Datolite on Pumpellyite

specimen number:
2062272

location:
North Lake Mine, Ontonogan Co., Michigan, USA

description:
Colorless crystal groupings of datolite to 0.4 cm in size across a matrix mostly coated with green crystalline pumpellyite. Interesting combination piece, in good condition.

The North Lake mine, located near Greenland in Ontonagon County, Michigan, is a historic underground copper operation situated within the southwestern portion of the Keweenaw Peninsula native copper district. Geologically, the deposit is hosted within the Portage Lake Volcanics, a thick sequence of Precambrian basaltic lava flows where hydrothermal solutions filled gas cavities and fractures to deposit elemental native copper alongside calcite, quartz, and epidote. The North Lake Mining Company was organized in 1908 to explore these horizons, focusing heavily on identifying extensions of the neighboring Adventure and mass copper lodes. Active shaft sinking began around 1909, with the company developing a primary multi-level underground shaft and conducting extensive diamond drilling across the property. Despite significant exploratory effort and the extraction of some mass copper, the mineral grades proved erratic and financially non-viable, leading to a total suspension of operations in 1920 with no further commercial production recorded from the site.

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