Zircon U-Pb-Hf and Trace Element Signatures Reveal the Petrogenesis of the Jiuyishan Granitic Complex, South China: Implications for W-Sn and Rare Metal Mineralization

The Jiuyishan granitic complex, located in the Nanling Range, South China, is composed of five granitic plutons (Xuehuading, Jinjiling, Pangxiemu, Shaziling and Xishan). Zircon U-Pb dating of four plutons (Jinjiling, Pangxiemu, Shaziling and Xishan) yielded similar ages of approximately 153 Ma, indicating indistinguishable ages within error. Three plutons except the Shaziling pluton, have consistent ε_Nd(t) (−7.8 to −5.8) and ε_Hf(t) (−9.1 to −2.2) values, which are similar to those of the lower crustal granulitic metasedimentary and meta-igneous rocks in South China. Compared to other three plutons, the Shaziling pluton has consistent ε_Nd(t) (−7.4 to −6.8) and ε_Hf(t) (−7.5 to −4.7) values and shows similar source, but the Shaziling mafic microgranular enclaves (MMEs) show variable ε_Hf(t) (−14.2 to 4.8) values, indicating a remarkable mantle magma injection of the Shaziling pluton. Zircon Ce/Sm-Yb/Gd, whole-rock CaO-P₂O₅ and CaO-TiO₂ linear trends reveal that from the Xishan to the Shaziling and from the Jinjiling to the Pangxiemu granites, they experienced apatite and titanite fractionation, respectively. Zircon Th, U, Nb, Ta, Hf, Ti, Y, P and rare earth element (REE) contents and whole-rock Sr, Ba and Rb contents also show that the Shaziling, Xishan, Jinjiling and Pangxiemu granites followed a discontinuous evolutionary series, but the Pangxiemu granites exhibit highly evolved nature. Four main controlling factors of W-Sn and rare metal mineralization in granitic rocks were discussed, and we found that the mineralization in Jiuyishan granitic complex was mainly controlled by the fractionation degree and crystallization temperature, but were rarely affected by oxygen fugacity and mantle material input. The Pangxiemu granites show particularly higher Rb and Ta contents than the other three plutons, implying that the ore deposits developed in the Jiuyishan Complex were directly related to the most evolved Pangxiemu pluton, with the occurrence of Rb and Ta as the most likely rare metal mineralization in the Jiuyishan District. A crystal mush model is proposed to interpret the petrogenetic and mineralizing processes of the Jiuyishan granitic complex.