Thermodynamic model for phase and chemical equilibria of chloride and carbonate aqueous fluids: prediction of ligand speciation and implications for metal complexing

• Applicant: Professor David Dolejs, Ph.D.
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 521637593

Aqueous-chloride and aqueous-carbonate fluids are the most common hydrothermal fluids in nature. Their potential for metal transport and mineralization is controlled by the activity of complexing ligands, specifically a/f(HCl) for metal-chloride, a/f(CO2) for metal-carbonate and a(Na2O) for alkali-bearing metal-oxide and hydroxide complexes. In this project we will develop and calibrate multicomponent thermodynamic models for the H2O-NaCl-KCl-HCl and H2O-Na2CO3-K2CO3-CO2 (H2CO3) systems over a wide range of hydrothermal conditions up to 800 oC and 5 kbar. These models will provide complete prediction of phase relations (e.g., liquid-vapor equilibria) and integral and partial thermodynamic properties including minor constituents (species). The free energy-based formulation will allow direct coupling with thermodynamic data and models for mineral assemblages and volatile-bearing silicate or carbonatite melts and allow for linking the fluid composition, a/f(HCl), a/f(CO2) etc. to rock-forming assemblages or melts via Gibbs energy minimization. The knowledge of activity or fugacity of complexing ligands will be a step forward to quantitative prediction of stability of metal complexes in hydrothermal fluids over a wide range of hydrothermal conditions and during phase separation, for instance boiling. Furthermore, we hypothesize that the alkalinity or aluminosity of the parental magma or mineral assemblage may exert significant control on the metal-complex concentration and transport in fluids rather than the metal budget and fluid salinity alone.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2238: Dynamics of Ore-Metals Enrichment - DOME