Uranium ore-forming systems of the - Geoscience Australia
Uranium ore-forming systems of the - Geoscience Australia
Uranium ore-forming systems of the - Geoscience Australia
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<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