Uranium ore-forming systems of the - Geoscience Australia

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Uranium ore-forming systems of the Lake Frome regionPRESERVATIONPERMEABILITY Event 2(Q2, Q4)TIMEQ1ENERGY(Q4)MINERAL SYSTEM TIME WINDOWPERMEABILITYEvent 1(Q2, Q4)SOURCES ofMetals, fluids,ligands, sulfur(Q3)focussingDEPOSITIONALGRADIENTS(Q5)Craton Province District Deposit MicroSCALEFigure 1.2: Generalised evolution of a mineral system at varying scales, showing essentialcomponents (sources, permeability, energy, depositional gradients) and some of the geological featuresdetermining the nature of these essential components. This scheme integrates the Mineral Systemsapproach of Wyborn et al. (1994)), the Five Questions (Q1-Q5) approach of Walshe et al. (2005) andBarnicoat (2007), and the schema of McCuaig & Beresford (2009), and adds the time dimension andpreservation component. Permeability architecture is a product of: tectonic/geodynamic history (Q1),fracture/fault/fold architecture (Q2), lithology, diagenetic evolution; Sources are a product of:geodynamic evolution, tectono-thermal evolution, and lithology; energy is a product of: geodynamicand tectonic evolution; depositional gradients are a product of: lithology, structure, and pressuretemperature-timeevolution; preservation is a product of: tectonic evolution, mantle composition, andclimate.The evolution of a mineral system may be represented as the large arrow, as metals and other orecomponents are progressively concentrated through time from regional- and district-scale sourcesinto the depositional regime. Whether or not a mineralised zone is preserved at a depth accessibleto exploration techniques is strongly dependant on the post-mineralisation geodynamic andtectonic evolution, and on climatic effects, all of which are operative at the full range of scalesfrom craton to micro.Figure 1.2 shows how Questions 1-5 of the pmd*CRC are important at differing scales andthrough the temporal evolution of a mineral system. Geodynamic evolution (Question 1) in partdetermines the character of the sources as well as the permeability architecture and nature ofenergy sources. Architecture (Question 2) is similar in concept to what is termed permeabilityhere, although permeability is perhaps more specific to the requirements of a productive mineralsystem. Through-going permeable pathways for fluids are likely to be a subset of the completearchitecture of the mineral system, and it is necessary to identify both the overall architecture andthose parts that represent the permeable pathways. Hydrothermal alteration, for example, marksthe passage of fluids and identifies permeability in the system. Question 5, fluid sources andreservoirs, is similar to sources in Figure 1.2 with the addition of metal, ligand and sulfur sourcesPage 5 of 151
Uranium ore-forming systems of the Lake Frome regionhere. Fluid flow paths and drivers (Question 4) combines aspects of the energy and permeabilitycomponents in Figure 1.2. Finally, metal transport and depositional processes (Question 5) partlycorresponds to depositional gradients here, although the transport aspects of Question 5 areembedded within the source component in our scheme. This is because a requirement of aproductive mineral system is the presence of fluids of appropriate composition enabling transportof metals.1.3 APPLICATION OF MINERAL SYSTEMS APPROACH TO URANIUM IN THE LAKEFROME REGIONThe diverse range of uranium deposit types in Australia and globally may be grouped into familiesof uranium mineral systems that share particular ore-forming processes and that involve threefundamentally different fluid sources (Fig. 1.3, Skirrow et al., 2009).Figure 1.3: Scheme of three families of uranium mineralising systems, and three end-member fluidtypes. For reference, numbered deposit types are from the IAEA Red Book, in order of economicimportance in Australia. Source: Skirrow et al. (2009).The principal known uranium deposits in the Lake Frome region (Beverley, Honeymoon, FourMile, Oban, Goulds Dam; Fig. 1.5) are conventionally placed within the ‘sandstone’ uraniumdeposit class, and include variations of the ‘paleochannel’ or ‘basal channel’ style (Beverley,Honeymoon) and perhaps ‘roll-front’ style (Four Mile). In a broader context, these ‘sandstone’uranium deposits can be viewed as members of the family of basin- and surface-related uraniummineral systems (Figs 1.3, 1.4). Meteoric waters, groundwaters and formation waters are theprincipal fluids involved in uranium ore formation in the shallow parts of basins, and result in acontinuum of deposit styles depending upon local basin lithology, structure and availablereductants to remove uranium from the oxidised ore fluids.Page 6 of 151
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