SIMS U-Pb zircon geochronological and geochemical study of the Sn deposits in Tengchong, north of the Southeast Asian metallogenic belt: Implications for the timing of mineralization and ore genesis

Abstract

The Tengchong-Lianghe Sn polymetallic metallogenic zone is located in the northern segment of the Southeast Asian tectonic region. It is an important part of the Southeast Asian giant Sn metallogenic belt and contains two large Sn deposits: the Xiaolonghe deposit in the north and the Lailishan deposit in the central region. The Sn mineralization is closely spatiotemporally related to Mesozoic and Cenozoic granitic magmatic activity. In the Xiaolonghe and Lailishan Sn deposits, the Sn mineralization is closely related to biotite granites. The SIMS U-Pb zircon dating analysis of the host biotite granites, integrated with the LA-ICP-MS U-Pb data from cassiterite, precisely constrain the formation of mineralization at Xiaolonghe and Lailishan Sn deposits to 75–76 Ma, the Late Cretaceous, and 50–51 Ma, the Early Eocene, respectively. Major and trace element analyses show that the host granites from the Xiaolonghe and Lailishan deposits have high silicon contents and are rich in potassium, somewhat alkali and metaluminous to weakly peraluminous, and highly differentiated (DI = 91–93). The granites belong to the ilmenite series, which formed under reducing conditions. Zircon δ18O of 6.82–7.99‰ and 5.54–7.30‰ for the granites from Xiaolonghe and Lailishan deposits, along with the results of previous zircon Hf isotope studies and regional data, indicates that the Xiaolonghe granitic magma mainly originated from the ancient lower crust, whereas the Lailishan granitic magma is mainly dominated by a crustal source with a small contribution of mantle material. Combined with the regional geology, we propose, for the first time, the tectonically genetic model for the two episodes of Sn mineralization present in the Xiaolonghe and Lailishan deposits. During the amalgamation of the West Burma block and the Tengchong-Moulmein block in Late Cretaceous to Early Eocene, a series of high silicic, high-potassium calc-alkaline, metaluminous to weakly peraluminous and collision-related granitic magma, including the crustal source for the Xiaolonghe deposit and the crustal source plus a small amount of mantle material for the Lailishan deposit, experienced a strong differentiation during which abundant ore minerals precipitated and intruded into the country rocks along deep faults and associated fractures, resulting in the development of the Xiaolonghe and Lailishan Sn deposits.