Crustal melts, fluids and ore-forming processes

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Although we have made substantial progress in understanding the processes by which crustal melts and fluids concentrate base and precious metals to exploitable levels in the Earth’s crust, there are still a number of outstanding issues to address. Moreover, recent technological advances, driven mainly by the need to mitigate the environmental impact of human activity, have created a demand for a new group of “critical metals”, for which understanding of the concentrating processes is in its infancy. My research aims to address some unresolved issues of base and precious metal ore genesis and develop models for the genesis of ore deposits of some critical metals, namely the REE and associated metals. In so doing, I plan to make fundamental contributions to science that will find application in the exploration for base, precious and critical metal deposits. An unresolved question for porphyry copper and epithermal gold-silver ore formation is whether the ore fluids are hydrothermal liquids or vapours. I and my students will address this issue by building on previous work by ourselves and others. To do so, we will analyse the compositions of the trapped fluids in suitable ore deposits (using microthermometry and LA-ICPMS) and conduct experiments designed to determine the solubility/speciation of the metals in vapour and their partitioning between liquid and vapour. A particularly interesting and largely ignored question for a number of sediment-hosted ore deposit types is whether liquid hydrocarbons could have been involved in metal transport. Recently, we have shown that this was the case for uranium in the Witwatersrand Au-U deposits, South Africa, where it occurs as uraninite nanoparticles in pyrobitumen and flocculated to form larger aggregates some of which have been previously misinterpreted as detrital grains. We will expand this research by analysing and imaging the hydrocarbons in MVT Pb-Zn deposits using LA-ICPMS and high resolution TEM techniques, and by conducting experiments designed to determine the solubility and speciation of metals in crude oil. Finally, we propose to document the nature of a selection of REE (associated in some cases with Nb and Zr) deposits in intrusive (carbonatite, nepheline syenite and granite) and non-intrusive hosts using field relationships, optical and SEM petrography, mineral/rock geochemistry, and fluid/melt inclusion studies), and investigate the metal concentrating and fractionating processes. These studies will be complemented by experimental studies of the stability of REE and Nb species in hydrothermal fluids. The proposed research has the potential to significantly advance understanding of how a variety of base, precious and critical metal deposits form, and help guide exploration for these deposits in Canada and abroad. It will also help train a new generation of geologists for careers in the mining industry, government and academia.