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By D. Pohl

The past decade has seen rapid expansion in the West African mineral exploration environment. This expansion has been largely driven by changes in ?Political climate ?Fiscal and legal regimes ?Exploration approaches ?West African geology. Major regional mapping and geochemical surveys by the UNDP, and the BRGM in the late 1970s and early 1980s laid the foundation for the rapid development of mineral exploration and resources during the past decade. An additional driving impetus was the discovery by native artisanal miners of many significant new gold occurrences at Libiri, Essakan, Bouda and Tirahori, during the great droughts of the late seventies and early eighties.

Jan 1, 1998

By M. Olalde, I. Watson

"The consequences of ineffective mine closure in South Africa are evident from the number of abandoned mines and operations on extended care-and-maintenance, the on-selling of mines to less well-resourced companies to close, and increasing illegal mining activities. However, the data to substantiate these observations and provide insight into the underlying issues has not been available. Through the Promotion of Access to Information Act, a list of mine closure certificates applied for between 2011 and 2016 and a list of certificates granted over the same period for all nine regions of South Africa was obtained. From the analysis of this data, we show that the mine closure system as implemented in South Africa is largely ineffective. Although closure certificates are being granted, these are for prospecting sites and small-scale mines, which have a relatively small environmental impact. No large mines of any environmental significance were relinquished over the period under review, with very few applying for closure certificates. Furthermore, the issuing of closure certificates varies significantly between regional offices, with the success rate for applications being generally low and issuing of certificates taking an extended period. IntroductionThere are a number of concerns with the mine closure process as practiced in South Africa, and these have largely been laid at the door of government. Alberts et al. (2017) stress that the legislation generally conforms to international best practice. However, the system is ‘complex and unwieldy’, involving various pieces of legislation and different government departments with overlapping requirements and different interpretations of the law. A further area of concern is the capacity and competence of government to implement legislation. The ‘shortage of relevant mine closure skills and knowledge within the regulator’ was identified by van Druten and Bekker (2017) as a key contributor to unsuccessful closure. Lack of capacity and resources within the regulator has also been highlighted by Botham, Kelso, and Annegarn (2011) and Milaras, McKay, and Ahmed (2014). A recent study of the mineral application process by Corruption Watch (2017) indicates that positions in the regulator have been frozen for many years, leading to a shortage of staff, and that unqualified individuals have been appointed. There is also the perceived reluctance of government to grant closure in order to limit transfer of the liability to the state and delay the inevitable job losses."

Jul 1, 2019

By N. Ogbonna

A mathematical model for bioleaching at the agglomerate scale is developed. The agglomerate is defined as a unit volume of a heap which contains a solid phase (a size distribution of ore particles), a liquid phase (stagnant and flowing leaching solution) and a gas phase (flowing air and air pockets). Leaching at the level of an ore particle is modelled using a diffusion-reaction equation, and oxidation by attached and detached microbes is treated separately. With the aid of the mathematical model, the effect of particle size distribution on the bioleaching of an ore containing a mixture of chalcocite and pyrite, and a culture of iron oxidizers, is investigated.

Jan 1, 2006

By W. Stumpf

Mill log analyses and complementary hot deformation studies were carried out on the as-cast structure and on a hot rolled structure of the same low carbon steel (SAE 1006) that had been processed according to the direct or hot charge route in a compact strip plant. The main softening mechanisms during hot rolling were found to be complete dynamic recrystallization during each pass above about 1000°C for the as-cast structure with an austenite grain size of 277µm and, secondly, incomplete static recrystallization after each pass with a finer austenite grain size of about 26 µm and tested below 1000°C. A two-stage hot working mechanism has also been found by others on a similar steel also processed by the hot charge route and this may appear to be a characteristic of this type of material. Constitutive constants determined from hot working studies were combined with other constants from the literature and incorporated into a grain size development model that correctly predicts the final ferrite grain size in the hot rolled strip steel. The predicted incomplete static recrystallization during the last three finishing passes in the plant appears to result in some retained strain in the hot rolled austenite as it transforms to ferrite on the run-out table. Analyses with the model predict relatively little sensitivity of the final ferrite grain size to process and product variables such as temperature and strain per pass for the last three passes and also the starting austenite grain size in the slab. Keywords: Low carbon steel, hot rolling of strip steel, rolling mill log analyses, austenite grain size, ferrite grain size, grain size modelling.

Jan 1, 2003

By J. M. Richards

For most of the 20th century optical petrography has been the primary petrological and mineralogical tool used to characterize coal. The development of quantitative SEM-based techniques, e.g. QEMSCAN®, for coal began only about a decade ago. The application of these techniques for coal lagged behind other commodities, but they are currently being developed with the aim to provide ?one complete analysis? for coal. Quantitative SEM-based techniques are supplemented by quantitative X-ray diffraction (XRD). Recent indications are that these more modern techniques cannot replace the ?standard? petrographic and chemical evaluations, but rather complement them where and when required. The great advantage of quantitative SEM-based techniques is that they are very rapid, with the result that large volumes of samples can be processed on a routine basis. This is ideal for coal type identification, since the results can be used in the creation of ?intelligent? composites. This can lead to the more speedy evaluation of coal deposits by reducing the number of samples on which detailed metallurgical and characterization test work is required, without an increase in the overall statistical error of the resource model. Coal petrography, however, remains important for the prediction of the coking characteristics of certain coals and coal products. As a consequence it is therefore important that any coal laboratory be able to produce data with confidence. This requires strict quality control and assurance protocols that adhere to international standards. Keywords coal petrography, coking strength, scanning electron microscopy, QEMSCAN®.

Nov 1, 2013

By John E. Leitch

The cost of corrosion as measured by such cost components as the renovation or replacement of coated steel, or the use of expensive coating systems on steel, is considerable. Extrapolating from figures for the USA would place the overall cost of corrosion for South Africa as a figure of the order of magnitude of something over 1% of the GNP. This is a sizeable amount, of which costs associated with atmospheric corrosion would be a significant proportion. The corrosivity of an atmosphere can be defined as the ability of the atmosphere to cause corrosion in a given metal or alloy (International Standards Organization [1]). The ISO Standard 9223 specifies the key factors in the atmospheric corrosion of metals and alloys, and defines categories of corrosivity on the basis of these factors. Prior to the publication of that ISO standard, Callaghan published the results of his twenty-year exposure programme and his excellent corrosivity map of Southern Africa [2]. The present author published updates of the corrosivity map in 1999 [3] and again in 2003 [4]. The summary of the individual areas of corrosivity around Southern Africa was published in the latter paper, and is reproduced here as the following TABLE 1. Of significance in TABLE 1 are the numerous regions of very high corrosivity (C5 or beyond), particularly the rural West Coast shoreline, the North East Coast (KZN) shoreline, and the coastal cities Cape Town, Durban and Richards Bay. The corrosivity map as published is obviously based on much extrapolation as only a small number of points have been measured. During the past three years further measurements have been made, mostly however at the same sites in order to give greater reliability and to monitor long-term trends with changes in pollution. These two aspects are incorporated in this update. There has become available a greater amount of air pollution data for centres in South Africa than was the case some years ago. In this present paper the pollution data are used to extrapolate the corrosivity over areas where little or no direct corrosivity measurement has been made. This methodology is described in ISO 9223.

Jan 1, 2006

By Du Sichen, K. Mukai, S. Seetharaman

Viscosities of slags constitute an important physical property needed for an understanding of the mass transfer phenomena in metallurgical processes. Viscosity is also the key that leads to a better understanding of the structure of slags. It is well known that the viscosities of silicate slags decrease with the addition of basic oxides due to the breaking of the silicate network. The measurements of slag viscosities often pose experimental challenges, especially to the choice of materials. The keynote lecture takes up the experimental problems and the various techniques adopted. Dynamic viscosity measurement, as a powerful tool towards an understanding of the kinetics of some high temperature reactions, is brought out. A number of semi-empirical models have been developed to estimate the slag viscosities in the case of multi component slags. A critical survey of these models is presented in the lecture. Earlier models by Riboud et al., Urbain et al. and Mills et al. have been developed further into a new generation of models. Some of the current important models are (1) Model by Iida et al. (2)CSIRO model (3) Pyro research Model (4) Model by Tanaka et al. (5) Model approach by Reddy et al. and (6) KTH-model. The predictions and capabilities of the various models are compared. Estimations of viscosities from thermodynamic data and prediction of liquidus temperatures from viscosities are presented. The concept of surface viscosities with reference to slags and viscosities of two-phase mixtures are also taken up in the presentation.

Jan 1, 2004

By S. Kamalpour

It has been observed that the productivity of ferromanganese furnaces, and the stability of metal and slag compositions, vary considerably according to the type of coke used as reductant. However, the desired properties of coke for optimum furnace performance are not well understood. In this investigation, the behaviour of four cokes, which exhibited a wide range of performance in ferromanganese production, was investigated by means of laboratory simulations of reducing conditions in the furnace. The Stationary Charge in Controlled Environment (SCICE) technique was used to simulate the conditions in the furnace shaft. Batches of raw materials, mixed in the same proportions as used in practice, were heated at fixed rates to 900, 1100 and 1300°C then cooled. The mass loss was used as a measure of the degree of reduction. Conditions in the lower part of the furnace were simulated by means of melt-reduction experiments in which lumps of coke were drilled out to form crucibles in which enriched ferromanganese slags were reduced at 1500 and 1550°C then cooled. An examination of the raw materials and the cooled, reacted charges using a variety of analytical and characterization techniques enabled the sequence of reaction and changes in morphology of the raw materials to be followed. This enabled an understanding of the behaviour of the cokes during reduction to be developed, which was then used to explain the observed performance of the cokes in practice. By relating the observed behaviour of the cokes in the laboratory tests to measurable properties of the unreacted cokes and to their observed performance in practice, it was shown that to achieve high productivity and good furnace performance, cokes should be selected to have moderately high reactivity towards CO2 (Boudouard reactivity) relative to conventional iron blast furnace cokes.

Jan 1, 2004

By B. Das

he flotation studies on hematite were carried out using di (2-ethylhexyl) Phosphoric acid (D2EHPA) as the collector. The possible mineral reagent interaction was studied through electrokinetic and dissolution studies. The shift in zeta potential (PZC) and decrease in dissolution of iron in the presence of D2EHPA indicated that D2EHPA was specifically adsorbed on hematite surface. The adsorption imparted necessary hydrophobicity for flotation of hematite. Hematite could be floated selectively from hematite and quartz synthetic mixture. Key words: Hematite, D2EHPA, flotation, electrokinetics, dissolution.

Jan 1, 2003

Application of Gy?s formula is appropriate for calculation of the Fundamental Error (FE) prior to samples being collected at any stage of the minerals process, provided that sampling parameters K and a (alpha) have been determined by calibration of the ores. Two types of calibration procedure are well established in the industry, the Hetrogeneity test and the 32-piece sampling tree experiment. The sampling tree experiment uses the variance and average grade of metal analyses from four series of samples at different nominal fragment size, as the basic input data. Pierre Gy suggested the cube as an appropriate exponent of the nominal fragment size for use in his equation. More recent work suggests that this exponent is variable and characteristic of specific ores and therefore requires calibration. The method described here explains the experimental procedure of the calibration. It is then possible to calculate a sampling nomogram using the sampling parameters K and a. This allows the sampler to determine a suitable protocol for the sampling event that will ensure that the FE does not exceed a predetermined precision at any point in the sampling procedure.

Jan 1, 2007

By M. C. Bhulose

Paper written on project work carried out in partial fulfilment of B. Eng (Mining Engineering) degree The purpose of this project was to identify constraints that could occur in the current sub-decline shaft at Turffontein Shaft should an increase in production take place. Particular attention was to be paid to the transportation of men and materials and to the broken rock and ventilation capacity of the shaft. This project is an in-depth evaluation of the logistic capacity of the sub-decline system at Turffontein Shaft in order to determine by how much production can be increased in this area to replace tonnages from the vertical shaft area, where ore reserves are rapidly becoming depleted.

Jan 1, 2004

By V. Mathebula

Paper written on project work carried out in partial fulfilment of B. Tech (Mining Engineering) degree The purpose of this study is to establish whether to mine the Bottom of Pit (BOP)/TOB 4 reserve before the commencement of the Block Cave or whether this should be disregarded and the reserve be extracted at the end of the life of the Cave. The primary goal of this report is to investigate and propose a practical mining method to safely extract the reserve given the set constraints. This report quantifies the additional revenue the TOB 4 will contribute to Finsch?s overall NPV thus enhancing Finsch?s business case and strategically enhancing the SBP. Several underground mining options have been investigated. The proposed mining method includes the installation of a series of extraction tunnels below the TOB 4 reserve from 53 level, with a slot access tunnel system. Ground will be loaded by LHDs from the draw points and tipped into 50-ton dump trucks at a transfer point, from there the ground will be transported to 53 level No. 1groundpass where it will join the existing ground-handling system. Primary development is scheduled to begin October 2002 and last for a period of approximately 7 months until early April 2003.The production is broken into 4 phases. Phase 1 is scheduled to begin mid-April 2003. The final production phase will be completed by November 2005. The production scheduling has been designed in order to remain ahead of the Block 4 undercut in order to ensure stability and safety. Due cognisance was taken of the health and safety of all employees concerned during the design of the mining and ground-handling processes for the Bottom of Pit. As far as is reasonably practicable, the BOP was designed and will be constructed and equipped to provide conditions for the safe operation of machinery and a healthy working environment for people underground. Relevant requirements of the Mine Health and Safety Act regulations pertaining to mining operations have been identified and adhered to during all phases of the design process.

Jan 1, 2004

By M. Q. W. Jones

This paper summarizes important features of a compilation of thermal properties of stratified rocks from Witwatersrand gold mining areas. The database consists of more than 1000 thermal conductivity measurements, more than 700 density measurements, and nearly 100 heat capacity measurements. Most important rock types and stratigraphic units are well represented. Heat capacity does not differ significantly from one rock type to another, and density is relatively uniform although particular rock types are characterized by distinct average values. Different rock types also have distinct thermal conductivities, but this parameter varies by a factor of four to five. Primary factors controlling the thermal properties are mineral composition, degree of metamorphism, and porosity. In addition, the temperature dependence of thermal conductivity and heat capacity of quartzite may significantly decrease the thermal diffusivity of this rock at deep mining levels.

Jan 1, 2003

High pressure grinding technology has gained further interest in various industries. So far in the mining industry, machines are in operation in diamond mines and iron ore applications. In gold and copper ore processing, test work has been conducted showing considerable operational and process benefits. Similar benefits can be expected from HPGR applications in the platinum industry due to the preferred ore breakage along grain boundaries, thus liberating the PGE particles. This paper will provide an update on the state of high pressure grinding roll technology. Developments in the design of high pressure grinding rolls, for minimized maintenance requirements and availability just as high as conventional mills, will be presented. Plant flow sheets and concepts will be discussed, which allow for a reduction of capital and operating cost in comparison to existing two-stage milling circuits.

Jan 1, 2004

By H. J. Glass

Collection, preparation, and analysis of blasthole chippings is expensive. Frequently, interpolation of grades at unsampled locations is considered using techniques like kriging. A pre-requisite for kriging is that an experimental variogram is established. In order to assess the quality of the experimental variogram, a measure is developed in this paper. The measure is derived from analysis of the time-honoured expression relating the variance, semivariance, and covariance. It reflects the weighted average deviation of the summed semivariance and covariance from the biased variance. The proposed measure allows assessment of the influence of key variables on the quality of the variogram. Using simulated data, it follows that the quality improves with an increasing number of samples, increasing density of the sampled locations, increasing regularity of the sampling pattern, and increasing uniformity of grades in the absence of correlation. Application to real data shows that the minimum number of samples could coincide with a marked decrease in the value of the measure. Establishing a threshold value is subject to further research. Keywords: variogram, variance, covariance, semivariance, minimization, sampling.

Jan 1, 2003

By J. Chirasha

Keywords: Pyrometallurgy, ferrochrome, smelting, investment, Zimbabwe Four smelting plants currently make up the ferrochrome smelting capacity in Zimbabwe. Zimbabwe Alloys and Zimasco represent more then ninety per cent of Zimbabwe?s ferrochrome smelting capacity, while Maranatha and Oliken contribute the difference. Very limited investment in the sector (even for the expansion of existing smelters) has been experienced over many years, despite the fact that about 95% of the world?s chrome ore resources are in the Bushveld Igneous Complex of South Africa and the Great Dyke of Zimbabwe. The Bushveld has a greater quantity but a lower grade than the Great Dyke. A ten per cent increase in Zimbabwean ferrochromium production has been recorded in the past ten years, showing an almost stagnant capacity investment.

Jan 1, 2011

By M. K. Roberts

The approximately 2800 Ma old Ventersdorp Contact Reef is a unique Witwatersrand orebody, from which about 6% of the world?s gold production is derived. A major portion of this production is mined at depths exceeding 2500 m and deepest levels of mining are at about 3600 m. The orebody?s hangingwall consists of volcanic rocks. This differs from the older Witwatersrand orebodies, which have quartzitic hangingwalls. The thickness of the Ventersdorp Contact Reef is generally about 1.20 m, but is highly variable, at an average dip of about 18°. A pronounced unconformity beneath this orebody is also expressed by varying footwall rock type characteristics and frequent rolling of the reef plane. These rolls follow topographic variations of the palaeo-surface. More geological than rock mechanics studies were performed on the Ventersdorp Contact Reef prior to 1992. Recently, however, a multidisciplinary team comprising various rock engineering and geological disciplines has delineated geotechnical areas by a novel technique. Geotechnical areas are defined by distinct footwall/hangingwall rock assemblages. The presence of three footwall and two hangingwall rock types results in the definition of six geotechnical areas across a distance exceeding 60 km, including about 10 gold mines. Distinct rock mass behaviour has been documented in three of the six geotechnically defined areas. Different rock mass behaviour is expressed by features such as mining-induced fracturing, closure rates, fall of ground characteristics and seismic character. Some geological features override the rock mass behaviour as defined for the individual geotechnical areas. These are undulations of the orebody or the frequency, characteristics and attitude of major discontinuities. It is concluded that the concept of geotechnically subdividing orebodies is not only important for facies delineation and the associated grade, but also needs to be considered for safety aspects, in determining factors such as the appropriate support to be employed.

Jan 1, 1999

By G. Lyman

The cross-belt sampler is a device that is very widely used even though it has not been ratified by the Standards associations. This paper is concerned with the bias testing of two cross-belt sampler designs against stopped belt samples and a cross-stream cutter at the belt end. The bias analysis is carried out using size distribution as the analyte and conventional t-testing and the Hotelling T squared test, which are compared for their effectiveness. The paper considers the issue of detectable bias and the statistical planning of bias tests.

Jan 1, 2010

The AMIRA Code of Practice and Guidelines for Metal Accounting was developed in response to demand from a number of sponsor companies, including one major platinum producer. Since its publication in 2007, the Code has become widely accepted in the mining industry world-wide as a guide for best practice in metal accounting. With the changes in the structure of the platinum mining industry in South Africa over the last 10?15 years, in particular, the starting up of a number of small platinum producers who must have their concentrate smelted and the contained valuable metals refined by third parties, the need for metal accounting systems that are accurate and have an acceptable level of precision has become even more critical to the success of a platinum-producing operation. The current state of metal accounting in the industry is discussed, and possible areas for improved accounting and associated metallurgical efficiencies are identified.

Jan 1, 2013

The extraction of minerals and coal at greater depth, employing higher-powered machinery to improve production levels, imposes an increased burden on the ability of a ventilation system to maintain an acceptable mine climate. Hence, mechanical mine cooling systems are often adopted, which can be expensive in terms of both their associated capital and operating costs. Consequently, in order to optimize the total mining costs, it is essential to provide the mine operator with a method with which to determine the most cost effective and efficient mine cooling system. In a previous paper1a novel energy analysis employing the concept of exergy was proposed and applied to cooling systems applied to two conceptual model mines, representative of UK deep coal operations, and their resultant subsurface thermal environ-mental conditions predicted. This paper presents an analysis of the results obtained from the application of this novel technique to assess the performance of various cooling systems applied to a current UK colliery that is experiencing climatic problems due to its depth and highly mechanized production and development workings. To perform this analysis, ventilation and climatic data collected at the case study mine were used to construct balanced mine ventilation and climatic network models to replicate the subsurface environment. Where air conditions exceeded specified climatic limits within identified climatically control zones, mechanical mine cooling systems were employed. A number of cooling system configurations were applied to these model to investigate the potential to satisfactorily regulate the thermal environment. The heat energy transferred out of the air stream by the various cooling methods was absorbed using a variety of chilled water systems, which were designed to operate at various water flow rates and temperatures. Models of various cooling system were developed and applied to control the underground climate within this mine network to within pre-set climatic limits. The results of a comparative analysis of the energy transfers that were produced by the application of the different cooling systems are presented in the form of exergy performance indices. The results produced by simulation models constructed to represent chilled water distribution networks to supply the various air coolers, are designed and balanced. The results of the exergy analyses applied to the operation of the various chilled water pipe networks are discussed and used to assess the exergetic performance of the application of each proposed cooling system to the mine ventilation network.

Jan 1, 2004