The H–O–S Isotope Characteristics and Diagenetic, Mineralization Ages of the Zhueryu Au Deposit from the Jidong Gold Belt, China

The Zhueryu Au deposit is one of the important quartz-vein type Au deposits. It is located at the western margin of the Jidong gold belt in China and characterized by ore bodies hosted in structural fractures within the Zhueryu syenite. The H, O, and S isotopes as well as the Rb–Sr isotope age of fluid inclusions from the quartz-polymetallic sulfide ore bodies (main stage) and the zircon U–Pb isotope age from the syenite were analyzed so as to discuss the source of ore-forming fluids and constrain the Au’s mineralization age. The textural characteristics of the fluid inclusions indicate that the fluid inclusions in the quartz (QzII) are from the same stage, with no evidence of secondary fluid inclusions from the later stage. Fluid inclusion microthermometry performed on the quartz (QzII) reveals a predominance of vapor–liquid two-phase inclusions, with homogenization temperatures ranging from 177 °C to 337 °C (average: 260 °C), characteristic of a medium-low temperature hydrothermal system. Furthermore, H, O, and S isotope analyses of the ore-forming fluids yielded δD, δ18O, and δ34S values ranging from +12.8‰ to +14.8‰, +9.15‰ to +9.51‰, and −8.395‰ to -1.918‰ (average: −5.826‰), respectively. These isotopic signatures, particularly the distinctly positive δD values, strongly suggest that the Zhueryu ore-forming fluids were primarily derived from metamorphic sources, contrasting with the magmatic-hydrothermal fluids implicated in the formation of many other Au deposits within the Jidong belt. The LA–ICP–MS zircon U–Pb dating yielded a concordia age of 242 ± 2 Ma (MSWD = 0.17), indicating a Middle Triassic crystallization age for the Zhueryu syenite. In contrast, the Rb–Sr dating of primary fluid inclusions hosted within quartz (QzII) yielded an isochron age of 181 ± 12 Ma (MSWD = 2.5), placing the Au mineralization event firmly within the Early Jurassic. This demonstrates that the Au mineralization is significantly younger than the host syenite, representing a distinct mineralization event. These results might have certain significance for studying the dynamics of Au mineralization in the Jidong gold belt.