Magmatic Processes of Granitoids in the Hongniu-Hongshan Porphyry-Skarn Copper Deposit, Southern Yidun Terrane, China: Evidence from Mineral Geochemistry

The Hongniu-Hongshan porphyry-skarn deposit is located in the southern Yidun terrane in the Sanjiang Tethyan Metallogenic Domain (STMD). Although its metallogenesis has been well constrained in the past decade, the magmatic processes for granitoids in the Hongniu-Hongshan deposit are still poorly understood. Herein, we provide new geochemical data on magmatic minerals (plagioclase, amphibole, and clinopyroxene) in the Hongniu-Hongshan granitoids to get a better insight into these processes. The complex zoning patterns of plagioclase phenocrysts indicate magma recharge and mixing. Physiochemical estimations indicate that clinopyroxenes were crystallized in hotter (919 ± 11 °C) and more mafic (FeO: 2.8–4.6 wt.%, MgO: 0.8–1.8 wt.%) magmas in a deep chamber (18.6 ± 0.9 km) compared with the colder (819 ± 29 °C), more felsic (FeO: 0.9–2.2 wt.%, MgO: 0.3–0.6 wt.%) and shallow magma chamber (13.4 ± 1.6 km) in which amphiboles crystallized. Therefore, we suggest that magmatic minerals in the Hongniu-Hongshan granitoids were produced by multistage magmatic processes within the upper–middle crust range. In this model, the deep-seated magmas recharged into the shallow reservoir and mixed with the shallow magmas therein. The recharged hot magmas may provide heat sources and rejuvenate the shallow magma reservoirs. On this basis, we further infer that ore-forming materials could be pre-concentrated in the crustal range and mobilized by the Late Cretaceous magmatism in the southern Yidun terrane.