Asociaciones minerales de muy bajo grado metamórfico vinculadas a alteración hidrotermal, sudoeste de Trevelin, Chubut, Argentina

mesozoic volcanic rocks outcrop in north patagonian andes, near trevelin locality, chubut province, argentina. basaltic andesites and basalts with porphyritic to aphyric textures -with calcium plagioclase, clinopyroxene, and olivine phenocrysts are the most common rocks. their groundmass texture is felly to intergranular. these units are affected by a hydrothermal alteration that replaced their phenocrystals and groundmass and filled veins, veinlets and amygdales minerals were analyzed by conventional microscopy, scanning electron microscopy-energy dispersive scan, x- ray diffraction, infrared spectroscopy, and fluid inclusions microthermometry. albite, prehnite, pumpellyite, epidote, metamorfismo de muy bajo grado y alteración hidrotermal, chubut, argentina clinozoisite, smectite/chlorite, laumontite, wairakite, mordenite, titanite, quartz, and calcite are the secondary minerals. textural relationship between secondary minerals and their chemical compositions evidence a very low-grade metamorphism in the high-zeolite fades, transitional to prehnite-pumpellyite fades. p-t conditions of the metamorphic eventwere <260°c and <1.5kb. moreover, feathery-flamboyant quartz, adularía, gold, and electrumfill other veinlets as the result of a low sulphidation epithermal system. volcanism, emplacement of granitoids and extensional events took place in the volcanic arc located in the western sector. these processes favoured fluid flow and gave a high temperature geothermal gradient. these conditions would be favourable for formation of a low-sulphidation epithermal assemblage and typical mineral assemblages of very low-grade metamorphism, as an alkaline hydrothermal alteration.