Uranium ore-forming systems of the - Geoscience Australia

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Uranium ore-forming systems of the Lake Frome region1. IntroductionRoger G. Skirrow1.1 PURPOSE OF THE STUDYAustralia holds the world’s largest share of uranium resources (983,000 t U, 34%) in theReasonably Assured Resources category, ‘recoverable at
Uranium ore-forming systems of the Lake Frome regionFigure 1.1: Location of the Lake Frome region study area. The coordinates of the northwest andsoutheast corners are 255 000mE, 6 850 000mN; and 600 000mE, 6 400 000mN, respectively (MGA94,Zone 54 coordinates). Crossed-hammer symbols show locations of uranium deposits and occurrenceswithin the study area.The essence of all of these proposed schemes is that major ore deposits are the product of crustaltodeposit- to micro-scale geological processes, and require the presence of (a) suitable sources ofmetals, fluids (aqueous, magmas, etc), ligands (for hydrothermal deposits), sulfur (for sulfidedeposits), (b) permeable pathways for transport of metals and for focussing and outflow of fluids,(c) energy source to drive the ore-forming system, and (d) chemical and/or physical gradientswhere the ore 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) betweenthe sources regions and the ore depositional environments. These relationships are illustrated inFigure 1.2, which introduces the important notion of timing of ore-forming processes. It is selfevidentthat an effective mineral system demands that sources of ore components and fluidsexisted during and/or before the period when permeability was created. Similarly, the timing ofenergy input is crucial and must overlap temporally and spatially with the creation ofpermeability, otherwise energy is dissipated without major mass transport of ore components. Onthe other hand, physico-chemical gradients may develop well before the period of 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’ of fluid flow (McCuaig and Beresford, 2009) at progressively smaller scales to achievethe generally high fluid/rock ratios inherent in most hydrothermal ore deposits.Page 4 of 151
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