U-Pb age and geochemistry of zircons from the Katebasu Au deposit, West Tianshan Mountains, Xinjiang, and their geological implications

The Katebasu Au deposit, located on the southern side of North Nalati fault, is a large-sized deposit with great prospecting potential. In order to study the genetic relationship between intrusions developed in the study area and the Au deposit, the authors separated zircons from two main types of ore, i.e., Au-bearing altered monzogranite and quartz-sulfide vein, for U-Pb isotopic concentrations and trace element content by using LA-MC-ICP-MS. The results show that the chondrite-normalized REE patterns of zircons are characterized by HREE enrichment relative to LREE, with evident positive Ce and negative Eu anomalies, typical of magmatic zircons. The logarithm of oxygen fugacity (Log(fo₂)) calculated using δCe of the analyzed zircons is -29.2 to 5.1, suggesting high oxygen fugacity of magma, which is beneficial for preliminary enrichment of Au to provide metallogenic material. The highly variable oxygen fugacity might have suffered from significant contamination of the upper crust. Meanwhile, the application of the Ti-in-zircon thermometer exhibits high temperatures of 765~975℃ for zircons extracted from the Au-bearing altered monzogranite, indicative of dehydration melting of the lower crust. The zircons from Au-bearing quartz-sulfide vein have relatively lower crystallization temperatures of 641~823℃, suggesting crystallization of amphibole before zircon. The obtained zircon U-Pb ages of 350.4 ±1.6Ma for altered monzogranite and 348.9 ±1.4Ma for quartz-sulfide vein are interpreted as the magma crystallization age of the monzogranite, which is the main host rock of the deposit. The crystallization ages are earlier than previously reported metallogenic age, probably suggesting little relationship between the monzogranite formation and metallization of the Katebasu Au deposit.