Geochemistry of the blue gem coal bed, Knox county, Kentucky

The Blue Gem coal bed (Middle Pennsylvanian Westphalian B, Breathitt Formation), has low-ash (with some sample sites having less than 1% ash) and low-sulfur contents through parts of Knox County, Kentucky. Most collection sites exhibit similar vertical elemental trends in ash geochemistry. The relatively high-ash (>1% ash) lower part of the bed displays enrichment in TiO₂, Zr, Cr, V and Ni; Co, Zn, Rb and Mn show enrichment at some sites. A low-ash (<1% ash) middle part of the bed displays enrichment in Sr, Ba and CaO; Fe₂O₃ is enriched in samples with carbonate minerals. The upper part of the bed contains >1% ash and a relative enrichment in SiO₂, K₂O and Rb and a relative decrease in Cu, Ni, Co, Ba and Mn when compared to the middle part of the bed. Principal components analysis indicates that the samples with an ash content 0.63–1.0% show associations for Ni, Cu, Cr and Co. Samples with between 1.01–2.0% ash display strong element associations that suggest increased clastic sediment contributions (TiO₂, Zr, K₂O, Rb, SiO₂). The low-ash content and the upwards decrease in trace concentrations both suggest that the Blue Gem peat swamp was ombrotrophic through at least a part of its geologic history.