Abstract:
The solubility of aluminosilicate components in aqueous fluids in the 1200 to 1400°C and 0.8 to 2.0 GPa temperature- and pressure-range, respectively, has been determined for three compositions on the join CaSi4O9-Ca(Ca0.5Al)4O9 with 0, 3, and 6 mol % Al2O3. The aluminosilicate solubility, Xsil, ranges from 0.5 to 4.2 mol %. Its temperature dependence is linear and ranges between 0.7 and 4.2.10-3 mol %/°C depending on pressure. The pressure-dependence of Xsil is also positive but nonlinear. The solubility decreases with increasing Al2O3 content.The solubility was fitted to the expression:Xsil(mol %)= -2.6+/-0.7-0.20+/-0.02.XAl2O3(mol %)+0.002+/-0.001.T(°C) +0.86+/-0.04.P2(GPa)R2=0.96 This relationship is qualitatively similar to that of equivalent compositions in the Na2O-Al2O3-SiO2-H2O system (2Na+ is exchanged for 1Ca2+). However, in the latter system, the solubility is 2 to 3 times greater. The magnitude of the pressure, temperature, and composition effects in the latter system is also greater.The partial molar volume of H2O in the Ca silicate-saturated aqueous fluids, VH2Ofluid, ranges between ~17 and ~27 cm3/mol depending on pressure, temperature, and compositions so that,VH2Ofluid=20.1+/-0.7-0.0019+/-0.015XAl2O3+7.0+/-0.5.10-4 T(°C)-6.97+/-0.08P,R2=0.995 where T is in K, P in GPa, and XAl2O3 in mol %. The molar volume of silicate-saturated aqueous fluid is nearly identical to VH2Ofluid because H2O is the dominant component.The isochors of Ca-aluminosilicate-saturated aqueous fluids differ from those of pure H2O. The pressure difference at given temperature ranges between 5 and 10% in the 0.8 to 2.0 GPa and 1000 to 1400°C pressure- and temperature-range. For comparison, in the Na2O-Al2O3-SiO2-H2O system this difference is between 5 and 30% depending primarily on fluid density and pressure. This difference between the Na- and Ca- system reflects the different solubility of Ca- and Na-silicate in aqueous fluids.
