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 19 AECOM 5.2 Gladstone Open Pit Runoff Water Quality PAF Pit Wall Runoff water quality has been derived by applying the mean (711 m3/day) and the 95%ile (3,583 m3/day) runoff volumes from the GOP Water balance1 (GHD, 2019) to the total predicted sulphate load (Table 4) based on the derived sulphate generation rate and the material available for oxidation (Table 5). Trace metal data has been calculated based on the molecular ratio of sulphate to trace element generation from the field column. NAF Pit Wall Runoff water quality for the GOP is based on field data from the Martha Pit representative of runoff interacting with NAF pit wall material. The derived pit wall runoff water quality is summarised in Table 6, alongside pit wall runoff data from the Martha Open Pit (NAF and Martha Fresh PAF). It should be noted that the Martha PAF samples represent a highly mineralised, intensely clay altered area of pit wall that represents a worst case in terms of Martha pit wall runoff. Post closure pit wall runoff from remaining pit wall areas will be assessed and managed Table 6 Gladstone Open Pit Wall Runoff Water Quality Pit Wall Type PAF (range) NAF Martha Fresh PAF Low High SO4 145 2390 160 2500 pH 2.5 4.1 7.1 2.5 Al 14 223 28 125 Sb 0.00001 0.0002 0.0002 0.0005 Ba 0.00015 0.002 - - Co 0.06 0.96 0.0002 0.30 Fe 9 151 0.020 125 Mn 0.06 1.04 0.010 2.35 Hg 0.00001 0.00002 0.00001 0.00040 Mo 0.0000 0.0003 - - Se 0.000 0.0003 0.001 0.008 As 0.04 0.73 0.001 0.15 Cd 0.000 0.002 0.000 0.002 Cu 0.03 0.50 0.001 0.32 Pb 0.0004 0.001 0.0001 0.0003 Ni 0.026 0.423 0.001 0.700 Zn 0.042 0.698 0.006 0.980 Cr 0.004 0.073 0.001 0.335 Ca 3 55 107 34 Mg 0.004 0.073 5- 59 All concentrations reported in mg/L. 1 Revised calculations pending updated modelling results from GHD.
RkJQdWJsaXNoZXIy MjE2NDg3