Title: Multiple fluid - mineral equilibrium calculations and their applications to geothermometry and hydrochemical processes 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(QJK) 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 .