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By N. Andersen

During the preliminary design phases and feasibility study of a proposed vertical shaft, a vertical diamond drill-hole is normally drilled on the site. This paper outlines how rock mass characteristics, in-situ rock stress, rock strength, hydrological characteristics, and structural parameters can be determined using wireline logging of this borehole. In addition, a rock mass classification scheme is developed, based on published work, and in particular the Q-factor is adapted to assess the stability of raise-bored shafts. The ‘stick plot’ is introduced, which combines all geotechnical parameters applicable to the stability of a vertical shaft into a colourcoded format where cross-correlations can readily be made on a day-today basis during the shaft-sinking process.

Jan 1, 2015

By C. A. Ozturk

The compressive strength of rock (sc) has an important effect on design of structures in rock engineering. Compressive strength can be determined in the laboratory using the uniaxial compressive strength (UCS) test. Some other index tests, such as the point load test, are also used, particularly when suitable samples for UCS are not available. The quantification of rock texture has introduced a new method in rock engineering for estimating the mechanical and physical properties of rock materials from microscopic investigations. The aim of this study is to quantify rock texture to estimate rock strength from the texture coefficient (TC), which is determined from a statistical assessment of thin section images. Rock texture is quantified by twelve different images from a single thin section to increase the reliability of texture analysis. A data-set is prepared to investigate correlations between TC and sc. The statistical correlations are computed after classifying of the rock samples based on their lithology as well as grain features. Equations derived based on the results of this study are used to predict the approximate value of compressive strength from the texture coefficient. This method is particularly useful for preliminary studies in rock engineering projects prior to detailed site investigation.

Jan 1, 2014

The compilation of the sampling nomogram is an essential tool in the optimization of a sampling protocol and allows the operator to track the change in relative variance of the sampling error (the Fundamental sampling error) during steps of comminution and mass reduction in the process of recovery of the aliquot for analysis. The data required for the compilation of the nomogram are centred on the sampling constant K and the exponent, alpha (a) of the nominal fragment size. Five methods for establishing K have been identified, but two of them, the duplicate sampling analysis method and the heterogeneity test method purport to provide such constant. The step by step procedure for each of these two methods was examined using broken ores from three mines, Mponeng mine, Kloof mine, and Lily mine. Two of these mines (Mponeng and Kloof) are typical Witwatersrand-type gold mines, and the third is an Archaean-type shear related gold deposit situated in the Barberton Greenstone belt. The results suggest that the factor K derived using the heterogeneity test is very accurate, but applies only to a single size fraction in the spectrum of comminuted materials. The calculation of gold grain sizes using this method appear to be too small and do not conform with the results from detailed mineralogical studies. The factors K and alpha derived using the duplicate series analysis are appropriate for use across a wide spectrum of comminution sizes and also provide realistic gold grain sizes, comparable with the equivalent circular diameter of gold grains identified in mineralogical studies of the ores.

Jan 1, 2010

By M. F. van der Merwe

Anglogold Ashanti?s Kopanang Gold Plant (previously No. 9 Gold Plant) treats ore from Kopanang and Tau Lekoa shafts. The plant is twin streamed and has dedicated treatment circuits, from milling to final product, for each shaft. Waste rock material is used to compensate for the mill gap on both streams. Each stream consists of three 4.85 m x9.15 m ROM mills in closed circuit with a single stage hydrocyclone, milling an average of 7 000 t per day. The liner configuration in each mill consists of six rows of 30 grid liners along with rectangular lifter bars. The topic of gold lock-up is not new and has been investigated and reported on many times, both within Anglogold Ashanti and the broader mining industry. Although the lock-up mechanism is understood, its measurement is neither practical nor precise. The initial lock-up in a new liner and the release as the liner wears down cannot be accurately quantified. Previous test work carried out on Kopanang Gold Plant (with a ?gold scanner?) measured the natural gamma radiation emitted by uranium. This radiation is in proportion to the mass of concentrate locked up in the grid liner pockets, as well as between the cast-on backing plate and the shell. The ratio of concentrate lock-up was estimated as 35% behind the liners and65% in the pockets. Mill gravity concentrates are recovered during routine relining operations from behind the grid liners at Kopanang Gold Plant. Prior to relining, the liners tend to release the concentrate from the pockets as the liners wear. Historical Kopanang data from actual ?mill gold? smelted indicates that an average of 29 kg gold is recovered from behind each row. This indicates a total lock-up of 250kg gold per mill. This locked-up gold should preferably be minimizedor eliminated for the following reasons: ?The cyclic build-up and release of gold in mills complicates accounting ?Gold concentrate arising from liners is a security risk and creates a major mechanism for gold theft ?Loss of interest on the value of 250 kg fine gold is significant and was a major driver for the project. These factors led to the need to develop techniques to eliminate or at least minimize the gold lock-up in the mills. Wave liners, with rubber inserts, have been successful in eliminating lock-up, and were tested at Kopanang Gold Plant in November 2000. However, due to increased load-slip and high wear rates associated with these liners, this option proved less economical in terms of liner wear. Grid liners, with rubber-filled pockets, demonstrated a very high wear life and eliminated pocket lock-up. This system was successfully trialed in January 2003, but unfortunately did not prevent lock-up behind the liners. Current developments have resulted in a system that eliminates both pocket and backing plate lock-up. The conventional grid liner design has been modified to remove its steel backing plate. Rubber inserts that are integrated onto a rubber backing plate, have been designed to be used with the newly modified grid. The backing plate and grid pockets are now completely occupied by rubber, thus completely eliminating concentrate build-up around the new grid liner system installed in November 2003. Results to date are promising and liner life is expected to exceed conventional performance.

Jan 1, 2005

By J. P. Bergh

The advent of low-quality export coal demand has brought a new range of possibilities to the South African coal industry. Products that traditionally were only of value to the domestic or combustion industry sectors now have the potential to be exported, with only minor amounts of upgrading required through beneficiation. Comparatively high steam-coal export prices can be obtained for lowquality export coal, which enhances the economic feasibility of expanding low-quality thermal coal exports. There are, however, increasing concerns about the feasibility of lower quality thermal coal exports and the broader implications. These concerns relate to the environmental impact of low-quality thermal coal production for export and the inherent threat to the security of domestic thermal coal supply in South Africa. Against this background, this paper serves to explain the extended value chain in the production of export coal. The technical and economic advantages and disadvantages of low-grade exports versus coal production for domestic use are evaluated. The value chain estimation is calculated by the beneficiation modelling and characterization of two coals. Based on the value estimation, the lowgrade export production scenario, and finally the modelling of potential pollutant distribution, are described. Keywords coal beneficiation, techno-economics, thermal coal, dense medium processing, dry processing, fine coal processing, environmental impact.

Nov 1, 2013

By B. P. Watson

Crush pillars have been incorporated into a mechanized, low-profile trackless system at South Deep Gold Mine. These pillars had to be designed to fail near the face and to ensure that pillar failure is contained within the pillar, to avoid bursting and the risk of high loads being generated during a seismic event, respectively. PoweRite backfill bags were recommended to maintain the integrity of the pillars; except in the main access drives, where the sidewalls were to be supported on 5.6 mm diameter weldmesh and yielding anchors. The results of a trial site investigation exceeded expectations, showing a residual pillar strength of about 37 MPa for a newly formed pillar and 8 MPa for a pillar subjected to seismicity and a closure of more than 300 mm. The introduction of these pillars has improved the rock mass conditions because of the active nature of the support, compared to the previous passive backfill method. Importantly, the pillars have increased mining efficiencies and improved face availability. A potential cost saving to the mine of R140.9 million could be realized over a period of 10 years.

Jan 1, 2014

The main objectives of the Mine Mechanisation and Automation program (MMAP) are to enhance health and safety in underground mining operations, facilitate mechanization and automation in narrow-vein and deep mines, provide sound science to regulatory agencies and improve mine profitability. The program, which has a unique underground and surface industrial scale facility, is involved in many multi-partner projects, like hydrogen fuelcell applications, electrification and hydraulification of underground mines, reduction of noise and vibration, miner location device, explosive-free blasting and hoisting. The paper presents an overview of the Mine Mechanisation and Automation Program of Natural Resources Canada and some of the main projects.

Jan 1, 2002

By G. J. de Korte

Dense-medium beneficiation of fine (minus 0.5 mm) coal is not a new concept and has been used in South Africa previously. The dense-medium fine coal plant at Greenside Colliery operated for almost 18 years and, despite proving a difficult plant to operate, did succeed in producing a fine coal product with a low ash content of 7%. No other beneficiation process available could achieve this. Dense-medium beneficiation of fine coal was also used in other countries, of which the plants at Homer City in the USA and Curragh in Australia were the best known. The first application of dense-medium cleaning of fine coal was, however, at the Tertre plant in Belgium1. This plant was built in 1957. About nine years later, a second fine coal dense-medium plant was built at the Winterslag Mine, also in Belgium. According to reports, this plant operated satisfactorily for a period of some 17 years.

Jan 1, 2002

By K. Woodward

"SynopsisSeismically active mines generally experience an increase in seismic hazard due to rock mass instability following blasting. Re-entry protocols commonly include measures to limit the spatial and temporal exposure of personnel to increased seismic hazard induced by blasting. The management of periods of increased seismic hazard requires the development of re-entry protocols for a unique mining environment. Identifying mining conditions that may result in significant seismicity following blasting relies on retrospective analysis, which is often focused on seismicity occurring within a certain period after blasting and within a certain radius of the blast in the broader context of site-specific experience.The analysis of seismicity without considering blasting times and locations allows for the relationship between seismicity and blasting to be investigated without prior assumptions concerning dependency. To achieve independent analysis, seismicity that is clustered in space and time (referred to as a seismic sequence) must be identified by assessment utilizing only seismic parameters. An automated algorithm is implemented that assesses the timing, location, and quantity of seismicity to identify seismic sequences, represented by the time of the first event and mean location of all events in the sequence.The relationship between sequences and blasts is assessed by calculating the distance and time from each sequence to the closest blast in space and time. Establishing an independent classification between sequences and blasting provides insight into the unique cases where seismic sequences are remote and/or delayed with respect to blasts and identifies cases when sequences exhibit a weak relation to blasting. The nature of seismic responses to blasting has direct implications for the management of the increased seismic hazard associated with seismic sequences.The approach presented in this study contributes to the management of seismic hazard by providing empirical support for the relationship between seismic sequences and blasting. These relationships indicate the portions of sequences that can and cannot be practically managed using tactical approaches. Furthermore, the analysis of sequences reveals the nature and evolution of rock mass responses to blasting. These results have implications for the extent of spatial or temporal re-entry restrictions required for the optimal management of time-dependent rock mass response to mining."

Jan 1, 2015

By V. C. Kelessidis

The interaction between rock and drill bit during drilling has been modeled for many years, but a complete understanding of the phenomena occurring has yet to materialize. Successful models will allow the prediction of rate of penetration in a given environment and optimal selection of drill bit and drilling parameters, thus minimizing exploration costs. In most rock-drilling models the value of the unconfined compressive strength of the rock (UCS) is used in the predictive equations, within the concept of specific energy, and the value of UCS is the percentage of the value of the stress applied on the drilling bit in order for the bit to advance. While the exact percentage depends on the model used and it is not known with certainty, good knowledge of UCS is nevertheless required before any decent prediction can be made on rate of penetration. Determination of UCS, normally done via destructive testing, requires not only the availability of sound rock core samples but also expensive testing and significant time for the test, which frequently are not available for routine drillability predictions. Hence, a multitude of methods and techniques has been proposed for estimating UCS from various indirect and/or non-destructive measurements, or combination of measurements with neural networks, such as point load index, block punch index, unit weight, and apparent porosity, water absorption by weight, sonic velocity, and Schmidt hardness. The many proposed approaches are critically reviewed and the results are compared, and what becomes apparent is that after many years, not only in mining but also in oil-well drilling, accurate indirect determination of UCS is still an elusive goal. An equation to predict UCS from sonic velocity data is suggested based on several data sets reported in the literature. Use of the specific energy equation with UCS or sonic data and utilization of drilling data allows an estimation of the efficiency of energy transfer from the bit to the rock and of the friction coefficient. Analysis of data reported in the literature, both from laboratory and field studies, has shown that this approach is sound and enables the determination of energy transfer efficiencies and friction coefficients, which for the cases studied range between 15 and 30% and 0.15 and 0.30 respectively. Thus, the suggested data analysis approach allows drillers to focus on inefficiencies and optimize drilling practices in future campaigns. Keywords Rock drillability, unconfined compressive strength, prediction.

Jan 1, 2011

By S. Parada, P. T. Jones, M. Guo, S. Smets

The corrosion behaviour of a high-quality rebonded magnesia-chromite refractory in contact with a vacuum oxygen decarburization (VOD) slag with high Al2O3content (15?20 mass per cent) is investigated under VOD process conditions by rotating finger tests in a vacuum induction furnace. The refractory degradation mechanisms are studied by the characterization of corroded microstructures using scanning electron microscopy, equipped with energy dispersive spectroscopy. The influence on the refractory wear of the process temperature and the Al2O3content in the slag is discussed. Keywords: corrosion, magnesia-chromite refractory, VOD slags, vacuum induction furnace

Jan 1, 2004

By H. J. Uananisa, M. J. Papo, C. W. Siyasiya, W. E. Stumpf

"SynopsisThe need to reduce weight while maintaining good mechanical properties in materials used in the automotive industry has over the years seen an increased exploitation of various steels to meet this new demand. In line with this development, the ferritic stainless steel family has seen a wide application in this industry, with the AISI 436 type increasingly being used for automotive trims and mufflers for exhaust systems, as well as a significant part of this steel’s application being for the manufacture of wheel nuts and wheel nut caps in trucks, mainly through the deep drawing process. However, there have been reports of some poor surface roughening of this material during deep drawing, with tearing and/or cracking also reported in some instances. This has been suspected to possibly be associated with some local differences in localized mechanical properties between grains and grain clusters of the rolled and annealed material.In order to investigate the poor surface roughness exhibited by AISI 436 ferritic stainless steel (FSS) during deep-drawing, Lankford values (R-mean and ?r), grain size, and microtextures of various sheet samples from this steel were studied. The chemical composition range for the samples was 0.013–0.017% C, 17–17.4% Cr, 0.9–1% Mo, and 0.4–0.5% Nb. The steels were subjected to various hot and cold rolling processing routes i.e. involving industrial direct rolling (DR) or intermediate annealing rolling (IR), and the drawability and final surface qualities of the steels were compared. It was found that the DR route gave an average R-mean and ?r value of 1.9 and -1.4 respectively, while the IR route yielded an average Rmean and ?r value of 1.6 and 0.52 respectively. The high ?r value for the DR processing route had a substantial adverse effect on the drawability. IR samples exhibited a smoother surface finish on visual inspection, while clear flow lines were visible on the DR samples, despite the fact that DR is the preferred industrial processing route due to the reduced production costs it offers. This observation was also confirmed through SEM examinations. The difference in the surface quality was attributed to microtexture. However, the mechanism responsible for this difference still needs to be identified."

Jan 1, 2015

By E. Pizarro, A. Videla, G. Compan

One of the main problems related to mining investment decisions is the use of accurate prediction models. Metallurgical recovery is a major source of variability, and in this regard, the Chuquicamata processing plant recovery was modelled as a function of geomining-metallurgical data and ore characteristics obtained from a historical database. In particular, the dataset gathered contains information related to feed grades, ore hardness, particle size, mineralogy, pH, and flotation reagents. A systemic approach was applied to fit a multivariate regression model representing the copper recovery in the plant. The systemic approach consists of an initial projection of the characteristic grinding product size (P80), based upon energy consumption at the particle size reduction step, followed by a flotation recovery model. The model allows for an improvement in the investment decision process by predicting performance and risk. The final geometallurgical model uses eight operational variables and is a significant improvement over conventional prediction models. A validation was performed using a recent data-set, and this showed a high correlation coefficient with a low mean absolute error, which reveals that the geometallurgical model is able to predict, with acceptable accuracy, the actual copper recovery in the plant.

Jan 1, 2015

By P. Turcotte, E. Karampinos, F. Mercier-Langevin

In some underground hard-rock mines, squeezing compressive ground conditions are influenced by the presence of rock foliation and high stress. In these cases, the orientation of the foliation with respect to the drift direction has a considerable impact on the magnitude of the resulting deformation. Irrespective of the reinforcement and support strategy, keeping drives developed sub-parallel to the rock foliation operational is difficult, and often requires excessive rehabilitation during the lifetime of the excavation. This study uses field observations and convergence measurements at the LaRonde and Lapa mines of Agnico Eagle Mines Ltd to provide guidelines of the anticipated squeezing levels at these operations.

Jan 1, 2015

By W. D. Northrop

This paper gives an account of the development of a technique whereby the vertical limits of geological horizons may be identified by the use of vertical variograms on the mineral of economic interest. This information may supplement or guide the correct subdivision of the individual horizons into meaning full data sets by diligent geological observation. This process then improves the quality of the variance modelling of the gold distribution in the plane of the individual layers and therefore enables better estimates to be made into the grids or blocks of the mine model. The technique is explained by an account of the development work, which was performed, on duplicate superimposed reef horizons in the Kimberley formations. The paper then shows how the correct approach was developed to evaluate the mineralized layers in a multiple stacked conglomerate layer sequence in the Elsburg reefs of the Witwatersrand Rand System at the Target deposit. The method of categorization of resources according to confidence in the estimate is also explained. The feasibility processes carried out on the three-dimensional model, in accordance with the SAMREC code are also described. An example of the development of a reconciliation process utilizing chip sampling is also explained.

Jan 1, 2003

By S. H. Yi, J. R. Kim, Y. S. Lee

The viscosities of CaO-SiO2-Al2O3-MgO-FeO slags were measured under conditions ofCaO/SiO2=1.15–1.6, 10–13 percent Al2O3, 5–10 percent MgO and 5–20 percent FeO. Slag viscosity decreased with increasing FeO content at a fixed basicity (CaO/SiO2) of slag. Slag viscosity at low FeO (<7.5 percent FeO) exhibited a minimum value by increasing MgO content in slag. Viscosity decreased with increasing slag basicity up to 1.3 while it increased as slag basicity increased from 1.3 to 1.5. Thus, it was proposed that the driving force for the decreases of slag viscosity would be an increase in depolymerization of silicate network at C/S=1.3, while the viscous behaviour at C/S>1.3 would be increased with increasing the chemical potential of primary solid phase e.g. dicalcium silicate. A thermodynamic approach for the activity of primary solid phase in molten slags resulted in a reasonable relationship between viscosity and slag components. Therefore, it was confirmed that slag viscosity in basic slags system (C/S>1.3) could be determined by the chemical potential of dicalcium silicate. Keywords: viscosity, basicity, bosh slag, blast furnace, slag structure, FT-IR

Jan 1, 2004

By R. C. D. Phillis

The management of critical resource inventories is an important productivity lever and a significant risk factor?risk in the sense that poor resource availability lends itself to disempowerment of workers, unsafe work practices, wasted spending (high unit costs),and poor quality of work (including mining waste/rework). Most underground platinum mines experience lost blasts that directly lead to reduced productivity. In most surveyed shafts, 30% of lost blasts can be attributed to shortages of critical material and/or equipment. The problem is prevalent despite the existence of conventional transitory surface and underground stores. This paper discusses the introduction of buffer stores as a complementary materials storage system in order to improve health and safety in mines as well as reduce lost blasts. Both quantitative and qualitative results have shown that buffer stores result in dramatic improvements in productivity and are readily acceptable by stakeholders. Keywords Buffer stores, lost blast.

Jan 1, 2011

By M. K. Elmouttie, G. V. Poropat

Mapping of exposed rock walls provides data on geological features such as joints, bedding planes, faults etc critical to the economics and the safety of mine operations. Traditional, manual methods of mapping can be time consuming, error prone and limited in their coverage. New methods have been developed to map exposed faces remotely and safely however the benefits of these methods are only fully realised when exposed structures can be quickly and easily mapped using automated methods. This paper describes the application of an automated method of analysis of 3D images that provides users with the capacity to map exposed structures automatically. The method is based on the use of vector classification methods used in some neural network systems and provides rapid and reliable identification of exposed planes. CSIRO Exploration and Mining is applying these methods to 3D images for a range of applications from pit mapping to machine automation.

Jan 1, 2006

By C. J. Pretorius

More than 30 percent of the global demand for zircon (ZrSi04) is supplied by South Africa. A significant amount of the zircon is exported, and beneficiated products are then imported for industrial applications locally. Beneficiating the zircon locally could have a positive impact on the local market, since zircon is only one of many such cases. Ammonium acid fluoride serves as an alternative anhydrous fluorinating agent for zircon in the synthesis of several metal fluorides1,2. It provides an effective dry fluorinating method and is easier to handle than hydrogen fluoride or fluorine gas. Zircon exposed to extreme plasma temperatures dissociates and becomes more reactive. The reaction of the plasma-dissociated zircon (Zr02.SiO2) with the ammonium acid fluoride (NH4F.XHF, where x= 1 to 5) forms two main intermediate compounds (NH4)3ZrFr(s) and (NH4) 2SiF6(s), the latter decomposing to form volatile products at relatively low temperatures, providing easy separation of the silicon and zirconium compounds. The ammonium zirconate compound decomposes to form zirconium tetrafluoride (ZrF4), which can be further manufactured into zirconium metal, to name but one product. Data on the kinetics of the reaction of ammonium acid fluoride with zircon and plasma-dissociated zircon, combined with the thermo¬dynamic parameters of the reaction, is essential for the development of an industrial process for the production of a precursor for the manufacturing of zirconium metal, namely anhydrous ZrF4. Both the reaction kinetics and reaction parameters will be included in this study, as well as some proof that the reaction proceeds to ZrF4 on a small batch scale. If the exact reaction parameters can be pinned down, a wide spectrum of anhydrous metal fluorides can be synthesized through this fluorination route.

Jan 1, 2012

By Phillip M. Dight

A number of impending and actual pit wall failures have been observed and documented which have been interpreted to initiate on newly generated structural features. This infers failure through intact rock. Failure mechanisms have been postulated resulting from circumferential stress, extensional strain and brittle flexure. These will be discussed in the context of the failures and the associated monitoring. The implications of failure initiating on ?unknown? features has a significant impact for deep open pit mines where designs are based on the expected structural regime. Being able to anticipate such failures is important for design. Equally important is management of such changes as they arise. In this context, monitoring using high resolution microseismic techniques will be discussed as a means of providing early warning of such failures.

Jan 1, 2006