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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


HISTORY OF THE CLASSIFICATION SYSTEM

Almost since their inceptions in 1879 and 1920, respectively, the U.S. Geological Survey and the U.S. Bureau of Mines have conducted modest ongoing programs in coal resource estimation and analysis. Between 1909 and World War II, tonnage estimates of the coal resources and reserves of the United States were summary totals derived for areas from estimates that were calculated by gross statistical methods. These early estimates were inadequate for the needs of the 1940's because they did not separate thin from thick coal beds, distinguish shallow from deeply buried coal, separately quantify identified resources and undiscovered resources, or discriminate the quality and rank of coal on the basis of physical and chemical criteria.

After World War II, requests from the public indicated the need for more detailed information about the occurrence, distribution, and availability of the Nation's coal resources. These requests indicated that a more detailed coal classification system was needed and that it should be based on bed-by-bed analysis of thicknesses of coal and overburden, reliability (distance from control points) of areal data, rank of coal, and several chemical parameters related to determining quality and usage. As a result, ongoing programs of the Geological Survey and the Bureau of Mines for geologic mapping and engineering evaluation were expanded, and programs for appraising the coal resources of the Nation on a State-by-State and a bed-by-bed basis were initiated.

After much consultation with potential users, the Geological Survey and the Bureau of Mines revised their procedures and prepared new definitions, criteria, and guidelines to be followed in estimating coal resources. The main elements of the programs used after World War II to 1976 were as follows:

1. Estimates of resources and reserves were based on existing information. Initially, attempts were not made to estimate the Nation's total coal resources or reserves; however, such estimates were long-term objectives.
2. Estimates of resources and reserves were prepared on a State-by-State basis.
3. Estimates of resources and reserves were divided into precisely defined categories such as rank, thicknesses of coal and overburden, and distance from points of information.

The estimates of coal resources and reserves from World War II to 1976 were prepared in formats suitable for use by geologists and engineers, coal specialists, and economists working for the coal industry and government. These formats included geologic maps, coal bed maps, tables, and diagrams of resource and reserve data segregated into categories suitable for comparison with similarly categorized data from other sources.

Experience with the classification system utilized from World War II until 1976 gradually showed the need for still greater detail. It also showed the need for rigidly enforced standards that would lessen individual geologic and engineering judgments in the interpretation of data and methods. Adoption of such standards should result in reproducible and comparable estimates from the same data and would allow adoption of computer technology.

In 1976, the Geological Survey and the Bureau of Mines adopted a modification of the 1944-75 system by publishing U.S. Geological Survey Bulletin 1450-B titled "Coal Resource Classification System of the U.S. Bureau of Mines and U.S. Geological Survey." This bulletin has been the standard reference for coal resource/reserve work by many Federal and State agencies.

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