Fire Assay Fire assay of gold has been used for several thousand years and is a well known technique to the traditional assayer. Very few assayers wish to use the method but to date there has been no viable alternative. Fire assay is expensive in labour, time, capital and running costs. Workers can be exposed to hazards and uncomfortable working conditions such as lead fumes, heat stress, dust and eye strain. The high capital cost of putting up the building and equipping it, together with running costs which increase annually at a prohibitive rate makes the technique less attractive each year. The main requirement in most assay laboratories is to maximise throughput economically. This is difficult with fire assay as it is impossible to automate. Each sample for analysis is handled by at least 12 people and each person represents a potential source of error. Record keeping and report generation has to be done manually which is both slow and prone to errors. Replacement of staff requires a considerable training period and with a large turnover of personnel this presents yet another problem. The presence of silver and dross in the gold sample affects the accuracy at low gold values. X-ray fluorescent analysis Two methods of XRF instrumentation have been used with limited success. The first type is a laboratory instrument employing L X-rays. Small samples of a few grams, which are not representative,

Jan 1, 1988

By Omar A. Muhtadi, David A. Milligan

7.1 INTRODUCTION The circulating fluid (generally an aqueous cyanide solution) is the major active component of heap leaching. This solution extracts precious metal from the heap and is then processed to recover the precious metal. The solution continuously recycles through the heap to recover more precious metal. With each cycle through the heap, water and chemicals are lost. Make-up water and chemicals must be added to balance losses from evaporation, seepage, entrainment, and chemical reaction in the heap, as well as any other processing losses. Adding more water than needed can result in a build-up of water as inventory in the various ponds and can eventually require that water be discharged from the operation. This is an extremely undesirable condition, and can often be very expensive in both investment in water treating facilities and operating costs. Most heap leach facilities operate under a zero discharge permit; thus, a situation requiring water discharge can result in permit violation. Chemical solution control must be managed to maintain the optimum pH, dissolved oxygen content, and cyanide content, while preventing "scaling". Calcium-based precipitation is a common scaling problem in mill reclaim waters. A buildup of these deposits can result in severe reduction of water flow, loss of pump efficiency and eventual interruption in metal production. In addition, problems of plugged sprinkler heads, blinded leach pads and fouled carbon (in carbon recovery systems) can be and often are experienced when scale control is not maintained. The remainder of this chapter discusses chemical solution control and scaling prediction/prevention in the context of a "closed" system. Sizing of ponds to accommodate precipitation and runoff, collection systems, and other similar design considerations are not discussed here. These topics are deferred to later chapters, e.g. Chapter 10 considers design of collection systems while Chapter 12 discusses pond sizing. 7.2 CHEMICAL CONTROL Chemical composition of the circulating solution must be controlled by the operator if the heap leaching process is to be successful. The primary or essential chemical control parameters in any heap leaching operation are:

Jan 1, 1988

By K. Hajmrle

The production of nickel coated mica composite powder by hydrogen reduction of a nickel ammine sulphate solution, followed by the production of molded plastic samples containing Ni/Mica is described. Sample preparation by injection or compression molding is outlined and the better results in compression molding are explained by the combination of better particle-to-particle contact, less particle breakage during processing, and more random particle distribution in the plastic. Three volume resistivity measurement techniques are described and compared. Two of them (conductive paint and silver-rubber electrodes) are found reliable and are used throughout the work. The influence of nickel content and particle size of Ni/Mica on volume resistivity is evaluated and the optimum product defined. One of the most important assets of Ni/Mica, its ease of injection molding, is demonstrated by the good electrical properties obtained with little optimization of the injection molding process. Surface roughness of molded plastics with and without Ni/Mica is briefly discussed. Shielding effectiveness of Ni/Mica in four plastics (PP, ABS, PBT and PC) is presented and correlated to volume resistivity data for the same materials. The addition of 15 to 50 weight % Ni/Mica (3 to 16 volume %) to plastics and subsequent injection or compression molding produces composite materials having low volume resistivities (0.03 to 1 ohm.cm) and high shielding effectiveness (40 to 70 dB).

Jan 1, 1988

By S. C. Sethi

The paper presents an analysis and discussion of the underground ventilation system at the waste Isolation Pilot Plant (WIPP), with particular emphasis on specific repository-related requirements and the gradual evolution of engineering designs relative to the WIPP Project scope. The underground facility has been constructed with three shafts. Additional studies, coupled with actual site-specific experience, have established? the need for construction of a fourth ventilation shaft to double the under-ground airflow. As a research pilot project, and the first of its type in combining mining and nuclear technologies, the WIPP Project is accumulating data and experience that may be fruitfully applied in the future designs of ventilation systems for planned commercial nuclear waste repositories.

Jan 1, 1988

By M. J. DeMarco

Beginning in late 1985 and continuing through 1987, Bureau of Mines personnel investigated longwall chain pillar and entry design in two-and three-entry gate-road systems at a deep underground coal mine located in central Utah. To evaluate their respective stability characteristics, four chain pillars and two longwall panels within the two separate entry systems were instrumented with Bureau of Mines hydraulic borehole pressure cells to continuously monitor vertical and horizontal pillar and panel stresses through adjacent panel retreat. In addition, supplemental entry closure information was obtained from sites located in the vicinity of the instrumented pillars. The findings presented in this report demonstrate the practicality of evaluating mine pillar stability using in situ methods and support three significant conclusions regarding ground control aspects of the investigated two-entry system: (1) Total areal entry loading was considerably less for the two-entry system, as opposed to the three-entry system, (2) a smaller percentage of opened ground in the two-entry system contributed to a marked reduction in roof falls, and (3) lower areal loading in the two-entry system suggests improved ground conditions when mining the underlying seam.

Jan 1, 1988

By Michael E. Kelahan, Glenn A. Gruber

A review of recent phosphate beneficiation developments shows that Flotaire cells, ranging from 0.20 m to 2.44 m in diameter, have been examined in pilot scale and commercial plants. Applications of the column cells have included sized feed fractions using anionic and cationic reagent systems. In plants where the Flotaire was installed as a test unit or as an optional circuit, its use has been largely discontinued. On the other hand, when management committed to installing the Flotaire as an integral part of the flowsheet, the performance expectations were met or exceeded.

Jan 1, 1988

By Wayne F. Crockett, Martin H. Col

Gold, as a precious metal, has been sought for several thousand years. During this time economics have generally determined whether or not a deposit is minable. Today, few would spend $500.00 or $1,000.00 to produce one ounce of gold, yet most gold deposits currently being mined would have such costs if they were mined using the methods of the 18th century. Innovation has been the key to success in the world of mining. We are constantly having to look for new ways to mine deposits of lower grade, at greater depths, or with higher stripping ratios. The mining of placer gold deposits has always been subject to the volatile swings of the world price and the constant rise in production costs. The rise in costs is compounded by the drop in overall ore grades. Occasionally, a major technological innovation will dramatically reduce the costs of placer mining to allow previously marginal or unminable deposits to be mined at a profit. The continuous bucketline dredge was the last such major innovation in the gold placer mining. The continuous bucketline dredge has allowed large volumes of placer deposits to be picked up and processed on a continuous basis. Unfortunately, as the overall grade of the deposit declines, it becomes impossible to process enough ore to pay for the operating costs. There are many gold deposits around the world waiting for the next technological innovation that will allow them to be mined. One such deposit has been the Grey River deposit near Greymouth in New Zealand. The deposit contains gold reserves of 8992 kg, yet the deposit has been sitting idle for many years because the average value

Jan 1, 1988

By Scott E. Broughton, Robert T. Tape

Heap leaching requires containment and storage of cyanide solutions, the volume of which may increase dramatically following an extreme storm event or extended wet periods. This paper describes a computer operated solution storage model developed to assist in the management of these requirements. It results from the accumulative efforts of various Klohn Leonoff engineers working on a number of heap leach projects throughout the western United States for the past several years.

Jan 1, 1988