the fluids responsible for the deposit must continue through the crust or into another medium, such as seawater, to maintain a high fluid flux. After formation of a metallic ore deposit, oxidation by meteoric water commonly remobilizes and disperses metals and associated elements, thereby creating geochemical and mineralogical haloes that are used in exploration. In addition, the process of mining commonly exposes ore to more rapid oxidation by meteoric water, which naturally affects the environment. Therefore, understanding the movement of fluids through the Earth, for example, through enhanced hydrologic models, will be critical for future mineral exploration, as well as for effectively closing mines that have completed their life cycle (NRC, 1996b).

The focus of research on geological ore deposits has changed with new mineral discoveries and with swings in commodity prices. Geoscientists have developed numerous models of ore deposits (Cox and Singer, 1992). Models for ore deposits that, when mined, have minimal impacts on the environment (such as deposits with no acid-generating capacity) and for deposits that may be amenable to innovative in-situ extraction will be important for the future. Because the costs of reclamation, closure, postmining land use, and long-term environmental monitoring must be integrated into mine feasibility studies, the health and environmental aspects of an orebody must be well understood during the exploration stage (see Sidebars 3-1 and 3-2). The need for characterizations of potential waste rock and surrounding wall rocks, which may either serve as chemical buffers or provide fluid pathways for escape to the broader environment. Baseline studies to determine hydrologic conditions and natural occurrences of potentially toxic elements in rocks, soils, and waters are also becoming critical. The baseline data will be vital to determining how mining may change hydrologic and geochemical conditions. Baseline climatological, hydrological, and mineralogical data are vital; for example, acid-rock drainage will be greatly minimized in arid climates where natural oxidation has already destroyed acid-generating sulfide minerals or where water flows are negligible.

A wealth of geologic data has been collected for some mining districts, but the data are not currently being used because much of the data is on paper and would be costly to convert to digital format. Individual companies have large databases, but these are not available to the research community or industrial competitors. Ideally, geological research on ore deposits should be carried out by teams of geoscientists from industry, government, and academia. Industry geoscientists have access to confidential company databases and a focus on solving industrial problems; government and academic geoscientists have access to state-of-the-art analytical tools and a focus on tackling research issues. Currently, geological research activities in the United States are not well coordinated and are limited primarily to studies of individual deposits by university groups and, to a much lesser extent, by the USGS. More effective research is being carried out in Australia and Canada by industry consortia working with government and academia to identify research problems, develop teams with the skills appropriate to addressing those problems, and pool available funding. Both Canada and Australia have resolved issues of intellectual property rights in the industry-university programs, but these issues have yet to be resolved in the United States.

Geochemical and Geophysical Methods

Surface geochemical prospecting involves analyzing soil, rock, water, vegetation, and vapor (e.g., mercury and hydrocarbons in soil gas) for trace amounts of metals or other elements that may indicate the presence of a buried ore deposit. Geochemical techniques have played a key role in the discovery of numerous mineral deposits, and they continue to be a standard method of exploration. With

SIDEBAR 3-1 Examples of Environmental and Health Concerns That Should Be Identified During Exploration

  • groundwater and surface water quality

  • trace elements in existing soils

  • trace elements in ores, particularly elements of concern, such as mercury and arsenic

  • the presence of asbestiform minerals associated with industrial-minerals operations

  • the potential for acid-rock drainage (amounts of sulfide minerals and buffering minerals, climate, and hydrology)

  • location of aquifers in relation to ore bodies

  • existence and location of sensitive biological communities

  • climatological impacts on mining operations, including precipitation and prevailing winds

  • socioeconomic and cultural issues, including sustainable development

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement