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

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Research Notes (RN) publications are intended to provide members of the geoscience community with an avenue for publishing independent research and for supporting scientific exchange and the preservation of observations and interpretations. These publications have not been subject to the typical Colorado Geological Survey review process, but submissions are screened for general relevance and basic technical quality. The views, information, or opinions expressed in this publication are solely those of the individual author(s) and do not necessarily represent those of the Colorado Geological Survey, the Colorado School of Mines, or their employees.

This publication examines limited sampling results in the coal-bearing strata of the Denver Formation, located within the Ramah-Fondis coal field. Included are field photos and observations, geologic log of sampled coal seam, and laboratory results for both major elements (XRF) and rare earth elements (ICP-MS). Sampling location is in El Paso County. Digital PDF download. RN-05D

From the abstract:

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.