Zircon U-Pb age, geochemical characteristics and metallogenic significance of ore-bearing porphyry of the Jiawula Ag-Pb-Zn deposit in Inner Mongolia

The Jiawula Ag-Pb-Zn deposit is one of the large-sized Ag-Pb-Zn deposits in the Deerbugan Cu (Mo) -Ag-Pb-Zn metallogenic belt of Da Hinggan Mountains.The authors carried out chronological and geochemical study of granitic porphyry and quartz porphyry related to mineralization.The zircon U-Pb age of granitic porphyry is 141.9±0.50 Ma (MSWD=1.2), suggesting Early Cretaceous.Petrogeochemical characteristics show that granitic porphyry and quartz porphyry belong to quasi-aluminous-weak peraluminous, high-K calc-alkaline series to shoshonite series, that the porphyry is enriched in large ion lithophile elements (LILE) Rb, K and incompatible high field strength elements (HFSE) U, Th, Pb, depleted in large ion lithophile elements (LILE) Sr, Ba and strongly depleted in high field strength elements (HFSE) Ti, Nb, Ta, which indicates that the porphyry is the product of magma with the mixing of mantle melt and new crustal melt.The ore-bearing porphyry in the Jiawula mining area might have been formed in the post-collisional extensional environment which was transformed from collisional orogenic environment to non-orogenic intraplate environment after the closure of the Mongolian-Okhotsk Ocean.The authors hold that the granitic porphyry and the quartz porphyry were more likely to be the channels between the deposit and the deep magma chamber which provided mineralizing materials and hydrothermal fluids.The water-rich melt facies which was differentiated from the deep magma chamber formed quartz porphyry and granite porphyry in the shallow part of the crust in the late stage, and fluids continuously dissolved from the melt facies to form the Jiawula deposit in the periphery of the porphyry.