Fluorite solubility in aqueous solutions of NaCl, CaCl2, and their mixtures at 40-600 degrees C and 2 kbar

The solubility of synthetic monocrystalline fluorite in individual aqueous solutions of NaCl (1-34.7 m) at 400, 500, and 600 degrees C, CaCl2 (0.5-5 m) at 500 and 600 degrees C), and in mixed NaCl-CaCl2 solutions (10 mol Cl-tot/kg H2O) at 500 degrees C was measured by the weight loss method. The log-log dependence of the isothermal solubilities on the chloride concentration, with the exception of the 400 degrees C isotherm, was linear over the whole range of chloride concentration studied. In the mixed solutions, the curve of constant chloride concentration has a minimum for Na/(Na + Ca) ratio near 0.95. The solubility in CaCl2 solutions exceeds that in NaCl solutions of the same concentration by more than a half-order of magnitude. From the slope of the isotherms, in NaCl solutions at 600 degrees C Na2ClF2 degrees was identified and NaCaClF2, Na2ClF2 + CaClF2, and Na2CaF2Cl2, at 500 degrees C; in CaCl2 solutions, Ca2Cl(2)F(2) degrees was identified at 500-600 degrees C. The conclusion was made that in a natural environment, fluorite can form not only as a result of direct cooling of a fluid, but also dilution of the ore-bearing fluid by colder, low-mineralized (vadose) waters.