Laboratory experiments using Salton Sea Geothermal Field brines at elevated temperatures are costly, time-consuming, and potentially difficult to perform. The LLL Geothermal Program is therefore also attempting to predict equilibria in the SSGF brines by computation. Two approaches to this problem are being taken. Modeling of chemical reactions in the brines is being carried out using the Helgeson-Herrick (HH) code. In addition, the precipitation of many solids is being studied individually using effective activity coefficients which take chloride complexing into account. The results of both methods are consistent with one another in predicting precipitation behavior in the temperature range 100-300 C. For example, results for Sinclair No. 4 brines at 200 C indicate that at low pH, SiO{sub 2}, MnO{sub 2}, and Fe silicates precipitate. As pH increases, Cu and Fe sulfides, Fe silicates and Fe oxides also precipitate. For the San Diego Gas and Electric Magmamax brine at 200 C, the HH code predicts results quite similar to those described above for the Sinclair No. 4 brine with one notable exception, PbS precipitated at pH greater than 4.0. This correlates with observations on the scale examined from the San Diego Gas and Electric test site
