Malachite

specimen number:
2062317

location:
Minnesota Mine, Ontonagon Co., Michigan, USA

description:
Green crystallized malachite quite rich across the top of matrix. Unusual locality example for the species. In good condition.

The Minnesota mine (often spelled Minesota), located near National Park in Ontonagon County, Michigan, was one of the most prominent early copper producers in the Lake Superior copper district. Geologically, the deposit is situated along the Keweenawan Peninsula's volcanic and sedimentary sequence, where low-temperature hydrothermal fluids precipitated exceptionally pure native copper within the amygdaloidal flow tops and interbedded conglomerates, famously yielding massive, multi-ton chunks of pure metal. The property was first explored in 1847 after prospectors discovered prehistoric mining pits, and formal operations began under the Minesota Mining Company in 1848. The mine experienced its peak production during the 1850s, paying out immense dividends, but as the massive copper sheets became scarcer and deeper to mine, production began a steady decline. Formal commercial mining by the original company ceased in 1870, though tribute miners and secondary companies intermittently worked the shafts and upper levels until the early twentieth century.

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