Analysis Of Metallogenic Mechanism Of The Nabuding Lead-Zinc Deposit In Tibet

The Nabuding deposit belongs to the South Gangdise magmatic arc and is adjacent to the Shamolei-Maila-Luobadui-Milashan fault and the Gangdise back-arc fault uplift belt of the Gangdise arc in the north.The complex geological structure environment and superior metallogenic geological conditions make the Nadi deposit become a skarn-type lead-zinc deposit with certain metallogenic potential in the Gangdise metallogenic belt.Therefore,from the perspective of regional metallogenic geological background,taking Nabuding lead-zinc deposit in Tibet as the research object,comprehensive field geological survey,petrography,main trace elements,sulfide S-Pb isotope,quartz O H isotope,zircon U-Pb isotope and other analytical tests were conducted to try to identify The metallogenic mechanism and metallogenic structure background of lead-zinc deposits have important theoretical and practical significanc.The Nabuding deposit is a skarn Lead-zinc deposit.The mineralization is mainly distributed in the vicinity of the contact zone between the intermediate-acid magmatic rocks and the ocean island unit carbonate rocks in the second rocks of the Xionglai Formation.The strike is affected by the fault structure and is like a structural lens,which is consistent with the fracture zone and is near east-west or north-east and south-east.It mainly went through skarn metallogenic period,hydrothermal metal ogenic period and supergene metal ogenic period.Granodiorite with the feature of quasi aluminum weak metaluminous Shoshonite Rock Series,belongs to type I granite(Caledonian type),diorite with quasi aluminum calcium alkaline-alkaline medium-high potassium diorite series features,both may be formed also provided at the edge of the ocean basin,the magma originated from depleted mantle,and the land-shell material was added during the formation process,which corresponds to the low-angle subduction geodynamic enviroment.Basalt features calc-alkaline-alkaline low potassium tholeiite basalt,which may be formed in volcanic arc environment.The sulfur isotopes of the Nabuding deposit show that sulfur in the mineralized fluid mainly comes from magma,and the sulfur isotopic fractionation equilibrium is reached during the metallogenic process.Lead isotopes indicate that the lead source of the deposit is characterized by the co-supply of metallogenic material by lead in the upper crust and mantle.Hydrogen and oxygen isotopes indicate that the composition of the ore-forming fluid of the Nabuding deposit is mainly meteoric precipitation,but there may be a tendency of mixing meteoric precipitation and magmatic water with the evolution of mineralization to a single meteoric precipitation in the early stage of mineralization.The study and discussion on the diagenesis and mineralization mechanism of the Nabuding Pb-Zn deposit prove that the upper limit of the hydrothermal mineralization age related to the mid-acid intrusive rocks in the subduction background of the Gangdise metallogenic belt was advanced to the Early Jurassic,during which the mid-acid intrusive rocks were identified as important prospecting targets.