Characterization of the mineralized albitite bodies at Biggejavri, Kautokeino Greenstone Belt, Finnmark, Northern Norway

Abstract

The Kautokeino Greenstone Belt in Finnmark, Northern Norway is host to the Biggejavri U-REE occurrence and the Bidjovagge Cu-Au deposit. The Biggejavri U-REE occurrence is hosted in albitite lenses within the amphibolite unit of the Suoluvuopmi Formation whereas the Bidjovagge Cu-Au deposit is hosted in shear structures crosscutting albitite lenses in the amphibolite of the Časkejas Formation in the west. Both Biggejavri and Bidjovagge occur in the same stratigraphic sequence, comprised of amphibolites, mica and graphitic schists, metadolerites and albitite lenses, with the high Mg amphibolite only occurring at Biggejavri. The Biggejavri U-REE occurrence is unique in its mineralogy with the predominant ore mineral being davidite-loveringite ((La,Ce,Ca)(Y,U)(Ti,Fe3+)20O38-(Ca,Ce)(Ti,Fe3+,Cr,Mg)21O38). The aim of this study is to better understand the formation of the complex mineralogy observed in the Biggejavri area. Amphibole from all units of the Biggejavri U-REE occurrence as well as the Bidjovagge Cu-Au deposit were analyzed using FE-SEM, automated mineralogy, EPMA, and LA-ICP-MS. Trace elements such as Ni and Cr are highest in amphibole in the high Mg amphibolite from the Biggejavri U-REE occurrence, whereas trace elements such as Ti and V are highest in amphibole from the albitite lenses. Biggejavri displays a unique co-location of mafic high Mg rocks and highly evolved felsic rocks. While trace element analysis of amphibole indicates that the high Mg amphibolite, formerly a komatiite, is highly enriched in elements such as Ni and Cr, the felsic albitite lenses within the high Mg amphibolite show enrichment in elements such as Ti, V, and REEs. During metamorphism, the aforementioned elements were released into the metamorphic fluid and formed rare minerals of the davidite-lovingerite solid solution series ((La,Ce,Ca)(Y,U)(Ti,Fe3+)20O38-(Ca,Ce)(Ti,Fe3+,Cr,Mg)21O38).