Uranium ore-forming systems of the - Geoscience Australia

Uranium ore-forming systems of the Lake Frome region4.3 VOXET LITHOLOGY MODEL OF EL5 AND 6The voxet model (Fig. 4.3) shows the upper surface of the Cretaceous Bulldog Shale dipping tothe west. It is unconformably overlain by the Cenozoic Eyre Formation which ranges in thicknessfrom 30 to 80 m. The upper surface of the Eyre Formation has greater relief than the other unitsurfaces and, like the Cretaceous surface, it dips to the west. There appears to be a thickening ofthe Eyre Formation sediments midway across the model to form a north-south trending ridge. Tothe west of this ridge the surface dips more steeply westwards. The surface of the Eyre Formationforms a disconformable contact with the overlying Namba Formation. The upper surface of theNamba Formation dips more gently to the west. It is the thickest unit in the voxet model, rangingup to 120 m thickness at the western edge of the voxet. The uppermost Quaternary unit is rarelymore than 20 m thick. Its upper surface also dips gently westward and has little relief, even withexaggerated vertical scale.The gentle westerly dips of the Cretaceous, Eyre and Namba surfaces in the area of EL5/6 to theeast of Lake Frome are opposite to dips of these surfaces in the Beverley area (e.g., Curtis et al.,1990, and Fig. 1.7). This may indicate a basinal structure of Cenozoic units, which is supportedby seismic data for the region (see Fig. 7.2, and further discussion of significance in section 8.1.3).56.5 km76.5 kmFigure 4.3: Voxet model of lithology and topography in the EL 5/6 area, east of Lake Frome.4.4 3D CHEMICAL ARCHITECTURE4.4.1 Redox Patterns in the Lake Frome regionThe 3D map of the Lake Frome region (Fig. 4.4) shows the scattered nature of the data with themost striking feature being the variability in the redox pattern between areas. Some areas, such asPage 47 of 151