Genesis and evolution of carbonatites, the main Rare Earth element deposits: Quantification of the concentration processes from source to metal-rich magma – GECO-REE

GECO-REE will identify and quantify the magmatic processes responsible for the genesis of the principal Rare Earth Element (REE) deposits on Earth (carbonatite igneous rocks) through an integrated study (from mantle source to the final REE-enriched product) of the only active carbonatitic volcano on Earth. This unique system represents a natural laboratory for carbonatite genesis as it provides samples documenting the successive steps of the REE concentration process, from the mantle source, through the plumbing system that acts as an enriching filter, to the final REE-enriched product. We will characterize the protracted differentiation of mantle melts to carbonatites, the evolution of the REE contents of those melts, and the composition of the successive associated cumulative mineral assemblages (the intrusive component), which correspond to REE-bearing minerals in currently mined deposits. The composition, temperature, pressure, and redox conditions required for the onset of carbonatite immiscibility during differentiation will be quantified for the first time. The partition coefficients that govern each step of the REE concentration process (=differentiation), and their dependence on temperature, composition, and volatile content will be quantified for both mineral-liquid and carbonatitic melt-silicate melt partitioning. GECO-REE is multidisciplinary, and will take advantage of the expertise of the young researcher consortium in igneous and raw material petrology, and trace element and isotopic geochemistry. GECO-REE will provide the first integrated metallogenic model for the genesis of REE deposits, and will represent a real industrial capital gain for exploration companies.