Ore Geology And Genesis Of Volcanic Rocks Of The Tuwu Copper Deposit In Xinjiang,China

The petrogenesis of the volcanic rocks of the Qi'eshan Group in the east Tianshan,Xinjiang has attracted much attention.The constraints on the regional magmatic evolution and mineralization process have been a hot topic and controversial issue.The ore-bearing rocks of Tuwu copper deposit are plagioclase granite porphyry and diorite porphyry.There are also different opinions on the relationship between the ore-bearing rock bodies and the surrounding rocks,the volcanic rocks of the Qi'eshan Group.In order to reveal the relationship between volcanic rocks of Qi'eshan Group in Tuwu Copper Deposit and ore-bearing rocks and their genesis,volcanic samples were collected of Qi'eshan Group systematically from the south to the north near the vertical strata from the point on the southern side of Tuwu copper deposit,and did Geochemical studies.SiO₂-Nb/Y diagrams show that the volcanic rocks of Qi'eshan Group are subalkaline series.The trace element characteristic of enrichment in Sr,Ba and U large ion lithophile elements,and relative loss in Nb,Ti,Th and P high field strength elements.The distribution pattern of rare earth elements inclines to the right as a whole,showing the characteristics of relative enrichment of light rare earth elements and relative gentleness of heavy rare earth elements.The volcanic rocks of the Qi'eshan Group were formed by the northward subduction of the oceanic crust on the southern margin of the Paleo-Asian Ocean,The value of Zr/Nb ranges from 24.08 to 49.72,indicating that the basalt is mainly derived from the depleted mantle.In Hf/3-Th-Ta and Nb*2-Zr-Y diagrams,the basalt projection locates in the island arc basalt area and MORB area,and has the composition of mid-ocean ridge and volcanic arc volcanic rocks.La/Nb-MgO,La/Nb-La/Sm,La/Sm-Zr/Nb diagrams all show weak correlation,Nb/U-SiO₂shows that some basalts show a weak trend of contamination,indicating that the volcanic rocks of Qi'eshan Group are limited crustal contamination.Nb/Zr-Th/Zr diagrams show that it is the product of fluid/melt metasomatism between lithospheric mantle wedge melt and subduction plate.The primitive magma of different compositions resulted in different rock compositions of the volcanic rocks of the Qi'eshan Group,which came from different source areas.Volcanic rocks from different source areas and tectonic locations are mixed and accumulated on the northern margin of the suture zone due to the collision between the Junggar-Kazakhstan plate and the Tarim plate.Based on the above results and the theory of"Small intrusions forming large deposits",the metallogenic model of Tuwu copper deposit is constructed on the basis of preliminary determination of magmatic evolution process:the deep magma chamber is formed by the rise of mixed magma produced by subduction slabs,the volatile-rich magma moves to the top of the magma chamber,the fluid shell is formed in the shallow part,the rich magma sinks,the new magma emplaces many times to fill the remaining space,the fluid reacts with the surrounding rock and metasomatizes,the mineralization material is extracted,and the fluid cooling.A large number of metallic sulphides are precipitated from the interior of the rock mass or the contact zone with the surrounding rock,thus unloading mineralization and forming the so-called small porphyry intrusions.