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ENGINE, Potsdam, 12.01.2007 Reactive transport model of silicification at the Mount Isa Copper deposit, Australia Michael Kühn1,3 and Klaus Gessner2,3 1Applied Geophysics, RWTH Aachen University 2School of Earth and Geographical Sciences, University of Western Australia 3Exploration and Mining, CSIRO pmd CRC Parallels between Soultz-sous-Forêts and Mount Isa • • • • Fluid flow in fractured systems Mineralization in crystalline rocks Precipitation / dissolution pattern Permeability evolution over time Hypotheses testing applying reactive transport Outline • Mount Isa Copper – location, deposit, model • SHEMAT / Processing SHEMAT • Fluid flow driver? – Free thermal convection – Hydraulic head driven flow • Silicification pattern (quartz body development) due to the fluid flow driving process • Conclusion – What have we learned? Mount Isa location Mount Isa Copper deposit 6 km x 5 km x 3 km Mount Isa fault Urquhart shale envelope Paroo fault goCAD to SHEMAT Field observations – quartz body Urquhart shale envelope Paroo fault Mount Isa fault SHEMAT / Processing SHEMAT (Clauser 2003) • Coupled flow, heat, transport, and chemical processes • Geochemical reactions between solids and fluids • Reactive Transport – PHRQPITZ (Pitzer’s approach) for low to high salinities but seawater system only – PHREEQC (Debye-Hückel) for low salinities but increased chemical system Free thermal convection (high permeability Urquhart) Urquhart shale envelope Mount Isa fault Paroo fault Free thermal convection (low permeability Urquhart) Mount Isa fault Paroo fault Quartz body: observation vs. simulation high permeability Urquhart shale envelope Mount Isa fault Paroo fault low permeability Forced flux / hydraulic head driven flow into faults Urquhart shale envelope Mount Isa fault Darcy flux 1E-08 m/s free convection flux Paroo fault Quartz body: observation vs. simulation Forced flux / no convection 50 % impermeable Conclusions • Process driving fluid flow? – free thermal convection – hydraulic head driven flow • Considering conditions required to form the observed quartz body suggests: rather hydraulic head driven flow than free convection Acknowledgements • Thanks to: – Florian Dobert who contributed to the presented work, – the pmd*CRC for financial support in previous years during my work with CSIRO, – Xstrata Copper for financial support and the contribution of valuable field data Thank you