Ferron Sandstone coal-bearing coastal plain deposits as a source of Rare Earth Elements and Critical Minerals

The shoreface and deltaic sandbodies of the Ferron Sandstone have long been associated with research focused on understanding subsurface shallow marine hydrocarbon reservoirs. Recent work, however, has examined the Ferron coal-bearing coastal plain deposits to ascertain their potential as a resource of Rare Earth Elements (REEs) and Critical Minerals (CMs). The Last Chance Delta system, the youngest of the Ferron delta wedges, was chosen for this study due to the presence of six laterally extensive, accessible, mapped and 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 capturing the entire Ferron stratigraphy have been geochemically evaluated via pXRF and ICP-MS elemental abundance methods to quantify their REE- and CM-enrichment. All of the named coal intervals analyzed show REE-enrichment, locally reaching >4800 ppm; a sample is considered enriched when REE abundance is >200 ppm. Where present, 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. The extensive dataset (>6640 pXRF and 87 ICP-MS measurements) illustrates that enrichment is geographically widespread and not confined to a specific location, stratigraphic position or named coal zone. These results suggest that REE-enrichment is lithologically controlled and appears to have been influenced by early 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.