Fig. 7
From: From freshwater inflows to salt lakes and salt deposits in the Qaidam Basin, W China
Calcium and sulfate content in waters and relationship to saturation with respect to anhydrite and gypsum. Saturation states and activities are calculated with phreeqe (Parkhurst & Appelo, 1999). A Saturation indices (SI) of anhydrite and gypsum for a Ca-SO4-saturated solution versus halite saturation at 22 ˚C and 1 bar. With increasing Na-Cl-content the activity of water decreases (standard state: pure H2O at P and T). B Calcium and sulfate content (meq/kg) of all waters. ‘Red numbers’ refer to the individual salt lakes. All brines saturated or slightly supersaturated with respect to gypsum and/or anhydrite (legend see C) follow the ‘red trend line’. C Activity of sulphate (log aSO4) versus activity of calcium (log aCa). The ‘blue dotted line’ shows the gypsum/anhydrite dilution line. The symbols indicate SIAnh of the brines (CaSO4). The ‘red line’ is the trend line for brines saturated with respect to anhydrite. The salt lake brines define the equilibrium constant KAnh of anhydrite dissolution at 22 ˚C and 1 bar (Eq. 2). The standard state refers to unit activity for a hypothetical one molal solution at infinite dilution