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By A. B. Phillips

The Randfontein Estates Gold Mining Company (Witwatersrand) Limited (REGM) operates three metallurgical complexes for the recovery of gold from the Witwatersrand Gold Reefs at the town of Randfontein, 40 kilometers west of Johannesburg. Mining operations in the. area commenced in March 1889 and ceased temporarily in 1965 when the viable ore reserves had been depleted. Exploratory drilling in the 1960's indicated viable deposits of gold in the Elsburg reefs, south of the Witpoortjie Horst Block, _which formed the Southern limit of the previously exploited areas. Three shaft complexes have been established to exploit this area, known as the Cooke secti'on. In 1983 the Doornkop shaft was sunk to the north of the Cooke section to mine Kimberley reef and the South reef.

Jan 1, 1992

By E. Ghali, L. Tremblay, M. Lanouette, J. McMullen, G. Deschenes

Since the start of this decade, our society has attached great importance to matters concerning environmental protection. Currently, most mining operations use the cyanidation process in working gold deposits. While this process is efficient, the dangerous aspects of cyanide are delaying the development and marketing of cyanidation in underground sites. There is a growing need to consider installing an underground leaching system that will make the processing of low-grade gold ore profitable by reducing certain major operating costs (transportation, crushing and grinding). Underground leaching is performed in two ways. The first way is in-site or underground and the second way is in-situ. CANMET (Harrison et al.), in collaboration with Dennison Mines, developed the underground leaching of uranium. This process is used commercially. Copper, salt and sulphur are recovered by in-situ leaching (Jacobson and Murphy). The recovery of gold and silver is under development (Van Staden and Laxen).

Jan 1, 1992

By Roger Nendick

The recent developments in refractory precious metal ore processing (Bio-oxidation, Autoclaving), and the revitalization of the more traditional roasting processes have attracted great attention in recent years and are indeed the focus of todays symposium. It must always be remembered, however, that the term refractory ore by definition means that the material 'must be capable of being treated at a profit". Given the high cost of the refractory processes, the requirement to be treated at a profit requires very close scrutiny during the evaluation phase of the property development. The M.G.M. film company has the latin motto Ars Gratia Artis meaning Art for Arts Sake. Ingeniatore Gratia Ingeniatoris (a very crude attempt at saying Engineering for Engineerings Sake) should not be the motto for mining companies intent on exploiting refractory gold deposits, but rather the wittily tilted heading for this paper "Take the money and run like a thief". The following hypothetical case studies show that the high technology solution is not always the best financial solution.

Jan 1, 1990

By Dale C. Matthews

The Getchell Gold Hine is located about 40 miles northeast of Winnemucca, Nevada. Gold was discovered at the mine in 1934 and production was started in 1938 and ended in 1967 for its first phase of operation. Gold production during this period was about 800,000 ounces. In 1983, FirstHiss Gold Inc. purchased the property and initiated an exploration program that proved minable reserves of about 1,300,000 ounces of gold remained in the mine. During the exploration period, metallurgical testing was conducted to determine the most economical process that could be utilized for recovery of gold from the very refractory ore. After extensive investigation, pressure oxidation of the ore was selected, Engineering for the new plant commenced in 1987 and construction was completed in 1989 at a cost of about $87,400,000.00, not including financing cost.

Jan 1, 1990

By Alan G. Fricker

Cyprus Gold NZ Ltd will be recovering residual free cyanide in barren gold pulp by air stripping. Laboratory investigations by DSIR have indicated additional advantages by recovering the cyanide from pregnant pulp. These are a lower leach pH, a greater cyanide recovery and less carbon consumption. They have a net economic advantage of $1.20/tonne over recovery from barren pulp. The realisation of these advantages is dependent on three crucial technical aspects -optimum pH for dissolution, the absolute loss of cyanide and the stability of the aurocyanide ion. The laboratory investigations described herein address these aspects. Earlier work had indicated that the rate of dissolution of freely revolving gold discs at constant cyanide ion concentration increased with decreasing pH from 11 to 8. Attempts to repeat the work in a more controlled manner by measuring the corrosion potential and current density have, to date, not been reproducible, but do not contradict the earlier observations. Cyanide recoveries and balances were obtained on leaches at pH 10.5 and 9 at the same cyanide ion concentration -the lower pH requiring three times as much total cyanide. Unaccounted-for losses, unfortunately, exceed the accounted-for losses, making interpretation of the balances difficult. Nevertheless, it appears that the additional amount of cyanide at the lower pH of 9 may not be fully recoverable. It may not, however, prove necessary in practice to use more cyanide at a lower pH. Both the gold and silver cyanide complexes remain available for carbon adsorption, as do mercury, copper and iron. Zinc, and probably cadmium, nickel and lead, may precipitate during stripping, which is an environmental advantage.

Jan 1, 1991

By H. N. McLeod, M. J. Thom

The use of cyanide in gold mining requires the careful handling and storage of cyanide rich tailings. Cyanide in groundwater can frequently be both persistent and mobile, so that tailings basins need to be designed to limit and collect seepage. Assessment of the potential environmental impact requires an understanding of the hydrogeologic regime, both before, during and after mining. Groundwater monitoring wells provide a basis for monitoring tailings pond behaviour and for assessing the impact of mitigative measures to reduce or control seepage. A case example of Cheni Gold Mines Lawyers Project in Canada is presented to illustrate the use of groundwater monitoring to determine the amount of cyanide degradation and attenuation between the tailings pond and the receiving environment.

Jan 1, 1991

By T. W. Mattioli

Restrictions on fugitive emissions and crushing operations continue to get tighter. Although fugitive dust control in the gold mining industry has historically been difficult, there are now several options that can make dust control both effective and efficient. Using new technology, mine operators can now design and maintain a dust control program that can reduce product losses, decrease equipment failure, cut cleaning costs, and meet air quality compliance standards as well as provide a better working environment. This paper discusses the sources of fugitive emissions related to the gold mining and crushing operations and describes effective new control methods.

Jan 1, 1998

By George Hope, Edward H. Smith

In late 1989, LAC Minerals purchased 65% of Bond International Gold and as a result became controlling shareholder of the El Indio Mine through Bond and San Jose. El Indio is a world class, complex sulphide gold deposit located in the hydrothermal alteration belt of the Andes mountains in the 4th Region of Chile. The mine is located in the high Andes about 185 km east of La Serena at an elevation of 4000 meters. The 1450 workers at El Indio live in the mine camp at 3200 m and on days off are bussed to La Serena. The El Indio mine was started in 1979 by St. Joe Minerals Corp., bought by Bond in 1987 and subsequently by LAC in 1989. The mine has produced 2.7 million oz. of gold, 9. 5 million oz. of silver and 170,000 t of copper since start of operation. The mill is currently operating at a rate of 2850 t/d and producing a copper/gold concentrate which is roasted to produce a copper/gold calcine and high quality, saleable crude As203• A small proportion of the precious metals are also produced as bullion from the leach circuit. Total production during 1989 was 224,197 ounces of gold, 1,309,342 ounces of silver and 26,968 tonnes of copper. The average cash cost of production for the period was U.S. $96 per ounce of gold, net of by-product credits. The average realized price was $5.30 per ounce of silver and $1.14 per pound of copper.

Jan 1, 1990

By Des B. Bolton, Neil P. Boland

Typically, environmental work on mine sites in Northern Australia involves addressing an individual problem as it arises. However, individual mining companies are moving toward a more holistic approach to managing the interactions between the environment and the mining process and are thus pre-empting environmental problems. This paper presents a broad overview of this holistic approach and provides a few examples, drawn from our own experience, which illustrate some of the tangible benefits to be gained from Environmental Planning.

Jan 1, 1991

By Jacob D. Baker

Sulphur dioxide is a versatile gas which has many uses throughout Pulp & Paper, Chemical, specialty Chemical, Mining and other industries. During recent years, S0 2 consumption and distribution patterns have resulted in renewed interests for liquid S0 2 and on site gaseous S02 manufacturing facilities. one relatively new use for S0 2 in the Mining Industry is its use for cyanide detoxification. Our purpose in this paper is to describe the process steps, economics and general technical features of so 2 gas generation using a Jet Type sulphur Burning System.

Jan 1, 1991

By Bryan A. Bartley

High intensity, autogenous grinding has been developed in the hard rock, quarry industry and is finding wide application in mineral processing. The autogenous vertical shaft impactor is described and action within the machine is illustrated. This machine is compared with the cascade mill, in the three characteristics of impact, inter-particle rubbing and nipping, of which impact is the most important. There is a seven fold increase in impact level over that of the cascade mill. The autogenous impactor has characteristics of crushing and grinding, preferential crushing, abrasion resistance and drying. These are illustrated by examples of industrial applications, where the machine is now used and range from abrasives, such as Carborundum to phosphate rock.

Jan 1, 1998

By E. A. Devuyst, G. Robbins

A unique process for removing cyanide and base metal complexes from industrial waste streams was patented by G.J. Borberly et al. (1984). The process uses SO2 (liquid or gas, or solutions of sulfite salts, or from burning elemental sulfur), plus air that is dispersed in the effluent using a well agitated vessel. Acid produced in the oxidation reactions is neutralized with lime at a controlled pH generally in the range 7 to 10. The reaction requires the presence of soluble copper as a catalyst which can be supplemented by copper sulfate if necessary. The process can be applied to the detoxification of gold and silver mining waste streams, such as carbon-in-pulp (CIP) tailing pulps, barren solution bleeds, pond waters and heap leach rinse solutions and also to plating shops wastewaters. The SO.jAir process has substantial advantages over two of the main alternative methods of cyanide destruction, namely alkaline chlorination and hydrogen peroxide. Alkaline chlorination is highly penalized in terms of reagent consumption. Chlorine is a strong oxidant reacting with species other than cyanide present in the effluent such as thiocyanate and sulfides. Furthermore alkaline chlorination is an incomplete detoxification process. Iron cyanide is not removed and the potential for harmful by-products species exist. Consequently final effluents may be subject to additional treatment in order to comply with regulatory demands.

Jan 1, 1991

By Ivan C. Machado

In full autogenous grinding (FAG Mills) the ore itself determines almost exclusively the product size that will be produced, as opposed to conventional steel-media grinding where the product size can be "engineered" by changing media size, feed size, feed rate, classifier cutpoint size, etc. SAG Mills are in the middle of the way, since they offer some room to engineer their product size by properly defining some critical process variables, such as feed size, ball charge and size, mill charge and speed. SAG Mill product P80 values are typically in the range of 500 µm (35 US mesh) to 2000 µm (10 US mesh.) Whenever it is possible to determine an optimum value for the SAG Mill product P80 value (which will be the Ball Mill fresh feed F80 value), the Engineer should define the process variables that will yield a SAG product size as close as possible to the optimum calculated P80 value. In general, a coarser SAG product will draw less power from the SAG Mill and more power from the Ball Mill, and conversely, a finer SAG product will draw more power from the SAG Mill and less power from the Ball Mill. Metal consumption analyses also have to be taken into consideration, for they typically account for 30% to 45% of the total grinding cost. This presentation addresses the issue of defining an optimum SAG Mill product size (X=P80), during the design phase of the SAG and Ball milling circuits, from a general perspective, i.e., the SAG product size that will lead to an overall SAG Mill - Ball Mill optimum performance. Bond's Third Law approach is used, as well as the SPI (SAG Power Index), and also the generally accepted equations and Engineering Practice currently utilized to design SAG Mill

Jan 1, 1999

By Stuart K. Nicol, Malcolm D. Engel, Neville T. Moxon

Ion flotation of gold is a process continuing to be developed to selectively beneficiate dilute aurocyanide liquors using a novel surface­active complexing agent. Aeration of these liquors causes accumulation of the precious metal species in the froth concentrate produced in a flotation column. Successful development of ion flotation for concentrating solids-free liquors would offer a low--cost method for recovering specific metals from heap leach runoff or waste tailings solutions. The cost of constructing and operating a 100 tph gold ion flotation facility has been compared with the relevant carbon adsorption plant costs. Reductions in operating costs of 25% and installed capital of 40% are possible in relevant expenditure areas. For an 'average' processing plant, this equates to annual operating savings of A$ 170 000 and a capital saving of A$ 515 000, with a three-point increase in total (mine and plant) site DCF ROI. High gold inventories are eliminated and the number of processing steps is reduced. The application of gold ion flotation will initially be confined to heap leach operations in the western U.S.A., although use of the process in mine abandonment programmes elsewhere is also an area of future development.

Jan 1, 1992

By John C. Gathje, Gary L. Simmons

Power Point slides

Jan 1, 2000

By Byron K. nelson, David Mathieson

Until quite recently concentration of free gold in gravity circuits ahead of froth flotation and/or chemical treatment was considered an uneconomical pursuit in many gold pi.ants in Australia. Over the past 10 yenrs since initial introduction of the Knelson Gold Concentrator, over 600 hnvc been surpl led world wide and they have been developed to the stage that Lhey can now be utilised in almost all instances where free gold appears in significant quantltles ln grinding circuits. They out perform and displace more conventional gravity sepnration equipment such as spirals, tables, sluices, jigs, drum separators etc.

Jan 1, 1991

By A. Bruynesteyn

Most ores and coals contain sulphide minerals such as pyrite, FeS2, the sulphur portion of which is a ready substrate for a variety of sulphur oxidizing bacteria. Although there are several bacteria capable of oxidizing sulphide minerals, the most often discussed culprit is Thiobacillus ferrooxidans.. Oxygen from the air slowly oxidizes pyrite into sulphuric acid, but T- ferrooxidans can increase this reaction rate several 100,000 times.

Jan 1, 1991

By F. Lincoln & B. Rodier, G. Poniatowski, N. Kawashima, T. J. White, J. H. Kyle, G. F. Eaton

The history of Australia is a narrative of the discovery and development of its mineral wealth. The gold strike at Ballarat, Victoria, in 1851 transformed the colony by triggering the first great influx of migrants to Australia, and the development of subsequent mineral discoveries lead to a vast resource industry. However, beneficiation of base and precious metal ores carried with it an environmental penalty, not addressed until the last quarter of this century. In particular, the extensive deposits of gold, silver, lead, copper and zinc reside in sulphurous ores which often contain arsenic, antimony and mercury as significant contaminants that are released as unwanted by-products during smelting and refining. Until recently, these toxic concentrates were discharged to the atmosphere or receiving waters, collected in tailings ponds close to the smelters, or dumped at sea. Although such procedures . were acceptable in the past, more stringent environmental controls have required a re-examination of these practices and encouraged intensive efforts to develop enduring solutions to the disposal of these wastes. From this research has emerged a promising new generic technology called Xtaltite (pronounced crystal-tight). In this approach, geochemical principles are employed, first, to reduce the toxicity of heavy metals to low levels, and second, to identify and engineer suitable repositories for the permanent disposal of the consolidated waste form. In this paper, we emphasise the application of Xtaltite to the disposal of arsenious smelter fumes derived from gold winning. The principles ofXtaltite will be described and its technical and economic performance compared with conventional technolo­gies.

Jan 1, 1995

By Peter Krag, Rob Henson

It is well known that titanium and zirconium alloys offer superior corrosion resistance in the oxidizing sulfuric acid environments present in sulfide pressure leaching operations. The use of these materials is limited, however, due to their pyrophoricity; several accidents attributed to titanium equipment have been described in technical literature, and other, minor incidents·occur regularly1 • We describe an application of a commercial titanium alloy, Nb-55 Ti, with suitable mechanical properties, corrosion resistance similar to Grade 2 Ti, and featuring a significantly reduced field of ignition conditions

Jan 1, 1992

By Robert M. St. Louis, Frank D. Wicks, John E. Huffman, Edward E. Maurer

The treatment of Mercur's refractory ores has been well published; however, the processing of the remaining semi-refractory or oxide ores has not been discussed. Although ore control at Mercur is efficient, refractory vestiges are left with the mill-feed, oxide ores. Also, these ores as mined are not necessarily completely oxidized at Mercur and should be termed semi-refractory ores. This paper will discuss those steps taken at Mercur to enhance the recovery of gold from partially oxidized ores at Mercur. The Mercur mill is a conventional SAG/ball mill grinding circuit feeding a GIL plant. The circuit has been well published and will not be further reviewed.

Jan 1, 1990