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Revista de la Asociación Geológica Argentina

versão impressa ISSN 0004-4822

Resumo

GARRIDO, Mirta M.; GOMEZ, M. Cristina; FERNANDEZ, M. Lis  e  LAMBRECHT, Soraya. Tourmaline breccia of San Jorge porphyry copper gold deposit (Mendoza): alteration, mineralization and origin of the fluids. Rev. Asoc. Geol. Argent. [online]. 2010, vol.67, n.1, pp.47-57. ISSN 0004-4822.

The tourmaline breccia (breccia pipe) associated to San Jorge porphyry copper ore deposit is developed in carboniferous sedimentites (Yalguaráz Formation) at the contact with the SW margin of a permian granodiorite. The breccia is clast supported and monomictic (sandstone), with scarce matrix and cement mainly composed of tourmaline. The degree of brecciation decrease until a stockwork and a lower vein density area in the bottom is reached. Hydrothermal alteration occurs as a replacement and as a fracture filling. A first potassium alteration is superposed by a phillic alteration which predominates in the middle and upper parts of the breccia. Fractures filled with tourmaline, potassium feldspar, sericite, pyrite and chalcopyrite have the higher copper grade of the deposit. Fractures later than the breccia are linked to veinlets of quartz and sericite; sericite; and quartz, pyrite, chalcopyrite and arsenopyrite. An early fluids related to potassic alteration is highly saline without boiling and other fluids related mainly to phillic alteration are of low salinity and present boiling. Homogenization temperatures of 400ºC, salinities lower than 10 wt % NaCl equiv., and assuming a hydrostatic environment, a depth of 1.5 km was estimated for the formation of the breccia. Isotopic values of δ18O between 8.45 and 9.75 ‰ and of δ D between -53.07 and - 63.07 ‰ determinate on tourmaline, do not vary with depth and indicate a magmatic source for the fluids responsible for the breccia. As for the origin, the breccia is classified as a magmatic hydrothermal supported by textures, fluid inclusions and isotopes evidences.

Palavras-chave : Tourmaline breccia; San Jorge porphyry copper gold; Mendoza; Fluid inclusions; Oxygen and deuterium isotopes.

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