Genesis And Uplift-Denudation Process Of Niyazitiekexie Gold Deposit,Western Tianshan

Niyazitiekexie gold deposit,as an important deposit,is located at?6 km north of Nalati fault,Western Tianshan.First,we used granitites to study the tectonic evolution of south margin of Yili block,and then analyzed their metallogenic significance.Second,we mainly used S and O stable isotope as well as 40Ar/39Ar method to analyze genesis of the deposit,and then proposed a model.Third,we utilized mineral pair method and zircon(U-Th)/He method to analyze the uplifting and denudation of gold deposit from south and north flanks.At last,we draw some conclusions:(1)Petrogeochemistry study of granitoid samples from late Proterozoic,middle Devonian and early Carboniferous shows that they are calc-alkaline island arc environment I-type granites.Diabase dykes were formed in late orogenic extension environment,and they were from depleted mantle wedge.Petrogeochemistry,total rock Sr-Nd isotope and ziron U-Pb methods show that the South Tianshan Ocean has existed from middle Devonian to early Carboniferous,and its north part has subduction polarity.From Late Devonian to early Carboniferous,a slab roll-back process occurred and young material generated.Sr-Nd isotopic analysis of granitoids shows that horizontal growth model and vertical growth model of continent growth exist in South Yili block.The old Cambrian base multistage activation can contribute to the preconcentration of metallogenic matter.From granitoids and tectonic environment study,it reveals that Niyazitiekexie gold deposit cannot be porphyry deposit type.Beyond that,the slab roll-back process leads to not only the mantle matter or lower crust matter but the geothermal anomaly which can give rise to the long and multi-stage preconcentration of metallogenic material.During late Carboniferous orogenic gold deposits were formed,and in early Permian depleted mantle matter upwelled along the large shear zone and got mineralized.Furthermore,multi-stage metallogenic features are presented.(2)S and O stable isotopic analysis of samples from mineralization alteration zone shows that Niyazitekexie gold deposit is orogenic.Besides,it shows the material source of marine stratum and magmatic hydrothermal fluid.40Ar/39Ar age of K-bearing minerals from alteration zone and pluton show the multi-stage metallogenic feature of Niyazitiekexie gold deposit.Based on the above evidences,we conclude that the metallogenic model of orogenic gold deposits in Nalati metallogenic belt,Western Tianshan.At?310-300 Ma,arc-land or land-land collision phase is the first stage of mineralization to form orogenic gold deposits.Then,at?290-280 Ma,late of orogenic extension stage,marine matter in depleted mantle migrated upward along the large-sized strike slip fault.Based on the black shale,turbidite metamorphic mineralizated fluids migrated by short distance and mineralized in early metallogenic sites.Meanwhile,it enriched the orogenic gold deposits.(3)By comprehensively applying thermochronology method,we found that after mineralized at 304.4 Ma,gold deposit denudated 11.69 km,south area of deposit denudated 8.51 km,and north area of deposit denudated 4.71 km.Hence,the gold deposit in the south is at?3.17 km underground,and the gold deposit in the north is at?6.83 km underground.The mineral pair study shows that,at 400.6-357 Ma and 357-310 Ma stages,the slow uplift and cooling in the study area lead to two stages of highly efficient metallogenic preconcentration.