Geology, C-H-O isotopes, and muscovite 40Ar-39Ar dating of the Qingbaishan gold deposit: Implications for tectonism and metallogenesis of early Devonian gold deposits in the Beishan orogen, NW China

Abstract

The Beishan orogen is an economically important gold mineralization belt that hosts more than 20 gold deposits. Most Au orebodies occur within large-scale fault zones, indicating a correlation between structural evolution and gold mineralization. Previous studies have demonstrated that Au mineralization generally developed in the Permian–Triassic; however, pre-Permian gold mineralization and its temporal relationship with tectonic evolution remain poorly understood. The Qingbaishan deposit, located in the Beishan orogen, NW China, is hosted by the Sanjiashan shear zone. A detailed field-based structural analysis revealed that the Sanjiashan shear zone has thrust and sinistral strike-slip characteristics, such as asymmetrical folds and S-C fabrics. The muscovite 40Ar/39Ar age from auriferous quartz shows that the Qingbaishan gold system formed around 399.7 ± 1.6 Ma, consistent with the time of Sanjiashan sinistral ductile shearing in the Beishan orogen. The carbon and oxygen isotope compositions of auriferous quartz suggest that the host rocks within the Precambrian Gudongjin Group would have been a significant source of ore metals and that the low δ18O values in quartz resulted from fluid reactions with 18O-poor host rocks. The Qingbaishan Au deposit is concluded to be a strike-slip-dominated orogenic-type system related to continental collision between the Tarim and Kazakhstan–Ili plates.By integrating the age data obtained from this study with previous geochronological results, two episodes of gold mineralization in Beishan are distinguished: an early episode around 399 Ma, when sinistral strike-slip zone-related orogenic gold deposits formed in a syncollisional setting, and a late episode around 298–231 Ma, when dextral strike-slip deformation produced deposits in a postcollisional extensional setting.