Calcite with K-Feldspar

specimen number:
2062281

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

description:
A colorless gemmy scalenohedral crystal of calcite 1.2 cm in height on matrix with black crystals of adularia. In great condition. Neat combination piece.

The Mass mine, located adjacent to Mass City in Ontonagon County, Michigan, was a notable underground native copper operation situated within the Western Upper Peninsula mining district. Geologically, the deposit is hosted within the Keweenawan Portage Lake Volcanics, a thick sequence of Precambrian basaltic lava flows interbedded with sandstones and conglomerates. Hydrothermal fluids circulating through this volcanic pile deposited elemental copper and silver, along with secondary silicates like datolite, inside the porous, vesicular flow tops known locally as the Evergreen, Butler, Mass, and Knowlton lodes. The Mass Mining Company was first organized in 1856 to exploit these strata, working underground through several shallow shafts until initial operations ceased in 1888. The property was subsequently revived and merged in 1899 to form the Mass Consolidated Mining Company, which expanded and modernized the underground infrastructure, producing millions of pounds of copper before permanently closing the operation in the 1920s.

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