SURFACE MINING

removal of the soil and rock (overburden) above a seam of coal or other mineral and extraction of the exposed mineral. When applied to the winning of coal, the technique is conventionally called strip-mining, which began when the supply of coal exposed at the surface of the Earthin ledges or outcroppingswas exhausted, and it became necessary to remove earth to lay bare the coal seams. The method is used to best advantage where the coal is not deeply buried, although many modern strip mines employ equipment capable of removing overburden nearly 200 feet (60 metres) in thickness. In Europe the technique is widely used for brown-coal deposits, while in the United States a large proportion of both anthracite and bituminous coal is so mined; surface mining also is used to obtain iron, copper, and phosphate ores (in these instances, the operation is called open-pit or opencast mining). Surface mining is most economical where flat terrain and horizontal seams permit a large area to be stripped. Where deposits occur in rolling or mountainous terrain, a contour method is used that creates a shelf with a slope on one side and an almost vertical wall on the other. Surface mining has been criticized, especially in the United States, because unless steps are taken to restore the lands, the area is damaged or destroyed. Several U.S. states and the federal government have legislated such restoration, and many producers now voluntarily practice it. See also placer mining.