The Interpretation of Na-K-Mg Relations in Geothermal Waters

Abstract

When using a Na-K/Mg triangular diagram as an aid in the interpretation of a geothermal water, the estimated temperature of last water rock equilibration may change by as much s 50°C, depending on which of the many Na/K geothermometers one assumes is correct. A particular geothermometers may work well in one place and not in another because of differences in the mineralogy of the phases that are in contact with the reservoir fluid. The position of the full equilibrium line that is used for geothermometry and for assessing degrees of departure from equilibrium also changes as the assumed K/Mg geothermometers equation changes. The degrees of ambiguity can be evaluated by utilizing the results of all the recently published Na/K geothermometers on a single Na-K-Mg triangular plot.