Cuprite

specimen number:
8282250

location:
Milpillas mine, Santa Cruz, Sonora, Mexico

description:

A superb example for the species, especially from this Mexican locality, with lustrous deep red crystals measuring to 1.7 cm in size across the front of this matrix. The specimen is in super condition.

The Milpillas mine, situated near Santa Cruz in the northern portion of Sonora, Mexico, was an advanced underground copper mining operation world-famous for producing some of the finest secondary copper mineral specimens of the modern era. Geologically, the deposit is a porphyry copper system structurally related to the Laramide-age magmatic arc, but it is highly unusual because the entire ore body is completely concealed beneath hundreds of meters of post-mineral gravels within a fault-bounded graben structure. Oxidizing groundwater circulating through this buried deposit created an exceptionally rich, deep supergene enrichment zone, where primary sulfides were transformed into high-grade chalcocite blankets and spectacular pockets of intense blue azurite, deep green malachite, and bright red cuprite crystals. Historically, the hidden deposit was discovered through deep exploratory drilling in 1998, and formal underground development began in 2004 under the management of Minera Maria, a subsidiary of Industrias Penoles. Commercial production via a deep vertical shaft and modern mechanization commenced in 2006, feeding an on-site leaching and solvent extraction-electrowinning plant to produce high-purity copper cathodes. Industrial underground extraction faced operational downscaling and a transition toward processing remaining surface stockpiles around 2020 as the primary economic underground oxide and supergene ore reserves neared depletion, with localized exploration and processing activities continuing into 2026.

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