Multiple fluid-mineral equilibrium calculations and their applications to geothermometry and hydrochemical procession in geothermal systems

Abstract

Thermodynamic geochemical approaches based on theoretical calculations and modeling have become increasingly accurate as regards understanding the various processes occurring in hydrothermal systems. The log(Q/K) diagrams give an indication of the equilibrium state by comparing measured constituent concentrations with theoretical saturation activities over a range of temperatures. Using the results of chemical analyses the WATCH program has been employed to carry out calculations, the results of which have made it possible to construct log(Q/K) diagrams for geothermal and related natural waters from Iceland and China. In this way, it has been shown which minerals are possibly in equilibrium with the fluid constituents at certain temperatures. This approach facilitates the choice of geothermometers and provides a better understanding of the system; i.e. the processes that are responsible for the presence or absence of an equilibrium situation, e.g. the influence of seawater in the case of a coastal aquifer and other processes like boiling and mixing with shallow diluted water.