From arc magmas to ores (FAMOS): A mineral systems approach

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Society is dependent on a reliable supply of metals and minerals for economic growth, improved standards of living, and development of infrastructure. Population growth means that even with increased recycling and resource efficiency, new mineral deposits still need to be discovered. The efficient exploration for, and discovery of, new resources requires new concepts and new tools. The Mineral Systems approach to exploration considers ore deposits on a lithospheric scale, in terms of the "ingredients", processes and environments that favour their formation. This approach amounts to a "source-pathway-trap" model, with an increased emphasis on predictive capacity, rather than just feature recognition. Historically, much research has focused on the trap, and characterisation of the ore deposits themselves; here we aim to focus deeper in the system by integrating ore deposit formation with concepts of magmatism that arise from igneous petrology and volcanology. Therein lies a challenge because extant models for porphyry systems are increasingly at odds with magmatic models for crustal construction and arc volcanism. Rather than seeing magmatic systems in terms of large, liquid-rich magma chambers, emerging petrological models for crustal magmatism are turning instead to crystal-dominated, volatile-bearing "mushy" systems that traverse most or all of the crust. The dynamics of such systems have important consequences not just for arc magmatism, but also for the chemistry of the volatiles that are exsolved. These same volatiles fuel mineralisation and this is the synergy that we aim to exploit by assembling a multidisciplinary team of researchers from economic geology, igneous and metamorphic petrology, volcanology, geochemistry, numerical modelling and fluid dynamics. Our team embraces almost everyone currently engaged in porphyry mineralisation research in the UK and capitalises on strong existing links between UK ROs and the mining industry, many of who are Project Partners. The research will involve analysis of minerals from a wide variety of mineralised and barren settings using a wealth of modern analytical tools that enable determination of an extensive suite of trace elements and isotope tracers. As each trace element responds to magmatic processes in subtly different ways due to the affinity of different elements for different phases (minerals, melts and fluids), so the multi-element approach affords many advantages over conventional proxies in which the full potential of the Periodic Table is not exploited. The analysis of natural systems will be underpinned by high pressure and temperature experiments to establish the phase relationships of ascending arc magmas and the partition coefficients that capture the affinities of elements for certain phases. As fluid accumulation and migration is an essential, but poorly understood, final step in ore deposit formation, we will develop, in tandem with the geochemistry, numerical models for fluid-bearing mushy systems. Finally, consideration will be given to critical metals that are passengers through the main ore-forming processes, but constitute important, often under-explored, by-products of porphyry mineralisation. The research proposed has a strong element of blue skies investigation, but a particular focus on outcomes that will benefit industry through improved exploration tools. Thus the project bridges the divide between academic and applied research in a way that is not normally possible through industry-funded projects. This bridging activity lies at the heart of the Highlight Topic call, specifically through the integration of new advances in the study of mineral systems, igneous petrology and geochemistry, with a view to identifying conditions that can act as pathfinders for new targets. A key outcome will be a range of trace element proxies that will enable the mining industry to establish the potential fertility of a magmatic arc on local to regional scales.