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By H. S. Sichel, Kleingeld

A frequency distribution model plays a fundamental role in ore evaluation, especially for the feasibility study of new deep gold mines. The geological complexity of the reefs being mined at present in the Witwatersrand basin poses some difficulties regarding the modeling of the underlying ore-value distribution. This geological complexity has given rise to a need for more applicable distributional models. This paper places the geology of the Witwatersrand basin in perspective and draws some important conclusions from the genesis of the deposition. In addition to the three-parameter lognormal model, two more-general distributional models are proposed. These are the compound lognormal (CLD) and log-generalized inverse Gaussian (LN-GIG) distributions. A detailed, although preliminary, comparative study of these two more-general models with the three-parameter lognormal model is described, and the efficiencies of the estimates and modeling are analysed. It is found that the broad assumption that gold grades follow a three-parameter lognormal law is not always the case, and the need to test for departures from log normality should be emphasized so as to ensure the use of appropriate models.

Jan 1, 1992

By A. Koursaris, H. M. Friede, A. A. Hejja

The features of smelting slags from South African prehistoric sites and of related cinder material are described. Chemical analyses of twelve slag samples found in the Transvaal, Swaziland, and Botswana are reported and discussed. An attempt is made to establish a relationship between these slags and the ores collected at the Early Iron Age site of Broederstroom, which date between AD 350 and AD 600. The liquidus temperatures of29 slags were determined by the use oh hot-stage microscope. The major mineral phases of 16 slags were identified by X-ray diffraction and microscopic examination. It appears that the slags investigated were formed at temperatures below 1250°C or - in some cases - at temperatures only marginally in excess of 1250°C.

Jan 1, 1982

By M. J. U. T. Van Wijngaarden, A. T. Pieterse

An account is given of the performance of a 37 MVA electric-arc .furnace in which bottom stirring with inert gas by an indirect-contact stirring-plug system was applied. The system, which was developed and patented by Thyssen-Stahl AG, and which is the first inert gas stirring system to be installed in South Africa, was commissioned in January 1992. Initial problems were experienced due to the blockage of stirring plugs by molten steel. The causes of these malfunctions are examined, and an account is given of how they were overcome. The system is described and evaluated. A comparison with direct-contact stirring systems shows why Iscor Vereeniging Works considered it to be more suitable for their Vaal Melt Shop. The results show that, through the successful application qf this technology, Iscor Vereeniging Works has achieved an annual cost saving of more than R2,5 million.

Jan 1, 1994

DECEMBER, 1971 The Wanders Club, Johannesburg Sunday, 9th April, to Friday, 14th April, 1972 The Tenth Symposium which is the first ever held outside the North American continent is being organised by the South African Institute of Mining and Metallurgy (with the South African Council for Scientific and Industrial Research and the South African Council for Automation and Computation), in collaboration with the previous co-sponsors. '" The programme includes over 60 papers from thirteen different countries. Attendance promises to be good and interested parties who have not yet registered are earnestly requested to do so without delay. The closure date for registration application is 31st January, 1972. The objective of this symposium is to pool experience and knowledge and to discuss new and potential developments for the planning and control of mineral projects. The papers which are to be presented will indicate the progress which has been made in this direction through the successful application of operations research, mathematical, statistical and computer methods. The intention is to bring together those persons responsible for managing various operations in the mineral industry with those engaged in the development of such mathematical and computer techniques as could assist this management. All interested parties are welcome. PRE-REGISTRATION (please return enclosed form as soon as possible). Applications for registration close on January 31, 1972. The fee payable on application will be R70. Late applications may, subject to vacancies being available,

By B. Strohmeier

The role of large, ultra-high-powered arc furnaces in a fully integrated steelworks for the production of flat products is outlined, and an account is given of the technological improvements that have been implemented over the past few years to enable the arc furnace to remain competitive against the conventional route using blast furnaces and top-blown-oxygen steelmaking (LD). Modern secondary refining facilities have been installed, enabling the arc furnace to operate at high production rates in the manufacture of high-quality flat products.

Jan 1, 1985

By S. J. Bluhm

Recommendations are given for the design of multi-stage spray chambers in which air flows horizontally through water sprays. A detailed description is given of one such spray chamber at Hartebeestfontein gold mine that is used for bulk cooling of the incoming ventilation air, and that has been constructed according to these recommendations. A method for predicting the performance parameters of horizontal multi-stage spray chambers is given, and the method is illustrated with some examples. The method is equally applicable to spray chambers in which the water, rather than the air, is cooled.

Jan 1, 1979

By E. J. Margi

Deep gold exploration such as is used for Witwatersrand gold deposits is both expensive and time-consuming. This paper provides quantitative guidelines as to the economic optimum number of boreholes and deflections within each borehole for a certain reef characterized by its variability pattern and depth below surface in order to maximize the level of confidence for a fixed drilling budget or to minimize the total drilling cost for a given level of confidence. Portions of the Basal, Vaal, and Elsburg Reefs that show a wide range of variability (sample logarithmic variances of 0,63, 1,05, and 2,06 respectively) are examined at depths below surface ranging from 1000 m to 4000 m over a simulated mining property covering 7000 ha (7000 m by 10000 m). It is concluded that four intersections per borehole are optimum in al the cases considered, which cover the majority of current Witwatersrand exploration, with the exception of the highly variable Elsburg Reef at depths of 1000 m and 2000 m, where boreholes with one and two intersections respectively should be preferred.

Jan 1, 1987

By E. H. van Niekerk

The production of high-strength Iow-alloy (HSLA) steels containing either niobium or vanadium as the principal micro-alloying element is discussed, including recent developments in steelmaking practice that have had a great effect on the development of HSLA steels; strengthening mechanisms, as well as the principles of thermomechanical treatment during controlled rolling on a hot-strip mill; and the results of production heats with various amounts of micro-alloying elements.

Jan 1, 1984

By H. H. Bird

The crux of reliable estimates of ore reserves lies in a comprehension of the related geological events and their controls on the formation and distribution of the economic mineralization, and on the rock types, lithology, and structures. Furthermore, mine geometry is based on the shape of the ore body, the types and distribution of the economic minerals, and the ground conditions. Asian mining The Institution of Mining and Metallurgy has been invited to organize an international conference on the occasion of the Asian mining 81 international exhibition.

Jan 1, 1980

By R. R. Mankowski

The work described here attempts to underscore the importance of the time lag between the end of a loading phase and the instant a winding drum begins its acceleration phase. Traces generated from a computer-simulation model show that the amplitude of the stress oscillations occurring in mine hoisting cable during the constant velocity-of-ascent phase is a direct result of the temporal sequence employed between the loading and the raising phases. While current and early literature indicates that extensive work has been undertaken on the isolated effects of these two independent sequences, the literature does not appear to contain any documented evidence to suggest an optimal control or interfacing between these two dynamic regimes.

Jan 1, 1995

By G. W. Healy

The smelting of calcium carbide has always been plagued by eruptions, too often with serious injury y or loss of life. To find their causes, the author calculated an internal energy balance using 1992 data for CaC2 and CaO, and older data for the remaining items. The heat content of the charge, and that of the hot gases formed at the reduction temperature, showed that only a fraction of its heat content can be supplied by these gases. Laboratory data on the electrical resistivity of fine mixtures of coke and non-conductive solids were extrapolated to a commercial carbide charge, and then used to calculate the heat produced by current flowing through the mix from the electrode surface to the hearth, which, under favourable conditions, sufficed to bring the charge to 1900 K and higher, at which temperatures reduction could take place.

Jan 1, 1995

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.

By S. R. Xie, S. Gong, E. P. Li, S. S. He, Y. J. Sun, S. J. Li

"Based on the complicated geological production conditions and abnormal strata behavior of the fully mechanized caving face No. 102 in the Xinyang Coal Mine, we analyze the breaking and forming process of distinguishing key block structures in close spaced coal seams. This analysis establishes an integrated mechanical model of these distinguishing structures. Furthermore, the horizontal force TAB generated by downward key blocks A and B is quantified, as is the Pressure PG exerted by key block B on caved gangue. Finally, the interaction mechanism is revealed. Analysis of the results using Mathematica reveal the following: 1. Both TAB and PG exhibit approximately inverse relationships to coal pillar width b; 2. TAB exhibits an approximately exponential relationship with mining height M of which the base is greater than 1; 3. PG exhibits an approximately arctangent relationship with mining height M. Combining these results with field observations, we conclude that the area in the vicinity of supports 100#–120# in the upper area of working face No. 102 is the likely zone of abnormal strata behavior. Thus, this area was classified as a key control area. Based on these results, the graded support control technique is proposed. Application of this technique in the field resulted in a reduction in the rate of hydraulic support system malfunction from 47% to 7% in the key control area. In addition, during times of periodic mining pressure, the roof caving height value never exceeded 0.3 m and the maximum spalling depth never exceeded 0.2 m. Overall, the results indicate that this new technique has markedly increased the stability of surrounding support rock material. IntroductionClose-spaced coal seams are widely distributed in China, and mining proceeds from the uppermost to the lowermost seam (Zhang et al., 2008). In the case of coal seams in close proximity, a particular set of risk factors becomes pertinent. These include disturbance of lower seams during the mining of overlying ones and the decrease in mechanical stability of lower coal seams following repeated movement of key blocks in main coal seam roofs. This inevitably results in behaviour such as heavy wall spalling and support damage to fully mechanized caving faces in lower-lying coal seams, which necessitates a significantly increase in the measures to support surrounding rock material (Zhang et al., 2010; Huang et al., 2013; Xie et al., 2013)."

Jan 1, 2016

By T. G. Maepa

"The creation of mine excavations alters the stress distribution in the surrounding rock mass. In modern mining, resin-grouted rockbolts are used as a means of support in order to redistribute stresses and reestablish equilibrium in the rock mass. The success of resin-grouted rockbolting depends on the design of the system and the correct installation of the support units.The support design and rockbolt installation procedure at a platinum mine in the Bushveld Complex were investigated. A number of issues that resulted in poor installation were identified, including resin admixture, incorrect length and orientation of support holes, over- or under-spinning of the resin, and incorrect rockbolt tensioning. The support design used at the mine was reviewed and its limitations identified. A number of recommendations were made for optimizing the support design by reducing the diameter of the drill bit and reducing the length of the support holes. These changes will enable the mine to use different combinations of resin capsules. Implementation of the proposed changes will lead to a significant reduction in the cost of installation per support hole, as well as improve productivity and safety.IntroductionThe creation of any mine excavation disturbs the virgin state of stress in the Earth’s crust. This results in stress concentrations that interfere with the stability of the rock mass surrounding the excavation. It is essential to modify the internal behaviour of the rock mass surrounding excavations in order to reinforce the ground and stabilize excavations. Resin-grouted rockbolts are extensively used for this purpose. Esterhuizen (2014) stated that when effectively installed, the rockbolt exerts a clamping force and a bonding strength that keeps the rock mass together. This increases the cohesive strength of all discontinuities in the rock mass and enhances the stability of the excavation. Poorly designed and installed ground support is ineffective and constitutes a safety hazard. It is therefore crucial for every mine to ensure that any form of ground support is designed and installed correctly. This research evaluates the installation of resign-grouted rockbolts and identifies challenges and solutions for improved safety as observed at an operating hard rock mine. The support design used at the mine was reviewed and the design parameters optimized. The outcomes will enhance the efficiency of support and minimize the costs associated with the installation of resingrouted rockbolts."

Jan 1, 2017

By J. Abdollahisharif

Optimal cut-off grade is one of the most critical parameters in open-pit mine design because it defines the ore and waste and thus determines the maximum net present value possible from the mining operation. Although the algorithm presented by Lane (Choosing the optimum cut-off grade. Colorado school of Mines Quarterly, vol. 59, no. 4, 1964. pp. 811-829) is the most common one in the literature, it does assume constant capacities of the mine, processing, and refinery. In this paper, Lane's original algorithm has been modified to consider variable processing capacities in order to determine the optimal cut-off grade in open-pit mines. The new algorithm proposed here is compared to both Lane's original algorithm and to a previous modification that incorporated rehabilitation costs into the cut-off grade estimation. The algorithm proposed here that permits variable processing capacities is shown to be superior for the determination of optimal cut-off grade to both these previous versions. In addition, a computer-based program was developed in Microsoft Office Excel© to calculate the optimal cut-off grade as proposed here.

Jan 1, 2012

By S. A. Abdel Sabour

Strategic decisions in the mining industry are made under multiple technical and market uncertainties. Therefore, to reach the best possible decision, based on information available, it is necessary to integrate uncertainty about the input variables and model financial risk of the project?s merit measures. However, this provides few useful insights to decision-makers unless accompanied by modelling management responses to uncertainty resolutions. It is widely acknowledged that conventional decision-support methods based on static, no-change, discounted cash flow (DCF) techniques such as net present value (NPV) and internal rate of return (IRR) tend to provide inaccurate value estimates. This could mislead the strategic decision-making process and result in significant value losses. This paper aims to model financial risk related to uncertainty about market variables such as metal prices and foreign exchange rates. Other sources of risk that are related, for example, to geology and production costs are not considered in this work. The article outlines a flexible financial model that integrates uncertainty about market variables and management flexibility to react to uncertainty resolutions into mine project valuation using a real-options valuation technique based on Monte Carlo simulation. Significance of information generated from this simulation-based flexible valuation model to the strategic decision-making process is tested using an illustrative case study of a Canadian mining project. The project is a typical multi-metal, open pit mine that produces copper and gold. In this case, there are three uncertain market variables, which are: copper and gold prices and US$/CAN$ exchange rate. Financial valuations are carried out using both the conventional static DCF method and a flexible real-options model. In the flexible model, management flexibility to decide whether to go ahead with the next expansion or terminate production operations is integrated. Results show how the flexible financial model can enhance the decision-making process.

Jan 1, 2009

By V. E. Ross

A computer program was developed that incorporates a novel analysis of the behaviour of the froth in full-scale cells to predict the performance of the froth over a wide range of operating conditions. The program has the distinct advantage that it can be easily implemented on a microcomputer, which allows rapid computation and processing of the results. The program utilizes experimental data obtained in flotation-plant and laboratory testwork to provide parameters for the froth model under an initial set of operating conditions. These parameters can then be used in conjunction with a model describing the transfer of material from the pulp to the froth to predict the performance of the cell when its dimensions and operating variables are changed during scale-up.

Jan 1, 1987

By D. E. Kraushaar

Ruhrkohle in West Germany evaluates and compares the net present values of long-term periods from its coal mines by a computer assisted long-term planning system. Two main parts of this system are computer programs for the prediction of: (a) mineable reserves and their distribution in longwall panels as a function of dependent geological variables; (b) daily outputs and costs of longwall panels as a function of dependent geo- logical, layout and operational variables. This paper describes the investigations, which ended in the above computer programs: ? the collection of information from past workings and their organization in databases; ? the statistical evaluation of the databases, and ? the resulting correlation formulas. The correlation formulas vary the mean dependent variables as a function of independent variables which can be indicated with high reliability for planning projects in the long run. The system thus serves the purpose of facilitating long-term planning and excluding biased individual judgement of local planning staffs.

Jan 1, 1987

By P. F. Ledwaba

"Artisanal and small-scale mining (ASM) in South Africa received official recognition after the change in government in 1994.The Reconstruction and Development Programme (RDP) recognized the sector as a vehicle for social and economic development for historically disadvantaged South Africans (HDSAs) who had previously been excluded from participating in the mainstream economy. Having recognized the ASM sector, government introduced several interventions and support structures to foster the development of ASM, to encourage participation of HDSAs, and to address challenges facing the sector. The objective of this paper is to assess the progress made, with particular regard to challenges in the sector. The paper focuses on the policy requirements that were deemed important for the growth of the ASM sector by the White Paper on Minerals and Mining Policy (1998). These can be collated into five categories: access to mineral rights, access to finance, access to markets, technology and skills, and institutional support. The paper provides a review of the support interventions, their intended roles and impact on the sector, and identifies existing gaps and possible ways of dealing with the challenges. There is a need for research to assess the real impact of these past and existing interventions on the ASM sector to draw lessons for future development.IntroductionThe significant rise in artisanal and smallscale mining (ASM) activities worldwide has led to many countries recognizing the sector. ASM takes place in approximately 80 countries (World Bank, 2013). It is estimated that the sector employs between 20 and 30 million people around the world (Buxton, 2013). This compares to between 3 and 3.7 million in 1999 (International Labour Organization, 1999). ASM activities are widespread, occurring mostly in developing countries in Africa, Asia, Oceania, and Central and South America (World Bank, 2013). There has been a significant increase in the number of people participating both directly and indirectly in the sector and this is expected to continue given the socio-economic realities of most developing countries. High levels of poverty and unemployment and growing inequality continue to be largest problems facing the majority of developing countries today. The ASM sector plays an important role as a source of livelihoods, particularly for those residing in rural areas with limited economic opportunities. In the majority of countries, the recognition of the ASM sector was driven by its increasing contribution to socio-economic development through job creation, poverty alleviation, and rural development. In response, a number of intervention strategies were introduced in support of the sector to address its negative impacts and to increase its potential benefits."

Jan 1, 2017

By D. P. Power

The development of an accounting code for the metallurgical industry has been debated for many years. Following the series of tumultuous economic events in the nineties and earlier this century that have affected business, there was much need for legislation to be passed to minimize potential risk. One of the consequences to affect the mining industry was the enhancement of existing geological codes for reporting. In parallel the sponsors of AMIRA have taken the brave step to develop a generic code for metal accounting that embraces the full gamut of industry. In this paper the code will be reviewed in the context of metallurgical accounting as it applies to coal preparation. This paper provides the background for this development and an insight into the mechanism for the debate for the generation of this code. The key elements of the code as it applies to the coal industry are explained but most importantly the key opportunities are highlighted.

Jan 1, 2010