Geological Characteristics And Exploration Direction Of The Pb-Zn Deposit In Xianiqu,Tibet

Xianiqu lead-zinc deposit is a hydrothermal vein type lead-zinc deposit located in the north of the Ag-Pb-Zn metallogenic belt in the north margin of Gangdese.Through the systematic study of deposit geology,petrogeochemistry,ore-forming fluid and material sources,this paper improves the genetic model of the deposit and points out the direction for further ore-prospecting work.The outcrop strata are mainly metamorphic clastic rocks of the Yongzhu formation of the lower carboniferous and volcanic rocks of the Dianzhong formation of the paleocene.A northward-southward thrust system consisting of three thrust faults and one normal fault.The ore bodies occur as veins in the northern fault fracture zone.The ore is of primary sulfide type.The mineralization process can be divided into five stages:quartz-epidote-chlorite stage,quartz-pyrite-chalcopyrite stage,galena-sphalerite-quartz stage,manganese-manganese calcite-quartz stage and calcite-quartz stage.Apart from the andestic and rhyolitic volcanic rocks in the Dianzhong formation,the magmatic rocks in the mining area also contain intrusive granite porphyry,which is closely related to mineralization.Granite porphyry belongs to peraluminous shoshonite series,light rare earth strong enrichment,Eu negative anomaly,the enrichment of Rb,Ba,Th,U large ion lithophile elements,and strong loss of Nb,Ta,Ti,P high field strength elements is apparent,the Sr also strongly losses.Zircon U-Pb age was 59.32±0.6 Ma,?Hf?t?has a value of-5.13?-2.46,the average of 3.87,shows that source area is mainly for shell source,mixed with a small amount of mantle source material.Fluid inclusions in different stages of the metallogenic types is mainly with L-V two phase inclusions,uniform temperature is 200??375?,salinity is 2.24%NaCl eqv?13.18%NaCl eqv,density is 0.57?0.92 g/cm³,in the overall performance shows low temperature and low salinity of fluid,and the tendency of decreasing from the early stage to late stage.The ?¹³Cv-PDB of the calcite in the five stages is-4.4‰?-0.2‰ and the ¹8Ov-SMOW is 4.7‰?11.5‰,indicating that the ore-forming fluid is mainly magmatic water with the addition of meteoric water.The sulfide³4S value is-0.7‰?4.0‰,and the average value is 2.43‰,indicating that sulfur is a single source of magma sulfur.The Pb isotope ratio of ²⁰⁶Pb/²⁰⁴Pb was 18.665?18.726,with an average of 18.695.²⁰⁷Pb/²⁰⁴Pb ranged from 15.727 to 15.788,with an average value of 15.758.²⁰⁸Pb/²⁰⁴Pb was 39.294?39.464,with an average value of 39.352,indicating that the lead came from the source area of the upper crust.The comprehensive results show that the Xianiqu Pb-Zn deposit is a hydrothermal vein type Pb-Zn deposit controlled by structure,which is closely related to granite porphyry intrusion,and has a similar metallogenic model with the peripheral vein type lead-zinc deposit of the Narusongduo deposit,which belongs to the same Gangdese Pb-Zn metallogenic belt.Therefore,it is speculated that there may be more potential ore bodies,such as cryptoexplosive breccia type and skarn type in the deep.The next step of prospecting should be to investigate the conditions of deep metallogenic and surrounding rocks.