THE FERRON SANDSTONE COAL-BEARING COASTAL PLAIN DEPOSITS AS A SOURCE OF RARE EARTH ELEMENTS AND CRITICAL MINERALS

The Ferron Sandstone has long been a focus of sedimentary research, with an emphasis placed on the stacking patterns and sequence stratigraphy of the shoreface and deltaic sandbodies that constitute these world class outcrop units, especially with regards to understanding subsurface shallow marine hydrocarbon reservoirs. Recent work however, has examined the coal-bearing coastal plain deposits within the formation to understand their possibility as a resource for rare earth elements (REEs) and critical minerals (CMs). The Ferron Sandstone has been chosen for this study due to the abundance of laterally extensive coal units within the Last Chance Delta system; it is highly organized and composed of eight deltaic sandstone units, each separated by a named coal interval (A, C, G, I, J, and M) that can be correlated throughout the county.

Core and outcrop samples covering the entire stratigraphy of the Ferron 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 six of the named coal intervals within the Ferron Sandstone show REE-enrichment, with one notable sample recording a REE abundance of >4800 ppm. Typically, the enrichment is concentrated in the claystones that define the base of each of the named coal seams. Overlying the claystones, enrichment typically decreases up through the named coal interval, and can persist for up to 6 ft vertical thickness, locally. Two of the named coals (A and C) record enrichment within the coal deposits themselves. In several of the named coals, this enrichment is geographically widespread and not confined to a specific location or mine. These results suggest that the level of organization in the coal stratigraphy has little to no impact on REE enrichment. Instead, it is lithologically controlled and appears to have been influenced by early diagenesis and fluid movement. These results also support the utilization of active mines and coal processing waste piles for the future of domestic REE extraction, offering economic and environmental solutions to pressing global demands.