Rb–Sr dating and S–Sr–Nd isotopic constraints on the genesis of the Hehuashan Pb–Zn deposit in the Middle–Lower Yangtze River Metallogenic belt, China

Abstract

The Hehuashan sediment-hosted Pb–Zn deposit is a large-scale (Pb + Zn＞1 Mt) deposit hosted in the Tongling mining district of the Middle-Lower Yangtze River belt (MLYB). The Pb–Zn ore bodies are composed of two main mineralization types, namely breccia type and massive type. The breccia type ore bodies are hosted by the Triassic limestone and dolostone, while the massive ore bodies are hosted by marble dolostone which are close to the diorite intrusions. The previous research showed that the Hehuashan Pb–Zn deposit is a Mississippi Valley-type (MVT) deposit formed in Middle Triassic and overprinted by late mineralization of magmatic-hydrothermal fluids in Yanshanian period. In this research, we aimed to declare the age of the late mineralization and it's relationship with diorite intrusions. The mineralization age (132.8 ± 3.1 Ma) of the massive ore rocks (late mineralization) is similar to the zircon U–Pb age of the diorite (133–130 Ma), showing that this type mineralization is contemporaneous to the Yanshanian intrusive events. Furthermore, similar initial ⁸⁷Sr/⁸⁶Sr values between sphalerite and diorite indicating a magmatic fluid was involved during the mineralization process and the emplacement of diorite also might have provided ore-forming materials. The heavy sulfur compositions (δ³⁴S = +8.6‰ to +12.8‰) of the sphalerite in massive ore rocks indicate that the sedimentary sulfate may have provided reduced sulfur for sulfides precipitation by sulfate thermochemical reduction process. Sr–Nd isotopic compositions of the diorite in the Hehuashan deposit area showed that the massive Pb–Zn mineralization was related to the intrusion of diorite in an extensional tectonic setting. In summary, the Hehuashan Pb–Zn deposit composes a late Yanshanian Pb–Zn mineralization event and represents a younger Pb–Zn mineralization in the Tongling district and MLYB. The Triassic carbonates have the potential for Pb–Zn deposit exploration in the Tongling district and Middle–Lower Yangtze River belt.