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The Altar Porphyry Cu-(Au-Mo) Deposit (Argentina): A Complex Magmatic-Hydrothermal System with Evidence of Recharge Processes

Maydagan, L.
Franchini, M.
Dilles, J.
Rey, R.
Published in Economic Geology. 2014, vol. 109, no. 3, p. 621-641
Abstract Altar (31o 29' S, 70o 28' W) is a large porphyry Cu-(Au-Mo) deposit with associated epithermal Au-(Ag- Cu) veins located in the Cordillera Principal of southwest San Juan province (Argentina). Altar is a complex magmatic-hydrothermal system formed from several magmatic and hydrothermal pulses during the middle- late Miocene. New LA-ICPMS U-Pb ages in zircons from the Altar porphyries indicate four discrete events of intrusions over an extended magmatic life time of ca. 3 m.y. It comprises a premineralization porphyry (11.75 ± 0.24 Ma), three mineralized porphyries (11.62 ± 0.21 and 11.68 ± 0.27 Ma, 11.13 ± 0.26 Ma, 10.35 ± 0.32 Ma) related to hydrothermal breccias, two postmineralization intrusions, and a postmineralization breccia (8.9 ± 0.4 Ma). The three mineralized porphyries (porphyries 2, 3, and 4) were emplaced within ~0.7 to 1.3 m.y. Amphibole phenocrysts from the porphyries crystallized from oxidized magmas (fO2 = NNO +1 to +2) at temperatures of 780° to 850°C and pressures between 0.9 and 1.8 kbars corresponding to depths of ~4 to 7 km. Anorthite- and Fe-rich rims in the plagioclase phenocrysts suggest that the magmatic chambers were episodically recharged by a less evolved magma. The middle-late Miocene intrusions are interpreted to have been derived from a deeper and relatively large magmatic reservoir that supplied magmas to smaller chambers located in the upper crust. The focused magmatic output to shallow levels during a period of a few million years in the Altar area has been a main requirement in the formation of this large porphyry copper deposit.
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Research groups Isotope Geochemistry, Geochronology and Thermochronology
Mineral Resources and Geofluids
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MAYDAGAN, L. et al. The Altar Porphyry Cu-(Au-Mo) Deposit (Argentina): A Complex Magmatic-Hydrothermal System with Evidence of Recharge Processes. In: Economic Geology, 2014, vol. 109, n° 3, p. 621-641. doi: 10.2113/econgeo.109.3.621 https://archive-ouverte.unige.ch/unige:34457

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Deposited on : 2014-02-25

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