Mapping Volcanogenic Mineralization: Study of the Westminster Terrane of the Mid-Atlantic Piedmont (2021-2023)
The Maryland Geological Survey (MGS) is working in cooperation with the U.S. Geological Survey (USGS) on an Earth Mapping Resources Initiative (EMRI) study on mineralization in the Westminster terrane, which is part of Maryland’s western Piedmont physiographic province. Historically known as the “Linganore District”, this area extends from New Market to Westminster in eastern Frederick County and western Carroll County and was a source of copper during the American Revolution and produced copper, zinc, and lead intermittently through the 1800’s and early 1900’s (Heyl and Pearre, 1965). Critical minerals known to occur in the Linganore district include zinc (Zn), barite (Ba), cobalt (Co), and manganese (Mn).
MGS revised bedrock contacts and nomenclature on two 7.5-minute geologic maps central to this region in order to better understand the distribution and origin of mineralized zones. Mineralized zones throughout the Linganore District were mapped and sampled for geochemical analysis of the soil and underlying bedrock. Mineralization is concentrated along the boundaries between the metavolcanic units and marble bedrock (Kavage Adams and Brezinski, 2023).
MGS mapped the distribution of these geologic contacts with traditional geologic field mapping. Sampling of known and potential mineralized areas was conducted through grab sampling, soil pits, and drilling, informed by USGS aeromagnetic surveys as well as more detailed MGS magnetic surveys by drone. These samples were analyzed by the USGS for their trace and major element content and examined petrographically by MGS geologists for mineral content.
Sample results showed that elevated levels of manganese and sometimes copper are concentrated in soils and bedrock near contacts between metavolcanic rocks and marble. These regions are spatially heterogeneous, and mineralization does not occur at every contact. Pink, variegated marble is found at the mineralized contacts between marble and metamorphosed basalt and commonly weathers to dark brown, highly manganiferous soil. Drilling and further field observations during this project indicate that mineralization also occurs at yellow-banded, sulfur rich intervals in marble that are interpreted to be submarine deposition of volcanic gas flows in a carbonate basin.
Geochemistry Samples
Trace and major element content for 102 soil and rock samples from the Westminster Terrane is available here:
Westminster Samples (zip, 69 KB - includes .csv & .shp) Mining Districts
Shapefile of the revised Linganore and Westminster mining districts is available here:
Mineralized Districts (zip, 125 KB - includes .shp)
PDF Maps & GIS Data
The following table includes Maryland quadrangles that have been mapped as part of Earth MRI. Any available maps and GIS data for each quadrangle is available for download under the Formats column.
Heyl, A.V., and Pearre, N.C., 1965. Copper, Zinc, Lead, Iron, Cobalt, and Barite Deposits in the Piedmont Upland of Maryland. Maryland Geological Survey, Bulletin 28, 72 p.
Kavage Adams, R. and Brezinski, D.K., 2023, Highly manganiferous residual soils overlying interlayered carbonate and volcanic bedrock in Maryland’s Western Piedmont,Geological Society of America Abstracts with Programs. Vol. 55, No. 2, abstract 23-6.
Contact Information
Christopher P. Williams, Program Chief, Coastal and Environmental
(410) 554-5559 | christopherp.williams@maryland.gov
Rebecca Kavage Adams, Geologist
(410) 554-5553 | rebecca.adams@maryland.gov