6.2 Geology Review of the geological map 1:250,000 geological map for the Rockhampton sheet SF5613 indicates that: ∕ The mine site is underlain by Paleozoic (Devonian-Carboniferous) volcanic, volcaniclastic, and intrusive rocks of the Calliope Inlier, comprising mainly felsic to intermediate volcanic units (e.g. tuffs, breccias, volcaniclastic sediments) that are variably altered, fractured, and weathered, and which form the regional geological basement and principal host to groundwater flow at depth. ∕ These units are unconformably overlain in elevated areas by Jurassic Razorback Beds, consisting predominantly of sandstone, siltstone, and minor conglomerate, which are preserved discontinuously along ridge crests and topographic highs surrounding the mine site and are largely absent from gullies and valley floors due to erosion. ∕ Quaternary sediments occur as thin to locally thick accumulations of colluvium and alluvium within gullies, drainage lines, and low ‑ lying areas (including Upper Mundic Gully), comprising heterogeneous mixtures of clay, silt, sand, gravel, and locally reworked mine materials, with a spatial distribution strongly controlled by topography and historic mining disturbance. ∕ Several faults have been mapped throughout the Mount Morgan mine; multiple concealed faults cut across the OCP in a northeast-southwest direction and terminate on other faults which run perpendicular in a northwest-southeast direction. ∕ Several mine landforms, including waste rock, spoil dumps and TSFs occur across the mining lease and consist of a range of geological material, excavated from the pit and deposited as tailings from the ore processing. An extract of the geological map is presented in Figure 39. 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). The hydraulic aquifer priorities of the underlying geology are described in Section 6.6.2. The UMG TSF area is located along the eastern margin of the Western spoil dump, west of the 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. West of the proposed TSF, on the opposite side of the local topographic high, this contact occurs at lower elevations (approximately 320 m AHD), suggesting a general westward dip of the Razorback Beds. The palynological and lithostratigraphic study undertaken by the University of Queensland (Playford & Cornelius, 1967) provides a detailed description of the Razorback Beds, with the key geological aspects relevant to the seepage assessment 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;
Project number: 25B061
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