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The iron oxide-Cu-Au deposit of Raúl-Condestable, Mala, Lima, Peru

Zuñiga Alvarado, Julio
Corfu, Fernando
Published in XI Congreso Peruano de Geología. Lima (Peru). Lima (Peru): Sociedad Geologica del Peru. 2002
Abstract The iron oxide-Cu-Au deposit of Raúl-Condestable is located around 90 km south from Lima, on the Peruvian coast, and has a cumulated production of >25 Mt with 1.7% Cu, 0.295 g/t Au, and 0.1940 Oz/t Ag. The ore consists of a chalcopyrite-pyrite-pyrrhotite-magnetite assemblage. The deposit is hosted by a shallow water volcano-sedimentary sequence of Valanginian (Morro Solar Group) to Middle Aptian age. An andesite-dacite lava dome occurs at the top of the sequence, which was alimented by a quartz-diorite porphyry sill–dyke complex, which in turn was intruded by a tonalitic stock. Preliminary U-Pb zircon data show that all the porphyry and tonalite intrusions took place between 116.5 and 113 Ma and that syn-ore sphene in veins is coeval. A late, regional, NW trending dolerite dyke swarm crosscuts all the intrusives, the volcano-sedimentary sequence, and the mineralization. Finally, the whole deposit area was tilted 30 to 40º to the SW. The deposit is centered on the quartz-diorite/tonalite complex, in a sub-volcanic position. Two hydrothermal stages are evidenced. Feeder veins of the first and main hydrothermal stage are mostly perpendicular to the stratigraphic plane and are oriented NE and NW, with some veins trending E-W. They cut the whole volcano-sedimentary sequence, the porphyry and the overlying andesite-dacite. Replacement and pore-infill took place, respectively, in carbonate rocks, porous tuffs, and lava breccia flow tops. These replacements and disseminations are directly connected to the feeder veins. The second hydrothermal event followed the emplacement of the dolerite dykes and is represented by a calcite-sulfide (sphalerite, galena, chalcopyrite, pyrite, and marcasite) assemblage emplaced in minor veins. The first hydrothermal stage started with the deposition of Na-Ca silicates (scapolite, albite, actinolite); followed by iron oxides (hematite-magnetite) with minor sphene and apatite; and finally sulfides (pyrite, chalcopyrite, pyrrhotite, ±sphalerite, ±molybdenite) with minor quartz, chlorite, and sericite. Hematite is widely pseudomorphosed to magnetite. The associated alteration developed a Na-Ca metasomatic core resulting in an assemblage of albite, scapolite (marialite), and actinolite. This assemblage was overprinted by iron metasomatism that formed hematite-magnetite with minor sericite and variable chlorite. Sericite-chlorite alteration is present as an outer core, and chlorite-hematite alteration is in a distal position. There is almost no potassic alteration in the system. Alteration associated with the second hydrothermal stage led to carbonatization. First stage sulfides are characterized by Δ34S values ranging from 2.7 to 26.3‰ (CDT), while late stage sulfides show negative Δ34S values between –31.1 and –22.9‰ (CDT). Data on first stage sulfur might indicate a strong contribution of marine or evaporite sulfate, while the late stage apparently involved biogenic sulfur, possibly leached from sediments. Hypersaline fluid inclusions with halite and iron chloride crystals occur in first stage quartz, together with vapor-rich inclusions suggesting phase separation. Late stage calcite fluid inclusions display salinities between 4 and 38 wt % equ. NaCl, with most values around 13 wt % equ. NaCl, and Th ranging between 146.8 and 191.7 °C, with a mean at 169.4 °C. Copper (-Au) mineralization appears to be directly connected to the tonalite intrusion, and a skarn-like genetic process involving external fluids is considered.
Keywords Iron-oxide-copper-goldIocgRaul-Condestable minePeruGeologyMineralogyAlterationsGeochemistryU-Pb agesSulfur isotopesFluid inclusions
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Proceedings (Author postprint) (83 Kb) - public document Free access
Research group Reservoir Geology and Sedimentary Basin Analyses
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DE HALLER, Antoine et al. The iron oxide-Cu-Au deposit of Raúl-Condestable, Mala, Lima, Peru. In: XI Congreso Peruano de Geología. Lima (Peru). Lima (Peru) : Sociedad Geologica del Peru, 2002. https://archive-ouverte.unige.ch/unige:101276

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Deposited on : 2018-01-09

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