O,H, and Sr isotope evidences of mixing processes in two geothermal fluid reservoirs at Yangbajing,Tibet, China |
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| Authors: | Qinghai Guo Yanxin Wang Wei Liu |
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| Institution: | (1) School of Environmental Studies, Key Laboratory of Biogeology and Environmental Geology of Ministry of Education, China University of Geosciences, 430074 Wuhan, Hubei, People’s Republic of China;(2) Zhongkai Mining Limited Corporation of Tibet, 850000 Lhasa, Tibet, People’s Republic of China;(3) Geo-Environmental Monitoring Institute of Tibet Autonomous Region, 850000 Lhasa, Tibet, People’s Republic of China; |
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| Abstract: | The Yangbajing geothermal field with the highest reservoir temperature among Chinese hydrothermal systems is located about
90 km northwest to Lhasa City, capital of Tibet, where high temperature geothermal fluids occur in two reservoirs: a shallow
one at a depth of 180–280 m and a deep one at 950–1,850 m. In this study, Oxygen-18 and deuterium isotope compositions as
well as 87Sr/86Sr ratios of water samples collected from geothermal wells, cold springs and surface water bodies were characterized to understand
the genesis of geothermal fluids at Yangbajing. The results show that the deep geothermal fluid is the mixing product of both
magmatic and infiltrating snow-melt water, whereas the shallow geothermal fluid is formed by the mixing of deep geothermal
fluid with cold groundwater. Using a binary mixing model with deep geothermal fluid and cold groundwater as two endmembers,
the mixing ratios of the latter in most shallow geothermal water samples were calculated to be between 40 and 50%. The combined
use of O, H, and Sr isotopes proves to be an effective approach to depict the major sources of geothermal fluids and the mixing
processes occurring in two reservoirs at Yangbajing. |
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