The 127 Ma gold mineralization in the Wulong deposit, Liaodong Peninsula, China: Constraints from molybdenite Re-Os, monazite U-Th-Pb, and zircon U-Pb geochronology

Abstract

The Wulong deposit is a large tonnage deposit (>80 t of Au), characterized by quartz vein style of gold mineralization in the Liaodong Peninsula, China. The auriferous quartz veins are mainly hosted by Late Jurassic gneissic two-mica granite (165–157 Ma) and Early Cretaceous granodiorite (129 Ma) and are structurally controlled by NNE- and NW-trending faults. Previous attempts to date the gold mineralization yielded ambiguous results (135–112 Ma). Here we report the first in-situ and direct age constraint for gold mineralization at Wulong. Five molybdenite samples from Mo-bearing quartz ± pyrite veins yielded an isochron age of 127.6 ± 2.3 Ma. In-situ SIMS U-Th-Pb dating of hydrothermal monazite that coexists with gold-bearing pyrite and quartz yielded a 208Pb-232Th age of 126.7 ± 3.2 Ma. These robust ages, together with new age data of the Wulong host intrusion and post-ore dike, allow for a better interpretation of the ore genesis of the Wulong deposit relative to a well constrained sequence of regional geological events. Zircon U-Pb dating of the Wulong host intrusion (gneissic two-mica granite), representing the oldest magmatic event at Wulong, gave a weighted mean age of 159.3 ± 1.4 Ma that is interpreted to be the magma emplacement age. Subsequent magmatic events are recorded by the Early Cretaceous dikes with zircon U-Pb ages between 127 and 113 Ma. A post-ore diorite porphyry dike that crosscuts the Early Cretaceous dikes has a U-Pb zircon age of 121.5 ± 1.5 Ma. All the lines of geochronology evidence suggest a distinct genetic link between the gold mineralization and the Early Cretaceous magmatism in the Wulong orefield. This episode of magmatism and mineralization corresponds to the lithospheric thinning within the northeastern North China Craton, which is triggered by the subduction of the Paleo-Pacific plate.