Search Documents

By A. D. Storrie

An underground wet shotcrete trial was completed last year to determine the effectiveness of wet shotcrete as an alternative support mechanism to dry shotcrete in the kimberlite environment. The wet shotcrete was manufactured at the underground batch plants, transported to site using an agiecar and transferred to the shotcrete pump. The wet shotcrete is pumped to the nozzle where compressed air at 7 bar and an accelerator, Meyco SA 160, is added and enables the shotcrete to be placed successfully onto the tunnel wall. No tunnel guard was previously placed on the sidewall and hangingwall. Geotechnical testing indicates that the Grace fibre performed extremely well with the energy absorption tests at 7 kg/m3and 8kg/m3where both achieved over the mine requirement of 750joules. The Grace fibre and wet shotcrete mix also achieved a compressive strength in excess of 55 MPa, well above the 45 MPa requirement for Premier Mine. The recommended wet shotcrete mix design is therefore based upon: [Material/ CriteriaQuantity/m3Units ?Lafarge 42.5 Duratech500kg ?Condensed silica fume40kg ?Rayton Sand1.558Ton ?Delvocrete stabilizer 103.6litres ?Glenium 27CH5.4litres ?Meyco TCC 7355litres ?Water230litres ?Meyco SA16025litres ?Fibre8kg ?Cement/Water Ratio2.35? ?Water/Cement Ratio0.43? ?Flow615 mm] If the wet shotcrete system is implemented there is a potential for Premier Mine to make major savings. In South Africa there are two suitable wet shotcrete machines available for the mining industry, the Spreymec, manufactured by Tamrock and the Fermel/Meyco wet shotcrete machine. The Spreymec is a fully imported machine. The Fermel component is manufactured in South Africa and the Meyco shotcrete components are imported and supported by MBT (Master Builder Technologists) in South Africa. The Fermel/Meyco machine is assembled in South Africa. Premier Mine has allocated some R2, 100,000 towards the implementation of the wet shotcrete system. If implementation is successful there should be an internal rate of return gain of 76% with regard to this project.

Jan 1, 2001

By W. Barnett

The Limpopo Metamorphic Belt is a complex geological terrane with at least three major deformational events. Tectonically juxtaposed lithology, open to isoclinal folding, crosscutting and re-activated shear zones and metamorphic gneisses and schists make pit slope design and maintenance a risky business. Venetia diamond mine?s Cut 3 is planned to reach 360 m by 2011. The difficult rockmass created problems in the original pit and a new more comprehensive slope design was necessary. Nearly 9 km of geotechnical drilling were undertaken to produce a new geological model and provide geotechnical information near the final Cut 3 face. All existing data from the pit were brought together into a database. SRK Consulting were brought into the project to audit the process and provide most of the manpower for the data analysis. Existing failures were back-analysed and the geotechnical domains identified. Analyses of only the southern domains are discussed in this paper. Geotechnical engineers can design slopes at any angle, but it is up to the managers at the mine to decide what risk they are willing to accept in a slope design. Once the issue of risk was discussed and settled in respect of the consequences of failure, each of the main geotechnical domains were analysed to produce a slope design at5% probability of failure with 15% above the first ramp. A risk assessment of the design was then undertaken to determine what risk the design placed on the equipment, personnel and the profitability of the overall mining operation. The risk assessment indicated minimal risk to the operation. One of the main assumptions of the final design is that the pit slopes will be dewatered. A project was immediately put in place to determine a groundwater model for the mine and to thereby determine the best dewatering procedure. However, it should be obvious that it is practically impossible to prevent benches from getting briefly saturated with water during storm conditions. It was therefore necessary to look specifically at supporting the crests of the ramps in the problematic southern domains to guard against the possibility of crest failure during heavy rains. The data available were re-analysed toward this objective. Spiles were recommended as the most cost-effective support system, and a probabilistic approach was used in the design. The final design has a 5% probability of failure, and the analyses indicate a strong sensitivity of the required spile spacing to the strength of the reinforcement material that will eventually be used. The pit slope parameters derived as per the discussion in this paper have just begun to be implemented at Venetia Mine.

Jan 1, 2001

By R. L. Lawson

I?ve been asked to appraise the global role of coal and mining, and the best place I can think of to begin is with the World watch Institute, which purports to monitor all things global. Last fall the institute?s magazine, entitled World Watch, in a cover story called for a worldwide campaign to outlaw the use of coal before this century?s end. To my mind the article began the campaign. However, the institute had to admit that no such ban will be possible unless there is special help and heavy intervention?that is, novel policies and punitive taxes. I?ll quote directly from the magazine to underscore the point: ?without them the market will continue to deceive us into thinking coal is cheap, abundant and irreplaceable?.

Jan 1, 2001

By A. M. Milev

A simulated rockburst was conducted underground at Kopanang Mine, previously called Vaal Reefs No. 9 Shaft. The rockburst was simulated by means of a large blast detonated in solid rock close to a crosscut sidewall. The simulated rockburst involved the design of the seismic source, seismic observations in the near and far field, high-speed video filming, a study of rock mass conditions such as fractures, joints, rock strength etc. Knowledge of the site conditions before and after the simulated rockburst was also gained. Some of the important findings are listed below: ?Two areas of damage were identified on the blasting wall: (i) an area of high-intensity damage in which ground velocities of 3.3 m/s were recorded by an accelerometer, which was subsequently ejected in a block of rock, (ii) an area of low-intensity damage where ground velocities of 1.6 m/s were recorded by an accelerometer which remained on the tunnel wall. ?High-speed filming revealed rock fragments being ejected from the wall at velocities in the range of 0.6 m/s to 2.5 m/s. The measurements were taken in the area of low-intensity damage. As planned, no gas pressure was directly involved in damaging the wall of the tunnel. ?The attenuation of peak particle velocities for the main blast in the near field (6 m to 30 m), as a function of distance R, was found to be proportional to R-1.7. ?The simulated rockburst was recorded as a local magnitude ML= 1.3 by the Klerksdorp regional seismic network. ?Peak particle velocities from nearby blasting, recorded on the tunnel wall after the simulated rockburst, were about six times greater then peak particle velocities recorded from the same source area before the simulated rockburst.

Jan 1, 2001

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 J. Maiti

This study examined the group differences in accident susceptibility among underground coal mine workers accounting for their personal and workplace characteristics. A logistic regression model was used for this purpose. Data were collected from five underground coal mines for a period of four years. The case study results revealed that different age and experience groups of workers bear no significant differences in their accident susceptibility; however, the workplace location and occupation groups show significant differences in their risk of injuries. It is inferred based on the logistic model results that among the three occupation groups, the face workers are more susceptible towards accidents/injuries compared to the haulage and other workers. Key Words: Mine Safety, Accident Susceptibility, Group Differences, and Logistic Regression.

Jan 1, 2001

By A. E. Lewis

Particle morphology is a term that is used to describe the overall external shape and appearance of particulate solids. From the physical point of view, a precipitated solid is characterized primarily by the size and morphology of the particles (Sohnel andGarside, 1992). If the morphology of the crystal structures is to be related to the processing conditions, then the morphologies need to be quantified in some way. This can be achieved by using surface area measurements as well as fractal dimensions. The key idea is that rugged and indeterminate systems can be described by using a fractional number that describes the ruggedness of the system (Kaye, 1989). In other words, when the complexity of a structure, such as an agglomerate, increases with increasing magnification, it is useful to employ fractal dimensions to describe the structure. Fractal geometry proposes that, instead of attempting to measure the length of an irregular boundary, the rate at which the length of the boundary approaches infinity with increasing resolution should be calculated. Cross-sectional profiles of rugged particles can thus be quantified using the fractal dimension, and a measurement of the ruggedness of the morphology obtained. One of the additional uses of measuring the fractal dimension is that the measured value can be related to the physical properties and formation characteristics of the particle (Kaye and Trottier,1995). The morphology of nickel crystals was quantified with fractal dimension calculations of particle cross-sections. Particle cross-sections were obtained by mounting the particles in resin and polishing back. These were then photographed using Scanning Electron Microscopy and the resulting profiles analysed using the structured walk technique.

Jan 1, 2001

Excavations in rock are commonly supported with wire mesh, shotcrete, wire mesh and shotcrete in combination, and shotcrete reinforced with various types of fibres. Wire rope lacing and various types of straps are additional forms of support installed over the above types, to cope with severe conditions. These support systems are very important items of ?membrane? rock support. With the recent development of several types of thin sprayed linings, the importance of membrane support is likely to increase in the future. In this paper, a wide range of mechanisms of membrane behaviour and mechanisms of loading of membranes, is described. The concepts of membrane components, which are single membranes that may be used on their own as rock support, and membrane systems, which are combinations of more than one membrane component, are introduced. Different situations have different requirements of membrane support, and differences between civil engineering and mining requirements are highlighted. With the different basic requirements in these two areas, the requirements of rock support are correspondingly different. A thorough understanding of the mechanisms of behaviour of the different types of membranes, and the different mechanisms by which the membranes are loaded, is essential before a selection of appropriate support can be made, before appropriate design methods and calculations can be determined, and before appropriate performance test methods for membranes can be defined. The material in this paper contributes towards the understanding of membrane support behaviour.

Jan 1, 2001

By A. P. Squelch

The high incidence of accidents and fatalities in the South African mining industry, in particular those associated with falls of ground, is often attributed to ineffective and/or inappropriate training methods and material. Recently introduced mine health and safety legislation in South Africa also requires that all mine workers receive appropriate and effective training to enable them to operate safely in their given mining environment. There can, therefore, be no doubt that methods to provide effective training, in particular safety related training, are urgently required in the South African mining industry. In the search for alternative and improved training approaches, attention has fallen on virtual reality (VR) technology as a possible solution. VR has found acceptance in a number of industries as an effective method of training for a variety of work place activities, including those of a safety related nature. VR has successfully been applied in a number of industries to improve the effectiveness of safety and hazard awareness training. The CSIR: Division of Mining Technology (CSIR Miningtek), in conjunction with the Safety in Mines Research Advisory Committee (SIMRAC), therefore evaluated the potential of VR to be used as a training medium in the South African gold and platinum mining industry. Aspects of the evaluation included an assessment of the technical capability of VR to represent a typical underground mining environment with sufficient realism and the relevance of the VR training concept for a largely illiterate workforce. For these purposes, a prototype PC-based VR hazard awareness training simulator has been developed by CSIR Miningtek, and a series of evaluation sessions conducted at a typical deep level gold mine. The conclusion from this evaluation work is that virtual reality technology has the potential to provide effective training systems that are relevant to the South African mining industry. Keywords: Virtual reality, mine training, safety training.

Jan 1, 2001

By H. C. van Zyl

Mine water in the Upper Olifants River Catchment in Mpumalanga(upstream of Loskop Dam) is at times discharged into local streams, resulting in local acidification and regional salination of surface water resources. Pollution of surface water can be prevented by collecting and treating mine water to a quality where it could be re-used without restriction (Cleanwater 2020 Initiative). Mine water in the Olifants River Catchment currently amounts to only 4,6% of the total water usage, but contributes 78,4% of the sulphate load. Limestone and lime treatment is the most cost-effective technology for neutralization and partial sulphate removal of acidic/sulphate-rich water to sulphate levels of less than 1500 mg/l due to precipitation of magnesium and removal of the associated sulphate fraction (through gypsum crystallization). Neutralized mine water of this quality may be suitable for irrigation. A number of alternative desalination treatment technologies were investigated (subsequent to gypsum crystallization pre-treatment) where treated mine water must meet more stringent quality requirements (e.g. less than 200 mg/lSO4). The capital cost of these processes varied between R4 million/(Ml/d) and R10million/(Ml/d) and the running cost between R2/m3and R5/m3. Water usage in the Upper Olifants River Catchment currently amounts to 947 Ml/d (including the power stations), and will increase to an estimated 1385 Ml/d by 2020. The additional water demand by2020 (438 Ml/d) will have to be supplied by importation from neighbouring catchments, and more efficient utilization of the local water resources, including excess mine water. Various levels of treatment are required to make mine water suitable for the following potential applications (acceptable treated water sulphate concentration shown in brackets): irrigation (2000 mg/l), coal processing plant (1000 mg/l), general industrial use (500 mg/l), discharge to public streams (500 mg/l), potable use (200 mg/l) and cooling water in power stations (20 to 40 mg/l). The following two options, or a combination thereof, can be considered for management of excess mine water in the Upper Olifants River Catchment: ?Collection and treatment of excess mine water to a quality suitable for selected urban and industrial applications (Option A) ?Collection and treatment of mine water to a quality suitable for irrigation (Option B). The estimated capital and running cost for Option A amounts to R528.5 million and R55.7 million/year, respectively, compared with R68,2 million and R11,9 million/year for Option B. It is recommended that Option B be investigated for implementation in the short to medium-term. Option B was selected due to cost benefits and the initial favourable results obtained by a joint Water Research Commission and Coal Industry initiative where mine water is used for irrigation. Option A may become feasible in the long-term to ensure maximum environ-mental protection and reduced treatment cost as a result of anticipated technological improvements over the next 5 to 10 years.

Jan 1, 2001

By S. Dalton

The use of coal for power generation is being questioned in many developed countries, as a result of ever-tightening environmental restrictions and concerns about the potential impact of CO2emissions on climate. Coal will continue to be the fuel of choice for new power plants for many developing countries with large percentages of the world?s population, because of its relatively low cost and broad availability. Even in many of the developed countries that are under pressure, coal will continue to fuel large percentages of power due to the installed base. Using coal efficiently and in an environmentally responsible manner will be a challenge for technology and politics in this new century, with the politics played out on the world stage. Coal use will vary in the next few decades, including short-term changes such as the use of more diverse coals and the increased use of efficient ultra-supercritical boilers to longer term ?refining? of coal to produce a range of energy and chemical outputs. This paper outlines EPRI?s Global Coal Initiative aimed at needed developments and demonstrations that support the long-term vision of environmentally sound and economical coal use for power generation, and discusses some of the forces that are driving this development effort.

Jan 1, 2001

By B. J. Vorster

AngloGold South Africa region currently consists of twelve gold plants. These plants use a combined total of $20 million of cyanide per annum. Of this, the major portion (60%) is consumed at two Ergo dump retreatment plants. Historically the primary motivation for cyanide control at Ergo has been one of leach/cost optimization. However, more recently, with the increased public awareness of cyanide in the environment, a secondary but increasingly important motivation for control has been to ensure that only the minimum amount of cyanide is added to the process whilst not compromising leach performance. Following a brief overview of the Ergo process, the methodology in determining the amount of cyanide to be added is described. The paper then traces the developments in cyanide control from very basic manual systems to the current automated control system. In line with the increasingly sophisticated control systems, developments also took place in regards to the method of cyanide analysis. The development of these analysers is also discussed. Whilst cyanide is one of the major drivers, if not the major driver of gold dissolution, it cannot be viewed in isolation particularly with respect to the relationship between cyanide and oxygen as ascertained from the Elsner?s well-known equation. Consequently, in order to control cyanide addition, knowledge of the relative cyanide/oxygen profiles is necessary. Various means investigated at Ergo for pulp oxygenation have therefore been included for the sake of completeness. Finally a comparison is made of the control achieved from the current system compared to the original manual system. The knowledge and experience gained at Ergo is now being used to draw up guidelines for the installation and optimization work at the other AngloGold plants. The net effect of this will be reduced cyanide consumption for the region, which also, apart from the obvious economic benefit, translates into a reduced environ-mental risk.

Jan 1, 2001

By G. H. Lind

This paper discusses the traditional costing approach currently used in the underground coal mining industry. Activity Based Costing (ABC) is identified as being a potentially more effective manner in which to cost underground coal mining systems. With the use of a costing framework developed by the author incorporating new thinking to eliminate the shortcomings identified in the traditional costing approach, a comparison of two types of underground coal mining systems, viz. continuous miner and longwall, is conducted. It is found that under certain criteria, in all cases, irrespective of the way in which the systems are costed, the continuous miner system is currently the better investment. It is also observed that when a system is costed using ABC that better investment decisions result when compared to costing the same system using traditional costing techniques. It is further seen that traditional costing techniques tend to overestimate the total costs of a mining system. This paper shows one application of ABC that can be incorporated as a management tool.

Jan 1, 2001

A South African gold mining rock-related fatal accident database has been analysed in order to determine rock-related fatality trends in the gold mining industry over the period 1990 to 1998. This analysis was extended further to include some of the individual reefs mined and focused particularly on the Carbon Leader Reef, the Ventersdorp Contact Reef, the Vaal Reef and the Basal Reef. Rock-related accident locations are also presented. A stope rock-related risk is proposed, where the fatality rate in terms of rock-related fatalities per million square metres mined for the gold mining industry as a whole is compared to individual reefs, allowing a stope rock-related risk to be attributed to the individual reef. This comparison is extended further by removing the contribution by the reef being evaluated from the industry data, thereby allowing this reef to be directly compared to the rest of the industry with respect to a stope rock-related risk.

Jan 1, 2001

By R. Hummel

When the slope angles of the southern side of the Venetia open pit were required to be flattened by some 20 degrees after an analysis completed by De Beers geotechnical engineering in conjunction with SRK, the additional waste stripping tonnage generated was in the order of some 70 million tons. The potential cost of having to move this tonnage had a significantly negative effect on the Net Present Value of Venetia Mine, challenging the viability of the third pushback and rendering a potential fourth pushback completely uneconomic. This paper details some of the innovation that went into the design and planning process undertaken to virtually negate the instantaneous effect of the flattened slope angles and the associated waste tonnage as well as further improve the NPV of Venetia Mine and bring the fourth pushback back into economic viability. This process has become known as NPV+ and is anon going exercise in waste reduction/deferment and revenue advancement.

Jan 1, 2001

By G. Broadbent

It is an honour to be invited as a speaker to this ICCR conference and a pleasure to be with you here in South Africa. I have been asked to talk about the competitiveness of coal versus other energy alternatives. Coal supplies nearly one-quarter of the global primary energy. Its most direct competitors are gas, nuclear and renewables. Oil is predominantly for transport fuels. Fuel oil is competitive with coal when crude is below its long-run average price and has some niche opportunities. But I will confine my comments to nuclear, renewables and particularly natural gas as the most potent current competitive threat to coal. Competitiveness is more than just cost and price; there is environmental acceptability, security or reliability and increasingly image. These factors are more of a spectrum than discrete issues. Dollars and cents remain the key issue for competitiveness but one must recognize the impact of politics in sustainable development and energy security.

Jan 1, 2001

Stope support systems, typically consisting of props and packs, are used extensively in the gold and platinum mining industry to stabilize the rock mass in the excavation vicinity and to reduce the hazard associated with rockfalls and rockbursts. The design of stope support systems was historically based predominantly on past experience and practices, and cost considerations. The recent development of a new and improved support design methodology, has led to the potential for significant increases in worker safety and support cost savings. This paper reviews some of the fundamental rock mass and support criteria that form the basis of the improved support design methodology. The considered design criteria are the height of potential fall; quasi-static stope closure rates; dynamic stope closure rates; compressive hangingwall stresses; discontinuity spacing, orientation and interface properties; effect of support length (stoping width); effect of compression rate; consistency of support performance; a real coverage; support spacing; and zone of support influence. The proposed support design methodology combines both the zone of influence and key block stability theories, resulting in optimized support systems for rockfall and rockburst conditions. The site-specific methodology consists of two stages: (i) a tributary area analysis, and (ii) a zone of support influence and a stability analysis, considering hangingwall failure due to buckling, shear and block rotation, which gives maximum safe spacing of individual support units. The methodology is suitable for designing support systems for both blocky hangingwalls and hangingwalls fragmented by face-parallel extension and shear fractures.

Jan 1, 2001

By P. Altounyan

Techniques used to safely control the roof in UK coal mines for some 10 years have been applied to a South African coal mine. This new approach known in the UK as advanced rockbolting technology, is based on applying four fundamental principles: ?Understanding the roof failure mechanisms ?Using an effective roof support system ?Designing this support using measurement ?Monitoring the performance of the system. The paper summarizes the approach in detail and describes how it is being applied by Anglo Coal, giving results obtained to date. Investigations at a number of South African coal mines, including stress measurements at two Anglo Coal mines, have confirmed that the mode of roof failure (lateral shearing due to horizontal stress) is the same as in other coalfields worldwide, and aspects of current world best practice, including the use of advanced technology rockbolting, are therefore relevant in South Africa. The stress measurements indicated a high level of stress field anisotropy and further investigation of stress conditions in South African coal mines is recommended. The most effective bolting system to resist shear failure is one with high bond strength and stiffness. Short encapsulation pull testing of existing South African systems confirmed that they have low bond strength and stiffness. An improved rockbolt system with the required performance, and features allowing rapid installation and installation quality and performance audit, has been developed and is currently under full-scale trial. Design by measurement and routine monitoring procedures including the use of a rotary telltale device are also under trial. It is anticipated that South African coal mines will be able to obtain significant safety and productivity benefits from the application of this technology.

Jan 1, 2001

By A. Bothma

The Impala No. 1A ventilation shaft is located approximately 15 kms north of Rustenburg and is accessed via the R510road from Rustenburg to Northam/Thabazimbi. This situation is shown on the location plan in Figure 1. The geology at the site consists of an upper layer of black turf of about 1 metre in thickness, grading into weathered norite. The depth of weathering is generally less than 5 metres. Zones of deeper weathering may occur along fracture zones associated with faults and dykes. Groundwater occurs mainly within the weathered/fractured aquifer system. The ventilation shaft is a 5.1 m diameter upcast shaft ,and forms part of a system of ventilation shafts to complement the existing infrastructure as mining progresses down the new twin decline extension of Impala 1 shaft. The principal reason for these shafts is to lessen the risk of an extended RAW and also to counter the effects of the heat build-up as the mining goes deeper, with the resultant effect that the existing cooling centre (fridge plant) becomes more remote from activities. The No. 1A shaft (upcast) is positioned approximately 1,2 km on down dip from the main shaft and the No. 1Bshaft (downcast) approximately 1,2 km further. Geological information was used from a borehole 1,2 km away on strike from the upcast shaft. The first shaft (1A) is a 5,1 m diameter hole to be fitted with two 2,2 MW fans, whilst the second shaft (1B) is 4,1 m diameter to accommodate a 7MW fridge plant.

Jan 1, 2001

Water represents 80?85% of the volume of mineral pulp processed in flotation circuits. Imperatives for a more detailed focus on circuit water quality and its control have come from increasing requirements to use relatively impure primary water supplies (e.g. high salinity, treated sewage) and high proportions of recycle from tailings dams, thickener overflows, dewatered and filter products. An integrated methodology for examining process water quality and its effect on minerals separation has been developed coupled with minerals surface chemistry across the complete processing circuit. Unrecognised factors, including varying proportions of water streams (daily or hourly), colloidal precipitation, highly variable pH and Eh, reaction and dissolution of minerals, minerals surface layer coatings, residual reagents and their reaction products, and microbiological activity have been studied in eight mineral processing circuits. The methodology combines: solution survey and modelling; microbiological surveys; minerals surface analysis and modelling; and process response. It has been possible to match the predicted (model) pulp chemistry with that measured from surveys of the solution and mineral surfaces. Treatment methods have included: monitored and balanced stream combinations; organic species removal; flocculation and aggregation; induced precipitation; dissolved air flotation; ageing (oxidation, UV exposure); and chemical surface conditioning of minerals. Some specific achievements from the methodology applied in plant and laboratory testing, with examples from case studies, will be described.

Jan 1, 2001