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
Table 6. - Areas of resource categories from figure 17 listed in proper reliability and thickness of coal and overburden categories
[Tonnage estimate for each area could be determined (1) by planimetering each area for acreage, and (2) by multiplying acreage by proper weight of coal per acre-inch by the average thickness of coal in the area. Thickness of coal for each area is obtained by referring to coal thickness isopach.]
| Geologic assurance category |
Coal thickness | ||
| 14 to 28 inches | 28 to 42 inches | 42 to 84 inches | |
| 0 to 500 feet overburden: | |||
| Measured | A, G, H | B, F | C |
| Indicated | I, N | E, J, L, M | K |
| Inferred | O, R | P, Q | None |
| 500 to 1,000 feet overburden: | |||
| Indicated | S, V | T, D, U | None |
| Inferred | W, Y | X | Do. |
| 1,000 to 2,000 feet overburden: | |||
| Inferred | Z | AA | None |
| Hypothetical | DD | None | Do. |
| 2,000 to 3,000 feet overburden | |||
| Inferred | BB | None | None |
| Hypothetical | CC | Do. | Do. |
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