Geological Characteristics And Metallogenic Tectonic Setting Of Changlingzi Pb-Zn Deposit In Inner Mongolia

The Changlingzi Pb-Zn deposit is located in Keshenketengqi,Chifeng City,Inner Mongolia.It is a newly discovered small skarn type deposit in the southern Great Xing'an Range metallogenic belt,consisting of two ore blocks.The orebodies hosted mainly in the Lower Permian Zhesi Formation and are controlled by fracture and interbedded fracture zones.Field research,crosscutting relationships,and petrographic observations indicate that the Changlingzi deposit has undergone two periods of hydrothermal mineralization:skarn and sulfide.The skarn period is classified into a stages:skarn stage?I?.The skarn period is classified three stages:Pyrrhotite–pyrite–chalcopyrite–quartz stage?II?,Sphalerite–galena–quartz±calcite stage?III?and Sphalerite–calcite stage?IV?.Fluid inclusion studies indicate that the same types of fluid inclusions occur in stage I and II,including liquid-rich aqueous inclusions?L-type?,vapor-rich inclusions?V-type?,and daughter-mineral-bearing three-phase inclusions?S-type?.Only L-type FIs were identified in the stage III and IV.The ore-forming fluids were medium-to high-temperature?Th=239.8⁴71.6°C?,high-salinity?32.08⁵8.22 wt.%NaCl eq?heterogeneous NaCl–H₂O fluids during the early stage,and it eventually evolved to low-temperature?Th=120.5²32.2°C?,low-salinity?0.7⁷.58%wt.%NaCl eq?homogeneous NaCl–H₂O fluids by late stage.Studies of the hydrogen,oxygen and carbon isotope compositions show that the ore-forming fluids gradually evolved from magmatic water to meteoric water.Sulfur and lead date suggest that the ore-forming materials were probably derived from magma and the Permian strata.The zircon U-Pb geochronology results show that the ages of the orthophyre,k-feldspar granite porphyry,and biotite granite porphyry in the ore district are 251.9±2.5Ma,140.45±0.89 Ma and 140.2±0.89 Ma,respectively.Their intrusion sequence is orthophyre?k-feldspar granite porphyry?biotite granite porphyry?.The Early Triassic orthophyre belongs to the origin of the adakitic rock,with the characteristics of medium-K calc-alkaline series and weakly peraluminous rocks.It is enriched in LILEs and LREEs and depleted in HFSEs and HREEs,and display high Sr/Y ratios.It may form form magmas generated by partial melting of thickened region of the lower crust,being related to the subduction of the Paleo-Asian Ocean.Early Cretaceous k-feldspar granite porphyry and biotite granite porphyry are the genesis of A-type granites,with high-k calc-alkaline series and metaluminous to weakly peraluminous rock features.They enrich in LILEs and LREEs and depleted in HFSEs?Ti,Nb and Ta?,and form under the extensional environment at post collision setting.Combined with regional metallogenic events and geological features of the ore region,Zn-Pb mineralization of the changlingzi ore district is spatially associated with Late Early Cretaceous granite porphyry.Therefore,the Changlingzi deposit is considered to formed under the extensional tectonic setting at post collision setting of the Early Cretaceous.