June 2022 G-14642.71-006-R-Rev0_FINAL 39 9.3 Review of the Geotechnical Assessment The OGC Studies Group carried out the geotechnical assessment at the PFS Level to establish the underground mine's geotechnical characteristics and design elements. The assessment (Appendix D) entailed the following: Understanding the geological setting of the gold deposit(s). Creation and population of an interpretable geotechnical property database based on the limited geotechnical core logging available at the time of this study. Collection and recording of suitable core samples for rock property testing in a laboratory, supported by field estimates (point loads) of rock strengths. Graphical representation and interpretation of recorded data, culminating in compilation of a written report that qualifies the geotechnical environment. Transformation of data into Barton's Q' value. Transformation of data into N’-values for assessing stope dimensions using the Stability Graph Method proposed by Matthew et al. (1981) and modified by Potvin et al. (1989). Numerical stress modelling of various stope sequences and layouts using MAP3D. 9.3.1 Data available for PFS design A total of 77 cored drill holes from the Wharekirauponga deposit were available to develop a geological model and for rock mass characterisation. Geotechnical information was captured during logging including lithology, estimated rock strength, oriented discontinuity data and RQD (rock quality designation). A 3D geological model and geotechnical database was developed from the drill hole data including the distribution of identified lithological units and major structural features (as illustrated in Figure 16 and Figure 22). 9.3.2 Discontinuities Characteristics of discontinuities in the rock mass have been evaluated during logging and data contributed into a geotechnical database. The database includes a large number of discontinuity orientations measured by oriented core techniques. A dominant discontinuity orientation parallel to the major vein systems has been identified from the database (refer to Appendix D). 9.3.3 Laboratory test results Rock strength within the ore body has been measured using 11 unconfined compressive strength (UCS) tests on core recovered from exploratory drill holes. Tests were completed on host rhyolite and the overlying andesite. The UCS results characterise each lithological unit: andesite 47 to 123 MPa; Northern Rhyolite Flow 138 to 191 MPa; and Eastern Rhyolite Flow 15 to 238 MPa. However, this is a small dataset and additional rock strength testing will need to be completed during development of the design. Note that the UCS test results available for PFS design did not include the tests undertaken on core from WKP-P05D described in Section 7.1.2, which are broadly consistent with the UCS results described above. In addition to the UCS tests, five tensile strength tests, ten Young’s modulus and Poisson’s ratio tests and three triaxial strength tests were also undertaken.
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