Abstract

D'ANNUNZIO, María Celeste  and  RUBINSTEIN, Nora. Origen y eventos de mineralización de las brechas de Quebrada del Diablo Lower West, distrito minero Gualcamayo, provincia de San Juan. Rev. Asoc. Geol. Argent. [online]. 2013, vol.70, n.4, pp.542-548. ISSN 0004-4822.

Gualcamayo mining district (68°38'26"W, 29°43'10" S) is located in the Central Precordillera, in the northeast of San Juan province. This sector is characterized by carbonate and sedimentary rocks of Ordovician-Permian age. This sequence is intruded by Miocene dacites and tonalites rocks. The district includes three deposits: Quebrada del Diablo Main, Amelia Ines-Magdalena and Quebrada del Diablo Lower West. Quebrada del Diablo Main is a Carlin-type deposit which is mined as an open pit. Amelia Inés-Magdalena is an iron, molybdenum, copper, zinc, lead and gold deposit, associated to magnesian skarns. Quebrada del Diablo Lower West is a blind ore body located between 500 and 600 metres deep. In Quebrada del Diablo Lower West, the gold mineralization is hosted by breccias with an wide variation in composition and relative abundance of clasts, matrix and cement, as well as the size of the clasts. The textural analysis of the mineralized breccias from Quebrada del Diablo Lower West suggests a tectonic origin. The mineral assemblage of pyrite, sphalerite and gold indicates low-sulphidation conditions and neutral to alkaline pH. The overprinted marcasite suggests a decrease in the concentration of sulfur in the mineralizing fluids. Later calcite veins with realgar, orpiment and gold indicate an increasing arsenic activity in the hydrothermal system.

Keywords : Gold mineralization; Tectonic breccias; Low-sulphidation; Central Precordillera; San Juan.

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