7th International Symposium on Andean Geodynamics (ISAG 2008, Nice), Extended Abstracts: www-www Diente Verde and Mario, Cañada Honda, San Luis, Argentina: porphyry-type deposits in the South Pampean flat-slab of the Central Andes Nilda E. Urbina 1 & P. Sruoga 1,2 1 Universidad Nacional de San Luis. Ej. de los Andes 950. (5700) San Luis, Argentina. urbina@unsl.edu.ar 2 CONICET. SEGEMAR. Av. J.A. Roca 651. Pso 10, Of. 21 (1322) Capital Federal. patysruoga@yahoo.com.ar KEYWORDS: San Luis, Porphyries, Gold-Copper, Flat-Slab, Mio-Pliocene INTRODUCTION The San Luis Tertiary Metallogenic Belt (SLMB) located in the Sierras Pampeanas of San Luis is related with the subduction zone shallowing between 27º and 33º S (Fig. 1 A). Mineralization and volcanic rocks occur within a west-northwest-trending magmatic belt from La Carolina in the west to El Morro in the east (Fig. 1 B). Mesosilicic magmas belong to normal to high-K calc-alkaline and shoshonitic types. In a close spatial and temporal linkage several mineralizations of epithermal and porphyry types are associated. Volcanic activity began at about 12-13 Ma in the west and ended at 1.9 Ma in the east (Ramos et al. 1991, Urbina, 2005, Urbina y Sruoga, In press). Volcanics and associated mineralization formed 600-700 kilometers east from the trench for about 10 m.y. and over a west-east distance of 80 kilometers. The Diente Verde and Mario deposits are copper-gold porphyry mineralizations genetically related to the Late Miocene-Late Pliocene volcanic activity. Both deposits are located at Cañada Honda district and are part of an arc-transverse magmatic lineament at 33º S coincidently with the change of the subduction angle. DIENTE VERDE DEPOSIT An intrusion centered district was suggested by Urbina et al. (1997) for Cañada Honda, based on the spatial distribution of several low-sulfidation epithermal veins with regard to the high-level stock at Diente Verde. Diente Verde is a gold-copper porphyry deposit consisting of stockwork sulfide veining associated with a small intrusion centered within an andesitic stratovolcano (Fig. 1 C). Hydrothermal alteration and mineralization have a symmetrical distribution surrounding the porphyritic subvolcanic intrusion. The sulfide ore-mineral assemblage occurs either disseminated or in a stockwork. The alteration affects the rocks of the core, and spreads outside from the volcanic edifice in an extensive hydrothermal halo (Fig. 1 C). K silicate alteration present in the central zone is characterized by the presence of quartz veinlets that may occur as multidirectional stockwork or subparallel arrays of closely spaced WNW-ESE, NE-SW, NW-SE-striking veinlets suggesting structural control on emplacement. Veinlets from a few millimeters to 5 cm in width, are planar to slightly sinuous, and have alteration halos composed mainly of biotite replacements accompanied by hydrothermal K feldspar. Quartz veinlets have centrally located sulfides grains. Chalcopyrite and magnetite are the principal hypogene minerals in K silicate alteration with traces of electrum, digenite, bornite, tennantite, covellite, enargite, pyrite and pyrrhotite, which are A-type veinlets (Gustafson and Hunt, 1975) (Fig. 2). Veinlets with central suture of www