Multiple skarn generations related to composite leucogranites in the Cuonadong Sn-W-Be deposit, Himalaya

Abstract

The newly discovered Cuonadong Sn-W-Be skarn deposit is related to fractionated leucogranitic intrusions hosted in the Cenozoic Himalayan gneiss dome, Tibet, however, temporal and genetic relationships between composite magmatism, skarn and mineralization remain unclear. Based on age and compositional features, three types of titanite were identified: Ttn1 and Ttn2 in the diopside-dominated skarn and adjacent greisenized granitic dike, and Ttn3 (subdivided into Ttn3a and 3b) in the Sn-mineralized garnet skarn. Ttn1 has a higher Ti content and yielded a U-Pb age of ∼35 Ma, consistent with the U-Pb ages of monazite from the pegmatitic granite (35.0 ± 0.6 Ma). Younger, recrystallized Ttn2 (∼28–27 Ma) is characterized by higher Al, F, Ta, Nb, Sn and Y contents and was likely formed by interaction between early Ttn1 and late fluids as indicated by the monazite U-Pb age of two-mica granite (28.8 ± 0.3 Ma). These two types of hydrothermal titanite are confined to the Oligocene unmineralized skarn and adjacent greisenized granitic dike.Titanite from the garnet-bearing Sn-mineralized skarn (Ttn3) provides the age of mineralization (16.8 ± 1.6 Ma), slightly younger than the emplacement age of the Miocene granite (monazite U-Pb age: 19.9 ± 0.3 Ma and columbite: 19.0 ± 0.4 Ma). The Sn-rich Ttn3b coexisting with garnet and interstitial cassiterite shows a deficit of Y and HREE and a high (Dy)N/(Yb)N ratio, implying that hydrothermal Sn metasomatism of Ttn3 occurred after garnet crystallization. Overall, our results shows that the Cuonadong multigenerational skarns were generated during three episodic magmatic-hydrothermal events, and mineralization occurred in the Miocene.