Petrogenesis,Mineralization Chronology And Genesis Study On The Mo Deposit Of The Haisugou Pluton,Inner Mgngolia

The Haisugou pluton is located in the southern part of the Daxing’anling orogenic belt.The Haisugou Mo deposit and the Xiaojingzibei Cu and Mo deposit occur in the pluton.At present,the origin of this pluton is still controversial and the difference between the two molybdenum deposits within this pluton has not been studied due to limited understanding of ore-forming materials.In this study,zircon U–Pb geochronological and geochemical data were utilized to decipher the origin of the Haisugou pluton.The S and Pb isotopic analyses were carried out on the metal sulfides in the Haisugou mining area,and Re–Os isotope studies on molybdenite in the mining area were conducted.The LA–ICP–MS zircon U–Pb dating results of the biotite granodiorite in the Haisugou molybdenum mining area show that it was emplaced at137.1±0.6 Ma and 143.6±0.8 Ma.The Re content of molybdenite in the Haisugou molybdenum deposit is 2.1×10^-6,and the molybdenite Re–Os model age is 143.9±2.9Ma.The dating result of LA–ICP–MS zircon U–Pb of the monzonitic granite in the Xiaojingzi copper-molybdenum deposit is 126.5±0.7 Ma.The granitoids in the Haishugou pluton belong to high-K calc-alkaline series I-type granite with metaluminous to peraluminous characteristics.They have SiO₂ content of 68.81–77.18wt.%,with K₂O+Na₂O ranging from 6.80 wt.%to 8.31 wt.%and CaO contents varying from 0.43 wt.%to 2.88 wt.%,and MgO ranging from 0.15 wt.%to 1.32 wt.%,and aluminum index（A/CNK）value varying from 0.97 to 1.07.Both rock types are relatively enriched in light rare-earth elements（La/Yb）_N=6.19–10.74 and the REE distribution pattern is right-dipping with a moderate negative Eu anomalies with aδEu value from 0.37 to 0.81.Combining with previous studies,It can be considered that the parental magma has experienced magma mixing and the fractionation crystallization may play a dominant role.The presence of MME in the pluton may indicate magma mixing or congenic products formed during the earlier stage.The timing of diagenesis and molybdenum metallogenesis of the Haisugou intrusive mass coincided with the time of the third phase of the large-scale diagenesis and mineralization within the Silamulun metallogenic belt,and the corresponding tectonic background was the transition of the tectonic system（from the extrusion environment to the tensile environment）to the lithosphere thinning environment.The δ³⁴S values of the main metal sulfides in the Haisugou molybdenum deposit range from 1.5‰to 2.8‰,and the Pb isotope ratios,²⁰⁸Pb/²⁰⁴Pb,²⁰⁷Pb/²⁰⁴Pb and²⁰⁶Pb/²⁰⁴Pb are 38.034–38.33,15.519–15.587,18.382–19.383,respectively.It is determined that the Haisugou molybdenum deposit has the same source of ore-forming materials as most molybdenum deposits in Inner Mongolia,and is a mixture of crust and mantle.The formation of unitary molybdenum ore in Haisugou molybdenum deposit is due to the dominant role of fractional crystallization during magma evolution.The mineralization of Cu in the Xiaojingzibei copper-molybdenum deposit may be stored in the magma with saturated volatiles,and the volatile matter of Cl（the fluid phase）carries the Cu elements to the shallow crust and undergoes enrichment and precipitation.The Haisugou molybdenum deposit and the Xiaojingzibei copper-molybdenum deposit belong to quartz vein types.