Hydrochemical Characteristics of High-fluorine Groundwater in the Plain of the Yarkant River Basin, Northwest China

Study on regional distribution of high-fluorine groundwater will help to understand migration and transformation of fluorine, and provide the theoretical basis of low-fluorine groundwater exploration in high-fluorine groundwater areas. In this study, 74 shallow groundwater samples collected from plain area of the Yarkant River Basin in Xinjiang were analyzed. Results showed that the type I (low-fluorine groundwater, F-<1mg/L) was distributed in the piedmont plain, the type II (high-fluorine groundwater, 1mg/L <= F-<2mg/L) was distributed in the central and northeastern part of the basin, and the type III (high-fluorine groundwater F->= 2mg/L) was continuously distributed along the flow direction of river water in the western part of the basin. The average concentration of groundwater fluorine was 1.26 mg/L, with an exceeding standard rate of 48.65%. Groundwater cations were dominated by Ca2+ and Mg2+ and anions were dominated by SO42- and Cl-. High-fluorine groundwater occurred under neutral to weak alkaline environment with pH ranged between 6.61 and 7.99, which is favorable for the dissolution of fluorine-bearing minerals. Average concentration of total dissolved solids (TDS) in type I, type II and type III groundwater were 1657 mg/L, 3522 mg/L and 3724 mg/L, respectively. High-fluoride groundwater generally had high TDS concentrations.