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MINES, MINING, AND ENVIRONMENTAL GEOCHEMISTRY



    Mines and mining activity inherently disturb the environment, because they involve the excavation and processing of rock and soil. This is the trade-off that many people accept to obtain the iron, coal, copper, gold, and other metals and minerals that maintain and improve our standard of living.


    The environment surrounding a minesite can sometimes be disturbed significantly through the migration of metals and nonmetals. This often takes place primarily in surface runoff and subsurface groundwater, collectively called minesite drainage. Thus, the science that assesses, predicts, and controls this water-borne migration is environmental geochemistry of minesite drainage or, somewhat shorter, minesite-drainage chemistry.


    The geochemical effects of mining originate with the exposure of the original, or primary, minerals to air and/or water during mining. This leads to the release, or leaching, of metals and, when sulfide minerals are present, to the generation of acidity. As a result, water passing over or through minesite components contains detectable concentrations of metals and nonmetals. At the same time, soluble metal-bearing secondary minerals can accumulate and then redissolve at a later time.


    The best known type of drainage chemistry is acid mine drainage (AMD), also known as acid rock drainage (ARD). Nevertheless, even pH-neutral and alkaline drainage can lead to significant environmental effects.


    The components of a minesite that can create drainage chemistry include the rock walls of open pits and underground workings, waste-rock dumps, low-grade ore stockpiles, tailings, roads, and broken-rock foundations for buildings.


    Many mining companies around the world pay close attention to the chemistry of waters draining from their minesites. A great deal of effort is put into assessing drainage chemistry by collecting, analyzing, and interpreting water analyses. Prediction of drainage chemistry is another effort, because a company must know whether the chemistry will improve, worsen, or remain the same for the next decades to centuries. Finally, companies initiate control measures for drainage water if its chemistry is unacceptable for discharge to the environment.


    Many of the points mentioned above are illustrated by case studies of real minesites in our publications and products and in our Internet Case Studies here at this site. Also, examples of underwater disposal of mining materials can be found here


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Created by K.Morin