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Russell Korsch, pmd*CRC (Australia)
Andy Barnicoat, pmd*CRC (Australia)
Richard Blewett, pmd*CRC (Australia)
Barry Murphy, pmd*CRC (Australia)
Tim Rawling, pmd*CRC (Australia)
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In undertaking a 'whole of system' approach to mineralisation, the Australian Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC) follows an integrated methodology across all scales using the Five Questions, as outlined by Price & Stoker (2002, Aust.J.EarthSci. 49: 595-600) and Barnicoat (this conference). Question 1 - What is the geodynamic, geological and PT history of the mineral system? mostly focuses on the continent to province scale to understand the mineral system in a whole of crust context. Many large mineral deposits appear to have formed late in the geodynamic history of a region, and may be associated with magmatic activity, but equally they may postdate the magmatic cycle. This suggests much of the prehistory is about the formation of a suitable architecture to permit the operation of a productive mineral system. It appears that quite subtle geotectonic triggers ultimately initiate the mineralising stage. Key issues here include: What geodynamic processes created the architecture - crustal stretching, subduction, thrust loading, delamination, inversion etc.? When did ore formation occur? What were the PT conditions of ore formation? In the eastern Yilgarn Craton, for example, the pmd*CRC has produced a revised geodynamic model to link the aspects of the geodynamic history into one coherent model, involving a para-autochthonous convergent margin. Question 2 - What is the architecture of the mineral system? focuses on the structural and lithological architectures and how they varied through time, along with understanding how the permeability structure evolved. Many ore deposits are sited at major crustal breaks, such as edges of cratons, sutures, paleotectonic margins or craton-scale fault systems. These features enable localisation of permeability and creation of thermal and chemical gradients required for the focussing of fluids (including magmas) necessary for the development of orebodies. Basement structures exert a fundamental control on fault and lithological architectures, dictating basin development and inversion, partitioning of fluid flow, and ultimately dictating the favourable sites for ore deposition. To understand the architecture, 3D geological maps are constructed of selected mineral provinces (Yilgarn, Mt Isa, Tasmanides), at a variety of scales, to examine regional scale controls on mineralisation and possible fluid migration pathways. To constrain the 3rd dimension, the pmd*CRC has been involved, with government and industry sponsors, in the acquisition and interpretation of several deep seismic reflection profiles. Such profiles are identifying the main crustal-scale architecture, which is the key to determining regional scale controls on mineralisation and possible fluid migration pathways. The resulting 3D maps are challenging our current understanding of the geology, ore deposit models and predictive discovery potential of Australia.
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