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By E. B. Viljoen

I. R. M. Chaston* As a gravity concentration man in the midst of so many eminent flotation experts I feel like Daniel. However, I would respectifully disagree with the opening remarks by Mr Viljoen. First, he suggested that gravity concentration of cassiterite was not effective in sizes below 30 microns. In a paper to the Institution of Mining and Metallurgy in 19621, I gave some figures for gravity concentration of deslimed material both for cassiterite and for wolfram which indicated that careful shaking table concentration of fine deslimed material could give recoveries of 75 to 90 percent in the size ranges above 13 micron. These were figures obtained from normal plant operation. It would be interesting to know if any tests were carried out on gravity concentration of the efficiently deslimed feed to this flotation plant to see what the recovery would be. Secondly, Mr Viljoen suggested that gravity concentration plants were expensive. He gives the cost of a flotation plant at R300 000 to treat a feed of 400 t.p.d. to the desliming section or 160 t.p.d. to the flotation cells. From his operating cost figures it would appear that the flotation cost is approximately R2 to R4 per ton of feed to flotation and the total operating cost about R2 per ton of feed. A table plant to treat this tonnage of deslimed feed would consist of about 30 tables and should cost considerably less to install and very much less to operate than the flotation plant. Third, Mr. Viljoen suggests that the concentrate grade from a gravity concentration operation would be unacceptably low. The paper quoted abovel showed that once a primary fine concentrate had been made, giving a suitably deslimed material, further gravity concentration could give concentrates of over 40 per cent Sn with high recoveries. Tailing from this dressing stage was naturally returned to the feed. To give these high grades, sulphides had been removed by flotation but this necessary flotation step is simple and cheap to operate and could be restricted to the final stage when the quantities involved are small. I would agree that flotation has a part to play in fine tin recovery but this role would only seem to become fully effective at sizes below 10 micron and would seem to require, as Mr. Viljoen has suggested, a mechanism for sizing which is effective down to, say, 1 micron. In the meantime it would be interesting to try tabling the flotation tailing to see if it was possible to recover the plus 20 micron cassiterite which is not recovered well by flotation. One point which has been made during discussion is the suggestion that cassiterite particles have a fully hydrated surface at normal pH. I wonder if this layer could materially affect the overall specific gravity of a very small cassiterite particle and, if so, whether gravity concentration of the very fine cassiterite would be improved if carried out in acid conditions, which would inhibit the formation of this hydrated surface. REFERENCES 1. CHASTON, I. R. M. 'Gravity concentration of fine cassiterite'. Trans. Inst. Min. and Met. Vol. 71, p. 4, 1961 and 1962, and discussion of this paper. Dr. R. P. King Mr Viljoen has drawn attention to the difficulties associated with the presence of very fine particles in the flotation pulp and he has indicated that, on the Union Tin plant, they must sacrifice 30 percent of the cassiterite in the minus 7 /Lm material which they separate and lose. He has also indicated that the rate of flotation of cassiterite remained high at these small sizes. The problem arises because the very small particles stabilize the froth making it impossible to handle. These stable froths cannot be easily broken and therefore cannot be pumped and processed. It seems that further fundamental research work on the properties of stabilized froths is urgently required. We have found another difficulty associated with the presence of very fine particles in phoscorite slurries; these particles can be easily floated but with very poor selectivity. We believe that it is possible that a purely physical mechanism such as entrainment is responsible for the collection of fine particles in the froth. We have also demonstrated that the presence of fine particles in the pulp adversely affects the rate of flotation of the larger particles. For esample, we have found an increase in recovery of + 100 um material from 2 percent to 17 percent in a standard laboratory batch flotation test on phoscorite when the - 37 um was removed from the feed. Such interactions between particles are not universally recognised as an important aspect of the complex flotation mechanism. They should appear in any quantitative formulation of the flotation rate process.

By M. C. van Blerck

This paper examines the South African fiscal system as it applies to the mining industry and, where components are found wanting, discusses possible alternatives. It is concluded that the South African system has long provided a stable environment for mining investment and growth. However, the introduction, of steep surcharges during the past decade or so (since abolished) and ring fencing (since relaxed but not abolished) has started undermining this stability.

Jan 1, 1994

By S. J. C. L. Peeters

Geographical information systems (GISs) provide sophisticated functionalities t1tat can be used by the personnel in many aspects of the mining industry to visualize, analyse, and manipulate spatial and tabular data. This paper presents an experimental case study for Hartebeestfontein Gold Mine. It shows how data from different computer systems can be brought together into a GIS by use of the Arc/Info and ArcView programs.

Jan 1, 1996

By F. P. A. Robinson, J. W. Fourie

Austenitic stainless steels are welded using low-heat inputs. However, owing to differences in the physical metallurgy of austenitic stainless steels and duplex stainless steels, low-heat inputs should be avoided for duplex stainless steels. This paper highlights the differences in solidification mode and transformation characteristics of these two types of alloys. Recent work on the effect of heat input on the properties of weldments of duplex stainless steels is reviewed.

Jan 1, 1990

By K. R. Noble

The planned extraction of the No. 1 shaft pillar at Blyvooruitzicht Gold Mine highlighted a number of potential problems. In spite of the relative shallowness, careful thought had to be given to stope phasing owing to the detrimental effect of the anticipated geology and the fact that uninterrupted hoisting was necessary. Extensive use was made of computer modellig to design the stope phasing, determine the influence of regional support and to predict the direction and magnitude of displacements in the shaft. The paper describes the success of this design approach, and measured displacements in the stoping horizon and shaft barrel are compared to those obtained from the original computer model

Jan 1, 1987

The first neutrinos in nature ever detected by man were "caught" in a unique laboratory some 3 km (over 2 miles) underground in one of the world's deepest mine shafts at East Rand Proprietary Mines (ERPM), Boksburg. Only 100 m from where gold is being mined from the rock face a small team of South African and American physicists work on one of the most fascinating and important fundamental research projects that is currently exciting the imagination of the scientific world. Neutrinos are sub-atomic particles just as are protons, neutrons and electrons, but they are unique in that they have neither electric charge nor mass. Cosmic neutrinos travel at the speed of light and penetrate stars and planets. Even a million kilometres of solid lead would not provide a satisfactory shield against them. Stars are believed to "burn" by means of nuclear reactions which produce enormous fluxes of neutrinos. The sun, for example, illuminates the earth with visible light, but also bathes it with neutrinos. After World War II, two American physicists, Profs Frederick Reines and Clyde Cowan, experimenting at a large nuclear reactor, succeeded in obtaining direct evidence of the existence of the laboratory-produced neutrino. It then became very important to establish whether neutrinos also existed in nature. This knowledge would lead to a greater understanding of the forces of nuclear physics, of the behaviour of nuclear particles and, indeed, is also relevant to astrophysics. From the start it was clear that the search for "natural" neutrinos would be difficult. Questions which arose were- * how could they be traced if they were without mass or electric charge? * how could other nuclear particles be screened off? * could these not be wrongly detected, or even prevent accurate detection of neutrinos? Neutrinos were known to be produced along with charged particles, by the reaction of primary cosmic rays with the constituents of the atmosphere. It was also known that when the neutrinos collided with matter, they themselves produced the same type of charged particle which could be detected if the unwanted charged particles from the atmosphere could be screened off. What was needed, therefore, was a laboratory where the particles produced in the atmosphere could be screened out, yet which would receive and detect the particles produced by the neutrons' collision with the matter (solid rock) in the vicinity of the laboratory. This meant that scientists either had to build a laboratory with an enormously thick lead shield for their detection work. . . or they could go as near as possible to the centre of the earth where only charged nuclear particles of the very highest energies could penetrate. ERPM was clearly the most suitable place in the world where so effective a "neutrino trap" could be set. Under more than 3 000 m of solid rock the apparatus for detecting neutrinos is well shielded against unwanted nuclear particles produced in the cosmic radiation which can reach the laboratory only in a steeply vertical trajectory. Other particles are easily stopped by the great thickness of rock. The air-conditioned laboratory is at one end of a 150 m long tunnel, 2,5 m high and wide, blasted from the rock. The electronic recording equipment is housed here, while the rest of the tunnel is filled with the detection system. When a charged particle passes through a detector element, it produces a minute flash of light which is recorded and which triggers a flash-tube array. This then defines the trajectory of the charged particle, which is also recorded on film for analysis. So far 82 neutrinos have been detected, 50 at the present level and 32 at a higher level, and the findings have borne out the physicists' theoretical expectations. In this joint project Profs Reines, J. P. F. Sellschop, Director of the Witwatersrand University's Nuclear Research Unit and M. F. Crouch of the Case-Western Reserve University of Ohio are the Chief Investigators. This unique endeavour has been made possible by financial support from the US Atomic Energy Commission, the University of the Witwatersrand and the Chamber of Mines of South Africa, as well as by the cooperation of the management and men of ERPM.

A theory is presented providing a concise mathematical description of the performance of a percussive rockdrill in terms of its principal mechanical dimensions. The theory defines the relationships between the values of thrust required to produce optimum rates of penetration at different throttle air pressures in terms of the piston areas and derives an equation for the prediction of these rates. An analysis of drillsteel life and bit wear is also made.

By B. H. Sandelowsky

Prehistoric metal-working in South West Africa by B. H. SANDELOWSKY*, Ph.D. (Visitor) This paper describes a three-hundred year old metal-working site at Rehoboth, and makes a plea for information on such sites elsewhere in South West Africa so that they can be investigated. The technique of ore smelting that was used at Rehoboth appears to be different from that practised elsewhere by Bantu peoples before the modern era.

Jan 5, 1974

By J. D. Austin

"Mining Projects: Evaluation, Finance, and Management" held in May 1980 rounded off a theme started with the colloquium on "Exploration Feasibility Studies and Investment Analysis" held in 1979. Seven papers on various aspects of the potential path of an ore-body from an exploration concept through to discovery, evaluation, and financing, to the management of the construction phase, were presented to the 300 delegates at the colloquium held at the National Institute for Metallurgy.

Jan 1, 1980

By G. P. Schoonraad, J. E. Clay

Treatment of zinc silicates by the Waelz Process by J. E. CLAY (M.I.M.M.) (Visitor) and G. P. SCHOONRAAD. Pr. Eng.. B.Sc. Eng. (Rand) (Member) A review is given of the Waelz process. The chemistry of the process and the mechanism of crust formation (accretions) are briefly dealt with. The plant of Kiln Products Limited and its operation are described. The problems encountered and methods for their elimination are presented.

Jan 8, 1976

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

I am a partner in a minerals' development company called A.B.F. Limited, that does minerals development in Africa and Asia. I have read your very fine magazine often at the Colorado School of Mines Library in Golden, Colorado. I would like to ask your assistance in trying to locate a South African smelter; preferably on the coast, but not totally necessary for the project, that can separate the first four metals (Au, Ag, Cu, and Pb).

Jan 1, 1980

By P. Greenfield

The German steelmaking industry has come up with a novel solution to the problem of waste plastics-grind them into particles and use them in the steelmaking process. Plastics make ideal agents for removing oxygen from iron ore in blast furnaces, and save on oil and coal as well. The aim of replacing heavy oil and coal with plastics in blast furnaces is to use them as reducing agents as well as an additional energy source.

Jan 1, 1996

By M. A. von Below

Environmental activists have targeted the mining industry in an attempt to prevent development, which has resulted in the industry's becoming defensive and retro-active. This paper argues that mining managements should go on the offensive and champion the environment through leadership in environmental policy and research and development, rather than reacting to anti-mining campaigns. In the formulation of an environmental policy for the mining industry, a clear understanding of the concept of sustainable development is of paramount importance.

Jan 1, 1993

By H. T. Clausen

This paper gives a brief review of the main environmental and ecological problems of slimes dams, both those created in the immediate vicinity of the dams and those influencing the region or catchment. Methods of dealing with these problems and influences on existing dams are described. The difficulties encountered in the growing of grass on steep slopes are explained, and, after an analysis of the conditions, a plea is made for flatter slopes on the sides of dams.

Jan 12, 1973

By G. J. McDougall

After defining activated carbon, the author describes its structure and outlines the physical characteristics distinguishing one type of activated carbon from another. The adsorptive properties of these carbons, the raw materials used, and the manufacturing processes-chemical activation, and physical or thermal activation-are outlined. The high-temperature thermal route (which is the most important for the products employed in gold recovery) using coconut shells or coal as the raw material is then discussed In some detail.

Jan 1, 1991

An International Ferro-alloys Congress, arranged by the Ferro Alloy Producers' Association of South Africa, the South African Institute of Mining and Metallurgy, and the National Institute for Metallurgy, will be held in Johannesburg, South Africa, in April 1974. The technical programme, occupying five days, will cover the following topics in relation to all ferro-alloys: 1. Burden preparation, blending, pelletization, handling, reducing agents. 2. Electric smelting furnaces-design, operation, management,- smelting optimization, shop practice, refractories. 3. Mineralogy, reduction behaviour, smelting reactions, slags. 4. Automation, Pollution control. 5. Applications, trends in comsumption, trends in composition specifications. There will be no parallel sessions. Papers in the above topics are invited; review papers will also be welcome. Proposed titles and abstracts in not more than 200 words should be submitted before the 30th of November, 1972, to The Chairman, Programme Committee, INFACON 74, Private Bag 7, AUCKLAND PARK, South Africa. The abstracts will be considered during January 1973, and papers accepted for the Congress must be submitted in final form before the 31st of July, 1973. The proceedings of the Congress will be published as a special volume. There will be a series of post-Congress tours to ferroalloy plants and other places of both technical and scenic interest. A full ladies' programme will be arranged. The First Circular, giving further details, can be obtained from: The Secretary of the Organizing Committee, INFACON 74, Private Bag 7, AUCKLAND PARK, South Africa.

By M. A. de Ruijter

Bracken Gold Mine ceased mining operations during February 1993. The clean-up of the gold plant, which had already commenced in September 1992, was completed in January 1994. The mine had been in production since early in 1962 but, because of a decreasing ore reserve, increasing working costs, and a relatively low gold price, closure had become inevitable. The closure had been under consideration since August 1983, when the first estimate was made regarding the amount of gold that could be recovered from the clean-up operations. Until that stage, it had been accepted that Bracken would conform to the commonly accepted idea that 0.25% of the total gold produced by the plant would be recovered during the clean-up operation. This idea was dispelled when the initial estimates indicated that the gold recovery would vary between 0.049 and 0.095%. The actual figure realized was 0.036%, showing that there is no generalforl1ula for the calculation of the amount of gold to be recovered from such clean-up operations. During the clean-up operation, Bracken became an unexpected contributor to the State's Reconstruction and Development Programme by having al the mine and plant buildings purchased and converted into a community development centre. This shortene4 the time available for the clean-up, and several of the buildings remained intact. However, the foundations and sub-soils had been sampled extensively, and it is considered that no recoverable gold was left behind.

Jan 1, 1996

Actual observations of rockburst damage, together with some theoretical considerations, strongly suggest that conventional approaches to the design of tunnel support are inappropriate where there is a significant seismic risk. The present widely used support systems, which are based on stiff, fully grouted re-bars, are inadequate where rock displacement velocities exceed 1 m/s. It is shown by means of a simple conceptual model that yielding of the support elements is essential to ensure their survival when they are subject to the high strain rates typical of severe rockbursts. The model proposes that the total load in the element is an impulsive tensile force imposed and sustained by a single 'tributary' block ejected from the tunnel wall. The stability of the system is determined from a comparison of the kinetic energy developed by the block with the energy of deformation absorbed by a grouted steel tendon. A novel test procedure was developed for the validation of this approach, and for an examination of the energy-absorbing capacity of stiff and yielding tendons. The results of an initial series of tests showed that the recently developed cone-bolt is an effective yielding device. It absorbs twenty times more impulsive-load energy than is consumed by the complete fracture of grouted re-bar of equivalent strength, and it remains totally unscathed. Importantly, the results demonstrate that the ejection model is not merely an explanatory concept, but can be used as a representative and valid design method.

Jan 1, 1994

By C. Hey

The cycloned gravitated tailings backfill system, also referred to as a soft or low density fill, has been implemented at Vaal Reefs. Inhibiting the success of the system was the problem of shrinkage after placement. The problem was overcome by a pressure fill technique which eliminated settlement, contained costs and allowed remote placement. The technique involves the preinstallation of disposable pipes which are filled cyclically until a residual pressure of 0,5 bar of active support is generated in the filled paddock.

Jan 1, 1988