Mineralogía de los rellenos vesiculares de la secuencia basáltica entre Bajada del Diablo y Marra-Có, Chubut

In this contribution we describe the textures and the mineralogy of eocene volcanic sequences from Bajada del Diablo and Marra-Co, Chubut province. They are composed of alkali basalt with three different sections. The two upper ones are characterized by the occurrence of secondary minerals among which amygdules filled by fibrous aggregates of natrolite are the most common ones. This species not only represents the last mineral precipitation but also the most important one. The alteration assemblages of primary minerals as well as the secondary assemblages, that fill each basalts’ cavities, suggest a very low-grade hydrothermal alteration with temperatures lower than 100°C and low silica activity