Using and abusing Giggenbach ternary Na-K-Mg diagram

Abstract

In the last decades, a growing number of works has increasingly focused on the study of thermal waters using the approach described by Giggenbach (1988). Based on the dependence on temperature of the equilibrium constants, the Na-K-Mg diagram is the combination of the Na-K and K-Mg geothermometers. The pristine approach proposed by Giggenbach (1988) included several constraints for its successful application. In spite of this, the Na-K-Mg diagram is often used out of the boundaries conditions of applicability. In order to promote a proper use of the diagram, a detailed description is given and several examples of mixing, dilution and concentration are discussed. The obtained findings highlight the need of cautiousness when using the diagram to estimate temperature of hydrothermal systems.