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San Cristóbal mine (Bolivia)
The San Cristobal mine in Lipez, Potosí Department, Bolivia is an open-pit silver, lead and zinc mine near the town of San Cristóbal, Potosí. The mine, operated by Sumitomo Corporation, produces approximately 1,300 metric tons of zinc-silver concentrate and 300 tons of lead-silver concentrate per day, , by processing 40,000 to 50,000 tons of rock. It is one of Bolivia's largest mining facilities and, according to Sumitomo, the world’s sixth-largest producer of zinc and third-largest producer of silver.〔 It is located in southwestern Bolivia and hosts approximately 450 million ounces of silver and 8 billion pounds of zinc and 3 billion pounds of lead contained in 231 million tonnes of open-pittable proven and probable reserves. As the ore body is open both at depth and laterally, reserve expansion potential is considered excellent.〔Apex Silver Mines Limited website on the San Cristobal project - ()〕 The mine has been in various stages of development since the early 1980s but only recently came into full operation.
==Geology==
Silver was discovered in what would become the Hedionda mine, during the 17th century, by A.A. Barba, a Spanish priest. Carbon dioxide poisoning limited the exploitation of the silver though. Compania Minera de San Cristobal operated the Toldos mine from 1870 to 1921. The Polish engineer J. Jackowski operated the Hedionda mine from 1896 to 1901, and from 1927 to 1936, using a groove in the floor to channel carbon dioxide out of the mine. P. Zubrzycki operated the mine from 1963, before transferring rights to the Lipez Mining Co. in 1966. The Cooperativa Minera Litoral started operating the Animas mine in 1965.〔Jacobson, H.S., Murillo, C., Ruiz, L., Tapia, O., Zapata, H., Alarcon, H., Delgadillo, E., and Velasco, C., 1969, Geology and Mineral Deposits of the San Cristobal District, Villa Martin Province, Potosi, Bolivia, USGS Bulletin 1273, Washington: US Government Printing Office〕
The geologic history from Tertiary and Quaternary periods includes 1) deposition and folding of the Potoco Formation, 2) erosion of this formation, 3) deposition of the Quehua Formation, 4) intrusion of the andesite porphyry stocks, 5) hydrothermal circulation altering rocks and depositing oxide-siderite-barite veins containing silver, 6) intrusion of dacite porphyry stocks, uplift of the Potoco and Quehua Formations, and deposition of dacite porphyry lava flows, 7) intrusion of breccia pipes and faulting, 8) deposition of dacite tuff, 9) hydrothermal circulation altering rocks and depositing galena, sphalerite, pyrite, native silver and barite, 10) erosion.〔
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