Silica geothermometer

Several chemical geothermometers are in widespread use. The silica geothermometer (Fournier and Rowe, 1966) works because the solubilities of the various silica minerals (e.g., quartz and chalcedony, Si02) increase monotonically with temperature. The concentration of dissolved silica, therefore, defines a unique equilibrium temperature for each silica mineral. The Na-K (White, 1970) and Na-K-Ca (Fournier and Truesdell, 1973) geothermometers take advantage of the fact that the equilibrium points of cation exchange reactions among various minerals (principally, the feldspars) vary with temperature. 

Arnorsson, S. 1975. Application of the silica geothermometer in low-temperature hydrothermal areas in Iceland. American Journal of Science, 275, 763-784. 

Silica geothermometer is also useful for an estimate of reservoir temperature because silica concentration of geothermal water which strongly depends oti temperature due to the dependence of solubiUty of silica minerals (quartz, opal, chalcedony, amorphous silica) on temperature (Fig. 1.18). Temperature estimated... 

The quartz geothermometer (Fournier, 1977) requires that the dissolved silica concentration in an ascending hydrothermal solution becomes quenched in as the fluid approaches the surface. On the other hand, the phase transfer model for the rate of quartz deposition, described in this chapter, requires that the LEA be valid. The conditions for which each of these models is appropriate can be found by calculating values of Da, and Pe. Figure 8.1 shows the temperature range for the transition from LEA to quenched conditions. 

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