There are numerous experimental measurements of quartz solubility has been studied over a broad spectrum of aqueous fluid compositions and temperature-pressure range. Here, we proposed an equation, which can calculate the solubility of aqueous silica in H2O-CO2-NaCl fluid mixture at high temperatures and high pressures from 0~1000℃ and 0~1.5GPa, as follows:
logmSiO2=A(T)+B(T)·logMH2O/VH2O*+C(t)·logxH2O
Here A(T)、B(T) and C(t) are polynomials of temperatures T(K) and t(℃),xH2O and VH2O* stand for the mole fraction and effective partial molar volume of H2O in fluid, respectively. The value of VH2O* is calculated from the relation Vmix=xHOVH2O*+ΣxsVs, where Vmix represent the molar volume of the fluid mixture, which is
calculated from the recent model of Mao et al.(2010), xs and Vs denote the mole fraction and the intrinsic volume of the solute, respectively. Values VCO2=29.9cm3/mol and VNaCl=30.8cm3/mol were adopted by this
thermodynamic model. The accuracy of our model is better than previous models, and our model is able to predict the solubility of quartz over a much wider T-P-xs conditions relevant to the deep crust, so that it could be used to evaluate aqueous silica transport in Barrovian metamorphic belts and subduction zones and so on. In addition, our model is helpful to establish quartz geothermometer, discover the formation mechanics of deposits relevant to the quartz veins. Online calculation of the solubility of quartz is available on: www.geochem-model.org.