The Koillismaa Layered Igneous Complex: general geology, structural development and related sulphide and platinum-group element mineralization

摘要

The Koillismaa Layered Igneous Complex (KLIC) belongs to the group of Early Proterozoic 2.45 Ga old layered intrusions of the Fennoscandian Shield. The structural evolution of the Koillismaa area is divided into four phases starting with stepwise rifting during which mafic magmas intruded to form the KLIC. Continued rifting led to the formation of a basin into which volcanic and sedimentary material was deposited. This was followed by a compressional regime resulting in the present day configuration of scattered smaller intrusion blocks. Three principal mineralization types are identified in the KLIC; basal Cu-Ni-PGE enriched sulphides, reef-type PGE mineralization within the Layered Series and and Fe-Ti-V oxide layer higher in the sequence. The PGE enriched sulphides at the base of mafic intrusions are commonly interpreted to be due to contamination of magma by sialic wallrocks. This also seems to apply at Koillismaa.