Editing Coal mining (section)

===Surface mining===
[[File:Cerrejonmine1.png|thumb|Trucks loaded with coal at the [[Cerrejón]] coal mine in [[Colombia]]]]
When coal seams are near the surface, it may be economical to extract the coal using [[Open-pit mining|open-cut]], also referred to as open-cast, open-pit, mountaintop removal or strip, mining methods. Opencast coal mining recovers a greater proportion of the coal deposit than underground methods, as more of the coal seams in the [[stratum|strata]] may be exploited. 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 mining method, 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 onto large trucks or conveyors for transport to either the coal preparation plant or directly to where it will be used.<ref name="CoalMining2009"/>

Most open cast mines in the United States extract [[bituminous coal]]. In Canada, Australia, and South Africa, [[open cast mining]] is used for both [[thermal coal|thermal]] and [[metallurgical coal]]s. In [[New South Wales]] open casting for steam coal and [[anthracite]] is practiced. Surface mining accounts for around 80 percent of production in Australia, while in the US it is used for about 67 percent of production. Globally, about 40 percent of coal production involves surface mining.<ref name="CoalMining2009"/>

====Strip mining====
Strip mining exposes coal by removing earth above each coal seam. This earth to be removed is referred to as 'overburden' and is removed in long strips.<ref name="T1">Ryan Driskell Tate, "Places of Overburden: Strip Mining and Reclamation on the Northern Great Plains," ''The Greater Plains: Rethinking a Region's Environmental Histories'' (Lincoln: University of Nebraska Press, 2021).</ref> The overburden from the first strip is deposited in an area outside the planned mining area and referred to as out-of-pit dumping. Overburden from subsequent strips is deposited in the void left from mining the coal and overburden from the previous strip. This is referred to as in-pit dumping.{{Citation needed|date=January 2021}}

It is often necessary to fragment the overburden by use of explosives. This is accomplished by drilling holes into the overburden, filling the holes with explosives, and detonating the explosive. The overburden is then removed, using large earth-moving equipment, such as [[dragline]]s, [[Power shovel|shovel]] and trucks, [[excavator]] and trucks, or [[Bucket-wheel excavator|bucket-wheels]] and conveyors. This overburden is put into the previously mined (and now empty) strip. When all the overburden is removed, the
underlying coal seam will be exposed (a 'block' of coal). This block of coal may be drilled and blasted (if hard) or otherwise loaded onto trucks or conveyors for transport to the coal preparation (or wash) plant. Once this strip is empty of coal, the process is repeated with a new strip being created next to it. This method is most suitable for areas with flat terrain.{{Citation needed|date=January 2021}}

Equipment to be used depends on geological conditions. For example, to remove overburden that is loose or unconsolidated, a bucket wheel excavator might be the most productive. The life of some area mines may be more than 50 years.<ref name="Interior 1987">U.S. Department of the Interior, Office of Surface Mining Reclamation and Enforcement (1987). ''Surface coal mining reclamation: 10 years of progress, 1977–1987''. Washington, D.C.: U.S. Government Printing Office.</ref>

====Contour mining====
The contour mining method consists of removing overburden from the seam in a pattern following the contours along a ridge or around the hillside. This method is most commonly used in areas with rolling to steep terrain. It was once common to deposit the spoil on the downslope side of the bench thus created, but this method of spoil disposal consumed much additional land and created severe landslide and erosion problems. To alleviate these problems, a variety of methods were devised to use freshly cut overburden to refill mined-out areas. These haul-back or lateral movement methods generally consist of an initial cut with the spoil deposited downslope or at some other site and spoil from the second cut refilling the first. A ridge of undisturbed natural material {{convert|15|to|20|ft|m|abbr=on|0}} wide is often intentionally left at the outer edge of the mined area. This barrier adds stability to the reclaimed slope by preventing spoil from slumping or sliding downhill.{{Citation needed|date=January 2021}}

The limitations of contour strip mining are both economic and technical. When the operation reaches a predetermined stripping ratio (tons of overburden/tons of coal), it is not profitable to continue. Depending on the equipment available, it may not be technically feasible to exceed a certain height of highwall. At this point, it is possible to produce more coal with the augering method in which spiral drills bore tunnels into a highwall laterally from the bench to extract coal without removing the overburden.{{Citation needed|date=January 2021}}

====Mountaintop removal mining====
{{Main|Mountaintop removal mining}}
Mountaintop coal mining is a surface mining practice involving removal of mountaintops to expose coal seams, and disposing of associated mining overburden in adjacent "valley fills". Valley fills occur in steep terrain where there are limited disposal alternatives.<ref>{{Cite web |title=Valley fills |url=https://archive.kftc.org/valley-fills |access-date=2024-04-23 |website=Kentuckians For The Commonwealth |language=en}}</ref>

[[Mountaintop removal mining]] combines area and contour strip mining methods. In areas with rolling or steep terrain with a coal seam occurring near the top of a ridge or hill, the entire top is removed in a series of parallel cuts. Overburden is deposited in nearby valleys and hollows. This method usually leaves the ridge and hilltops as flattened plateaus.<ref name="Christman, R.C. 1980"/> The process is highly controversial for the drastic changes in topography, the practice of creating ''head-of-hollow-fills'', or filling in valleys with mining debris, and for covering streams and disrupting ecosystems.<ref>{{cite web|url=http://mountainjusticesummer.org/facts/steps.php|archive-url=https://web.archive.org/web/20051029154012/http://mountainjusticesummer.org/facts/steps.php|archive-date=29 October 2005|title=Mountain Justice Summer – What is Mountain Top Removal Mining?|date=29 October 2005}}</ref><ref>U.S. Environmental Protection Agency, Philadelphia, PA (2005). [http://www.epa.gov/region3/mtntop/eis2005.htm "Mountaintop mining/valley fills in Appalachia: Final programmatic environmental impact statement."]</ref>

Spoil is placed at the head of a narrow, steep-sided valley or hollow. In preparation for filling this area, vegetation and soil are removed and a rock drain constructed down the middle of the area to be filled, where a natural drainage course previously existed. When the fill is completed, this underdrain will form a continuous water runoff system from the upper end of the valley to the lower end of the fill. Typical head-of-hollow fills are graded and terraced to create permanently stable slopes.<ref name="Interior 1987"/>