The latest Yanshanian magmatic and metallogenic events in the middle-lower Yangtze River belt: Evidence from the Ningzhen region

The Ningzhen region in Jiangsu Province represents the easternmost magmatic region in the middle-lower Yangtze River belt. The formation of the polymetallic deposits has close genetic relationships with Early Cretaceous intermediate-acid intrusions. In this study, LA-ICP-MS zircon geochronology of two Mesozoic intermediate-acid intrusive rocks (including the Shima porphyritic granodiorite and Gaozi quartz diorite porphyry) in the Ningzhen region were systematically investigated. These new geochronological data demonstrate that the intermediate-acid magmatism in the Ningzhen region dates to approximately between 109 and 101 Ma. We present new ⁴⁰Ar-³⁹Ar phlogopite ages for the Cishantou skarn iron deposits that constrain the timing of the mineralisation in the Ningzhen region. The phlogopite in the Cishantou skarn deposits yielded a ⁴⁰Ar-³⁹Ar plateau age of 104±1 Ma. This result coincides with the ages of the Anjishan and Tongshan Cu (Mo) deposits in the Ningzhen region. Our high-precision geochronological data together with recent high-precision geochronological studies (such as zircon LA-ICP-MS U-Pb, zircon SHRIMP U-Pb, molybdenite Re-Os and single-mineral ⁴⁰Ar-³⁹Ar dates) reveal that there were four periods (152–135 Ma, 135–127 Ma, 127–121 Ma, 109–101 Ma) of magmatism and ore formation in the middle-lower Yangtze River metallogenic belt. The Mesozoic intermediate-acid magmatism and mineralisation in the Ningzhen region belong to the latest episode in the middle-lower Yangtze River metallogenic belt.