LOOKING FOR CRITICAL MINERALS IN CARBONIFEROUS CLAYS BENEATH COAL DEPOSITS IN PENNSYLVANIA: A MULTIPRONGED APPROACH

Domestic sourcing of critical minerals, especially REE, is a high priority in the US since it forms a key component in many technologies for energy transition and national defense infrastructure. However, at present, relatively few economic deposits are known in US for these minerals. Recent work has shown that clays underlying coal deposits in the Appalachian can be a promising source of REE and leverage the historical infrastructure and geological knowledge associated with coal mining. However, a critical challenge with making this source viable is to pinpoint the REE rich layer from amongst the 100s of feet of underclays. Recent gamma ray logs on cores taken from the Eckley Coal Mine in Pennsylvania suggested the clays underlying coal deposits (the Buck Coal) may be enriched in REEs and can be mapped across multiple cores.

In this study, we evaluate this more closely using a multipronged approach that combines a number of analytical techniques – XRF, SEM-EDS, thin-section petrography, LA-ICPMS, etc. Preliminary XRF work demonstrated elevated levels of Cerium, Praseodynium, Neodymium, Vanadium, Zinc, and Zirconium above those of normalized chondrite in nearly all samples. Significant Lanthanum spikes were found in just a couple of samples. This work also seeks to address two key scientific questions - what is the scale of spatial heterogeneity of REE elements in the core, analyzed with EDS mapping, and what processes are responsible for the REE concentration.

Portions of the cores were powdered and examined with a benchtop XRF. In concert, splits of the same core were crushed to separate out zircons, which were dated by LA-ICPMS technique - we don't find any distinctive zircon age spectra for samples with and without REE enrichments suggesting that to first order, sediment provenance is not a key control on REE abundance. Future work combining EDS mapping with thin section petrography to see if critical mineral distribution is dispersed or governed by sedimentary processes.