Apatite (U-Th)/He thermochronology and Re-Os ages in the Altar region, Central Andes (31°30?S), Main Cordillera San Juan, Argentina: Implications of rapid exhumation in the porphyry Cu (Au) metal endowment and regional tectonics

LAURA MAYDAGÁN; MASSIMILIANO ZATTIN; CONSTANTINO MPODOZIS; DAVID SELVY; MARTA FRANCHINI; LUIS DIMIERI

MINERALIUM DEPOSITA

SPRINGER

Lugar: Berlin; Año: 2020 vol. 55 p. 1365 - 1384

0026-4598

Altar (31°30?S, 70°15?W) is a large porphyry Cu (Au) deposit located in thesouthern portion of the Pampean flat-slab segment of the Andes, Cordillera Principal,Argentina. Although, this region hosts telescoped porphyry-epithermal deposits,suggesting a high degree of uplift during their formation, thermochronological studiesof this region of the Andes are scarce. We present new AHe ages from the EarlyPermian and Late Eocene plutons and Middle Miocene subvolcanic stocks of the Altarregion that all reflect an exhumation pulse during the Middle Miocene (15.02 to 10.66Ma) for the Cordillera Principal of Argentina at 31°30?S.New AHe and Re-Os ages presented, in combination with previous U-Pbgeochronology, demonstrate that this rapid uplift and exhumation pulse occurredsimultaneously with the intrusion of the subvolcanic stocks (~12 - 10.3 Ma) associatedwith Cu-Au mineralization. The Re-Os molybdenite ages indicate that Altar East (11.16± 0.06 Ma) and Altar Central (10.38 ± 0.05 Ma) orebodies were associated with twomagmatic hydrothermal centers formed at temporally distinct periods. In Altar-LosPelambres region, the rapid cooling and uplift during the formation of the hydrothermalsystems resulted in an increased focused metal endowment (Au-Cu grades) due to thetelescoping of epithermal mineralization over the rapid uplifted porphyry system.The 11-10 Ma exhumation event coincides with the collision of the W-E segment of theJuan Fernández Ridge with the trench, at this latitude. The collision of the ridge may have driven this pulse of rapid cooling and exhumation, that has not been documented to date nor to the north or south of the El Altar-Los Pelambres region.