Internally-consistent thermodynamic model for hydrothermal transport of Pb-Zn-Ag-Au-As-Sb: development and application to formation of sediment-hosted Pb-Zn and epithermal Ag-Au-As-Sb deposits

• Applicant: Professor Dr. Thomas Wagner
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 439373061

Hydrothermal ore deposits are large metal enrichments in the Earthʼs crust and the formation of world-class 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-mineral interactions are essential processes that lead to formation of world-class ore deposits such as magmatic-hydrothermal porphyry Cu-Au Mo and epithermal Ag-Au-As-Sb deposits, and sediment-hosted Pb-Zn deposits. Geochemical-thermodynamic modeling of the fluid processes driving ore deposit formation and hydrothermal alteration is a powerful approach for developing next generation ore systems models. Robust thermodynamic datasets are an essential prerequisite to accurately simulate metal and mineral solubilities and fluid-mineral reactions. This proposal seeks funding for developing a new internally-consistent geochemical-thermodynamic model for hydrothermal transport of Pb-Zn-Ag-Au-As-Sb, thereby significantly extending our existing dataset. The dataset will be applied to numerically simulate the first-order geochemical processes that control formation of sediment-hosted exhalative and carbonate hosted Pb-Zn deposits and of epithermal Ag Au-As-Sb deposits. The modeling will address key questions related to formation of these globally important ore deposit types, namely the relative role of reduced acid and oxidized brines in sediment-hosted Pb-Zn systems, the link between exhalative and carbonate hosted Pb-Zn deposits, and the effect of the metalloids As and Sb on the hydrothermal transport of Cu, Pb, Zn, Ag and Au. The project is organized as three work packages that will jointly lead to fundamental understanding of how hydrothermal sediment-hosted Pb Zn and magmatic-hydrothermal Ag-Au-As-Sb deposits form in the Earthʼs crust. In work package A, a new internally-consistent thermodynamic model for hydrothermal transport of Pb-Zn-Ag-Au-As-Sb will be developed, based on our new data regression approach that was recently developed. Critically evaluated experimental solubility and spectroscopic data for Pb-Zn-Ag-Au-As-Sb will be used for global fitting of the standard Gibbs energies of aqueous species to derive a consistent thermodynamic model for hydrothermal metal transport. In work packages B and C, geochemical modeling using the GEMS3 software will address the first-order processes that control formation of sediment-hosted Pb-Zn deposits and intrusion-related epithermal Ag-Au-As-Sb deposits. This project will make important contributions to the overaching goals of the DOME priority program, by collaboration with a counterpart project addressing the formation of epithermal systems, by producing a thermodynamic dataset ready for use by other DOME participants, and by generating modeling predictions that can be tested by field-based studies of other DOME projects.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2238: Dynamics of Ore-Metals Enrichment - DOME
• International Connection: Australia, Switzerland
• Cooperation Partners: Dr. George Miron; Dr. Tobias Schlegel