Greenland is endowed with several significant REE deposits hosted in various geological settings. The largest of these is the highly peralkaline Ilímaussaq intrusion of the Mesoproterozoic Gardar province in the south, which hosts two advanced REE projects, Kringlerne and Kvanefjeld. The Gardar is an ancient rift zone that was volcanically and tectonically active between 1300 and 1100 million years ago. Although the province is no longer active, it is of major interest to geologists because the subsequent uplift and glacial erosion have cut deep into the rift and exposed the rocks and magma chambers that once lay well below the surface. Magma that stalled at upper crustal levels in the Gardar rift evolved to very extreme compositions. This generated high concentrations of incompatible elements, including uranium, thorium, niobium and tantalum, in the tops of these magma chambers. As a result the Gardar Province hosts some of the world's best mineralised magma bodies and our field work aimed to identify the roof zones of these alkaline complexes and understand more about the processes that concentrate the so–called 'rare–earth elements' (REE).
The focus of the St. Andrews group of the HiTech AlkCArb team (Adrian Finch, Will Hutchison) was the roof zones of the alkaline complexes Ilímaussaq and Motzfeldt. These complexes are only 50 km apart, host significant REE resources and yet their composition and magmatic evolution appears to be quite different. By comparing and contrasting these two unique complexes we wanted to understand whether or not the same underlying processes were taking place.
Intriguingly, despite the compositional differences between the Ilímaussaq and Motzfeldt complexes, during fieldwork the St. Andrews team found that the magmatic processes taking place in the roof zones were very similar. In both cases they were able to identify sinuous alkaline dykes and sheets penetrating the country rock, and comparable chemical alteration textures were visible around the margins of each intrusion. We collected a range of geological samples and our next objective is to characterise rigorously their mineralogy and alteration using petrographic and microanalytical geochemical tools. they are developing a set of geochemical indicators for alkaline roof zones and use these new tools to evaluate other complexes in Europe (e.g., Kaiserstuhl, Germany) and understand whether or not these prospects might offer comparable REE resources to those in the Gardar.
Simplified geological map of southern Greenland (Goodenough et al., 2002), showing the principal divisions of the Ketilidian orogen and the location of the main areas of Gardar rocks. The Nunarssuit–Isortôq (N–I) and Tugtutôq–Ilímaussaq–Nunataq (T–I–N) dyke swarms are shown diagrammatically.
Some of the HiTech AlkCarb team on fieldwork in the Gardar province, Southern Greenland 2017 (L-R, First mate; Sam Weatherley, Adrian Finch, Paul Bons, Anders, Will Hutchison, Pete Siegfried, Gregor Markl, Emma Humphreys-Williams, Ellen, Ben Walter, Inouk, Tom Andersen, Eimear Deady, Jindrich Kynicky, Michael Marks).
Recent publications on/including the Gardar Province by HiTech AlkCarb members:
Finch et al., 2019 From Mantle to Motzfeldt: A genetic model for syenite-hosted Ta,Nb-mineralisation, Ore Geology Reviews
Marks, M A W, & Markl, G. 2017 A global review on agpaitic rocks, Earth-Science Reviews