The Argentine pyroclastic loess are vulcanogenic deposits, which have their sources in the circumnpacific rim. The object of this work is to realize a de- tailed mineralogical characterization of this sediments, to use it like a geo logic outline which regiters discordance or similarity in them, The sampling zone extend from 714N-4125 to 622W-339S. The descriptions of these sediments was considered like basic, mesobasic or acid rocks. The basic sediments, looking like andesite-basaltic composition, are fill- ing the andean valley. The mesobasic one have a similar composition with a pyro- clastic dacite rock, and have been found in marshy pleistocene sediments in the intermountain valley and in the pampeana prairies. The acid ashed conform rhyoda- cite-rhyolite sediments which form the pampeana loess covers in the prairie.