Stratabound scheelite and stratiform tourmalinites in the Archaean Malene supracrustal rocks, southern West Greenland

Abstract

The Malene supracrustal rocks form large enclaves in the late Archaean Nûk gneisses within an area of at least 36 000 km² on the west coast of Greenland and have been repeatedly deformed and metamorphosed under amphibolite facies conditions. Stream sediment sampling has shown that scheelite occurs in the supracrustal enclaves throughout the area. It occurs stratabound in amphibolites, micaceous quartzites, siliceous cordierite-bearing metasediments and tourmalinites. A detailed geological map has been made of the central part of Store Malene mountain close to Nuuk. Banded metavolcanic Malene amphibolites and siliceous cordierite-bearing metasediments contain stratiform tourmalinites, often with appreciable scheelite, in addition to common accessory tourmaline. The tourmaiinites predate the earliest recognisable phase of deformation as well as prominent simple pegmatites. The tourmaline probably originated as primary sea floor precipitates, and the primary or diagenetic tourmaline crystals were later overgrown with tourmaline during metamorphism. The scheelite and tourmaline are probably syngenetic and of submarine exhalative origin, and boron complexes may have played a role in transporting tungsten in hot brines.