The Ferron Sandstone Coal Zones as a Source of Rare Earth Elements and Critical Minerals

The shoreface and deltaic sandbodies of the Ferron Sandstone have long been a focus of sedimentary research, especially with regards to understanding subsurface shallow marine hydrocarbon reservoirs. Recent work, however, has examined Ferron coal-bearing coastal plain deposits to ascertain their potential as a resource for Rare Earth Elements (REEs) and Critical Minerals (CMs). The Last Chance Delta system of the Ferron Sandstone was chosen for this study due to the presence of six laterally extensive named coal intervals (A, C, G, I, J and M coals) that cap seven of the eight highly organized deltaic sandstone units.

Core and outcrop samples covering the entire Ferron stratigraphy have been geochemically evaluated via pXRF and ICP-MS elemental abundance methods to quantify their REE- and CM-enrichment; a sample is considered enriched when REE abundance is >200 ppm. All of the named coal intervals analyzed show REE-enrichment, locally reaching >4800 ppm. Enrichment is typically concentrated in claystones within, or adjacent to, the coal seams, with only two of the named coals recording enrichment within lower-grade coals (brown and dull). Enrichment is geographically widespread and not confined to a specific location or mine. These results suggest that REE-enrichment is lithologically controlled and appears to have been influenced by diagenesis and fluid movement. These results also support the utilization of active mines, decommissioned mines and coal processing waste piles for the future of domestic REE extraction, offering economic and environmental solutions to pressing global demands.