Geochronology and origin of the Qi189 porphyry gold deposit in Qiyugou Orefield, Qinling Orogen, China

Abstract

The Qi189 gold deposit is a recently discovered porphyry system in the Qiyugou Orefield, located in the northeastern Qinling Orogen along the southern margin of North China Craton. The orebodies are hosted in the porphyritic granite emplaced in the Taihua Supergroup. Three molybdenite and five pyrite samples from the ores yield Re–Os isochron ages of 129.5 ± 2.8 Ma and 127.5 ± 8.2 Ma, respectively, which are coincident with the zircon U–Pb age of the porphyritic granite within analytical error (128.6 ± 0.8 Ma). Zircon grains from the post-ore quartz monzonite yield weighted mean 206Pb/238U age of 124.7 ± 0.6 Ma (n = 31, 1σ, MSWD = 0.23). These ages constrain that the Qi189 gold system was formed in the period of 130–127 Ma. The porphyritic granite and quartz monzonite show high-K calc-alkaline affinity, enrichment of LREE and LILE, depletion of HREE and HFSE, and negligible Eu anomaly. Zircon grains show negative εHf(t) values of −20.7 to −14.9, with TDM2(Hf) ages of 2.49–2.13 Ga. This indicates that the Qi189 porphyry system originated from a source mixed by the materials from the North Qinling Accretion Belt and the basement of North China Craton, with minor contribution from the mantle, and developed under a post-collisional tectonic setting.