Fig. 4

Biplot diagram between Ca2+ ratio and chloro-alkaline indices. a, b Plot diagrams compare for CAI-1 and CAI-2, respectively, three types of groundwaters from hot spring sites, High-Cl−, Low-concentration, and High-HCO3− fluids. Ca2+ ratio denotes proportion of calcium ion among four major cations (Na+, K+, Ca2+ and Mg2+) in milliequivalent concentrations