2 Site description Upper Mundic Gully is located to the northwest of the OCP and previously flowed to the west of the OCP where is joined up with Sandstone Gully and Mundic Gully, but is now impounded by a large mine spoil dump across the entrance on the eastern side. A stormwater diversion tunnel was excavated through the hillside to the northeast of the mine spoil dump to divert the ponded water from Upper Mundic Gully to Dam 8 (located to the east of Upper Mundic Gully). WSP undertook a site visit to reconnoitre Upper Mundic Gully on 24 July 2024 and observations are summarised in Section 3. Key site features and geology identified from historic imagery and geological maps are presented in Appendix A.
2.1 Site geology
The Upper Mundic Gully TSF location consists of two primary geological formations, based on the geological mapping presented in Appendix A: — Diorite – Igneous rock consisting of coarse-grained crystallised feldspars and quartz — Arenite – Sedimentary rock consisting of coarse-grained sandstone with minimal fine grained matrix material (less than 15% clay and silt). The mapping indicates that the diorite rock formation underlies the mine spoil dump and proposed TSF embankment footprint, which is consistent with observations made onsite noting that the stormwater tunnel portals are surrounded by high strength igneous rock (refer Section 3 and Photo B.3). The mapping also indicates that tailings potentially underlies portions of the mine spoil dump.
Project No PS213278 Upper Mundic Gully TSF Concept Design to RL 390 m Mount Morgan Project Heritage Minerals
WSP October 2025 Page 3
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