EGL Ref: 9215 23 June 2022 Page 50 This report shall only be read in its entirety. File: WAI-985-000-REP-LC-0002_Rev0.docx 9.0 OPTIONS FOR DISPOSAL OF TAILINGS AND MINE PIT OVERBURDEN The Global Industry Standard on Tailings Management (GISTM, Ref. 18) recommends that projects consider and evaluate different options for disposal of tailings. This also applies to disposal of mine pit overburden. Options for the Waihi Operation are discussed in the following sections. 9.1. Options for tailings disposal Tailings can be disposed of in different ways including: • In-pit • Underground paste • Above ground paste • Central thickened discharge • Dry stacks • Mixed waste • Downstream and centreline construction embankment dams • Upstream embankment construction is another option but is not considered an option for new TSFs by OGNZL. 9.1.1. In-pit disposal Tailings can be disposed in the pits left after excavation of the overburden and ore. This method has been successfully undertaken at both Macraes and Reefton Mines in New Zealand by OGNZL. In-pit disposal requires any stopes to be secured, installation of a liner with underdrainage and tailings underdrains unless reliance on hydraulic containment can be demonstrated. Earth or geosynthetic liners can be used as is done in landfills. In-pit disposal also requires stabilisation of pit slopes above the retained tailings for health and safety reasons and to avoid displacement and release of tailings in the event of a pit wall landslide into the TSF. In-pit disposal can be complicated by risk of breach into underground mines or sterilisation of potential ore resources. The benefit of in-pit disposal below the crest of the pit is that it avoids the risk of a dam break or slope failure due to geotechnical factors associated with above surface methods such as dams or dry stacks. If there was seepage out of the pit into the surrounding ground it may be more difficult to mitigate due to the depth below the ground surface tailings are placed.
RkJQdWJsaXNoZXIy MjE2NDg3