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By D. G. Krige

For the purpose of determining confidence limits for ore grade estimates, an extensive simulated data base was used, which included 1728 ore blocks with ‘actual’ grades and the corresponding estimates based on ordinary and simple kriging. The practical results show that conditional unbiasedness is essential and that acceptable confidence limits can then be set using Normal theory for the simulated error distribution based on the logarithms of the ratios of ‘actuals’/estimates with a variance related to the kriging variance. The mean of the data used to prepare the variogram and the estimated block grade are to be used properly in this approach. A practical analysis was also done of the actual point and block data from a very large mined out Carbon Leader area. The distributions of the actual grades for two levels of block sizes with different levels of variability were fitted using three models, ie. 2-. 3- and compound-lognormal. The trends of tonnages, grades and relative profits for a range of pay limits, as well as the usual tonnage-grade curves, show a practical insensitivity for the choice between the three lognormal models considered.

Jan 1, 2003

By T. O. Hagan

A simulated rockburst experiment was conducted underground at a deep level gold mine. This was done by means of a large explosion detonated in solid rock close to a tunnel sidewall. The resultant shake-out damage is typical of that associated with a small seismic event in close proximity to a tunnel that is subjected to the estimated field stress, as in this case, of 50 MPa. The experiment involved: ?the design of a blast to mimic a seismic source ?seismic monitoring using a dense seismic array ?high speed video filming ?a study of rock mass conditions (fractures, joints, rock strength etc.) before and after the simulation using mapping and ground penetrating radar ?special investigations to evaluate the mechanism and the magnitude of the damage ?a study of support behaviour under excessive dynamic loading.

Jan 1, 2001

By André de Jager, Henk Ludik

Navachab Mine experiences difficulties with pit wall stability in certain areas of the mine. The main reason for the instability is the fact that the geology comprises many joints and faults. Blasting, without impacting negatively on the stability of the pit walls, poses a major challenge. The mine has installed a technologically advanced seismic monitoring system with monitoring sensors positioned at various locations and depths throughout the pit. The electronic data recording system records all relevant information on a continuous basis with early warning signals in cases of potential danger. From the information recorded by this micro-seismic system it was established that the energy release into the high-wall is predominantly influenced by the mining rate, water content and mining tempo and to a lesser extent by the blasting operations. To limit the negative effects of blast vibrations, the use of Electronic Delay Detonators (EDDs) was introduced. The optimal delays were determined through signature trace analysis. The vibrations obtained during blasts initiated by means of electronic delay detonators were monitored and compared to those traditionally obtained when standard pyrotechnic delay detonators had been used. The measured vibration data indicated an improvement of 25% to 100% drop in vibration amplitude compared. The accuracy and programmability of EDDs presented huge potential for blast optimization in terms of limiting the vibrations without compromising fragmentation. The whole project was conducted over a twelve week period with some 4000 EDDs. The average size of a blast was in the order of 350 holes using about 40kg explosives per hole, which equates to 14,000 kg explosives over 12 different blasts. The paper deals in detail with the blast optimization process with regard to: - determining the rock response time; - establishing the signature traces; - analyzing the wave interference patterns; - predicting the direction of constructive and destructive wave interferences; - optimizing of the inter-hole and inter-row delay periods; - measuring the ground vibrations. The results obtained during electronic blasting are compared to those obtained during pyrotechnic blasting. Comparisons are being made with regard to the following: - ground vibration measurements; - pit wall stability measurements; - blast safety.

Jan 1, 2006

By P. Mogodi

The purpose of the project was to propose a coal clearance system (coal transportation system from the mining face to the plant) that could be used for the planned underground operations at Zondagsfontein Colliery. Components of the current coal clearance system were overlooked during feasibility studies. Subsequent studies of the coal clearance system revealed that the combined capacity of the two trunk belts does not match that of the shaft (main) belt. As a result production downtimes will be encountered due to bottlenecks in the system. Ways of addressing this challenge were analysed by weighing both advantages and disadvantages and ultimately a surge bin option was selected. Belt conveyor simulations were conducted in order to determine the optimum capacity of the surge bin. The configuration of the surge bin in relation to the two trunk belts was chosen by considering development cost, advantages, and disadvantages of each option. It was concluded and recommended that a 500 tonnes capacity surge bin is required to remove the bottleneck from the system.

Jan 1, 2010

By M. Rafie, M. Rinne, F. Samimi Namin

"SynopsisRock mass classification systems constitute an integral part of empirical underground excavation design. One system that is commonly used to classify rock mass is the Rock Mass Rating, or RMR, system. The RMR system has evolved over time to better reflect the perceived influence of various rock mass factors on excavation stability. While the introduced modifications have enhanced the applicability of this classification system, there are still areas that cause potential ambiguity. The RMR system cannot deal with input data ambiguities, uncertainties, and vagueness. To deal with the uncertainty, a Fuzzy Rock Mass Rating (FRMR) has been developed. This study aims to describe the main concept of the fuzzy approach, which is implemented in the FRMR to classify rock mass. The FRMR considers the uncertainty associated with the input data (uncertain variables) used in rock mass classification. The Gol-e-Gohar (GEG) area 3 iron ore deposits in the south of Iran were chosen as the case study for investigating the applicability of FRMR. The results of this study show that the FRMR software tool can easily be used for rock mass classification, even if uncertain input parameters have been used. FRMR consists of three parts, each of which is suitable for certain conditions.IntroductionNowadays, rock engineering classification systems, which constitute the backbone of the empirical design approach, are widely employed in both civil engineering and mining engineering. Rock mass classifications have recently been quite popular and are being used mostly for the preliminary design and planning purposes of projects. According to Bieniawski (1989), a rock mass classification scheme is intended to classify the rock masses, provide a basis for estimating deformation and strength properties, supply quantitative data for support estimation, and present a platform for communication between the exploration, design, and construction groups."

Jan 1, 2015

By V. V. Nazimko, A. I. Hohotva, S. N. Alexandrov, V. P. Sazhnev, V. S. Zaharov

Ground behaviour in the vicinity of a roadway has been investigated using a physical model and in situ tests during a roof fall. It was discovered that behaviour of the ground is governed by irreversible displacements of adjacent rock clusters. The cluster is a short-living sector of a rock mass that moves as a solid body. For the lack of degree of freedom, the rock mass must be divided into clusters that are forced to move one after another in space and in time. These clusters permanently rearrange and reform during irreversible (inelastic) ground deformation. The crowded clusters have to yield to each other and alter their velocity and direction of movement to accommodate their motion into the excavation. Such behaviour involves uneven and irregular vertical deflection and the movement of adjacent rock blocks in the roof, sides and floor of an opening. Such movement destroys the symmetry of horizontal displacements with respect to the centre line of the opening. A set of indicators that a roof fall is imminent has been identified. Horizontal displacements and dilation must be controlled in order to maintain the stability of an underground opening. Such a state retains the self-supporting effect of the roof and contributes to rock bolts bearing capacity.

Jan 1, 2003

COALTECH 2020 initiated a research project to provide the coal mining industry with a modelling tool to determine the expected types of subsidence, risks and the investment required in post-closure funds to cater for subsidence associated with bord and pillar mines. A detailed literature review was conducted to determine the most important parameters in calculating the cost associated with surface subsidence. A subsidence prediction model was developed to determine the likelihood of different types of subsidence. The study made use of current knowledge of failure mechanisms and its aim is to assist the industry and government in arriving at the most suitable arrangements when authorities require financial instruments to assure compliance with environmental regulations.

Jan 1, 2003

By B. Derin, T. Uzunoglu, O. Yücel

In this study, reduction behaviours of Turkish chromite concentrate (48 % Cr2O3, 13.30 % FeO, 18.33 % MgO, 12.37 % Al2O3, 5.76 % SiO2) and nickel oxide by Fe-C alloy in graphite crucible were investigated. In the first stage of experiments, steel scraps were melted in graphite crucibles and were saturated with carbon at 1600 °C and 30 min. In the second stage, mixtures of different amount of chromite concentrate, nickel oxide and flux additives (CaO,SiO2 and CaF2) were charged into the graphite crucible containing the Fe-C alloy and heated to 1600 °C for different reduction times (0-180 min) under argon gas. The highest Cr and Ni con-tents in alloys were found as 11.41 and 14.37 % and the highest Cr and Ni recoveries were found as 88 and94 %, respectively at 180 min.

Jan 1, 2007

By S. Ganguly, R. Kononov

Carbothermal reduction of manganese oxides and manganese ores in the solid state was studied in hydrogen, helium and argon at different temperatures, ore compositions and carbon to manganese oxide ratios. Wesselsore (South Africa) and two grades of the Groote Eylandt ore (Australia) with different level of impurities were examined. Ores were characterised by XRD, X-ray fluorescence, optical microscopy and scanning electronmicroscopy. Isothermal and temperature programmed carbothermal reduction experiments were conducted in a fixed bed reactor in a vertical tube furnace, with on-line monitoring of gas composition by the CO-CO2 infrared sensor. The reduced samples were characterised by XRD, SEM and LECO analyses. Extent of reduction was calculated using data on the off-gas composition, and LECO carbon and oxygen contents in the reduced sample. Manganese oxides in the ore were reduced to a-Mn and carbides Mn23C6 and Mn7C3 depending on the carbon to ore ratio. The reduction rate of manganese ores in hydrogen was higher than in helium and argon. Key words: Manganese, Carbothermal Reduction, Hydrogen, Argon, Carbon Monoxide, Helium, Kinetics.

Jan 1, 2007

By S. Rolseth, J. Thonstad

The traditional electrolyte for aluminium electrolysis is based on molten cryolite (Na3AlF6), acting as solvent for the raw material, alumina (Al2O3). Over the years there has been a trend to increase the content of excess aluminium fluoride (AlF3) to the cryolite-based electrolyte, in order to enhance the current efficiency of the process. In most cases one has ended up at 11?13 wt% excess AlF3because higher contents makes it difficult to control the heat balance of the process. This problem may be overcome if sensors are developed that will allow online control of electrolyte temperature and composition, and we may then see a surge towards still higher AlF3contents. In the development of new anode materials to replace the carbon anode with inert, oxygen-evolving anodes, focus is on anode corrosion, and a low electrolyte temperature is then highly desirable. While the conventional process operates at around 960°C, electrolyte temperatures as low as 750°C are being tested. This is achieved by having large excess contents of AlF3(40 wt%). The consequences of using such electrolyte compositions are discussed.

Jan 1, 2004

By R. J. Kendall

As we enter the new millennium, the South African mining industry has to ensure that it becomes more competitive if it is to survive in the ever more demanding global environment. Traditionally, mechanization in narrow stopes has been limited to the use of scraper winches, and numerous mechanization attempts have been restricted to pilot projects operated on an extremely limited scale (with varying degrees of success). The benefits of hydropower are well documented, and Northam Platinum has shown these benefits to be achievable on a mine-wide basis. However, the equipment originally developed for hydropower systems has followed the traditional labour-intensive approach commonly used in deep level narrow stoping operations. The problems experienced with the hydropower system are discussed and the rationale for developing alternate technologies is explored. The hydropower system has shown to be a versatile powering medium which can be harnessed for a diversity of uses. It (hydropower) enables the mining engineer to change traditional paradigms and to design an entirely new approach for optimizing the mining operation based on explosive techniques. The system developed for Northam consists of the following: ?Purpose-built stope drill rig operated off the hydropower system with special features to ensure accurate drilling patterns throughout the length of the blast hole ?Purpose-built high rate cleaning system for rapid transfer of fractured ore to the stope orepass ?Redesigned stope layout to facilitate in-stope water control and to recover fines from the run-off water ?Purpose-built drill rig for rapid establishment of reef raises and advanced strike gullies ?Purpose-built drill rig for flat end development. On both types of development end rig, emphasis is placed on ensuring accurate drilling patterns throughout the length of the hole to maximize linear advance per blast. The paper discusses the implementation of the Northam system on a large scale as well as current initiatives to further improve on the efficiencies of mining operations. It concludes by emphasizing that mechanized hydropowered stope technologies are in their infancy and thus offer unlimited scope in progressing beyond today?s paradigms to present as yet unthought of solutions for optimizing deep level ore extraction.

Jan 1, 2000

By K. Kotwica, P. Gospodarczyk, J. Sosnica, J. Pawlik, Z. Iwulski, K. Pawlik

The paper presents problems resulting from the mobile mining machines functioning and requirements concerning a machine control system, which controls successive operation stages of such machines. The problem is presenting on the example of a mobile hydraulic support to remove residual pillars in copper ore mines. The paper describes an algorithm and a flow chart to be followed when designing a supports control system. Design of control systems to ensure machine function under given circumstances is also presented.

Jan 1, 2003

The effect of microwave radiation on the processing of Palabora open pit ore has been investigated. Significant reductions in Bond work index are demonstrated for microwave treated samples. Reductions in work index were found to be sensitive to applied power level and method of application. After single stage magnetic separation tests, improvements in recovery of FeO were noted. However, these were curtailed by oxidation of the magnetite species as a result of continued heating. The effects of microwave radiation upon the recovery of copper after froth flotation were also quantified. Small initial increases in recovery of copper were note dafter microwave treatment. However, with prolonged exposure, recovery was found to decrease. Overall recovery of copper was not affected except for samples treated for extended duration. The influence of microwave treatment upon the conventional Palabora grinding circuit has been quantified with the use of USIMPAC software. Conclusions are made regarding the economics of microwave treatment for this ore. Keywords : Microwave; Grinding; Magnetic Separation; Flotation; Economic Analysis

Jan 1, 2000

By Y. Poornachandra Rao, P. C. Sudhakar, L. Malakondaiah

NBV commissioned a 27.6 MVA furnace in the year 2005. This paper explains: a)Furnace design features b)Furnace process control, Direct slag granulation c)Continuous casting, Waste heat recovery, Sintering d) Gas cleaning plant, Protection of Environment. Keywords: Furnace Equipment, SiMn Production, Casting, Heat Recovery and Low hood

Jan 1, 2007

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 G. Kang

The ferroalloys industry has generated historically substantial solid waste. The accumulated waste causes serious problems to the environment. However, it is possible to transform the solid waste into an environment-friendly resource to serve the human being. Consequently, the construction of plants that are ?environment-friendly? and that accommodate ?recycling? has become a target of most ferroalloy producers in the world to ensure sustainable development. This paper introduces the practice of Shanxi Jiaocheng Yiwang Ferroalloys Works, the biggest manganese metal producer in China, in the development of an ?environment-friendly and recycling? process. The process includes power generation using coal gangue, waste from local coal mines; hollow bricks manufacture using slag and fly ash from the power station; cement production using slag from ferroalloy smelting; recovery of ferrous and non-ferrous elements in the dust from the furnace gas cleaning system; application of silica dust in construction and so on. The final objective of the plant is to realize zero discharge of solid waste. The profit of the ?environment-friendly and recycling? process compensates in part for the operational expense of the environment facilities.

Jan 1, 2004

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 R. T. Jones

Technical publications in the field of mining and metallurgy have existed for a long time. Recent developments in electronic publishing on websites make it possible to disseminate information more widely and cost-effectively than before. Professional societies have an opportunity to serve their members and their industry by publishing high-quality peer-reviewed papers on their websites as well as in printed form. Older publications can be scanned, and optical character recognition used to provide searchable text. Various business models exist around this process. This paper outlines the approach used by the Southern African Institute of Mining and Metallurgy (SAIMM) to provide free open access to their journal papers and conference proceedings, as well as the work being done by OneMine.org to collect technical papers from a number of international societies and make them available to subscribers via a large database. An approach is outlined that should be of benefit to authors, readers, and society at large.

Jan 1, 2012

A physical modelling study has been carried out to simulate the slag-metal dispersion induced by a high-strength bottom gas injection. Water and kerosene were utilized to simulate metal and slag respectively. A water model of CLU (Creusot-Loire Uddeholm) vessel was used with three different nozzle orientations, namely, off-centre, triangular off-centre and centre. The gas flow rates changed from 0.00599m3/sec to 0.01081m3/sec. Height of heavy and light phases was kept fixed at 0.23 m and 0.02 m respectively. The dispersed phase holdup was determined at various axial and radial distances, gas flow rates, and tuyere configurations. The observations revealed that at a fixed gas injection rate, as the vertical distance increased in the centerline, straight off-centre orientation resulted in greater dispersed phase hold up values than those of the centre configuration and the triangular off-centre orientation. The dispersed phase holdup was found to increase with gas injection rate and decreased with axial distance. The variation of the dispersed phase hold up with the dimensionless axial distance and the gas injection rate was correlated by using the Modified Froude Number. The experimental values of the dispersed phase holdup were found to be in good agreement with the correlated values obtained from the modelling equations. The findings of the present study may be utilized in the ferroalloy refining vessels in terms of designing tuyere locations for optimum processing conditions.

Jan 1, 2004

By P. I. Page

In mineral exploration the place that yields the first significant result is marked and two questions are posed immediately. Where should the next sample be drawn and how big should it be? At present the answers are arbitrary and ad hoc. They depend on personal experience and sentiment?that is hunch. The thought processes involved in reaching the decisions are unsatisfactory and unsatisfying for professionals. This paper proposes guidance on choosing sample spacing and sample size. The guidance is obtained from the grades of the samples. The grades also imply the extent of influence of each sample assay. Thus sampling and assay are integrated. The integration is achieved by changing the unit of value in which assays and grades are expressed and by exposing meanings and functions of grade beyond that of measuring rock value. The proposals are extended to guide comminution of particle size in sample size reduction and to deal with the problem of erratic high assays. Also, elucidation becomes possible of the computation of a reliable figure for average grade as a statistical weighted mean.

Jan 1, 2005