Physicochemical Conditions And Uplifit History Research Of Porphyry Deposits In East Section Of Eastern Kunlun Mountains

The East Kunlun Orogenic Belt,located in the south edge of the Qaidam block,primarily constitutes the northern Tibetan Plateau.This near EW-trending orogenic belt can be simply divided into eastern and western segments by the Wutumeiren Town.In this dissertation,it is focused on the eastern segment and mainly consisted of two scientific issues:(1)the physicochemical conditions of porphyry-type copper mineralization;(2)the post-mineralization evolution processes and mechanism of porphyry-type ore deposits.The analysis of fluid inclusions,stable isotope and oxygen fugacity is to reveal the physicochemical conditions of porphyry-type mineralization in the eastern East Kunlun Orogenic Belt.The fluid inclusion data indicate that the porphyry-type ore deposits in the eastern East Kunlun formed principally in the temperature of99.6-423.8°C(270.83°C in average)with uniform salinity ranging from 0.18 to20.37 wt%Na Cl(6.76 wt%Na Cl in average).The fluid density ranges from 0.49 to1.05 g/cm~3 with 0.81 g/cm~3 in average.The metallogenic pressure is between 8.37 and45.86 MPa with 24.37 MPa in average.As a result,the depth of mineralization is calculated between 0.84 and 4.13 km with 2.37 km in average.Based on the fluid inclusion study,it is inferred that porphyry-type ore deposits in the eastern East Kunlun Orogenic Belt formed primarily in shallow crust with low-medium temperature,and the ore-forming fluid is of low-medium density with low-medium salinity.The stable isotope data show that the metallogenic fluid of porphyry-type ore deposits in the studied area was principally from magma and had been more or less affected by the atmospheric precipitation,e.g.the atmospheric precipitation had exerted a profound influence on the metallogenic fluid of Jiadanggen mining area,while,the metallogenic fluid from Harizha and Halongxiuma mining areas was slightly affected by the atmospheric precipitation.Deep-source mantle magma is suggested to provide the sulfur for porphyry-type ore deposits.Granite porphyry,granodiorite porphyry and Cu-bearing granodiorite porphyry samples were tested for the oxygen fugacity analysis.The average?FMQ of the Harizha,Halongxiuma,Dongshangen,Qingshuihe and Aikengdelesite mining areas are 4.16,4.28,4.43,4.34and 4.00,respectively.The oxygen fugacity of porphyry-type copper deposits is between that of Qulong giant porphyry-type Cu-Mo deposit and Dexing porphyry-type copper deposit.The oxygen fugacity of the Halongxiuma porphyry-type Mo deposit and Aikengdelesite Cu-Mo deposit is higher than that of Shapinggou and Dabaoshan Mo deposits,which indicates that porphyry-type ore deposits are of high oxygen fugacity and are regarded as an ideal background for porphyry-type mineralization.Fission track analysis is applied to detect the uplift history and reveals the evolution processes and mechanism.21 samples are analyzed by the apatite fission-track dating method.The apatite fission-track ages have been divide into three groups:135-112,103-93 and 87-65 Ma.One age group of 135-112 Ma shows as the uplift of Qaidam Basin,inferred a northwards collision between Gandese and Lhasa block.The rapid uplift of northern Tibetan Plateau and the movements of the Altyn Tagh strike-slip fault were recorded by the fission-track age group of 103-93 Ma.The age group of 87-64 Ma is possibly a record of the continuation of the early tectonic movement.Three cooling stages are obtained for study area as:(1)a rapid cooling stage between 160±5 and 90±5 Ma with cooling and uplift rates of 1.67°C/Myr and0.048 mm/a;(2)a stable stage between 90±5 and 20±5 Ma with cooling and uplift rates of 0°C/Myr and 0 mm/a;(3)a subsequent rapid cooling stage since 20±5 Ma with cooling and uplift rates of 2.25°C/Myr and 0.064 mm/a.The cooling rates of the first and third stages are higher than the average cooling rate(approximately 0.027mm/a),which means that large-scale tectonic movements took place during these stages.As a result,some meaningful and profound tectonic movements in were recorded by the apatite fission-track age groups of 135-112 and 103-93 Ma,respectively.The rapid cooling stage since 20±5 Ma is consistent with the extensive uplift history of the Tibetan Plateau starting from the Miocene.