Petrogenesis of the Yupo W-bearing and Dali Mo-bearing granitoids in the Dayaoshan area, South China: Constraints of geochronology and geochemistry

The geological significance of Early Paleozoic (Caledonian) magmatism and associated mineralization in South China is, as yet, poorly understood compared to the well-documented Mid-Late Mesozoic (Yanshanian) magmatism and associated mineralization. The Early Paleozoic granitoids were previously thought to be rarely mineralized. Both Caledonian granitoids and Yanshanian granitoids occur in the Dayaoshan area from the Qin–Hang metallogenic belt, South China. Zircon U–Pb ages of granodiorite at the Yupo skarn W deposit and the monzonite and granodiorite at the Dali porphyry Mo deposit, all I-type granites, analyzed by Sensitive High Resolution Ion Micro-Probe (SHRIMP) and/or laser ablation inductively coupled mass spectrometry (LA–ICP–MS) are 441.9 ± 1.9 Ma (2σ), 104.6 ± 1.6 Ma (2σ) and 105.3 ± 1.4 Ma (2σ), respectively. Both elevated zircon δ¹⁸O_V-SMOW values (5.8–7.7‰) and negative ε_Hf(t) values (−3.2 to −0.2) indicate that these plutons formed via partial melting of a Mesoproterozoic continental crust with minor mantle materials. The Caledonian W-bearing Yupo granodiorite is relatively reduced (FMQ−0.57), whereas the Yanshanian Mo-bearing granodiorite at Dali (FMQ+1.11) is more oxidized than the associated ore-barren monzonite (FMQ+0.52). Thus, it is likely that the contrasting mineralization between the two plutons was controlled by redox states of granitic magmas.