Fluid transport through minerals and element mobilization within the Earth

Category Mineral processing
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Putnis, Christine۱; Austrheim, Haakon۲; Putnis, Andrew۱; Engvik, Ane۳
Holding Date 08 October 2008

Previous explanations for the movement of aqueous fluids through rocks have concentrated on the availability of pre-existing pathways, such as grain boundaries and stress fractures (Kostenko et al., 2002). Such pathways undoubtedly play a major role in allowing easy access for fluid transport. However, there is a lot of evidence that fluids migrate through minerals, which are reactive in the presence of an interfacial fluid layer (Putnis et al., 2005; Putnis and Putnis, 2007). Using time-lapse photography, fluid movement through single crystals of simple salts is observed at room T and P and presents a model for more complex mineral systems, showing similar textural and compositional equilibration features. The pseudomorphic replacement of one phase by another is characterised by the development of porosity in the product phase. This porosity provides the pathway for mass transport through the parent phase, which is replaced by the product at a moving interface within the mineral during an interface-coupled dissolution-reprecipitation replacement process. Such a mechanism allows for the remobilisation of elements which may be transported by the fluid phase and concentrated as an ore deposit. Replacement textures commonly occur in relation to fluid-driven regional metamorphism and large scale metasomatism and these processes are often related to mineralisation, such as in western Norway, where albitisation of gabbro is associated with many ore deposits. Similar albitised rocks are also characteristic of the Curnamona Province, Australia. This suggests that interface-coupled dissolution-reprecipitation and consequent porosity generation is an important mechanism of large scale fluid transport and element mobilisation.
References: Kostenko O., Jamtveit B., Austrheim H., Pollok K. and Putnis C. (2002), Geofluids 2, 1-13. Putnis C.V., Tsukamoto K. and Nishimura Y. (2005), Am. Mineral., 90 1909-1912. Putnis A. and Putnis C.V. (2007), J. Solid State Chem., 180, 1783-1786