Geochronology, Petrology, and Genesis of Two Granitic Plutons of the Xianghualing Ore Field in South Hunan Province: Constraints from Zircon U-Pb Dating, Geochemistry, and Lu-Hf Isotopic Compositions

Two small-sized granitic plutons, outcropped in Xianghualing ore field, South Hunan (South China), have a close relationship with the super large-scale Sn-W polymetallic mineralization in this ore field. The Laiziling and Jianfengling plutons are composed of medium- to coarse-grained two-mica and coarse-grained biotite granites, respectively, and have zircon U-Pb ages of 156.4 +/- 1.4 Ma and 165.2 +/- 1.4 Ma, respectively. Both of the Laiziling and Jianfengling granites are characterized by extremely similar elemental and Lu-Hf isotopic compositions with high contents of SiO2, Al2O3, Na2O, K2O, high A/CNK ratios, negative epsilon(Hf)(t) values (ranging from -3.86 to -1.38 and from -5.44 to -3.71, respectively), and old T-DMC ages (ranging from 1.30 to 1.47 Ga and from 1.32 to 1.56 Ga, respectively). These features indicate that they both belong to highly fractionated A-type granites, and were formed in an extensional setting and from the same magma chamber originated from the Paleoproterozoic metamorphic basement of South China with a certain amount of mantle-derived magma involved with temperatures of ca. 730 degrees C and low oxygen fugacity.