Geochemical Characteristics And Genesis Of The Dashuixiabei Crystalline Graphite Deposit In Dunhuang Block

The Dashuixiabei crystalline graphite deposit is located in the east of Dunhuang block,and belongs to the Dongbatushan block area of Dunhuang block.It is located on the north side of the Altun fault.It is adjacent to the Early Paleozoic rift zone of Qilian Mountains to the south and Beishan Paleozoic rift zone to the north.In this thesis,through the comprehensive study of the field geological survey,petrography,whole-rock major and trace,XRD experiments,and carbon isotope in the Dashuixiabei crystalline graphite deposit,protolith restoration and paleoenvironment of the metamorphic rocks are carried out,and the genesis,the source of ore-forming materials and the metallogenic model of the deposit are discussed.(1)The occurrence of Dashuixiabei graphite ore body is related to the second member of the second rock group of the Dunhuang Rock Group,which is mainly produced in stratified.The two-mica-quartz schist graphite ore are mainly composed of graphite,quartz,biotite and muscovite.The ore mainly shows lepidoblastictexture and t schistose structure.X-ray diffraction analysis shows that the graphitization degree of graphite in this deposit is high.The metamorphic rocks from this deposit have reached medium-deep metamorphism.(2)Based on the comprehensive analysis of the field occurrence of the ore body,the mineral compositions,structural characteristics of the ore and the whole-rock major and trace element geochemical characteristics of metamorphic rock samples in this ore deposit,the relevant discrimination diagrams were used to reveal that the protolith is a set of sedimentary-volcanic rock composed of greywacke,shale sandstone,quartz sandstone,clay rock and basic volcanic rock.The protolith is fromed at shallow marine sedimentary environment.The material source is terrigenous clastic material mainly composed of felsic and quartzitic rocks from the upper crust and containing a small amount of igneous rock material source.The protolith of metamorphic volcanic rocks is basic volcanic rocks,and the tectonic environment formed by metamorphic rock samples in the area is active continental margin.(3)The carbon isotope?¹³C of the Dashuixiabei crystalline graphite deposit shows that the carbon source of the Dashuixiabei crystalline graphite deposit is organic carbon deposits.(4)Combined with the study of metallogenic geological characteristics,carbon isotope analysis and regional tectonic evolution,it is concluded that the type of Dashuixiabei crystalline graphite deposit is belonged to regional metamorphic graphite deposit.