RN-05 Reconnaissance of Critical Minerals in Denver Formation Coal-Bearing Strata, Denver Basin, Ramah-Fondis Coal Field, Colorado

Coal and coal-related stratigraphy may contain elevated concentrations of critical minerals and/or materials as defined by the U.S. Geological Survey and U.S. Department of Energy. Based on recent limited sampling results, Late Cretaceous-Paleocene Denver Formation coal in the Denver Basin contains elevated concentrations of rare earth elements (REEs) ranging from 359 to 1,026 parts per million total REEs. Elevated concentrations of REEs occur in lignite-dominated beds of the Upper Paleocene portion of the Denver Formation within the Ramah-Fondis coal field located in the Denver Coal Region. These REE concentrations are higher than most of the concentrations reported for coals and coal-related stratigraphy in the Uinta and Greater Green River coal regions in western Colorado. Shallow (<150-feet of overburden) Denver Formation lignite occurs in a wide area (>660 square miles), in four informal coal zones from ~1 to 30 feet thick, and contain abundant partings including tonstein, clay (especially kaolinite), and other lithologies. Although the lignite might not be a resource with regards to electricity generation, it could be a potential resource with regards to REEs - the deposits are widespread, at a relatively shallow depth, and may contain sufficient tonnage to be a resource albeit at a lower concentration than other conventional economic REE deposits. In order to better determine the potential for REE resources in the Denver Coal Region, future investigations should include: additional sampling and analysis of available coal seams in the Denver Formation as well as the Upper Cretaceous Laramie Formation coals; mineralogical studies to determine the mode of REE occurrence; extraction/recovery tests to determine the recovery potential of REEs; and additional assessment of other potential REE-bearing formations in the region including the Fox Hills Sandstone and the Denver Basin Group D1/D2 regional paleosol.