Geochemical Characteristics And Their Implications For Mineralization Of The Eocene Granites In The Zhongba,Tibet

The Gangdese belt has extensive and intense magmatism in the Eocene.There are a large number of Eocene granites and coeval volcanic rocks in the area,and many Eocene deposits have developed.Based on the previous work research,this paper focuses on the Eocene granitoids in the Zhongba area of the western Gangdese,through petrology,mineralogy,geochemistry,zircon U-Pb geochronology and zircon Hf research work on isotopes,to solve the problems such as the rock genesis of the samples,the characteristics of magma evolution and the significance of the mineralization indications.The rock types in the study area are mainly porphyritic monzonitic granites and potassium feldspar granites.They have granitic structures,massive structures,and occasionally chalcopyrite and molybdenite.The zircon U-Pb chronological experimental data show that the formation age of granite is about 48.11±0.83 Ma,and the formation age of granodiorite is 48.69±0.56 Ma and 47.85±0.55 Ma,which can represent the diagenetic age of rock and time.It coincides with the main collision period?65-40Ma?of the collision between India and Eurasia.The geochemical experimental data showed that the Si O2 content of granodiorite was 62.73-66.84%,the average value was 65.13%,the ?REE content was 251.116-309.85?g/g,the average value was 293.97?g/g,and the light rare earth element?LREEs?was enriched.?La/Yb?_N=12.94-18.55,the average value is 16.44,enriching elements such as Rb,Th,U and Pb,and obviously delete elements such as Ba,Nb and Ta.The SiO₂ content of the granite is 73.57-78.30%,the average value is 75.76%;the A/CNK value ranges from 1.041-1.142.?REE content is 112.42-242.28?g/g,the average value is 184.03?g/g,enriched with light rare earth elements?LREEs?,?La/Yb?N=12.01-30.74,the average value is 17.84,enriched Rb,Th,U And elements such as Pb,obviously delete the elements such as Ba,Nb and Ta.Combined with the zircon Hf isotopic characteristics,the granodiorite sample ZB-21,whose ?Hf?t?results show from-6.4 to-3.8?average of-5.1?and ZB-37,its ?Hf?t?results show-5.3 to-1.3?average-4.2?;granite sample ZB-28?Hf?t?results from 1.2 to 3.8?average 2.7?.It is believed that the granitoids may form a slab window due to the slab breakoff in the northward subduction process of the Neo-Tethyan oceanic plate,which causes the upflow of the asthenosphere material and the partial melting of the upper part of the asthenosphere.The crust is mixed and formed into a magma chamber.By comparing with the geochemical characteristics of the Jiru Eocene granite,it is found that there is little difference in geochemistry between the Eocene granites in the eastern and western parts of the Gangdese,and it is possible to increase the prospecting exploration in the western section of Gangdese in order to discover new minerals.