Quantifying metasomatic high-field-strength and rare-earth element transport from alkaline magmas

Abstract Alkaline igneous rocks host many global high-field-strength element (HFSE) and rare-earth (REE) deposits. While HFSEs are commonly assumed to be immobile in hydrothermal systems, transport by late-stage fluids associated with alkaline magmas is reported. However, the magnitude of flux conditions poorly constrained yet essential understanding formation REE-HFSE ores. We examined alteration country (“fenitization”) accompanying emplacement a syenite magma at Illerfissalik Greenland, through analysis changes rock chemistry, mineralogy, texture. Our novel geochemical maps show 400-m-wide intrusion aureole, within which we observed typically tenfold increases concentrations elements, including HFSEs. Textures suggest both pervasive structurally hosted fluid flow, initial reaction occurring protolith's quartz cement, leading increased permeability enhancing chemical interaction mixed Ca-K-Na fenitizing fluid. estimated HFSE masses transferred from fenite this found ~43 Mt REEs were mobilized (~12% syenite-fenite system total rare-earth-oxide [TREO] budget), mass comparable tonnages some world's largest resources. argue that can yield crucial information about tipping points evolution because retention and/or loss volatile-bonded alkali key factors development magmatic zirconosilicate-hosted ores (e.g., Kringlerne, Ilímaussaq), or syenite-hosted Nb-Ta-REE (Motzfeldt-type) roof-zone