Metallogeny of the syenite-related Dongping gold deposit in the northern part of the North China Craton: A review and synthesis

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The Dongping gold deposit is located at the northern margin of the North China Craton in Hebei Province, China; it is the largest alkaline pluton-related Au deposit in China. The ore deposit is hosted in the 400–386Ma (LA-ICPMS and SHRIMP zircon U–Pb method) Shuiquangou syenite intrusion, which cuts Archean-aged metamorphic rocks. The ore bodies consist of a set of en echelon lenses and veins controlled by shear zones. The ores can be divided into auriferous quartz vein, stockwork, and disseminated ores. Two stages of gold mineralization can be distinguished, the first stage mineralization consists of high grade (>10g/t) grayish quartz veins enveloped by stockwork and disseminated ores, whereas the second stage mineralization occurs as low grade (<10g/t) milky white quartz veins. The ores are sulfide-poor and enriched in Te. Gold is mainly present as native gold, calaverite, electrum and petzite.Studies of fluid inclusions in quartz indicate that the ore-forming fluids have low salinity (0.7–8.1% NaCl equivalent) in the H2O–CO2–NaCl system and have homogenization temperatures varying from 310 to 350°C. The ore-forming fluids have δ18O values varying from −1.7 to +6.9‰ with an average of 2.9‰ and δD values from −108 to −66.5‰ with an average of −85‰, indicating a magmatic origin with some involvement of meteoric fluid. The ore-forming fluids have initial 87Sr/86Sr385Ma ratios of 0.705–0.706 and 3He/4He ratios of 0.3 to 5.2 Ra (Ra being the atmospheric ratio of 1.0), indicative of a mantle contribution of the fluids. The ores have bulk δ34S values varying from −1 to +2‰, similar to those of the host syenites (δ34S=1.8–3‰) and the Archean metamorphic rocks (δ34S=0.04 to +4.4‰). Lead isotope analyses of sulfides, stock and disseminated ores, quartz veins, fresh host syenites and the Archean metamorphic rocks have a linear correlation of 208Pb/206Pb and 207Pb/206Pb, indicating a genetic link between the gold mineralization and the syenites. Hydrothermal zircons from the high grade ores of the first stage can be distinguished from magmatic zircons based on internal textures on cathodoluminescence images and rare earth element patterns; these zircons have been dated at 389±1.0 to 385±5.7Ma, whereas those from the second stage low-grade auriferous quartz vein were dated at ~140Ma (LA-ICPMS and SIM U–Pb methods).We propose a model for the formation of the Dongping gold deposit involving a late-magmatic hydrothermal process related to a Devonian mantle sourced syenites with a Late Jurassic–Early Cretaceous hydrothermal overprint.