Uranium ore-forming systems of the - Geoscience Australia

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Uranium ore-forming systems of the Lake Frome regionPRESERVATION: Cenozoic age & lack of erosion; switch to dryer climate?TIMEE (Q4)NERGYTopographyRadiogenic granitesTectoniccompressionSOURCES ofmetals, fluids,ligands, sulfur(Q3)Fluid focussing: paleochannels; Poontana Inlier faultsPERMEABILITY (Q2, Q4):Cambrian Cenozoic & Beverley sandsbasin faults; Mesozoic Eyre FmAquifer units basin faults; Cadna-owieNamba Fm;Eyre Fm; Cadna-owie FmUranium: Proterozoicigneous and/or Cenozoicand/or Mesozoic basinsediments.Fluids: Meteoric water orgroundwater or formationwaters.Cenozoic sediments:Organic matterPyriteIlmeniteBacteria?Mesozoic seds:C, Fe 2+ , S 2-Cambrian seds:CH 4 , H 2 S?DEPOSITIONALGRADIENTS(Q5)Craton Regional/basin District Deposit MicroSCALEFigure 1.6: Mineral system model for basin-hosted uranium mineralisation in the Lake Fromeregion.A published deposit model for uranium mineralisation in the Beverley – Four Mile area is shownin Figure 1.7. This site-specific model is based on the conventional generic model for sandstonehostedroll-front type deposits, shown in Figure 1.8, which also shows the potential role of mobilereductants sourced from oil or gas reservoirs. Figure 1.6 differs in that it allows for multiple oreformingscenarios, for example involving a range of depositional gradients or uranium sources.By identifying and mapping the mineral system components without bias towards any particularmodel we aim to generate new ‘search spaces’ for uranium exploration in the region.Figure 1.7: Schematic cross section of the Mt Painter Inlier - Lake Frome area, from Brugger et al.(2005).Page 9 of 151
Uranium ore-forming systems of the Lake Frome regionFigure 1.8: Diagrammatic section of sandstone (yellow unit) hosted uranium system, showing processof infiltration of oxidised U-bearing groundwaters and formation of roll-front and tabular styles ofuranium deposits. The potential role of mobile reductants is also shown. Source: Jaireth et al.(2008a).1.4 REPORT STRUCTUREThis report is structured around the mineral system components illustrated in Figures 1.2 and 1.5.Following this Introduction, Chapter 2 addresses aspects of the uranium source by describing thelithostratigraphy of Proterozoic basement and Cambrian, Mesozoic and Cenozoic basin sediments.Chapter 3 describes the permeability architecture and evolution in terms of regional structuralevolution including neotectonics, and geometry of aquifer units in the Lake Frome region. Basedon compilations of existing public-domain data including seismic data, these 3D datasets(viewable as 3D pdf files) highlight the geometry of basin-controlling faults of different ages.Aspects of the energy driver component of the mineral system are also discussed in this chapterbecause a key driver of fluid flow was topography, which is largely a product of tectonicprocesses and climate.Depositional gradients at district to deposit scales are described in Chapter 4. A new method ofmapping and visualising geology and mineralogy in 3D is introduced, with application to mappingvariations in oxidation-reduction potential within basin sequences (chemical architecture).In Chapter 5 we describe uranium deposits of the Lake Frome region based on a review ofpublished information. These descriptions focus on the deposit-scale geology including aspects ofthe permeability architecture and depositional gradients at this scale.Detailed new petrographic descriptions for the Four Mile deposit are presented in Chapter 6. Thiswork addresses the depositional gradients at deposit- to micro-scale, and identifies some of thekey mineralogical characteristics representing the processes of uranium ore deposition.In Chapters 2-6 a range of sources, permeable pathways, energy drivers, and depositionalgradients are described for uranium mineral systems of the Lake Frome region. It follows thatdiffering combinations of these geological components will result in a range of hypotheticalscenarios of uranium ore formation, each with possibly different implications for exploration. Thescenario published by Brugger et al. (2005) is just one of several that can be tested for the LakeFrome region. Chapter 7 presents the results of numerical modelling of regional- and district-Page 10 of 151
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