Distribution of characteristic elements in the radioactive rocks of the northern part of Kvanefjeld, llímaussaq intrusion, South GreenJand

Abstract

About 600 one-metre drill core sections from lujavrites and country rock xenoliths of northem Kvanefjeld were analysed for Li, Be, F, Na, K, Ca, Ti, Mn, Fe, Cu, Zn, Y, Zr, Nb, Pb, Th and U. The samples were taken from 7 of the 23 drill cores of the 1977 drilling operations. The analysed rocks were divided into seven rock groups: (1) naujakasite lujavrite, (2) naujakasite lujavrite with visible villiaumite, (3) arfvedsonite lujavrite, (4) arfvedsonite lujavrite with visible villiaumite, (5) volcanic rocks (lava and gabbro), (6) sheared volcanic rocks, and (7) sheared volcanic rocks with visible Nb minerals. Naujakasite lujavrite (both groups) has high concentrations of Th, U and Y at relatively low Zr contents. Arfvedsonite lujavrite (both groups) has high Zr contents but lower contents of Th, U and Y than naujakasite lujavrite. Thorium, U and Y generaIly accumulate at upper levels of lujavrites, mostly at the contact to xenoliths. This is thought to be caused by temperature gradients at the contacts. Zirconium enrichment occurs at lower levels of mainly arfvedsonite lujavrites expressing gravity settling of eudialyte during crystallisation. Naujakasite lujavrite is regarded as the youngest and most differentiated lujavrite. Microscopic and chemical investigations of two transition zones of lava and gabbro at contacts with lujavrites revealed typical features of metasornatic action, Le. formation of aegirine, arfvedsonite, albite, microcline, pectolite and other minerals. A general increase of sodium from the unaffected volcanic rocks towards the lujavrite contact is accompanied by a depletion of silicon and other elements. Niobium mineralisation is confined to sheared marginal zones of country rock xenoliths. Resource evaluation for Zr, Nb, Zn, Be, F, Li and rare earth elements of the rocks of northem Kvanefjeld suggest Nb and rare earth elements as potential by-products of a possibie uranium extraction process of the Kvanefjeld ore, while F should be extracted for mainly environmental reasons.