Surface mining is called Open pit mining, also known as strip mining, is the practice of extracting minerals in open air. While most mining is done underground or deep into the mountains, open pit mines require no tunneling or digging to reach the minerals to be mined.
For extracting coal which lies close the surface, huge drag-line shovel machines remove the topmost layers of soil and rock, exposing the coal, which is then removed by smaller machines. Surface mining may involve removing sections of hills or top layers of a flat surface area. The layers of rock and dirt covering the coal are reserved for until the coal is removed, at which point the the dirt and rock is replaced, the mine covered over, and the environment restored as much as possible to its original condition.
When coal seams are near the surface, it may be economical to extract the coal using open cut (also referred to as open cast, open pit, or strip) mining methods. Open cast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the strata may be exploited. Large open cast mines can cover an area of many square kilometers and use very large pieces of coal mining process equipment. This equipment can include the following: Draglines which operate by removing the overburden, power shovels, large trucks in which transport overburden and coal, bucket wheel excavators, and conveyors. In this coal mining process, explosives are first used in order to break through the surface, or overburden, of the mining area. The overburden is then removed by draglines or by shovel and truck. Once the coal seam is exposed, it is drilled, fractured and thoroughly mined in strips. The coal is then loaded on to large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used.
Open pit mines are dug using electromechanical shovels, which can load up to 100 tons of minerals at once, as well as controlled multi-motor crawlers and other large pieces of equipment. For those mines that are expected to be functional for long periods of time, it's common to build tracks for a small railway to go up and down the sides of the mountain.
Countries with large mountain or deserted areas are more likely to have open pit mines. In the U.S., Montana, New Mexico and Arizona have the most open pit mines. Hibbing, Minnesota has the world's largest open pit iron mine. The largest open pit gold mine is in Indonesia.
After being completely mined, open pits need to be rehabilitated, meaning the area needs to be flattened out, covered with soil and stabilized. This is to prevent cave-ins in the area but also to avoid sulfuric acid, a common by-product of mining, to escape into the air. Fences are usually built around the closed pits to avoid animals and people from venturing nearby.
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