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 plagio...
