[Hydrochemical Characteristics and Possible Controls of Groundwater in the Xialatuo Basin Section of the Xianshui River].
In order to study the characteristics of groundwater chemistry and groundwater flow system in the Xianshui River fault zone, samples of precipitation, surface water, groundwater, and hot spring samples in the Xialatuo Basin were collected and tested. Through the test data, the main ions and the sources of recharge were analyzed by means of ionic relations, correlation analysis, Gibbs plot, Piper triangular diagrams, and saturation index. The groundwater recharge sources in the basin were studied using combined hydrogen and oxygen isotope information. Results show that all the water samples in the study area were weakly alkaline. The predominant cations were Ca2+, Mg2+, and Na+. Among these, Ca2+ accounted for 2.6%-53.6%, with an average value of 28.84%, Mg2+ accounted for 2.7%-57%, with an average value of 40.6%, and Na+ accounted for 6.2%-93.1%, with an average value of 28.6%. The anions were mainly HCO3-, accounting for 82.4%-98% of the total anions and with an average value of 89.6%. HCO3- and Na+ accounted for most of the ions with 93.1% and 98%, respectively, in the Zhanggu hot spring. The total dissolved solids (TDS) of the groundwater ranged from 116.11 to 372.75 mg·L-1, and with an average value of 281.91 mg·L-1. The hydrogeochemical type of groundwater was HCO3-Mg·Ca and HCO3-Ca·Mg. It is controlled by carbonatite dissolution with a circulatory depth range in dozens of meters. The hot springs are controlled by the fault zone and are mainly distributed along the main stem of the Xianshui River fault. Their water is of the HCO3-Na type. The hydrogeochemical process is controlled by silicate dissolution with a circulatory depth range in thousands of meters.