Just fluids

Abstract

Fluids are among the most effective agents for the transport of material in the Earth’s crust and, possibly, the upper mantle. Aqueous, hydrothermal fluids are responsible for the formation of most ore deposits and for much of the control of sea water chemistry. In addition, fluids play a major role in many metamorphic reactions. Prediction of the behavior of radioactive and hazardous waste in hydrothermal environments requires understanding of fluid chemistry. Fluids, as used in the present context, are most often H₂O-rich, and are either liquids or, at temperatures above about 400°C, supercritical fluids. These fluids have minor to major amounts of dissolved NaCl and may contain significant amounts of CO₂ or CH₄. In order to understand processes involving fluids, we need to know the thermodynamic properties of their major and minor constituents, the solubilities of a wide range of minerals, and how those solubilities change with P, T, pH, and ${f_{{O_2}}}$. We must also know their transport properties, such as viscosity and thermal conductivity. A good understanding of fluid properties requires identification of the molecular grouping, or speciation, of elements in fluids and how that speciation changes in response to P, T, and the internal stucture of the fluid as a whole. In this chapter we begin by describing experiments to measure properties of the major molecular constituents, especially H₂O, and then examine some of the methods of determining the behavior of minor species.