Preliminary account of the geology of the Kvanefjeld Area of the Ilímaussaq Intrusion, South Greenland

Abstract

The Kvanefjeld area is situated in the northernmost part of the nimaussaq intrusion. The area represents a section through the roof zone of this intrusion. The roof is composed of sandstone, basaltic lavas, sheets of gabbro and dykes of dolerite and trachyte. Large masses of anorthosite are also found in the roof zone, The oldest members of the intrusion are augite syenite and alkali syenite which together with large masses of naujaite (poikilitic sodalite syenite) are enclosed in various types of fine-grained lujavrite. The lujavrite also intrudes the lavas of the roof. The bodies and veins of lujavrite are mainly located in zones of deformation in the rocks of the roof zone. The lavas of the roof are strongly altered in contact with the lujavrite and are locally enriched in epistolite-murmanite minerals. The latest member of the intrusion is a medium- to coarsegrained lujavrite which forms sheets and veins in most of the abovementioned rocks. The earlier fine-grained lujavrites and the contactmetasomatized lavas have concentrations of steenstrupine, monazite and thorite (?) in contact with the medium- to coarse-grained lujavrite and may contain up to 0.3 % U and three to four times this amount of thorium. This mineralization has been studied by mineralogical, geochemical and radiometric methods and in a number of drill holes. Analcime-rich veins rich in niobium and beryllium minerals are of widespread occurrence. The present paper gives a preliminary account of the geology of this region with special reference to the structural geology. A detailed examination of the economic geology of the Kvanefjeld area is currently being undertaken.