Anhydrite data, equilibria

This equation shows that activity of Ca + is related to pH, concentration of H2CO3 and temperature. Because pH is related to the concentration of Cl for the equilibrium curves 1 and 2 in Fig. 2.14, the relationship between the concentrations of Ca " " and Cl" can be derived for calcite-albite-sericite-K-feldspar-quartz equilibrium (curves 4 and 7 in Fig. 2.14) and calcite-albite-sericite-Na-montmorillonite-quartz equilibrium (curves 5 and 8 in Fig. 2.14) with constant w2h2C03- The range of zh2C03 in the solution in equilibrium with calcite is assumed to be 10 to 10 . The other equilibrium curves for the assemblage including Ca minerals are also drawn (Fig. 2.14). These assemblages are wairakite-albite-sericite-K-feldspar-quartz (curve 3), Ca-montmotillonite-albite-sericite-Na-montmorillonite-quartz (curve 6), Ca-montmorillonite-albite-sericite-K-feldspar-quartz (curve 9) and anhydrite (curve 10). The effect of solid solution on the equilibrium curves is not considered because of the lack of thermochemical data of solid solution. 

The equilibrium relations of epidote-K-mica-K-feldspar-pyrite-chlorite, hematite S jq = pyrite -I- H2S, anhydrite-magnetite-pyrite-clinozoisite and pyrite-hematite-magnetite assemblage are shown in Fig. 2.27. Based on the equilibrium curves and analytical data on epidote and chlorite, /hjS of the epithermal Au-Ag vein ore fluids for some propylitic alterations is also estimated (Shikazono, 1985a). 

Figure 20.5. Effect of NaCl concentration on the equilibrium temperature of the anhydrite-gypsum reaction at 1 bar. Data from Ref. 16.

Figure 5.35. If RH over a saturated solution of sodium sulphate decahy-drate (A-B) is reduced, the solution is dehydrated and solid decahydrate is formed. When below a certain RH value, decahydrate emits the chemically bound hydrate water and is transformed into anhydrite (B-D). The boundary curve denotes RH over a decabydrate-anbydrite salt pair in thermodynamic equilibrium. The curve B D corresponds to this expression (b) measurement values denote the experimental data, cf. Timmermanns.

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