Coal Resource Classification System of the U.S. Geological Survey
By Gordon H. Wood, Jr., Thomas M. Kehn, M. Devereux Carter, and William C. Culbertson
GEOLOGICAL SURVEY CIRCULAR 891
APPLICATIONS OF CRITERIA
The criteria are to be applied only to those deposits of coal that are currently or potentially feasible for economic extraction by underground mining, surface mining, and (or) in situ gasification methods. Coal beds that are thinner than 14 inches (35 cm; anthracite and bituminous) and 30 inches (75 cm; lignite and subbituminous) generally are excluded from resource consideration unless currently being mined. All coal beds deeper than 6,000 feet (1,800 m) are excluded. These limits are imposed as the result of consultations with geologists and mining engineers throughout the international coal community. In the United States, beds that contain more than 33 percent ash also are excluded; because of a shortage of energy in some countries, however, coal containing more than 33 percent ash is being mined and is classified as reserves.
Coal beds thinner or more deeply buried than the imposed limits have been mined locally at several places in the United States and are mined in other parts of the world; however, their extraction in the United States has generally not proven economic. Where such mining is taking place, the coal should be classed as a reserve and recorded at the time of assessment in the coal resource figures. With the few exceptions owing to current mining and similar future exceptions, the imposed limits should be adhered to. See general guideline No. 7.
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