EVALUATING CRITICAL MINERAL CONTENT OF PENNSYLVANIAN AGED BLACK SHALES IN EASTERN KANSAS

This study aims to evaluate the distribution of critical mineral content in Pennsylvanian aged phosphatic black shales within the Cherokee-Forest City Basin (CFCB) of eastern Kansas. Prior studies have demonstrated that black shales can serve as potential sources of critical minerals (CM), including V, Ni, Co, Mo, and Platinum Group Elements (PGEs) that become concentrated in phosphatic nodules or lamina. This research focused on P, V, Zn, Mo, U and Pb to identify zones of CM enrichment. Due to their strong affinity for euxinic conditions several of these elements (Mo, U, V, and Zn) can be used as proxies to inform upon redox conditions, depositional environment, and mode of emplacement.

Eight organic-rich phosphatic black shales were sampled from drill cores and outcrops for analysis via ICP-MS and portable x-ray fluorescence (pXRF). Select samples were also collected for evaluation of TOC. In ascending stratigraphic order, these shales include the Excello, Binkley (historically known as the Little Osage), Anna, Lake Neosho, Nuyaka Creek, Mound City, Hushpuckney, and Stark shales. The Hushpuckney Shale is the most enriched in V (average 1060.5 ppm), followed by the Stark Shale (980.2 ppm). Additionally, the Hushpuckney Shale is the most enriched in Zn, averaging 1676.8 ppm.

Enrichment of targeted elements corresponds to a increasing TOC values supporting the origin of CMs in CFCB black shales in low-oxygen environments. These black shales likely represent widespread flooding surfaces of a restricted water mass within the CFCB, as many of them are in direct contact with underlaying coals. The lateral extent of these shales and the punctual onset of euxinic conditions suggest significant regional influences. Recent hypotheses propose that formation of the Arkoma Foreland Basin and Ouachita Orogen likely forced the migration of deep anoxic waters, rich in CMs, onto the margins of the CFCB into active coal settings. The data presented here provides support for such a depositional setting as the primary mechanism for CM enrichment. However, later development of nodular, and/or laminar phosphatic horizons within the upper part of black shales would suggest post depositional alteration, likely through burial, or hydrothermal activity when proximal to brine pathways and fault systems.