Chalcocite

specimen number:
2062276

location:
Flambeau Mine, Rusk Co., Wisconsin, USA

description:

An excellent grouping of iridescent chalcocite crystals without matrix. This is in super condition. From the early to mid 1960s.

The Flambeau mine, located near Ladysmith in Rusk County, Wisconsin, was a short-term, high-grade open-pit copper operation situated within the Pembine-Wausau terrane of the Penokean orogen. Geologically, the deposit is a Paleoproterozoic volcanogenic massive sulfide (VMS) body formed approximately 1.88 billion years ago via hydrothermal vents on an ancient volcanic seafloor. Subsequent tectonic collision tilted the strata to a near-vertical orientation, while extensive periods of supergene weathering leached the upper zone, enriching it into a high-grade layer composed primarily of chalcocite alongside significant gold and silver values. Discovered via an airborne geophysical survey in 1968, the project faced decades of regulatory and environmental scrutiny before the Flambeau Mining Company, a subsidiary of Kennecott Minerals, received permits to begin construction in 1991. Active extraction and rail shipment of ore ran from 1993 until the high-grade reserve was fully depleted in March 1997. Following the cessation of mining, an extensive reclamation program was completed by 1999, which involved backfilling the 220-foot-deep pit with neutralized waste rock and blending it with limestone to prevent acid rock drainage before restoring the surface to native prairie and woodland contours.

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