The ore assemblages and textures displayed by some sulphide deposits associated with mafic intrusions
in the Bamble area are the product of three stages of ore formation: primary orthomagmatic
crystallisation, Sveconorwegian metamorphic crystallisation, and supergene alteration. Immiscible
sulphide-oxide melts segregated from several contaminated noritic melts during their passive emplacement, probably during the very early stages of the Sveconorwegian Regeneration (1200-1160
Ma).At Nystein and Meikjær, primary pyrrhotite-chalcopyrite-pyrite-pentlandite ores partially recrystallised during Sveconorwegian metamorphism to sulphur-enriched, pyrite-rich secondary assemblages, locally containing millerite and nickeloan pyrite. Primary pyrrhotite-chalcopyrite-pentlandite
ores at Østerå and Seljåsen remained largely unaltered during the Sveconorwegian event. The Seljåsen ores, which contain cobaltian pentlandite and accessory cobaltite, crystallised from an ultramafic-associated, cobalt-rich mett. The ores at this locality are predominantly hosted by pyroxenite, which appears to have formed as a direct response to the assimilation of siliceous country rocks during emplacement of the intrusion. Supergene violaritisation is ubiquitous in all of the deposits, and in the Seljåsen ore body it has resulted in the widespread formation of cobaltian violarite.