Copper

specimen number:
8311559

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

description:

Fine grouping of elongated sharply formed native copper crystals, the largest 2.2 cm in length. In great condition. A very fine miniature.

The Mass mine, situated near Mass City in Ontonagon County within the southwestern copper district of the Keweenaw Peninsula, Michigan, United States, was a highly prominent and productive underground native copper operation famous for extracting enormous solid masses of pure metal. Geologically, this stratiform deposit is hosted within the Mesoproterozoic-age Portage Lake Volcanics of the Midcontinent Rift System, where extensive hydrothermal fluids mineralized a series of stacked, porous, and brecciated amygdaloidal basalt lava flows, including the Evergreen, Ogima, Butler, and Mass lodes, precipitating pure native copper and native silver alongside secondary minerals like epidote, quartz, calcite, and prehnite. Historically, industrial operations began when the Mass Mining Company was formally organized in 1850, with miners sinking early shafts to exploit the rich outcropping lodes until economic pressures forced a temporary suspension in 1860, followed by decades of intermittent leasing to independent tributor miners. A major industrial renaissance occurred in 1899 when the property was consolidated with the adjacent Ridge, Ogima, and Hazard mines to form the Mass Consolidated Mining Company, which constructed a modern stamp mill, sunk three major new shafts named A, B, and C, and operated continuously until post-World War I market stagnation and escalating production costs forced a permanent cessation of all underground mining in 1919.

Questions about this specimen?
Send an email or call us: 314-341-1811.