Geochemistry and mineralogy of the Jebel Aja Igneous Intrusion and the associated exotic pegmatites, Arabian Shield, Saudi Arabia

We describe the Jebel Aja igneous intrusion (JAII), which sits at farthest northeastern edge of exposed Arabian Shield in Saudi Arabia. The JAII consists late Neoproterozoic post-collisional A-type granites, and was emplaced during tectonic extension. It is a composite pluton consisting granitic core (monzogranite, syenogranite alkali feldspar granite) surrounded by later phase alkaline peralkaline granites. Pegmatites occur as pockets dykes contact between alkaline/peralkaline granites syenogranite. pegmatites have sharp contacts with their host show variable colors (principally pink white), grain sizes, textures, mineral compositions. report here that white unique mineralogy includes first observation pyroxmangite, thortveitite thalénite-(Y) whole well novel (Sc, Y, vacancy)-rich pyroxenoid vacancy-rich bustamite excess octahedral Si. pyroxmangite-dominated lithology also features accessory quartz, albite, spessartine, pyrochroite, muscovite, fluorite. presence pyroxmangite rather than rhodonite, together Si-excess pyroxenes, suggests an elevated pressure emplacement. are highly evolved undergone extreme fractional crystallization feldspars, leading to increases concentration volatile incompatible elements residual melt, resulted eventually injection coeval into mostly solidified granite. granite contain sodic amphibole geochemical characteristics common among within-plate rare-metal bearing rocks. They positive Nb-Ta anomalies increase from pegmatite mineralized contains high concentrations Nb (1540–1769 μg/g), Ta (103–136 Y (1116–1616 Zr (6362–9707 Hf (215–264 Th (278–384 U (110–147 ∑REE (2334–3251 μg/g).