Copper

specimen number:
2062274

location:
Keweenaw Peninsula, Michigan, USA

description:
A superb branching crystallized grouping of native copper. The most prominent crystals measuring to almost 2.0 cm in size and very sharply formed. In great condition all around.

Copper mining in the Keweenaw Peninsula region of Michigan represents one of the earliest and most significant metal mining booms in American history, characterized by the extraction of unprecedented volumes of elemental native copper and copper sulfides. Geologically, the district is situated within the Midcontinent Rift System, where Precambrian volcanic basalt flows and interbedded felsic conglomerates of the Portage Lake Volcanics were tilted into a major basin structure, alongside overlying sedimentary rocks like the Nonesuch Shale. Hydrothermal fluids migrated upward through these strata, precipitating native copper in porous volcanic flow tops and conglomerate beds, while also depositing copper sulfide minerals like chalcocite within the younger shale horizons. While indigenous peoples mined surface exposures for thousands of years, commercial mining began in earnest in 1845 following the opening of the Cliff mine, triggering a massive migration of miners to the region. Giant operations like the Calumet and Hecla Mining Company dominated the global market for decades, utilizing deep underground shafts to pull billions of pounds of copper from the peninsula, with production peaking during the early twentieth century. Declining ore grades and high costs led to a steady contraction of the native copper industry by 1968, but large-scale regional production continued southwest at the White Pine mine in Ontonagon County until low metal prices and high operating costs forced its permanent closure in September 1995.

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