Na2CO3-bearing fluids: Experimental study at 700°C and under 1, 2, and 3 kbar pressure using synthetic fluid inclusions in quartz

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 systems containing sodium sulfate and fluoride (Kotel’nikova and 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 immiscibility in the presence of vapor within a temperature range of 200 to 400°C. The solutions of various concentrations, including oversaturated solutions in the presence of solid phase, underwent recurrent heterogenization. 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.