The soluble fluorine compounds (HF, KF, and NaF) are the most important dissolving agents of ore components in natural processes. The ore elements form strong complex compounds with F and their content in hydrothermal solutions strongly depends on F concentration. The study of fluid inclusion composition in minerals provides grounds for assuming that the total F concentration in solutions did not exceed 0.n mol/kg H_2O and was much lower than the total Cl concentration. Calcium that forms up a low-soluble compound with F (fluorite) and can pretend to be an indicator and limiter of F concentration in hydrothermal solution. Fluorite solubility was studied in various solutions within a wide range of physicochemical parameters. In natural Ca-depleted systems, such as strongly altered metasomatic rocks, veins, and ore lodes, F content is controlled by the solubility of vil-liaumite (NaF), which is much less soluble than KF. At temperatures above 250℃, villiaumite is characterized by retrograde solubility in water at > 125℃ and belongs to salt of the second type with two critical points (P and Q). The solubility of villiaumite virtually equals zero at critical point P and may exceed 10 wt at point Q. At T > T_Q (700-750℃) and P > P_Q (> 2000 bar), the solubility of villiaumite in two-phase fluid of the NaF-H_2O system may be considerable.
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