Rare Earth Occurrences in Coal and Their Association with Tonsteins, Diapirs, and Igneous Activity

摘要

Rare earth elements (REE) are often found to be associated with coals and coal waste products in numerous coal basins throughout the United States. Identifying the source of the REE can be somewhat enigmatic. Recent work, however, in both eastern and western coal basins suggest that both regional ash falls and localized diapiric or other intrusive activity can account for some REE occurrences. Lesser amounts of REE may be sourced from fluvial detrital material, but these sources are probably not significant. Data from the Appalachian Basin of eastern Kentucky, southwestern, and central Pennsylvania and from the Raton Basin of south-central Colorado suggest that igneous activity has played an important role in introducing REE material into these coal basins. In some instances, the occurrence of REE is associated with stratigraphic kaolinitic-rich altered volcanic ash and tuff layers (tonsteins) whose occurrence in the basins should be predictable and widespread, possibly allowing for careful mine management to segregate the coals and waste materials as a possible source of REE materials. Presented will be empirical data derived both from the literature and from recent field studies showing the correlation of REE in coals with such igneous features.