Study On The Genesis Of Delite Fluorite Lead Polymetallic Deposit In East Kunlun Orogenic Belt,Qinghai Province

The East Kunlun orogenic belt is located in the northeastern part of the Qinghai-Tibet Plateau,in the western segment of the Central Orogenic System.There are many deep EW-trending faults in the orogenic belt.Among them,the Kunbei fault and the Kunzhong fault divide the East Kunlun orogenic belt into the Kunbei Caledonian back-arc rift zone,the Kunzhong basement uplift granite belt and the Kunnan composite collage.The Delite Fluorite-lead Polymetallic Deposit is located in Dulan County,Qinghai Province,in the Kunnan composite collage belt in the East Kunlun orogenic belt,gold,jade(rare,rare earth)metallogenic belt.The exposed strata in the mining area include the Meso-Neoproterozoic Wanbaogou Group,the Carboniferous Halaguole Formation,the Haoteluowa Formation,the Triassic Babaoshan Formation and the Quaternary.The structure of the mining area is mainly a NWW compressional torsional fault structure,which controls the output of the ore body.The magmatic rocks in the mining area have strong intrusive activities,mainly Caledonian-Indosinian acidic intrusive rocks.At present,6 ore bearing alteration zones are found in the mining area,mainly No.I ore bearing alteration zone,including 8 fluorite ore bodies,10 Pb ore bodies and 3 Pb fluorite composite ore bodies.Ore minerals can be divided into non-metallic ore minerals and metal ore minerals.The ore minerals in non-metallic ores are mainly fluorite,the ore minerals in metal ores are mainly galena and sphalerite,and the gangue minerals are quartz,calcite,kaolinite,chlorite and sericite.Wall rock alteration includes silicification,kaolinization,chloritization and carbonatization.The mineralization in the mining area is divided into three stages,and the main mineralization stages are quartz galena stage and quartz fluorite stage.The temperature measurement of fluid inclusions shows that the ore-forming fluid has the characteristics of low temperature(107?180?),low salinity(0.18%?9.07wt.%NaCl eqv)and low density(0.930?0.991 g/cm³).It belongs to the hydrothermal solution of NaCl-H₂O system.The calculated ore-forming pressure is 7.15?15.55 MPa and the ore-forming depth is 715?1555m.S isotope shows that crust derived components may have been added during the emplacement of mantle derived magma,and H-O isotope shows that the ore-forming fluid is mainly atmospheric precipitation.In this study,the LA-ICP-MS zircon U-Pb chronology test of the newly discovered granite porphyry rock mass in the lower part of the ore body in the mining area determines that its age is 155±11 Ma,which is the late Jurassic,and it is considered that the formation time of the deposit is 155±11 ma.In conclusion,the fluorite precipitation mechanism is that the ore-forming fluid reacts with the surrounding rock,and the deposit is obviously controlled by rock mass and faults.Combined with the field geological characteristics,fluid inclusions,H-O and s stable isotope characteristics,the genetic type of Delite Fluorite Lead-polymetallic Deposit is a low-temperature hydrothermal vein deposit jointly controlled by rock mass and structure.