Evaluation of Ni-Cu occurrences in the Uppermost Allochton of the Scandinavian Caledonides of Nordland, I: Field relationships

Abstract

The report gives a description of the geology and field relationships of Ni-Cu mineralisation in 7 ore fields that occur in the Uppermost Allochthon (UmA) of the Scandinavian Caledonides in Nordland where they occur associated with a variety of metamorphosed and\/or metasomatically altered mafic-ultramafic rock units. The occurrences in Markafjell in Brønnøy commune, Esjeholmene in Lurøy commune and Utvikåsen in Bodø commune are associated with ultramafic rocks in dismembered ophiolites whereas the ore-bearing ultramafic intrusion at Tverrbrennfjellet in Bodø commune comprises pyroxenites that have become \u201Cgabbroic\u201D by mingling with a tonalitic magma. Mineralisation hosted by gabbroic intrusions are comprised by the Høgsetdalen showing in Gildeskål commune and the Lilleålegden deposit in Beiarn commune, as well as the Måløy deposit in Steigen commune. The latter two deposits have been the sites of small-scale mining in the past due to high-grade ores exceeding 1 wt. % (locally massive pentlandite with ca. 33 wt. % Ni). The Steinåga mineralisation in Beiarn commune comprising low-base metal pyrrhotite ore (< 0.1 wt % Ni or Cu) is hosted by ultramafic amphibolites possibly representing meta-volcanites.