WKP PFS – Geotechnical Section Approved by: Approval Date: TBA OceanaGold PEX-000-PLN-046-A Page 12 of 22 1.6 Mining method selection The mining method selected is open stoping. Open stoping will be applied to all stopes that will be developed and extracted within the proposed mining footprint. The aim of open stoping is to induce free draw of the ore zone while maintaining the stability of the host rock, and lagged introduction of rock fill. Cemented rockfill (CRF) will be required where sub-parallel ore zones are separated by less than a 7.5m pillar. A pumpable cemented aggregate fill (CAF) will be required for the extraction of the 340 level sill pillar located (-25 RL to -45 RL). Due the relatively high-grade nature of the WKP ore body, it is not envisaged that permanent rib pillars will be used to control stope stability. The mine design and sequencing were based on the following assumptions: • Bottom-up mining sequence, starting from the 360 level (-25 RL). • Longitudinal retreat along the ore drives back to a central access. • Nominal stope dimensions of 15m along strike prior to backfilling with uncemented rockfill. The general shape and geometry of the ore bodies is shown in the Figure 9 below and can be summarized as follows: • Dip ranging from 60 to 80 degrees. • Minimum mining width for ore drives is 5m. • Stope widths can range from 2m to 12m • Some stoping blocks are as wide as 20m, but these wider areas will be stoped and backfilled into 2 to 3 separate blocks to avoid the formation of extremely wide spans across the backs. • Surface ranges from the 180 RL up to the 260 RL; the nominal surface is assumed to be the 220 RL for the purposes of estimating the vertical stress. • The backs of the highest ore drives are at the 120 RL. • The floors of the lowest ores are at the -125 RL • The nominal depth of stoping ranges from 100m to 325m below surface. Figure 9: Cross section view (looking north) through South Decline Access
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