Field and Laboratory Identification of Lithium-Enriched Clay from the Mercer Formation in Central and Western Pennsylvania

Abstract:

Lithium is a critical resource used for modern energy storage - electric and hybrid vehicles, home energy storage systems, portable electronics, and the aerospace industry all currently use lithium ion batteries. Most commercial lithium is mined in China and South America, although significant unexploited resources are known to exist in the US. Of particular interest domestically are non-traditional resources including lithium-rich clays. The Mercer clay, part of the Pottsville Group underlying central and western Pennsylvania, is a high-alumina clay formerly mined for use in refractory ceramics. The Mercer was previously found to have lithium concentrations ranging from a few hundred ppm to >2,000 ppm. We used field and laboratory geochemical analytical techniques to assess lithium abundances in a stratigraphic section at a site in Clearfield County, PA. Field analysis revealed Li concentrations >1,000 ppm in a ~40 cm layer immediately underlying a thin coal seam. Stratigraphic sampling and laboratory analysis by ICP-MS confirms the presence of a lithium-rich (~1,000 ppm Li or more) clay layer in a paleosol tens of centimeters thick immediately underlying the Mercer coal at this and two other locations in Clearfield County. The mineral host of lithium in the Mercer clay is still under investigation, and may be the lithium-bearing chlorite group mineral cookeite (clinochlore was identified by XRD in several samples). Our study confirms that 1) the high-alumina clays immediately underlying coal in the Mercer Formation are potentially a significant domestic lithium resource, and 2) field and laboratory techniques can be utilized in tandem to identify high-lithium strata in sedimentary units.