Transcrustal magmatic system of highly fractionated granite in Lingshan, South China: Implications for rare-metal mineralization

The transcrustal magmatic system (TCMS) paradigm has significantly advanced the understanding of silicic magmatism, yet its application to highly fractionated granites and associated rare-metal mineralization remains underexplored. This study integrates petrological and geochemical analyses of the Lingshan complex in South China to reconstruct its TCMS and clarify its role in granite petrogenesis and rare-metal mineralization. The complex comprises central, marginal, and outermost units. The central unit, consisting of coarse-grained porphyritic granite (CPG), contains abundant phenocrysts (35−70 vol%) with complex zoning, constituting the primary mush zone of the magma reservoir. The marginal unit, composed of medium-grained granite, displays gradual petrological and geochemical transitions toward the CPG and features a chilled margin near country rocks, indicating its role as an early magma cap enclosing the mush. A fine-grained porphyritic granite (FPG) stock in the upper-middle part of the central unit progressively transitions from weakly fractionated at the margin to highly fractionated at the core, representing a solidified magma pocket formed by crystal-melt separation within the mush. Fine-grained granite network veins within the CPG are geochemically similar to the FPG, indicating melt transport in the reservoir. Magma replenishment, evidenced by abundant enclaves containing high-An plagioclase with fluorite inclusions, provides thermal energy and volatiles for prolonged reservoir evolution. The outermost unit, comprising mineralized medium- to fine-grained granite, is characterized by low Ba and Sr but high F and Nb/Ta, indicative of F- and Nb-rich melts and fluids derived from highly silicic magma. Pressure discrepancies (230−330 MPa in granites versus 280−560 MPa in enclaves) suggest the existence of multiple magma reservoirs at varying depths, collectively constituting the Lingshan TCMS. The TCMS governs granitic magma differentiation and rare-metal mineralization through source processes and multistage crystal-melt-fluid interactions.