| Summary: | The Notträsk gabbroic intrusion is located 6km NE of the Boden city in northern Sweden.The investigated intrusion is undeformed, funnel-shaped and considered to be a differentiate of the early-Proterozoic (Svecokarelian) synorogenic Haparanda granite series. The intrusion is well preserved indicating a younger age than the main rock series. The mafic intrusive rocks of the Notträsk area have been explored for Ni and Cu by many companies. The intrusion has been intermittently explored for PGE-Au by SGAB in between 1986 and 1989. SGAB drilled five holes in a profile and concentrated its effort mainly to the inner parts of the intrusion The present work is an attempt to understand the geotectonic setting of the inner part of the intrusion in which PGE’s were deposited. The analysis of samples taken at different locations from the SGAB drill holes and magnetometer measurement taken across the intrusion constituted the base for the work.Geochemical data suggests the presence of separate Al-rich and Fe-Ti rich liquids. The central part of the intrusion has higher contents of Mg, Na, Ca and Al where as the Fe Ti and K contents are much lower than the outer part of the intrusion. Total magnetic field also reveals that the outer part is highly magnetite rich compared to the inner part which is plagioclase and olivine rich. These facts points out the existence of two separate magmas, the outer is earlier and inner being later. Out of 67 samples analyzed by SGAB and this project, the anomalous high values of PGE and gold were found in 5 samples which belong to anorthositic olivine gabbro. So PGE’s are concentrated in the rocks that has olivine as the dominate silicate together with low but considerable amounts of sulphides. The rocks of the central part of the intrusion were generated by fractional crystallization giving olivine (+Cr) and plagioclase cumulates that would have given raised PGE grades if available. It is suggested that rocks were formed from a liquid more or less poor in PGE’s, but gold is still of interest ...
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