NEW METHODOLOGIES FOR ASSESSING THE ABUNDANCE OF RARE EARTH ELEMENTS AND CRITICAL MINERALS WITHIN THE CRETACEOUS COAL-BEARING, COASTAL PLAIN DEPOSITS OF EASTERN UTAH

Recent work has shown that the Cretaceous coal deposits of eastern Utah and western Colorado are potential sources of rare earth elements (REE) and critical minerals (CM). The Ferron Sandstone, the focus of this study, is one of the coal-bearing deposits within this region; it was selected for study due to the presence of six laterally extensive coal deposits (coal intervals A, C, G, I, J, and M) that can be correlated locally and the ease by which these coals can be accessed. These coal intervals are currently mined at several locations throughout the study area, with the coal primarily used for energy production.

All six of the Ferron coals have been sampled at outcrop and/or within cores. A pXRF was used for the geochemical evaluation of these Ferron Sandstone samples, allowing the for rapid quantification of La, Sc, Ce, Pr, Y and Nd abundance. In this study, a sample was considered to be enriched if these five elements combined to give an abundance >200 ppm.

Due to the large number of coal-bearing intervals, and the large lateral extent of these deposits, a consistent methodology for analysis was developed to increase the sample resolution and to standardize the sampling process. In core, these methods consisted of measuring samples at 0.1 ft intervals, through the named coal seams, including 1 ft above and 1 ft below each seam. At outcrop, large samples (>500 g) were collected at 4–8-inch intervals through the coals, with additional samples collected 1 ft above and below the coal seams; these large outcrop and mine samples allow for the completion of additional pXRF scans on enriched samples, validating sample enrichment. So far >1200 intervals, from 10 cores, have been analyzed by pXRF, accompanied by the completion of >1600 pXRF scans of outcrop and mine samples. This high-resolution sampling methodology has shown that all six of the named Ferron coal intervals contain lithologies that have REE-enrichment >300 ppm, with several outcrop samples totaling 3000+ ppm REE-enrichment, which otherwise would have been missed without the practices established within this methodology.

These promising results suggest that there REE and CM resource potential in the Ferron Sandstone coal intervals.