Cornwall Mines

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

Information leading to the delineation of this focus area

Basis for focus area Former mines in the vicinity of Cornwall, Pennsylvania. Favorable geology and past production.
Identified resources Historical production of cobalt, copper, gold, and silver.
Production Cornwall mine (intermittent from 1732-1973): produced 106,000,000 tons of ore containing about 40% Fe, 0.3% Cu, 1.3% S, 0.001 oz/t Au, and pyrite with 1.4% Co; Grace mine (1958-1977): produced about 45 million tons of ore with 43.7% Fe, 0.06% Cu, and 0.02% Co.
Status Past mining. The Cornwall mine closed in 1973 and is currently inactive.
Estimated resources Cornwall mine (1973 estimate): In-situ reserves of 22,675,000 mt ore 0.06% Cu and 0.056% Co.
Geologic maps Berg and others (1980), scale 1:250,000; Lapham and Gray (1973), scale 1:24,000.
Geophysical data Inadequate; aeromagnetic and aeroradiometric data: Rank 4 aeromagnetic data, Rank 5 aeroradiometric data. See Bromery and Griscom (1967).
Favorable rocks and structures Skarn-type magnetite deposits replace limestone, dolomite, and marble adjacent to the York Haven diabase sheet.
Deposits Cornwall mine (MRDS dep_id: 10299283; USMIN Site_ID: PA00001), Grace mine (MRDS dep_id: 10067406).
Evidence from mineral occurrences MRDS; USMIN.
Geochemical evidence Locations and analyses of selected early Mesozoic copper occurrences in Pennsylvania (Smith and others, 1988); geochemical data (Rose, 1972).
Geophysical evidence Previous aeromagnetic studies from the 1940s and 1950s identified several magnetic anomalies throughout the Mesozoic basins, including the Grace mine deposit which had no surface exposure. The quality of existing data are low.
Evidence from other sources Unknown.
Comments Depositional temperatures are estimated at 400-500 degrees C, based on phase stability. Ore fluid speculated to be a sedimentary brine heated locally in sediments along the diabase contact. Metals are believed to have been acquired from both the diabase and Triassic sediments (Rose and others, 1985).
Cover thickness and description Open-pit mining.
Authors Nora K. Foley, Stephen G. Shank, Kristen Hand.
New data needs Geophysical data, geologic mapping, and geochemical analyses.
Geologic mapping and modeling needs Detailed mapping 1:24,000 scale.
Geophysical survey and modeling needs High resolution aeromagnetic and aeroradiometric data to delineate deposit and for framework geology. Aeromagnetic data may be especially sensitive to iron.
Digital elevation data needs Lidar complete.