Resumo

MUGAS LOBOS, Ana Cecilia; MARQUEZ-ZAVALIA, María Florencia  e  GALLISKI, Miguel Ángel. Petrography and geochemistry of the gondwanic rock units from Don Sixto mining project, Mendoza. Rev. Asoc. Geol. Argent. [online]. 2010, vol.67, n.3, pp.392-402. ISSN 0004-4822.

Don Sixto mining project is a low sulphidation epithermal Au-Ag ore deposit located at the southeast of Mendoza province; the gold resource of the deposit is close to 900.000 ounces. In the study area, the mineralization is mainly disseminated and it is hosted by rhyolitic volcanic and pyroclastic sequences of the Choique Mahuida Formation and dikes from the El Portillo Group, both included in the upper section of the Choiyoi Group. The geology and petrography of these volcanic-pyroclastic rocks indicates that the Choique Mahuida Formation is represented by rhyolites interlayered with rhyolitic ignimbrites and isolated levels of "pyroclastic lenticular deposits". The rhyolitic porphyritic dikes from the El Portillo Group, that strikes NW-SE and N-S, were probably developed in relationship with the evolution of large regional fault zones. Geochemically these gondwanic rhyolites, based on the distribution of their trace and rare earth elements, behave as a suite genetically related to evolved magmas, even more than other units from the upper section of the Choiyoi Group. The geochemical characteristics of these magmas are similar to others from equivalent rock units outside the study area, from which the upper section of the Choiyoi Group is interpreted as evolving from a volcanic arc into an intraplate tectonic setting.

Palavras-chave : Epithermal; Choiyoi Group; Permian-Triassic; Petrography; Geochemistry.

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