Ore deposits, tectonics and metallogenesis of the continental Aysen region, Chile

Four main map units are recognized in the Aysen region: the Paleozoic metamorphic basement (220-390 Ma); Upper Jurassic-Cretaceous calcalkaline andesitic to rhyolitic volcanic and marine sedimentary rocks (70-160 Ma); the Patagonian batholith (60-160 Ma and 3-20 Ma); and Upper Cretaceous to Miocene basalts (3-77 Ma) and marine and continental sedimentary rocks (Oligocene-Miocene). The Upper Jurassic-Cretaceous volcanic and sedimentary rocks and the Patagonian batholith formed in a volcanic arc-back arc setting superimposed on the Paleozoic metamorphic basement.; Mineralization in the Aysen region consists mainly of epithermal precious metals, Zn-Pb skarn and associated polymetallic vein deposits. Based on lead isotope studies and on geologic-tectonic setting, ore deposits in the region may be assigned to three distinct groups, the El Faldeo group, the Fachinal group and the El Toqui group.; Mineralization of the El Faldeo group (El Faldeo and Lago Azul districts, and Lago Chacabuco and Lago Cochrane polymetallic veins) is the oldest recognized in the region (Late Jurassic). Deposits are hosted by Upper Jurassic volcanic and sedimentary rocks and/or by rocks of the metamorphic basement. Lead isotope studies indicate an orogenic source of lead with an important upper crust component. The El Faldeo group is dominated by Zn-Pb skarn and associated polymetallic massive sulphide veins locally overprinted by late Au-rich epithermal mineralization.; Mineralization of the Fachinal group (Fachinal and Mina Silva and Manto Rosillo deposits, Quebrada Chica prospect and Rio Amarillo and Halcones-Leones areas) is of Early Cretaceous age. Deposits are hosted by Lower Cretaceous felsic volcanic rocks or by rocks of the metamorphic basement. Lead isotope studies indicate an orogenic source of lead. Except for the Mina Silva and Manto Rosillo deposit, a Zn-Pb skarn, mineralization in this area is of the precious metals epithermal type, and was formed at a shallow crustal level.; Mineralization of the El Toqui group (El Toqui, Santa Teresa and Katerfeld deposits, and Lago Aro area) is of Early Cretaceous age. Deposits are hosted by andesitic to dacitic volcanic, intrusive and marine sedimentary rocks formed in a volcanic arc-back arc setting. Lead isotope studies indicate a mixed source for lead composed of orogenic, mantle and upper and lower crust leads. The El Toqui group comprises Au-rich Zn-Pb skarn mineralization and associated polymetallic veins, as well as polymetallic Au-Ag rich epithermal type mineralization, depending on the level of emplacement.; Three metallogenic provinces and two metallogenic epochs are recognized in the Aysen region: the El Faldeo metallogenic province of Late Jurassic age; and the Fachinal and El Toqui provinces, of Early Cretaceous age. Mineral potential in this region is probably limited to small skarn and precious metals epithermal deposits. (Abstract shortened by UMI.)...