Chalcocite

specimen number:
8311505

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

description:
Choice cluster of attractive iridescent chalcocite crystals from this famous locality. Minimal damage present, this still in good condition.

The Flambeau mine, situated just south of Ladysmith in Rusk County, Wisconsin, United States, was a highly concentrated, short-lived open-pit copper-gold operation noted for its remarkably rapid development, extraction, and environmental reclamation cycle. Geologically, this deposit was a classic Paleoproterozoic-age volcanogenic massive sulfide (VMS) system hosted within the early Proterozoic Penokean volcanic belt, where hydrothermal fluids on an ancient seafloor deposited a steeply dipping lens of primary chalcopyrite, pyrite, and sphalerite. A subsequent, multi-million-year period of intense subaerial weathering and supergene enrichment altered the upper portion of the orebody, creating an incredibly rich secondary blanket dominated by high-grade chalcocite, bornite, native copper, and gold embedded within a soft kaolinite matrix. Historically, the deposit was discovered in 1968 by the Kennecott Copper Corporation, but extensive regulatory battles and strict environmental permitting delayed actual quarrying and construction for over two decades. The Flambeau Mining Company finally commenced active open-pit ore extraction in May 1993, operating around the clock to systematically excavate the compact, high-grade zone until the commercial orebody was completely exhausted in March 1997. Following the cessation of mining, an immediate and rigorous backfilling operation began, utilizing the original stockpiled country rock and imported limestone to completely fill the pit by late 1997, followed by comprehensive surface contouring and revegetation to restore the site into a public nature park with wetlands and woodland trails. Through 2026, the fully reclaimed property remains under strict, long-term environmental monitoring for groundwater quality, serving as a prominent regulatory and industrial case study for modern, high-grade VMS extraction and successful surface reclamation.

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