State Line district/BMC (Baltimore Mafic Complex)

Region East, Northeast
Mineral systems
Deposit types
Critical minerals
Other minerals

Information leading to the delineation of this focus area

Basis for focus area Metamorphosed ultramafic rocks mapped as the Baltimore Mafic Complex (Drake and others, 1989) and the Liberty Complex (Linder and others, 1992). Shown as "PZu;0" in Pennsylvania and "um;7" in Maryland in Horton and others (2017). Occurs as numerous bodies from Pennsylvania to Maryland (Thayer and Lipin, 1979; Goff and others, 2000; Van Gosen, 2006; Mosier and others, 2012). Suggest selecting the "PZu" and "um" polygons in Pennsylvania and Maryland. Or use the generalized polygon of the "Central Appalachian province" of Thayer and Lipin (1979), but the selected (buffered?) polygons will be more accurate.
Identified resources Identified resources and historical mining of chromite and related commodities.
Production Unknown.
Status Past mining.
Estimated resources Between 250,000 and 300,000 tons chromite (Thayer and Lipin, 1979).
Geologic maps Blackmer (2005), scale 1:50,000; Higgins and Conant (1990), scale 1:62,500; Southwick and Owens (1968), scale 1:62,500; Bosbyshell (2005), scale 1:24,000; Plank and others (2000), scale 1:24,000; Pearre and Heyl (1960), scale 1:125.000.
Geophysical data Inadequate Rank 4 aeromagnetic and Rank 5 aeroradiometric coverage.
Favorable rocks and structures Ultramafic rocks.
Deposits Wood mine (MRDS dep_id: 10083862), Reed mine (MRDS dep_id: 10267083).
Evidence from mineral occurrences MRDS; Goff and others 2000); Pearre and Heyl (1960).
Geochemical evidence Known elevated Cr concentrations.
Geophysical evidence Gravity anomalies associated with ultramafic deposits.
Evidence from other sources >15,000 tons of chromite extracted from stream placers in Maryland (Pearre and Heyl, 1960).
Comments Historical deposits in the I-95 and US 1 urban corridor. Red Pit yielded 90% of the lode ore (Thayer and Lipin, 1979).
Cover thickness and description Variable cover and saprolite, some urban areas.
Authors Gregory J. Walsh, Bernard E. Hubbard, William Junkin.
New data needs Chemistry of ultramafic rocks, modern mapping.
Geologic mapping and modeling needs Some 1:24,000 mapping exists, but incomplete.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric coverage needed. Aeromagnetic data expected to image mafic rocks and associated structures, radiometric data can help with geologic mapping in vegetated terrane.
Digital elevation data needs Lidar complete except for Baltimore County portion of focus area.