Aurichalcite with Hemimorphite

specimen number:
2102351

location:
79 Mine, Gila Co., Arizona, USA

description:
Attractive blue acicular crystals of aurichalcite across the top of matrix with many small micro crystals of hemimorphite. In good condition.

The 79 mine, located on the southern slopes of the Tortilla Mountains near Hayden within Gila County, Arizona, United States, is a historically significant underground silver-lead-zinc-copper operation celebrated internationally for producing some of the finest oxidized secondary minerals in North America. Geologically, this complex structural deposit is hosted within deeply dipping, fault-bounded Paleozoic-age sedimentary rocks, primarily the Pennsylvanian-age Horquilla Limestone and Mississippian-age Escabrosa Limestone, which were extensively fractured and intruded by Late Cretaceous-age quartz diorite and porphyry dikes. High-temperature hydrothermal fluids migrated through these shattered contact zones, replacing the limestone beds with massive primary sulfides that later underwent intensive, multi-stage supergene oxidation, carving out vast dissolution cavities filled with world-class, bright orange to yellow-orange crystals of wulfenite, bright blue aurichalcite, smithsonite, and abundant sprays of colorless to white hemimorphite crystals. Historically, the initial outcroppings were discovered in 1879, giving the mine its distinctive numerical name, though systematic commercial development did not begin until 1919 when the Seventy-Nine Mining Company initiated formal shaft-sinking and tunnel extraction. The facility produced ore continuously through both world wars under various corporate operators, including the Callahan Zinc-Lead Company, utilizing a 450-foot main shaft and miles of underground drifts until declining base-metal prices and the exhaustion of easily accessible high-grade pockets forced the permanent cessation of regular corporate mining operations in 1951.

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