WKP PFS – Geotechnical Section Approved by: Approval Date: TBA OceanaGold PEX-000-PLN-046-A Page 18 of 22 1.8 Numerical stress modelling summary A MAP3D numerical stress model was constructed for the Life-of-Mine mining sequence using the PFS mine design for WKP. The main issues that were analyzed in the numerical model included the following: • Stress damage zones after all mining has been completed with particular attention to the stress damage in the final crown pillar above the backs of the highest ore drive at 120 mRL. • Effects of horizontal pillar distance and mining sequence with two separate subparallel ore bodies in close proximity. • Stand-off distance and mining sequence required for the stability of ore pass and waste pass infrastructure located close to the ore body. The pre-mining in situ stress used in the numerical model is given below in Table 10. The vertical stress is assumed to be vertical with the magnitude estimated from the average rock density. The maximum principal stress, S1, is assumed to be oriented parallel to the strike of the EG Vein (025o). The magnitude of S1 is assumed to be 2.5 times the vertical stress. The magnitude of S2 is assumed to oriented toward 115o with a magnitude of 1.5 times the vertical stress. This stress field is similar to the orientations and magnitudes described by previous authors (He et al., 2020) for numerical modelling work at Martha. Table 11 shows the material properties used in the model. Note that that extremely UCS and UTS values were used for all backfill types. MAP3D cannot model backfill strength, but it can model the affects of the regional support that it provides the overall rock mass. Table 10: In situ stress magnitudes and orientations assumed for WKP Table 11: Material properties used in the model WKP In-situ Stresses Component S1 = Sv*2.5 S2 = Sv*1.5 S3 = Sv Bearing 25 115 295 Dip 0 0 90 MPa/m 0.063 0.038 0.025
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