The Significance of Cumulus Chlorapatite and High-temperature Dashkesanite to the Genesis of PGE Mineralization in the Koitelainen and Keivitsa-Satovaara Complexes, Northern Finland

  • Tapani Mutanen
  • Ragnar Törnroos
  • Bo Johanson

Abstract

Several PGE mineralizations are known from the 2435 Ma-old Koitelainen layered intrusion and the adjacent Keivitsa-Satovaara (K-S) complex. In Koitelainen, transient sulphide separation gave rise to sulphidic PGE mineralizations (Pd-Pt- Au) in the lower zone and upper main zone. PGE, without visible sulphides, occur in Lower Chromitites (Pd-Pt) in the lower zone, in ultramafic pegmatoid pipes (Pt) in the main zone, and in the Upper Chromitite layer (Ru-Pt-Pd) of the lower upper zone. A peculiar peridotite-mixed rock in the main zone is underlain by a Pt-enriched layer, a setting reminiscent of the Stillwater PGE reef. PGE removed by these mineralizations had little effect on the overall buildup of PGE in the rest of the magma; by far the most of PGE precipitated with the last sulphide saturation at 95% level, in magnetite gabbro (Pt-Au-Pd). In the upper part of the K-S complex, assimilation of sedimentary sulphides triggered the deposition of massive sulphides. PGE occur only in overlying meagre disseminations (Pt-Pd-Au), and reach the highest concentrations in chromite-rich rocks (Os-Pt-Pd) at the roof. The distribution of PGE in these intrusions has an unusual pattern. Disseminated and massive sulphides in lower parts, with low PGEsulph (down to ≤10 ppb), are overlain by sulphide-poor mineralizations with high PGEsulph(from 20–13 000 to ∞ ppm). This feature persists, and even increases during crystallization, the principal PGE concentrations being located at or near the roof. Association of PGE with primary Cl-minerals suggests that the odd behaviour of PGE was due to an association between PGE and chlorine.

Keywords

Massive Sulphide Lower Zone Mafic Magma Main Zone Unusual Pattern 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Copyright information

© Elsevier Science Publishers Ltd 1988

Authors and Affiliations

  • Tapani Mutanen
    • 1
  • Ragnar Törnroos
    • 1
  • Bo Johanson
    • 1
  1. 1.Geological Survey of FinlandEspooFinland

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