Geochemical Characteristics And Geological Significance Of Ophiolite At Zhaheba In East Junggar Of Xinjiang

The ophiolite is an important research topic in the geological background of tectonic evolution and mineralization,and geologists both domestic and abroad have carried out a lot of research on it.The East Junggar region of Xinjiang is a very important polymetallic mineralization area,which has received widespread attention.In recent years,a great deal of geological,mineral and tectonic work has been carried out in the Zaheba region,which is located in the Altay region at the northeast edge of the Junggar Basin in Xinjiang and has yielded fruitful results.In this paper,the Zaheba ophiolite is studied in detail,and the degree of serpentinization of peridotite in the ophiolite of the region is identified.At the same time,through the study of the elemental geochemistry and inter-elemental migration characteristics of ultramafic rocks and basal rocks,the role of mineralization in the Zaheba region is further discussed.The Zaheba ophiolite zone is controlled by fracture zones,and most of the strata in the zone are Paleozoic strata,among which Devonian and Carboniferous strata are widely distributed.The strata of the Ordovician and Permian strata are distributed in the central and southeastern part of the study area.The Cenozoic strata are widely distributed in the east and southwest of the census area.The ultramafic rocks and basal rocks of this area are more complete,specifically:(1)Ultramafic rocks: the rocks of this unit are mainly strong serpentinized oblique gabbro peridotites,with small amounts of pure olivine,oblique gabbro peridotite,diphyllite,and monophyllite.The lower part of the unit rocks is pure olivine,and the upward gradient transitions to oblique olivine.(2)Fe-magnesian rocks: The unit rocks are mainly basaltic rocks,including a small amount of gabbro,saprolite and interspersed phyllite.Through some tectonic diagrams and previous studies,it is concluded that the serpentine greenstone of Zaheba region has the characteristics of SSZ-type serpentine greenstone,and the light rare earth elements(LREE)are relatively deficient and heavy rare earth elements(HREE)are relatively abundant.The samples show a negative anomaly of Eu.In addition to a high Th elemental signature,the samples also have a high Th/Yb ratio,which tectonographically makes the cast point deviate from the trend of mid-ocean ridge-island basalts to island arc basalts,possibly forming in a post-arc environment.From the comparison of the migration characteristics of the main trace elements in elemental geochemistry,it is found that Al elements in monophyllite,phyllitic olivine and diphyllitic olivine samples all show a tendency to migrate.As the degree of serpentinization increases,all the rare earth elements except Tm and Lu do not have any obvious migration characteristics,and all the other rare earth elements move in,showing an overall enrichment state,but the migration of light and heavy rare earths is different.In terms of mineralization elements,Fe and Mg elements in ultramafic rocks and basal rocks show a tendency to migrate out,and Fe and Mg elements in monophyllite olivine,phyllite-bearing pure peridotite and diphyllite samples show a tendency to migrate out as the degree of serpentinization deepens.For Cr,it is enriched in ultramafic rocks,and shows a trend of migration.In the gabbro and basalt samples,the overall migration trend is out,and the enrichment of Cr decreases gradually with the deepening of serpentinization,and chromite is more easily enriched in the weakly serpentinized areas.The iron group elements and the copper-loving elements V,Co,Ni,Cu,and Zn,except Ni,all show a trend of migration in the ultramafic samples.In the gabbro and basalt samples,all the elements show a tendency to migrate out except Ni.Therefore,it is likely that the Cu and Co mineralization elements in this area were migrated from the basal rocks in the study area to the ultramafic rocks during hydrothermal activity.In addition,the Au elements show a tendency to migrate out of the ultramafic rocks,so it is likely that the gold ore in this area is related to the ophiolite zone in terms of its genesis.