Episodic emplacement of the Lingshan Granitic Complex and related two-stage molybdenum mineralization in the Dabie orogenic belt

Abstract

The Lingshan Granitic Complex consists of a granitic batholith and its proximal Mushan and Xiaofan porphyry stocks, and hosts stockwork-type Mo mineralization within the porphyry stocks and the fine-grained monzogranite, and several vein-type Mo occurrences in the coarse-grained porphyritic monzogranite. All these rocks show similar values of the whole-rock initial 87Sr/86Sr (0.70442–0.70987), εNd(t) (–17.2 to –11.0), and zircon εHf(t) (–27.2 to –9.3), indicating their derivation from partial melting of the Paleoproterozoic-Neoarchean recycled continental crust induced by basaltic underplating at the crust-mantle boundary. The zircon U-Pb and molybdenite Re-Os geochronological results indicate that the Lingshan Granitic Complex was formed by at least two pulses of magmatism at 140–137 Ma and 128–125 Ma, accompanied by two periods of Mo mineralization, which is the epitome of the peak granitic magmatism and related Mo mineralization in the whole Dabie orogenic belt. Combined with previous data, it can be concluded that the discontinuous and episodic nature of magma emplacement in the whole Dabie Mo metallogenic belt has significant consequences for large-scale, multi-staged Mo mineralization. Although Mo mineralization can occur in various lithofacies of the Lingshan Granitic Complex, the industrial Mo enrichment mainly lies within the small shallow emplacement granite porphyry stocks and subordinately within the fine-grained phase of the pluton. These features indicate that the Mo industrial enrichment is not only related to the highly evolved magma, but also more closely related to mechanism of magma emplacement. Rapid decompression induced by rapid ascent of the Mo-bearing granite porphyry stocks, and rapid crystallization of magma induced by quickly cooling due to conductive heat loss to the sidewalls of the fine-grained phase of the outer zone of the granite batholith, are favorable for the ore-fluid exsolution responsible for the magmatic-hydrothermal Mo mineralization.