Miocene Pb-Zn Mineralization in the Eastern Gangdese Metallogenic Belt: Evidence from in situ Rb-Sr Dating of Mica and Trace Element Geochemistry of Sphalerite

Four Pb-Zn deposits, namely Bangpu (BP), Digei (DG), Nabuding (NB) and Cuoga (CG), are located within a 20 km distance of each other in the Gangdese porphyry copper belt (GPCB). The age and nature of the Pb-Zn mineralization, especially its relationship to magmatism, remain uncertain. In order to address this issue, mica from the four deposits was selected for in situ Rb-Sr dating, with sphalerite additionally being selected for in situ trace element analysis. Detailed geological research has revealed that the BP and NB deposits are primarily skarn-type Pb-Zn mineralization, while DG and CG are associated with magmatic hydrothermal breccia and are characterized by banded-type mineralization. The Rb-Sr isochron ages of syn-mineralization muscovite at the BP and CG deposits are 11 ± 6 Ma and 19.7 ± 0.7 Ma respectively. Fe, Cd, In, Mn and Sn occur as lattice substitutions in sphalerite from the four deposits. Cu exists as microinclusions in BP, but occurs isomorphically in the DG, NB and CG deposits. The formation temperatures of the four deposits, as calculated from sphalerite geothermometry, range from approximately 200°C to 300°C, indicating that they belong to medium temperature deposits. BP and NB are classified as skarn Pb-Zn deposits, while DG and CG are categorized as hydrothermal filled Pb-Zn deposits. These results suggest that, in addition to porphyry Cu mineralization, the GPCB also contains significant Miocene Pb-Zn mineralization.