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Dynamics of HFSE transfer in high level alkaline intrusions: the role of multiple melt - fluid – solid interaction

Alkaline magmatic systems have an exceptional potential to fractionate and partially enrich incompatible elements and form rare metal deposits. However, the roles and relative importance of different magmatic processes on rare metal enrichment in such systems have not been fully explored. Potentially relevant processes include melt undercooling in flux-rich systems, or melt-fluid interaction, where ligand concentrations and the chemical evolution of the fluids exerts first-order control over the melt-fluid transition and fluid mediated transport of metals. The Iivaara complex (Finland), exposing the roof zone of an alkaline intrusion and the surrounding fenite aureole which both locally show Ti-dominated enrichment of high-field-strength elements, offers optimum conditions to study the impact of these phenomena on the transfer and enrichment of metals in a high temperature magmatic-hydrothermal system. The study will be based on the production of a comprehensive set of petrographic, microthermometric and elemental composition data of melt and fluid inclusions of all melts and fluids that are linked to different magmatic and post-magmatic stages. This includes potential high field strength ore elements and ligand-forming volatiles (C, O, P, S, Cl, Br, I) determined by in-situ high-resolution laser ablation-ICP-mass spectrometry and Raman spectroscopy. Apatite will be a further target for secondary ion mass spectrometry analysis to investigate the trace element, halogen and δ37Cl fluid record allowing to distinguish magmatic, crustal or meteoric fluid sources contributing to metal transfer. The data set generated in this project will be applied to distinguish and to evaluate the roles of magmatic as well as of melt-fluid- or fluid-rock-interaction processes for transport and enrichment of high-field-strength elements in the roof zone of the Iivaara alkaline complex serving as natural laboratory. The proposed project addresses key research problems in theme area A of the DOME Priority Programme, because it investigates high-temperature magmatic-hydrothermal metal deposit-forming processes in a continental setting of Europe. Likewise, project results will yield valuable constraints for other projects in the Priority Programme that are oriented towards experimental and numerical modelling approaches.