Rich masses of chalcocite throughout a calcite matrix with minor silver. Collected in 1997.The Isle Royale Mine, located in Houghton County, Michigan, began operations around 1852 during the early Keweenaw copper boom, experiencing various periods of inactivity before closing permanently in 1931. Geologically, the mine is situated within the Keweenaw Peninsula's Portage Lake Volcanics series, where native copper deposits occur primarily in amygdaloidal basalt flows and conglomerate beds, most notably the Isle Royale amygdaloid lode.
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