THE NORTH ATLANTIC IGNEOUS PROVINCE
Lavas and mineralizations on Ubekendt Ejland, West Greenland

Stefan Bernstein, Lotte Melchior Larsen, and Chris Pulvertaft, in collaboration with Christian Tegner (Univ. Århus), Bob Duncan (Univ. Oregon), and Dennis Bird (Stanford Univ.)

The research on Ubekendt Ejland, which is situated between the Nuussuaq and Svartenhuk peninsulas, focusses on both the regional aspects of flood basalt evolution and on the potential for gold mineralization in hydrothermal systems.
The youngest lava formations on Ubekendt Ejland are significantly younger (by 8–10 my) than the tholeiitic Vaigat and Maligât Formations at 60 Ma. This age difference is interesting in the light of our research in East Greenland on the origin of post-break-up igneous activity (Bernstein et al., 1998).
The post break-up volcanism has been shown to be surprisingly extensive in East Greenland, and the recent age information obtained from West Greenland suggests this may also be the case here. The aim of this study is to perform a geochronological and geochemical study of the Eocene, post-break-up volcanism in West Greenland, which mainly occurs to the west of the Itilli fault system.
The lavas on Ubekendt Ejland correlate timewise with the Kanissut volcanics on the western Nuussuaq peninsula. The alkaline Erqua Formation on Ubekendt is some 150 m thick. The underlying Nuuk Takitsoq Member has a transitional chemistry similar to the chemistry of the Kanissut volcanics; it is some 700 m thick, whereas the Kanissut volcanics themselves measure up to 2000 m in thickness. The existing geochemical data of these volcanics are of preliminary nature, so the correlation is somewhat uncertain. Gold mineralizations have been found in several of the large hydrothermal systems that cut Vaigat Formation picrites on the SE part of Ubekendt Ejland and plagioclase-phyric basalts in the western part of the island. The hydrothermal systems are characterized by several stages of quartz-carbonate-sulphide mineralizations and brecciations along fault planes, with quartz-carbonate veins up to several metres wide, surrounded by alteration halos up to tens of metres wide. Gold mineralization is in some places associated with massive sulphide mineralizations (Fe–Pb–Zn) and with infiltration of hydrocarbons into the vein systems. We are presently engaged in the preliminary sampling of the hydrothermal veins with the aim at understanding the nature of gold and base metal mineralizations.

References
Bernstein, S., Kelemen, K.B., Tegner, C., Kurz, M.D., Blusztajn, J., and Brooks, K.C., 1998: Post break-up basaltic magmatism along the East Greenland Tertiary rifted margin. Earth and Planetary Science Letters 160, 845–862. Bernstein, S., and Knudsen, C., 2004, Epithermal gold and massive sulphide mineralization in oil impregnated Palaeogene volcanic rocks of Ubekendt Ejland, West Greenland: Review of Survey Activities. Geological Survey of Denmark and Greenland Bulletin 4, 77–80.

Figure texts 1. Geological map of Ubekendt Ejland showing the distribution of volcanic formations, generally with the oldest Vaigat Formation picrites in the East and younger formations towards the west. 2. Quartz-carbonate vein systems cutting picritic lavas of the Vaigat Formation, Ubekendt Ejland. Height of cliff is about 150m.