Copper

specimen number:
2062140

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

description:

A very fine example of what is known as a copper skull specimen. This is in terrific condition.

The Centennial Mine, located near Calumet in Houghton County, Michigan, was a major native copper producer situated along the Kearsarge Lode. Geologically, the mine exploited a mineralized basaltic amygdaloid flow within the Portage Lake Volcanics, where native copper filled the gas vesicles and fractures of ancient lava. Historically, the Centennial Mining Company was organized in 1876 to work the northern extension of the rich Kearsarge Lode, but the mine faced early financial struggles and underwent several reorganizations. It eventually became part of the Calumet and Hecla (C and H) Consolidated Copper Company. The mine operated intermittently through the late 19th and early 20th centuries, with significant production periods ending in the 1960s. A final attempt to revive the mine occurred in the 1970s before the pumps were pulled for the last time in 1977.

In the context of Michigan copper mining, a "skull" refers to a unique formation where native copper precipitated around a rounded cobble or boulder within a conglomerate bed. Geologically, as mineral-bearing hydrothermal fluids moved through the porous Calumet and Hecla Conglomerate, copper would plate onto the exterior of rhyolite pebbles. If the internal stone later weathered away or was removed, it left behind a hollow, bowl-shaped shell of solid copper that resembles a primitive helmet or a cranium. These "skulls" are highly prized by collectors as they perfectly preserve the shape of ancient geological sediments in solid metal, providing a tactile record of the mineralizing processes in the Lake Superior district.

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