Mechanisms for Concentrating Critical Metals in Granitic Complexes: Insights from the Mourne Mountains, Northern Ireland

Four types of critical metals anomalies were located in granite bedrocks of the Mourne Mountains using Tellus (Northern Ireland) stream sediment and deep soil geochemistry data, and analysed to develop a multi-stage model for enrichment of critical metals. 1. Nb, REE, Th and U soil anomalies correlated with late-stage and eutectic minerals in the roof zone of the most peralkaline F- and volatile-rich granite body. 2. Li, Be, B, As, Sn, Mn3+ and Ce4+ partitioned into pockets of late-stage heterogeneously distributed F-rich silicic residual melts and relatively oxidising halide-rich magmatic fluids. Isolated soil anomalies correlated with amorphous Mn3+− and Ce4+−rich masses infilling drusy cavities, which resulted from short-distance percolation of small volumes of late-stage magmatic fluids. 3. A significant As plume emanated from a greisen that hosted multiple critical and base metals including Sn, from reactions between large volumes of magmatic As + halide-rich fluids and mafic silicate + diverse accessory minerals. 4. Diverse, small-scale REE anomalies in the soil data along structural features correlate with vein mineralisation resulting from episodic migration of hydrous fluids of variable composition, probably with a much smaller magmatic component than elsewhere.