Mineralization Characteristics of the Laoliwan Ag-Pb-Zn Deposit and Geochemical Features of the Ore-Bearing Granite Porphyry in the Southern North China Craton:Implications for Ore Genesis

Li Xiaoming; Li Zhanke; Xiong Shengke; Gao Kai; Chang Jia; Li Jianwei

Abstract：The newly discovered Laoliwan large Ag-Pb-Zn deposit is located in the Xiaoshan district, southern margin of North China Craton, which is different from other types of Ag-Pb-Zn deposit in the area since the ore bodies are mainly hosted in the Laoliwan granite porphyry and controlled by the regional faults.The mineralization could be subdivided into two periods:the hydrothermal period and the supergene period.The hydrothermal period consists of four stages:the quartz-siderite stage, the quartz-pyrite stage, the quartz-polymetallic sulfide stage, and the quartz-carbonate stage.LA-ICP-MS zircon U-Pb dating results of two samples from the Laoliwan granite porphyry are 129.0±1.7 Ma and 129.0±1.1 Ma, respectively, indicating the granite porphyry intruded during Early Cretaceous.Based on the rock geochemical analysis, the granite porphyry is characterized by high silicon, high alkali, and weak peraluminous.The REE and trace elements characteristics display enrichment of large ion lithophile elements (LREE, Rb, Ba, Sr, Pb) and depletion of high-field elements (HREE, Nb, Ta, Ti, P) and moderately negative anomaly of Eu.These features are similar with other Early Cretaceous granites in the area, indicating the magmatic activities are probably related to contemporaneous tectonic transition and lithosphere thinning in eastern China.Based on mineralization characteristics and regional geochronological data, it is supposed that the Ag-Pb-Zn mineralization formed later than the granite porphyry and they have no direct genetic relationships.However, they may be the products of activities of the same deep magma chamber.This study of the Laoliwan Ag-Pb-Zn deposit suggests that the superposition of faults and granite rocks could be the prospective places for exploring Ag-Pb-Zn deposits in the Xiaoshan disctrit, which is confirmed by the recent prospecting work at Zhonghe which is in north of Laoliwan.Compared with Xiaoqinling and Xiongershan area, the exhumation of the Xiaoshan area is quite shallower.It is potential to find porphyry molybdenum deposit under the Ag-Pb-Zn ore bodies of Laoliwan.