Mid-Late Jurassic magmatism and its mineralization potential in the Dayaoshan district, southwest Qinhang metallogenic belt, South China

Abstract

The Mid-Late Jurassic is a significant period characterized by extensive magmatism and mineralization within the Qinhang metallogenic belt. However, the genesis and metallogenic potential of these Mid-Late Jurassic granitoids in the Dayaoshan district, the southwest part of the Qinhang metallogenic belt, remain inadequately investigated.

The Dayaoshan Mid-Late Jurassic granitoids primarily comprise the Fuqing granodiorite (161.5 ± 3.2 Ma), Dabang granodiorite (157.4 ± 2.4 Ma), Dabang granodiorite porphyry (155.9 ± 2.8 Ma), Shangdong granodiorite (153.7 ± 2.8 Ma), Fenghuang granodiorite (162.6 ± 1.1 Ma), and Yuanzhuding granite porphyry (154.3 ± 1.7 Ma). These rocks exhibit typical I-type affinity, marked by lower A/CNK values (0.9–1.1) and the presence of magnetite. Whole-rock Nb/Ta ratios (9.0–14.0), biotite major elements, apatite trace elements, Mg^# value (35–63), and zircon ε_Hf(t) (–19.7–4.2) and T_DM2 (2440–834 Ma) indicate that the Dayaoshan Mid-Late Jurassic granitoids likely originated from remelting Precambrian metamorphic crustal material with some mantle material inputting. The higher Mg^# value (52–63) and more positive ε_Hf(t) value (–6.3–4.2) of the Yuanzhuding granite porphyry, genetically associated with porphyry Cu-Mo mineralization, suggest it contains more mantle-derived material compared to other granitoids. Regarding magma evolution, apatite and/or whole-rock trace elements show that the Fuqing granodiorite is dominated by amphibole fractionation, while the Dabang granodiorite, Dabang granodiorite porphyry, and Shangdong granodiorite are characterized by plagioclase fractionation. Based on the existing research on the Mid-Late Jurassic tectonic-magmatic activities in the Qinghang metallogenic belt, it is inferred that the Dayaoshan Mid-Late Jurassic granitoids are products of asthenospheric upwelling caused by the subduction of the Paleo-Pacific plate. The Dayaoshan Mid-Late Jurassic granitoids, excluding the Yuanzhuding granite porphyry, generally exhibit characteristics of low differentiation, low oxygen fugacity, and crust-mantle mixed source, thereby excluding the possibility of associated W-Sn and Cu mineralization. The mineralization age (Mid-Late Jurassic) along with S–Pb–H–O isotope compositions of lode gold deposits in the Dayaoshan region support their genetic linkage with the Mid-Late Jurassic magmatism, consistent with high water and gold content and low differentiation of the Dayaoshan Mid-Late Jurassic granitoids (except Yuanzhuding). This research highlights a good prospect for lode gold deposits around the Mid-Late Jurassic granitoids in Dayaoshan.