EGL Ref: 9215 23 June 2022 Page 17 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx. permeability and strength of the tailings deposit formed depends on the tailings properties, degree of dewatering, and placement method. Tailings which are transported as a slurry can be discharged: • Sub-aqueous (below a water surface); or • Sub-aerial (above a water surface). Discharge methods include: • Simple discharge from the end of a large pipe called end pipe discharge; • Discharge from a series of smaller pipes known as spigot pipe discharge; • Discharge from a tailings cyclone, a device which separates the coarse and fine fractions of the tailings and some of the water from the solid particles before final discharge. Pastes can be deposited in underground workings or above ground in impoundments. Slurries without binders are typically limited to tailing impoundments, either in-pit or above ground tailings dams. Tailings which are filter pressed to form a soil are tipped from trucks at their final location and spread out by a bulldozer and compacted to form soil stockpiles. 4.2.2. Ore-bearing rock The existing consented ore sources at the Waihi Operation comprise the existing Martha Open Pit (MOP) and Martha Underground (MUG) mines. Ore associated with the Waihi North Project will be sourced from the proposed new mines (Gladstone Open Pit (GOP) and Wharekirauponga Underground Mine (WUG)). The ore bearing rock is andesite at MOP, MUG and the GOP, and rhyolite at WUG. Some of the ore is PAF and therefore a proportion of the tailings are also PAF (estimates based on testing on MOP and MUG ore indicate about 60% tailings are NAF and 40% PAF). The predominant heavy metals in the ore from MOP and the existing underground workings that could leach from the tailings are manganese, copper, iron, antinomy, and selenium. Monitoring of tailings pond water and seepage indicate levels to date are very low. The closure design is for a perimeter capping and pond. This will ensure the tailings remain saturated which will prevent oxidation of the tailings and potential release of heavy metals. 4.2.3. Process and water treatment plant setup At the current Waihi Process Plant the processing operations consist of a twostage grinding process followed by a conventional carbon-in-pulp (CIP) circuit. The current circuit is designed to grind the ore to a target particle size of 80% passing 75 μm on Martha ore. Ore associated with the Waihi North Project is proposed to be ground to a target particle size of 80 % passing 53 μm. Chemicals used in the process include sodium cyanide, oxygen, lime, and flocculant. The tailings are currently pumped to the TSF as a slurry between 38 to 43% solids by weight, with up to 200 ppm of WAD cyanide and at a pH
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