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 3. - Summary of coal resource criteria
| Depth1 Feet (Meters) |
Thickness1 Inches (Centimeters) |
|||||
| Identified and undiscovered resources: | ||||||
| Anthracite and bituminous coal | £ 6,000 | (1,800) | ³ 14 | (35) | ||
| Subbituminous coal and lignite | £ 6,000 | (1,800) | ³ 30 | (75) | ||
| Reserve base and inferred reserve base: | ||||||
| Anthracite and bituminous coal | £ 1,000 | (300) | ³ 28 | (70) | ||
| Subbituminous coal | £ 1,000 | (300) | ³ 60 | (150) | ||
| Lignite | £ 500 | (150) | ³ 60 | (150) | ||
| Reserves2, marginal reserves, and inferred reserves2: | ||||||
| (Criteria same as reserve base and inferred reserved base but with factors based on engineering and economic analysis applied.) | ||||||
| Subeconomic resources: | ||||||
| Anthracite and bituminous coal | 0-1,000 | (300) | 14 (35) | -28 (70) | ||
| 1,000(300)-6,000 | (1,800) | ³ 14(35) | ||||
| Subbituminous coal | 0-1,000 | (300) | 30 (75) | -60(150) | ||
| 1,000 (300)-6,000 | (1,800) | ³ 30(75) | ||||
| Lignite | 0-500 | (150) | 30 (75) | -60 (150) | ||
| 500 (150)-6,000 | (1,800) | ³ 30(75) | ||||
1The metric thicknesses shown in parentheses are not exact equivalents of the thicknesses shown in feet; for convenience, they have been rounded to the amounts shown.
2Includes some beds that are thinner and (or) deeper than the general criteria permit, but that are being mined currently.
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