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MINERAL RESOURCES AND SUSTAINABILITY: CHALLENGES FOR EARTH SCIENTISTS 4 MINING AND THE ENVIRONMENT Mining inevitably disturbs the environment. Its environmental consequences are perhaps best understood in terms of the stages in the life of a mine (see Eggert, 1994). During mineral exploration and mine development, environmental damages are generally minor, localized, and can be remediated relatively easily. The initial assessment of a region, for example, relies largely on satellite images, airborne geophysical surveys, and large-scale geological maps; environmental effects are minimal. Subsequent subsurface examination of small areas through drilling and trenching causes more significant environmental impact. But such effects can be mitigated by reclaiming drillsites and trenches and by revegetating roads. In some remote areas helicopters have eliminated the need for roads to deliver drilling equipment. During development a company prepares a mineral deposit for production and constructs the facilities needed for mining. At this stage environmental impacts are greater than during exploration but still less extensive than during mining itself. During mining and beneficiation (initial processing) the most visible effects are disturbed land and the runoff water on the disturbed land. Actually, mining uses much less land than agriculture, urban development, forestry, or national parks and wilderness areas. A study by Johnson and Paone (1982) estimates that between 1930 and 1980 only 0.25 percent of the total land area of the United States was used for surface mining and the disposal of wastes from surface mines, underground mines, and beneficiation facilities. Coal mining accounted for about half of this land. The key factor, of course, is not how much land is used for any particular activity, but whether that use can
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MINERAL RESOURCES AND SUSTAINABILITY: CHALLENGES FOR EARTH SCIENTISTS be made compatible with maintaining ecological integrity. As mining uses comparatively little area, maintaining the ecological system should be more feasible than with uses such as urban development. Mining and beneficiation create three types of solid waste: overburden, soil and rock removed to gain access to a mineral deposit; waste rock, separated from ore during mining; and tailings, fine waste particles produced during beneficiation. In the absence of water, these solid wastes would cause mainly aesthetic environmental damage. But when they interact chemically with surface or ground waters they can be the source of acid-mine drainage, probably the most serious environmental problem of mining and beneficiation. The nature and extent of actual environmental damage caused by solid mine waste and acid mine drainage vary considerably from case to case, depending on a number of factors. As noted by Eggert (1994, p. 9): The type of mineral deposit is important: sulfide-poor deposits, for example, will generate less of the sulfur needed to create sulfuric acid than sulfide-rich deposits, and high-grade deposits will have fewer tailings per unit of recovered metal than low-grade deposits. Mining and beneficiation techniques are important: underground mining. . . creates much smaller volumes of waste per unit of metal than does surface mining, and the higher the recovery rate during beneficiation, the smaller the amount of tailings. Climate is important: in arid regions, there is little of the water necessary to create acid-mine drainage. Location and population density are important: acid-mine drainage that enters streams feeding into sources of human drinking water not only destroys fish and wildlife habitats but also damages human health. Finally, the environmental manage-
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MINERAL RESOURCES AND SUSTAINABILITY: CHALLENGES FOR EARTH SCIENTISTS ment practices of mining companies are important: waste piles that are revegetated or in some other way sealed, for example, are much less likely to be accessible to the water necessary to create sulfuric acid. Because of this variability the amount of solid waste alone is not a good measure for the amount of actual or potential environmental damage. The final stage is closure and rehabilitation. Companies typically seal or plug underground mines. For surface mines and waste piles, companies usually revegetate the surface and stabilize slopes. When acid-mine drainage continues, some type of drainage control may be required. Special problems are caused by abandoned mines that have not been properly rehabilitated; society as a whole then has to bear the costs of either unmitigated environmental damage or rehabilitation. “Sustainable” mining, therefore, has two dimensions: first, that an appropriate balance be found between the benefits of mining and the associated damages or costs; and second, and more important, that new and better methods of mining and mineral processing be developed to reduce both production costs and environmental damages. The environmental hazards at the mine site itself are matched by potential adverse effects of off-site processing. These effects may be removed from the mining area, but must be considered as one consequence of mineral production. As with activities at the mine site itself, technical advances may be able to reduce and minimize adverse environmental off-site effects.
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MINERAL RESOURCES AND SUSTAINABILITY: CHALLENGES FOR EARTH SCIENTISTS Challenges Concerning the Environment Challenge #5: To develop better data on the environmental consequences of mining, on the costs of environmental compliance, and on the best practices in environmental management of mining. Much of the discussion about mining and its environmental consequences is based on anecdotal and partial information. Moreover, much is based on past practices that have been changed. Earth scientists should take the lead in assembling data and information in the three areas listed above. Systematic data on the environmental consequences of mining are difficult to come by, at least in a form that emphasizes risks to human and natural environments. Yet these data are a necessary input to realistic estimates of environmental damage in the national income and product accounts. This parallels the efforts noted earlier to include resource depletion in these accounts (see Carson, 1994). In addition, little is known about how much environmental compliance has cost the mining industry. The absence of information on both environmental damages and on compliance costs makes it difficult to determine whether existing policies are appropriate. Finally, systematic data on best practices in environmental management would provide a standard against which to compare current and future performance of individual companies. Challenge #6: To use basic science to improve environmental management and restoration ecology associated with mining and mineral processing. One aspect of this challenge is to develop “environmental” ore-deposit models. Mineral exploration is guided by traditional ore-deposit models, idealized geologic representations of specific deposit types developed to help predict where an ore deposit should occur. Environmental ore-deposit models would enlarge the models to include characterization of the ore and associated waste rock in terms of its environmental risks. These risks could be
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MINERAL RESOURCES AND SUSTAINABILITY: CHALLENGES FOR EARTH SCIENTISTS evaluated in terms of various climate and topographic settings. Such characterizations might identify types of deposits that, for example, could not be mined in certain environments without high risks of serious environmental damage. They could also help identify types of deposits that require special efforts to restore the environment after mining. Challenge #7: To communicate to policymakers and the public how mining affects the environment and how environmental degradation can be minimized . As with the issue of resource depletion, better science and data are necessary but not sufficient. Sustainability challenges earth scientists to communicate more clearly with both policymakers and the public. Environmental management in mining and mineral processing has undergone a revolution over the past several decades. But most people are unaware of exactly how mining affects the environment and of what measures can be taken to control and minimize environmental damage.
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