Role of water-rock interaction in the formation of La Azul fluorite deposit, southern Mexico

摘要

A comprehensive geochemical study of La Azul, a fluorite deposit in southern Mexico near the city of Taxco, includes petrography, microthermometry of fluid inclusions, stable and radiogenic isotope analyses, geochemistry of REE, and (U-Th)/He geochronology. We differentiated three stages of mineralization using a correlation between REE patterns and their concentrations in fluorites and absolute ages of the ore-forming events estimated from (U-Th)/He ratios in fluorites. The early fluorite precipitated with a high Sr and low REE content by replacement of Cretaceous limestone from a hydrothermal fluid associated with Eocene-Oligocene rhyolite intrusions at T ～ 150℃. The later stages are characterized by more oxidized fluid at lower temperature, higher concentrations of REE and lower Sr concentrations. The Sr-Nd isotopic systematics of fluorites suggests a mixed source of the ore-forming fluids with no more than 10% of Sr leached from magmatic rocks.