Search Documents

By William J. McDonough

Advanced materials are polymers, metals, and ceramics fabricated as intermaterial compounds, alloys, or composites. The resultant components have higher strength-to-density ratios, greater hardness and wear resistance, and one or more superior thermal, electrical, or optical properties when compared with traditional materials. Advanced materials, the basis for many of today's emerging technologies, offer savings in total energy consumption, improved performance at reasonable cost, and less dependence on imports of strategic and critical mineral resources.

Jan 1, 1992

By Medhurst TP, Trueman R, Hutchinson IN

A breaker line support (BLS) monitoring system, BLSmon, has been designed and constructed by the CSIRO and installed and commissioned at Laleham No.] Colliery, Queensland. This system was designed to record hydraulic leg pressure and canopy position measurements and relay these, in real time, to the surface. The system has shown itself to be capable of operating on the BLSs without any adverse affect on production. Analysis of the results of the monitoring exercise has shown that rate of change of leg pressures on the BLSs could be used as an aid in the prediction of adverse mining conditions. Under favourable mining conditions the supports were observed to initially unload from the set pressure, this unloading reduced with time and by the end of a typical lift cycle had either ceased or reversed slightly. This behaviour was considered to be due to one of four possible causes, these being; the compaction of floor debris, and/or compaction of the floor, and/or crushing of the roof and /or support creep. The actual cause can only be determined through detailed monitoring of both roof and support convergence. However observational data would suggest that compaction of debris and softened floor material beneath the supports was the most likely cause. The few positive loading rates recorded under these conditions were of short duration and occurred towards the end of individual lifts. Where mining conditions were unfavourable the negative rates of change of pressure, unloading of the support, were reduced throughout a lift, in both duration and magnitude, when compared with favourable mining conditions. Over the same period the positive rates of change were observed to be greater. The rate of change of loading and convergence can be utilised to identify the onset of instability in the lift area. However, before this facility can be utilised by the mine for the reliable prediction of instability more monitored data and sophisticated processing techniques are required.

Jan 1, 1992

By G. Skybey

The Skybolt is a new bolt concept, point anchored with resin in large diameter holes of specific sizes 38 mm and 45 mm. The new design achieves the optimum annular spacing required for mixing the resin anchor components which is essential for optimum resin bonding of the bolt to the surrounding rock. This paper explains the load transfer mechanisms between bolt/resin/rock, unique to this bolt concept. It compares the pull-out test results to those of paddle and expansion shell type bolts, and highlights the versatility of Skybolt over existing, currently used, rock support systems and the benefits mine operators can achieve when using the Skybolt.

Jan 1, 1992

By F. J. Menzer, E. M. Schern

The Morenci/Metcalf porphyry copper mining operation, located in southeastern Arizona, currently processes approximately 91,000 tonnes of ore per day and has copper ore reserves estimated to be in excess of one billion tonnes. Functional groups within the Geology Department (currently staffed with six professional and two support personnel) include mine geology, project geology, and hydrogeology. The primary task of mine geologists is daily preblast bench face mapping with grade and mill amenability estimates. Auxiliary duties include detailed in-pit metal distribution evaluation, mineragraphic work and flux quarry geology. Project geologists conduct exploration and preliminary development projects both within and outside the Morenci district and provide support to ore reserve block modeling and geotechnical work performed by the Morenci mine engineering group. Hydrogeologists handle exploration for and development of groundwater resources and groundwater flow modeling, mine dump leach solution penetration and recovery evaluation, and tailing dam water reclamation.

Jan 1, 1992

By Pat Gochnour, Jim V. Rouse

Advances in the design and construction of heap­leach pads and process plants have greatly reduced. the potential for accidental releases of process olut1on. While workers in the field, and regulatory agencies such as the EPA have long recognized that the potential effects of any spills would be short term in nature due to cyanide attenuation and degradation (Engineering-Science, September, 1986, Pyrih, 1990, Rouse and Pyrih, 198, Rouse and Pyrih, 1991 ), unfortunately the general pubhc has held a perception that such a spill would be an environmental catastrophe. Few factual data on actual accidental releases have been available to dispel such a concept. Such data now exist and shoul? be disseminated to show that prompt response, using a combination of chemical oxidation, natural attenuation, and enhanced biodegradation of cyanide, can limit the effects of such rare releases, in both time and space.

Jan 1, 1992

By Ben Ainsworth

I am going to discuss gold mining in Mexico during the last twenty centuries and try to suggest some of the futures that may develop in this industry in the next decade. Before I start this rapid review of such a long developing mining tradition, T must give credit to my sources. I an, talking here as an associate of Commoditi,c,s Reseflrch Unit Ltd. of London (better known as CRU) and as a principal of Ainsworth-Jenkins Holdings, an international mineral resource consultant group that has been exploring and deveJoping mining properties in Mexico and Central America for the last six years. CRU is the leading consultancy providing industry, governments and financial institu­tions with analysis and advice on the metals and the mining industries. They recently completed a three volume study entitled Gold Mining Opportunities in Mexico. This .<1tudy describes Mexico, the business environment, its geology and details its gold mining potential with property descriptions and maps. I have adopted and adapted the s11mmari.zed Mexican government statistics and rlrawn on some of the historical comments in these volumes. However, I do not have ti me (nor would it be appropriate) to be giving the details of the CRU work. Jorge Ordonez, whose shoes I am trying to fill today, was a major contributor to the study and it was an honour to be asked by Willem Beunderman, the Principal Editor, to step in when Jorge was unfortunately unable to be here. Jorge has been an enormous help to Ainsworth­Jenkins and a consistent friend of foreign investment in Mexico. Our own work in Mexico has allowed us to obtain a few useful in­sights into this most interesting slice 0f Mexican history.

Jan 1, 1992

By Thomas E. Weyand, Wolfgang Baum

PMET is engaged in the development of reuse operations for process wastes from the natural resources industry. Most of the current remediation practices with mining wastes are concentrated on stabilization techniques. Once stabilized, valuable resources are no longer readily available for recovery and reuse. Additionally, stabilized materials, unless protected from weathering influences, pose lingering liability for the generator.

Jan 1, 1992

By Martin F. Grier

The Mt Todd Gold Project is located 300km to the south of Darwin in the Northern Territory of Australia. The identified resource comprises 46 million tonnes at 1. 65g/t using a 1. 0g/t cut-off ( 50 million short tonnes at 0.05oz/st). The resource is open to the north and at depth. Mineralisation comprises easterly dipping sheeted quartz/sulphide veins, typically 10 to 20 millimetres in thickness, hosted by hornsfelled greywackes. The majority of the ore body is primary ore with only 10% classified as oxide ore. Early testwork showed that the ore was not suitable for heap leaching, giving only 50% recovery at a -3mm crush size. Acceptable recoveries were obtained at a P80 of 75 micron. However, the ore is extremely hard.

Jan 1, 1992

By Martin H. Col, Thomas W. Steele

The ability to make a good profit in the mining industry is becoming more and more difficult. Typically, grades are lower, sites are more remote, and environmental restrictions are getting tighter than ever before. While the price of the materials P.roduced, such as gold and silver, have stayed flat or declined, the external costs (goods and services) have increased. Increasingly difficult environmental restrictions have increased the lime and costs of develoJ?in9 new deposits, while often placing restrictions on a mme s production rate. Environmental costs for mine closure and site reclamation also make it very difficult to show a long-term profit while mining. Typically, the answer to this cost/price squeeze has been technological innovation. The whole concept of heap leaching low-grade gold ore is one innovation that provided some very goocf profits to the mining companies; but, today, those profits are being eroded by the continuing cost/ price squeeze. This paper will discuss material handling in a heap leach stacking operation and the alternatives of trucks, grasshopper conveY.or systems and mobile conveyor systems.

Jan 1, 1992

By Peter Maltby

A $20M pressure oxidation facility is under construction at the Nerco Con Mine, Yellowknife. Plant commissioning will start in the third quarter of 1992. Roasting of arsenical auriferous concentrates prior to 1970 left 45,000 tons each of highly toxic gold-bearing arsenic trioxide sludge and roaster calcine at the minesite. Safe disposal of these wastes has been a high priority. In 1983 an arsenic trioxide plant was built by the former owner to re-treat the sludge and to sell the product. Due to a poor market and high operating losses, the plant was closed by Nerco in 1989. Mine production in the future will revert increasingly to refractory ore as a replacement for free-milling ore which has been the mill feed since the roaster was shut down. With this fact in mind, Nerco management saw the potential of a proven process to recover the gold from a combined feedstock of refractory flotation concentrate, sludge, and calcine waste. A further requirement was the stabilization of all the arsenic as an insoluble ferric arsenate. By the end of 1989, after the completion of a literature search and a study of process economics, pressure oxidation was selected. Extensive bench and pilot plant work was completed in 1990 and early 1991 to develop the process parameters and to complete environmental testing of the autoclave products. Management approval for construction of a pressure oxidation facility was made in December 1990. Plant capacity is 96 tpd requiring a 40 tpd VSA oxygen plant on site. Detailed engineering began in March 1991. The pressure oxidation building was completed by the end of 1991. The autoclave arrived on site and was mounted on its foundation in December 1991.

Jan 1, 1992

By Kurt O'Bryan, Gary Beerkircher

WaterFlush Technology offers maximum comminution performance benefits over to­day's more common comminution methods. These benefits will be presented with case studies of existing installations, and the projected performance gains for circuits scheduled to begin operation in 1992.

Jan 1, 1992

By Walter Hoecker

The dissolution of gold in cyanide_ leaching has been we11 published with the genera1 acceptance that gold is oxidised by oxygen and stabilized by complexation with cyanide [1]. The dissolution of gold is essentially an electrochemical process. The rate of the anodic gold dissolution is controlled by the cyanide concentration. - (2) While the cathode reduction of oxygen is controlled by dissolved oxygen concentration - (3) There are a number of factors influencing the concentration of oxygen, and if 1owered substanth.lly will effect the efficiency of the leaching plant. These include: "' salinity "' temperature "'partial pressure "'oxygen consumption rate The use of pure oxygen for· cyanidation is only beneficial if oxygen is rate limiting, Conversely a slurry saturated with air (typically 5 - 8 ppm) may not be enough for maximum leach rate. The diagram below shows the maximum dissolved oxygen levels obtainable with pure oxygen and air. DISSOLVED OXYGEN (MAXIMUM) IN WATER At steady state, the rate of the cathodic reaction must equal the rate of the anodic reaction. Thus the rate of gold dissolution is dependent on both the· cyanide and oxygen concentrations. - (4) Using an average of Do/Den =· 1.5 [2] (where Do and Den are the oxygen and cyanide diffusion coefficients) the table below illustrates the maximum effective oxygen concentrations for given cyanide levels in clean water [3].

Jan 1, 1992

By H. D. R. Browner, D. A. Marsh

The need for a product dewatering step between the milling/classification and leach/carbon stages of gold plants has traditionally been performed by thickeners. Whether these be the 'conventional' or 'high-rate' types both require considerable initial capital outlay even without provision for standby facilities. In addition, their sensitivity (both mechanically and metallurgically) to changing feed conditions often results in these being considered 'high-risk' items of equipment, requiring a high degree of attention from operating personnel.

Jan 1, 1992

By William R. Bond, Jim V. Rouse, Laura L. Damon

As noted by Damon (1990), "The time that a heap (of gold ore) is on the reusable leach pad is of critical economic importance." The Interim Neutralization Study, conducted by Brohm Mining Corporation (Brohm), at the request of the South Dakota Department of Water and Natural Resources and reported by Damon indicated that improvements could be made in leaching and pointed out the need for a better understanding of the gold ore leach procedures. To provide data on an actual heap, personnel from Brohm and GEOCHEM installed a series of pressure/vacuum lysimeters in an active Brohm heap, and conducted subsequent testwork to evaluate the efficiency of leaching. The objectives of the testwork included efforts to:

Jan 1, 1992

By Abbas Zaidi, Betty L. W. Ou

Wastewaters generated during the extraction of gold from the ore can contain a variety of contaminants such as cyanide, heavy metals and arsenic. Proper management of these wastewaters is therefore necessary to minimize the negative impact of gold mining and milling operations on the environment. The Wastewater Technology Centre (WTC),located in Burlington, Ontario, Canada, has been involved in several studies related to the evaluation of various effluent treatment technologies which are relevant to the treatment and proper management of gold mill effluents. These studies have included bench and pilot scale tests, and the evaluation offull-scale systems. Furthermore, the WTC staff developed protocols for cyanide analysis in gold mill effluents, and a mathematical model for predicting the degradation of cyanide in tailings ponds. The information generated by the WTC staff has been referenced in several reports and papers published over the last ten years (Schmidt et.al. 1982, Simovic & Snodgrass 1989, Whittle et.al. 1989, Zaidi et.al. 1989, Zaidi et.al. 1991). Recently, the WTC has started to develop a micro­computer based expert system for use by decision makers in the gold mining industry and relevant government agencies who are involved in process design, process evaluation, costing, evaluation of the best practicable technology, approval of suggested effluent management systems, and so on. This paper presents some relevant background information and a discussion of the latest version of the expert system being developed by the WTC.

Jan 1, 1992

By Frank Ladwig, Stephen Gos

Tailings and/or wastewater generated from gold extraction plants employing cyanida­ tion must often be treated to remove the cyanides and heavy metals for environmental reasons and/or gold extraction inhibition reasons, due to the presence of heavy metals like copper, which have a detrimen­ tal effect during cyanidation. In recent years, the treatment of effluents contain­ ing cyanides and heavy metals has been widely studied, Among chemical treatment methods, the use of hydrogen peroxide has been universally employed as a viable option. However, in some cases, effluents containing high concentrations of heavy metals and/or solids decompose the hydrogen peroxide, an undesirable side reaction. The addition of stabilizers or other peroxygen compounds together with hydrogen peroxide can, however, considerably reduce the rate of decomposition and thus result in detoxi­ fication costs, which are considerably less than the standard detoxification process using hydrogen peroxide. In some cases, the reaction rate can also be increased, resul­ ting in lower investment costs for new detoxification plants. This paper deals with the results of developmental work performed in the recent past and introduces some new processes with the aim of optimizing reagent consumption and costs.

Jan 1, 1992

By Hans von Michaelis

Metallurgists are trained to seek synergisms and to optimize trade-offs in the selection of processes and flowsheets. The subject of my paper and the focus of this entire conference is on synergisms involving more than just metallurgical recovery, but encompassing mining and environmental management too. Operators have always known that by recycling tailings water they could recover some cyanide and lime values or reduce the amount of new flotation reagent additions. The trade-offs have changed at many US mines today where concern about avian mortality necessitates that water in the tailings pond be detoxified. This is just one example of how selection of processes and technology today requires integration of environmental management. MUDDER & GOLDSTONE (1989) showed how cyanide can be recovered from tailings slurries by an acidification­volatilization-reabsorption (A VR) process which was installed in New Zealand, and which in 1992 is being commissioned also at Nerco DeLamar Silver Mine as described by OMOFOMA & HAMPDEN (1992). FRICKER (1990) and FRICKER & OWERS (1992) show how using A VR to recover cyanide from pregnant pulps ahead of gold recovery improves the yield of recoverable cyanide while improving the performance of the gold recovery step and detoxifying the tailings. This is an excellent example of the synergisms that can be achieved ,y applying a "systems approach."

Jan 1, 1992

By Ulf Marklund, Manfred Lindvall

Fighting the challenge of diminishing ore grades, low base metal prices and a changing pattern of ore supply, Boliden has now taken the second generation of the fully­autogenous grinding concept on stream, Using new design and a highly-developed process control system the benefits of conventional two stage autogenous grinding technology are obtained with a wide range of ore types. The APC grinding system has been developed further. A new design of the Boliden Pebble Extractor together with an advanced control strategy make the performance of the APC concept superior to all other grinding systems with any ore quality. The capacity and simplicity of the autogenous grinding concept is equivalent to the best SAG installations but the operational costs are up to 25 % lower than for SAG or other primary ball or rod mill systems. The concept is as flexible as conventional crushing and rod mill installations but investment and operating costs are of the order of 25 % lower. Also, from the metallurgical point of view, the different types of autogenous grinding system outperform all other comminution systems including SAG. From 1989 to 1991 four fully autogenous grinding sections have been installed at various concentrators at the Boliden company. Old crushing plants and rod and pebble grinding circuits have finally been replaced by highly productive and cost-efficient autogenous grinding equipment. Significant savings in operational costs have already been reported. Power consumption and maintenance costs have been reduced significantly. Productivity expressed as milled tonnes per operator has been improved. Metallurgical results have developed favourably.

Jan 1, 1992

By G. Henry, S. J. Domvile

Arsenic management practices at the Con Mine in Yellowknife, Northwest Territories have evolved over the last fifty years of operations under changing regulatory, economic and technological conditions and incentives. As a result of a processing upset in the mine' s arsenic trioxide reclamation plant circuit in August 1988, arsenic levels in the mine' s tailings pond rose from 30 to over 100 mg V. At these arsenic levels, water treatment operations were unable to meet water licence discharge criteria and the mine itself was under risk of closure due to limited water storage capacity. Under these internal pressures, the mine initiated its own research initiatives designed to restore water treatment operations. The new process developed from the mine's research, utilized the mine's existing water treatment plant hardware but introduced a pretreatment step involving a discrete sludge recycle and removal system. In February 1989, water treatment operations resumed under the new process.

Jan 1, 1992

By Wolfgang Baum

The selection of roasting technology is a complex task which is primarily dependent on the ore mineralogy. Key roasting parameters are directly linked to mineralogical characteristics of the feed and vary considerably between different ore types even in the same deposit. In addition to sulfide refractoriness, other refractory conditions frequently exist. Together with various mineralogical features of the feed, they may complicate roasting testwork and process design. For most roasting scenarios, the critical economic factors are gold recovery, capital cost and environmental performance. This paper will show how these economic factors are influenced by the mineralogical ore characteristics.

Jan 1, 1992