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 regionFigure 1.1: Location <strong>of</strong> <strong>the</strong> Lake Frome region study area. The coordinates <strong>of</strong> <strong>the</strong> northwest andsou<strong>the</strong>ast corners are 255 000mE, 6 850 000mN; and 600 000mE, 6 400 000mN, respectively (MGA94,Zone 54 coordinates). Crossed-hammer symbols show locations <strong>of</strong> uranium deposits and occurrenceswithin <strong>the</strong> study area.The essence <strong>of</strong> all <strong>of</strong> <strong>the</strong>se proposed schemes is that major <strong>ore</strong> deposits are <strong>the</strong> product <strong>of</strong> crustaltodeposit- to micro-scale geological processes, and require <strong>the</strong> presence <strong>of</strong> (a) suitable sources <strong>of</strong>metals, fluids (aqueous, magmas, etc), ligands (for hydro<strong>the</strong>rmal deposits), sulfur (for sulfidedeposits), (b) permeable pathways for transport <strong>of</strong> metals and for focussing and outflow <strong>of</strong> fluids,(c) energy source to drive <strong>the</strong> <strong>ore</strong>-<strong>forming</strong> system, and (d) chemical and/or physical gradientswhere <strong>the</strong> <strong>ore</strong> metals are deposited. Suitable sources, permeability architecture, and physicochemicalgradients occur only in specific ‘fertile’ terranes that have experienced favourable ageodynamic evolution that permits an efficient physical link (permeability architecture) between<strong>the</strong> sources regions and <strong>the</strong> <strong>ore</strong> depositional environments. These relationships are illustrated inFigure 1.2, which introduces <strong>the</strong> important notion <strong>of</strong> timing <strong>of</strong> <strong>ore</strong>-<strong>forming</strong> processes. It is selfevidentthat an effective mineral system demands that sources <strong>of</strong> <strong>ore</strong> components and fluidsexisted during and/or bef<strong>ore</strong> <strong>the</strong> period when permeability was created. Similarly, <strong>the</strong> timing <strong>of</strong>energy input is crucial and must overlap temporally and spatially with <strong>the</strong> creation <strong>of</strong>permeability, o<strong>the</strong>rwise energy is dissipated without major mass transport <strong>of</strong> <strong>ore</strong> components. On<strong>the</strong> o<strong>the</strong>r hand, physico-chemical gradients may develop well bef<strong>ore</strong> <strong>the</strong> period <strong>of</strong> through-goingpermeability creation, for example a lithological contrast across a fault. Permeability is importantacross all scales from regional to micro. The permeability architecture must allow focussing or‘throttling’ <strong>of</strong> fluid flow (McCuaig and Beresford, 2009) at progressively smaller scales to achieve<strong>the</strong> generally high fluid/rock ratios inherent in most hydro<strong>the</strong>rmal <strong>ore</strong> deposits.Page 4 <strong>of</strong> 151
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