Genetic link between concealed granite and tin mineralization in the Yuling tin deposit, Nanling Range, South China: Constraints from zircon and cassiterite U-Pb dating, geochemistry, and Lu-Hf isotopes

Abstract

The Nanling Range in South China is a world-renowned tin (Sn)-tungsten (W) metallogenic belt. The Yuling deposit is a representative Sn deposit newly discovered in the Nanling Range in recent years. The mineralization of Sn and accompanied Pb-Zn(-Sb) is controlled by faults and hosted in shallow metamorphic sandstone of the Cambrian, with concealed granitic intrusion in the deep. Here, we report for the first time precise in-situ U-Pb dating of zircon and cassiterite, petrogeochemistry, zircon trace element and Hf isotope data from the Yuling Sn deposit to clarify the genetic link between Sn mineralization and the concealed biotite granite. The U-Pb ages of the concealed granite and Sn mineralization are 155.1 ± 0.7 Ma and 154.4 ± 1.4 Ma, respectively, indicating that Sn mineralization occurred simultaneously with Late Jurassic granitic magmatism. Combined with the geological observation that Sn mineralization developed locally near the roof of concealed granite, further attests to the close genetic link between the Yuling Sn deposit and the deep-seated concealed granite. The zircon ε_Hf(t) values range from −5.14 to −1.37 (mean = −2.87), and the two-stage Hf mode ages (T_DM2) range from 1.29 to 1.52 Ga (mean = 1.38 Ga), indicating that the source rocks of the Yuling granite primarily originated from the remelting of ancient crustal rocks in the Mesoproterozoic of South China, with the involvement of some juvenile mantle-derived components. The Yuling granite exhibits high content of SiO₂, K₂O, K₂O + Na₂O, low content of MgO, CaO, Ba, Sr, Ni, Cr, relatively flat REE patterns and significant negative Eu anomalies. Petrographic and whole-rock geochemical data show that the Yuling granite has an A₂-type granite affinity and formed in an intraplate extensional setting of intense crust-mantle interaction similar to that of numerous A₂-type granites associated with Sn-W mineralization during the early Yanshanian in the Nanling Range. It may be related to the extension and thinning of the continental lithosphere and asthenosphere upwelling induced by northwestward subduction of the paleo-Pacific plate. Moreover, the factors controlling the Sn mineralization potential of granitic magma were evaluated using zircon trace elements and petrogeochemical data. These findings indicate that the Yuling granite crystallized from higher temperature, lower water content, F-rich, and highly-fractionated reduced granitic magma. Such granitic magma is conducive to generating Sn-rich fluids and has high Sn mineralization potential.