Copper

specimen number:
8311550

location:
Osceola Mine, Houghton Co., Michigan, USA

description:

Fine sharp loose mostly single crystal of native copper. Sharply formed and in great condition, this is a superb thumbnail specimen.

The Osceola mine, located just south of Calumet in Houghton County within the historic Keweenaw Peninsula copper district of Michigan, United States, was a massive and long-lived underground native copper operation. Geologically, this deposit is hosted within the Mesoproterozoic-age Portage Lake Volcanics of the Midcontinent Rift System, where hot, metal-bearing hydrothermal fluids mineralized the highly porous and vesicular amygdaloidal top of the Osceola basalt lava flow, precipitating pure native copper and native silver alongside secondary epidote, calcite, quartz, and chlorite. Historically, the Osceola Mining Company was organized in 1873 by Edward J. Hulbert to exploit what he initially believed was a continuation of the nearby Calumet conglomerate lode, but miners quickly discovered and shifted focus to the rich, underlying Osceola amygdaloid lode instead. The operation expanded rapidly into a multi-shaft complex, came under the control of the prominent Calumet and Hecla Mining Company in 1909, and worked continuously until a severe post-World War I copper market collapse forced a temporary shutdown in 1921. Mining resumed on a modified scale and continued through the mid-twentieth century, including vital production spurts during World War II, until escalating deep-mining costs, declining ore grades, and a major regional labor strike finally forced a permanent cessation of all underground operations in 1968.

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