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By G. P. Dyke

With the removal of the majority of the shallow mineral reserves there has been an increase in the mining depths in the South African mining industry. This has, in turn, changed the industry?s and stakeholders? perceptions of risk associated with mining-induced instability. In recent years the increased mining depth, particularly in open pits, has led to an increase in pit slope failures, which has highlighted the need for appropriate and effective pit slope management programmes. Such a programme comprises many facets, including mine hazard plans, regular slope inspections, cleaning of interim and final pit faces, blasting practices, histories of failures, pit depressurization, stormwater control and evacuation procedures. However, it is arguably in the field of slope monitoring that the most significant strides have been made in terms of new technologies and best practice in open pit mining geotechnics, with the introduction of technologies such as laser scanners and slope stability radar. This paper seeks to illustrate the operational benefits associated with the implementation of new technologies into open pit mining, using AngloGold Ashanti?s Geita Gold Mine in Tanzania as an example.

Jan 1, 2009

By D. P. Enright, D. D. Howat

Austenitic manganese-steel castings are very widely used in crushing and grinding in the' gold-mining industry in South Africa, The service life of a casting in a short-head crusher is difficult to predict because there are no clear-cut criteria by which such a judgement can be made, The addition of molybdenum and zirconium to the castings for crushers failed to result in improved performance, The results of extensive tests with through-hardened steel castings were very disappointing, mainly because of a design factor in the bowl liner. The design of the bowl liner is an important determinant of the life and performance of these castings. The extent to which the material in a crusher is reduced in size has profound effects on the consumption of metal and power, and on the effective life of a casting. Tests on manganese-steel castings in an 8 ft by 12 ft rod mill provided data on the total consumption of metal, and on the variations in the pattern and rates of wear of liners over lengthy periods. Progressive changes in the wear profiles of the lifter bars and the other liner components showed unexpected features. There are clear indications that, whereas a set of lifter bars will at first lift the charge strongly with relatively little slippage, there is a later period characterized by more slippage and greater wear on all the liner components.

Jan 1, 1980

By P. J. A. Beukes, C. C. La Grange

INTRODUCTION Some years ago the authors proposed a modified procedure1 for carrying out micum index determinations2. The modifications consisted of using a drum of 50 cm internal length, i.e. half the length of the standard micum drum (a modification also adopted by the B.S.J.3), and the use of a + 25 mm coke instead of + 60 mm coke for the test. The proposed modified test and formulae for converting results obtained from it to standard micum test results and vice versa were based on the results obtained during the investigation of about 200 test cokes made in ovens of the South African Steel Industrial Corporation Limited (Iscor), the Fuel Research Institute co-operating with the experiments. Extensive testing of cokes has since been done at the Fuel Research Institute using both the standard and the modified procedures. The numerous test results obtained during this trial period fully support and strengthen the confidence originally expressed by the authors in the modified testing procedure. The scope of the modified micum index determination has in the meantime been extended by applying the testing procedure also to test cokes made in the Institute's experimental coke ovens, and also in this case the modified procedure has proved its usefulness. A difficulty is that when comparing the characteristics of cokes made in the Institute's two experimental coke ovens with each other and with those of cokes made from similar blends in commercial coke ovens, for example those of Iscor, the index values obtained invariably do not check exactly due mainly to inherent differences between the different types of oven4. For instance, resistance to abrasion of a coke made in Iscor's ovens is always appreciably higher than that of a coke made from the same blend (and having a similar moisture content) in the experimental ovens. This makes direct comparisons and the prediction of quality to be expected from commercial products, based on experimental coke oven results, difficult. It may also be added that workers in Great Britain some years ago reported a similar experience5. In the authors' opinion the main reason for the discrepancy is the relatively low height of the experimental ovens resulting in a much lower static pressure on the charge during coking than that obtaining in a commercial oven. The difficulty was pointed out and briefly discussed in a publication4 which appeared at a time when the micum test for coke evaluation had only just been introduced at the Institute, so that only B.S. shatter and abrasion test results were available for discussion in the publication. Needless to say, the introduction of the micum test by no means solved nor even alleviated the problem. On numerous occasions during the past few years the Institute has had to conduct contract investigations in its experimental coke ovens on behalf of companies which invariably desired an indication of the quality of coke likely to be obtained from certain coals or blends when coked commercially, more particularly in Iscor's type of coke ovens. It was, therefore, essential to accumulate statistical data which would enabe the prediction to be readily made. Fortunately the compilation of comparative coke-quality index values for the three types of oven under consideration has become possible as a result of coking investigations conducted in co-operation with Iscor over a number of years. During this period Iscor, on numerous occasions, kindly made available to the Institute portions of coals and blends coked in the Corporation's coke ovens, thus enabling parallel coking tests to be carried out in the Institute's experimental ovens. In this way enough statistical data became available to establish relationships between coking results obtained in Iscor's ovens and results obtained on similar coal charges in the Institute's ovens. The most practical and acceptable method of overcoming the problems of finding a suitable and simple basis enabling direct comparison between the cokes of the different origins mentioned to be made, is the assignment of descriptive arbitrary quality ratings, as indicated below, to the cokes obtained, it being argued that the quality rating assigned to coke made from a given coal or blend in the different coke ovens under standardized conditions should be the same, irrespective of differences in the index values obtained when subjecting the cokes to the usual coke evaluation tests. The system, which should enable the sponsors of coking investigations in the Institute's experimental ovens to make their own interpretations of the results obtained, is explained below. ARBITRARY QUALITY CLASSIFICATION OF COKES The Ml0m index1 (percentage material smaller than 10 mm after the test) of a blast furnace coke is a measure of its tendency towards breeze formation during handling -a low value indicating a low tendency. This is generally of greater importance under ruling South African conditions, than the M'40 index1 (percentage material larger than 40 mm after the test), which can be regarded as a measure of resistance to shatter. In fact, if the M10m value of a coke as made in Iscor's ovens is higher than about 11, the tendency of the coke to form breeze during handling and in the blast furnace is relatively so high that hardly any notice need be taken of its M'40 value, even if this is comparatively high. For this reason, therefore, much more weight should normally be assigned to Ml0m indices in the quality evaluation of cokes made from South African coking coals and blends, as the coals

By P. Sebola, S. Rasmeni, K. Seripe, D. Chetty

"South Africa’s Northern Cape Province hosts semi-precious and gemstone occurrences that are sporadically mined on a small scale by local communities. Tiger’s eye, a gemstone known for its chatoyancy properties, is found in important deposits located near the town of Prieska, where is it intermittently mined. Challenges faced by small-scale and informal mining include mining without proper permits, risky mining practice in dangerous terrain, and illegal export of raw material without concerted effort at domestic beneficiation. As part of a study aimed at job creation and social upliftment in the region, tiger’s eye deposits in the Prieska area were assessed to assist small-scale miners to understand tiger’s eye grades and their distribution. This will allow not only more efficient and safer mining of these deposits, but also beneficiation of the raw product into tumbled stones, cabochons, jewellery, and other small artefacts for sale. A hub established in Prieska by Mintek trains locals in the beneficiation of tiger’s eye. Supply to the hub must make use of a consistent grading system, which is discussed in this paper. Together with proper mine licensing, such an approach will develop mining and beneficiation skills, and create and sustain employment for the local community. IntroductionTiger’s eye is a semi-precious stone known for its chatoyancy property, which is caused by parallel, silicified asbestos fibres that impart a silky lustre to specimens. Deposits of tiger’s eye in the surrounds of the town of Prieska, Northern Cape Province, formed the focus of a study aimed at small-scale mining and beneficiation of this commodity. The Prieska tiger’s eye deposits are located along the N10 route to Upington (Figure 1). Tiger’s eye is unevenly distributed and occurs as lenses of various sizes, interbedded in gently folded metasedimentary rocks of mostly banded iron formation (BIF). The tiger’s eye occurrence in the Northern Cape Province, especially in the Prieska area, has not been extensively researched. There is thus limited information available in the public domain. The lack of knowledge on tiger’s eye distribution has resulted in local small-scale miners adopting a trial-and-error method of mining. Basic geological mapping and field evaluation of the deposit, coupled with professional judgement, are important aspects of any small-scale mining operation and can contribute significantly to the formulation of various acceptable and equally viable mining methods and practices."

Jan 1, 2016

By P. S. Pashkovsky, S. N. Smolanov

The essence of the method consists in creation of drop of opposite sign at the isolating stoppings, by which air losses through the accident district change direction of their motion. The period of reversal is selected in that way so that air may not find itself in the zone of burning. The method of fighting the fire considered was repeatedly used in the coal mines of the Ukraine. The theoretical basis of efficiency and two examples of use of this method by fighting the underground fires are adduced in the paper.

Jan 1, 2003

By F. Shi , D. Lay, C. Antonio

High Voltage Pulse (HVP) technology has the potential to transform traditional mineral processing practice in the mining industry. HVP pre-treatment has been shown to enable ore preconcentration, achieve ore pre-weakening and improve mineral liberation. In order to improve the efficiencies of these novel HVP applications, it is essential to understand how HVP operational factors affect ore breakage in HVP pre-treatment. A two-level fractional factorial experiment using two rock samples, a gold-copper ore and a basalt sample, was performed to determine which factors have statistically significant influences on breakage probability, size reduction, and energy efficiency, and which factors have insignificant influences. Operational factors investigated include applied voltage, electrode gap, number of pulse discharges, the number of rocks being processed per batch, and rock size. In total, 1920 batch tests were conducted. For ore breakage characterised in terms of breakage probability and the degree of size reduction during HVP pre-treatment, the dominant factors were identified to be the number of pulse discharges, voltage, and the number of particles present in the processing zone. As all these three factors are related to the specific energy, it is concluded that the specific energy is the most important factor controlling ore breakage in HVP treatment. In terms of the efficiency by which spark energy is transferred from the generator energy, the factors found to have the most dominating influence were the particle size, the number of rock particles present in the processing zone and the voltage. Increasing the values of these factors reduced the loss of HVP energy during the energy transfer process. The factorial experiment using the two ore samples with vastly different mineralisation produced similar results. This proves that the dominant factors affecting HVP breakage are generally applicable to different ores types. Keywords: High voltage pulse, ore breakage, factorial experiment, specific energy

Jan 1, 2020

By M. -O. Suk, S. -K. Jo, S. -C. Shim, J. T. Kim, S. -H. Kim, C. -W. Seo, J. -S. Kim

An equilibrium study was carried out at 1873 K to ascertain the effect of carbon in CaO-SiO2-Al2O3-MgO-MnO-FetO slag systems on their FetO and MnO activity coefficients, representing the slag?s thermodynamic potential for steel reoxidation. Both ?FetOand ?MnO showed not only a sharp increment, but also a simultaneous slow decrement by increasing carbon content in slag, suggesting opposite roles of the carbon according to its stable forms. XPS (X-ray photoelectron spectroscopy) was introduced to clarify the stable forms of carbon in slag. XPS results prove that carbon dissolves in slag as carbonate, and carbide ions under oxidizing and reducing atmospheres, respectively. It was concluded that carbonate ions increase ?FetOand ?MnO, and that carbide decreases them. This paper suggests an application method of the present results to actual ladle refining processes, in order to enhance steel cleanliness without decreasing (FetO + MnO) content in slag. Keywords: carbon, slag, activity coefficient, FetO, MnO, carbonate, carbide, XPS, reoxidation, cleanliness

Jan 1, 2004

Limestone formations in the United States can be subject to relatively high horizontal stresses due to the existence of tectonic loading of the limestone strata. Underground limestone mines use the room-and-pillar method, in which 12- to 18-m-wide rooms are typically excavated. The stability of these excavations can be compromised by the horizontal stress, resulting in a rockfall hazard. Rockfalls are the cause of 15% of all reportable injuries in underground limestone mines. Horizontal stress related damage can occur in the form of guttering along one or more sides of an excavation, roof beam buckling or oval shaped roof falls, with the long axis perpendicular to the major horizontal stress. Numerical analyses show that the pillar layout and orientation of the mine workings have an effect on the horizontal stress distribution within the roof. The effects of high horizontal stresses can be mitigated by orientating the heading development direction parallel to the maximum horizontal stress, reducing the number of cross-cuts and offsetting the cross-cuts to limit the potential lateral extent of horizontal stress related roof falls. The modeling approach described in this paper can be used as a tool to evaluate potential roof failure and optimize the stability of room and pillar layouts.

Jan 1, 2008

By J. C. M. De Souza

The Samarco pipeline, the longest in the world for iron ore slurry transportation, started operation in 1977 to transport concentrate from the Germano facilities, in the state of Minas Gerais, to the pelletizing plant, located 396 km away, in the state of Espirito Santo, on the south-east coast of Brazil. Designed for a nominal capacity of 12 million tons per year, the pipeline reached 15.5 million/year due to operational improvement and, in late 2005, it was resized to transport 16.5 million tons per year, with the installation of a booster station. In order to ensure the accurate performance of the system, a pipeline cleaning programme was carried out and, since it has been 29 years from the operation start-up, precise knowledge of the pipe condition would be fundamental to guarantee the success of the project. The cleaning programme demonstrated the potential of operational gains from this initiative, and its effect on the corrosion control and future measures, which should be permanently adopted to maintain the improved capacity. The intelligent pig runs provided essential data used to establish a pipeline integrity programme that allowed Samarco to develop a pipe repair plan based on the severity and significance of the features and to implement a future pipe replacement plan.

Jan 1, 2007

By Y. He

The nature of the density distribution in a gas-solid phase fluidized bed for dry coal separation is an important factor in influencing the performance. However, during coal processing, fine slime would mix with dense medium of magnetite powder and accumulate in the bed, and its influence will affect the density of the bed. The mathematical model of the density distribution with fine slime behaviour was studied in an experimental laboratory system. The functional relationship between the density of the air dense medium fluidized bed and the coal slime content were fitted, applying the principle of least-squares method with damping factors. With the model, by analysing the trial testing data, the mechanism of the density distribution of the bed was studied and applied to a coal separation test with a pilot scale separator. Keywords: dry coal separation, gas-solid phase, model fitting.

Jan 1, 2002

By E. J. Magri, D. M. Hawkins

This paper deals with an experimental programme carried out with a gold analyser in the period June to September 1979 at Loraine Gold Mines. The results were found to be reproducible, with no overall or conditional bias when the measurements were compared with those obtained from chip samples. The standard error of estimation of a 3 m reef exposure, which was the sampling interval, can be reduced by a factor of 2,5 if the complete stretch is scanned, rather than the taking of one chip sample in its centre. Complete statistical and computational procedures were developed for the fitting of the normal-Iognormal model to observed analyser data and for the determination of the most likely gold grade for a particular analyser measurement. (This corection procedure is necessary since a significant number of negative analyser measurements can be observed.) Panel averages of uncorrected scans showed a small conditional bias relative to those of corrected scans. However, uncorrected panel averages can be used for on-the-spot decisions regarding whole panels. For standard calculations of ore reserves, use should be made of corrected scans. Under reasonable assumptions, the use of the detector in the selective mining of low-grade narrow reefs such as the Basal Reef at Loraine Gold Mines, when compared with the conventional chip-sampling method, can result in a saving of as high as R40 million in present-money terms over the life of a project. The difference could be even larger in a highly variable reef like the B Reef at Loraine Gold Mines.

Jan 1, 1987

By K. G. Lomberg, M. D. Lionnet

The Bafokeng Rasimone Platinum Mine (BRPM) is a joint venture between Rustenburg Platinum Mines Limited and Royal Bafokeng Resources (Pty) Ltd (Bafokeng). The mining lease has been granted over Boschkoppie 104JQ and is located approximately 10km south of the Pilanesberg Alkaline Complex. The Merensky Reef, which constitutes the principal ore body, is geologically complex. A relationship between its geological variability and the associated mineralisation has been established by defining a number of facies types. The Merensky Reef has been sub-divided into seven distinct facies types: the pegmatoidal facies, contact facies, FW1 pothole facies, FW3pothole facies, FW6 pothole facies, and FW7 pothole facies. The Merensky Reef, which does not form part of the potholed reef, has a large component of footwall mineralisation. The pothole facies, in contrast, has mineralisation located in the hangingwall. Statistical analysis of the facies types indicates that they are unique populations and hence need to be evaluated independently. The mining lease has distinct structural domains that have added additional complications to evaluation of the Merensky Reef. The Merensky facies on BRPM exhibit unique geological and statistical characteristics within well-defined structural blocks. Due to the extreme variability of the Merensky Reef on BRPM a unique approach has been developed, within Anglo Platinum, to evaluate the deposit. Mining cuts are defined and composited for the individual facies types, and then modelled individually by applying known geological controls. The resultant grade models are weighted based on statistical and local geological knowledge. The object of weighting the facies is to replicate the variability observed in the ore body. The introduction of stringent geological controls to the evaluation process has resulted in increased confidence in the in situgrades estimated as an input to the mine planning process

Jan 1, 2006

By R. W. O. Kersten

Backfilling is one of the options available to the mining engineer in mine design. The decision as to the type of backfill is dependent on the purpose for which it will be used. For example, in a situation where high-grade, steeply dipping multiple reefs are to be mined, the purpose would be the following: ? to facilitate maximum extraction; a ? to minimize loss of fines; ? to allow closely spaced multiple reefs to be mined; and a ? to create a working platform. The physical properties required which will satisfy the abovementioned requirements can then be defined; the design of the fill plant, as well as the transport of the fill, will be governed by these considerations. The same procedure is also adopted in deciding on backfill in single- reef gold mines. The first question to be asked is the purpose of the fill. It may be to reduce the energy release rate, for environmental reasons, to reduce timber usage, to improve productivity, to reduce stoping costs, to obtain higher mining extraction, and so on. Only after one, or a combination, of these factors has been selected, can the specifications for the fill be decided on, and the plant designed accordingly. The introduction of backfill at Sheba Gold Mine will be used to illustrate the procedure adopted by Anglovaal in determining the type of fill required.

Jan 1, 1988

By A. Refahi

For predicting the energy consumption during the size-reduction process, the Bond approach is often used. In this work, the PFC3D discrete element method (DEM) software was employed to model the crushing behaviour of some rocks with different mechanical properties in a laboratory jaw crusher. FLAC3D software was adopted to analyze the stress distribution in the rocks. The rocks studied were modelled as granular assemblies in the shape of a sphere and/or a cube located between two jaws, and the work done by the jaws in the crusher was determined. Nine different types of rocks were studied and the energies consumed by the crusher were compared to those of the Bond comminution energy estimated from the Bond index. There is considerable difference between Bond crushing energy and work done by the jaw crusher for rocks. It appears that the Bond approach is not a suitable method for predicting single particle fracture energy done by the crusher. To verify the results obtained from DEM models, the fracture behaviour of the crushed rocks was examined and was compared to the PFC3D results. The tensile mode of fracturing is favourably modelled by the PFC3D software while the delamination mode cannot be well modelled by PFC3D software. Keywords: jaw crusher; discrete element method; crushing energy; Bond index

Jan 1, 2009

By R. M. Göktan

A theoretical comparison is made between point-attack and wedge-shaped picks in regard to their cutting efficiencies in coals having different strength characteristics. With specific energy as a criterion of cutting efficiency, it is shown that a mathematical expression can be derived for the assessment of the relative performances of these two groups of picks as a function of coal-strength parameters and pick-tip angle. The ratio of tensile to compressive strength of coal is found to play a significant role in the determination of relative cutting efficiencies, lower ratios favouring the use of point-attack picks.

Jan 1, 1992

By J. P. Coetzee

Dr. K. Gebhard In his excellent and comprehensive survey on the future development of the Iron and Steel Industry in South Africa, Mr. Coetzee has also mentioned the direct reduction processes as a possible method of converting iron ore to iron. Mr. Coetzee has made it quite clear that at this stage one should not consider these processes as a 'magic formula' which herald a 'break through'. I agree entirely with this point of view. Once upon a time I held the opposite view, but in the meantime I have revised my views. To do so, I had 40 years at my disposal. In 1930 I had the privilege of being connected with the first commercial sponge iron plant in Germany1 - a plant which was capable of producing 40 tons of sponge iron a day. We were determined to prove that the blast furnace would become obsolete in the near future. We considered it as an unnecessary detour to convert iron ore first into an iron-carbon alloy, which contained further quite a number of undesirable elements, and to remove this carbon by an endothermic process. Direct iron-making seemed to be a logical short cut. Unfortunately, we were not able to establish this 'short cut,', but the life of our sponge iron plant was cut short. We had solved all technical but not the economic problems. Basically the positon is still the same today - mainly economic and to a lesser degree technological aspects determine the rate at which sponge iron plants are installed. More has been said and written than done about direct reduction plants. I think that there are two main reasons for this stagnation in the introduction of direct reduction processes. The first reason is that modern blast furnaces are just too good and too economic ever to be replaced by direct reduction processes on a large scale. This, of course, already limits the field of application for direct reduction plants. The second reason is that sponge iron production and utilisation is based on technical considerations, which increase not only the production cost of sponge iron but also the conversion cost to steel to such an extent that under special conditions only are direct reduction plants an economic proposition. Are these technical considerations still as forceful and valid today as they were when 'direct steelmaking' was first contemplated? The development of sponge iron production as a method of direct

Jan 3, 1971

By A. Montini

The problems encountered in the design of control systems for milling cir- cuits when the model of the system and the model parameters are uncertain are discussed. Considering these uncertainty factors has led to the development of a technique that gives a quantitative assessment of real system stability, reveals the trade-offs between performance and stability and helps the designer in deciding what level of model complexity to use in the controller design. Furthermore, it allows for on- or off-line optimization of the milling circuit performance as it provides the base for the design of a controller which is stable over the plant operating range.

Jan 1, 1987

High pressure grinding roll (HPGR) technology is used in an increasingly diverse range of applications, predominantly iron ore , gold and diamonds. KHD Humboldt Wedag HPGRs are applied world-wide, and consistently prove to be well designed and reliable operating units, with their performance meeting the pre-set standards. This publication summarizes some of the features and experiences for recent applications in treatment of copper ore, coarse iron ore, and gold ore. Summary data of roll surface wear life and operating data are given, together with operational observations. In addition, effects of feed segregation and truncated feed are discussed, as well as the implications of a product recycle flow sheet.

Jan 1, 2012

By A. J. Reynolds

In recent years, rapid depletion of the higher grade reserves, allied to decreases in paylimits, has led to the exploitation of secondary, erratically mineralized placer horizons on various marginal and low grade gold mines. On Blyvooruitzicht Mine, the rich Carbon Leader Reef has limited reserves, necessitating exploration of the lower grade Middelvlei Reef. This placer has always presented evaluation and exploration problems, to such an extent that it was, at one stage, considered uneconomic. Despite an extensive underground drilling programme no ore reserve targets of reasonable size were apparent. However, when a certain degree of parallelism between sedimentological trends in the Middelvlei Reef and the underlying Carbon Leader was recognized, a meaningful exploration model could be developed. Firstly, all historical sampling records for the Carbon Leader were entered into a computerized system; the database comprised in excess of 340 000 data points. Variables captured consisted of gold value, uranium value, con- glomerate thickness and total reef thickness. The raw data were then averaged into blocks, and plots of different variables were computer-generated for further analysis. This enabled the Carbon Leader to be modelled sedimentologically and, thereby, exploration targets for the Middelvlei Reef were generated, based on the Carbon Leader facies trends. Geostatistical analysis of sampling data in exposed areas of the Middelvlei Reef underground has confirmed the sedimentological breakdown of the placer into distinct facies areas. A facies model relating value distribution patterns to depositional trends, both for the Carbon Leader and the Middelvlei Reef, has thus been incorporated into a mine planning strategy.

Jan 1, 1987

By A. Cichowicz

The objective of this work is to quantify the effect of the rock mass surrounding a stope or a tunnel on the seismic signal so that the rockburst damage on the excavation can be derived. It has been shown that the transfer function of rock mass surrounding an excavation can be modelled using a damped oscillator. The method of estimating the transfer function is extended in this paper. The parameters of a damped oscillator are estimated using inversion techniques and the transfer function is modelled as a time-varying system. The technique is tested on data acquired at three different sites in two deep gold mines. Employment of a modal model of the transfer function was suitable in two cases. Application of this technique is essential to track the time variation of the natural frequency during ground motion caused by a seismic event.

Jan 1, 1999