Copper (CU-0018)

specimen number:
9273166

location:
Phoenix Mine, Keweenaw Co., Michigan, USA

description:

A choice branching crystallized grouping of native copper. In excellent condition, the crystals are quite sharply formed in the largest measuring to 2.5 cm in size.

The Phoenix mine, situated in Keweenaw County, Michigan, was one of the earliest underground native copper operations developed in the Lake Superior district. Geologically, the deposit is centered on a series of nearly vertical fissure veins, most notably the Phoenix vein, which cut across the gently dipping basaltic lava flows of the Mesoproterozoic Portage Lake Volcanics. Hydrothermal fluids traveling along these structural fractures deposited elemental native copper and native silver within a gangue matrix of calcite, quartz, and prehnite, occasionally yielding massive copper boulders weighing several tons. Organized mining at the property began in 1845 under the Lake Superior Copper Company, making it one of the first commercial attempts to exploit the regional copper veins. The property underwent numerous corporate reorganizations and closures over the decades, operating under the Phoenix Copper Company through several distinct phases of underground development and stamp mill production until final commercial extraction ceased entirely in 1917 due to ore depletion and high operational costs.

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