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M. Devereux Carter and Nancy K. Gardner

U.S. Geological Survey Open-File Report 89-362

Chapter 8 - GLOSSARY

Available coal resources:

Remaining coal resources that are thick and shallow enough to be mined by either surface or underground methods and that are unencumbered by land-use, environmental, societal, regulatory, or technologic restrictions as they may apply in a given State or region. In this study, available resources are derived by the following formula:


Locally applicable averages for mining recovery factors may be applied after available coal resources axe calculated, but are not applied in this study.

Buffer zone: Area surrounding a restrictive feature (mine, town, ceme- tery, oil or gas well) in which mining is not permitted, i.e., barrier pillar around an active or abandoned underground mine

Coal Resources: Naturally occurring concentrations or deposits of coal in the earth's crust in such forms and amounts that economic extraction is currently or potentially feasible.

Colluvium: Loose deposits of rock debris usually at the foot of a slope or cliff brought there chiefly by gravity (mostly on aslope).

Compliance coal: Coal that meets new-source performance standards (NSPS) of EPA for sulfur dioxide (SO2) emission without use of SO2-reduction processes such as scrubbers. Current maximum limit on sulfur dioxide emissions from new-source coal-fired power plants is 1.2 pounds of S02 per million btu of heat input.

Deep coal resources: Those coal resources that would most probably be mined by underground mining methods.

Deep-mine barrier pillars: Coal left unmined around the peripheries of active or abandoned underground mines required for mine safety. Also referred to as deep-mine barrier in this report.

Digital elevation model (DEM): Arrays of topographic elevations at regularly spaced 30 meter (approximately 100 feet) intervals that correspond in coverage to standard 1:24,000-scale 7.5-minute quadrangles; produced by the U.S. Geological Survey and distributed in tape format.

Displacement fault: A fracture in the earth wherein the rocks have moved vertically and/or horizontally relative to one another. The displacement may range from several inches to many miles, and may be disruptive or prohibitive to the mining of coal in the immediate vicinity of the fault.

Floor rock: Stratigraphically, the rock immediately underlying a coal bed.

Inertinite: An organic component of coal that is inert, or partially inert, during coking processes. Inertinite could prevent complete and rapid burning of the coal in power-generation boilers unless the plant was specially designed to handle that particular coal.

Interburden: The rock between two coal beds. When two potentially minable coal beds occur within a minimum acceptable distance above or below one another, one will not be mined --often the thinner of the two.

Land-use restrictions: Constraints placed upon mining by societal policies to protect those surface features or entities that could be affected by mining. Laws and regulations can be modified or repealed; therefore, the restrictions may change.

Lost-in-mining: The unrecoverable coal remaining in the ground within a mine after all feasible extraction is completed. Includes coal that is

  1. left to support mine roofs,
  2. too thin or impure to mine,
  3. unsafe for mining, i.e, bad roofs, faults or
  4. unmined around oil, gas, water, and disposal wells, shafts, conduits, haulageways, tunnels, and airways.

National Coal Resources Data System (NCRDS): The U.S. Geological Survey computer system for storage, retrieval, and manipulation of stratigraphic, geochemical, and coal resource-related data. The NCRDS stratigraphic data base contains information on more than 150,000 coal data points; the geochemical data base includes analyses on nearly 13,000 coal samples. The NCRDS graphics programs calculate and tabulate resources according to the specifications of the USGS coal-resources classification system (Wood and others, 1983). A national network of users and State cooperators is tied into NCRDS for interactive data retrieval, manipulation, and coal resource assessment.

Original coal resources: The amount of coal, containing 33 percent or less ash, in the ground prior to production under less than 6,000 feet of overburden that is either 14 or more inches thick for anthracite or bituminous coal or 30 or more inches thick for subbituminous coal and lignite in such form and amount that economic extraction is currently or potentially feasible.

Outcrop: That part of a coal bed or rock strata that appears at the surface (crops out).

Overburden: Any material, consolidated or unconsolidated, that lies between a coal deposit and the surface.

Pennsylvanian: A time period in geologic history between 270 million and 300 million years ago. The term also applies to a sequence of rocks deposited during the Pennsylvanian period.

Recoverable coal: The coal that is or can be extracted from a coal bed during mining.

Recovery factor: The percentage of total tons of coal estimated to be recoverable from a given area in relation to the total tonnage estimated to be in the ground prior to mining. The estimated recovery factors generally are 50 percent for underground mining methods and 80 to 90 percent for surface mining methods. More precise recovery factors can be calculated by determining the total coal in place before mining occurred and the total coal mined in any given area.

Remaining coal resources: The coal resources in the ground after coal mined and lost-in-mining have been subtracted from the original resources.

Restricted coal resources: Those remaining coal resources that are determined to be unminable because of current land-use or technologic restrictions.

Roof rock: Stratigraphically, in underground mining, the rock immediately overlying a coal bed. Often the upper part of a coal bed is left unmined to serve as a roof to the mining operations.

Subsurface coal bed: A coal bed that is completely below drainage and does not crop out at the surface nearby, so that for all underground mining of that coal bed, the coal could only be reached by shaft. Costs associated with shaft mining are higher than any other conventional method.

Surface coal resources: Those coal resources usually within a few hundred feet of the surface that would most probably be mined by surface mining methods.

Surface mine: A coal-producing mine that extends no deeper than a few hundred feet down from the surface. Material above the coal (overburden) is removed to expose the coal bed, which is then mined by surface methods such as area, contour, mountaintop removal, strip, open-pit, or auger.

Technologic restriction: Constraints relating to economics and safety placed upon mining by the state of technology or prescribed by law. The restrictions could change with advances in science or modifications in the law. Geological factors are included as technologic restrictions in this report.

Underground mine: A mine where coal is produced by first tunnelling into the earth to the coal bed and then extracting the coal by underground mining methods, such as room and pillar, longwall, and shortwall, or through in situ gasification. Underground mines are classified according to the type of opening used to reach the coal, i.e., drift (level tunnel), slope (inclined tunnel), or shaft (vertical tunnel). Deep mine is synonymous with underground mine.

Washout: Area where a coal bed, or its precursor, has been eroded away, or washed out. This may occur before or after burial.

Chapter 7   Appendix

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