U-Pb dating and trace element of titanite and garnet as indicators of the age and ore-forming condition of skarn W deposit: A case study of the Xiaoyao W polymetallic deposit in southern Anhui, China.

The Xiaoyao deposit is a newly discovered large-scale tungsten-polymetallic deposit in southern Anhui, China, and its precise magmatic-hydrothermal timing and ore -forming processes are still unclear. In this study, analyses of U-Pb dating and trace element of titanite and garnet from the Xiaoyao deposit were carried out. Multi-stage of titanite ( including magmatic titanite and hydrothermal titanite) were identified. Magmatic titanite coexist with quartz, magnetite, and feldspar, while hydrothermal titanite was closely related to quartz, calcite, molybdenite, and chalcopyrite. Both garnet and titanite in the Xiaoyao deposit contain a certain amount of U, with an average U content of 15. 9 x 10(-6) in garnet and higher U content ( > 100 x 10(-6)) in magmatic and hydrothermal titanites. U-Pb isotopic dating of garnet and titanite shows that both the magmatism and W polymetallic mineralization occurred at 150 Ma, confirming the genetic relationship between granodiorite and mineralization. The mineral assemblage of magmatic titanite, K -feldspar, quartz, and magnetite indicates that the Xiaoyao causative magma was derived from an oxidized and H2O -rich environment. Garnet from Xiaoyao is dominated by andradite and enriches in W and Sn, indicating that the early ore -forming fluids were oxidized. In addition, the high enrichment of High Field Strength element ( HESE) in the Xiaoyao hydrothermal titanite indicates that the hydrothermal fluid was formed in an alkaline and F-rich system, providing favorable hydrothermal conditions for tungsten, lead, zinc, copper, silver, and molybdenum polymetallic mineralization. In summary, garnet and titanite can effectively indicate the ages and characteristics of skarn-type W mineralization.