The Genesis And Tectonic Setting Of Shapinggou Porphyry Molybdenum Deposit

The Qinling-Dabie Orogenic belt, which is the world’s largest molybdenum mineralization zone, is located in the junction between the two blocks of North China and Yangtze. In recent years, we found Shapinggou porphyry molybdenum deposit in eastern section of the East Qinling-Dabie Orogenic belt. We present new LA-ICP-MS zircon U-Pb chronology, petrography, major and trace elements, Sr-Nd-Pb-Hf isotope data of the magmatic rocks, and studies on fluid inclusions and S、Pb、H-O isotope data in the Shapinggou porphyry molybdenum deposit. We made new progress through the study.1. Detailed LA-ICP-MS zircon U-Pb dating indicates that the crystallization age of the magmatic rocks in Shapinggou porphyry molybdenum deposit is Cretaceous (113-139Ma), inherited zircon ages are divided into Triassic, Neoproterozoic and Paleoproterozoic. The Re-Os calculated isochron age of molybdenum (112.7±1.8Ma) is agree well with the crystallization age of granite porphyry in potassic zone (113.9±1.9Ma), suggesting that molybdenum mineralization occurred in the late period of early Cretaceous.2. The field, microscopic, geochemical features and geochronological results of the magmatic rocks in the Shapinggou porphyry molybdenum deposit suggest that: granitoids in the Shapinggou porphyry molybdenum deposit are classified as K-rich and K-feldspar porphyritic calc-alkaline granitoid (KCG); the Cretaceous magmatic rocks in Shapinggou porphyry molybdenum deposit are related to orogen collapse after the collision following subduction/exhumation of South China Block. They are formed by partial melting of subduction of continental lithosphere during collisional orogenic belt thickening.3. The characteristics of fluid inclusions suggest that the homogenization temperature decreased from the early to the end. Ore-forming fluids were boiling at potassic alteration stage and phyllic alteration stage. The characteristics of fluid inclusions at late stage suggest that fluid system tended to open with the reduction of temperature and pressure at late stage. There may be the mixing of meteoric water at this time.4. The evolution of the gas phase composition of fluid inclusions also suggests boiling of the ore-forming fluids. some type Ⅰ fluid inclusions contain CO2, other type Ⅰ fluid inclusions do not contain CO2, type Ⅱ fluid inclusions also contain CO2, and type Ⅲ fluid inclusions only contain a little, which can be explained that at the time of boiling of ore-forming fluids, CO2and water are immiscible.5. Hydrogen and oxygen isotopic compositions are also within the range of magmatic water during the main mineralization. There may be the mixing of meteoric water at late mineralization, which is agreed well with the result of fluid inclusions. The sulfur isotopic measurements on ore sulfides (molybdenum) from Shapinggou porphyry molybdenum deposit show a magmatic source. The Pb isotopic compositions of molybdenum obtained to indicate the origin of ore show that they are mostly from the lower crust.