OceanaGold Waihi North Project Vibration Performance Assessment Page 14 of 41 Project Number: HP2006-2 Heilig & Partners Save Date: 21/06/2022 5:55:00 PM ABN 56 082 976 714 File Name: WAI-985-000-REP-LC-0018_Rev 0 Blasthole diameter: Development blasting utilises a small blasthole diameter commonly in the range of 45mm to 51mm. Production blasting uses larger blasthole diameters in the range of 64mm to 89mm; Blasthole length: The maximum blasthole length for a development blast is around 4 metres compared with up to 18 metres or more for a production blasthole; Blast yield: The yield from a development blast is typically around 280 tonnes compared with several thousand tonnes from production blasting; Blast duration: Development blasts are initiated over a 10 second window compared with the production blasts which are shorter (complete within several seconds); Explosive quantity: Development blasts typically use around 200 kilograms of explosive in total, with each blasthole containing up to 5 kilograms of explosive. Production blasts may contain several hundred kilograms of explosive in total with each hole containing up to 30 kilograms. With respect to the vibration generated by the different types of blasting, development blasting generally produces significantly lower levels of vibration than that produced by production blasting. This is by virtue of the lesser explosive quantity associated with the smaller diameter blasthole and the smaller length of blasthole. The lower level vibration however persists longer than that produced from a production blast due to the different initiation systems. 8. PROPOSED WNP CONDITIONS 8.1. Gladstone Open Pit The conditions of the existing land use consents held by OceanaGold are based around the Hauraki District Plan standards, although include a number of additional constraints to possibly reflect the sensitivity of the residents to vibration and to ensure that the OceanaGold adheres to best engineering practices as well as an operation that protects the amenity of persons within the environment. Both the Australian Standard and the ANZEC Guidelines propose peak values consistent with the Hauraki District Plan, the Mining Licence following the 2017 variation, and Project Martha. Imposing a peak permissible value for the protection of amenity on WNP less than the current 5mm/s would further increase the disparity between the Waihi conditions and those applied elsewhere and result in very inefficient use of the mining resource by having to leave large areas sterilised because of an inability to undertake an effective scale of blasting. Previous assessments of mining at Waihi have shown that even a small reduction in the permissible vibration from 5mm/s to 4mm/s renders the operation uneconomic while achieving little to no amenity improvement, e.g. the difference in effect is at the human detection limit. Given the consistency of the existing consent conditions with the peak vibration criterion expressed in the Australian Standard and ANZEC Guidelines, which are also shown to be conservative when compared to other standards, the current OceanaGold conditions not only require that mining at Waihi employ world’s best practices to achieve compliance, but they are also protective of the amenity of the residents to a far greater degree than would be ensured through adopting any other internationally accepted standard or guideline related to blasting. For the blasting in the GOP it is proposed that there is an amended blasting condition similar to that granted for the open pit portion of Project Martha, amended to closely align with s8.3.2.3(2)(a) of the Hauraki District Plan, namely: The level of vibration for all blasts must be monitored and the peak level of vibration at any non-company owned residence comply at the 95th percentile with 5mm/s between the hours of 7am to 6pm, Monday to Saturday, excluding public holidays. The 95-percentile with 1 mm/s will apply for all blasts at all other times.
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