Heterogeneous fluid equilibria in the second type H 2 O-Na 2 CO 3 system in the presence of SiO 2 or SiO 2 + NaAlSi 3 O 8 were studied experimentally. Phase diagrams of the second type systems are briefly described. Fluid inclusions in quartz were synthesized by healing of fractures in 1 M Na 2 CO 3 solution at 700°C and under 1, 2, and 3 kbar pressure. Some runs were carried out in the presence of albite gel. The microthermomemtric study of the synthesized inclusions showed that under experimental conditions the fluid was heterogeneous and did not remain inert with respect to quartz and albite. Some inclusions contained a glass like phase, and liquid released from this phase by heating. Having been heated, some inclusions revealed liquid immiscibility. Comparison of the water-silicate-sodium carbonate system with similar sys tems containing sodium sulfate and fluoride Kotel'nikov, 2008, 2010) shows that they have much in common. In all cases, the aqueous salt bearing fluid did not remain inert relative to the quartz under relatively low PT conditions. The inclusions entrapped in the upper heterogeneous region revealed immisci bility in the presence of vapor within a temperature range of 200 to 400°C. The solutions of various concen trations, including oversaturated solutions in the presence of solid phase, underwent recurrent heterogeniza tion. Near 400°C, vapor is either dissolved in one of immiscible liquids or absorbs this liquid. When heating progresses to higher temperature, inclusions commonly become unsealed.

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550-850°С and 500-1330 bar is consistent with other experimental results, Bodnar et al. (1985) concluded that the effect of quartz on the binary system is mini mal. In addition, solubility of quartz in water and NaCl solutions with the given parameters do not exceed 1 wt %. This also indicates that the effect of quartz on equilibria in fluid is insignificant (Bodnar et al., 1985). Similar conclusions were drawn by Zhang and Frantz (1987) and Kotel'nikova and Kotel'nikov (1988). In many publications concerning synthetic fluid inclusions, the interaction between quartz and fluid during experiment is not mentioned at all, except for communications by Zhang and Frantz (1989), Kotel'nikova et al. (1999), andKotel'nikova andKotel'nikov (2002) concerning the interaction of aqueous CaCl 2 and NaF solutions with quartz to form wollastonite, malladrite, and sodium silicate. Zhang and Frantz (1989) added a small amount of CaCl 2 into salt solutions to inhibit hydroly sis and following interaction of hydrolyzates with quartz. Kotel'nikova et al. (1999) reported a similar reaction of fluid with quartz to form wollastonite. Flu orine bearing fluid also interacted with quartz.Owing to high temperature hydrolysis, calcium hydroxide formed, CaCl 2 + H 2 O = Ca(OH) 2 + 2 HCl, and then reacted with quartz to form wollastonite: Abstract-Fluid inclusions in quartz have been synthesized from Na 2 SO 4 and NaF solutions at 700-800°C and 1 and 2 kbar using the fracture healing method. Some experiments have been carried out in the presence of albite gel. Microthermometry of the synthesized inclusions showed that under experimental conditions, the fluid was heterogeneous and reactive in respect to quartz and albite. Soluble sodium silicates formed in the presence of (alumino)silicate matter, whereas malladrite appeared when fluid interacted with NaF. When the fluid was entrapped in inclusions cooled from 400 to 250°C, it became heterogeneous again. Appearance of the second liquid phase depended on the composition of the (alumino)silicate phase. It has been shown that three noncrystalline phases coexist at such a low temperature. Silicate matter affects heterogeneous fluid equilibria, even when the salts of the second type are contained in fluid in insignificant amounts. Fluid immis cibility appears to be more widespread than is commonly suggested and is the most important mechanism of matter redistribution, including ore substances.