Bournonite with Sphalerite, Jamesonite

specimen number:
2262346

location:
Casapalca, Lima, Peru

description:
Lustrous twinned crystals of bournonite to 0.7 cm in size on matrix with fibrous jamesonite and crystals of sphalerite. In good condition.

The Casapalca mining district, situated at high altitude in the Huarochiri Province of the Lima Department, Peru, is a historic polymetallic mining center. Geologically, the deposit is hosted within the Tertiary Casapalca Formation, which consists of a thick sequence of continental red beds, sandstones, and volcaniclastic sediments cut by later subvolcanic intrusions. The ore bodies occur as steep hydrothermal veins and replacement mantos rich in silver, lead, zinc, and copper sulfides, dominated by minerals like galena, sphalerite, chalcopyrite, and tetrahedrite-tennantite that precipitated during late-stage Andean magmatism. Organized corporate mining began in 1889 with the founding of the Backus and Johnston Company, which established a local smelter and extensive underground galleries to exploit the rich silver-lead veins. The operations were acquired by the Cerro de Pasco Corporation in the 1920s, which significantly expanded the underground infrastructure, followed by state ownership under Minero Peru in the 1970s and eventual privatization back to domestic Peruvian mining companies in the late twentieth century, with production continuing steadily into the twenty-first century.

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