The Bjerkreim-Sokndal intrusion is the largest layered intrusion of Northern Europe and the deposits of apatite, ilmenite and vanadium-rich magnetite represent a possible future resource of 280 million Tons of norite holding approximately 30 % of the three minerals together.
The geology of the Rogaland Anorthosite Province draped on the topography. The Bjerkreim-Sokndal Intrusion is shown in red and greenish colours while anorthosites are shown in blue.The Bjerkreim-Sokndal layered intrusion forms part of the Rogaland Anorthosite Complex situated in the south-western edge of Norway. The entire complex of anorthositic and noritic intrusions was formed in a prolonged intrusive event at a late stage of the Sveconorwegian Orogeny, where large volumes of melt (magma) migrated from deep in the Earth¿s crust to higher levels. The magmatic activity was completed with the formation of Bjerkreim-Sokndal intrusion at around 920 Ma.
During the course of crystallisation in the deep seethed magma chambers certain minerals started or stopped crystallising giving rise to certain crystallisation cycles. At various points of the crystallisation new magma arrived at the same crustal level or even into the previous formed magma chambers to reset the crystallisation cycle. These processes acted in much the same way as a refinery giving rise to the concentration of certain mineral to certain zones.
Principal sketch the showing formation of layered intrusions. "Skorpe" means crust, and "Mantel" means mantle. Modified from Ashwal.
The crystallisation process leading to the formation of the Bjerkreim-Sokndal Intrusion left behind six "mega-layers" or cycles of which three host a zone with apatite in addition to elevated amounts of ilmenite and magnetite. The total amount of the three mineral in these zones is approximately 30% of the host norite and each zone can be traced for several kilometres through the intrusion.
A contact between to major geological units is seen at the hill of Storeknuten. To the left of the arrows the vegetated hills represent apatite-magnetite- and ilmenite-rich norite. To the right the rocks consist of norite and troctolite without apatite and magnetite.
More information
Further information on the mineral resources of the Bjerkreim-Sokndal intrusion, geology, geochemistry, and mineral chemistry is available here.
You may also contact Gurli Meyer.
Published: 13. February 2008