TRACE ELEMENT MOBILITY FROM WEATHERING OF BLACK SHALES IN EASTERN KENTUCKY

Black shales of Devonian and Mississippian age occur throughout the Appalachian Basin. Units at or near the surface around the flanks of the Cincinnati Arch in Ohio, Kentucky and Tennessee have been identified as potential targets for shale oil extraction (Dyni, 2005). In the Knobs region of eastern Kentucky, these shales contain concentrations of several trace elements that exceed the world shale average by one to two orders of magnitude with the highest concentrations found in the Mississippian Sunbury Shale (e.g, mean concentrations of 30 ppm Cd and 300 ppm Mo). A comparison of unweathered whole-rock from cores and fresh excavations with weathered rock from roadcuts exposed for several decades reveal that the weathered rocks contain significantly less Cd, Co, Cu, Ni, and Zn than the fresh rock (a = 0.05). No significant differences were found in the concentrations of Cr, Mo, or V, suggesting these elements are primarily associated with refractory phases (e.g., Al-silicate mineral phases). Elemental mass loss calculations, assuming average losses measured between fresh and weathered rock for both Sunbury and Ohio Shales and typical unit thicknesses as measured in the study area, indicate that between 5,000 (Cd) and >400,000 kg (Zn) per hectare could be mobilized to the environment from weathering or anthropogenic activities, such as surface mining for oil shale. Additional studies are being made to determine the impact of hydrous retorting on elemental release from these black shales.