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By G. van Aswegen

The geometry and morphology of a set of low-angle fractures around a stope in a deep Witwatersrand gold mine are explained in terms of extension fractures forming under variable conditions of stress. Primary extension fractures (E1) form some distance ahead of an advancing stope along the s1, s2 plane. With stope advance, a couple of these fractures end up in a stress regime conducive to transpressional shear and a secondary set of extension fractures(E2) is formed at a high angle to the primary fractures. i.e. at a low angle to the stope. As the E2 fractures are undermined, they migrate into a stress regime of transtensional shear and a third set of extension fractures (E3) may develop between E2 fractures. These have sigmoidal shapes, being parallel to the E2 fractures at the E2 discontinuity where s3 is negative, and curved through the un-fractured rock between E2 fractures where s3 is positive at the instant of fracturing. The fractures all display fractographic features characteristic of dynamic extension failure with striae indicative of the direction of rupture propagation and the local, instantaneous orientation of s1.

Jan 1, 2012

By H. Ogasawara

To study the preparation process of an earthquake, we should get closer to the hypocentre. In co-operation with ISS International, we had an experimental field (~200 m x~200 m) without dykes and faults in a South African deep gold mine. We have monitored more than 20,000 seismic events (M<2) with borehole tri-axial accelerometers. We used a data acquisition system with 15 kHz sampling and 120-dB dynamic range. In a remnant area at a distance of 100?200 m, an earthquake sequence associated with an M~2 event occurred. Significant changes in seismic parameters such as stress drop, b-value, energy index were observed associated with the sequence. We installed Ishii?s borehole strain meters and could monitor as large a strain change as 10-4associated with mining. However, sampling was only 4 times per hour and 12 bit A/D. A distance from the M2 sequence was ~100 m, being not close enough. Therefore, we found another field with several crosscut tunnels excavated across a fault where an M=2-3 event is expected. We installed the strain meter within several metres of the fault to monitor both shear and normal strains on the fault. The strains are continuously digitized with a 24-bit 25-Hz A/D conversion. The Earth Tide (10-8)is clearly detected. Seismicity induced by longwall mining can be compared to earthquake swarm induced by fluid intrusion to vertical dykes. We also found a decrease in energy index in the source area of M>5events a few days before the major events. Keywords: seismic monitoring, strain monitoring, seismic parameters, preparation process of an earthquake, South African gold mine.

Jan 1, 2002

By D. J. Young

Alloys used at high temperature must resist both creep and corrosion. Design for corrosion resistance is based on the formation of a slow-growing, protective oxide scale by selective oxidation of an appropriate alloy component, usually chromium or aluminium. A successful scale will exclude other corrodents, notably carbon, which can otherwise cause extremely rapid corrosion at high temperatures. Selective oxidation of an alloy component necessarily lowers the concentration of that metal in the alloy subsurface region. Under thermal cycling conditions, mechanical damage to the scale leads to renewed oxide growth and accelerated alloy depletion. Eventually, a point is reached where diffusion of a corrodent into the alloy becomes competitive with the outward diffusion of alloy metal to repair the protective scale. Two examples of alloy failure by carbon attack are considered. In the steam cracking (pyrolysis) process, centrifugally cast tubes of heat-resisting alloy are exposed to a gas stream of hydrocarbon and steam, at a carbon activity of unity. Formation and repair of the surface chromia scale causes alloy depletion, Kirkendall void formation, and subsequent internal precipitation of chromium-rich carbides. Their formation makes chromia scale formation much more difficult, and generates internal stress. Eventually, the tubes fail by creep rupture. In other processes (e.g. steam reforming, heat treatment), synthesis gases are supersaturated with carbon at intermediate temperatures. Once the alloy&apos;s protective scale is breached, carbon attacks the depleted substrate. In the case of ferritic alloys, it forms a surface scale of Fe3C. As this scale thickens, the supersaturated carbon precipitates as graphite within its outer regions. The resulting volume expansion causes disintegration of the cementite in a process known as metal dusting. In the case of austenitic alloys, no metal carbide is formed. Instead, carbon dissolves in the depleted metal to diffuse inward and precipitate as graphite within the metal matrix. Again, volume expansion causes disintegration of the alloy, and metal dusting results. Dusting occurs at an extraordinarily rapid rate, and leads to failure by section loss or even penetration.

Jan 1, 2013

By A. Bouvard, N. Hoteit, E. Boidy, F. Pellet

In the context of the construction of an Underground Research Laboratory devoted to the feasibility studies of radioactive waste deposits, it appears of the utmost importance to study the long-term behaviour of rock, over a long time period. In this paper, some results of tests performed on the argillite from the Meuse-Haute-Marne site test in Eastern France are presented. Then a numerical simulation of one of this test using the viscoplastic damaging constitutive law proposed by Lemaitre is presented. Finally, this law is used to simulate numerically the behaviour of the rock at the wall of a circular tunnel in order to determine the extension and the change along the time of the Excavated Damaged Zone (EDZ). Advantages and limitations of the model are discussed. Dans le cadre de la réalisation d’un laboratoire de recherche souterrain conçu pour étudier la faisabilité d’installations de stockage de déchets radioactifs, il apparaît fondamental de caractériser non seulement le comportement viscoplastique à très long terme des matériaux mais aussi les phénomènes d’endommagement consécutif à la redistribution de contraintes provoquées par l’excavation des cavités. On présente ici les résultats d’essais réalisés sur les argilites du site de Meuse/Haute-Marne et destinés à caractériser leur comportement visco-endommageable. Il est ensuite procédé à une application de la loi viscoplastique endommageable de Lemaitre pour simuler l&apos;un de ces tests. Les apports et les limites d&apos;un tel modèle sont mis en évidence par des simulations numériques du comportement de la roche au pourtour d&apos;une galerie circulaire permettant de suivre l’évolution au cours du temps de la zone endommagée (EDZ) à la paroi . Im Rahmen des Baus eines unterirdischen Forschungslabors für die Untersuchung der Machbarkeit von Deponien für radioaktive Abfälle erweist es sich als äußerst wichtig, das langfristige Verhalten von Gestein über einen langen Zeitraum zu untersuchen. Im vorliegenden Artikel werden einige Ergebnisse von Untersuchungen vorgestellt, die mit Tonschiefer aus der Meuse-Haute-Marne in Frankreich durchgeführt wurden. Anschließend wird eine numerische Simulation der Untersuchungen unter Verwendung des von Lemaitre vorgeschlagenen viskoplastischen Verformungsgesetzes vorgestellt. Schließlich wird dieses Gesetz auf die numerische Simulation eines Kreistunnels angewandt, um die Ausdehnung und die zeitliche Entwicklung der Auflockerungszone (EDZ) zu bestimmen. Es werden die Vorteile und Grenzen des Modells diskutiert.

Jan 1, 2003

By K. Lombard

"‘Roof support awaiting time’ (RSAT) is a term used at Goedehoop Colliery’s Simunye Shaft to describe the potential production time lost due to the continuous miner (CM) standing idle waiting for roof support to catch up. Investigations revealed that in 2013, Simunye Shaft had approximately1400 hours of RSAT, which suggests that the mine could have potentially produced an additional 280 000 t of coal. This project consisted of two parts. Firstly, the causes of the high RSAT and means to improve the situation were investigated. Secondly, as insisted by mine management, the CM cutting sequence was investigated as a possible cause of high RSAT. Machine-related challenges due to the roofbolter installing support too slowly, geological conditions (mostly hard roof conditions and slips),logistical challenges pertaining to the CM cutting sequence, man-related challenges related to operator fatigue, re-support, operator inexperience, and the absence of support targets were identified as main contributors to RSAT. Furthermore, results showed that the roofbolters in the sections at Simunye Shaft are slower than the CMs. A target of 28% reduction in RSAT was set. Experts from Kennametal and Fletcher were consulted to find solutions for the identified causes. In total, eight solutions for RSAT were identified, but the solution that contributed most significantly to reducing RSAT was to use hard roof drill bits as a standard product at Simunye Shaft. Calculations showed that by using hard roof drill bits, RSAT can be reduced by 43%, which is more than the specified 28% target. The cutting sequences at Kriel, Greenside, and Simunye Shaft, togetherwith three newly developed cutting sequences, were simulated using the UCMS (Underground Coal Mining Simulation) program. A re-aligningprinciple was incorporated into the newly developed cutting sequences toalign the cutting sequences to general support work and to reduce RSAT. A decision matrix revealed that a cutting sequence in which boxing takesplace in R3 (third road to the right of the belt road) and in which the re-aligning principle has been incorporated will be the best option for Simunye Shaft. The recommended cutting sequence will lead to a 5% increase in production.The work presented in this paper was carried out as partial fullfilment for the degree BEng (Mining Engineering)"

Jan 1, 2015

Due to the reduction in frictional resistance, the characteristics of joint infill have a major role to play on rock mass instability. This paper elucidates the laboratory behaviour of graphite infilled joints based on a large-scale shear apparatus under constant normal stiffness (CNS). Discontinuities in a graphite mine have been simulated using high strength gypsum plaster, with the joints infilled with compressed graphite layers. The Fourier series was employed to characterize the joint surface, and the method of using the Fourier coefficients for the prediction of dilation and normal stress with displacement is explained. Die Charateristik von Verbindungsfüllungen hat einen wichtigen Einfluss auf Felsmassenstabilität aufgrund der Verringerung des Reibwiderstandes. Diese Veröffentlichung untersucht das Verhalten von Graphit gefüllten Verbindungen im Labormaßstab mit einer Methode die auf einem gross-umfang Apparateprinzip unter konstanter Normal-Steifheit beruht. Unregelmässigkeiten in einer Graphit Mine wurden mit Gypsum Gips von hoher Festigkeit simuliert, die Verbindungen wurden mit kompressierten Graphitschichten gefüllt. Fourier Reihen wurden angewandt um die Verbindungs Fläche zu Characterisieren. Die Methode die verwendet wurde um die Ausdehnung und Normalkraft mit der Verschiebung mit Hilfe von Fourierkoeffizienten zu bestimmen wird beschrieben. Due à diminution des résistances par frottements, les caractéristiques des joints de remplissage joue un rôle majeur sur les instabilités de la roche. Cet article étudie le comportement en laboratoire des joints de remplissage en graphite à partir d’un dispositif de friction à grande échelle sous rigidité normale constante. Les discontinuités dans une mine de graphite ont été simulées grâce à un plâtre à haute teneur en gypse, dont les joints ont été remplis de couches de graphite compressées. La caractérisation de la surface des joints a été réalisée avec les séries de Fourier. La méthode utilisant le coefficient de Fourrier pour la prédiction de la dilatation et de la compression en fonction du déplacement est également expliquée.

Jan 1, 2003

By P. L. Duncanson, J. D. Toth

Since 1995, when "freeze lining" refractory systems were introduced to the ferroalloy industry, they have gained in popularity, due to the freeze lining?s reputation for reliability, safety, and the contribution it makes to profitability. As with many popular and effective technologies, however, the freeze lining has spawned low-cost pretenders that claim the "freeze lining" name. On the surface they appear to contain some of the components of the technology, such as thermally conductive materials, but they fail to incorporate all of the principles that define a true Freeze Lining. The term "freeze lining" refers to the refractory system?s ability to maintain a temperature profile that is low enough to freeze a layer of process material on its hot face, which insulates the refractory and prevents direct contact with molten metal and slag. In doing so, the common wear mechanisms found in the submerged arc furnace - chemical attack, erosion, and thermal stress - can be prevented. These wear mechanisms are all related to high temperature; thus, they are prevented by maintaining low temperatures. Certain refractory properties and design concepts are absolutely necessary for the lining system to function as a true Freeze Lining. The paper explains these requirements and why they are important - the Truth of freeze linings - and further explains why systems that ignore one or more of these requirements cannot claim to be freeze linings, thereby exposing the Myths.

Jan 1, 2004

By C. S. Chenga

Sustainable development is currently an extremely relevant concept worldwide, especially in developing countries like South Africa. Mining and metals companies are also directly affected by the sustainable development agenda. The Mining Charter?s requirements as well as new legislation (Mineral and Petroleum Resources Development Act) expect, among others, for mines to support infrastructure and poverty eradication projects in the communities surrounding the mines. The aim of this paper is to, against the background of a qualitative study of mining communities in the North-West Province of South Africa, put forward some critical factors for the sustainability of social development projects in the mining sector.

Jan 1, 2006

Sulphide minerals, such as pyrite and sphalerite, are leached by ferric sulphate. This reaction produces ferrous sulphate and other dissolved products. The ferrous sulphate is re-oxidized to ferric sulphate by bacteria. These reactions can be written as: [ ] However, in 1964 Silverman and Ehrlich proposed that this is not the only role that is played by bacteria. These researchers proposed that T. ferrooxidans enhances the rate of oxidation of pyrite above that achieved by chemical reaction with ferric sulphate at the same solution conditions. This enhancement in the rate of dissolution was proposed to occur by direct microbiological action, possibly by the extra cellular secretion of an enzymatic oxidant. Since the Silverman and Ehrlich proposal, different authors have made opposing claims concerning the action of T. ferrooxidanson pyrite. This ?direct mechanism? of bacterial dissolution of pyrite can be given by the following reaction: [ ]

Jan 1, 2000

By J. P. Piguet, Y. Wileveau

ABSTRACT : An experimental programme for damage assessment was performed in the vicinity of the main shaft of Andra’s Underground Research Laboratory, currently under construction in the East of France, when the shaft is crossing the Kimmeridgian marls between 80 and 100 m depth. The mechanical behaviour was analysed by mean of convergence and displacement measurements. The disturbance into the wall was assessed using numerous methods such as measurement of sonic velocities, permeability measurement and VSP measurement in radial boreholes. The intensity of the damaged zone is low, and its extension does not exceed 0.5 time the radius of the shaft. It does not seem to depend on blasting patterns. ZUSAMMENFASSUNG : Ein Forschungs- und Versuchsprogramm wurde aufgestellt, um die beschädigte Zone im Bereich der Kimmeridgemergel zwischen 80 und 100 Meter Tiefe beim Zugangsschacht des im Bau befindlichen Andralabors im Osten Frankreichs zu berechnen. Das mechanische Verhalten der Formationen wird auf der Grundlage von Konvergenz- und Verschiebungsmessungen ermittelt. Verschiedene Messmethoden, wie z.B. mikroseismische Geschwindigkeite Messungen, Permeabilitäs- und Beschleunigungsbestimmungen in strahlenförmigen Bohranordnungen, erlaubten die Ermittlung des Beschädigungscharakters der Schachtwand. Die Intensität der beschädigten Zone ist niedrig, ihre Ausdehnung übersteigt nicht die Hälfte des Radius des Zugangsstollens und scheint unabhängig vom Schema der Sprengstoffanordnungen zu sein. RESUME : Un programme expérimental visant à évaluer la zone endommagée autour du puits d’accès du Laboratoire de Recherche Souterrain de l’Andra actuellement en construction dans l’Est de la France a été mis en œuvre lors de la traversée des marnes du Kimméridgien entre 80 et 100 m de profondeur. Le comportement mécanique des formations est évalué à partir de mesures de convergence et de déplacements. La mise en œuvre de nombreuses méthodes, telles que des mesures microsismiques, des mesures de perméabilité et d’accélérométrie en forages radiaux, a permis de caractériser l’endommagement en paroi du puits. L’intensité de la zone endommagée est faible et son extension ne dépasse pas 0,5 fois le rayon du puits. L’endommagement semble indépendant des schémas de tirs testés.

Jan 1, 2003

By A. Rejeb

ABSTRACT: This paper contributes to the study of underground structures in argillaceous media, especially Tournemire argillites (Aveyron, France). The basic results obtained over six years in two experimental drifts at the Tournemire site are presented. In situ measurements cover drift wall temperature, humidity and convergence. Delayed convergence represents around 50-65% of the total measured convergence. Analysis of the measurements has shown that delayed convergence is explained by the viscoplastic behaviour of the argillaceous formations. Lemaitre’s rheological model has been extended to the orthotropic case, as Tournemire argillite is naturally anisotropic. The triaxial creep test results on samples at different orientations enabled the parameters of the Tournemire argillite to be identified in terms of orthotropic viscoplastic law. A plane deformation model, using this rheological law and the initial stress field in the site, was developed to interpret the convergence measurements in the drifts. The computed results match the measurements well, especially during the excavation phase. KEY WORDS: Argillite, convergence, time-dependent behaviour, creep, viscoplasticity, modelling. ZUSAMMENFASSUNG: Der vorliegende Artikel ist ein Beitrag zur Untersuchung der unterirdischen Strukturen tonhaltiger Milieus, insbesondere der Tongesteine von Tournemire (Aveyron, Frankreich). Die wichtigsten Ergebnisse, die in zwei Forschungsstrecken am Standort Tournemine über einen Beobachtungszeitraum von sechs Jahren zusammengetragen wurden, werden hier vorgestellt. Gemessen wurden in situ Temperatur, Feuchtigkeit und Streckenkonvergenz. Von der insgesamt gemessenen Konvergenz sind etwa 50 bis 65 % auf zeitlich verzögerte Konvergenz zurückzuführen. Die Auswertung aller Messungen hat ergeben, dass die zeitverzögerte Konvergenz mit dem viskos-plastischen Verhalten des Tonsteinmassivs zu erklären ist. Aufgrund der naturgemäßen Anisotropie des Tongesteins von Tournemine wurde das rheologische Modell von Lemaitre auf den orthotropen Fall ausgedehnt. Triaxiale Kriechversuche bei jeweils unterschiedlicher Ausrichtung dienten der Ermittlung der einzelnen Parameter des orthotropen, viskos-plastischen Gesetzes. Zur Auswertung der Konvergenzmessungen innerhalb der beiden Strecken wurde unter Beachtung dieses rheologischen Modells sowie des ursprünglichen Spannungszustands vor Ort ein flächiges Deformationsmodell entwickelt. Die Rechenergebnisse zeigen eine gute Übereinstimmung mit den Messungen, insbesondere während der Vortriebsphase. SCHLÜSSELWÖRTER: Tongestein, Konvergenz, zeitlich verzögertes Verhalten, Kriechen, Viskoplastizität, Modellbildung. RESUME : Cet article est une contribution à l’étude des structures souterraines dans les milieux argileux, notamment les argilites de Tournemire (Aveyron, France). Les principaux résultats obtenus pendant six années, dans deux galeries d’expérimentation au site de Tournemire, sont présentés. Ces mesures portent sur la température, l’humidité et la convergence des parements des galeries. La convergence différée représente environ 50 à 65% de la convergence totale mesurée. L’analyse de l’ensemble des mesures a montré que la convergence différée est interprétée par le comportement viscoplastique du massif argileux. Etant donné que l’argilite de Tournemire est naturellement anisotrope, le modèle rhéologique de Lemaitre a été étendu au cas orthotrope. Les résultats des essais de fluage triaxial, sur des échantillons à différentes orientations, ont permis de déterminer les paramètres de la loi viscoplastique orthotrope. Un modèle en déformation plane, utilisant cette loi rhéologique et l’état de contrainte initiale dans le site, a été développé en vue d’interpréter les mesures de convergence dans les galeries. Les résultats des calculs sont en bon accord avec les mesures et plus particulièrement durant la phase de creusement. MOTS-CLEFS : argilite, convergence, comportement différé, fluage, viscoplasticité, modélisation.

Jan 1, 2003

By A. K. Singh, R. Singh, P. K. Mandal

On the basis of in situ study of pillar loading at different sites, an attempt is made in this paper to visualize the development of mining induced stress under varying geo-mining conditions. Field study demonstrated interesting interaction between size of pillar and nature of roof rock mass under the influence of increasing dimension of the excavation. Stiffness of pillars/overburden, extraction ratio and depth cover are observed to be the important parameters for the estimation of mining induced stress over the pillar. These parameters influence, both, the value of ultimate induced stress (vertical) and its range of influence ahead of the face line. Further, it is observed that the change in width/height (w/h) ratio of a pillar has got considerable influence over the nature of mining induced stress over it. Impact of highly dynamic nature of mining induced stress over the natural supports is observed to be the most serious factor for the safety of working under a hard and massive roof rock mass. On the basis of these observations, a conceptual model of interaction between the natural support and overlying strata is discussed in the paper. ZUSAMMENFASSUNG: Aufgrund ist in situ Studium von Säule Beladung an verschiedenen Stellen, ein Versuch in diesem Papier gemacht, die Entwicklung des Bergbaus vostellen sich, Spannung unter Änderung von Geo Bergbau von Bedingungen hat veranlaßt. Feld Studium hat interessante Wechselwirkung zwischen Größe von Säule und Natur von Dach Felsen Masse unter dem Einfluß von Vermehrung Dimension des excavation vorgeführt. Steifheit des Säulen Overburden, Herausziehung Verhältnisses und Tiefe sind beobachtet bedeckt, die wichtigen Parameter für die Schätzung des Bergbaus zu sein, Spannung über der Säule hat veranlaßt. Diese Parameter beeinflussen, beide, der Wert allerletzter veranlaßter Spannung (senkrecht) und sein Bereich des Einflusses voraus von der Gesicht Linie. Weiter ist, es beobachtet, daß die Änderung in Breite Höhe (W H) Verhältnis einer Säule beträchtlichen Einfluß über der Natur des Bergbaus erhalten hat, Spannung hat darüber veranlaßt. Schlag sehr dynamischer Natur des Bergbaus ist Spannung über den natürlichen Stützen beobachtet hat veranlaßt, der ernsteste Faktor für die Sicherheit des Arbeitens unter einer harten und massiven Dach Felsen Masse zu sein. Aufgrund dieser Beobachtungen, ein begriffliches Modell der Wechselwirkung zwischen der natürlichen Stütze und der überlagernde strata ist im Papier diskutiert. RESUME: En se basant sur dans l&apos;étude de situ de chargement de pilier aux sites différents, une tentative est faite dans ce papier pour envisager le développement de creuse la tension persuadée sous varier de conditions de geo creuse. L&apos;étude de champs a démontré l&apos;interaction intéressante entre la taille de pilier et la nature de masse de rocher de toit sous l&apos;influence d&apos;augmenter de dimension de l&apos;excavation. La raideur de piliers overburden, la proportion d&apos;extraction et la couverture de profondeur est observée pour être les paramètres importants pour le jugement de creuse la tension persuadée par-dessus le pilier. Ces paramètres influencent, les deux, la valeur de tension persuadée ultime (vertical) et sa gamme d&apos;influence en avant de la ligne de face. Plus, il est observé que le changement dans la largeur hauteur (le w h) la proportion d&apos;un pilier a reçu l&apos;influence considérable par-dessus la nature de creuse la tension persuadée par-dessus il. L&apos;impact de nature extrêmement dynamique de creuse la tension persuadée par-dessus les soutiens naturels est observé pour être le facteur le plus sérieux pour la sûreté de fonctionnement sous une masse de rocher de toit dure et massive. En se basant sur ces observations, un modèle conceptuel d&apos;interaction entre le soutien naturel et les couches recouvrant est discuté dans le papier.

Jan 1, 2003

By M. van Schoor

The bulk of the world?s platinum production originates from the Merensky and UG2 reefs within the Bushveld Complex, South Africa. Both the Merensky and UG2 reefs are disrupted by faults, dykes, potholes and iron-rich ultramafic pegmatite bodies (IRUPs)?features that impact negatively on production, planning and safety. It is therefore advantageous to know of their presence and geometry ahead of mining. To date, no geophysical technique has been successfully applied to the routine mapping of mine-scale potholes and IRUPs. These disruptive features may vary from a few metres to several tens of metres in diameter. In this paper the applicability of in-mine electrical resistance tomography (ERT) to map potholes and other disruptions to the continuity of the Merensky and UG2 reefs ahead of mining is demonstrated using two case studies.

Jan 1, 2005

By S. M. Spottiswoode

Crush pillars are widely used in mine workings on the Merensky Reef in the Bushveld Complex to prevent panel collapses. Crush pillars are expected to fail as or soon after they emerge from the face and failure should occur non-violently. Unfortunately, violent failure occurs frequently and is said to be the main cause of seismicity associated with mining of the Merensky Reef. Recent work by Napier, Malan, and du Plessis has shown that limitequilibrium quasi-static models are able to simulate pillar failure using three states of strength of rock in pillars, namely intact, residual after failure, and decayed strength after later time-dependent (viscous) weakening. We have previously introduced an additional state of strength to account for the dynamic failure that results in seismic events, and found that this approach could be used to generate synthetic seismic catalogues similar to observed seismicity for deep-level gold mines, where seismicity takes place mostly on advancing faces. The less brittle seam material of the Merensky Reef, compared to the brittle quartzites and lavas of the Witwatersrand reefs, results in little or no face bursting and is modelled with an assumed plastic strain of some 0.005 over an effective stope width of 2 m before failure. When this plastic yield is surpassed, we allow the reef to fail ?seismically?. We show that synthetic seismic catalogues modelled in this way have some of the features of observed seismicity. Analysis is greatly facilitated using our custom-built software that reads the mine?s survey data into a database and presents results in an interactive graphical form.

Jan 1, 2014

By J. A. Luckmann

"SynopsisThe purpose of this paper is to introduce an innovative approach to risk management in surface mining operations, namely, positive risk. Traditionally, risk management focused on mitigating losses (negative). Positive risk, on the contrary, reverses the approach and focuses on exploiting a project’s inherent benefits (positive).The inability to accurately determine project objectives during the project planning phase and the failure to achieve those objectives during the execution phase is a major problem for any project management in the mining environment.The advance of computer aided design models for mine planning enables mining engineers to examine various options within a very short time. Employing positive risk management combined with drivers-based risk management when evaluating these options provides an ideal opportunity to investigate areas for improving the mining project’s profits. Furthermore, harnessing positive risk returns during the planning phase contributes immensely to the successful achievement of project objectives.Mining has inherent business risks, which can appear overwhelming when considering the risks associated with a mining project schedule, cost, and safety or resources, etc. The question is – how to manage risks in a surface mining environment, and what process methodologies, work methods, processes, and standards should be used when considering the surface mining risks. Applying the principles of positive risk management to manage surface mining risks is not only relevant, but definitely beneficial to mining projects and to the mining industry as a whole.It would be beneficial for risk managers and risk professionals to understand the roles of positive risk ‘drivers’, also known as ‘propitious attractors’. Identifying, analysing, estimating, and understanding the propitious attractors, their behaviour and their influence on project risk events helps considerably during the planning and execution phases. The theoretical and practical knowledge of both sides of the risk – the downside risk (negative risk) and upside risk (positive risk) – can add substantial value to any organization when downside risk is adequately mitigated and upside risk is beneficially exploited."

Jan 1, 2015

By W. A. Naismith

On 16 July 2004, at 07:10 a collapse of about 1.8 million m3 (about 4 ½ million tons) took place on the north wall on Nchanga Open Pit. This collapse was the result of a developing instability that was first identified when the benches in this area were exposed during September 2002. The NOP geotechnical and survey departments closely monitored the development of the failure. Control measures were implemented to reduce risk to men and equipment. These measures were continually improved and adjusted in reaction to observations and changing conditions. The purpose of this paper is to describe in detail the monitoring results that were obtained both by traditional methods and the novel slope stability radar system (SSR). Difficulties encountered in establishing critical deformation levels and deformation rates that can be used to predict the onset of collapse are described. Details of the monitoring and control measures, which led to the successful completion of mining in the area, are also described in this paper.

Jan 1, 2005

Paper written on project work carried out in partial fulfilment of B. Eng (Mining Engineering) degree The stability of a ferrosilicon dense medium suspension is one of the most important parameters to keep under control since it determines the density gradient of the medium in the separation zone and thus directly influences separation sharpness. The stability of ferrosilicon suspensions were characterized using settling tests employing a differential pressure method. Particles smaller than 45 µm and especially the ore fines played an important role in the settling behaviour of the solids. High medium stability is favoured by ore fines, fine medium particles, and high medium densities. Keywords: dense media, ferrosilicon, dense medium stability, ore fines

Jan 1, 2002

By J. A. Cox

The Ashanti mine is located within the Lower Proterozoic Birimian of Ghana, and covers a concession of 474 square kilometres at its Obuasi operations which comprise large scale underground, surface and tailings treatment facilities. The mine had operated for a century at the end of 1997 and had produced nearly 25 million ounces of gold, a significant proportion of which came from the underground operations. This paper covers the strategy under which exploration for both surface and underground mineral resources was instrumental in enabling the expansion programme to go ahead together with the methodologies and results that have developed in the exploration area over the last five years. Within capital expenditure constraints, the objective on surface is to replace oxide depletion with a secondary objective of discovering new sulphides in areas other than the main trend. In the underground, the exploration strategy is directed at replacement of both underground and surface sulphide depletion, minimising finding costs and assisting the development of long lead time infrastructure. The exploration application describes the methodologies in use for both surface and underground exploration that have been developed in recent years in conjunction with a description of a major review conducted in 1995/96 of the exploration database using an integrated approach, geochemistry, geophysics, remote sensing and structural geology. A revisit of soil geochemical data in particular, and modification of exploration methodology led to the success in finding relatively significant new oxides in 1997.

Jan 1, 1999

By L. K. Witika, J. H. Masinja

"Investigations of flotation characteristics of Lumwana and Kansanshi ores using formulated frothers were carried out. Of the six frothers tested, two came from the alcohol family, two from the glycol family and last two were formulated products. The initial work involved determining the optimum mesh of grind and frother dosage for Lumwana and Kansanshi ores. Further work involved carrying out surface tension, bubble size and froth stability measurements. Finally, water recovery tests were conducted at Lumwana and Kansanshi mine sites. For froth stability tests, six frothers were tested on a two-phase (water–air) system using the Bikerman column flotation cell, while water recovery tests were conducted using a total of seven frothers, including the standards for each plant. The results of the testwork showed that (i) although a stable froth is essential for optimum recovery of valuable minerals, a higher molecular weight frother, like Dowfroth 250, caused poor selectivity when used on fine ores and (ii) a lower molecular weight frother was suited for Lumwana ore, while a mid to higher molecular weight formulated product was suitable for Kansanshi sulphide ore. INTRODUCTION Investigations of flotation characteristics of Lumwana and Kansanshi ores using formulated frothers were carried out. The initial work of this project involved determining the optimum mesh of grind and frother dosage for Lumwana and Kansanshi ores. Further work involved carrying out surface tension, bubble size and froth stability measurements. Finally, water recovery tests were conducted at Lumwana and Kansanshi mine sites. In order to investigate the gangue entrainment levels in the Lumwana and Kansanshi sulphide ores, two well-known methods (froth stability and water recovery) were used. Firstly, froth stability tests were conducted using six frothers, two from the glycol family (Dowfroth 200 and Dowfroth 250), two from alcohol family (MIBC and pine oil) and other two from the formulated family (Betafroth 20 and Betafroth 245), at the University of Cape Town’s Centre for Mineral Research (CMR) laboratories. Froth formation and stability measurements were conducted using the Bikerman column flotation cell."

Jan 1, 2015

The paper examines the design issues associated with the integration of mineral processing within underground mining systems. It demonstrates conceptual integrated system design options appropriate to a range of geological scenarios. Particular reference is then given to a case study of stoping in narrow base metal veins. The performance of such integrated systems in terms of productivity, economic and environmental criteria is demonstrated by means of simulation. Particular attention is given to the potential benefits to mine waste management. Processing technologies appear to offer genuine potential benefit, whilst underground mining methods may need to evolve further to facilitate full integration. This paper is based on industry supported research aimed at developing selective and clean underground mining systems.

Jan 1, 2003