Selenium distribution and mode of occurrence in the Kanawha Formation, southern West Virginia, USA

Selenium concentrations were measured in five rock cores from a mine in Boone County, West Virginia to determine their relationship to sulfur, rock type and stratigraphic location. The samples spanned the Winifrede and Coalburg coal beds of the Middle Pennsylvania upper Kanawha Formation and included coals and clastic lithologies. The coals generally contained the highest concentrations of Se and the sandstones the lowest, No correlation was observed between total Se and sulfur concentrations for either the entire data set or for individual lithologies. Better correlations were identified for log concentrations between total Se and total organic carbon. Principal component analysis identified a strong sulfur-acid component, interpreted to be due to sulfide mineral presence, which correlates well with S but not with Se. Coal sample chemistry is more likely to load onto this component while elastic rock chemistry is more likely to load onto the second, non-sulfur component. Se concentrations load onto both components indicating they are not controlled by a single overriding chemistry. Selective extractions indicate that Se is distributed between both sulfide and organically-bound fractions, as defined by the test. Overall, the lack of correlation between Se and S, the distribution of Se among extracted fractions, and the loading of Se onto both sulfur and non-sulfur components support that the Se in these rock layers is distributed in more than one chemically-bound form. Non-coal rock units with the highest concentrations of Se were found adjacent to coal beds, suggesting that redistribution of Se may have occurred post-deposition. The acidic domed swamps that formed these coals were low in sulfur and a reasonable chemical setting to accumulate Se if it were introduced. The preservation of Se in the domed swamp peat coupled with post-depositional redistribution may partly explain the data presented. (c) 2007 Elsevier B.V. All rights reserved.