Source Characteristics and Metallogenic Potential of Early Paleozoic Highly Fractionated Granites in the Lhasa Terrane

The discovery of the super-large Gari’atong Rb polymetallic deposit and the Jiagang W-Mo deposit in the central Lhasa terrane reveals the significant rare-metal potential of Cenozoic highly fractionated S-type granites. However, the rare metal metallogenic potential of the Early Paleozoic S-type granites, which are also extensively developed in this region, remains poorly understood. Therefore, this study systematically investigates multiple sets of Early Paleozoic granites from the central Lhasa terrane, utilizing whole-rock geochemistry and Sr-Nd-Pb-Hf isotopes to constrain their source characteristics and evaluate their metallogenic potential.

The results show that these granites formed between 530–480 Ma. They are characterized by high SiO₂(72–80 wt.%), peraluminous nature, strong negative Eu anomalies, and significant depletions in Sr and Ba, belonging to highly fractionated S-type granites. In addition, δCe values close to 1, along with generally low V/Sc and Cu/Zr ratios, collectively indicate that the magmatic system was in a non-high oxygen fugacity environment. Some samples exhibit notably low Nb/Ta and Zr/Hf ratios, closely resembling the geochemical fingerprints of typical Nb–Ta–Sn-W type rare metal mineralizing granites. Isotopically, the granites exhibit negative εNd(t)（-10.7~-5.9）values with significantly high initial ⁸⁷Sr/⁸⁶Sr ratios, and negative εHf(t)（-10~-2) values corresponding to two-stage Hf model ages of 1.3–2.3 Ga. Comparison with contemporaneous mafic rocks indicates that their material source was primarily ancient crust.

Integrating the above characteristics, this study concludes that the Early Paleozoic S-type granites in the Lhasa terrane represent a highly fractionated granitic system formed by partial melting of ancient crust in a collisional setting. They possess certain potential advantages for rare metal mineralization, providing a new prospecting direction for ancient metallogenic systems in the Tibetan Plateau.