PGE reefs as an in situ crystallization phenomenon: the Nadezhda gabbronorite body, Lukkulaisvaara layered intrusion, Fennoscandian Shield, Russia

• Published in: Mineralogy and petrology 2008, Vol.92 (1-2), p.211-242
• Main Authors: Latypov, R. M., Chistyakova, S. Yu, Alapieti, T. T.
• Format: Article
• Language: English
• Subjects: Crystallization; Earth and Environmental Science; Earth Sciences; Geochemistry; Geology; Inorganic Chemistry; Magma; Mineralization; Mineralogy; Petrology; Sulfides
• ISSN: 0930-0708; 1438-1168
• DOI: 10.1007/s00710-007-0189-1

Summary The 100 m thick and 700 m long Nadezhda sill-like gabbronorite body, emplaced in the mafic-ultramafic Lukkulaisvaara layered intrusion, is associated with Cu-Ni-PGE mineralization that is mostly confined to mottled anorthosites developed from host gabbronorites and norites along the margin of the entire body. PGE and Au show distinct positive correlation with Cu, Ni and S suggesting that the noble metals are mainly controlled by sulphides. A mineralized layer about 1 m thick contains on average 0.74 wt.% S, 1.77 ppm Pt and 7.96 ppm Pd. Marginal location of PGE-rich sulphides and their absence in the Nadezhda body suggest that the mineralizing process must have been gravity-independent and not related to the bulk saturation of the magma in sulphides. We propose that the Nadezhda Cu-Ni-PGE mineralization formed as a result of local sulphide saturation that was achieved in situ at the margins as a result of the flux of ore-bearing fluids from the interior of the body towards its margins. The sulphides became PGE-rich due to interaction with a large volume of ore-bearing fluids that were introduced into the Nadezhda body during a juvenile stage of its development as a conduit through which a large volume of magma has passed on its way to the main chamber.