GEOLOGY, HYDROTHERMAL ALTERATION AND FLUI D INCLUSIONS OF LA-VOLUNTADPORPHYRY COPPER-DEPOSIT, NEUQUEN PROVINCE, ARGENTINA

In La Voluntad porphyry copper deposit the mineralization is related t o a tonalite from the Chachil Plutonic Complex (Permian) intruded in t he metamorphites of Piedra Santa Formation (Lower Paleozoic). Rhyoliti c volcanic rocks from the Choiyoi Group (Triassic) cover unconformably the tonalite. The low mineralized vein densities indicate an hydrothe rmal system of low permeability with a weak fracturation atributed to a low hydrothermal fluid volume. The mineralization-alteration proceed ed in two main stages. During the first stage, a low intensity pervasi ve potassic hydrothermal alteration with disseminated pyrite and chalc opyrite and scarce molybdenite was developed. During the second, a hig h intensity fracture related phyllic alteration was overprinted to the early potassic alteration. The mineralization consists of pyrite, cha lcopyrite, bornite, molibdenite, sphalerite, arsenopyrite and scarce w olframite. Fluid inclusions indicate absence of hypersaline and presen ce of moderate to low salinity fluids, with temperatures between 240-4 20 degrees C and sporadic boiling during main mineralization. This dep osit belongs to a permo-carboniferous metallogenic cycle of unknown po tential, related to a magmatic are which trend SE south of Cerro Chach il, obliquely to the Andean Range.