Characteristics of hydrochemical compositions and stable carbon isotope of natural water in the Daggyia geothermal field,Tibet,China

The objective of this work is to investigate the hydrochemical compositions of the geothermal wa-ter,lake water,river water,and ice-and snow-melt water as well as control factors of provenance in the Daggyia geothermal field of Tibet.The field surveys and sampling were conducted in August 2014.The main cations and anions of samples were measured using the ICP-OES and UV-visible spectrophotometer.The iso-topic ratios of dissolved inorganic carbon (DIC)were analyzed using a gas stable isotope ratio mass spectrom-eter.The results show that the concentrations of total dissolved solids (TDS)range from 977.13 mg/L to 1 279.50 mg/L for geothermal water,and K+ and Na+ are the main cations,and HCO 3 - and Cl- are the main anions.The concentrations of TDS of the lake waters range from 77.81 mg/L to 810.94 mg/L,Ca2 + ,Na+ , HCO 3 - (CO 3 2 - )and SO 4 2 - occupy the majority of ions.The hydrochemical types of both geothermal water and lake water are the type of bicarbonate-sodium.The ion concentrations of river and melt water are low, and the hydrochemical type is bicarbonate-calcium.The concentrations of DIC in geothermal water range from 9.2 mmol/L to 15.4 mmol/L,and that of δ1 3 CDIC ranges from -9.09‰ to -0.95‰.The concentra-tions of DIC in lake water are 1.1 mmol/L to 9.7 mmol/L,theδ1 3 CDIC values are -8.84‰ to -0.27‰.The Gibbs boomerang envelope of water samples indicates that the hydrochemical characteristics are mainly con-trolled by silicate rocks weathering in the area,and the major processes are the albite and potash feldspar weathering,while the hydrochemical compositions of geothermal water are also affected by dissolution of e-vaporation of salt rocks.The carbon sources of silicate weathering around the lakes are mainly soil carbon di-oxide.Meanwhile the deep carbon dioxide input is the main source of silicate hydrolysis in hot spring areas.