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May-June 2011

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News from the Keweenaw: Part 4—Recent Mineral Finds in Michigan's Copper Country (Seventeenth in a series of articles on the mines and minerals of Michigan's Copper Country)

The Michigan Copper Country, also known as the Lake Superior native copper district, is located on the isolated, rugged, and scenic Keweenaw Peninsula, which juts out into Lake Superior at the western end of Upper Michigan. The now-dormant copper mining industry, which flourished from 1844 through 1976, produced 10,525,922,136 pounds of copper (Rosemeyer 2009b) from fissure veins, amygdaloidal flow tops, and conglomerate beds collectively known as the Portage Lake Volcanics (PLV). The lodes were all deposited during the same general period of mineralization and are contemporaneous even though the hosting fractures, lava flows, and conglomerate beds are of differing ages.

The Copper Country is host to 135 mineral species, plus another 12 that have been reported but not verified (Robinson 2004). Present collecting is concentrated on less than a dozen mineral species that can still be found in limited quantities on the mine dumps. These minerals include copper, silver, porcelaneous datolite nodules, prehnite, quartz, calcite, epidote, analcime, fluorapophyllite, and pumpellyite (variety chlorastrolite). Even though mining is now only a memory, each summer the Keweenaw Peninsula still attracts hundreds of mineral collectors who scour the mine dumps for mineral specimens.

Tom Rosemeyer, a native of Upper Michigan, is a graduate of Michigan Technological University in Houghton. He now spends summers in the San Juan Mountains and the Copper Country researching and writing articles on the mineralogy of the districts.

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