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Konkola No 3 shaft experienced severe mining-induced stress and time-related deterioration in ground conditions in an area where an over-cut and bench (OCB) mining method was used to extract a shallow dipping wide orebody. This caused an unacceptable risk for safe mining operations to sustain the required levels of production. After a review of the conditions it was decided to change the mining method to CASCADE to recover ore in the affected area and modify the OCB method and use a modified over-cut and bench method (MOCB) for new mining sections. This paper describes the geotechnical criteria included to derive the mining standards for the MOCB. The geotechnical risks are identified and taken into account to develop stope design parameters, stoping sequences and support requirements. A monitoring programme to assess conditions as mining progresses is also discussed.

Jan 1, 2005

By C. Musingwini

The subject of optimal planning of level and raise spacing for inclined narrow reef deposits has received intermittent attention over the years because the subject matter is inherently complex. Previous work has approached the problem as simply that of simultaneously minimizing the total excavation and haulage cost associated with the development workings. However, when level and raise spacing are altered, other factors such as productivity are negatively affected, thus requiring a delicate trade-off of contradicting planning or optimization criteria. The paper concludes that the problem is actually of the multi-criteria decision analysis (MCDA) type, contrary to traditional thinking that the planning problem is achieved solely by minimizing waste development.

Jan 1, 2010

By D. B. Rebuli

Seismic networks in deep gold mines of South Africa are often planar owing to the tabular geometry of the orebody and, therefore, the mining infrastructure. Consequently, seismic event locations are poorly constrained in the direction perpendicular to the reef plane, and symmetrical locations above and below the reef plane may fit the observed data equally well. This problem may be resolved in situations where the strata above and below the reef plane have significantly different seismic velocities, which is the case for the Ventersdorp Contact Reef at Kusasalethu mine (previously Elandskraal, the amalgamation of Deelkraal and Elandsrand). A location method using a layered location model that takes into account the velocity contrast between the layers was tested. Observed direct- and head-waves were used to determine the velocity bounds of the P-wave velocities in the two-layer model. The data-set was also used to find the best P- and S-wave velocities for the two layers by grid searching over a range of velocities and minimizing the sum of the travel-time residuals. The results from the grid search and those from the calibration of velocities using direct- and head-waves give similar P-wave velocities for each of the two layers. A second set of seismic events was then relocated with this layered model and locations closer to reef were found. This simple layered location method goes some way to reduce the reefperpendicular location errors for Kusasalethu mine in particular. Keywords mine seismology, velocity model, location methods.

Jun 1, 2013

By A. Nieto

A vehicle proximity warning–collision avoidance system is being developed using GPS and wireless local area networks to improve safety of off-highway trucks in open pit mines. After two-and a-half years of research, software development, and laboratory testing, field tests were carried out at operating limestone quarries and open pit mining operations to evaluate GPS accuracy and overall system effectiveness under rugged operating conditions. This article describes the progress made on this NIOSH-funded project and discusses the GPS accuracy tests and overall system tests that were carried out during the year 2001 at the Colorado School of Mines Survey Field and at the Morenci open pit copper mine in Arizona. Keywords: GPS, Advanced Mining, Virtual Reality, Wireless Networks, Proximity Warning

Jan 1, 2003

South Africa remains the largest global producer of gold, accounting for 11.3 per cent of total world mine production, which amounted to 2520.2 t in 2005. The benefits and disadvantages associated with hedging practices in general, and among South African gold producers is examined. The wide variety and unique nature of risks faced by the mining industries provide a strong case for hedging. Only the principles of hedging, such as selling ounces of gold in the ground at a pre-agreed price for delivery at a future date as a cost-effective mechanism for price risk management, is discussed. Progressive and cumulative increases in the volume of forward sales in the major producing countries are considered by many to be the cause of the declining gold price over the past decade. In spite of negative publicity, forward selling continued as an industry-wide practice until recently (2002) when the global hedge book contracted by 352 t; contraction amounted to 158.6 t in first quarter of 2006. The objectives and benefits of hedging include continuity and stability of cash flows, stability in price achieved, reduction of frictional costs, and creating an effective management tool. The importance of a defined hedging strategy in reducing uncertainty about the hedging objectives is essential to a successful hedging policy. Historical patterns in hedging revenues at an industry level indicate five distinct periods during which the fortunes of hedgers have fluctuated. Finally, since 2001 the rising gold price and reduced price volatility through the consolidation in the global price means that the need to stabilize revenue flows is less urgent. This has meant that hedging is becoming progressively less important for the mining industry at large.

Jan 1, 2007

By A. M. Hearn, J. G. Roos

Energy consumption, being a large proportion of the input of the ferroalloy production process, can be measured in terms of the efficiency with which the energy is utilized and the effectiveness with which it is used. The efficiency of the usage of energy revolves around the specific consumption of the energy for the production of the alloy, which encompasses the thermodynamic aspects of the process and is more of a metallurgical function that will not be addressed further in this paper. The effectiveness with which the energy is utilized is determined by the optimisation of the electricity supply from the utility (in this case Eskom). The South African electricity supply industry is on the brink of considerable restructuring, implying changes in ownership, structure and regulation. In other countries, however, restructuring has often seen higher prices. Owing to the diversity of growth prospects in South African markets, Eskom is turning to new market management and generation strategies. In future, Eskom will develop pricing strategies to increase demand from attractive customer segments such as paper & pulp, iron & steel, aluminium, and other metallurgical industries. There will be a broader spectrum of product offerings, including dynamic pricing options and demand-side management incentives. In a future electricity market that will become more dynamic and demanding, it will become increasingly important for electricity consumers to optimise their electricity supply. There are many facets in optimising the electricity supply, which include optimal utilisation of the tariff, integrating energy cost management into the production planning process, implementation of demand-side management actions, modelling, scenario planning (.what-ifs?.), optimisation, maintenance scheduling coordinated with the tariff periods, etc. This paper gives consideration to the status of the development of technology at the manganese alloy works of Samancor at Meyerton, South Africa in order to increase the effectiveness with which energy is utilized.

Jan 1, 2004

By Ö. Erdem

The investment decision making process in the insurance and finance industries is affected by new advances such as simulation techniques. These advances have improved the discounted cash flow method (DCF). In DCF, a dynamic and flexible model construction is not possible because it does not consider uncertain conditions. Each project should be evaluated taking into account the related uncertainties because the related uncertainties determine the characterization of the project. Related uncertainties can be processed in dynamic DCF, which is applicable to both financial and non-financial industries with different kind of uncertainties, such as power generation and petroleum projects. The dynamic DCF method can estimate net present value (NPV) while managing related project uncertainties with a simulation method like Monte Carlo Simulation. The simulation method is preferred because its output is unbiased. Therefore, a more realistic financial evaluation of the project can be concluded. In spite of the improvement of dynamic DCF, this project evaluation method is not used frequently in mining industry. However, the mining industry is ideally suited to this concept because it is highly dependent on estimations such as orebody size and ore grade. During the project evaluation stage, these uncertainties can be included with the dynamic DCF method. This study aims to contribute to increasing the usage of this method in mining projects. A copper reserve in Turkey is selected as a case study to apply uncertainty assessment for the evaluation of NPV.

Jan 1, 2012

Recently, work was carried out by the Shotcrete Working Group to study anisotropy in steel fibre reinforced shotcrete using strain-controlled, compressive strength testing methods. The shotcrete materials used and specimen preparation procedures as well as testing methods are described. The test results are discussed and it is concluded that, because of the anisotropic nature of fibre reinforced shotcrete, it may be worthwhile investigating the degree of such anisotropy in practice using strain-controlled, strength testing techniques.

Jan 1, 2001

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'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 R. M. Goktan

Point-attack picks are one of the most widely used tools for the mechanical excavation of rock and coal. In the literature, some practical formulas have been developed to estimate their performances under varying cutting conditions such as the pick geometry, cutting depth and cutting geometry. In this study, it is shown that Evans?s theoretical model, the most cited in the literature, has serious limitations concerning the changes in the cutting geometry. Analysis of the two independent full-scale linear rock cutting experimental data reveals that both his theory and its recent modification can not fully explain the mechanism of rock breakage under asymmetrical attack. The cutting force predictions made by employing such models are shown to be too significantly weak to be of any service in practice. In this study, a semi-empirical approach was followed by means of which cutting forces under varying cutting geometries could be made. By analysing the full-scale rock cutting test data, prediction equations of the peak cutting force and mean cutting force have been developed. Comparisons of laboratory determined and predicted force values indicate that the suggested prediction equations are applicable to quite different rock materialsm which have uniaxial compressive strength in the range of about 30?170MPa, and valid for different cutting geometries. It is also shown by regression analysis that the established prediction equations are statistically significant.

Jan 1, 2005

By L. W. Burger

The need to establish and harmonise methodologies to quantify air emissions, atmospheric dispersion and the consequences of air pollutants (especially hexavalent chromium) from the ferrochrome industry became important aspects with the increasing demands for comprehensive impact assessments. The paper includes a synthesis of current knowledge on the following aspects: ? Locally and internationally accepted methodologies for the quantification of chromium emissions, including sampling methods and emission factors; ? A compilation of recognised and accepted air quality sampling and laboratory analysing techniques; and, ? Dispersion modelling and impact assessment tools. Depositing and removing materials from the chromium ore stockpile and wind erosion of exposed stockpiles result in mainly chromite emissions unlikely to contain significant amounts of hexavalent chromium. Pre-treatment processes such as drying, crushing and screening also produces chromium emissions, but mainly as trivalent chromium. The smelting of chromium is the major source of chromium emissions - open furnaces have the highest uncontrolled chromium emissions, followed by semi-closed and closed furnaces, respectively. Based on the current knowledge on emission rates, interim emission factors for particulate, total chromium and hexavalent chromium releases are provided. Ambient sampling and analytical methods to determine environmental exposure of the general public require that hexavalent chromium needs to be quantified in very low concentrations. Suggested sampling and analytical methods for both source characterisation and ambient monitoring are provided. The selection between dispersion models needs to be based on the size of the modelling domain and the complexity of the terrain. The discussion on dispersion models includes the US EPA?s Industrial Source Complex Model (Version 3), the AERMET/AERMOD suite of models and the CALMET/CALPUFF suite of models. Guidelines are also proposed for environmental exposure assessments including cancer and non-cancer health effects.

Jan 1, 2004

By T. Wettainen

Malmberget town is located in northern Sweden, approximately 70 km north of the Arctic Circle. Parts of the town overlie more than 20 iron orebodies, consisting mainly of magnetite with smaller quantities of haematite. The mine is operated by the mining company LKAB. Mining started in the 17th century, but not until the railway to the coastal city of Luleå was completed in 1888 did large-scale production commence. Around 1920, mining proceeded underground and today sublevel caving is the only mining method used. Sublevel caving causes subsidence of the ground surface, and buildings and residential areas have been relocated due to the mining activities for more than 50 years. The number of seismic events accompanied by strong ground vibrations is now increasing. In 2008 the mine received a permit from the Environmental Court of Sweden to increase production to 20 Mt of crude ore per year. A prerequisite for the permit was that the mine conducts a number of investigations regarding the environmental impact on the residents of Malmberget. One of these investigations concerned how seismicity will change as production increases and what measures could be taken to reduce inconvenience to the town residents. Today the mine possesses an extensive seismic monitoring system with more than 180 underground and surface geophones. For this study, eleven seismically active volumes in Malmberget mine were identified, and for each of them, a yearly future maximum magnitude interval was estimated based on the current production plan. Relationships between historical seismic events and measured ground vibrations in the town of Malmberget were established, and future ground vibrations caused by expected seismic events were estimated using a probabilistic approach. The outcome was the number of intervals of expected ground vibration per year and per monitoring point. Possible measures to reduce inconvenience for the town residents include blast restrictions, sequencing, and possibly preconditioning. The ultimate long-term solution is an almost complete relocation of Malmberget town. This process has recently been formalized and LKAB is taking an active part in realizing this goal.

Jan 1, 2014

By D. J. Fourie

During the production of pure TiO2for the pigment industry, ilmenite, containing 35?60% TiO2, is reduced to high titania slag, containing 70?95% ?TiO2? and pig iron. The high titania slag produced, consists mainly of titanium in different oxidation states and FeO in equilibrium with liquid iron. To predict the phase and chemical reaction equilibria in a furnace, a suitable solution model is required with accurately determined binary interaction parameters, as slag melts tend to behave very non-ideally. This paper investigates two popular slag models, namely, modified quasi-Chemical (MQC) model and the cell model and provides the binary interaction parameters based on recently published data of the ternary system and critically assessed published unary and binary data. Very few modelling results have been published on the ternary Ti-Fe-O system pertaining to high titanium slags. The solution models, with their regressed interaction parameters, can subsequently be implemented in commercial software of the slag-metal phase equilibria to predict how much and which type of solids will precipitate for a given bulk slag chemistry and operating temperature or, alternatively, above which temperature should a furnace be operated to avoid excessive solids precipitation.

Jan 1, 2005

By E. Laine

Rock density determinations are necessary for ore resource evaluations from estimated block grades in g/t. Rock density depends on the mineral composition and, thus, it is specific for each rock type. The rock density distributions for different rock types are often symmetric. Hence, the arithmetic mean is a good approximation for the average density for lithological units. However, there may exist spatial variation in density values due to alteration, fracturing and original heterogeneities such as layering. This study compares the kriged density model with the one with constant density values for different lithological units in the evaluation of metal amounts in rock blocks. The case study consisted of rock densities measured from the drill cores at Ahmavaara PGE deposit in northern Finland. The used Ni contents were simulated in accordance with the spatial distribution of rock densities. The Ni amounts in 2x2x2 m3blocks are higher for the kriged densities than for the average densities. The difference is increasing with the increasing metal amounts due to the nonlinear correlation between Ni content and rock density. The final effect on the resource estimation depends on the cutt off grade and prices of the metal, for example, for a very valuable metal the small differences are significant

Jan 1, 2003

This paper summarizes the results from a project aimed at adapting scroll centrifuges for application to the dewatering of flotation concentrates. The main impetus for the project was to reduce the high cost and footprint size of the technology currently used to dewater fine coal. The technical challenge was to enhance solids capture by incorporating a laser-cut screen into the design of the basket. The project has shown that a pilot-scale scroll centrifuge can be used to dewater froth concentrate. A number of different basket designs were tested, the best results being achieved with a basket comprising a laser-cut screen of aperture 70 µm. The best result on a sample of untreated flotation concentrate, which was taken from the open trough flotation cells at a coal preparation plant (CPP) in NSW was a solids recovery of 82 wt% at a product moisture of 24.3wt%. By comparison the best product achieved with a conventional wedge wire basket was a similar moisture content but solids recovery was only 64 wt%. This could only be achieved after the feed had been artificially thickened. Conditioning of the centrifuge feed with polymer flocculants led to an increase in recovery up to 88 wt% with a moisture content of ca 25 wt%. It is thought that optimizing additive selection and conditioning parameters, as well as screen aperture and open area, could improve performance still further. The results were obtained using centrifuging conditions (centrifugal force, feed solids, feed rate) in the pilot-scale machine which should be possible to translate into conventional designs of commercial scale machines, without downgrading solids throughputs. However only with full-scale trials will it be possible to establish this assertion with certainty.

Jan 1, 2001

By M. van Schoor

Coal remains South Africa?s most abundant and cheapest source of energy, and there is an ever-increasing necessity for optimal and safe extraction of the remaining reserves. Increasing focus on cost-effective mining and zero harm to the environment and miners has resulted in a shift in attitude towards the application of geophysics in local coal mining and exploration. Furthermore, technological advances have contributed to geophysics being embraced more readily by the coal mining industry, compared to a decade or two ago. Predictably, the growing interest in geophysical technologies has also created a need for education and training in the basic principles and application of geophysical methods, as local coal mining companies generally do not have in-house geophysicists. Consequently, the Coaltech Research Organisation?s Geology and Geophysics working group forum compiled a textbook aimed at addressing this need: to produce a guide for applying geophysics to coal mining problems in South Africa. The target audience for such a book would be coal geologists, mine surveyors, mine planners, and other mining staff with limited or no geophysics background. This paper provides a very brief overview of the book by summarizing key sections and selected examples. In doing so, the value of geophysics to solving a range of coal mining and exploration problems is highlighted.

Jan 1, 2014

By J. Gunaselvam

This article deals with an investigation into the specification and use of appropriate seating systems to reduce whole-body vibration (WBV) exposure in typical vehicles used in the SA mining industry. The EU Directive EU/44/2002 to be legislated in 2005 in European countries, provides legal and economic motivation for this project. The criteria for seat selection can be condensed to the requirements in the directive, which mandates an action level of 0.5 m/s2and a vibration exposure limit of 1.15 m/s2 for an equivalent 8-hour daily exposure period. As part of this study six suspension seats, which the manufacturers claim satisfy the requirements in ISO 70966, were tested to determine the most suitable seat for an articulated dump truck. Six test subjects, three ?light? and three ?heavy? as specified in ISO 70966, were used to estimate the seat transmissibility functions in the vertical direction of the six different suspension seats. Transmissibility functions were measured in the laboratory with two excitation levels of 1 m/s2 and 2 m/s2 r.m.s. in the 0.5?30 Hz frequency range, as well as one spectrum approximating the EM5 spectral class. SEAT values were calculated for road vibration data measured on a typical articulated dump truck. A set of seat selection guidelines that can be followed by vehicle manufacturers and suppliers, procurement officers and and the technical staff on a mine is proposed in this article. It is recommended that additional studies of the use and operating conditions of seating systems in the SA industry, as well as an epidemiological survey be commissioned to gather additional information on this subject. Nomenclature ADT Articulated dump truck DSTF Dynamic seat testing facility EM1 Frequency spectra associated with earth moving equipment (?articulated or rigid frame dumper?) according to ISO 7096 EU European Union ISO International Standards Organisation PSD Power spectral density r.m.s .Root mean square SEAT Seat effective amplitude transmissibility WBV Whole-body vibration

Jan 1, 2005

This paper provides an overview of possible approaches for structuring the ventilation systems for mines that will become operational within the next decade. Features addressed in the paper include: aspects of airway design and layout in the absence of centralized vertical return shafts, the impact of using diesel-powered trackless equipment in conjunction with conveyor belts in the development and production phases of the project, and the need to balance increasing electrical power costs against the requirement for reduced capital expenditure. The paper provides brief descriptions of the strategies employed in real-life situations and presents an overview of various operational parameters affecting the design of ventilation systems that will be used as ?platforms? for much deeper mines in the future.

Jan 1, 2007

By J. Gholamnejad

The aim of short-term production scheduling is to decide which blocks of ore and waste to mine in which time period (shift, days, weeks or months) so that several operational and geometrical constraints can be satisfied simultaneously. Since 1960s several mathematical programming approaches were developed for solving production scheduling problems that are based on a combination of various operational research approaches such as linear programming (LP), integer programming (IP), dynamic programming (DP), etc. A number of models have been developed in the past three decades but some models have limited application especially to geometrical mining constraints. One of the geometrical constraints is block accessibility. All blocks must be accessible to mining equipments on the same bench. In this paper a binary integer programming model is developed in order to incorporate block accessibility constraints in an efficient manner. This mathematical model insures that each block has been open and can be loaded and transported easily by shovels and trucks.

Jan 1, 2008

By J. H. Zietsman

It has previously been observed that industrial high-titania slags display a compositional invariance, remaining close to stoichio-metric M3O5. The present study focuses on this invariance and the phenomena which may cause it. The invariance was studied using thermochemical calculations and a mechanism is proposed for the observed behaviour. The mechanism suggests that a combination of thermochemical equilibrium and transient slag solidification and melting results in the observed compositional invariance. The proposed mechanism provides new insights and prompts questions about other mechanisms in the smelting process.

Jan 1, 2004