Re–Os isotope geochemistry of Tertiary picritic and basaltic magmatism of East Greenland: constraints on plume–lithosphere interactions and the genesis of the Platinova reef, Skaergaard intrusion

• Published in: Lithos 1999-06, Vol.47 (1), p.107-126
• Main Authors: Brooks, C.K, Keays, R.R, Lambert, D.D, Frick, L.R, Nielsen, T.F.D
• Format: Article
• Language: English
• Subjects: PGE deposit; Plume signature; Re–Os geochemistry
• ISSN: 0024-4937; 1872-6143
• DOI: 10.1016/S0024-4937(99)00010-9

Re–Os abundance and isotopic studies on a small number of samples from the lowermost part of the East Greenland lava pile and the nearby Skaergaard intrusion show that picrite and ankaramite lavas tend to have high Os abundances and low Re/Os ratios, with most rocks having near-chondritic values for initial 187 Os/ 188 Os . One olivine basaltic sample with very high 187 Os/ 188 Os has most likely been affected by upper crustal contamination. There is no clear evidence for recycled crustal material in the ancestral Iceland plume source or for a significant degree of interaction of the picrites with ancient subcontinental lithospheric mantle of the North Atlantic craton. The Platinova Reef, the precious metal enriched zone in the Skaergaard intrusion, has very high Au and Pd contents but very low Pt and Os contents compared to platiniferous horizons in other layered intrusions. These characteristics are almost certainly due to the very late stage in the evolution of the Skaergaard magma chamber at which the Platinova Reef formed. The Platinova Reef yields a Re–Os T CHUR model age that is younger than the age of the intrusion, which was most likely produced by some form of post depositional disturbance to the Re–Os isotopic system. The high PGE contents of the East Greenland volcanic rocks indicate that they were formed from magmas that had the potential to form major accumulations of Ni–Cu–PGE sulphide deposits. Had similar magmas undergone significant interaction with continental crust elsewhere in East Greenland, they may have formed massive magmatic sulphide deposits. Thus, the potential for the discovery of large magmatic sulphide deposits of the Noril'sk-Talnakh-type in East Greenland must be considered excellent.