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Kori Kollo, La Barca, La Joya |
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Bolivia |
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Au Ag
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The La Joya district deposits are located in the eastern part of the Andean Altiplano, some 40 km north-west of the city of Oruro in Bolivia. It contains four main Au-Ag-(Cu-Pb-Zn) deposits, namely Kori Kollo, Llallagua, La Barca and La Joya.
The deposits of the district are hosted by 15.7 to 14 Ma dacite porphyry volcanic domes, which unconformably overlie and cut the basement Silurian Catavi Formation clastic sedimentary sequence. The domes are in turn partially overlain by Neogene - Quaternary lacustrine and alluvial sediments. The domes define a ring pattern spatially related to the younger Lago Soledad caldera.
The Au-Ag rich polymetallic ores in the La Joya district were emplaced along NE trending structures, generally dipping between 60° NW and vertical. Mineralisation is present principally in fractures and veinlets, but also in breccia zones, stockworks and as disseminations. The sulphide ores include pyrite, native gold, tetrahedrite, zinkenite, arsenopyrite, chalcopyrite, galena, chalcocite, sphalerite, realgar and marcasite. The oxides include limonite, alunite, goethite, jarosite and silica. In the sulphide zone the gold occurs as 5 to 14 micron grains between stibnite and tetrahedrite crystals with disseminated pyrite. In the oxide ore gold is as 2 to 15 micron grains associated with quartz, pyrite, limonite and jarosite. In all deposits the precious metals overlie a zone of base metals.
At Kori Kollo relatively high grade ore occurs in structurally controlled breccias, while veinlets are found in medium grained dacite. Both sulphide and oxide ores are present at Kori Kollo, with a resource of 10.10 Mt @ 1.61 G/t Au, 24.7 g/t Ag in the oxide cap, and 53 Mt @ 2.32 g/t Au, 14.5 g/t Ag in the sulphide zone.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1993.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
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Selected References:
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Columba C. M, Cunningham C G 1993 - Geologic model for the mineral deposits of the La Joya district, Oruro, Boliva: in Econ. Geol. v88 pp 701-708
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