OceanaGold Waihi North Project Vibration Performance Assessment Page 21 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 Each plate in Appendix B shows the modelled vibration contours for blasting the WUG decline with the maximum weight capped according to a standard 4 metre advance length with a 45mm diameter blasthole with a 5 kilogram explosive weight. Appendix C shows the same vibration contours for developing the tunnel between WUG and the processing plant with the same standard 4 metre advance length, 45mm diameter blasthole and 5 kilogram explosive weight. In simple terms, where a vibration contour of say 2mm/s is shown, all locations between the blasting area and the extent marked by this contour are predicted to receive vibration at some stage during the year at a level of vibration that exceeds 2mm/s. The modelling therefore identifies the maximum expected level of vibration that could be expected to receive in each year, irrespective of the source of the blasting. The vibration may occur from small scale blasting at nearby locations or from larger scale blasting at a location farther from the contour. The same applies for other vibration contour levels. Where a particular contour for a given vibration level is not shown, the contour does not ‘daylight’ on the surface and modelling predicts this level of vibration is not reached. The modelled results for each of WNP orebodies and accesses are assessed separately. 11.1. Gladstone Open Pit The GOP is set to commence in 2024. The blasting is scheduled for 6 years with completion of the lower limits of the pit in 2029. Blasting commences on the upper pit rim. Explosive weights will be consistently around 16 kilograms for a 5 metre bench height. There are no restrictions on the scale of blasting that are necessary to comply with the 5mm/s level at the adjacent residential properties in East Waihi. These explosive quantities are typical of those used for the blasting in the Martha Open pit when mining with a 5 metre bench height. Properties adjacent to the Martha Open pit were nearer than the 300 metre separation for the GOP. During the later stages of mining, blasting will have progressed both deeper and further from the nearest receivers to permit increased explosive weights with some areas able to extend the bench height beyond 5 metres. Blasting at the Martha open pit over the previous 25 years has utilised explosive weights like those planned for the GOP. There are no areas of the GOP where the scale of blasting will be restricted to less than a 5 metre bench. At the deeper areas of the pit, mining with a larger scale of blasting would be possible should grade control and geology allow bench heights greater than 5 metres or more than two 2.5 metre flitches per blast. The mining of the GOP changes the existing vibration environment for only a small, isolated area at the eastern end of Moore and Clarke Streets and Boyd Road. The location of the GOP virtually eliminates any combined effects from the existing Martha underground blasting or other blasting at the Martha open pit when this recommences. The envelope of impact for the GOP is estimated as around 50 properties with most of these subjected to only low and marginally perceptible levels of vibration. Fewer than 5 properties are modelled to receive more than 2mm/s with no property greater than 5mm/s. The vibration contours presented in Appendix A for the life of the GOP show those areas around the pit where perceptible vibration may be experienced. The 1mm/s vibration contour extends to Barry Road towards the north and George Street towards the west. The few properties along Heath Road are modelled to receive vibration between 1 and 2mm/s when mining occurs in the southern areas of the mine. 11.2. Willows Access Decline and Development The Willows Access decline extends from the Willows Portal at the Willows Road site through to the WUG orebody where the decline links with the main orebody development. The distance of the decline
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