46-8 Geologic trends in rare earth element enrichment in Cretaceous coal-bearing strata, Utah and Colorado

Session: Research to Accelerate Recovery of Critical Minerals from Primary and Secondary Resources

Presenting Author:

Lauren Birgenheier

Authors:

Birgenheier, Lauren P.¹, Coe, Haley Hallett², Fausett, Peyton D.³, Wilcock, Laura⁴, Morris, Emma A. ⁵, Fernandez, Diego P.⁶, Gall, Ryan⁷, Vanden Berg, Michael David⁸, Giebel, Andrew R.⁹, Free, Michael¹⁰

(1) Geology and Geophysics Department, University of Utah, Salt Lake City, UT, USA, (2) Geology and Geophysics Department, University of Utah, Salt Lake City, UT, USA, (3) Geology and Geophysics Department, University of Utah, Salt Lake City, UT, USA, (4) Geology and Geophysics Department, University of Utah, Salt Lake City, UT, USA, (5) University of North Carolina - Wilmington, Wilmington, NC, USA, (6) Geology and Geophysics Department, University of Utah, Salt Lake City, UT, USA, (7) Utah Geological Survey, Salt Lake City, UT, USA, (8) Utah Geological Survey, Salt Lake City, UT, USA, (9) Colorado Geological Survey, Golden, CO, USA, (10) Materials Science and Engineering Department, University of Utah, Salt Lake City, UT, USA,

Abstract:

Rare earth elements (REE) are used in technology products and are necessary for the clean energy transition and defense. Coal and related material have been identified as a prospective secondary REE and critical mineral resource. However, the geologic trends and controls on REE-enrichment in coal-bearing strata remain enigmatic. A geochemical and stratigraphic study of Cretaceous bituminous coal-bearing strata across central Utah and western Colorado was performed to evaluate geologic REE-enrichment trends. Portable X-ray fluorescence (pXRF) (n = 6424 analyses) was combined with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) (n = 222 analyses) to quantify REE enrichment. Sampling and geochemical analyses from 32 mine, core, and outcrop localities from the Ferron Sandstone and Blackhawk Formation (Utah) and the Mesaverde Group (Colorado) were performed with an emphasis on lithologic and stratigraphic context. REE-enrichment (> 200 ppm) is most commonly found in mudstone units overlying, underlying or within coal zones, with a strong preference of REEs in claystone sublithologies. Coal lithologies are generally not REE-enriched, with notable exceptions. REE-enriched coals exhibit lower coal quality (i.e., dull and brown colored bituminous coals). Additional petrography combined with scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) reveal silt-sized detrital monazite grains, as well as clay-sized REE-enriched domains in the matrix and organic matter. REE-enrichment results from a combination of paleo-depositional and diagenetic mechanisms. These geologic trends can be used as an REE resource prediction tool, particularly in bituminous coal-bearing successions worldwide. We provide a recommended coupled pXRF and ICP-MS approach for quantifying REE in secondary resources, broadly.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11184

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