Genetic links of porphyry Mo-epithermal Pb–Zn–Ag mineralization system: a case study of the Shipingchuan polymetallic deposit, South China

Compared with the porphyry Cu-epithermal Au mineralization system, detailed studies on the porphyry Mo-epithermal Pb–Zn–Ag–Au mineralization are rare due to limited exposures. The Shipingchuan polymetallic deposit, located in the South China Mo Province (SCMP) represents a typical example containing both porphyry Mo and epithermal Pb–Zn–Ag mineralization. The Mo mineralization mainly occurs as molybdenite-quartz veins in veinlets or as disseminated molybdenite within the potassic, silicic, and sericitic syenogranite. The Pb–Zn–Ag mineralization is characterized by veinlet-type sphalerite–galena–pyrite–quartz–calcite vein within the volcanic rocks accompanied with silicification and propylitization. Five molybdenite samples yield a Re–Os isochron age of 104.7 ± 0.7 Ma that is consistent with the zircon age (107.5 ± 2.1 Ma) of the ore-bearing syenogranite within errors. Together with previous reported Ar–Ar ages (106.6–121.8 Ma) of Pb–Zn–Ag related volcanic rocks, the Mo and Pb–Zn–Ag mineralization belong to a magmatic-hydrothermal event in the Early Cretaceous. Meanwhile, the total Re contents of molybednite range from 1.28 to 45.55 ppm, indicating the ore-forming materials were from a mixture between the mantle and crustal material. Moreover, previous sulfur isotopic values (3.7–4.3‰) of the pyrites from the porphyry Mo mineralization were consistent with the reported range of 4.0–6.1‰ of the sphalerites from the Pb–Zn–Ag mineralization, implying that the sulfur of two-types of mineralization was derived from magma. The above-mentioned spatial, temporal, and isotopic lines of evidence suggest that the Mo and Pb–Zn–Ag mineralization of the Shipingchuan deposit was formed from the same metallogenic system. In consideration of regional tectonic evolution history, we propose that the porphyry Mo-epithermal Pb–Zn–Ag mineralization formed in an extensional tectonic setting caused by the continued rollback and the eventual slab break-off of the subducting Paleo-Pacific plate.