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Chronology, geochemical characteristics and the significance of Shesuo copper polymetallic deposit, Tibet

ZHAO YuanYi1, CUI YuBin2, LV LiNa1 and SHI DengHua31. MRL Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resource, Chinese Academy of Geological Sciences, Beijing 100037, China2. China University of Geosciences, Beijing 100083, China3. No.5 Geological Party, Tibet Bureau of Geology and Mineral Exploration and Development, Golmud 816000, China  
Shesuo deposit is located in the north of Shenzha county, Tibet. It is near the Bangong Lake-Nujiang metallogenic belt, and a small skarn type copper-richen polymetallic deposit. This paper is based on the systemic field geological survey, indoor rock and ore appraisal, zircon LA-ICP-MS U-Pb dating, test of major and trace element, H-O, C, S and Pb isotopes, Raman spectra, temperature and salinity of fluid inclusions, and find out its chronology and geochemical characteristics. The age of granodiorites which is metallogenic rock is 116Ma, A/CNK value is near 1.0, A/NK value 1.62~1.88. The roceks belong to transition types between metaluminous and ultraluminum. In the spider diagram of trace elements, big ion incompatible elements Rb, Th, Pb and Ti are rich, and Nb is poor. The distribution pattern of rare earth elements is right-trending type, and the curve of heavy rare-earth elements is gentle, ∑REE is range from 89.89×10-6 to 97.92×10-6, ∑LREE/∑HREE=7.47~9.31, δEu=0.75~0.89, and namely it has no obvious negative Eu abnormalities. Bangong Lake-Nujiang oceanic crust subducts southward (Gangdes plot). The deposit formed in island-arc environment. Pb isotopes of granodiorites which are metallogenic rocks reflects that it belongs to crust source. The date of H and O isotopes of inclusions in sulfide-quartz veins shows that it mainly belongs to the magma water. The δ13CV-PDB of calcite ranges from -3.6‰ to -2.0‰; The δ34SV-CDT=10.3‰~2.7‰, and they are negative values, and mainly appear -8.5‰ and -3.5‰ two peaks, δ34S of molybdenum reflects larger negative values. In the structure model image, Sr-Nd isotope dates is located near the mantle,and is affected by lower crust. All inclusions are gas-liquid two phase inclusions, and the gas phase composition is mainly CO2 and a little with CH4 and N2. The ratio of gas to liquid is between 5% and 45%, and the size is of 3×6~33×20μm. Uniform temperature ranges from 130℃ to 290℃, and is mainly 180~260℃; and the salinity in mainly 3%~6% NaCleqv and 10%~18% NaCleqv, and overall it shows the low temperature and salinity characteristics. The ore-forming materials are provided by magama and strata together.
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