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Julcani |
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Peru |
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Ag Au Cu W Bi Pb Zn
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Julcani mining district is located near the crest of the central Andean Cordillera, approximately 200 km south-east of Lima, Peru. Mining has been carried out in the district since early Spanish colonial times with the production of free milling gold from near surface quartz-wolframite veins. Since the 1940's the district has produced bismuth, silver, copper, lead, zinc and tungsten. More recently it has been exploited mainly for silver.
The district consists of at least six mineralised centres in a 16 sq. km. late Miocene dacite to rhyolite dome complex deposited on a 3000 m thick Palaeozoic to Mesozoic sequence of clastic sediments. Mineralisation is genetically related to a geologically brief pulse of late Miocene (~10 Ma) calc-alkalic magmatic activity. The Julcani volcanic centre was apparently to have been localised by an anticlinal flexure in Palaeozoic and Mesozoic strata, and perhaps by longitudinal and/or transverse faults. Early eruption of voluminous pyroclastic material was succeeded by the emplacement of interpenetrating volcanic domes of dacitic to rhyodacitic composition (Petersen et al., 1977; Dean et al., 1994).
Hydrothermal alteration and mineralisation took place concurrently with the intrusion of late-stage volcanic domes and dykes. Complex systems of fractures and faults that channeled hydrothermal solutions and localised the various late-stage dykes were produced by repeated pulses of magmatic doming, perhaps aided by renewed movement along regional faults. Mineralisation was emplaced within 0.5 m.y. after the youngest dome formation, but was prior to the emplacement of an anhydrite bearing dacite dyke (Petersen et al., 1977).
The ores comprise Ag-Cu-Pb-W-Bi-Au assemblages occuring as fracture fillings in the domes and underlying tuffs. Mineralisation is almost exclusively confined to fracture fillings, with only subordinate replacement of sheared country rocks within the vein structure. Fracture controlled acid sulphate alteration is characterised by vuggy silica cores with successive quartz-alunite and quartz-kaolinite envelopes overlapped and followed radiating swarms of tourmaline-pyrite-breccia dykelets (Petersen et al., 1977).
Several centres of mineralisation developed at 0.5 to 2 km intervals along reactivated regional structures, following the dacite dyke, possibly related to a concealed intrusive. Ore fluids spread upward and laterally from these centres, producing clearly defined zoning patterns. The central part of the district is characterised by the pyritic gold-tungsten (quartz-pyrite-wolframite) mineralisation. The next assemblage outwards was enargite-pyrite-tennantite/tetrahedrite, then complex silver and bismuth-sulphosalts with bismuthinite, and at greater distances galena-barite followed by lead sulphosalts, orpiment and realgar. Late stage siderite and/or botryoidal pyrite overprint all zones (Petersen et al., 1977; Dean et al., 1994).
Published reserves and resources as of December 31, 2011 (Compañía de Minas Buenaventura S.A., 2012) were:
Reserves - 0.364 Mt @ 637 g/t Ag, 2.04 % Pb, 0.48% Cu, 0.79 g/t Au;
Resources - 0.302 Mt @ 660 g/t Ag, 2.02 % Pb, 0.43% Cu, 0.48 g/t Au;
Production during 2011 amounted to 0.127 Mt of ore @ 638 g/t Ag, 1.61 % Pb, 0.75 g/t Au, for 77 tonnes of recovered silver.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1994.
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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Deen J A, Rye R O, Munoz J L, Drexler J W 1994 - The magmatic hydrothermal system at Julcani, Peru: evidence from fluid inclusions and Hydrogen and Oxygen isotopes: in Econ. Geol. v89 pp 1924-1938
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Petersen U, Noble D C, Arenas M J and Goodell P C, 1977 - Geology of the Julcani mining district, Peru: in Econ. Geol. v.72 pp. 931-949
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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