Pablo Rodrigo Leal

Mutinaíte in zeolite assemblage in metabasalts of villegas, northern Patagonian Andes, Rio Negro Argentina

Abstract In Northern Patagonian Andes, mutinaite in assemblage with clinoptilolite in amygdales of altered Jurassic/Cretacic metabasalts was found. The zeolites were studied by optic, SEM, EDS and XRD methods. The rocks have fresh pyroxene and andesine altered to pumpellyite, in a matrix with albite, interstratified chlorite/smectite, pumpellyite and epidote. There are veins with laumontite and amygdales infilled with heulandite/clinoptilolite and mutinaite. This last mineral is white and pinky with perfect cleavage parallel to {100} and imperfect cleavage parallel to {001}. It is orthorhombic, the elongation is negative, 2Vα = 70°/80° and a 0 = 19.166A, b 0 = 21.025A, c 0 = 14.558A. Amygdales filled by mutinaite-clinoptilolite-quartz and veinlets with wairakite-laumontite suggest that their crystallization was related to low grade hydrothermal/geothermal metamorphism. The temperature of formation should be 200°C/250°C range.