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ROLE OF BEDROCK GEOLOGY AND MINERAL RESOURCES IN ECOSYSTEMS


Lithology affects both physical and chemical parameters of ecosystems. Physical parameters are affected because lithology provides the context for landscape development. Lithology controls the potential for the occurrence of mineral deposits, and, thereby, the potential for man-made disturbances through exploitation of these deposits. Chemical parameters of ecosystems are affected by lithology because geologic materials and processes control initial availability of nutrients, acidity and oxidation-reduction potential, and metal contents of soils and water. Extreme enrichment of minerals in the lithosphere, e.g., a mineral deposit, can create correspondingly extreme conditions by natural weathering or when exposed during mining. Undisturbed mineral deposits may cause local or regional elevated geochemical backgrounds in waters, soils, plants, or rocks. The composition of ores and host rocks control the nature and severity of impacts resulting from exploitation of mineral deposits.

The presence of mineral deposits in bedrock is especially significant because of socioeconomic issues and potential environmental risks, which can create conflicting land-use options. Development of mineral resources is a socio-economic benefit, not only in creating high-paying jobs and tax revenues in the local area, but in providing secondary jobs and contributing to regional and national economic growth. However, social concerns are that inadequate planning or unforeseen problems during development can create hazards to human and environmental health. The interplay among social concerns, economic forces, and resource needs can create conflicts that make land management decisions about mining and areas with potential for mineral deposits complex and controversial. The ability to predict the potential for the occurrence of mineral deposits can be used to assure that the kinds of studies that will be needed are done. A scientific information base that anticipates the potential for mining is essential to development of adequate, reasonable, and timely plans for mitigation and remediation of the impacts of mineral development.

The interaction of some minerals, such as iron sulfides, with the atmosphere or hydrosphere, can produce toxic conditions even in their naturally occurring, undisturbed condition. Under certain conditions, weathering of iron sulfides can produce acid waters and base metal sulfides can produce a low level bioavailability of metals. Disturbance of high sulfide zones, whether through mining, road building, or community development, increases the amount of surface area available for reactions to take place and can increase potential for toxicity and acidity of soils and waters. An example is fish kills in the Great Smoky Mountains, which resulted when water drained through iron-sulfide rich rocks that were used as rip-rap in the base for highway construction and subsequently entered streams.

Knowledge of the types of deposits that can occur in a region provides a basis for identifying areas that have the potential for developing naturally occurring toxicity in surface or ground waters. Identification of land areas with potential for specific types of mineral deposits and associated mineralization can be used to assess the environmental risk associated with disturbing mineral concentrations. For areas with high potential for mineral deposits of the types that might cause environmental hazards, more detailed geologic maps and geo-chemical baseline studies allow land managers to anticipate and prevent hazardous conditions.

In addition to potential environmental hazards, some rock types, such as limestone form a natural buffer for acidic waters. Carbonate rocks serve as a calcium source, thereby increasing initial availability of one of the nutrients that are derived from bedrock.


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Contact: Sandra H. B. Clark (shbclark@usgs.gov )
U.S. Geological Survey
Mineral Resource Surveys
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Reston, VA 20192 USA
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