Mining

Mining is the removal of materials from the earth's surface or underground that are useful and economically valuable. Strip mining

Surface mines, such as this uranium mine, cause more than just visual scars to the surrounding environment— waters flowing from mines contain substances that are harmful to plants and animals. Additionally, the chemicals used in processing at mines are toxic and can produce gases that are released into the atmosphere. (UN photo)

Surface mines, such as this uranium mine, cause more than just visual scars to the surrounding environment— waters flowing from mines contain substances that are harmful to plants and animals. Additionally, the chemicals used in processing at mines are toxic and can produce gases that are released into the atmosphere. (UN photo)

occurs where the material occurs in long bands and is near the surface. Coal, a fossil fuel, is an example of a commodity that occurs in extensive, relatively thin layers that are usually strip mined.

Open pit mines are somewhat circular, and occur where large amounts of the mined material are removed. Sand and gravel deposits and some types of copper deposits are examples of materials that are removed in that way. Placer mining is the removal of valuable minerals that are enclosed in loose sediments, such as beach and stream deposits. Quarrying refers to surface mining of solid rock that is used for building purposes. Surface mining leaves visual scars on the land by permanently altering the topography and, usually, by piling up large amounts of unwanted materials associated with the mining operation. Normally, the impact can be reduced substantially by putting the materials back into the excavation, covering them with topsoil, and using the surface for agriculture and home building. In some cases, for example sand and gravel pits, most of the material is removed, and all one can do is regrade the surface to its new configuration.

Underground mining does not usually leave a very large scar on the surface. In this kind of mining, the deposits are usually in bands or veins, and as little extraneous material is removed as possible. However, where the operations are extensive, there usually are large piles of unwanted debris. One way to get rid of this material is to backfill the mine, seal it, and restore the hillside where the opening had been. This process also prevents the mine, especially if it is not too far below the surface, from collapsing and leaving large depressions on the surface. Very often the timbers of old mines rot away, causing such collapses in long-forgotten mines.

There are other environmental effects of mining that are more important than the creation of visual eyesores. One has to do with water that accumulates in the mine as ground-water seeps into the opening. Depending on the nature of the ores, the water can become acidified as it dissolves some of the minerals in the mine. For example, many metallic ores are associated with sulfides that oxidize to form sul-furic acid. When these acidified waters flow out of the mine into the surrounding countryside, they can harm forests and animals. There are large numbers of old and abandoned mines that still drain acid waters, and little is done about them. In a few places in the world, where stricter laws are in effect, mine operators must capture this water and put it in holding tanks or lined reservoirs, where it is neutralized.

Often the dumps contain materials that upon weathering are released and wash into the environment. These harmful elements include mercury, arsenic, and cadmium, which contaminate both surface water and ground-water. Very often chemicals used for the processing of minerals are toxic and also produce unwanted gases that are released into the atmosphere.

Materials that are mined are usually divided into two groups, metallic and nonmetallic. We are familiar with the basic metals such as iron, copper, aluminum, lead, zinc, silver, gold, and chromium. Most of these are mined on or below the surface. Nonmetallic resources include sand and gravel, building and crushed stone, limestone for building and making cement, phosphates for fertilizer, salt, and gypsum for making plaster and gemstones. Except for salt, these are usually all removed from surface excavations.

—Sidney Horenstein

See also: Erosion; Geology, Geomorphology, and Geography; Pollution

Bibliography

Evans, Anthony M. 1997. An Introduction to Economic Geology and Its Environmental Implications. Malden, MA: Blackwell Science; Montgomery, Carla. 1999. Environmental Geology, 5th ed. Dubuque, IA: Wm. C. Brown Publishers; Syms, Paul M. 1997. Contaminated Lands: The Practice and Economics of Redevelopment. Malden, MA: Blackwell Science.

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