A gold-bearing volcanogenic-exhalative horizon in the Archaean(?) Saqqaq supracrustal rocks, Nuussuaq, West Greenland

Abstract

The Saqqaq supracrustal rocks in southern Nuussuaq, West Greenland, host stratiform gold mineralisation in a 3–4 m thick impure chert horizon of volcanogenic-exhalative origin; chip samples average c. 0.8 ppm Au (thickness 3.3 m) over a strike length of 8 km, including 1.1 ppm Au (thickness 3.7 m) over a strike length of 1.6 km. Silicate minerals in and adjacent to the mineralised horizon include chrome-bearing tourmaline, staurolite, fuchsite, and manganiferous garnet. The Saqqaq supracrustal rocks form an almost 30 km long, NW-striking and SW-dipping sequence, which is presumed to be of Archaean age and consists of amphibolite facies mafic and ultramafic metavolcanic rocks, associated minor volcanogenic-exhalative horizons, and quartzo-feldspathic metasediments. The sequence is surrounded by Archaean(?) orthogneisses and intruded by an up to c. 100 m thick trondhjemitic sill, and appears to outline a large asymmetric, isoclinal fold (possibly of Archaean age) which was refolded in the lower Proterozoic