NaF-bearing fluids: Experimental investigation at 500–800°C and P = 2000 bar using synthetic fluid inclusions in quartz

Fluid inclusions in quartz were synthesized by the method of crack healing at 2 kbar and temperatures of 500, 700, 750, and 800°C from solutions containing sodium fluoride (±chloride). Critical phenomena occur in the saturated solution of NaF. Thermometric and cryometric measurements were carried out. Fluid interaciton with quartz was observed under all the parameters of our experiments with the formation of intermediate compounds, which were also sometimes trapped in inclusions. Based on the results of cryometric investigations of inclusions synthesized from solutions of different concentration, the solubility of NaF was estimated as 3.9 wt % at 500°C. It was shown that at temperatures higher than 700°C, heterogeneous entrapment occurred in most cases. Complex unmixing processes took place in the inclusions synthesized under the conditions of the upper heterogeneous region. All our observations suggest that coarse dispersed emulsions of two liquids exist in the upper heterogeneous region: an essentially aqueous phase and a water-rich silicate-dominated phase. At temperatures of 206–389°C, liquid immiscibility occurred in the presence of vapor, and three equilibrium noncrystalline (fluid) phases coexisted. Under the experimental conditions, the addition of NaCl to the fluidgenerating mixture did not exert a significant influence on the phase state of fluorine-bearing fluid.