The Project has recently installed three monitoring bores named WGMB01, WGMB02 and WGMB03 within the proposed TSF area. Review of the geological bore logs indicates that the subsurface is generally characterised by a thin layer of residual soil or highly fractured bedrock, which transitions into competent volcanic units of Paleozoic age at shallow depths (i.e. less than 2 m from surface). Copies of the geological logs are included in Appendix A. The locations of these bores are presented in Figure 4.3. The UMG TSF area is located along the eastern margin of the Western spoil dump, west of the Open Cut Pit (OCP), and partially overlies spoil material and limited areas of exposed Paleozoic bedrock; however, most of the TSF footprint is underlain by the Jurassic Razorback Beds occurring within the upper section of the backscarp surrounding the TSF area. The published geological map indicates that the contact between the Paleozoic bedrock and the overlying Razorback Beds varies locally between approximately 335 m AHD and 350 m AHD within the TSF area.This has recently been mapped by HM at higher elevations and will be reported in Stage 2 (Figure 3.1). The palynological and lithostratigraphic study undertaken by the University of Queensland [8] provides a detailed description of the Razorback Beds, with the key geological aspects summarised as follows: — The Razorback Beds comprise non‑marine sedimentary deposits of Lower Jurassic age, identified through palynological analyses and stratigraphic relationships, and correlated to the Precipice Sandstone occurring in the Surat Basin in Central Queensland. — The sequence unconformably overlies Paleozoic ore‑bearing volcanic and intrusive rocks, indicating a significant erosional hiatus prior to Jurassic deposition. — Lithologically, the Razorback Beds consist predominantly of protoquartzite sandstones, which are extensively cross‑stratified, reflecting deposition under high‑energy fluvial conditions. — Interbedded silty claystones and minor conglomerates occur, particularly within the basal portions of the sequence, indicating variable energy conditions during early stages of deposition. — The Razorback Beds form a distinctive topographic unit, preserved mainly along ridge crests and elevated landforms, where sandstones contrast with surrounding eroded Paleozoic bedrock. The palynological and lithostratigraphic study presents a lithostratigraphic cross section of a Razorback Beds outlies, understood to be located to be in proximity to the mine site. This cross section is included in Figure 4.4, while the tabulated lithostratigraphic description is presented in Table 4.1
Project No PS213278 Mount Morgan Mine - Upper Mundic Gully TSF Seepage Management Plan Heritage Minerals
WSP May 2026 Page 13
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