Preliminary geochemical characterization of the Granito Flores, NE North Patagonian massif: an insight into the mineralogical controls on Th distribution.

LÓPEZ DE LUCHI, M.G., RAPALINI, A.E., TOMEZZOLI, R.

Facultad de Ciencias Exactas y Naturales,Universidad de Buenos Aires

Otro; 8º Reunión de Mineralogía y Metalogénesis; 2006

Asociación Mineralógica Argentina

ABSTRACT: The Granito Flores represents the epizonal plutonism of the Early Jurassic Complejo Plutónico-Volcánico Treneta. Two magmatic facies made up the intrusions: a medium to coarse grained pink to reddish somewhat porphyric biotite monzogranite and a fine grained leucomonzogranite with very scarce biotite. These high-K and ferroan granites correspond to a mildly peraluminous suite with a trend towards per-alkaline compositions and straddle the fields of the sub-alkaline to medium alkaline types in the TAS diagram. Alkalies show an opposite behaviour against SiO 2 whereas K 2 O exhibit a negative correlation Na 2 O correlates positively indicating enrichment in sodium at the most evolved terms. Rubidium contents range from 200 to 400 ppm whereas the rocks are depleted in Sr and Ba. The granites are relatively enriched in Y, Nb, Ta, Cs, and Th. The coherent behaviour of Th against K, Fe, Ti, La, Ce, Nd and Hf suggest that biotite and other mafic minerals are the sink for Th. U is decoupled from Th and therefore it may form its own minerals or may have been mobilized. A trend towards increasing Na with SiO 2 does not reflect increasing depth of crystallization but may be connected with the presence of fluorine as fluorite is an ubiquitous, albeit scarce, constituent of the alteration assemblages of feldspar and biotite. Palabras Clave : Geoquímica-Torio-Granito Flores-NE Macizo Norpatagónico Keyword s: Geochemistry-Th -Granito Flores- NE North Patagonian Massif