Distinguishing magmatic and metamorphic processes in the Norra Kärr alkaline complex, Southern Sweden

The Norra Kärr rare metal deposit in Southern Sweden represents one of the largest resources of rare earth elements (REE) in Europe. The mineralization is hosted by deformed agpaitic nepheline syenites covering an area 350 by 1100 m in size. REE-bearing minerals include eudialyte-group minerals (EGM) and minor mosandrite and britholite-group minerals. Zr is hosted by catapleiite and EGM.
The intrusion was emplaced between 1.55-1.40 Ga within the Transscandinavian Igneous Belt in an anorogenic (post Svecofennian) environment and deformed and metamorphosed during the Sveconorwegian (Grenvillian) orogeny between 1.25-0.85 Ga (e.g. Andersson et al., 2007). Microtextures and compositional variations in clinopyroxene and EGM are used to distinguish magmatic and metamorphic processes during the evolution of this rare metal mineralization.
Clinopyroxenes are invariably sodic and are characterized by early magmatic Zr-rich cores, euhedrally overgrown by presumably late magmatic aegirine, anhedrally overgrown by metamorphic Al-rich aegirine (jadeite). Similarly, EGM show complex distribution patterns of major and minor elements suggesting multiphase influence of fractional crystallization, recrystallization, fluid-induced re-mobilization and late alteration.