Chalcocite

specimen number:
2133291

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

description:
Good thumbnail from this closed locality, an example of botryoidal crystallized chalcopyrite. These are iridescent. Often referred to as blister copper. In very good condition.

The Flambeau mine, situated just south of Ladysmith within Rusk County, Wisconsin, United States, is a famous and historically significant open-pit base metal operation noted for producing highly unusual, lustrous, and distinct specimens of chalcopyrite exhibiting a rare botryoidal, or rounded grape-like, growth habit. Geologically, this deposit was a supergene-enriched volcanic-associated massive sulfide (VMS) ore body hosted within highly deformed, Paleoproterozoic-age metavolcanic rocks of the Penokean volcanic belt. Long-term weathering during the Mesozoic Era deeply oxidized the upper portions of the copper-rich iron sulfide body, creating a highly enriched secondary zone where descending copper-bearing groundwater solutions slowly precipitated secondary minerals, including beautiful crusts of botryoidal chalcopyrite, bornite, and chalcocite inside open solution cavities and fractures. Historically, the deposit was discovered in November 1968 by the Kennecott Copper Corporation, but extensive environmental permitting delays meant that active open-pit quarrying and extraction did not commence until July 1993 under the subsidiary Flambeau Mining Company. The highly efficient, small-scale operation ran continuously for four years, extracting approximately 1.9 million tons of high-grade copper and gold ore before economic reserves were completely exhausted, leading to the permanent cessation of mining in March 1997. Following closure, a comprehensive reclamation project backfilled the open pit with original waste rock and lime, completely restoring the surface topography to natural contours by 1998.

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