Abstract

Zircon LA-ICP-MS and CA-TIMS and molybdenite Re-Os geochronology for the El Abra porphyry copper deposit (Chile) document a ~8.6 Ma protracted magmatic-hydrothermal history. Initial magmatic events occurred at ~45 Ma, and continued to ~36 Ma. An ~1.8 m.y. magmatic lull is recorded in the early stages of magmatism, which is characterized by equigranular rocks from the Pajonal suite. Magmatism from ~41 to ~36 Ma, corresponding to the El Abra Granodiorite Complex, is more recurrent, ending in a ~1.4 m.y. period of porphyritic intrusions, which are coeval with Cu-Mo mineralization. Late porphyritic units reveal subtle zircon inheritance likely associated with early magmatic pulses. The young stages of magmatism indicate system rejuvenation based on plagioclase phenocryst compositions, suggesting that the porphyry system is ultimately linked to a less evolved magma. Although there are multiple porphyry and veining events, molybdenite Re-Os ages define a focused mineralization episode from 36.34 to 36.18 Ma. Molybdenite Re-Os ages from nearby related prospects belonging to the El Abra cluster expand the mineralization period in the district up to ~1.0 m.y., suggesting a multistage, long-lived hydrothermal system. Integration of the molybdenite Re-Os dates and those from previous works at the El Abra and Toki clusters, accompanied by available tectonic reconstruction along the Domeyko fault system suggest the development, by late Eocene times, of a single, large (~30 km across) porphyry copper cluster, which was subsequently separated by an offset of ~35 km along the West fault.

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