High-technology metals in alkaline and carbonatitic rocks in Greenland: recognition and exploration

Abstract

High-technology metals such as Zr, Y, Nb, Ta, ree and Ga are generally associated with alkaline and carbonatitic rocks. The recognition of alkaline magmatic provinces or carbonatitic complexes is, therefore, a first step in the exploration for high-technology metals. Low-density exploration data over large parts of South and West Greenland including airborne gamma-ray spectrometry and stream sediment surveys clearly delineate the extension of a major Proterozoic alkaline igneous province and two Phanerozoic carbonatite complexes. On a reconnaissance scale, Nb in stream sediment is the best indicator and gave distinct anomaly patterns over all of the alkaline and carbonatitic intrusive complexes. The anomaly patterns for Y, Zr, Ga, Mn, Sr, Zn, U, and Th also reflect the alkaline/carbonatite intrusions but they are less regular and consistent. In the alkaline Gardar igneous province in South Greenland, two prospects in the Ilimaussaq intrusion relate to rock units rich in eudialyte (Zr, Y, ree). Some of the eudialyte-rich zones were located by geological mapping and visual recognition of this red mineral; elsewhere in the fine-grained eudialyte-bearing rocks, analyses of chip samples and drilling were used. In the Motzfeldt intrusion of the Gardar province, zones of intense hydrothermal alteration are enriched in Nb, Ta, Zr, ree, U and Th. The mineralised zones were located by helicopter-borne gamma spectrometry and subsequently grid sampled to assess Nb and Ta contents. In the Sarfartôq carbonatite complex, alteration zones with massive pyrochlore (Nb) were located by airborne and ground radiometry combined with detailed stream sediment sampling. In the Qaqarssuk carbonatite, minor pyrochlore concentrations and ree-bearing veins have been discovered during exploration for apatite. Based on this experience it is concluded that alkaline and carbonatite complexes are easily recognised in low-density geochemical data. Ore zones have been located using radiometric methods combined with geological mapping and detailed geochemical surveying.