Discussion on Genesis of the Liba Gold Deposit in the West Qinling: Evidence from Fluid Inclusions and Zircon U-Pb Dating in Gold Bearing Quartz Vein

Objective‌ and Methods The Liba gold deposit is located 2 km outside the Zhongchuan pluton in the West Qinling Orogen. Based on the latest exploration results of the Liba gold deposit, the geological characteristics are analyzed in detail, and the fluid inclusion and zircon U-Pb dating in the gold bearing quartz vein are studied. The mineralized alteration types of Liba gold deposit are pyritization, sericitization and silicification, which are obviously different with the metamorphic characteristics of the Zhongchuan pluton contact zone.

Results Mineralized alteration, ore body and vein rock are strictly controlled by faults, but the scale and mineralization degree of vein rocks are lower than ore body, indicating that magmatic activity may not provide main fluid and material for metallogenesis. The study of fluid inclusions indicate that the ores were deposited from medium-high temperature (220～360 ℃), low salinity (5% NaCl_eq～10% NaCl_eq) NaCl-H₂O-CO₂-(CH₄) fluids, similar to metamorphic fluid. The zircons in the gold bearing quartz veins are mostly sub rounded, indicating that they may undergone the process of transportation and rounding sedimentation. Zircon U-Pb ages can be divided into four spectral segments: 397～585 Ma, 673～1023 Ma, 1097～1868 Ma, and 1963～2575 Ma, which are very close to the age characteristics of detrital zircons in the host rock Liba Group, indicating that they were captured from the stratum during the activation and migration of ore-forming fluid.

Conclusion The Liba gold deposit can be grouped with other orogenic gold deposits that have similar characteristics, which is formed under the transition tectonic background from collision to extension. During the emplacement of Zhongchuan pluton, faults were developed along its margin, providing favorable spaces for the precipitation of ore-forming fluid and the emplacement of vein rocks. This caused the granitic pluton, vein rocks and gold bodies are together with space and time, but it may not have an inherent genetic relationship.