Geochemical study on boron isotopes in the Yangbajing geothermal field,Tibet
Lu Yuanyuan1,2, Zhao Ping3, Xu Ronghua3, Xie Liewen3
1. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037;
2. Key laboratory of Saline Lake Resources and Environment, Ministry of Land and Resources, Beijing 100037;
3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029
Based on previous geothermal tracing researches by boron isotopes,and by utilizing the state-of-art MC-ICP-MS analytical technique for measuring boron isotope ratios,the mixing processes between deep geothermal water and surface cold water of the Yangbajing(YBJ)geothermal field in Tibet were determined.The δ11B values of geothermal water range from -10.5‰ to -9.1‰,indicating the non-marine sources.And further we propose that B is derived from host altered granite according to regional geological features,and the host altered granite should have similar boron isotope ratios to the deep geothermal water.Shallow geothermal water samples suggest that there is fractionation of B isotopes in the YBJ shallow reservoir.Accordingly,some complicated factors will be introduced into the two end-member mixing model in the YBJ since there is only little difference of boron isotopes between two end-members.Therefore,we discussed in details that exploitation,water-rock interaction,separation between vapor and liquid phase and scaling are some possible factors for yielding B isotopic fractionation.