Transforming Mining Systems for Waste Management

International Journal of Surface Mining, Reclamation and Environment

ISSN: 1389-5265 (Print) 1744-5000 (Online) Journal homepage: http://www.tandfonline.com/loi/nsme19

Mining Waste: Transforming Mining Systems for Waste Management Malcolm Scoble , Bern Klein & W. Scott Dunbar To cite this article: Malcolm Scoble , Bern Klein & W. Scott Dunbar (2003) Mining Waste: Transforming Mining Systems for Waste Management, International Journal of Surface Mining, Reclamation and Environment, 17:2, 123-135 To link to this article: http://dx.doi.org/10.1076/ijsm.17.2.123.14129

Published online: 09 Aug 2010.

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International Journal of Surface Mining, Reclamation and Environment 2003, Vol. 17, No. 2, pp. 123±135

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Mining Waste: Transforming Mining Systems for Waste Management

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MALCOLM SCOBLE1, BERN KLEIN1; AND W. SCOTT DUNBAR1 ABSTRACT Mining environmental management primarily focuses on concerns over the impact of waste disposal on the surface, in the form of tailings and waste rock. Traditionally waste products have only been returned to the mining void in limited quantities and surface disposal technologies have been paramount. Mining systems need to be reengineered, based on a new paradigm that mining is a business whose success is fundamentally dependent upon waste management. Strategies are available to shift this paradigm and to minimize the surface impact of waste disposal. Firstly, mining methods need to be developed that are more selective. A more futuristic strategy may be the implementation of solution mining. Pre-concentration and even the full integration of mineral processing within the mine workings could be important in this strategy in the interim. Secondly, technologies enabling the return of waste securely to the void should be pursued. This paper considers the design of new mining methods that minimize waste output. It then reviews technologies for in situ pre-concentration. Finally it addresses the issues associated with the return of waste to mined voids.

Keywords: waste management, environmental management, resueing, pre-concentration, in situ leaching, paste back®ll, co-disposal.

1. INTRODUCTION Awareness of the potential environmental impact of mine waste disposal has intensi®ed recently, fostered by the increasing scale of mining, and the evolution of environmental technologies, legislation and ENGO's. The power of the media and the sequence of tailings dam failures in recent years have heightened this awareness. The paradigm has been proposed that ``mining companies are waste management companies'' [1]. The growth in larger, surface-mined deposits at very low grade has prompted this viewpoint. It is possible that many new surface mines will ®nd it dif®cult in the future to gain permission to operate without agreeing to back®ll their mined voids. Address correspondence to: Bern Klein, Tel.: 1-604-822-3986; E-mail: [email protected] 1 Department of Mining Engineering, University of British Columbia, 2329 West Mall, Vancouver, B.C., Canada, V6T 12A. Tel.: 1-604-822-3986; Fax: 1-604-822-5599.


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In this paper, waste is considered in a mineralogical context. It is the geological material encountered in a mining operation that is below the cut-off grade. The implication therefore is that waste may become ore if commodity prices rise, or vice versa. It is possible to seek new marketable uses for what exists currently as waste, for example, witness the efforts expended in Europe to ®nd new uses for waste materials from coal mining. The disposal of marginal waste, that is encountered as mining proceeds, would therefore best be undertaken so that the material is still accessible in the future in the event of a rise in commodity prices. This is an example of the need to build in operational ¯exibility within waste disposal. The technology and markets for waste utilization can also change with time. Deposits of past waste, whether from mining, other industrial activity or domestic refuse will likely be commonplace orebodies of the future. Mining will be an integral part of the process of recycling in sustainable development. Responsibility for more ef®cient and total recovery of ore deposits will increase as global populations and expectations expand in the future. Such sustainable development principles are being applied increasingly by mining companies. The disposal of waste will also become an increasingly challenging issue for underground mines. Several of Canada's underground mines are mature and face the need to mine at much greater depths [2]. In such circumstances, there is a major incentive to leave waste in the mine rather than suffer the costs of transporting it to surface. In underground mines there is at least the opportunity to dispose off the waste back in the mined voids during the life cycle of the mine. This may also be the case in open-caste or strip mining on surface, but in open pit mines this is only the case at the end of the mining operation. Many of the older open pits are now looking to continue as underground operations. This is possible only where low-cost, bulk mining is feasible, generally by using a caving method of working. Unfortunately such methods do not facilitate the underground disposal of waste. An obvious solution for many of these issues is not to mine so much waste in the ®rst place, i.e., the practice of selective mining. This means the minimization of waste production but may not necessarily correspond to maximizing the recovery of the mineral resource. A further step to minimize waste generation is to employ mineral pre-concentration or concentration close to the mining face, so that signi®cant waste is removed from the ore and disposed into the void rather than transported out from the mine, processed and then disposed on surface. Comminution of development and stoping waste at the face presents the opportunity for pre-concentration as well as for slurri®cation and hydraulic transportation in pipelines either to back-®lling sites or the mill. The preconcentration requirements as well as the hydraulic transport constraints would determine the degree of comminution. Unfortunately, ®ne processed waste is often reactive and contains water. The evolution of paste back®ll and co-disposal technologies may well overcome some of these issues. Heap leaching has been more successful in surface mines than

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underground. But on surface this still entails large movements of waste and liquors. There is much to be gained by the integration of the mine and mill through a new paradigm ``processing at the face.'' The ultimate extension in a more futuristic form of mining will be in situ mining, where only the metal/mineral of value is extracted from the deposit. Parsons and Hume [3] place the following waste management practices in order of decreasing preference:


waste avoidance, i.e., practices that prevent the production of waste; waste reduction, i.e., practices that reduce waste; waste re-use, i.e., direct re-use of waste materials; waste recycling or reclamation, i.e., using components of waste in other processes; waste treatment, i.e., to reduce hazard, usually at the site of generation; waste disposal.

Mining companies use the last three options extensively. Other industries, notably the chemical industry, have made use of the ®rst three options by modifying or changing processes. The problem with application of the ®rst three options to mining wastes is that in the current mining paradigm, as ore grades become lower, more waste is produced. Major rethinking of mining, mineral processing and waste management technology and its use is necessary for the mining industry to take advantage of these more preferable waste management options. 2. SELECTIVE MINING The ability to mine selectively is strongly dependent upon the knowledge of the variability of the mineralization and its host rock-mass. The orebody complexity is dependent upon the variability in grade distribution, morphology, and geotechnical characteristics. The quality of the initial exploration program and the subsequent delineation phase governs the degree of selectivity attainable. A recognition of this has prompted signi®cant current research into geophysics: more traditional gravity, magnetic, re¯ection seismic, electromagnetic and radiometric methods, plus sonar, crosshole seismics, seismic tomography, resistivity tomography, borehole radar, mine seismic pro®ling, radio tomography and ground penetrating radar. This has been accompanied by the realization of the need to integrate data into multidimensional Spatial Information Systems, capable of integrating disparate data sources, database operations, visualization and spatial analysis [4]. Open pit mining does not facilitate the same degree of selectivity as in underground mining. There is reduced ¯exibility in terms of the ability to change sequencing and mine in areas of choice within the orebody. Selective mining in low grade, disseminated mineralization brings much less bene®t than in situations where


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ore is high grade with clear boundaries. The degree of selectivity is dependent upon the morphology of the orebody: irregular outline ore-bodies require more precise mining methods, based upon more detailed delineation. The bene®cial impact on reducing dilution by employing selective mining systems will be proportionately greater in narrower orebodies. Bulk, high productivity mining tends to be applied to large orebodies where selectivity has less impact. Selective methods generally entail smaller volumes of ore excavation in order to follow complex ore outlines more closely, tending to reduce productivity. Selective mining methods can also employ segregation of ore and waste in the excavation process itself. This is the principle of the resueing method of stoping, where waste and ore are broken in separate cycles to segregate ore and waste right from the outset within the stope. The waste can then be left within the stope. This enables waste minerals or those deleterious to downstream processing in zones within orebodies, e.g., arsenic-rich zones in base metal deposits, to be broken and dealt with separately. Selective mining can also be important for segregating and dealing with potential contaminants, such as reactive sul®des, that propagate acid rock drainage. This entails selective waste disposal, which is a sensible practice when ranges of reactive waste are to be handled. Selective mining then presents the opportunity to be proactive in anticipating waste management issues.

Fig. 1. An overview of the factors controlling the implementation of selective mining.


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Selectivity governs mining losses and dilution. Knissel et al. [5] de®ned selectivity as the measure of the recovery (relative losses) and cleanliness achieved (relative dilution) within the mining process. The preceding paragraphs describe only some of the factors that control the implementation of selective mining. A more detailed overview of the factors that need to be considered [6] is shown in Figure 1.

3. MINERAL PROCESSING 3.1. Processing Underground Ore is transported from the mine to the mineral processing plant where valuable minerals are separated from tailing waste. The valuable minerals usually comprise only a small portion of the mined ore, leaving the bulk to be transported to waste dumps, tailing ponds or returned to underground workings. From a mineral processing perspective, waste management objectives are to: Minimize the amount of reactive ARD generating wastes, Minimize the production of ®ne waste, and Minimize handling and transport of waste.

The extent to which these objectives can be achieved is related to the geographical setting, the geology and mineralogy of the ore deposit and several other logistical factors that are speci®c to each ore deposit. Integrated mining and recovery systems, such as underground mineral processing/ pre-concentration, can help to achieve the waste management objectives. Processing the ore underground would reduce the costs of bringing ore to the plant and of returning back®ll waste to the mine workings. As mines become deeper, cost savings from underground processing become more signi®cant. While the reduced transport costs are clearly an incentive, there are constraints upon the construction and operation of an underground processing plant [7]: The physical volume of the processing facility should be as small as possible, The waste should be suitable for back®ll with regards to its physical properties and volume, The process should be robust with respect to being capable of treating ore at a range of feed rates and grades while maintaining high metal recoveries.

Underground crushing facilities are common, however there are few examples of other underground processing facilities. The most noteworthy is the Andina Mine in Chile, where the mineral processing plant was built underground because of the extreme climatic conditions [8]. The processing plant was constructed in two large


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underground chambers, one housing the grinding section and the other the copper ¯otation plant. Ore is transported from open pit and underground workings to the plant where it is processed at a rate of approximately 33,000 tpd. While the Andina Mine is an extreme example, it represents a precedent for the design and construction of other underground processing plants. A more conservative underground mineral processing facility would preconcentrate the ore to reduce the amount of material transported to surface and leave a signi®cant portion of the waste behind for back®ll. The packing volume of the broken rock limits the amount of waste rock that can be returned to the excavation. Based on the packing density, approximately 60% of the tonnage mined can be replaced in the excavations [7]. The main technology used for pre-concentration is dense media separation, which has been applied to the separation of metal bearing sul®des from siliceous gangue for particles ranging in size from 0.25 to 500 mm. An underground processing facility would include crushing, screening, dense media separation and a dense media recovery circuit. The products are essentially dry (with the exception of surface moisture) for transport. For ores that require further particle size reduction to achieve liberation, underground grinding and coarse particle ¯otation circuits have been proposed [7]. In this case, pumping would be required to transport a bulk concentrate to the surface and to return the tailings to the underground excavations. 3.2. Pre-concentration The objective of pre-concentration is to reject barren waste at as coarse a particle size as possible. The ability to achieve this objective is determined by the liberation characteristics of the ore. The potential bene®ts of pre-concentration include: Reduced environmental concerns, since the coarse barren waste product can be disposed of separately and less ®ne reactive (sul®de) waste is produced for disposal in tailings ponds or as back®ll; Smaller footprint for processing facility at the surface; Reduced capital and operating costs resulting from reduced material handling, and smaller grinding and downstream processing facilities; Reduced operating cost per ton of ore processed, by lowering grinding work index and abrasion as a result of rejecting siliceous material prior to grinding.

For pre-concentration, dense media separation (DMS) is the most suitable process due to its high processing capacity and ability to make sharp separations at coarse particle sizes. Schena et al. [9] developed a methodology to assess the economic bene®ts of pre-concentration. Other coarse particle processing technologies that are



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being developed and may be applied to pre-concentration include dry high intensity magnetic separation using rare earth magnets and optical sorting [10]. The dense medium consists of an aqueous suspension of ®nely ground particles (typically magnetite, ferro-silicon or galena) that has an effective density between the densities of gangue (siliceous) and valuable mineral (sul®des) components. The medium imparts a buoyant force on particles causing low-density particles to ¯oat while allowing high-density particles to sink. There are two basic classes of dense media separators referred to as static separators and dynamic separators. Static separators, such as drums, vessels and baths, are suited for particle sizes ranging from approximately 2 mm to 500 mm and have a unit capacity of up to 300 t/h. Dynamic separators, such as the DSM Cyclone, Dyna-Whirlpool and Tri-Flo utilize centrifugal acceleration to achieve separation. Large diameter separators (up to 1 m) can process particles up to 100 mm at a rate of up to 400 t/h. Through optimization of dense media rheology, the size limit that can be effectively separated has been lowered to 0.25 mm. Dynamic separators are more compact than static separators and the centrifugal ¯ow produces a sharper separation. Despite the potential bene®ts of pre-concentration, it is often overlooked during ¯owsheet design. An example is the McKinnon Creek lead, zinc, gold, silver prospect in British Columbia, where metallurgical studies conducted over a twenty-year period had neglected to evaluate pre-concentration. In 1997, simple heavy liquid ¯oat sink testing revealed that crushing to minus 2 inches followed by heavy media separation would reject 40% of the plant feed while recovering greater than 97% of the metals. The coarse reject contained low sul®de grades, which allowed for easy disposal or the possibility to be sold as aggregate. Pre-concentration signi®cantly improved the economic viability of the project, partially due to the reduced waste disposal and transport costs. An operating scenario that involved pre-concentration indicated that the project was economic with an internal rate of return of 18% based on gold $350/ oz, silver $6.00/oz, zinc $0.55/lb and lead $0.30/lb [11, 12]. Pre-concentration has been used at Cominco's Sullivan lead zinc mine in British Columbia since 1949 [13]. Crushed 3/16 inch ore is processed at a rate of 500 t/h with two static dense media baths to separate siliceous minerals from sul®de minerals. The dense media (S.G. 2.95) is prepared from ®ne galena, which is produced in downstream ¯otation. DMS rejects approximately 30±35% of mill feed weight as a low sul®de waste product. Dense media cyclones have been used in a similar application at the Mount Isa lead zinc silver mine in Australia since 1982. The plant rejects 30±35% of the run-of-mine ore while maintaining 96±97% metal recovery [14]. More recently, AMT have elected to install dense media separation for pre-concentration at its Copper Creek project near San Manuel, Arizona. Crushing to 13 mm followed by DMS will reject 75±80% of the feed while maintaining copper recoveries of 93±95% [15]. Although


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the primary incentive for these installations is increased plant capacity and reduced capital and operating costs, bene®ts are also realized for waste management. For most ores, liberation of metal bearing sul®des requires further particle size reduction that can be achieved only from grinding. One innovative process was designed by the Chamber of Mines of South Africa Research Organization for underground processing of gold ores from the Witwatersrand [7]. The process design was based on consideration of underground space limitations for a processing facility, mineralogical/liberation properties of the ore and the capacity to return waste back®ll to excavations. The raw ore is ground in a centrifugal mill and screened at 3 mm. The minus 3-mm fraction is ¯oated in specially designed ¯otation cells for use with very coarse particles to recover gold and gold bearing sul®de minerals. The ¯otation tailings are classi®ed using hydro-cyclones, which return coarse gangue, moderately coarse valuable minerals and locked valuable minerals to the mill. The cyclone over¯ow is a waste product, which is thickened for back®ll. The estimated gold recovery is 98% while rejecting 60% of the raw feed. Peters et al. [16] addressed factors governing the feasibility of underground preconcentration: The orebody characteristics are key parameters for the selection of the most suitable mining method. While bulk mining methods have the lowest operating costs, their application typically increases ore dilution. Selective mining methods, on the other hand, limit ore dilution, but do necessarily result in considerably higher costs (typically increased by a factor of 1.5±2.0). The ability of a pre-concentration/ concentration plant to effectively eliminate most of the gangue minerals prior to hoisting of the ore could therefore have an impact on the selection of the most suitable mining method. Geology. The characteristics of the rock-mass hosting the mineral processing plant play an important part in controlling the stability of the excavation and need for long-term support. Faults in particular have to be identi®ed and stability analysis has to consider the ground support required for maintaining the excavation security. It is advisable to install the processing plant at some distance from the mining activities to limit the risk of damage caused by seismic events. Distance of mine from concentrator. A concentrator located in close proximity to the mine permits the utilization of both conventional handling systems as well as pumping systems. As the distance of the concentrator increases, then a pipeline application becomes less feasible due to the associated high capital requirements for its construction. Back®ll requirements. The back®ll requirements are primarily a function of the selected mining method. Apart from caving methods, every mining method can facilitate the use of back®ll material. Back®ll strength requirements, however, vary with the applied mining sequence and the deposit geology. In order to ensure the


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back®ll strength, geotechnical strength tests have to be conducted on samples of the processing plant rejects. Rejects from gravity separation circuits are the preferred back®ll materials, since long-term chemical reactions are not to be expected due to the absence of reagents. The potential for oxidation of sul®de minerals in the back®ll and its impact should also be assessed.


3.3. ARD Prevention by Segregation of Waste Products The legacy of past mining practices is large quantities of acid generating waste rock and tailings. In 1995, estimated acid producing and potentially acid producing mine wastes in Canada were 1,877.7 million tonnes of tailings and 738.9 million tonnes of waste rock. The corresponding estimates of acid producing liability were $1.52 billion and $0.40 billion, respectively [17]. Although grossly oversimpli®ed, these translate into costs of $0.81/tonne acid generating tailings and $0.54/tonne acid generating waste rock. The cost/tonne values are signi®cantly under-estimated, as the estimated liability does not include waste stored sub-aqueously. A speci®c example is the former Britannia Mine in British Columbia, where oxidation of sul®de minerals in underground mine excavations produces acid rock drainage that ¯ows into Howe Sound. A comparison of alternative treatment scenarios indicated that the most cost-effective option would involve high-density sludge treatment and off-site storage of the sludge. For a facility treating 500 m3/h, the capital cost was estimated to be $4.66 million and the annual operating cost was $0.96 million [18]. It is believed that the ef¯uent would need to be treated in perpetuity. A pro-active approach to waste management can reduce the ARD liability. Feasby and Tremblay [16] describe the role of mineral process engineers in the prevention of acid generation from sul®de-containing wastes. For waste rock, acid formation can be prevented for the short term by adding alkaline materials such as lime or limestone. The acid generating waste rock can be either placed in a dump with bedded layers of alkaline material or blended with the alkaline material. For selective ¯otation of base metal sul®des, lime is added to depress pyrite and pyrrhotite. The addition of lime contributes to the alkalinity of tailings. Based on sul®de mineral contents of the tailings, more lime may be added to reduce the acid generating potential. Sul®de removal from tailings allows for several disposal options. The isolated sul®de material can be stored below the surface of the tailings to limit the potential for oxidation. Alternatively, separate underwater disposal in a lined containment has been proposed. As discussed above, pre-concentration of metal bearing sul®des using dense media separation isolates the sul®de minerals from non-reactive gangue prior to grinding.


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At several existing plants, high sul®de cleaner ¯otation tailings are often combined with low sul®de scavenger tailings. In this case, the high sul®de cleaner tailings can be isolated for disposal by installing a separate pumping system. Such steps can substantially reduce the acid generating potential of the bulk of the tailing material. Sul®de removal can be achieved by froth ¯otation however; ¯otation of gangue sul®de minerals in base metal sul®de processes may not be trivial. In base metal plants, selective ¯otation against pyrite is commonly achieved by adding lime to increase the pH. Subsequent pyrite ¯otation from the tailings may require the addition of acid to lower the pH. An alternative approach would involve bulk sul®de ¯otation to recover all sul®de minerals followed by depression of the gangue sul®des during selective ¯otation. This approach would involve redesign of ¯otation circuits. For some ores, depressing gangue sul®de minerals that had been activated for ¯otation may be problematic. At the University of British Columbia, research is underway to evaluate a continuous centrifugal gravity concentrator for the separation of sul®des from tailings. These types of concentrators are a relatively new technology that may have application in this area. Most noteworthy are the Falcon C, Knelson CVD, Kelsey Jig and Mozley Multi-gravity Concentrator. They represent a clean non-chemical technology that could separate sul®des from the tailing stream and would not interfere with upstream metal recovery processes. The potential for these technologies may be limited, since sul®de particles in tailings are often ®ner than the siliceous gangue particles. Oxidation of sul®de minerals in a controlled environment using autoclaves can eliminate the acid generating potential. Autoclaves are used at some gold mines to oxidize gold bearing sul®de minerals (refractory gold) prior to cyanidation. Treatment of waste in this manner is not economic, however, controlled oxidation may be justi®ed in some situations. At the Miramar Con Mine, arsenic trioxide waste from roaster operations that accumulated over decades from mining in the area is presently being treated in this manner [19]. ``Tailings rheology engineering'' involves thickening of the tailings prior to placing in a pond, which helps to maintain a high water table in tailing ponds by capillary action. If the water table can be kept above sul®de layers, the rate of oxygen diffusion and sul®de oxidation will be limited. The addition of lime to the tailings can increase the apparent viscosity, which reduces particle size segregation, improves the moisture retaining capacity and decreases oxygen diffusion. Similarly, non-reactive tailings with low permeability can be used for layered covers. 4. PASTE AND CO-DISPOSAL OF WASTES Paste back®ll is a reconstituted form of tailings formed by separating the coarse and ®ne-grained fractions of the tailings in a hydro-cyclone. The coarse-grained fraction



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(the cyclone under¯ow) is allowed to drain naturally and the ®ne-grained fraction (the cyclone over¯ow) is de-watered in thickeners or by ®ltration. The two size fractions are then re-combined together with cement and other coarse-grained materials may be added to enhance strength and decrease water retention. The result is a viscous material that can be moulded relatively easily into a desired form. The fundamental problem in the design of a paste production system is to reduce the water content of the tailings suf®ciently so that the size fractions do not segregate and so that the paste can be transported in a pipeline. These are con¯icting requirements but an optimum amount of de-watering can be found for a broad range of tailings materials by simply varying the particle size distribution. It is desirable to reduce the content of particles of size 20 microns or less since electrostatic charges surrounding these particles attract water molecules thus increasing moisture retention. The usual design goal is to reduce the < 20-micron fraction to a minimum of 15±20% by weight [20, 21]. Paste is commonly considered for use as back®ll support in underground voids and has been considered for use to reshape surface landforms near mining sites. If paste back®ll is used as support to facilitate further mining, the paste production operation requires very close integration with the mine plan. The paste must be available when and as needed; there is no opportunity to ``stockpile'' paste. As a paste production operation involves several types of equipment including hydro-cyclones, ®lters, mixing tanks, and storage silos, the issue of system reliability arises. To some extent this can be dealt with via redundancy or by designing equipment so that it is easily repaired, if necessary. An equally important issue is the design of a paste production system that can adapt to changes in particle size distribution, mineralogy, or moisture content. Relatively small variations in these properties can result in large changes in paste viscosity and the ability to transport the paste and in the long-term stability of the paste back®ll. Sensor and control systems are currently available to handle changes in moisture. Further development of such systems, improvements in pumping or transporting technology and in additives to improve ¯ow are all necessary so that paste production plants can be designed to deal with a wide variation in tailings properties. Paste technology potentially allows for a considerable amount of innovation in mine waste management. Co-disposal of tailings and waste rock, where waste rock would be used as part of the coarse fraction of the paste, is one such possibility [22]. Alternatively, a waste rock and tailings paste could be deposited on land. Combinations of these alternatives could be considered to provide more ¯exibility. Currently these possibilities suffer from the uncertainty associated with the long-term chemical and physical stability of tailings/waste rock combinations. Paste can be considered as a form of waste reduction since it reduces the amount of water to be managed in a tailing pond. Although, the water extracted from the tailings


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may be used for processing, it must be treated and disposed of after the mine is closed. This is likely a better alternative than the long-term liability associated with having water remain in a tailings pond after mine closure where it can generate acid or high metal concentrations in surface or groundwater for some years after the mine is closed. Capital investment for a paste production plant is high compared to other back®ll systems. In most cases, this is offset by lower operating costs and increased productivity. Even more important is the avoidance of long-term liabilities associated with tailings ponds and waste rock dumps. Although dif®cult, it is important to take these factors into account when evaluating waste management systems. 5. CONCLUSION A more holistic approach to the design of mining and milling systems in mines is needed which accounts for the different aspects of environmental and social costs and bene®ts. This should optimize the engineering design of excavation, transport and processing in terms of more global economic factors. Waste management costs would then be transparent and taken into account in the mining and milling design. Technology development should be focussed on integrated selective and ¯exible mining systems. ACKNOWLEDGEMENTS This paper was presented at the Sixth International Conference on Environmental Issues and Management of Waste in Energy and Mineral Production, Calgary 2000, and appears here on the invitation of the Editorial Committee of the International Journal of Surface Mining, Reclamation and Environment. Although different in scope and focus, portions of this paper have appeared in the CIM Bulletin of the Canadian Institute of the Canadian Institute of Mining, Metallurgy and Petroleum [23]. REFERENCES 1. Moss, A.: Looking into the Crystal Ball: The Industry in the 21st Century. Global Mining Conference, PricewaterhouseCoopers, 1999. 2. Scoble, M.: Competitive at Depth: Re-Engineering the Hard Rock Mining Process. Keynote Lecture, 1st North American Rock Mechanics Symposium. Austin, Balkema, Rotterdam, 1994. 3. Parsons, A.S. and Hume, H.R.: The Contribution of New Technology to Improved Environmental Performance in the Mining Industry. UNEP Industry and Environment, October±December, 1997, pp. 38±43.



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4. Francis, H., Salter, D. and Scoble, M.: Intelligent Ore Delineation: Integrating Geosensing and GIS. 100th Ann. General Meeting, Can. Inst. Min. Metall., Montreal, 1998, CD ROM. 5. Knissel, W., Jurgen, H. and Fahlbusch, M.: Signi®cance of Selective Mining Exploitation for Economical and Environmentally Bene®cial Underground Ore Mining. Int. Jnl. Min. Resources Engineering, Imp. Coll. Press 5(2) (1995), pp. 165±174. 6. Francis, H.: Internal Ph.D. Report, Department of Mining and Mineral Process Engineering, University of British Columbia, 2000. 7. Lloyd, P.J.D.: The Potential of Integrated Mining and Extraction Systems on the Witwatersrand. Proc. 11th Int Commonwealth Mining and Metallurgy Congr. IMM, Hongkong, 1978. 8. Brewis, T.: Andina Develops for the Future. Mining Magazine. London, February 1995, pp. 78±87. 9. Schena, G.D., Gochin, R.J. and Ferrara, G.: Preconcentration by Dense-Medium Separation ± An Economic Evaluation. Trans. IMM, 99 (Section C) (1990), pp. C21±C31. 10. Arvidson, B. and Reynolds, M.S.: New Photometric Ore Sorter for Conventional and Dif®cult Applications. Processing for Pro®t Conf., Industrial Minerals. Amsterdam, 1995. 11. Trafford, G.T.: Company Receives Scoping Study. News Release, Weymin Mining Corporation, October 26, 1998. 12. Trafford, G.T.: Results Nearly Double Grade to 13 Grams Gold Per Tonne. News Release, Weymin Mining Corporation, January 20, 1998. 13. Winckers, A.H.: The Use of Rubber Mill Liners at Cominco's Sullivan Concentrator. 13th CMP Annual Meeting. Ottawa, CIM, Montreal 1981, pp. 300±310. 14. Munro, P.D., Schache, I.S., Park, W.G. and Watsford, R.M.S.: The Design, Construction and Commissioning of a Heavy Media Plant for Silver-Lead-Zinc Ore Treatment ± Mount Isa Limited. XIV Int. Min. Proc. Congr., VI-6., Toronto, 1982, 1±20. 15. McCulloch, W.E., Bhappu, R.B. and Hightower, J.D.: Copper Ore Pre-concentration by Heavy Media Separation for Reduced Capital and Operating Costs, Copper 99, Phoenix Arizona, 1999. 16. Peters, O., Scoble, M. and Schumacher, T.: The Technical and Economic Potential of Mineral Processing Underground. Annual General Meeting, Can. Inst. Min. Metall., Calgary, CD ROM, 1999. 17. Feasby, D.G. and Tremblay, G.A.: Role of Mineral Processing in Reducing Environmental Liability of Mine Wastes. 27th Annual CMP Meeting, Ottawa, CIM, Montreal 1995. 18. O'Hearn, T. and Klein, B.: A Comparison of Acid Rock Drainage Treatment Scenarios at the Former Britannia Mine. Sixth Int. Symposium on Environmental Issues and Waste Management in Energy and Mineral Production. Calgary, A.A. Balkema, Rotterdam, 2000, pp. 581±588. 19. Young, P.D. and Allan, M.: Commissioning and Early Operation of the Con Mine Pressure Oxidation Plant. 26th CMP Annual Meeting, Ottawa, 1994. 20. Brackebusch, F.W.: Basics of Paste Back®ll Systems. Mining Engineering, October, 1994, pp. 1175± 1178. 21. Cincilla, W., Landriault, D., Newman, P. and Verburg, R.: Paste Disposal. Mining Environmental Management, May 1998, pp. 11±15. 22. Wilson, G.W.: Co-disposal of Tailings and Waste Rock. Geotechnical News 19(3) 2001, pp. 44±49. 23. Klein, B., Dunbar, W.S. and Scoble, M.: Integrating Mining and Mineral Processing for Advanced Mining Systems. CIM Bulletin 95 (1057), pp. 63±68.