Abstract

GOMEZ, Anabel L. R; RUBINSTEIN, Nora A  and  GEUNA, Silvana E. Análisis mineralógico de las magnetitas hidrotermales del pórfiro DE CU-(MO) San Pedro, provincia de Mendoza. Rev. Asoc. Geol. Argent. [online]. 2015, vol.72, n.3, pp.326-331. ISSN 0004-4822.

The formation of Fe-Ti oxides is controlled by the mineralogy of the host rock and the physico-chemical conditions of the hydrothermal fluids. Therefore a correlation between the mineralogy of a hydrothermal alteration stage and a specific magnetic mineralogy could be expected. Textural and mineralogical analysis of magnetites from the San Pedro porphyry deposit allowed recognizing magnetite veinlets associated to an early potassic stage and disseminated magnetite associated to a late potassic stage, both with slightly differences in MnO and TiO2 contents. Disseminated magnetite includes homogeneous crystals associated with biotitization linked to the late potassic stage and magnetite-ilmenite composite crystals interpreted as a product of magmatic oxi-exsolution. The ilmenite crystals are oxidized to hematite + rutile which are interpreted as a product of oxidation at low temperature in hydrothermal conditions. In veinlets, magnetite show hematitization produced by a long-lived hydrothermal activity which allowed the chemical reequilibration of the igneous magnetite that led to a final composition similar to that of the hydrothermal magnetite. Moreover, slight differences in the chemical composition of the different types of hydrothermal magnetite suggest variations in the ions mobility during the evolution of the hydrothermal system.

Keywords : Magnetic mineralogy; Textural/chemical analyses; Potassic alteration; Porphyry copper; San Rafael Massif.