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By A. Ward, A. Smith, D. Harpley

Methods for the prediction of seepage quality from waste-disposal facilities are evaluated for input to the design of desalination treatment facilities. This is done by reference to a waste dump seeping into a near-surface aquifer, the contaminated seepage being collected by scavenger wells. As the quality of contaminated water intercepted by the wells will vary with both space and time, it is necessary for predictive methods to accommodate such variations. One-dimensional and two-dimensional predictive solute transport models are described and applied to the seepage and scavenger-well example mentioned above. The advantages and disadvantages, interims of overall applicability, data requirements, and possible accuracy, are described and discussed. While one-dimensional models have the advantages of speed, simplicity, and cost, the frequent requirement of prediction in both space and time necessitates more complex, two-dimensional simulation.

Jan 1, 1987

By H. J. N. Winhoff

The tailings dam at Consolidated Murchison Limited by H. J. N. WINHOFF, Ing. Grad. (Visitor) The history of tailings dam operations at Consolidated Murchison Limited is briefly recounted, and a mechanical method of dam-wall construction is described and illustrated in some detail.

Jan 12, 1973

By G. Chitiyo

Prediction of pothole characteristics is a challenging task, confronting production geologists at the platinum mines of the Bushveld Complex. The frequency, distribution, size, shape, severity and relationship (FDS3R) of potholes has a huge impact on mine planning and scheduling, and consequently cost. It is with this in mind that this study was initiated. Quantitative analysis of potholes indicates that pothole size (area covered) can be described by two partly overlapping lognormal distributions. These are referred to as Populations A (smaller) and B (larger). The range of observed pothole sizes conforms to a simple double exponential growth model based on Newton's Cooling Curve. A third size range of very large potholes (Population C) that could not be modelled properly within the proposed growth model is interpreted as to represent a very early phase of aggressive regional thermo-chemical erosion and potholing. In general, potholes are dominantly quasi circular with only a subordinate tendency of elongation. In the UG2, potholes with elongated forms are more prevalent in the size range between 20 and 500 m diameter. In the Merensky Reef elongated potholes are more common in the size range above 50 m in diameter. Although not distinctly visible, elongation of potholes in both the UG2 and the Merensky Reef show a net north/south orientation. Using shapes of pothole rims and floor areas, documented for the UG2 in the Waterval Shaft area, it is demonstrated that the northern, down-dip edges of potholes have steeper dips than the southern, up-dip edges. Spatial distribution studies using a uniform quadrant method suggest that in both the UG2 and the Merensky Reef, the potholes are randomly distributed, with a tendency towards clustering. Clustering appears to be more prevalent in the smaller Population A potholes. Bearing all findings in mind, it is found that the model of thermo-chemical erosion of the cumulus floor by new influxes of superheated magma best explains the observed data. Partial to complete melting of the cumulate floor occurred in three phases. The first represents the emplacement of hot magma. This magma, due to turbulent flow and high chemical and physical potential, aggressively attacks the existing floor (crystal mush on the magma/floor interface). Regional erosion is manifested by large, often coalescing potholes. During the second phase, when the magma emplacement process ceased and cooling in situ started, two distinct periods of pothole formation ensued. The first is related to rapid cooling along the relatively steep part of the Newton Cooling Curve, when Population B potholes nucleated randomly and grew rapidly with concurrent convective overturn and largely laminar flow condition. The second period of cooling occurred on the shallow-dipping part of the Newton Cooling Curve. Population A pothole growth became more subdued and nucleation appears to have been, at least locally, clustered. The final phase of this proposed 'super magma cycle' was introduced when chromitite crystallization and precipitation terminated pothole formation. This was followed sequentially by pyroxene and plagioclase crystallization to form the typical cyclic units of the Critical Zone. No suitable proxy could be found for the prediction of pothole density of potholes associated with the UG2 (likely due to limited spatial data coverage), and these are best predicted by extrapolation. The Merensky Reef slope index, in contrast, provides a proxy for pothole density, enabling prediction with reasonable confidence. This predictive model has been verified using underground information. The findings made during the course of this investigation have, when implemented, significant impact. Successful implementation will not only allow enhanced resource and reserve definition, but also better mine planning and scheduling.

Jan 1, 2008

By O. Korhonen, T. Leskinen

The use of large OK-16 flotation machines at the concentrators of Outokumpu Oy by o. KORHONEN and T. LESKINEN(Visitors) The development ofthe OK-16 flotation machine is described briefly, and an account is given of its use at various concentration plants in Finland. The benefits arising from the use of larger flotation machines are listed, and the technical specification of the OK-16 machine is detailed in an appendix.

Jan 6, 1976

By G. E. Blight

The load-compression characteristics of mine supports are usually evaluated by means of relatively rapid tests, whereas in the mine they are subjected to much slower strain-controlled compression. The effects of slow strain rates on the load-bearing properties of mine supports were explored by means of straincontrolled tests on model timber packs and timber-filled steel telescopic props. It is shown that the load-compression characteristics of these supports are considerably influenced by the rate at which they are compressed. The species of timber influences the behaviour, but to a relatively minor extent. Preloaded supports are shown to lose a significant proportion of their preload by relaxation.

Jan 1, 1978

What is a nugget effect? In the early development of geostatistics, the term ?nugget effect? was coined for the apparent discontinuity at the beginning of many semi-variogram graphs. This name was chosen to reflect the large differences found between neighbouring samples in ?nuggety? mineralizations such as Wits gold reefs. Geostatistical theory assumes that the difference between a sampled value and a potential repeat sample at the same location is actually zero. Included in this ?nugget effect? would be true variation between contiguous samples due to the nature of the mineralization, micro-fracturing, nugget or crystal size and so on. Also included in the nugget effect would be any ?random? sampling variation which might occur due to the method in which the sample was taken, the adequacy of the sample size, the assaying process, etc. Arguments were put forward that ?sampling errors? actually exist at zero distance. Some geostatistical schools actually maintain that ?nugget effect? is all sampling error. This would imply that ?perfect? sampling would eliminate the nugget effect entirely. There is now a dichotomy both in the geostatistical world and in the software packages provided for geostatistical analyses. It may seem academic to argue over whether the semi-variogram model should take a value of zero, a value equal to the nugget effect or a partial value at distance zero. However, the decision can have a profound effect on both the estimated resource and in our confidence on that resource. Whereas most geostatistical texts define the semi-variogram model as taking the value of zero at zero distance, others imply that the full nugget effect should be used at zero distance. For example: ?The nugget effect refers to the nonzero intercept of the variogram and is an overall estimate of error caused by measurement inaccuracy and environmental variability occurring at fine enough scales to be unresolved by the sampling interval3. ?Christensen4 has shown that the ?nugget effect?, or non-zero variance at the origin of the sernivariogram, can be reproduced by a measurement error model. ?The nugget effect is considered random noise and may represent short-scale variability, measurement error, sample rate, etc.5. In many training texts and web courses, the definition of the semi-variogram is ambiguous as the formulae for semi-variogram models is not actually specified at zero distance6,7,8.

Jan 1, 2009

By H. W. Read, L. G. D. Napier

Change is endemic in our society. Future change will be accelerated by an explosion in technology, communication, and political thought. To meet these challenges, rapid structural changes have been taking place in mining organizations both here and abroad. The management of shaft-sinking projects is a case in point. Shaft sinking is a seminal element in the sustained well-being of a deep level mining venture. Its accomplishment is fraught with risk, involves a high level of capital expenditure, and is a precursor to profitable mining investment. The purpose of this paper is to present a concise and practical picture of the concepts, methods, and techniques of professional project management as applied to shaft-sinking projects.

Jan 1, 1994

By A. A. Bradley, K. H. Stanton, P. J. D. Lloyd

A theory for the dynamic balancing of centrifugal mills is presented that takes account of the mass and shape of the charge in a gyrated grinding tube and the way in which the charge lags behind the centrifugal force vector. predicts that a corresponding lag in the angular position of the counterweight centres of mass is necessary, and that the fractional filling should be increased if the ratio of gyration diameter to tube diameter is decreased. A worked example is given for a I MW centrifugal mill that was balanced adequately by the methods described.

Jan 1, 1983

By G. Peinaar

Superhardening is a new development by which a substantial increase in hardenability above the normal can be achieved in Iow-alloy steels. This paper concerns the reversible temper-embrittlement behaviour of steels with a superhardenability characteristic. Steels of type BS 530A40 with manganese modifications varying from 0,72 to 1,27 per cent in the superhardenable and conventional condition were compared. It was concluded that superhardenability in itself does not affect the susceptibility of a particular steel to temper embrittlement. However, an increase in manganese content, which was intended to increase the base hardenability of the steel, caused serious deterioration of the temper-embrittlement properties. As the use of manganese, chromium, and nickel to increase base hardenability results in an increase in susceptibility to temper embrittlement, it is suggested that this effect should be countered by the addition of 0,2 to 0,3 per cent molybdenum.

Jan 1, 1984

By A. Whillier

Recovery of energy from the water going down mine shafts by A. WHILLIER, Pr. Eng., Se. D. (M.I.T.) (Fellow) The influence of energy-recovery systems on the rise in temperature of water going down mines is examined. It is concluded that the, cost benefit of such systems, deriving partially from the reduced temperature rise in situations where cold water IS sent underground from surface, would more than justify the installation cost.

Jan 4, 1977

By R. L. Attridge

Namibia's newest mining enterprise, the Navachab Gold Mine, was officially opened by President Sam Nujomo during June 1990. The mine is a joint venture between Erongo Mining & Exploration Company Limited, Metal Mining Corporation of Canada, and Rand Mines Windhoek (Pty) Ltd. Erongo has a 70 per cent interest in the mine, while Metal Mining and Rand Mines hold 20 per cent and 10 per cent respectively. Anglo American Corporation and its associates hold two-thirds of Erongo shares and CDM (Pty) Ltd one-third. The Mine is managed by Erongo Mining & Exploration Company. The property is located some 10 km southwest of the town of Karibib and 170 km west-northwest of the Namibian capital of Windhoek (Fig. 1), the name of the Mine being taken from the farm on which the gold deposits were discovered. Navachab is an opencast operation and was brought into production in December 1989 at a cost of around R84 milion-RS,2 million under budget. The plant is designed to treat 840 kt annually at an average gold grade of 2,6 g/t. This wil produce 1900 kg of gold per year, which at today's prices will earn Namibia more than R60 million in foreign exchange.

Jan 1, 1991

By S. K. De Kok

Over a period of three years, since samples first became available, laboratory and pilot plant experiments have been conducted to develop a method of treatment to recover copper and zinc in saleable grades of concentrates from the Prieska complex sulphide orebody. These experiments have been based on adaptations of principles investigated by research workers and applied to similar ore types throughout the world. The differential flotation process finally worked out involves a comparatively coarse grind, flotation of the copper at near-neutral pH with the use of a zinc-cyande sphalerite depressant, followed by flotation of the reactivated sphalerite. This procedure has had such success that the construction of a full-scale plant is proceeding with confidence that the small-scale operations will be duplicated or improved upon. It is to be expected that the large plant will follow the pattern of almost every flotation plant that has been built in that modifications to the circuitry and reagent systems will be made as experience is gained.

By Q. P. Campbell

Activated carbons used in the precious metals extraction industry are characterized by large internal surface areas and a great affinity for metal ions. The purpose of this research is to prepare activated carbon from a South African bituminous coal by physical activation that is suitable and cost-effective for use in the extraction of metals. The quality of the coal-based activated carbon may not prove to be as good as activated carbon produced from other traditional sources, but the production costs involved may make South African coal a feasible alternative feedstock. The activated carbons produced were characterized by Brunauer, Emmett, and Teller (BET) surface area, activated carbon pH, and phenol adsorption studies and the results compared to the results from a commercially available activated carbon, Norit RO 0.8 (control sample). Bituminous coals from various sources including Witbank Seam 4 and Free State coal were used in this study. The preparation method chosen was physical activation using superheated steam. The effects of process variables such as activation time (1-3 h) and temperature (600-800°C) were studied in order to optimize those parameters. The activated carbon surface area was characterized by means of nitrogen adsorption isotherms at 77K. BET surface area analysis showed that Witbank Seam 4 coal activated at a temperature of 800°C and activation time of 3 hours resulted in a surface area of 340 m2/g. Quality control of each sample was performed by measuring the pH of a known amount of the prepared activated carbon in distilled water over time. Results showed that the pH of some of the prepared activated carbons reached a value of 11. Phenol adsorption results for the different activated carbons prepared corresponded well to the results obtained for the Norit RO 0.8 activated carbon sample.

Jan 1, 2012

By Z. Levinson, R. Dimitrakopoulos

A mining complex is an engineering system where raw materials are extracted from several mines, processed, transported, and sold to the market. The uncertainty and local variability of material grades and their locations within the related mineral deposits are critical for determining the optimal life-of-mine extraction sequence, destination policy, operating modes, and capital investment decisions, which define the production schedule of a mining complex. Infill drilling is used to further characterise a mineral deposit and reveals information that changes the representation of the resource model and potentially the resulting optimal long-term production schedule. A self-learning reinforcement learning approach is proposed to determine the optimal drilling locations that maximise the net-present value of the long-term production schedule and the associated financial forecasts by adapting the schedule to additional information. A case study at a copper mining complex demonstrates a $70 M increase in project value by collecting drilling information with a $1 M budget.

Sep 1, 2021

COLLOQUIUM ON SHAFT SINKING The 'Star' published a report on the colloquium on 15th November, 1972. As this will be of interest to members, it is re-printed by kind permission of the 'Star'. Mac Thain The super-Mines of the future envisaged by Mr Jeff Goode, president of the Chamber of Mines, in his Gold Symposium address in London, will be entirely different from those producing today - not merely amalgamations of properties into bigger units.

By P. A. J. Cabassi, B. K. Loveday, M. J. Wilkinson, P. H. Radcliffe

The recovery of gold, uranium, and pyrite from accumulated residues at mines in the Orange Free State is adversely affected by the presence of pyrophyllite, which is naturally floatable and must be prevented from floating with the desired constituents by the use of a mica depressant, and of thucholite (uraniferous kerogen), which contains significant quantities of uranium and gold but does not float readily in the presence of a mica depressant. In laboratory tests on these residues, the use of a mixture of MIBC (methyl isobutyl carbinol) and paraffin in addition to the suite of reagents normally used was found to increase the gold recovery substantially, but the sulphur grade was lower. The recovery of thucholite also increased considerably, but the proportion of uranium associated with this mineral was small. Plant trials, which are continuing, have been encouraging, indicating an increase in the gold recovery of 4,6 per cent.

Jan 1, 1983

By D. Rankin, H. J. Stucke, W. K. B. Loftus

SYNOPSIS Planning for the Finsch opencast mine is described with particular reference to the proposed stages of mining, the method used to determine the limits of surface waste rock stripping and the derivation of the waste rock mining rate. Actual mining practice is described and the possibility of installing a skipway into the open mine at a later date is discussed. In addition, the waste dumping policy is referred to: this includes the cutting of slots through the hill on the west side of the pipe to increase tramming speeds. The crushing, washing and recovery sections of the treatment plant are described together with the various changes being made to the circuit. The most important of these are the installation of X-ray sorters for the final recovery of + 7 mesh diamonds, and the vibrating grease belt for the recovery of - 7 mesh diamonds. INTRODUCTION The Finsch Mine, a subsidiary of De Beers Consolidated Mines, Limited, is situated approximately 90 miles west of Kimberley, and some two miles from the village of Lime Acres, in the Northern Cape. Lime Acres is a company village shared with the Northern Lime Company which operates a limestone quarry and works near the township. The mine is near the southern end of a well mineralized belt producing limestone, asbestos, diamonds, manganese and iron ore, and the whole area has developed rapidly in the last 20 years. Power for mining operations is drawn from the Electricity Supply Commission. The mine is conveniently close to the main Kimberley-Postmasburg railway line. Water is drawn from the Vaal River through a 57 mile State-owned pipeline at present temporarily operated by mine staff. DISCOVERY AND PROSPECTING OPERATIONS The diamondiferous orebody is situated on the farm Brits, which is State-owned ground that has been leased to the Company for the period of mining operations. There are indications of interest in the area by prospectors (Richter, de Bruin and others) over a period of some 30 years and the discovery would possibly have been made years earlier but for a law preventing prospecting for precious stones on State-owned land. Although the pipe formed a clear depression on the hill where it was situated, it was overlain by some 5 to 40 ft of banded ironstone rubble which was washed into the depression from the hillside above the pipe and obscured the deposit. In 1958, Mr Allister Thornton Fincham applied for, and was granted, the right to prospect for base minerals on the farm Brits. Asbestos is known to occur in the area and, initially, was Mr Fincham's primary interest. However, during the prospecting operations, garnets were discovered and it was realised that diamonds might be present. In 1960, when the Precious Stones Amendment Act was passed, a company

A knowledge of the steady-state mass and energy requirements of a particular process is essential to a determination of the economic feasibility of that process. A predictive simulation technique can be of great value in this respect. A versatile computer program based on a fundamental thermodynamic approach has been developed for the prediction of process requirements. The equilibrium composition of a multiphase system is determined by the technique of free energy minimization. Energy-balance calculations are performed using the appropriate thermodynamic data for the chemical species present in the composite materials used. All models for the process units under consideration are written in modular form, the output being calculated from the input and the specified operating conditions. The computer program is written in such a way that it can be used easily by anyone familiar with the processes involved, even though he may have no previous experience with a program of this type. The program is structured so as to facilitate the varying of one parameter without any alteration to the others, thus simplifying the investigation of the effects of any parameters considered to be important. The program has the advantage of being able to compare existing and new processes on the same basis, namely from the ores to the molten metal.

Jan 1, 1987

By P. J. D. Lloyd, Jill Urban, M. R. Urban

The adsorption of gold from cyanide solutions onto constituents of the reef, and its role in reducing the efficiency of the gold-recovery process by M. R. URBAN. M.Sc. (Chem. Eng.) Rand (Visitor). JILL URBAN. B.Sc. (Chem. Eng.) Rand (Visitor) and P. J. D. LLOYD. Ph.D. (Cape Town) (Fellow) Evidence for the adsorption or re-precipitation of gold from cyanide solutions onto gangue minerals of the Witwatersrand reefs has been gathered over a number of years by various investigators. The evidence from tests using radioactive tracers is conclusive and indicates thlt adsorption contributes about 0,1 g/t to the total gold loss from conventional reduction works. The loss is a function of the alkalinity and cyanide concentration of the solution, and it appears to be affected by the extent of time between milling and cyanidation. The heavy minerals appear to be the strongest adsorbers, and the clay minerals somewhat less strong adsorbers. A sensitive qualitative test based on thin-layer chromatography permits the extent of adsorption and desorption to be readily determined.

By B. W. Wallace

Permitted explosives in South Africa are those explosives approved by the relevant State authority for use in fiery coal mines. The main tests that an explosive must pass for this approval are the gallery tests derived from the Buxton (U.K.) classification. These tests are described briefly. In addition, the safety of permitted explosives is affected by their ability to deflagrate, and to produce a naked flame after blasting, rather than to detonate fully. Tests done on this phenomenon are discussed. A further potential hazard of explosives is after-blast fume. The testing and behaviour of several permitted explosives in this respect are covered, both in the laboratory and in the field. Performance testing of permitted explosives, specifically the double-pipe, underwater, and ballistic mortar tests, and their relationship to field use, are considered in some detail. The application of traditional and new tests to permitted explosives leads to guidelines for the safe and efficient formulation and use of these products.

Jan 1, 1986