Pb-Isotope and trace elements analyses by LA-Q ICPMS of Galena from Argentinian epithermal deposits: a preliminary analyses.

LAURA MAYDAGÁN; MCFARLANE, C; LENTZ D.; BOUHIER V. ; CAFFE P. ; RAINOLDI A. L.; PONS M. J.; FERNANDEZ M.; FRANCHINI M.; LUNA G.

Salta

Simposio; 15th Quadrennial IAGOD International Association on the Genesis of Ore Deposits Symposium; 2018

International Association on the Genesis of Ore Deposits-SEGMAR

The study region (31°30? S, 70° 15? W) is located in the southwestern sector of San Juan Province (Argentina), in the southern portion of the Pampean flat-slab segment and northeast end of the la Ramada fold and thrust belt of the Andes Main Cordillera. This region is a continuation of the Miocene and Pliocene porphyry copper belt of Chile that hosts three of the largest copper deposits in the world (El Teniente, Río Blanco - Los Bronces and Los Pelambres). Numerous Cu (Au) prospects with high mining potential have been discovered in this area. Some of them show the overlap between porphyry-type and high sulfidation epithermal deposits, indicating a high degree of uplift during their formation. The Altar deposit is a large porphyry Cu (Au-Mo) with associated high sulfidation epithermal veins (measured resources of 995 Mt @ 0.35% Cu and 0.083 g/t Au, Maydagán et al., 2014). The basement of the area is characterized by a late Carboniferous tonalitic batholith (~ 297 Ma, U-Pb, Maydagán, 2012) that crops out to the east of the Altardistrict. Cretaceous volcanic rocks outcrop to the west, in the Chile-Argentina border, between the Pantanosa Fault to the east and Tres Quebradas Fault to the west (Bergoeing, 2016). Early Miocene volcanic rocks that crop out in the study area (Lower Volcanic Complex, Maydagán et al., 2011) were intruded by porphyritic stocks of andesitic-dacitic composition in the middle to late Miocene (Maydagán et al., 2011, 2014) that contains most of the Cu-Au mineralization. Igneous rocks of Altar region were grouped in the lower Miocene early volcanic complex (21.6 ± 1.2 Ma to 20.8 ± 0.3 Ma, U-Pb zircon, Maydagán et al., 2014), that consist of an intercalation of basaltic andesite and porphyritic andesite-dacite lavas, levels of andesitic- dacitic lapilli tuff, and pyroclastic breccia that grade upwards to an upper unit of compacted and thick rhyolitic tuff, and the upper subvolcanic suite of middle-late Miocene age (11.75 ± 0.24 Ma, 8.9 ± 0.4 Ma, U-Pb zircon, Maydagán et al., 2014) that consists of a series of porphyritic intrusions, dykes, and magmatic-hydrothermal breccias. LA-ICPMS U-Pb zircon ages from the Altar porphyries indicate four discrete events of intrusions over an extended magmatic life time of ca. 3 m.y. It comprises a pre- mineralization 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 post-mineralization intrusions, and a post-mineralization breccia (8.9 ± 0.4 Ma, Maydagán et al., 2011, 2014). In this study we present new apatite (U-Th)/He data (AHe) in order to quantify the extent of tectonic-related exhumation in the Andes Main Cordillera in Argentina and compare the results with the exhumation patterns fromthe Coastal, Frontal and Main Cordilleras at similar latitudes in Chile. The aim of our research is to identify possible pulses of tectonic exhumation in the region given their importance to emplacement of subvolcanic intrusions related To Cu (Au) mineralization.