Geology And Geochronology Of The Haobugao Skarn Pb-Zn Deposit In Inner Mongolia,China

Haobugao Pb-Zn deposit is a typical skarn deposit located in Bahrain Zuoqi,Inner Mongolia.It is a representative large deposit in the Huanggangliang-Ganzhuermiao metallogenic belt.In this paper,through the study of petrology and ore geochemistry in the Haobugao Pb-Zn polymetallic deposit,we get the following conclusions:1.The Haobugao lead-zinc polymetallic deposit occurs in the contact position of the Cretaceous granite and the Dashizhai Formation.Ore bodies are controlled by the marble stratum.The fold fault develops in the mining area,and its NE-trending fault is the main metallogenic structure.2.The Haobugao mineralization can be divided into two metallogenic epochs and five metallogenic stages:(1)early skarn stage;(2)late skarn stages;(3)oxide stage;(4)early sulfide stage;(5)late sulfide stage.3.Trace element composition of zircon from the Haobugao deposit found: Chondrite-normal REE patterns show significant positive Ce anomalies and negative Eu anomalies and steep MREE-HREE patterns.The positive correlations between U and Th,Nb and Ta,indicate the zircon crystalize from the cogenetic magma.Zircon data plot predominately in the U-Yb versus Hf(and Y)field of continental zircon.Using zircon oxygen fugacity empirical equation,the data points of zircon mainly fall within the field near FMQ.4.Three distinct generations of garnets were identified in Haobugao,main andradite less grossular and a little pyralspite,the petrographic observations of Haobugao garnets reveal that oscillatory zoning patterns are common.5.The La-Icp-Ms U-Pb dating of zircon from mineralization-related granite porphyry in Haobugao deposit indicates that the mineralization age range from 136-142 Ma which is consistent with the molybdenite Re-Os isochron age(140.3±3.4Ma),which indicate that the Haobugao mineralization occurred in the Early Cretaceous epoch.