Prehnite with Calcite, Copper

specimen number:
2062136

location:
Silver Pit, Copper Falls, Keweenaw Co., Michigan, USA

description:
Attractive sparkling green slightly translucent botryoidal crystallized prehnite across the front of matrix with minor calcite and tiny crystals of native copper. Good example for the species from this area, in good condition. Collected September 5, 1999.

The Silver Pit was a specific exploration and mining site within the larger Copper Falls Mine property in Keweenaw County, Michigan. Geologically, it was situated on the Owl Creek vein, a fissure deposit that cut perpendicularly through the regional volcanic strata. While the primary target of the Copper Falls Mine was native copper, the Silver Pit was specifically noted for its unusual concentration of native silver, which occurred as wires, plates, and small nuggets within a calcite and chlorite matrix. These hydrothermal veins formed during the Mesoproterozoic Era as mineral-rich fluids filled fractures in the Portage Lake Volcanics. Historically, the Copper Falls Mining Company was organized in 1845, making it one of the earliest operations in the district. The Silver Pit area saw its most focused activity during the mid-19th century as miners chased high-value silver pockets, though the broader mine continued intermittent operations until it finally closed in 1893. Today, the site is a classic locality for collectors, celebrated for producing some of the finest native silver specimens ever found in the Lake Superior copper district.

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