Geochemistry of the Neoproterozoic Qinglongdong leucogranite, Fanjingshan (Jiangnan Orogen, South China): Implications for Precambrian tungsten mineralization

The Neoproterozoic represents the earliest period of W(-Sn) mineralization in South China. Granitic magmatism and associated mineralization during this period developed in the Jiangnan Orogen, rendering this region critical for investigating the geochemical discriminants between barren and ore-related granitic systems. In this study, we conduct systematic investigations of the Neoproterozoic Qinglongdong (QLD) leucogranite (barren), and compare it with ore-related leucogranite from the Fanjingshan batholith in the Jiangnan Orogen. LA-ICPMS zircon U-Pb dating reveals that the QLD leucogranite crystallized at 829.8 ± 4.4 Ma. The granite is classified as an S-type granite, characterized by high SiO₂ contents (72.5-75.8 wt%) and peraluminous affinity (A/CNK >1.2 and presence of primary peraluminous minerals), absence of covariance between SiO₂ and P₂O₅ contents, relatively low zircon saturation temperature (655 oC to 726 oC), and reduced conditions (low Ce⁴⁺/Ce³⁺ ratios and logf_O2 values of zircon). Extensive fractional crystallization is indicated by the geochemical compositions of mica (Li positively correlated with Rb, Ta, Cs, and negatively correlated with Nb/Ta), the downward REE distribution of apatite, the whole-rock flat Chondrite-normalized REE pattern, extremely low ΣREE concentrations (7.13 ppm-31.3 ppm), and depletion of Eu, Ba and Sr. The ε_Hf(t) and ε_Nd(t) values range from -0.5 to -10.0 and from -4.6 to -10.2, respectively, with corresponding model ages of 1.8-2.4 Ga and 1.9-2.3 Ga. These features suggest derivation from partial melting of ancient metasedimentary basement rocks, followed by extensive magmatic differentiation. In comparison with Neoproterozoic ore-related granites in the Fanjingshan batholith, we propose that elevated W(-Sn) concentrations in the source region, a high degree of fractional crystallization, and interactions with fluid are key factors controlling Neoproterozoic W(-Sn) mineralization in the Jiangnan Orogen. Among these, late-stage magmatic-hydrothermal interactions were pivotal in the formation of mineralized granite.