Copper

specimen number:
2262293

location:
Houghton Co., Michigan, USA

description:
Large crystallized grouping of native copper with little attached matrix. In good condition. The specimen comes with a previous collection data card with an acquisition date in 1967.

The Keweenaw Peninsula mining district, situated in the Upper Peninsula of Michigan, was a world-class underground and surface copper-producing region internationally famous for its massive deposits of pure native copper. Geologically, the deposits are hosted within the Proterozoic-age Keweenawan Rift system, a massive tectonic fracture zone filled with thick sequences of basaltic lava flows interbedded with conglomerate sandstones. Hot, deep-seated hydrothermal fluids migrated upward through these porous volcanic and sedimentary layers, precipitating elemental native copper along with silver within the amygdaloidal flow tops, structural fractures, and conglomerate matrices, completely lacking the sulfur compounds typical of most global copper ores. Historically, indigenous peoples mined the surface outcrops for thousands of years before the modern American copper boom was sparked by Douglas Houghton's geological report in 1841, leading to a massive mining rush in 1843. Large-scale industrial underground operations flourished under major corporate syndicates like the Calumet and Hecla Mining Company, sinking some of the world's deepest vertical shafts to extract millions of tons of premium copper from lines of ore that peaked during the late nineteenth and early twentieth centuries. Commercial extraction steadily declined following World War I due to high production costs at extreme depths and competition from western open-pit operations, leading to the systematic closure of major mines throughout the mid-twentieth century and culminating in the permanent cessation of all primary corporate mining operations on the peninsula by late 1968.

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