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By A. G. Royle

The reasons for constructing a model of an orebody for which both the parent population and the sampling distribution are known are discussed and details of the model are given. A brief summary of Matheron's theory of regionalized variables is included, with particular reference to his kriging estimators and their variances. Using the model, a comparison is then made between these kriging estimators and other commonly-used estimators. These are compared to find the one with the minimum variance, and an analysis is included to investigate whether any of the estimators is biased. Also included is a comparison between theoretical and experimental variances for some of the estimators.

Jan 1, 2014

The modelling of lithological domains is a critical step in mineral resource and reserve evaluation. Deterministic models rely on an interpretation of the available drill hole data and expert knowledge, but do not account for the uncertainty in the spatial extent of the lithological domains. Instead, probabilistic models based on conditional simulation can be used to map the probabilities of occurrence of the domains within the deposit, which reflect the uncertainty in their presence or absence at unsampled locations. The mineral grade model is then obtained by weighting the predicted grades associated with each lithological domain by the probability of occurrence of this domain. Such an approach accounts for the continuity of the grades proper to each lithological domain and for the uncertainty in the spatial extent of these domains within the deposit. An application to a porphyry copper deposit is presented. Keywords: spatial uncertainty; plurigaussian simulation; geological control; kriging; geostatistics.

Jan 1, 2007

By Wilson. D.

The Vaal Triangle Branch of The South African Institute of Mining and Metallurgy was established on 20th November, 1986, at a meeting enthusiastically supported by local members. In attendance were special guests Dr H. Wagner (President, SAIMM) and Dr O.K. H. Stefen (Junior Vice-President, SAIMM).

Jan 1, 1987

In ilmenite smelting, the FeO content of the feed material (nominally FeO.TiO2) is decreased by reduction with carbon. In a parallel reaction, a significant amount of the TiO2is reduced to Ti2O3.One of the striking features of these reactions is a consistent relationship between the extents of FeO and TiO2reduction; this relationship is independent of furnace size. It was recently proposed that this relationship follows from the solidification behaviour of the slag, where the final slag composition corresponds to the minimum melting point (?eutectic groove?) in the FeO-TiO2-Ti2O3phase system; the hypothesis is that solidification equilibrium with the freeze lining stabilizes the slag composition. If this is the case, the system of slag and freeze lining must be capable of correcting two types of disturbances: thermal and compositional. Thermal disturbances result from incorrect power input, for the feed rates of ilmenite and reductant. For example, excessive power input will tend to overheat the slag, causing the freeze lining to melt partially, establishing a new steady-state heat loss from the furnace. Compositional disturbances result from an incorrect reductant input for the given power and ilmenite input. In this work, the dynamic response of the slag and freeze lining to different inputs (flow rates of ilmenite and reductant, and power input) is modelled. The model is based on solidification equilibria, and quantified heat loss through the freeze lining. The conclusion is that the solidification equilibrium cannot constrain the composition to the eutectic groove for typical operating conditions. Keywords: ilmenite smelting, freeze lining, solidification, high-titanium slag

Jan 1, 2004

By A. J. Dickson, A. M. Starfield

This paper reviews the progress made to date in the development of computer models of heat and moisture transfer from rock surfaces to the ventilating air in deep-level mines. The application of these programs to ventilation planning and design is discussed.

Jan 1, 2014

By P. H. S. W. Kulatilake, B. Malama

To simulate brittle rocks, a mixture of glastone, sand and water was used as a model material. Thin galvanized sheets were used to create joints in blocks made out of the model material. To investigate the failure modes and strength, both the intact material blocks as well as jointed model material blocks of size 35.6 × 17.8 × 2.5 cm having different joint geometry configurations were subjected to uniaxial and biaxial compressive loadings. Results obtained from the intact model material blocks are used to validate a new intact rock failure criterion for biaxial loading. Results obtained from both the intact and jointed model material blocks are used to develop a strongly non-linear new rock mass failure criterion for biaxial loading. In this failure criterion, the fracture tensor component is used to incorporate the directional effect of fracture geometry system on jointed block strength. The failure criterion shows the important role the intermediate principal stress plays on rock mass strength. Zur Simulation spröder Gesteinsarten wurde ein Modellmaterial aus Dentalgips, Sand und Wasser hergestellt. Daraus wurden Blöcke gegossen, in denen mittels dünnen, galvanisierten Blechen Trennflächen erzeugt wurden. Die Blöcke mit Abmessungen von 35.6 × 17.8 × 2.5 cm wurden in einaxialen und biaxialen Druckversuchen belastet. Es wurde das Versagensverhalten und die Festigkeit von intakten Blöcken sowie durchtrennten Blöcken mit unterschiedlicher Trennflächengeometrie untersucht. Aus den Ergebnissen der Versuche an intaktem Material wurde ein neues Versagenskriterium für biaxiale Belastungen validiert. Die Ergebnisse der Versuche an intakten und durchtrennten Blöcken wurden verwendet, um ein neues stark nicht-lineares Versagenskriterium für geklüftetes Gebirge unter biaxialer Belastung abzuleiten. Darin wird der Bruchtensor verwendet, um den Einfluss der Trennflächengeometrie auf die Festigkeit zu erfassen. Das Versagenskriterium stellt heraus, welche Bedeutung die mittlere Hauptspannung für die Gebirgsfestigkeit hat. Un mélange de platre dentaire, de sable et d’eau a été utilisé pour développer un matériau analogue des roches fragiles. De fines feuilles galvanisées permettent de créer des discontinuités représentatives des discontinuités naturelles dans des bloques fabriqués avec ce matériau analogue. Les modes de rupture et la résistance, tant pour le matériau intact que pour le matériau avec ses discontinuités, ont été étudiés sur des blocs de 35.6 × 17.8 × 2.5 cm soumis à des efforts de compression uniaxiaux et biaxiaux. Différentes configurations de géométrie de discontinuités ont été considérées. Les résultats obtenus à partir des blocs intacts permettent de vérifier un nouveau critère de rupture pour les roches intactes soumises à des efforts biaxiaux. Les résultats obtenus, tant avec les blocs intacts qu’avec les blocs avec discontinuités, sont utilisés pour développer un nouveau critère de rupture, fortement non linéaire, pour les massifs rocheux soumis à des chargements biaxiaux. Dans ce critère de rupture, un tenseur de fractures est introduit pour caractériser les effets directionnels de la géométrie des systèmes de discontinuité sur la résistance des blocs avec discontinuités. Ce critère de rupture démontre le rôle important de la contrainte principale intermédiaire sur la résistance des massifs rocheux.

Jan 1, 2003

By M. Nicolle

The Tati Activox® Project will be the first full-scale implementation of the patented Activox® process (The Tati Activox® project was deferred in 2008. Please refer to the Norilsk Nickel press issue on the topic for more info). The process was developed by Norilsk Process Technology and has been tested on Tati mine sulphide concentrates in laboratory, pilot and demonstration plant scales and demonstrated its viability. There are inherent risks to the final scale-up of the process from the demo plant and one of them will be investigated in this paper. Compartment 1 is designed to leach approximately 77% of the total nickel leached. For this reason agitation requirements in the first compartment of the autoclave are reviewed. An attempt is made to minimize the process and mechanical risks associated in achieving oxygen mass transfer into the slurry solution. The agitator powers for oxygen mass transfer are calculated using empirical correlations and compared to demonstration plant testwork. The resulting gassed power per unit volume (P/V) is higher than most commercial autoclaves and raises uncertainty on the viability of using such high unit power inputs. Additionally, there is concern about the ability of the autoclave shell to withstand and support the higher loading of large agitators. An alternative solution to designing for the increased P/V is assessed in which the number of compartments within the autoclave is reduced from 5 to 4 by removing the compartment wall separating compartments 1 and 2. This results in an enlarged first compartment containing 3 agitators instead of 2. Therefore the compartment 1 oxygen demand is supplied through 3 agitators, which lowers the P/V per agitator. The reduction in the number of autoclave compartments raises the potential for short-circuiting the mean flow pattern by slurry particles. Short-circuiting and low velocity zones could result in a lower recovery of metal and localized hot spots, respectively. A computational fluid dynamic (CFD) analysis was conducted to quantify these concerns and also to evaluate further design considerations. The results indicate that the proposed design change to 4 compartments affects short-circuiting. The impact of increased short-circuiting on the overall autoclave recoveries is not quantified, however; it is expected to be negligible based on testwork done in the Tati Demonstration Plant and similar modifications made to another operating autoclave. The CFD analysis also suggests that there will be no low velocity zones within the compartment.

Jan 1, 2009

To the members of The South African Institute of Mining and Metallurgy We have audited the annual financial statements of The South African Institute of Mining and Metallurgy set out on pages 451 to 460 for the year ended 30 June 2002. These financial statements are the responsibility of the Institute?s Council. Our responsibility is to express an opinion on these financial statements based on our audit. Scope We have conducted our audit in accordance with statements of South African Auditing Standards. Those standards require that we plan and perform the audit to obtain reasonable assurance that the financial statements are free of material misstatement. An audit includes: ?examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements, ?assessing the accounting principles used and significant estimates made by management, and ?evaluating the overall financial statement presentation. We believe that our audit provides a reasonable basis for our opinion. Audit opinion In our opinion, the financial statements fairly present, in all material respects, the financial position of the Institute at 30 June 2003 and the results of its operations and cash flows for the year then ended in accordance with South African Statements of Generally Accepted Accounting Practice. Auditors 29 July 2003 Council?s approval of the annual financial statements The annual financial statements for the year ended 30 June 2003 set out on page 451 to 460 were approved by the Council on 26 July 2002 and are signed on its behalf by:

Jan 1, 2003

By Jo Katembo, Patty Bwando, Patient K. Ilunga, Yves Kalubi, Emman Mulaj

"From 2010, the dolomite concentration in the ore fed to the Usoke Plant increased, resulting in a significant increase in the gangue acid consumption and Mg build-up in the circuit, and thus an increase in the Mg:Co ratio in the plant solutions. This affected the Co salt grade, reagent consumption, filtration and drying capacity. Efforts were put in place to minimise the acid consumption and consequently the Mg dissolution (such as use of pre-diluted acid), but the benefits were negligible. Various efforts were then initiated by CHEMAF to improve the cobalt plant productivity (quantity and quality) by process changes, dual precipitation and seed recycle. The positive results obtained in the laboratory were successfully implemented on plant scale. A change in the process from a single-stage precipitation with Na2CO3 to dual precipitation using a combination of Na2CO3 and NaOH improved the capacity of the Co salt filtration by 30%, the Co salt grade and drying capacity by 50%, and reduced the reagent consumption by 22%. Implementation of precipitate seed recycle increased Mg rejection by 40%, improving the Co salt grade from 20% to 25%, and yielding a further drop in reagent consumption. INTRODUCTION CHEMAF (Chemicals of Africa), a mining company located in Katanga province of Democratic Republic of Congo (DRC), has been operating since 2003. The Usoke hydrometallurgical plant treats the Cu-Co ore from the Etoile pit to produce Cu cathodes via a leach–solvent-extraction (SX)–electrowinning (EW) circuit and Co salt via a selective precipitation process. The plant was designed to treat run-of-mine (ROM) ore grading 6% Cu and 1.5% Co; but, in 2008, due to a decline in grades, a heavy-media separation (HMS) plant was commissioned to enrich the low-grade ROM (3.5% Cu and 0.5% Co) up to 8% Cu and 1% Co before feeding it to the hydrometallurgical plant. Co is recovered by precipitation of Fe and Al with limestone, followed by Co precipitation as Co carbonate using sodium carbonate (Na2CO3), also known as soda ash. 85% of the final effluent from cobalt precipitation is recycled back to the plant as process water; the balance, 15%, is bled out and compensated for by fresh water top up to control and retard the rate of sodium sulfate build up."

Jan 1, 2015

By E. Uslu

The kinetics of the reduction of chromite from the LG-6 layer of the Bushveld Complex in Fe-Cr-C alloys were studied in the temperature range 15OO°C to 1680°C under an inert argon atmosphere. The rotating cylinder technique was used, and the rotational speed of the chromite cylinder ranged from 0 to 1000 r/min. The melt consisted of 30 to 80 per cent chromium and 2 to 8 per cent carbon. The initial chromium-te-iron ratios of the melts varied between 0,42 and 4,95. The reduction of chromite spinel was analysed in terms of the decarburization of the metal. It was found that decarburization increased with an increase in the temperature, the carbon content of the bath, and the rotational speed of the cylinder up to 400 r/min, after which it remained almost constant. Decarburization also increased with an increase in the chromium content up to about 50 per cent chromium but, at higher chromium contents, it decreased. In the early stage of the reduction, up to about 30 minutes of reaction time, the liquid-state mass transfer of oxygen was found to be the most likely rate-determining step. The apparent activation energy was calculated to be 84,864 kJ per mole of oxygen. In the later stage, diffusion of iron and/or chromium in the solid state is the most likely rate-determining step. The apparent activation energy for the diffusion was calculated to be 471,18 kJ/mol.

Jan 1, 1991

By M. W. John, I. D. Matthews

SYNOPSIS This paper describes the process adopted for the recovery of gold from a dump originating from clean-up operations at Durban Roodepoort Deep Gold Mine. The gold-bearing dump material was refractory in nature, not being amenable to cyanidation because of the high level of carbonaceous material present. The laboratory tests on the material involved particle-size and chemical analyses, a mineralogical examination of the material, preliminary tests, and optimization of the process for the treatment of the dump material. The preliminary tests included tests on roasting, flotation, pre-leaching, adsorbent-in-leach, and blinding. Of these options, carbon-in-leach showed the greatest potential. The rate of gold dissolution, the rate of gold adsorption by the carbonaceous material, and the ratio of carbon to pulp were then investigated. It was determined that the ratio of carbon to pulp necessary to yield a reasonable gold recovery resulted in a carbon loading that was not high enough for economic elution and regeneration. A process incorporating washing of the carbon with cold acid between adsorption cycles was tested, and reasonable gold recoveries and carbon loadings were obtained. Durban Roodepoort Deep Gold Mine piloted the conceptualized process and determined that it was economically feasible. Two Browns tanks on site were modified, and an acid-wash tank was installed. The capital outlay for the plant was recovered within some 3 months.

Jan 1, 1990

By C. A. Snyders

The research presented in this paper investigated the practical aspects of the recovery of platinum group metals (PGMs) from a dilute cyanide leach solution containing base metals, in a manner similar to that used for gold extraction in a typical CIP process, and focuses on both the adsorption and elution stages. The carrier-phase extraction of precious metals using activated carbon offers significant advantages over other processes in terms of simplicity, the high pre-concentration factor, rapid phase separation, and relatively low capital and operating costs. As a sorbent, activated carbon is still by far the most important material because of its large surface area, high adsorption capacity, porous structure, negligible environmental toxicity, low cost, and high purity standards. Adsorption tests were conducted on a pregnant alkaline leach solution (0.15 ppm Pt, 0.38 ppm Pd, 0.1 ppm Au) resulting from cyanide extraction performed in column leach tests. The initial adsorption rates of Pt, Pd, and Au were very fast and recoveries of these three metals were approximately 90 per cent after 2 hours, and 100 per cent for Pt, 97.4 per cent for Pd, and 99.9 per cent for Au after 72 hours. The parameters that influence the extraction of PGMs and Au were examined to assess their relative importance during the adsorption process in order to provide the basis for process optimization. The concentration of thiocyanate was not identified as significant factor for PGMs adsorption, while Ni concentration was the most significant extraction process parameter. Base metal cyanide complexes adsorb and compete with the PGM complexes for sites on activated carbon, and while copper adsorption can be minimized by adjusting the residence time, Ni adsorbs at approximately the same rate as the PGMs, influencing the loading capacity and adsorption kinetics of the PGMs. The feasibility of eluting platinum and palladium cyanide complexes from activated carbon using an analogue of the AARL process was investigated. Platinum and palladium elute from activated carbon almost to completion in 4 to 5 bed volumes at 80°C, while the elution of gold at this temperature is slow, with a significant amount of gold still to be eluted after 16 bed volumes. The equilibrium loading of gold is exothermic in nature (Fleming and Nicol, 1984) which will result in an increase in gold elution kinetics with an increase in temperature at similar pre-treatment conditions. A similar result was found for the elution of Pt and Pd. Cyanide pre-treatment was found to have a significant influence on PGM elution. Higher cyanide concentration in the pre-treatment step results in more efficient elution up to a point, and results suggest the possibility of an optimum cyanide concentration, beyond which elution efficiency starts decreasing due to increased ionic strength.

Jan 1, 2013

By S. Kahraman

The correlations between the modulus ratio and penetration rate of rotary and percussive drills were statistically investigated using the raw data obtained from the experimental works of different researchers. An inverse power law was found between the modulus ratio and the penetration rate of rotary and diamond drills. The penetration rate of rotary drills and diamond drills decrease with an increasing modulus ratio. The penetration rates of percussive drills increase with an increasing modulus ratio. There are significant linear correlations between the penetration rates of percussive drills and the modulus ratio. In one of the cases of percussive drilling, a strong correlation between the penetration rate and the modulus ratio was found for the rocks having a porosity value lower 1.23 %. It can be concluded that the modulus ratio might be a representative measure of rock drilling efficiency. However, further study is necessary to check the validity of the derived equations for other rock types. The effect of porosity on the correlations between the modulus ratio and penetration rate needs to be further investigated.

Jan 1, 2003

By D. D. Howat

In the field of high temperature smelting processes there have been two dramatic changes in the past twenty years. These are, first, the application of tonnage oxygen for direct injection for the refining of molten iron and other metals and to provide the means of enriching air used for the combustion of fuel. Second, the application of electric power for the generation of high temperatures in place of the combustion of fossil fuels. Of these two developments the application of tonnage oxygen for the refining of molten iron has virtually revolutionised the steel industry throughout the world. The magnitude of this development is exemplified by the fact that less than 5 per cent of the world's steel production in 1960 was made by this process or 16 million tons out of a total of 350 million tons of steel produced, while in 1970 over 40 per cent of the world steel production was made by this process, ie, 251 million tons out of 628 million tons total. In the same period the proportion of steel produced by the old-established open-hearth process has shrunk from 75 per cent to 38 per cent. In the whole history of the development of high temperature metallurgical smelting processes there has never been anything remotely approaching this. The other development, the application of electric power for the generation of high temperatures has not had the impact of the oxygen injection process but I believe that what we should call the electric smelting revolution in metallurgical processes has very far-reaching ramifications for steel production and other pyrometallurgical processes. This may seem a bold and brash statement but it must be remembered that the oxygen injection process constitutes a link in the chain critically dependent upon the production of vast tonnages of molten iron from very large modern blast furnaces. The Achilles heel of this chain of processes, upon which such a large percentage of the world's supply of steel depends, is the availability of metallurgical coke in turn dependent on natural resources of coking coal. Without any exception each industrial country in the world faces a shortage of resources of coking coal and in some cases a critical shortage. Certainly within the present century the major iron and steel producing countries of the world will face this critical shortage of coking coal and major modifications to steel making processes will become inevitable. W. F. Cartwright (Deputy Chairman of B.S.C) said recently that there are considerable doubts as to whether the world will be able to provide enough coking coal to meet world steel demands from the late 1970's onwards if the B.F.remains the main means for making iron from ore. This is one of the supreme ironies of the world metallurgical situation to-day when the technology of iron and steel production has reached an extremely high peak of technical efficiency. The newest modern iron blast furnace capable of producing 6 000 to 8 000 tons per day of molten iron represents probably the most efficient piece of high temperature metallurgical plant and operation known to man. The conversion of this molten iron into steel by the oxygen injection process has made available to the engineering industry steel of a quality and at a price which is quite remarkable. Yet this vast metallurgical pyramid rests on the completely insecure and uncertain foundation of inadequate world resources of coking coal. The shortage of reserves of coking coal in this country is acute and it is possible that these resources will be exhausted within the next twenty years. Yet unless some completely unexpected catastrophe occurs the demand for steel in this country will probably rise at a faster rate than in the Western world due to the expansion of the Bantu population and the increased standard of living. To offset the inevitable shortage of coking coal are our much greater resources of bituminous coal which although of low grade provide a suitable fuel for electric power generation. The geographical disposition of the coal fields in relation to the great industrial areas of the Transvaal makes it inevitable that the development of the pyrometallurgical industries must depend heavily on electric power. The position in this country with regard to electrical power generation and consumption is rather anomalous. Per capita consumption of electric power is high - in 1964 almost twice the world average of 870 KWH and twenty-five times the average of 34 KWH for the Continent of Africa. In 1964 fifty-four per cent of the total world electric power was used in industry - the ratio being approximately 1/9 mining to manufacturing uses. As shown in Table I in 1969 67.2 per cent of the total output of electric power from ESCOM was used for mining and other industrial uses but almost in the ratio 6/4 mining to industrial uses. These figures emphasise the enormous importance of the mining industry to the economy of this country and underline the major contribution made by the gold mining industry. What is of very significant importance is that although the mining industry remains by far the largest single consumer of electrical power the consumption of power for industrial uses is rising rapidly as shown in Table II.

By M. Cuba

Geostatistical modelling aims at providing unbiased estimates of the grades of elements of economic interest in mining operations, and assessing the associated uncertainty in these resources and reserves. Conventional practice consists of using the data as error-free values and performing the typical steps of data analysis - domaining, semivariogram analysis, and estimation/simulation. However, in many mature deposits, information comes from different drilling campaigns that were sometimes completed decades ago, when little or no quality assurance and quality control (QA/AC) procedures were available. Although this legacy data may have significant sampling errors, it provides valuable information and should be combined with more recent data that has been subject to strict QA/QC procedures. In this paper we show that ignoring the errors associated with sample data considerably underestimates the uncertainty (and consequently the economic risk) associated with a mining project. We also provide a methodology to combine data with different sampling errors, thus preserving the relevant global and local statistics. The method consists of constructing consistent simulated sets of values at the sample locations, in order to reproduce the error of each drilling campaign and the spatial correlation of the grades. It is based on a Gibbs sampler, where at every sample location, the actual sample value (with error) is removed and a conditional distribution is calculated from simulated values at nearby sample locations. A value is drawn from that distribution and kept only if it satisfies some statistical requirements-specifically, the global relative error and local means and variances must be reproduced. All sample locations are visited and simulated sample values are generated iteratively, until the required statistics are satisfactorily attained over all sample locations. This generates one realization of possible sample values, respecting the fact that the actual samples are known to carry an error given by the global relative error. Multiple realizations of simulated sample values can be obtained by repeating the procedure. At the end of this procedure, at every sample location a set of simulated sample values is available that accounts for the imprecision of the information. Furthermore, within each realization, the simulated sample values are consistent with each other, reproducing the spatial continuity and local statistics. These simulated sets of sample values can then be used as input to conventional simulation on a full grid to assess the uncertainty in the final resources over large volumes. The methodology is presented and demonstrated using a synthetic data-set for clarity.

Jan 1, 2012

By A. Golder, I. Roy

The Jayant opencast operation is one of the largest opencast coal mines in India. Prior to 2008 the mine experienced a number of dragline dump failures, which was a major hindrance in sustaining production. Northern Coalfields Limited (NCL) and the mine management engaged several design, research, and academic institutions to carry out dump slope stability studies, particularly of dragline dumps. BirlaInstitute of Technology prepared a report on the investigations in May 2009. In this paper we review the findings of the report and the measures taken to tackle the safety aspects of dragline dumps.

Jan 2, 2022

By D. S. Dihalu

A generalization of Gy?s model for the fundamental sampling error introduced the new ?parameter for the dependent selection of particles?, denoted as Cij. This allows for modeling deviations from the ideal situation where the selection of a pair of particles is composed of two independent selections. The generalized model potentially leads to more accurate variance estimates in the case of clustering of particles, differences in densities or sizes of the particles or repulsive inter-particle forces. A straightforward and practically applicable method is needed for the determination of this parameter for miscellaneous mixtures in industrial settings. In this contribution, the feasibility of using digital image analysis to determine this parameter Cij, will be demonstrated. Line transect sampling of a digital image was used to construct a transition probability matrix. A new algorithm to derive quantitative estimates for Cij will be presented and discussed. The applicability was verified by a photograph of zirconium silicate particles of sizes typical for industries dealing with pharmaceutical, food/feed, and environmental applications. Conditions affecting the practical applicability are identified and potential pitfalls will be discussed, including e.g. how a potential unrepresentative surface can affect the quality of the estimate of Cij.

Jan 1, 2010

By R A. Lynch, D A. Malovichko

The implementation of routine real-time micro-seismic monitoring of open pit mine slopes has been discussed. Some examples of seismic arrays have been given, and a recommendation of suitable seismic sensors made. Unfortunately near-surface sensors are required for good location accuracy, and the effects of reflection, mode conversion and surface waves must be accepted and compensated for during processing of the seismograms. It makes sense that mining at the base of a slope and levels of seismic activity within the slope should be related, and this is confirmed using both 2002-2003 and 2005 seismic data recorded at Navachab mine. An example of how seismic data can be used to gain information about seismically active geological structures has been described. The removal of broken rock, and not blasting nor the breaking of supporting rock, has been found to cause slope micro-seismicity. While the standard Brune source model is suitable for some 20% of the seismic events, unreasonable results are obtained for the rest. A moment tensor inversion has been performed after S-wave splitting and surface effects have been filtered out. This approach confirms a predominantly shear mechanism for a typical high frequency source.

Jan 1, 2006

By B. M. Munyungano

Rössing Uranium Mine operates a recovery circuit with continuous ion exchange followed by solvent extraction. Serious organic degradation problems were encountered during 1985/6, 2000 and 2005 in the solvent extraction plant. The preferential loss of the tertiary amine extractant was observed during the above-mentioned period. Previous investigations revealed that the tertiary amine was breaking down to nitrosamine, which cannot take part in the exchange reaction with U3O8. A reduction in the redox potential of the solvent extraction plant feed to below 500 mV halted this preferential loss. A lot of effort has been made to try and understand the actual mechanism for nitrosamine formation. Current understanding for the degradation is that formation is due to high nitrates on the strip side of the circuit emanating from nitrates from the precipitation process using ammonia. It is the current belief that pH lower than 3.7 on the strip side results in loading of nitrates onto the solvent. If oxidizing conditions prevail on the extraction side of the solvent extraction circuit, the tertiary alamine will then degrade into nitrosamine. This phenomenon is yet to be established and verified. It has, however, been established that the above process is brought about the following conditions ?High redox potential greater than 550 mV predominately caused by a high Fe3+/Fe2+ratio (4:1) ?Perception that if Fe2+<0.5 g/lit will contribute to high redox ?High concentrations of NO-3 in the conc eluate (feed to SX)/ammonium sulphate (NO-3> 4 g/l based on historic values) ?Presence of Mo as a catalyst ?Tests also have proved that the presence of nitrous acid in a concentration of 1 g/lat 550 mV leads to formation of nitrosamines from alamine.

Jan 1, 2007

"Chairman: Professor C. O. Frush Rapporteur: Mr A. C. SchmidtPapers:Planning of underground copper mining by J. K. Williams, L. Smith and M. P. WellsLinear programming models of copper leach and solvent extraction plants by W. P. C. Duyvesteyn, J. R. Cutland and J. R. L. RusselPlanning and forecasting stope production by D. W. Kappes and P. F. X. Moussett-JonesA proposed method of dynamic ore reserve assessment for a caving system of mining by A. F. Spinks and S. P. NicholsThe initial point made by Mr L. Smith in presenting his paper was that the planning aid outlined in the preprint was neither sophisticated nor complicated. However, it was a system which worked and was a very real way in which the computer was being used to assist miners, in particular, who at the present moment have very little experience in the use of computers.Mr Smith apologised for the fact that the editors of the paper had eliminated all reference to &apos;time&apos;. This was very unfortunate because the essence of the system was that it saved time, which was one of the main points made in the paper.The operations being planned by this means cover the Rokana orebody which is a stratiform body mined by open stoping.The planner has to decide how much ore to mine from each base in each time period of his plan, that is, from three to four months hence to a year ahead. Normal procedure is for the planner to have discussions with the underground manager on some of the information he requires. The sort of information needed is (i) tramming limits for each face, (ii) extraction and grade factors, (iii) the present status of mining operations so that the planner knows where to start the new plan, and, (iv) details of any other mining consider¬ations that need to be incorporated in the plan.The objective at this point is to produce an initial plan for discussion purposes. All the information required comes from one sheet per stops and shows, inter alia, the stope identifier, the length along strike, the ore tonnage, the copper and cobalt grades and, finally, the extraction and grade factors.The program itself, among many other things, checks the data for validity, compatibility, completeness and credibility and prints error messages accordingly. Output from this system is in the form of a summary of production from each face, as well as giving the figures of ore reserve depletion. This summary indicates which slopes are to be mined in this time period, the original survey grades (copper and cobalt), the estimated production grades, how much is to be mined from each stope and the copper and cobalt production accordingly."

Jan 1, 2014