K2GWB: Utility for generating thermodynamic data files for The Geochemist's Workbench ® at 0-1000 °C and 1-5000 bar from UT2K and the UNITHERM database

The Geochemists Workbench ^® (GWB) is a versatile geochemical modelling software package capable of reaction path modelling, equilibrium fluid speciation and activity diagramming, although it is restricted by the availability of thermodynamic (log K) data files with a temperature range of 0-300 °C and pressures on the critical curve for water. The K2GWB (log K to GWB) utility is used to produce a usable Geochemists Workbench data file from a generic log K and system file generated by the UT2K utility complementing the UNITHERM thermodynamic database system. The GWB data files can be generated for pressure-temperature conditions within the bounds of the modified Helgeson-Kirkham-Flowers model (0-1000 °C, 1-5000 bar). Data can be generated with any combination of pressure-temperature log K grids required, allowing the Geochemists Workbench to be used to model a wide range of geological scenarios under polythermal and polybaric conditions, as well as the generation of activity diagrams over a wide range of pressures and temperatures. A comparative HCh and Geochemists Workbench model using the same thermodynamic dataset was run to benchmark test the validity of the new data files. Modelling the cooling of 2 molal NaCl-H ₂O fluid in equilibrium with a ganodiorite-type rock from 600 to 300 °C gave close to identical results between the two codes, validating the thermodynamic data conversion process described here. An investigation of the speciation of Au across a temperature-pressure gradient from 550 °C and 1500 bar to 150 °C and saturated vapor curve pressures has been used to illustrate the usefulness of coupling thermodynamic data file generation at wide temperatures and pressures from a central database and the functionality of The Geochemists Workbench.