Copper, zinc and nickel occurrences in the Nuuk region, West Greenland

In the Nuuk region two ages of Archaean supracrustal rocks occur; Early and mid-Archaean. The Isua supracrustals are Early Archaean, and host an abundance of small copper showings. These are mainly disseminations, thin veins and stringers in banded amphibolites. Locally also sulphide facies iron-formation contains appreciable amounts of chalcopyrite.

The mid-Archaean Malene supracrustal rocks occur as enclaves over an area of more than 30,000 km2. Malene supracrustal rocks is a term used here for convenience for supracrustals younger than the Isua supracrustals. The Nuuk region can be divided into terranes in which supracrustals occur. The relative age of these terranes are uncertain and it is not known whether the supra-crustal rocks occurring in the different terranes are spatially related or whether they are of quite different ages. The Malene supracrustal rocks comprise mafic and ultramafic volcanics with minor metasediments and rare thin layers of banded iron-formation. Within the volcanic rocks anthophyllite gedrite zones up to a few metres wide are found. These zones can be traced with intervals for kilometres. They often contain semi-massive sulphides: pyrrhotite, pyrite, chalcopyrite, sphalerite, molybdenite as well as small amounts of gahnite. The zones also contain trace amounts of tin and tungsten.

The Malene anthophyllite-gedrite zones closely resemble anthophyllite-ged rite zones elsewhere such as in Western Ontario where they underlie massive sulphide deposits e. g. the Geco deposit in Manitouwadge and the Winston lake massive sulphide ores. The anthophyllite-gedrite zones in Western Ontario are interpreted as metamorphosed hydrothermal alteration zones, an explanation which seems valid for the Malene occurrences.

In the southern part of the Nuuk region a large anorthosite complex occurs. In some anorthosite layers as well as in some of the mafic layers pyrrhotite, chalcopyrite and pentlandite have been observed, although as yet not in economic proportions.