Digenite with Pyrite

specimen number:
2282020

location:
Butte, Silver Bow Co., Montana, USA

description:
A rich metallic masses of digenite with minor pyrite. The specimen comes with an old label from Denver dealer Robert Roots.

The Butte mining district, located in Silver Bow County, Montana, is a historically monumental copper mining complex often referred to as the Richest Hill on Earth. Geologically, the deposit is a premier example of a giant porphyry copper-molybdenum system overprinted by massive, structurally controlled lode veins, all hosted within the Late Cretaceous Boulder Batholith. Intense hydrothermal alteration filled deep fissure veins with dense clusters of rich copper sulfide ores, including chalcocite, bornite, enargite, and covellite. Placer gold mining began in 1864, quickly transitioning to silver underground mining in the 1870s, and exploded into massive industrial copper extraction by the 1880s as the electrical age dawned. Underground mining via hundreds of miles of shafts dominated until 1955, when operations shifted to the vast Berkeley Pit open-pit mine, which operated until 1982. Industrial mining continues in the district today at the active Continental open pit, marking over 160 years of nearly continuous metal production.

Digenite is a copper sulfide mineral that crystallizes in the trigonal system, though it often forms pseudo-cubic crystals at elevated temperatures. Geologically, it occurs as a primary or secondary mineral in the enrichment zones of copper sulfide deposits, frequently associated with related minerals like chalcocite, bornite, and djurleite. The mineral typically displays a dark blue to black color, often tarnishing to a distinctive dull metallic blue, and possesses a subconchoidal fracture and a metallic luster. At world-class deposits like Butte, digenite forms major components of the high-grade copper ores, where it typically manifests as dense massive aggregates intergrown with other sulfides rather than distinct individual crystals.

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