Titanite in situ SIMS U–Pb geochronology, elemental and Nd isotopic signatures record mineralization and fluid characteristics at the Pusangguo skarn deposit, Tibet

The Pusangguo skarn is a newly discovered Cu-Pb-Zn deposit in the Gangdese metallogenic belt, Tibet. In order to constrain the age of the deposit and the source of hydrothermal fluids, various types of titanite and coexisting minerals in the Pusangguo deposit were studied. The titanite occurring interstitially in fresh granodiorite is magmatic and characterized by high REE, Y, Mn, and Lu/Hf ratios, and high crystallization temperatures (700 to 750 °C). The titanite growing with, or included in, diopside in the prograde endoskarn, or occurring with epidote, calcite, and quartz in the retrograde exoskarn, is hydrothermal titanite characterized by low REE, Y, Mn, and Lu/Hf ratios. The titanite in the retrograde exoskarn typically contains a REE-enriched early core characterized by a negative Eu anomaly, and an overgrowth REE-depleted rim with a positive Eu anomaly. The secondary-ion mass spectrometry U-Pb dating of titanite drilled from thin sections of retrograde exoskarn shows intercept ages of 14.91 ± 0.31 Ma, which are consistent with the granodiorite age (14.63 ± 0.30 Ma), indicating coeval emplacement of granodiorite and skarn mineralization at ~ 14.7 Ma. In addition, in situ epidote and calcite Sr isotopes and titanite Nd isotopes, all analyzed in the same retrograde exoskarn thin section, show similar Sr-Nd isotopic compositions to magmatic plagioclase and granodiorite (whole rock), indicating that the retrograde hydrothermal fluids were directly derived from, or had the same origin as, the granodiorite.