Hydrochemical Characteristics and Constraints of Hot Springs in Dagejia Geothermal Field, Tibet, China

The hot water samples DJ1-DJ116 were collected in 2009.Cations and trace elements were analyzed by the ICP-OES method,Cl^- content was tested by the titration method,and the other anions were tested by the UV-visible spectrometry method.Through analyzing the chemical indicators of hot springs we study the characteristics and constraints of the water.The hydrochamical type of the hot springs is HCO₃-Na,the average salinity is 1 524 mg/L and Na/Cl value is high.The evolution level of the water is equilibrium water and water-rock reaction in thermal reservoir has reached equilibrium.The waters are with very low partial pressure of oxygen and higher partial pressure of dioxide carbon.The saturation index of three kinds of silica minerals in most water samples are 0.The average equilibrium temperature of thermal reservoir is 251.36℃,which is calculated by K-Na geo-thermometer.The activities of Na⁺,K⁺ are constrained by albite and K-feldspar minerals.The characteristics of trace elements portfolio show that they are originated in granite.Take the whole,the hydrochemical characteristics of the hot springs in Dagejia geothermal field are constrained by the regional geological background.