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The aspect ratio (mill diameter/mill length) of autogenous and semi autogenous mills varies widely and can be as high as three or as low as 0.5. The literature on the subject of what effect aspect ratio has on grinding mill performance or energy efficiency is almost non-existent. However, at the design stage of many grinding circuits the subject is often vigorously debated amongst metallurgists. In this paper the performance characteristics of mills with different aspect ratios are examined to determine whether process performance characteristics are a function of aspect ratio and whether high aspect ratio mills are any more or less energy efficient than low aspect ratio units. Data from both pilot and full-scale mills are used for this purpose in open and closed circuit configurations.

Jan 1, 2007

By W. A. Lenhardt

During the past five years, several research projects on the causes of mining induced seismicity have been carried out by the Rockburst Research Department at Western Deep levels Limited. This paper summarizes the results of these investigations. Several types of mining-induced seismic events are addressed, and models of their mechanisms are presented. It is shown that most of the seismicity results from mining in geologically disturbed areas, and ways and means are discussed to reduce the seismic potential. Stabilizing pillars, for instance, have been introduced to reduce stresses at the stope face and to alleviate the facebursting problem. Facebursts still occur in areas of very low stresses, and pillars became the source of very large seismic events (M >3). At this stage, the understanding gained of pillar-associated events allows a review of current mining practices. Further, it makes possible an examination of the efficiency of measures to alleviate the effects of various seismically prone situations.

Jan 1, 1992

"Chairman: Dr R. E. ROBINSON Rapporteur: Dr R. P. COLBORNPapers:The simulation of crushing plants by W. J. WhitenSimulation of multi-component flotation plants by B. K. Loveday and G. R. MarchantComputer control of flotation at the Ecstall concentrator by M. P. Amsden C. Chapman and M. G. ReadingModel for the design and control of flotation plants by R. P. KingIn presenting his paper Dr W. J. Whiten outlined the basic concepts on which the control model was based and emphasized the fact that empirical models based as much as possible on theory were used to simulate each unit of the crushing plant. The final parameters of each model were computed using data collected from the plant. Unfortunately, the system did not permit accurate extrapolation but was successful when operating in the region from which the parameters were calculated.He concluded from the results of the test work that the crusher amperage was a critical parameter and that the utilization of the model gave a 15 per cent increase in the plant output. This was because the model predicted that a marginally fine grind would provide a significant increase in throughput. Dr Whiten elaborated on what constituted the multiple spline regression, explaining that it was a least-squares curve-fitting technique in one or more dimensions, where the calculation of coefficients in analytic expressions was replaced by the calculation of typical points on a very smooth curve called a spline function. The emphasis was placed on the shape and value of the curve or curves instead of on the coefficients as in analytic regression. A spline function was the line drawn between all points constituting the data set.Dr B. K. Loveday commented that the simulation was unusual in that the optimum throughput was considered to be the maximum throughput, which, surely, was limited by the crusher size. He also emphasized the importance of the interaction between both crushing and grinding circuits and added that in practice the optimum operating conditions were inter-dependent. Dr Whiten replied that in the case of the plant under consideration, the crushing process was not, in fact, the limiting operation.Mr C. E. Clifford indicated that the model was being used to simulate a number of crushing and grinding circuits at Mount Isa Mines. He reported that the model simulated the circuit satisfactorily for primary and secondary gap settings of 0,625 in. to 0,375 in., but that adjustment had to be made to the model parameters for gap settings of 0,250 in. to 0,125 in.In reply to a question from Dr D. M. Hawkins, Dr Whiten said that he preferred to use low-order splines with smaller segments rather than high-order spline functions with large segments."

Jan 1, 2014

By T. M. Espach

This paper gives an account of the changes that have taken place since the previous paper on trackless mining equipment at Prieska Copper Mines (August 1973). Details are given of the modifications to the equipment. the maintenance of equipment and road ways. the training of operators. and the operating costs.

Jan 1, 1979

By R. G. Jurd

This paper considers the introduction of large-scale longwall mining into South African coal mining, instead of the conventional mechanized bord-and-plllar mining that is widely practised at present. The two methods are compared, and longwall mining is found to have the advantage in several respects in some seams. The most cogent reasons for the introduction of the longwall method In some seams are associated with safety strata control and increased labour costs.

Jan 1, 1978

By C. J. Van Niekerk, C. C. Begley

SYNOPSIS The paper opens with brief descriptions of the history, occurrence, and regional geology of South Afri¬can zinc deposits, and follows with descriptions of the resources, mining methods, and processes for the concentration of the sulphide minerals and the extraction of zinc as practised in South Africa. The end uses in the form of alloys or as salts are given in some detail. Statistics on the production and consumption of zinc in South Africa are given, and the current market situation and future prospects are discussed briefly.

Jan 1, 1991

By H. M. Friede

An experimental study of iron-smelting techniques used in the South African Iron Age by H. M. FRIEDE, Ph.D. and R. H. STEEL (Visitors) The main factors involved in the primitive smelting of iron (ore, charcoal, temperature, air supply, process control) were evaluated in an experimental furnace that was constructed to the pattern of an Iron Age furnace found at Melville Koppies Nature Reserve, Johannesburg. In particular, the characteristics, action, and efficiency of skin bellows were investigated to gaina better understanding of the air-supply system used. Sixteen specimens of iron ore, slag, and metallic iron (excavated material and material produced in the experimental furnace) were submitted to analysis. The results of the analyses are reported and discussed.

Jan 6, 1977

By D. Visser, P. D. Toens

The development of a continuous recording scintillation counter mounted on a cyclometer by P. D. Toens (Fellow) and D. Visser (Visitor) In order to facilitate ground radiometric surveys the Atomic Energy Board has developed a continuous recording device attached to a scintillation counter which is mounted on a cyclometer. Details concerning the construction are given.

By R. P. H. Willis

This paper describes the economics of backfilling, hydro-power, and mechanization when they are combined in an integrated stoping system. These three technologies have been shown to be viable, and the mines of the Gold Fields Group are introducing backfilling where the depths exceed approximately 2000 m below surface and in other highly stressed areas. addition, a number of mines are installing hydro-powered systems, and the first trackless stope within the Group may soon be a reality. The main emphasis in the paper is placed on the quantifiable effects of trackless stoping, including a basic risk analysis by use of a spreadsheet model. It is concluded that a substantial decrease in working costs and an increase in revenue are possible, resulting in a marked increase in working profit.

Jan 1, 1989

By B. Jack, A. Vervoort

During pillar extraction, sidewall fracturing and spalling at some collieries constitute a severe stratacontrol problem. In order to obtain a better understanding of this phenomenon, a survey of pillar corner conditions before and during pillar extraction was conducted at one particular site. For the various successive mining steps, the vertical stresses on the pillar corners were calculated by use of a three-dimensional boundary element program. A significant correlation was found between the calculated vertical stress prior to the extraction of the panel and the sidewall conditions. During the extraction of the panel, a significant deterioration of the sidewall conditions at a pillar occurred only when the adjacent pillar was mined, causing an increase in vertical stress on the remaining pillar.

Jan 1, 1992

There are presently no suitable underground mine production scheduling optimisation models available for application to sublevel stope mining. Scheduling underground production for maximum return is therefore still a manual process, which generally involves scheduling production from the next available highest cash flow stope within the operational constraints of the project. In most mining operations, the scheduling problem is too large and complex to guarantee truly optimal results through manual scheduling. This paper reviews some general optimisation studies that have been proposed for underground hard rock mining. Furthermore, an example of a mixed integer programming model is presented for a small conceptual sublevel stoping operation. Comparative results of a schedule generated by a mixed integer programming (MIP) production scheduling model and a manually generated model on a nine stope example is presented. Results indicate that the potential benefits of the MIP production scheduling model for the purpose of maximising NPV are significant. Finally, a new constraint was formulated to limit multiple exposures of fill masses for use in an existing MIP production scheduling model. Testing of the formulation took place on the central stope of the nine stope example, which showed that the formulation performed its task without breaking other operational constraints.

Jan 1, 2007

The Annual General Meeting of the South African Institute of Mining and Metallurgy was held in Kelvin House on Wednesday, 22nd August, 1979. Dr M. G. Atmore (President) was in the chair and declared the meeting open at 16h00. Obituaries President: It is my sad duty to announce the death of the following Members of the Institute : Brigadier R. S. G. Stokes, Honorary Life Fellow and Past President ; J. A. Arthur, C. L. Cartwright, R. B. Greaves, A. A. Haynes, G. Ross, M. W. Richards, W. T. Stobart, E. Veres, G. V. White, and A. G. Williams, Life Fellows; A. J. H. Pole, D. T. McMurray, P. G. O. Pretorius, A. E. D. Rubidge, A. M. Seccombe, and R. R. Uren, Fellows; R. E. Oltman, R. B. Richardson, and G. P. Rundle, Members; S. F. Dench and S. van Wyk, Associates. As a mark of respect to the memory of the deceased, and in sympathy with the bereaved, please rise and observe a few moments' silence. Minutes President: May we confirm the minutes of our last Annual General Meeting, which was held on 23rd August, 1978, as published in the November issue of the Journal? Agreed.

Jan 1, 1979

By A. L. Hinde, P. J. D. Lloyd, D. Hebden

The philosophy behind the design of a rougher cell for the handling of coarse feed and for the maximization of recovery within a given time is presented. The application of this philosophy in cells of 22-litre, 320-litre, and 3 m3 capacity is outlined, and the results of the process testing of these cells are given. In this testing, particular accent was placed on the recovery of water as a guide to the recovery of the finest size of particles, and the rate of recovery of various mineral species. It is concluded that a promising concept has been identified, but that further testing is needed for the firmer establishment of optimal operational parameters in a production environment.

Jan 1, 1983

By F. Q. P. Leiding

SYNOPSIS A technique is described for measuring the change in volume in a borehole drilled in a rock mass subjected to stress and strain. It is shown that the volumetric strain or change in volume provides a practical estimate of the the stress in the rock.

From a consideration of the functional requirements of a stope-support pack, simple design principles were developed. The material and dimensional properties of the different components of the pack were determined from a series of laboratory tests. The most important requirement for an adequate pack is that the cushioning layers of timber between the concrete brick layers should provide sufficient transverse reinforcement. The tendency of the compressed timber to creep is shown to be a serious limitation to pack performance and must therefore be an important consideration in the overall design of supports.

Jan 1, 1978

By A. G. Ramsay, P. G. Kahles, L. E. Kun

A method for the clarification of uranium pregnant solutions using a high-rate floc blanket was developed from laboratory scale through pilot-plant testing to full-scale production by the Anglo American Research laboratories. A two-stage clarification process (hopper plus leaf) was commissioned at the Western Deep levels uranium plant in October 1980. The high efficiency of the hopper clarification permitted its use on its own. The leaf clarifiers were therefore taken out of service in September 1981, since when the secondary clarification is achieved by further unaided gravity settling in the semi-clarified and clarified pregnant-solution storage tanks. As a result, a daily 12000 to 17000 t of countercurrent-decantation overflow with a suspended-solids concentration of 500 to 600 mg/I is continuously clarified to a suspended-solids concentration of less than 30 mg/I. Secondary gravity settling reduces the suspendedsolids concentration to under 20 mg/I. The cost of the single-stage hopper-clarification process is RO,O020per ton of liquid treated. The removal of the leaf clarifiers from the circuit resulted in an approximate visible saving of RI00000 per annum.

Jan 1, 1983

By A. O. Filmer

The techniques used in this study of the non-oxidative dissolution rates of high- and Iow-grade nickel mattes in hydrochloric acid involved leaching and the use of a rotating ring-disc electrode. It was found that the rate of metal dissolution depends on the potential at which the matte dissolves, a maximum rate of dissolution being observed at -0,2 V to 0,3 V (relative to a saturated calomel electrode). The results are comparable with those obtained in work on the dissolution of synthetic nickel and iron sulphides. The adverse effect of excess sulphur on the rate of nonoxidative dissolution is explained in terms of the mixed potential of the reaction. The leaching studies showed the feasibility of processing a high-grade nickel matte by non-oxidative dissolution, and indicate that maximum rates can be obtained in the presence of fairly Iow concentrations of oxidant. A relative selective dissolution of iron can be obtained from the Iow-grade matte under reducing conditions, thus resulting in a significant upgrading of this material. Letter to the Editor Dravo Corporation is seeking information concerning a special method of transporting explosives to aid in designing a large underground oil shale mine in the mountains of Colorado.

Jan 1, 1981

By R. J. Dippenaar, W. H. Van Niekerk

The relationships between coal properties, the strength of coke, and the performance of a blast furnace were investigated by means of correlation studies, and a linear programming model was developed for the prediction of a coal blend based on these relationships. The unique feature of this approach is that it utilizes a knowledge of the minimum blast-furnace coke requirements, rather than the maximum attainable coke quality. The model predicts the least expensive coal blend that would still comply with the minimum coke-quality requirements of blast furnace. The study also confirms the existence of a relationship between the rank and caking parameters of coal, and the hot strength of coke. The effect of coke-oven operating parameters on coke quality is also discussed.

Jan 1, 1991

By M. C. van Blerck

Since its introduction in 1956, the capital allowance has been increased and its scope widened. At present the allowance is 10% in respect of two categories of gold mine (post-1973 and other deep level mines) and 6% in respect of natural oil mines. The allowance is a significant incentive encouraging the development of new mines, to the benefit of both the fiscus and the South African economy as a whole. A strong case can be made for increasing the amount and the scope of the allowance. The Margo Report recommendation that the allowance should possibly be replaced with a system of direct grants is, in theory, neutral. However, practical difficulties exist with cash grants and there is concern with the implications elsewhere in the Margo Report that the capital allowance is excessive and that, as a consequence, such direct grants will represent an effective reduction in this incentive. I believe that the best course of action would be the retention (and enhancement) of the capital allowance and the expansion of its scope.

Jan 1, 1988

By P. Valicek, M. Farren, G. Harrison, G. van den Berg, P. van Dorssen, P. Kramers

Full mechanization of the stoping operation using rockbreaking methods other than blasting has been a target of research for decades because of the considerable payoffs in terms of increased face advance rates, productivity and safety. However, the unavailability of economically viable rock breaking tools has prevented progress so far. This has changed with the invention of activated cutting tools, which achieve significantly reduced operating forces, power consumption and wear compared to non-activated tools and thereby permitted the development and evaluation of the first mining system using this technology. Targets for the mining system were a face advance of 100 metres per month on a double shift basis for a 30 metre long panel and eventually fully automated man-free stoping. The purpose of this paper is to describe the design, development and evaluation of the mining system. This was a major collaborative effort between Anglo Platinum’s Rustenburg Platinum Mines Rustenburg Section — Townlands Business Area, Anglo Platinum’s Research and Development Department within the Mining Technology Division, the inventor of the technology Bechem GmbH, the equipment manufacturers Long-Airdox Ltd and Zollern GmbH, and CSIR Miningtek who managed the project. A structured process was followed during the development to minimize the risks involved in using such leading edge technology. The system was rigorously evaluated to ascertain the economic viability of the method and to collect data for the design of a production system.

Sep 1, 2001