Calcite dissolution/precipitation in seawater-freshwater mixing

[SPC2014]

I used Phreeqc program to calculate the CaCO3 solubility function of salinity (Cl- concentration) at pCO2=1 atm-closed system (for the dissolution experiment) and at pCO2=10-3.5 atm-open system (for the precipitation experiment) and I got the attached plots. My question is that I understand that the CaCO3 solubility is equal to zero for pure freshwater (s=0) and for pure saltwater (s=1) for the dissolution experiment but this is not the case for the precipitation experiment at s=0 and at s=1 (please see the attached jpeg file). it is true?How is this possible / How I can interpret this?

Thanks a lot in advance

[dlparkhurst]

We discussed this off-line. The main feature of precipitation from all mixtures was caused by the initial condition. The starting solution was in equilibrium with calcite at a pCO2 of 1 atm. Subsequent calculations reduced the pCO2 to 10^-3.5, which caused precipitation in all cases.