Características geológicas de los pórfiros dacíticos y su roca hospedante, quebrada del Pe？asquito, Precordillera occidental de San Juan

at pe？asquito creek, in the sierra del tontal (s 31o 40' 44,5" - w 69o 14' 05"), western san juan province, at an altitude of 2,953 m.s.n.m, a succession of dacitic dykes of unknown age are recognized, intruding subconcordantly sandstones of the don polo formation of ordovician age. the sandstones intruded by the dykes present short wavelength symmetrical folding (400 m). the dikes have attitudes of n0o/85oo-n30o/75oo, with thicknesses ranging between 3 and 25 m. microscopically, they present a porfiric texture, composed of quartz, plagioclase, biotite and hematite. a deep alteration (oxidation) confers a yellowish color to the dykes, easily visible by means of satellite imagery. there are numerous folded veins of quartz that accompany the dikes, associated to anticline folds, fractures and shear zones, with sigmoid structures and cinematic indicators with dextral displacement indicators. the dikes may correspond to a permian-triasic or miocene magmatism. the closest dacitic magmatism of permian age has been recognized to the south of the area, in pampa de los pozos and yalguaraz, with copper mineralization. however, pe？asquito′s dykes have a greater similarity with dacitic dikes described at carrizal creek, 7 km to the north of the study area. for this reason are assigned to the miocene magmatism recognized in the region. exploratory studies are suggested to determine the presence of mineralization.