Cooling and exhumation of the mid-Jurassic porphyry copper systems in Dexing City, SE China: insights from geo- and thermochronology

Abstract

The Dexing porphyry copper and Yinshan polymetallic deposits in Dexing City, southeastern China are both giant porphyry ore systems. Located 15 km apart, they formed synchronously and share a similar magma source and metallogenic evolution, but their metal endowment, dominant rock types, and alteration assemblages differ significantly. In this contribution, we investigate the cause of these distinctions through new molybdenite Re–Os ages and zircon and apatite (U–Th)/He thermochronology data. Dexing has a molybdenite Re–Os age of ~170.3 Ma, zircon (U–Th)/He (ZHe) ages of 110 to 120 Ma and apatite (U–Th)/He (AHe) ages of 7 to 9 Ma. In contrast, Yinshan has older ZHe ages of 128 to 140 Ma and an AHe age of ~30 Ma. Viewed in combination with previously published data, we conclude that the apparently slow cooling experienced by these bodies is primarily a reflection of their experiencing multiple episodes of thermal disturbance. We tentatively infer that both deposits were exposed in the Late Miocene or more recent time, with the Dexing deposit more deeply exhumed than Yinshan. Our study has exploration implications for deeper porphyry-style ores at Yinshan and for porphyry deposits in non-arc (intraplate) settings in general.