Mercury content and petrographic composition in Pennsylvanian coal beds of Indiana, USA

A suite of high volatile bituminous coals of Pennsylvanian age from Indiana has been studied for their mercury (Hg) concentration and relationship between mercury content and maceral and lithotype composition. The coals ranged in Hg content from 0.02 in the Danville Coal Member to 0.31 ppm in the Upper Block Coal Member. Our study indicates that relationships between petrographic composition of coal and mercury content are site specific. This lack of a consistent relationship is explained by the fact that most Hg occurs in pyrite and not in the organic matter itself. Comparison of Hg content in durain/vitrain pairs shows that durain has more frequently a higher Hg content than vitrain, but the difference in frequency is inconsequential and shows no consistent pattern for a single coal bed or a single location. We suggest that increased concentration of Hg in vitrain is related to the presence of epigenetic pyrite in cleats.