Oceana Gold Waihi North Project Waihi North Project Geochemical Assessment – Geochemistry of Tailings and Overburden, Treatment and Mitigation Revision 0 – 17-Jun-2022 Prepared for – Oceana Gold (New Zealand) Limited – Co No.: 2274246 20 AECOM 5.3 Geochemical Modelling Sump water quality modelling was undertaken utilising the geochemical modelling software PHREEQC Interactive version 3.6.2 and the Minteq.v4 database. PHREEQC is utilised to assess geochemical reactions of the combined water qualities reporting to the sump in order to account for and assess overall pit sump water quality that a mass balance approach will not account for. Calculated PAF and NAF pit wall runoff were mixed at a ratio of 0.73:0.27 respectively to account for their relative proportions in the final exposed pit walls. The results of the modelling are shown in Table 7 where the range of predicted trace elements and pH concentrations are given. Table 7 Modelled Sump Water Quality Predictions Min Med Max pH 2.5 4.0 4.4 Al 13 77 234 As 0.042 0.23 1.2 Ba 0.0001 0.0007 0.002 Ca 32 46 85 Cd 0.0001 0.0006 0.0018 Co 0.055 0.30 1.0 Cr 0.004 0.02 0.08 Cu 0.03 0.16 0.51 Fe 2.5 45 150 Hg 0.00003 0.00003 0.00004 Mg 1.4 2.3 2.3 Mn 0.06 0.33 1.1 Mo 0.00002 0.00009 0.0003 Ni 0.02 0.13 0.43 Pb 0.0001 0.0004 0.0011 S 180 785 2,470 Sb 0.0001 0.0001 0.0002 Se 0.0003 0.0012 0.0035 Zn 0.04 0.22 0.71 All concentrations reported in in mg/L.
RkJQdWJsaXNoZXIy MjE2NDg3