Colusite with Quartz, Pyrite

specimen number:
2102419

location:
East Colusa Mine, Butte, Montana, USA

description:
Metallic micro crystals of colusite across a crystallized quartz with minor pyrite. In good condition.

The East Colusa mine, located on the east side of the Butte Hill in the historic Butte District of Silver Bow County, Montana, was a highly productive underground base-metal operation. Geologically, the mine exploited the rich copper-sulfide vein systems hosted within the Late Cretaceous-aged Butte Granite, a massive quartz monzonite pluton that forms part of the Boulder batholith. Hydrothermal mineralization occurred along major structural fractures, depositing high-grade copper ores characterized by massive chalcocite, enargite, and covellite, as well as the rare copper-vanadium-arsenic sulfide mineral colusite, which derived its name from this specific vein complex. The original Colusa claim was acquired in the late 1870s and developed heavily by the Lewisohn brothers under the Montana Copper Company, which later became the Boston and Montana Consolidated Copper and Silver Mining Company in 1887. The East Colusa shaft yielded immense mineral wealth throughout the late nineteenth century, and it continued continuous operations until it was consolidated into the expanding Amalgamated Copper Company, which later reverted to the Anaconda Copper Mining Company, around 1901. Deep-level extraction eventually ceased as the district transitioned toward centralized mining operations, and the historic mine site was ultimately consumed by the widening excavations of the open-pit Berkeley Pit during the mid-twentieth century.

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