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Operations in which overburden and coal are removed in large stair-step configurations (called benches). Electrically powered shovels and draglines are the predominant digging equipment. Large (up to 300 tons capacity) trucks are the most common equipment for moving both overburden and coal, although overland conveyors are gaining popularity.

This mining method has been particularly effective in dealing with very large coal seams in the Powder River Basin, but most Wyoming surface mines use at least some open pit techniques. Reclamation of mined land is facilitated because 1) dirt can be moved and placed fairly precisely with reclamation in mind; 2) reclamation and mining can take place simultaneously.

Usually refers to surface mining operations in which overburden is removed in long, straight lines ("strips") by a dragline. This term can also mean exactly what it implies - a mine in which overburden is "stripped" off the top of the coal, regardless of the method employed. Economy is a major virtue of mines using draglines. Reclamation techniques differ from those of the open pit method but are equally effective. "Strip mine" is term sometimes used as a pejorative by mining opponents.

Dirt, rocks and other unbumable materials which lie on top of coal seams (hence, overburden).

Any of several mining techniques which are carried on under the surface of the earth. In most cases, underground (also "deep") refers to mines employing a series of vertical shafts and horizontal tunnels used to remove and transport coal. Digging is usually accomplished by specially designed continuous miners - machines with powerful wheels or chains which tear coal out of the seams. Haulage is by conveyer or specially designed underground vehicles.

Underground mining was once common in much of Wyoming; now, it is limited to the coal fields along the southern border.

Basic technique of underground mining in the U.S. coal industry. As mining proceeds, coal is removed from selected rectangular sections, or "rooms," in a carefully designed pattern. Huge "pillars" of coal are left in place to support the overburden, or "roof," above the coal seam.

Room and pillar mining has seen many modifications aimed at improving productivity. For example, one entails removing the remaining pillars while "retreating" toward the mine entrance.

An underground mining technique in which coal is, in effect, scraped off the coal face in continuous strips several hundred feet in length. Longwall mining is growing rapidly in popularity in the U.S.

The amount of unbumable material (usually overburden) which must be removed in comparison to the amount of coal which can be removed. The lower the ratio of overburden to coal, the lower the cost of mining. One advantage of the Powder River Basin deposits is their low mining ratio - less than 2:1 in some cases.

Historically, about 90 percent of Wyoming's coal is produced on federal leases. State and private leases make up the remainder. (Geological Survey of Wyoming, Minerals Management Service, Wyoming State Land office.)

Last Update 01/28/01

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