New maps of Federal coal
Compilation and analysis of publicly available data on Federal coal are resulting in voluminous map sets showing coal isopachs, structure contours, and overburden isopachs on each known minable coal bed. As of the spring of 1981, there are available from the U.S. Geological Survey Open-File Services Section in Denver map sets at 1:24,000 scale or microfiche sets covering approximately 470 of the ultimately 1,400 quadrangles in the program. Because Congress in 1976 mandated the prompt “inventorying” of all unleased Federal coal for Government land-use planning, and because dollars but not employee positions were provided for the work, the U.S. Geological Survey was obliged to contract for the compilations. A typical map set has a short text and about 20 plates, including a data sheet; a Federal mineral ownership map; and correlation charts. For each coal bed, there are isopachs, structure contours, stripping limits, and mining ratios extending as far as the data will permit, regardless of coal ownership. Reserve base tonnages and relative development potentials are calculated, but only for unleased Federal coal areas. Termed “minable” are coal beds at least 1.524 m (5 ft) thick and less than 914.4 m (3,000 ft) deep. For conventional underground mining methods, beds dipping more than 15° are excluded; also excluded are all but 3.66 m (12 ft) of thick beds. For in situ conversion methods, the minimum dip is 15° except for the deep thick beds in the Powder River Basin. Arbitrary parameters classify the development potential of each unleased 16.19-hectare (40-acre) tract as high, moderate, low, unknown, or negative. The former Secretary of the Interior announced his intention to restrict leasing in general to tracts classified as having high to moderate potential for development. Many geologists will find these systematic map compilations to be useful bases for adding new data points and making their own interpretations, correlations, extrapolations, and reserve estimates.