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