Geochemistry, Geochronology and Lu‐Hf Isotopes of Peraluminous Granitic Porphyry from the Walegen Au Deposit, West Qinling Terrane

Abstract

AbstractWalegen Au deposit is closely correlated with granitic intrusions of Triassic age, which are composed of granite and quartz porphyries. Both granite porphyry and quartz porphyry consist of quartz, feldspar and muscovite as primary minerals. Weakly peraluminous granite porphyry (A/ CNK=1.10–1.15) is enriched in LREE, depleted in HREE with Nb‐Ta‐Ti anomalies, and displays subduction‐related geochemistry. Quartz porphyry is strongly peraluminous (A/CNK=1.64–2.81) with highly evolved components, characterized by lower TiO2, REE contents, Mg#, K/Rb, Nb/Ta, Zr/Hf ratios and higher Rb/Sr ratios than the granite porphyry. REE patterns of quartz porphyry exhibit lanthanide tetrad effect, resulting from mineral fractionation or participation of fluids with enriched F and Cl. LA‐ICP‐MS zircon U‐Pb dating indicates quartz porphyry formed at 233±3 Ma. The ages of relict zircons from Triassic magmatic rocks match well with the detrital zircons from regional area. In addition, ∊Hf(t) values of Triassic magmatic zircons from the granite and quartz porphyries are –14.2 to –9.1 (with an exception of +4.1) and –10.8 to –8.6 respectively, indicating a crustal‐dominant source. Regionally, numerous Middle Triassic granitoids were previously reported to be formed under the consumption of Paleotethyan Ocean. These facts indicate that the granitic porphyries from Walegen Au deposit may have been formed in the processes of the closing of Paleotethyan Ocean, which could correlate with the arc‐related magmatism in the Kunlun orogen to the west and the Qinling orogen to the east.