The marginal border group of the Porttivaara layered intrusion and related sulphide mineralization

Basic magma intruded between the Archean gneisses and the discordantly overlying volcanics in the Early-Proterozoic era, and, following Fenner's series of differentiation crystallized into a layered sequence of the Porttivaara massif. A relatively complicated border group developed between the layered sequence and the Archean gneisses consisting of the following units, from the bottom upwards: albite-quartz rock, contact gabbro and ultramafitolites. The border zone contains sulphide dissemination which consists mainly of chalcopyrite, pentlandite and pyrrhotite. The sulphide dissemination formed during the intrusion of the magma, as contamination lowered the solubility of sulphides in the magma.

Abstract licence: CC BY-NC

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