Volatiles in zircon-hosted apatite from the Escondida porphyry copper district, northern Chile

Apatite inclusions armoured in zircon are ideal candidates to fingerprint the original volatile component (S, Cl, F, OH) of ore-forming magmas. A thorough investigation of such inclusions, together with matrix apatite, is hereby used to elucidate the volatiles sources and pathways throughout the magmatic-hydrothermal stages of individual porphyry Cu deposits at Escondida, northern Chile. We selected a suit of least-altered samples, mineralised and barren, to resolve the physico-chemical conditions of the melt/fluid responsible for the Cu-Mo +/- Au mineralisation in Escondida during the long-lasting late Eocene-Oligocene (44-33 Ma) arc magmatic activity. SEM-BSE-CL imaging, together with measurements of halogens and sulfur concentrations with electron micropobe allowed us to build a comprehensive insight into the volatile content and geochemical signature of apatite. We also measured high precision d34S values in apatite via SIMS to elucidate the S isotope signature of apatite inclusions and matrix apatite. Our preliminary data show that detailed mineral chemistry, microtextural studies, and sulfur isotope measurements applied to apatite inclusions in zircon and matrix apatite provide a unique insight into the geochemical behaviour of sulfur and halogens in ore-forming magmas.