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November-December 2017

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Collector's Note: A Glacial Treasure Unearthed from a Pleistocene Grave in Michigan's Keweenaw Peninsula

This article details the discovery, recovery, and preservation of a large boulder of rich copper-bearing Calumet and Hecla Conglomerate float that was discovered in August 2013 by Jay and Chad Just near Calumet, Michigan. The boulder was ripped loose from the conglomerate lode outcrop by glacial action and exhibits the extreme richness of the ore mined early on by the Calumet and Hecla Mining Company. The Calumet and Hecla Conglomerate is one of the twenty-odd sedimentary beds intercalated in the Portage Lake Volcanics of Middle Proterozoic age. The conglomerate is made up of a variety of well-rounded felsite, granophyre, and quartz-feldspar porphyry pebbles, suggesting a diverse terrane source. The copper-bearing conglomerate lode was discovered by Edwin J. Hulbert in 1864 and was developed into a profitable mining operation. The orebody produced 4.2 billion pounds of copper from 1865 to 1976 and accounted for 28.9 percent of the copper produced in the district. The Calumet and Hecla Conglomerate lode was and still is the largest single native copper deposit mined in the world and made many early Boston stockholders millionaires many times over. 


Tom Rosemeyer, a native of Upper Michigan, is a graduate of Michigan Technological University in Houghton. He now spends a good part of the year in the Copper Country collecting and writing articles about the district.

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