PALEOENVIRONMENTAL ANALYSIS OF THE GLENALUM TUNNEL COAL AND ROOF ROCK, SOUTHERN WEST VIRGINIA—IMPLICATIONS FOR SULFUR ORIGIN AND TRENDS

Unexpected variations in sulfur were encountered in 2012 during drift mining of the Glenalum Tunnel Coal . A geological analysis was initiated to determine the cause of the sulfur variations and provide a predictive tool for anticipating high sulfur anomalies during future mining operations.

Stratigraphic sections were evaluated from a low to high sulfur area within the mine. Benches were incrementally sampled and analyzed for ash, sulfur, sulfur forms, and coal petrography. The lower 3 benches are consistently low sulfur (< 1 %). The upper 3 benches range from low to high sulfur with individual benches as high as 6 %. The majority occurs as finely disseminated pyrite . The paleoclimate had high rainfall and a significant dry season. The peat accumulated in a mire with elevated and domed stages under optimum, acidic freshwater conditions that minimized the formation of sulfur and ash. Core drilling revealed that the coal is overlain by an interval averaging 6.7 m thick consisting of laterally and vertically variable facies. This interval is overlain by the Oceana Shale marine unit. The coal is overlain by a dark gray, lacustrine shale. Avulsion diverted a deltaic distributary channel into the area which downcut into the shale. As sea level rose, thoroughly burrowed sandstones, locally containing crinoids and brachiopods, formed in tidal channels that locally downcut to the coal. The lake became a coastal bay. A thin ravinement bed of burrowed, sideritic sandstone unit occurs at the base of the Oceana Shale.

Roof rock attributes from 42 boreholes were compared to 1.5 float sulfur values in the underlying coal. Scattergram trendlines were evaluated with power or polynomial regression to determine the correlation coefficients. A sinuous belt of high sulfur coal correlates with areas where the lacustrine shale of the immediate roof is less than 30-60 cm thick (R=0.50), and where the stratigraphic interval between the coal and the Oceana Shale is comprised of at least 80% sandstone (R=0.65). High sulfur areas are attributable to 1) the local influence of brackish to marine waters from tidal or deltaic distributaries that carried these waters and eroded down to the peat, and/or 2) thinning or removal of impermeable roof shale by channel erosion and hydraulic connection of the Oceana Shale marine pore fluids to the peat.