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The Pocahontas Formation (Carboniferous) in southwestern Virginia and West Virginia ranges in thickness from 600 to 750 ft (183 to 229 m). A major mineable coal seam known as the Pocahontas No. 3 (P3) is a laterally continuous, low-sulfur coal extending throughout Russell, Tazewell, and Buchanan Counties. It lies within 1,500 to 2,000 ft (457 to 610 m) below the surface and ranges in seam height from 0 to 72 in. (0 to 1.8 m).
Identification of potential roof hazards in the preliminary drilling stages of mine development is possible by reconstructing the depositional setting of the P3. Rock types overlying the P3 coal primarily consist of coarsening-upward shales and sandy shales, and thin-bedded graywacke sandstones deposited in the central and northwest parts of the study area. In addition, thin coals overlying clay partings and massive, fining-upward, cross-bedded graywacke sandstones are present in the east and southeast. Thus, the depositional setting is interpreted as an upper delta front system of distributary channels, splays, and adjoining interdistributary bays which prograded from the southeast over the transitional environment of the P3 seam.
Knowledge of this setting, integrated with previous in-mine research, revealed potentially hazardous areas with respect to continuous and longwall mining practices. Also, preliminary evaluation techniques developed in this study make it possible to initiate a more effective secondary drilling program resulting in the definition of stable areas for the driving of mine entries.
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