Rory McNeill Reference No. 20148384_7407-012-LR-RevA_DRAFT OceanaGold Corporation 08 September 2021 6 Between 300 m to approximately 1100 m both shallow tunnel alignments would be in completely to moderately weathered rhyolitic ignimbrite that is either welded or non-welded. Between 1100 m and Vent Shaft 1 (Willows Connection) the shallow tunnel alignments are expected to be entirely within andesite. At about 2200 m the tunnel is expected to encounter the Waihi Fault, which may comprise a zone of highly sheared, weak ground. A simplified description of the tunnel geology of the deeper alignments follows: The geology at the Portal consists of andesite with a surficial volcanic ash layer. With increasing distance to the northeast, the deep alignments intersect sandy and welded ignimbrites6,7. Near the portal the alignments will transition into ignimbrite and the first 300 m will be mainly within the ignimbrite. Between about 300 m and 700 m the deeper tunnel alignments will transition to the underlying andesite. During this interval, several possible configurations could occur: ▪ There could be single abrupt change from ignimbrite to andesite, ▪ There could be several changes from ignimbrite to andesite and back, ▪ There could be a prolonged mixed face situation with the tunnel encountering both ignimbrite and andesite. Between about 700 m and Vent Shaft 1 (Willows Connection) the deeper tunnel alignments are expected to be entirely within andesite. At about 2200 m the tunnel is expected to encounter the Waihi Fault, which may comprise a zone of highly sheared, weak ground. The logs do not provide specific data on the geotechnical characteristics of the materials that we would use for designing tunnels. We also have useful relevant data from the Willows Road farm site to characterise the ground conditions at that end of the tunnel extension where the tunnel will likely mainly encounter weathered andesite. In the area between the Waihi Fault and vent shaft 1 (WNDD007) elevation is increasing so hole depth of any exploratory drill holes will need to be greater to reach the tunnel alignment (up to several hundred metres). There are a few dips in elevation that we might be able to utilise to reduce hole depths. 5.0 IMPLICATIONS FOR TUNNEL DEVELOPMENT The geological information that is currently available indicates that the tunnel alignment will encounter a suite of volcanic rocks including flows, breccias or pyroclastic materials. Based on the available drill core reviewed as part of this assessment, the layers appear to be in the order of metres to tens of metres in thickness and oriented sub-horizontal or gently inclined. The strength of the material is difficult to determine based on the available drill core information provided by OGL near the portal. We have inferred that the andesite encountered at the Willows Connection end will be either the Whiritoa Andesite or the Waipupu Formation andesite, which are inferred to comprise geotechnically similar materials. The material in WNDD007 had an 6 Engineering Geology Limited 2020. Proposed polishing pond stockpile geotechnical stability assessment. Prepared for Oceana Gold (New Zealand) Limited, dated 16 November 2020. Ref. 9094. 7 Engineering Geology Limited 2021. Storage 1A – Tailings Storage Facility Raise to RL182 Detailed Design Report. Prepared for Oceana Gold Limited, dated 11 August 2021. Ref. 8981. D R A F T
RkJQdWJsaXNoZXIy MjE2NDg3