Solubility of Ore Minerals and Complexation of Ore Metals in Hydrothermal Solutions
Scott A. Wood, Iain M. Samson, 1998. "Solubility of Ore Minerals and Complexation of Ore Metals in Hydrothermal Solutions", Techniques in Hydrothermal Ore Deposits Geology, Jeremy P. Richards, Peter B. Larson
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Knowledge of the solubility of ore minerals and the speciation of ore metals in hydrothermal solutions is required for a complete understanding of the genesis of hydrothermal ores. In this chapter, we explore the factors that control solubility and speciation, demonstrate how to carry out quantitative calculations, and review the current state of knowledge for a number of economically important metals. The term solubility refers to the sum of the concentrations of all dissolved forms of a given metal in a hydrothermal solution in equilibrium with a mineral (or minerals) containing that metal. We use the term speciation to denote the relative concentrations of the various forms of a metal in solution.
The solubility of a mineral provides an upper limit to the amount of dissolved metal that a hydrothermal fluid can transport, assuming thermodynamic equilibrium. Although a given solution may temporarily carry more metal than permitted by the equilibrium solubility of relevant minerals owing to sluggish reaction kinetics, the equilibrium solubility is nevertheless an important benchmark. Given enough time, equilibrium solubility cannot be exceeded, and systems will proceed in a direction toward the equilibrium state. Also, knowledge of equilibrium solubilities is required for modeling rate processes. Metal concentrations may be maintained below the equilibrium solubility either by sorption processes, which remove metals from solution before saturation is reached with respect to a given mineral, or if there is insufficient metal available in the system to saturate the solution. pointed out in Chapter 1, the extent to which a solution