Research Of Crustal Properties Of Duolong Ore Concentration Area In Tibet

Ore accumulation area of Duolong is located at the southern margin of the Qiangtang-sanjiang composite ground plate,the north side of the Bangong-Nujiang suture zone,belongs to the Bangong-Nujiang copper gold polymetallic metallogenic belt in Duolong ore concentration area.With the progress of the exploration work,Duobuza copper deposit has become a public representatively large copper polymetallic deposit in Bangong-Nujiang metallogenic belt.For the metallogenic geological background of Duolong ore concentration area,Xu Zhiqin believes that there is an ancient crust in the region of Duolong ore concentration area,even if the existence of the subduction is the continental margin arc environment.Pan Guitang believes that the region is a new crust,however,namely the typical island arc environment.In this paper,32 samples of magmatic rocks in Duolong ore concentration area were tested by LA-ICP-MS zircon U-Pb isotope.Studied 1708 points of these samples,I found that those zircon were formed in different times that The ancient age was proterozoic and the the latest age was neogene.The number of zircon which formed in cretaceous was maximum.It turn out that the magmatic activity in the region is the strongest in the cretaceous.The ancient zircon which formed in proterozoic? archean and so on were captured from surrounding rock.So we can determined that the area in where ore accumulation area of Duolong was located has Old crust.We can judge the zircons which formed in different ages were continental zircon or ocean crust zircon through the U-Yb diagram and U/Yb-Y diagram.Figuring the geochemical data of zircons formed in different ages,we can found that most of them were continental zircon.There was none or little crust zircon in every ages except some zircons formed in the Jurassic.Combining with the formation ages of zircon,it turned out that the area in where ore accumulation area of Duolong was located has ancient continental crust.And the morphological characteristics of zircon can infer the properties of regional crustal structure,the widespread acidic intrusive bodies was evidence which also supports the existence of ancient continental crust.Based on the above research,it can be concluded that the deposits of Duolong were formed in the active continental margin environment(continental margin arc).With the determination of the crustal structure in Duolong ore concentration area,the orientation of ore prospecting in the study area and its periphery should be changed accordingly.The prospect for exploration of porphyry Cu-Mo deposits is very large in this area.The key exploration should be putted on the superposition of passive margin epicontinental magma arc of the south of Qiangtang.