| Project Description | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 16 Figure 2-7 Revised layout of the Processing Plant 2.4.1 Gold Room The mercury content of GOP and WUG ore is higher in some areas of the resource than the mercury content of the ore that has been processed at Waihi to date. The MUG ore which is currently processed at the site has a mercury content of appropriately 0.30ppm. The average mercury content of the WUG and GOP ores are respectively expected to be approximately 2 and 11 times higher than the mercury content of the MUG ore (i.e. 0.6ppm and 3.3ppm7). The proportion of the mercury which is retained in the GOP ore tailings is also expected to be lower and therefore, if unmitigated, a higher proportion of the mercury content of the ore is expected to be emitted. Therefore, emissions of mercury from the Processing Plant would be expected to increase in response to changes in the ore mercury content and the increased ore processing rate. To mitigate the expected increase in mercury emissions, OGNZL is proposing to install a retort oven. The gold bearing sludge produced by the electrowinning process will be dried in the retort oven. During the drying process, the mercury content of the sludge is vapourised and drawn through a water-cooled retort condenser. The retort condenses the gaseous mercury back into a liquid which is then collected minimising discharges to air. 7 Short term peaks in the GOP ore may be as high as 3.62ppm
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