Ductile shear deformation and gold mineralization in the Hetai goldfield of the Yunkai Massif, South China Block

摘要

The Hetai goldfield, located at the northern edge of the Yunkai Massif in South China, is a significant gold deposit hosted within the Hetai ductile shear zone (HSZ). The deformation history of HSZ and its correlation with the gold mineralization are problematic. In this study, we conducted detailed field observations and microstructure analyses together with zircon U-Pb and muscovite Ar-40/Ar-39 geochronology on mylonitic granites, aiming to study the deformation features and processes of the ductile shear zone (DSZ) along with their further implications to the gold metallogenic mechanisms of the Hetai goldfield (HGF). The HGF and its periphery have undergone three phases of ductile shear event (DS) since the Palaeozoic: The first DS developed from 468 to 413Ma, with deformation temperatures above 500 degrees C, accompanied by the formation of large-scale migmatite and magmatism. The second DS developed from 239 to 211Ma, with deformation temperatures ranging from 400 degrees C to 500 degrees C and resulted in a low-angle, top-to-the-SE thrusting. The third DS developed from 198 to 162Ma, with deformation temperatures between 300 degrees C and 400 degrees C and formed steep, dextral strike-slip shear zones. The DSs in the HGF have close connection with the gold mineralization. The first DS is coeval with the small-scale gold mineralization or sulfofication and laid the foundation for later large-scale gold mineralization. The second DS had no obvious gold mineralization, but the DSZ that developed in this period, together with the earlier DSZs, may have provided a migration pathway for the later gold ore-forming fluid. Occurrence of the third DS was combined with the main gold mineralization, but the large-scale gold mineralization mainly occurred during 175-157Ma, that is, the middle and later periods of dextral strike-slip. Overall, multiphase DS dominated the large-scale gold mineralization in this area.