Geochemical Sampling and Regional Interpretation (Illinois and Appalachian Basin) of High Alumina Underclay Deposits in the Central and Eastern U.S. (2020-2022)
The Maryland Geological Survey, in conjunction with other state geological surveys and the U.S. Geological Survey (USGS), are studying the critical mineral potential of aluminum-rich, kaolinitic clays associated with coal beds in Pennsylvanian-aged strata. These clays have historically been utilized for brick-making in Maryland (Watts et al., 1922) and are called “underclays” because they often occur beneath coal beds. Recent studies suggest that Pennsylvanian underclays contain elevated concentrations of lithium (Li), aluminum (Al), and rare earth elements (Rozelle et al., 2021).
Underclays have been sampled by eight state geological surveys throughout the Appalachian plateau of Maryland, Pennsylvania, West Virginia, and Ohio; as well as a portion of Kentucky, through the Illinois Basin and into Iowa. Geochemical analysis is currently being completed by the USGS. This reconnaissance effort will pinpoint specific stratigraphic intervals of interest, capture regional variations, and determine the presence or absence of elevated concentrations of associated critical mineral commodities.
Trace and major element content for 120 underclay samples from 15 locations in or near Garrett County, Maryland can be found below. Preliminary results show elevated Li (>300 parts per million) in claystone from the Lower and Middle Kittanning coal intervals of the Allegheny Formation.
Rozelle, P. L., Feineman, M. D., White, T. S., Crescenzo, N. A., Kump, L. R., Larson, A. R., & Pisupati, S. V. (2021). The Mercer Clay in Pennsylvania as a Polymetallic Mineral Resource: Review and Update. Mining, Metallurgy and Exploration. https://doi.org/10.1007/s42461-021-00452-5
Watts, A.S., Schurecht, H.G., Swartz, C.K., and Hall, G.M., 1922. The fire clays of Maryland. Maryland Geological Survey, Volume 11, p. 291-480.
Maryland Geological Survey, October 2022
Contact information
Maryland Geological Survey
Richard A. Ortt, Jr., Director
David K. Brezinski (410) 554-5526
david.brezinski@maryland.gov