\\na.aecomnet.com\lfs\APAC\Christchurch-NZCHC1\Legacy\Projects\605X\60544823\6. Draft Docs\6.1 Reports\Waihi North\App F - PHREEQC Outputs\WNP_App F_PHREEQC_25.05.22.docx Revision 5 – 07-Aug-2020 Prepared for – Anderson Lloyd – Co No.: 5719274 Appendix F – Raw PHREEQC Data F1 Introduction Water quality modelling for the Waihi North Project was completed using the geochemical modelling software PHREEQC Interactive version 3.6.2 and the Minteq.v4-database for modelling completed pre December 2021 and PHREEQC Interactive version 3.7.3 for modelling post December 2021. F2 Ion Balance Water chemistries must be charge balanced this is achieved using the following chemical Na+ and Cl- as they have high solubilities and therefore have minimal effect on other mineral phase solubilities. F3 Equilibrium Phases Equilibrium phases in each model run are selected based on the pH and redox condition of the predicted water being modelled, review of the solution chemistry and consideration of whether the predicted water is likely to reach geochemical equilibrium. This is particularly relevant for iron species as multiple iron mineral phases will potentially be over-saturated to varying degrees, however some mineral phases will more rapidly reach equilibrium than others. F4 Adsorption Adsorption of trace elements onto HFo is a significant control on trace element levels in modelled solutions. Sensitivity analysis has been completed for selected model runs around the amount of HFo sites made available for adsorption. In all cases where HFo is modelled the sites are limited to the amount of the iron mineral phase oversaturated as defined in section F3 with the ratio of strong to weak sites based on Dzombak and Morel. F5 Reported Tables The following tables have been included in the Waihi North Project Geochemical Assessment report prepared by AECOM New Zealand Limited and were generated based on PHREEQC modelling. The details of the model file performed by the PHREEQC modelling software are provided.
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