Geologic setting and characterization of coals and the modes of occurrence of selected elements from the Franklin coal zone, Puget Group, John Henry No. 1 mine, King County, Washington, USA

Higher As and Hg contents in the coals result from post-Eocene hydrothermal mineralization. Mines in the nearby Green River Gorge contain cinnabar, metacinnabar, realgar, and orpiment. Realgar and orpiment were found in fractured sandstone above the No. 10 coal bed. Kleinite and cinnabar, both mercury-containing minerals, were identified in coal samples and native mercury was found in one parting sample. Thermal and XANES studies on coal samples indicate that there are at least two modes of occurrence for Hg in the Franklin coals: (1) organic complexes containing Hg, and (2) Hg-bearing minerals within the coal and associated partings. Pyrite may also contain trace amounts of As, Hg, and Ni.