Temporo-Spatial Distribution and Evolution of Ore Deposits in the West Sector of the Northern Qilian Mountains

The west sector of the northern Qilian Mountains is well-known for the Jingtieshan-type iron deposits. A new breakthrough has been made in prospecting for gold and copper in recent years. In this paper, the distribution characteristics of ore deposits in the study area are discussed from the viewpoint of tectonic evolution. It is suggested that there are 9 stages of mineralization from the Palaeoproterozoic to Indosinian. Four minerogenetic series and two minerogenetic subseries of ore deposits are recognized. Iron mineralization occurred in several stages, while most of the metals were accumulated in large amounts in the Caledonian. The enrichment and mineralization of gold is related to large-scale shear-strike-slip faults and the ascent and unloading of deep-seated fluids.

What are the keys to influence the life satisfaction of eco-migrants in the northern foot of the Qilian Mountains?A test based on the livelihood risk interaction

Eco-migrants'ability to adapt to livelihood risks and their satisfaction with lives directly affect the ecological and economic benefits of ecological migration engineering.To formulate an effective livelihood risk prevention system and welfare guarantee mechanism,we took the ecomigrants in Wuwei City as an example,developed an integrated analytical framework for life satisfaction and employed linear regression models to identify the interactions between livelihood risk and life satisfaction.Our findings indicate that 94.66%of eco-migrants in Wuwei City are threatened by livelihood risks after relocation.High living expenses,poor quality of redistributed production goods,and re-poverty constitute the main risks.The risk multiplicity index is 2.96.Besides cultural types,there are no significant differences in regions and livelihoods.A total of 55.73%of eco-migrants are satisfied with their lives,with the Liangzhou district scoring the highest.Except for satisfaction with development potential and public services,no significant intergroup differences were found among regions and livelihood patterns.Eco-migrant's life satisfaction is significantly affected by livelihood risks.Eco-migrants'satisfaction with living income,social integration,farmer-friendly policies and overall life is negatively affected by the risk of repoverty and inadequate social security.An ecomigrant's satisfaction with development potential and community construction is not influenced by one type of risk alone,but the interaction between risks has a strong influence.The interaction of welfare risks with economic risks and policy risks will balance and weaken the adverse effects of a single risk on those elements in the economic and policy spheres.This study offers novel ideas for rural revitalization,hollow governance,and well-being assurance.

Fluid Activity and Tectonic Evolution in the Northern Qilian High-pressure Metamorphic Belt

The Northern Qilian high-pressure metamorphic belt has experienced multipledeformation-metamorphism, which consists of at least four stages. In 550.8-526 Ma, eclogites wereformed. High temperature and pressure caused the escape of a large quantity of gas-liquid fluidsfrom rocks while silicate melt was generated. In the late stage, small amounts of CO_2 and H_2Oinfiltrating along fractures were introduced. In the formation of glaucophane schist (447-362 Ma),devolatilization reactions were dominated during the subduction-uplift stage of the paleoplate. Inthe uplift-exhumation stage (400-380 Ma) the increase of internal space of fractures in the rocksfavoured fluid infiltration and concentration. These fluids participated in hydration reactions inthe retro-metamorphism. The fluids participating in the mineral reactions have the compositions ofCaCl_2-NaCl-H_2O. In subsequent thrusting (<380 Ma), the metamorphic terrain was uplifted to theshallower crust and ductile-shearing deformation took place, which caused mainly dehydrationreactions of minerals. In a near-surface environment the metamorphic terrain experienced brittledeformation, forming many accompanying fractures. Immiscible CO_2 and low-salinity aqueous fluidsoccurred in these secondary microfractures and were trapped and sealed. The thermodynamic conditionsof different deformation-metamorphic stages of the metamorphic terrain were calculated and thecorresponding P-T-t path was deduced, showing that the metamorphic terrain has experienced aclockwise path indicated by T- and P-rising, and T- and P-falling processes. This reveals that thesubduction zone has undergone multiple tectono-dynamic processes, i.e. initial deep burial,subsequent quick uplift and near-surface tectonism.

Geology,Geochemistry and Minerogenesis of the Shijuligou Zinc-Copper Deposit in Gansu,China

The Shijuligou deposit was separated by an arcuate ductile shear zone cross the center of the deposit region, resulting in the difference between the southern and northern ore bodies. The lead （Pb） isotopic data of ores of the Shijuligou copper deposit have averages of 206Pb/204pb, 207pb/204pb, and 20spb/204pb in 17.634, 15.444, and 37.312, respectively. It has been shown that ore-forming metals originated from intrusive and extrusive rocks in the upper part of ophiolites. The sulfur isotopic data of pyrite and chalcopyrite in the northern part change from ＋7.61‰ to ＋8.09‰ and ＋4.95‰ to ＋8.88‰ in the southern part. Isotopes of δ18O in the Shijuligou copper deposit are between ＋11.1‰ and ＋18.6‰, with the calculated δ18OH2O at ＋0.65‰. It is suggested that the mineralized fluid is a mixture of magma fluid, meteorological water, and seawater through circulating and leaching metals from the volcanic rocks. The zircon uranium-lead （U-Pb） dating of gabbro is 457.9_＋1.2 Ma, and the lower crossing age of the discordant and concordia curves of pyroxene spilite of zircon is 454_＋15 Ma. It is indicated that the Shijuligou deposit formed in a new ocean crust （ophiolite） of the back-arc basin in the late Ordovician. Mineralization should occur in the intermittence period after strong volcanic activity, and the age should be the late Ordovician. Moreover, the mineralization of ophiolite-hosted massive sulfide deposits in the ancient orogenic belt of the late Ordovician in the northern Qilian Mountains was controlled by the primary fault/fracture, with the forming of a metallogenic hydrothermal system by a mixture of volcanic magma fluid and seawater, which circularly leached the metallogenic metals from the volcanic rocks, resulting in their accumulation. The ore bodies were transformed with morphology and metallogenic elements. Jasperoid is an important sign for prospecting such deposits. There were many island arcs in the continent of China. This study provides evidence for understanding and exploration of ophiolite-hosted massive sulfide deposits in western China, especially in the area of northern Qilian Mountains.

^(40)Ar/^(39)Ar isochron ages of lawsonite blueschists from Jiuquan in the northern Qilian Mountain,NW China,and their tectonic implications

Using laser 40Ar/39Ar dating method,we have gotten the metamorphic ages of lawsonite blueschist and epidote blueschist from Jiuquan,northern Qilian Mountain,NW China.The high quality laser 40Ar/39Ar dating of glaucophane from lawsonite blueschist gives an isochron age of 413±5 Ma.The isochron age obtained from phengite in epidote blueschist is 415±7 Ma.These data,combining with peak metamorphic P-T conditions and regional geological setting,allow us to infer that the lower limit of the ages of the prograde subduction metamorphism from lawsonite blueschist facies to epidote blueschist facies occurred at ca.413-415 Ma,which also suggests that the formation of lawsonite blueschist in the northern Qilian Mountain maybe resulted from the corner flow in the cold subduction zone.This study shows that the final closing time of the northern Qilian remnant oceanic basin is about 413-415 Ma,which also represents the convergent age between the North China Craton and the Qaidam block.