Hydrothermal transport of Cu and Fe: internally-consistent thermodynamic model and application to formation of world-class iron-oxide-copper-gold (IOCG) ore deposits

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Hydrothermal ore deposits are large metal enrichments within the Earth´s crust. The formation of world-class ore deposits requires highly efficient extraction of metals from large volumes of source rocks, efficient transport by hydrothermal fluids and localized and effective metal precipitation. Fluid-rock interactions are essential processes during metal dissolution, transport and precipitation of ore minerals. Geochemical-thermodynamic modeling of fluid processes involved in ore deposit formation and hydrothermal alteration is a powerful tool for developing next-generation mineral exploration models. Robust thermodynamic datasets are an essential prerequisite to accurately simulate metal and mineral solubilities and fluid-rock reactions. This proposal seeks funding for developing a new internally-consistent geochemical-thermodynamic model for Cu and Fe transport in hydrothermal systems and applying this dataset to model the ore-forming processes that control mineralization and alteration in world-class iron-oxide-copper-gold (IOCG) and Copperbelt-type shale-hosted copper ore deposits. The proposed research builds on earlier work that addressed the key hydrothermal processes of the world-class Prominent Hill IOGC deposit in South Australia, based on ore geology, alteration lithogeochemistry, stable isotope and fluid inclusion studies. The project is organized as four work packages that will jointly contribute to fundamental understanding of how hydrothermal Cu ore deposits form in the Earth´s crust. In work package A, the new thermodynamic data regression module GEMSSPEC that can simultaneously treat experimental mineral solubility and optical spectroscopic data will be developed. Work package B will generate an internally consistent thermodynamic dataset for fluid-mineral equilibria in the system Na-K-Mg-Fe-Cu-Al-Si-C-S-Cl-O-H based on a new data regression approach recently developed at ETH Zürich. Carefully selected experimental Cu and Fe mineral solubility and spectroscopic data will be used for global fitting of the standard Gibbs energy of aqueous species to derive a consistent model for Cu and Fe transport in hydrothermal fluids. In work package C, the new thermodynamic dataset will be applied to the world-class Prominent Hill IOCG deposit for which datasets for rock composition, alteration mineralogy and the chemistry of ore fluids have been established. Geochemical-thermodynamic modeling using the GEMS3 code will result in a quantitative process model for the Prominent Hill deposit, which can be used to understand IOCG systems worldwide. In work package D, the new thermodynamic model will be used to address the first-order processes of Copperbelt-type shale-hosted Cu ore deposits.