Colusite

specimen number:
2262064

location:
Colusa Mine, Butte, Montana, USA

description:
Metallic crystalline and massive colusite on matrix.

The Colusa Mine, located in the historic Butte District of Silver Bow County, Montana, is a significant hydrothermal vein deposit hosted within the quartz monzonite of the Boulder Batholith. Geologically, it sits within the central copper-rich zone of the district, where intense fracturing allowed for the deposition of massive sulfide veins during the Late Cretaceous to Early Paleogene. The mine is the type locality for colusite, a rare copper-vanadium-tin-germanium sulfide that typically occurs as bronze-colored to gray metallic grains or small tetrahedral crystals within a matrix of massive pyrite and enargite. Historically, mining and quarrying at the Colusa began in the early 1880s, shortly after the discovery of the district's rich silver and copper ores. It became a major producer under the management of the Boston and Montana Consolidated Copper and Silver Mining Company before eventually being absorbed into the larger operations of the Anaconda Copper Mining Company. While underground production at the Colusa shaft continued through the early 20th century, operations eventually shifted toward larger-scale consolidated mining efforts in the Butte area as the district evolved. As of 2026, the Colusa Mine remains a foundational locality in mineralogical literature for its unique complex sulfides and its role in the early development of Montana's mining heritage.

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