Colusite

specimen number:
2262282

location:
Colusa Mine, Butte, Montana, USA

description:
Rich metallic masses across matrix. From the type locality. The specimen comes with a previous collection data card as shown at the end of the video. This gives an acquisition date in 1960.

The Colusa mine, located on the legendary "Richest Hill on Earth" in Butte, Silverton County, Montana, was a major underground copper and silver producer that helped establish the district as a global mining powerhouse. Geologically, the deposit is hosted within the late Cretaceous-age Butte Quartz Monzonite pluton, which was subjected to intense structural fracturing and subsequent hydrothermal alteration. This geologic activity produced a vast network of closely spaced, high-grade polymetallic veins and massive replacement bodies composed of copper-rich sulfides like chalcocite, enargite, and bornite, along with substantial quantities of native silver and secondary copper minerals. Historically, the outcrop was located in 1875 by prospectors initially looking for silver, but its massive copper potential was unlocked when the property was split into the North Colusa and South Colusa claims, drawing heavy investment from early mining tycoons including William Andrews Clark. Large-scale industrial shaft sinking began in the early 1880s, and the mine operated heavily under the Anaconda Copper Mining Company through the late nineteenth and early twentieth centuries, serving as a critical source of high-grade ore during the peak of underground operations. Deep commercial extraction at the Colusa shaft continued until declining reserves, shifting corporate priorities, and the transition toward massive open-pit mining at the nearby Berkeley Pit led to the permanent closure of the underground facility in the 1940s.

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