PNNL

Abstract

The Dean (Fire Clay) coal in Knox County, Kentucky, does not contain the megascopically-visible ash-fall tonstein present in most other sections of the coal bed. Like the Fire Clay tonstein, a low-ash portion of the coal is enriched in rare earth elements (>2400ppm, on ash basis). In addition to kaolinite produced in the diagenesis of volcanic glass, transmission electron microscopy studies indicate the coal contains primary kaolinite, La Ce Nd Th monazite, barium niobate, native gold, and Fe Ni Cr spinels. The mineral assemblages, particularly the kaolinite-monazite association and its similarity to the tonsteins in coal to the east, demonstrate the coal was subject to the REE-enriched volcanic ash fall, apparently just at a more dilute level than at locations where the tonstein is present.