Sniffs of IOCG-style(?) chalcopyrite mineralisation in Northwestern Greenland GREENLAND

The Nutaarmiut Complex was identified during a 2016 field campaign in the Paleoproterozoic Rinkian Orogen. It is notable for: 1) blebby chalcopyrite and extensive malachite staining, and 2) being low grade and undeformed compared to the adjacent strongly deformed and granulite-facies lithologies. Field mapping defined locally chalcopyrite mineralized, gabbro and syenite layers. Further petrologic, geochronological, geochemical, and isotopic investigation has since demonstrated that these lithologies rather form locally mineralized metasomatic rocks.

The ‘felsic’ layers comprise sericitised orthoclase and albite. At least two generations of assemblages are observable in the ‘mafic’ layers: 1) quartz+albite+epidote+biotite+chlorite+sericite, and 2) an overprinting assemblage of hematite+ilmenite+chalcopyrite+apatite+monazite+zircon. The second assemblage contains abundant iron oxides that are intimately associated with blebs and stringers of chalcopyrite. Sulfur isotope measurements of chalcopyrite yield δ34S of +10‰, indicating sourcing of sulfur from an oxidised fluid. A‘felsic’ layer yielded metamict uraniferous (up to 8000 ppm) zircon. The zircon with the lowest uranium content (<2000 ppm) are used to constrain a 207Pb/206Pb age of ca. 1783 Ma. Regionally, this hydrothermal event follows peak high-T metamorphism by about 40 m.y., coinciding with the timing of metamorphic titantite and resetting of hornblende Ar-Ar ages. In the Churchill Province, this age corresponds to magmatism of the post-orogenic Nueltin Suite, which is sourced from lower crustal and mantle melts. Petrological observations, geochronology, sulfur isotopes and mineralisation style define a package of metasomatic rocks that is consistent with fluids that, in other areas, form IOCG-style mineralisation. This remote area of northwestern Greenland could be prospective for IOCG mineralisation.