METALLOGENY AND TECTONIC EVOLUTION OF THE EARLY PROTEROZOIC SKELLEFTE DISTRICT, NORTHERN SWEDEN

The various mineralizations in the Early Proterozoic Skellefte district are discussed and placed in a palaeotectonic context. The metallogeny, together with volcanic stratigraphy, geochemistry, isotope studies, and structural geology, favour a former destructive plate margin. At approximately 1.89 Ga the area resembled a modem island arc environment where volcanogenic massive sulphide and gold-rich porphyry-type deposits formed. Mafic to ultramafic sills and dykes hosting Ni mineralizations intruded a greywacke sequence immediately south of the Skellefte district as a result of large scale rifting at the end of the volcanic period. Gold was emplaced 20-60 Ma later during peak metamorphism at the end of the Svecofennian orogeny. Finally at approximately 1.80 Ga, after accretion of the island arc to the Archaean continent in the northeast, large granitoids intruded. Some of these have associated W, U, Mo, and Li mineralizations-an evidence for a crustal or cratonic influence.