Na-K-Ca geothermometer

It is well known that the atomic ratio of Na/K in natural waters depends on temperature (White, 1965, 1968 Ellis, 1969, 1970). This relationship has been also 

Summary of fluid compositions of Japanese geothermal systems (Chiba, 1991) 

Shikazono (1976) attempted to interpret this Na-K-Ca geothermometer based on thermodynamic equilibrium calculation. 

As noted already, the first approximation of electroneutrality relation is 

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Fournier, R.O. and Truesdell, A.H. (1973) An empirical Na-K-Ca geothermometer for natural waters. Geochim. Cosmochim. Acta, 37, 1255-1275. 

Shikazono, N. (1976) Thermodynamic interpretation of Na-K-Ca geothermometer in the natural water system. Geochem. J., 10, 47-50. 

Paces, T., 1975, A systematic deviation from Na-K-Ca geothermometer below 75 °C and above 10-4 atm Pco2- Geochimica Cosmochimica Acta 39, 541— 544. 

Fournier and Truesdell (1973) obtained Na-K-Ca geothermometer representing the relationship between Na, K and Ca concentrations and temperature of geothermal water. Shikazono (1976) derived this relationship based on the chemical equilibrium among Ca-Na-K-feldspars, calcite and wairakite. 

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. 

Fournier, R. O and R. W. Potter II, 1979, Magnesium correction to the Na-K-Ca chemical geothermometer. Geochimica et Cosmochimica Acta 43,1543-1550. 

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