Reworking of a Caledonian (Early Paleozoic) granodiorite porphyry in a collisional zone in South China and its contribution for tungsten mineralization

A newly discovered ore-bearing granodiorite porphyry in the Chuankou tungsten (W) ore field is the largest W deposit formed during the Indosinian (Triassic) collision event in South China. As such, its genesis and relationship to W mineralization in the region remains ambiguous. Zircon U–Pb dating demonstrates that the Chuankou granodiorite porphyry was emplaced at 436.1 ± 0.8 Ma, predating the Triassic W mineralization in the ore field. The granodiorite porphyry is characterized by low Zr + Nb + Ce + Y concentrations (100–294 ppm), 10000 Ga/Al values (2.09–2.62), indicating that it is a weakly fractionated I-type granite. Variably negative ε_Hf(t) values of −10.2 to −2.48 and T_DM2 values of 2.06–1.06 Ga suggest crystallization from a partial melt of amphibolite, with minor contributions of metasedimentary rock in the middle–lower crust during the Caledonian collisional event. Given its low degrees of differentiation, the Chuankou granodiorite porphyry is inferred to have low mineralization potential. The presence of abundant fluorite in the granodiorite porphyry, coupled with elevated whole-rock F contents (0.4–4.1 wt%), suggests that volatile (F) involvement in Indosinian W mineralization might partially originate from the Caledonian granodiorite porphyry. Furthermore, the elevated whole-rock W contents, which exceeds those of granites related to W mineralization from regional (including Indosinian granites in the Chuankou W ore field), and other regions worldwide, indicate that W in the granodiorite porphyry was likely added to the ore-forming fluids during Indosinian magmatic–hydrothermal events. Consequently, we infer that W in the Caledonian Chuankou granodiorite porphyry was mobilized by F-rich fluids and potentially served as a partial source for the Indosinian mineralization.