Zircon LA-ICP-MS U-Pb and molybdenite Re-Os dating of the Dabaoshan polymetallic deposit in northern Guangdong Province and its geological implications

Abstract：LA-ICP-MS U-Pb dating of zircons from subdacitic porphyry samples yielded a weighted mean 206Pb/238U age of 174.6±1.5 Ma (MSWD=0.7) in the Dabaoshan polymetallic deposit of northern Guangdong Province. Re-Os dating of three molybdenite samples from porphyry and skarn ores yielded consistent model ages from 163.2±2.3 Ma to 165.2±2.4 Ma. These ages are consistent with the molybdenite Re-Os model age (164.7±3.0 Ma) measured by Mao et al. for the stratiform Cu-Pb-Zn ore body, and they can yield a weighted mean of 164.0±2.5 Ma (MSWD=0.16). These data imply that Mo-W and Cu-Pb-Zn mineralization in the ore district are products of the same mineralization event, which coincides closely with the event of Mo-polymetallic mineralization elsewhere in the Nanling region and corresponds to the second episode of Mesozoic metallogenesis in South China. Geological data, together with stable isotopic data of fluid inclusions (δ18O =－3.75‰～7.0‰, δD =－50.7‰～－56.1‰) and ore sulfides (δ34S =－2.00‰～3.00‰), suggest that the Dabaoshan ore deposit is a magmtic hydrothermal ore deposit associated with the granodioritic porphyry and the subdacitic porphyry. This is different from previous studies which argue for the existence of superimposition of multiple mineralization events comprising Caledonian exhalative deposition and Yanshanian superimposed mineralization or two Yanshanian mineralization stages. Based on geochemical diagrams of Y+Nb-Rb and Rb/30-Hf-Ta×3 in combination with previous studies, the authors suggest that the Dabaoshan polymetallic deposit is related to post-collisional lithosphere extension in the Nanling region of South China.