Chalcopyrite

specimen number:
2102344

location:
French Creek Mines, St. Peters, Pennsylvania, USA

description:
Classic Pennsylvania specimen with large somewhat skeletal crystals of chalcopyrite in a cluster with little matrix. Pyrite is present as well. This is in good condition.

The French Creek mines, also known historically as the Elizabeth and Keim mines, situated near Saint Peters within Warwick Township of Chester County, Pennsylvania, United States, represent a legendary underground iron and copper operation celebrated as one of the premier mineral localities in the eastern United States. Geologically, this classic skarn-type deposit is hosted along the contact zone where an Early Jurassic-age diabase sheet intruded into the calcite-rich Precambrian-age Franklin Marble and associated graphite gneisses. Intense contact metamorphism and hydrothermal activity metasomatically replaced the country rock, depositing massive, high-grade bodies of magnetite ore alongside rich concentrations of chalcopyrite, pyrite, and apophyllite within dense silicate zones. Historically, small-scale surface digging for iron ore began at the site during the late colonial era, but large-scale industrial underground development did not commence until 1845 under the leadership of the E. and G. Brooke Iron Company. The facility expanded into a highly mechanized complex featuring multiple vertical shafts, including the prominent Elizabeth shaft, which reached an ultimate depth of over 1,500 feet to supply iron to the nearby Birdsboro furnaces. The complex operated heavily for over eight decades, providing crucial metals during the American Civil War and World War I, until the depletion of easily accessible high-grade reserves and severe post-war economic downturns forced the permanent cessation of all commercial mining operations in 1928.

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