Caledonian Sn Mineralization in the Yuechengling Granitic Batholith, South China: Geochronology, Geochemistry, Zircon Hf Isotopes, and Tourmaline Chemistry and B Isotopes of the Lijia Sn Deposit and Its Hosting Granites

The Lijia Sn deposit, located in northeastern Guangxi Zhuang Autonomous Region of south China, occurs on the eastern margin of the Yuechengling granite batholith. The Sn deposit contains quartz vein type and greisen type ores and is spatially associated with the medium-coarse-grained biotite granite and the fine-grained tourmaline-bearing biotite granite. LA-ICP-MS zircon U-Pb dating gave an emplacement age of 431.7 ± 2.5 Ma for the medium-coarse-grained biotite granite and of 430.2 ± 2.4 Ma for the fine-grained tourmaline-bearing biotite granite. LA-ICP-MS cassiterite U-Pb dating yielded Tera-Wasserburg lower intercept ages of 429.1 ± 3.4 Ma and 425.7 ± 3.3 Ma for the quartz vein type and greisen type ores, respectively. The ages demonstrate near coeval Caledonian granitic emplacement and Sn mineralization events that have been considered uncommon in south China. Both granites might be derived from partial melting of the Paleoproterozoic basement, as evidenced from zircon ɛHf(t) values of −3.13 to −10.31 and TDM2 from 1627 Ma to 2134 Ma. Three different types of tourmalines have been identified, including (1) tourmaline in quartz–tourmaline nodules in the fine-grained tourmaline-bearing biotite granite (Tur 1), (2) tourmaline in quartz veins (Tur 2a), and (3) tourmaline in greisen (Tur 2b). Most of the tourmalines belong to the alkali group and the schorl-dravite solid-solution series. The hydrothermal tourmalines of Tur 2a and Tur2b showed similar δ11B values to those of the Tur 1 tourmalines in the fine-grained tourmaline-bearing biotite granite, suggesting ore-forming materials derived from granitic magmas. The hydrothermal tourmalines of Tur 2b had slightly lower δ11B values than Tur 1 and Tur 2a tourmalines as a result of progressive 11B depletion during early tourmaline crystallization.