Preliminary thermodynamic model for Bi-minerals in the San Francisco de los Andes Bi-Cu-Au deposit, Cordillera Frontal, San Juan, Argentina

TESTA, FRANCISCO JOSÉ; COOKE, DAVID

Perth, WA

Encuentro; Solomon Meeting: five-day mineral systems forum; 2011

The Commonwealth Scientific and Industrial Research Organisation (CSIRO)

ABSTRACT San Francisco de los Andes mine (30º 50´ 08´´S - 69º 35´ 58´´W) is located on the eastern flank of the Cordillera Frontal, San Juan province, Argentina (fig 1). The Cordillera Frontal is a geological province on the eastern flank of Cordillera de los Andes that extends from northern San Juan to southern Mendoza. The orebody is hosted by a tourmaline-cemented breccia pipe that has cut carboniferous sedimentary rocks (Llambías et al, 1969). The sedimentary rocks have been intruded by the Tocota Pluton, a Permian intrusive complex that ranges from tonalite to granite in composition. We have initiated geochronological studies in order to determine whether the breccia pipe is related to Permian or younger magmatism. San Francisco de los Andes is characterized by complex Bi-Cu-Pb-Zn-Mo-As-Fe-Ag-Au mineralization, including native elements, sulfides, and sulfosalts. This article reports the occurrence of two different Bi-Cu-Pb mineral assemblages at opposite sides of the NW-SE trending elliptical breccias pipe. By means of detailed analytical studies and fluid inclusion data we have developed a preliminary thermodynamic model for both assembles at a minimum temperature of 230°C and a maximum temperature of 400°C. We aim to constrain tentative fS2 and fTe2 values for the hydrothermal solutions using the previously determined sulfide and telluride mineralogy.