Preliminary study of the REE composition and fluid inclusions in hydrothermal fluorites of the Ancasti range, Catamarca, Argentina

Abstract

This paper is a preliminary contribution of the REE composition, petrography and microthermometry of fluid inclusions of hydrothermal fluorite veins of the El Portezuelo - Los Mudaderos fluoritic district, northwestern Ancasti range, Sierras Pampeanas, Catamarca province. The veins are located in Sauce Guacho (333.9±10.7 Ma) and Los Mudaderos (369.8±5.3 Ma) granites and in the metamorphic basement (Ancasti Formation). The microthermometric data of fluid inclusions were obtained from granular violet fluorite exfoliation plates from Dal mine, while the REE composition was measured by ICP-OES in fluorite from three different veins. The REE content varies from 6.70 to 64.33 ppm. LREE/HREE > 1, high La_n/Yb_n values ​​and distribution patterns indicate enrichment in LREE, suggesting mineralization from early and weakly fractionated hydrothermal fluids. Negative Eu anomaly indicate low oxygen fugacity during fluorite formation. The geochemical data of Tb and La indicate a hydrothermal origin, consistent with the geological and textural-mineralogical features that, in addition, show more than one mineralizing pulse and low formation temperatures. Fluid inclusions vary in size and shape, are predominantly biphasic and show average homogenization temperature of 126 °C. The eutectic was registered between -21 °C and -24 °C and final ice melting was metastable and always ≥0 °C. The veins and host rocks textural features show a shallow emplacement for the fluorite veins.