Study On The Genesis And Prospecting Direction Of Polymetallic Deposits In The Zexue Area,Tibet

In this paper,three typical deposits in the Zexue area,Tibet(Dexin Pb-Zn deposit,Zhazhalong Pb-Zn deposit,and Narusongduo Pb-Zn deposit)were selected as the research objects.Combined with the geological characteristics of above deposits,we conducted a series of studies,including the mineralogy,zircon U-Pb geochronology,rock geochemical,fluid inclusions,and H-O-S-Pb isotopes,in order to find out the genesis of the deposits,and discuss the metallogenic mechanism.Based on these studies,we summarized the deposit types and metallogenic regularity,build the metallogenic model,and conduct geochemical anomaly selection.The results are as follows:1.Summarize the typical ore deposit geological characteristics and metallogenic geological condition in the Zexue areaIn the Dexin?zhalong Pb-Zn deposits,orebodies occur in the structural fracture zone,which control the ore distribution and supply the space for the ore deposit.Those structures,especially the mutiperiodic activity of structure and two groups of faults intersection,composite parts,such as E-W fault and N-W fault,are favorable for mineralization.In the Narusongduo Pb-Zn deposit,the ore bodies in the east of the ore-district develop in the contact zone of granite porphyry and volcanic rock,and the breccia tube and the half-life crevasse are the main ore-bearing structures,The orebodies in the west of the ore-district occur in the skarn belt developed in the contact zone between the quartz and the lower strata.2.Conduct the zircon U-Pb analysis of the main rocks in the deposits(Dexin,Narusongduo,and Zhazhalong)within the Zexue area,which provides a reference for the limitation of the metallogenic age.The Linzizong volcanic rocks record the India Asia continent collision process.The volcanic rocks of Dianzhong Formation display the continental arc characteristics,which also show similarities with those of the subduction igneous rocks.The volcanic rocks of Dianzhong Formation formed in the Palaeocene stage(61.7 Ma),whereas the two satges of porphyry rocks formed at 61.56 ~ 63.38Ma(early Paleozoic)and 58.54 ~ 60.36 Ma(middle new epoch).The ore-related age of the quartz diorite in the Dexin depsoit is(56.81 + 0.39)Ma,and the ore-related age of the quartz diorite in Zhazalong depsot is(62.99 + 0.94)Ma.The porphyry in the east of Narusongiduo mine is formed at 58.54 ~ 60.36 Ma,and the age of porphyry in the west of ore-district is 61.56 ~ 63.38 Ma.The porphyries stated above show similarities with other,and also have some differences in the lithology,mineralogy,and geochemical characteristics.However,the similar rock-forming ages,and coexisting characteristics in the Zexue area indicate they were controlled by the same tectonic-magmatic thermal event that related to the main collision of India and Eurasia.3.Find out the genesis of typical Pb-Zn deposits in the Zexue area,and discuss the metallogenicv mechanism.The dexin and Zhazhalong Pb-Zn deposits belong to the same type deposit that is typical of the medium temperature hydrothermal type lead-zinc deposit.The Narusongduo deposit consist of two types ore-bodies,of which the eastern orebody is the cryptoexplosive breccia type lead-zinc deposit and the western orebody belong to the skarn Pb-Zn deposit.4.Ensure the main metallogenic type in the Zexue area,establish the regional metallogenic model,summarize the metallogenic regularities and ore controlling factors,and provide the prospecting direction.The main ore deposit types in the study area are mainly the hydrothermal vein type Pb-Zn polymetallic(Dexin,Zhazhalong deposits),followed by the skarn Pb-Zn polymetallic type(Narusongduo and Zongrongqu deposits),and the cryptoexplosive breccia type Pb-Zn polymetallic(Narusongduo deposit).The metallogenic models are as follows:Since from the late Cretaceous,the rollback of the subducted Neo-Tethys ocieanic slab caused the oceanic slab dehydration,leading to the partial melting of the mantle Wedge.The underplated basaltic magmas induced the remelting of ancient Lhasa crust,Which generated large amounts of parent magmas.Generally,the parent magmas provided the initial source for the Linzizong volcanism and subsequent mineralization.Parts of the ore-froming fluids driven by temperature and pressure along migrated along the faults beside the volcano mechanis.When encountering Carbonate-Permian the carbonate,they Would form the skarn Pb-Zn deposits.The ore-forming fluid generated by the magmatic crystallization and differentiation usually migrated along the deep fauts.The ore-forming fluids continued to transport along the fault structures under the drive of thermal power and regional tectonic stress,and finally assembled at the leading edge of fractures due to the resistence of the overlying rocks.Subsequently,the cryptoexplosion occurred When the pressure decreased abruptly,and formed the cryptoexplosion breccia type Pb-Zn-Ag-(Au)deposits.The contitued migrated ore-froming fluids Would precipitate at the secondary fault structures(caldera,ring and radial fractures)When the metallogenic environment changed.Hence,they Would formed the hydrothermal veined Pb-Zn-Ag-Sn(Au)deposits.5.Divide five metallogenic prospect areas in the study areaFive metallogenic prospect areas in the study area could be divided,including two A-type zones,such as Narusongduo-Dexin Pb-Zn polymetallic metallogenic prospect area(A1)and Langgala-Suobogongba-Zongrongqu Pb-Zn polymetallic ore prospecting area(A2).Two B-type ore prospecting areas,mainly consist of the Zongani-Rendui Pb-Zn polymetallic metallogenic prospect area(B1)and Dingqie-Jile Pb-Zn polymetallic metallogenic prospect area(B2).The only one C-type ore prospecting area is Pudang-Rendui Pb-Zn polymetallic metallogenic prospect area(C1).