Zircon U–Pb and molybdenite Re–Os geochronology and geochemistry of Jinchang porphyry gold–copper deposit, NE China: Two-phase mineralization and the tectonic setting

Abstract

Whether multiple mineralization styles in porphyry deposits are the result of one or multiple pulses of magmatism is unknown. In this paper, we present new age and geochemical data on the Jinchang porphyry gold-copper (Au-Cu) deposit, an important deposit in NE China and in the eastern Central Asian Orogenic Belt (CAOB). Field geological study suggests that both the mineralization and ore-causative magmatism at Jinchang are multiphase. LA-ICP-MS zircon U-Pb dating of the monzogranite ore host yielded 197 ± 1 Ma, which is considerably older than the ore-causative monzonite (115 ± 3 Ma) and granodiorite (107 ± 2 Ma). Molybdenite Re–Os dating on the breccia pipe-hosted Au-Cu ores yielded a well-defined isochron age of 114 ± 3 Ma, coeval to the monzonite emplacement. The Au-Cu mineralization was followed by another phase of crypto-explosive breccia pipe-hosted, disseminated/vein-type Au mineralization. This Au-only mineralization phase was auriferous pyrite Re–Os dated to be 103–101 Ma, coeval to the granodiorite emplacement. Geochemically, the monzonite and granodiorite are enriched in LILEs and LREEs, but depleted in HFSEs and HREEs. The ore-causative rocks are I-type and display continental arc geochemical affinities. We suggest that the monzonite and granodiorite were generated in an intracontinental extensional setting, probably caused by the Early Cretaceous subduction roll-back of the Paleo-Pacific Plate.