POTENTIAL FOR A CRITICAL MINERAL RESOURCE IN THE UNDERCLAYS OF WEST VIRGINIA

Aluminum-rich clays associated with coal horizons (underclays, fireclays, tonsteins, Bolivar clays) are known throughout northern and central West Virginia, and adjacent areas. These clays have the potential to be under-appreciated low-grade, large-volume, critical mineral resources that offer several advantages including: large volumes that are structurally simple and laterally continuous; deposits that are at or near the surface and easily exploited by open-pit mining; and locations in areas that have long histories of mining and abundant infrastructure. Past studies show that alumina is routinely above 20% in these clay layers and up to 40%, and layers have mean thicknesses up to 9 m in areas of existing and past coal mining. Preliminary and unpublished geochemical data indicate that some clay layers host anomalously high (>300 ppm) ion-exchangeable rare earth element (REE) concentrations. Similar clays are thought to host high lithium (Li) concentrations, and the presence of elevated aluminum makes elevated concentrations of gallium and indium possible.

The origins of these clays (volcanic versus pedogenic) are not known, and there has been negligible further study of the economic potential of clays in West Virginia. Similar clays in Pennsylvania have elevated Li concentrations, which have been correlated with elevated alumina in Pennsylvania and Kentucky deposits. The potential for developing critical metal extraction in West Virginia is hampered by a lack of modern geochemical data and understanding of the distribution of metals in different lithologies and stratigraphic positions. Current work includes mapping known deposits and determining the stratigraphic and lithological intervals with the greatest promise of hosting these elevated critical mineral resources. A more advanced understanding will require completing a mineral inventory of REEs (as well as Li and other critical metals) in the underclays as well as revisiting prior study sites, identification of new sites, in situ lithofacies characterization with semi-quantitative elemental analysis, and collection of a stratigraphically and spatially representative sample suite for assaying in order to provide data necessary to estimate the economic potential of this resource.