Ruby occurrences in Greenland

Ruby is the red and pink gemstone variety of the mainly colourless mineral corundum. Gem-corundum in all other colours are called sapphire. Many small and a few larger ruby and red/pink non-gem quality corundum occurrences are found in Greenland. These include the ruby deposit at Aappaluttoq, near Fiskenæsset in southern West Greenland.Blue sapphire on the other hand, has so-far only been observed in microscopically small grains on Disko Island. All rubies and red/pink corundum in Greenland are related to ultramafic (mantle-derived) rocks in contact with felsic sheets (cross-cutting molten rock rich in silica and aluminium) or with aluminium-rich rocks.

The ruby and corundum occurrences in Greenland were investigated both in their outcrops for their size, distribution, geological history and surrounding mineralogy, as well as in the laboratory with the aim to characterise the rubies for possible fingerprinting characteristics. Fingerprinting is the geochemical and optical characterisation of gemstones with the aim to define their country or region of origin. The results of these investigations are shared here.

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Main Greenlandic Ruby Occurrences

Aappaluttoq is part of the Fiskenæsset Complex, where rubies occur in ultramafic rocks in contact with aluminium-rich rocks including both anorthosites and leuco-gabbroic rocks. The ruby forming reaction is triggered by felsic sheets intruded c. 2.7 billion years ago into the ultramafic country rocks. This probably makes rubies from the Fiskenæsset Complex the oldest in the world. Over 40 localities have so-far been discovered in the Fiskenæsset Complex and occurrences have a large variation in size and gem quality.

Several smaller ruby and corundum occurrences have been found in the fjord-system inland from the Greenlandic capital Nuuk. Most occur on the island of Storø, where ultramafic rocks are found in contact with aluminium-rich meta-sediments. The rubies and corundum observed here are often large with inclusions but show nice barrel-shaped crystal forms that are attractive for mineral collectors. A large, geologically similar occurrence is found near the town Maniitsoq in the Kangerluarssuk fjord.

Both rubies and corundum have been discovered in several small localities in the area around the town of Tasiilaq in East Greenland. The most important outcrops are found north and south of the fjord at Nattivit Kangertiva. Most rubies are of the plumasite type (an ultramafic rock cut by a felsic sheet).

Geochemical and optical characterisation of rubies

The Greenlandic rubies and corundum have been investigated with a range of laboratory techniques. The most important techniques and results are also included in the interactive map and are described here.

Twenty-two trace elements were analysed with laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS), but the best results for ruby characterisation of occurrences was obtained for Cr, Fe, Ti, V and Ga. Analyses were performed at the Geological Survey of Denmark and Greenland. A NWR213 frequency-quintupled Nd:YAG solid state laser system from New Wave Research/ESI, employing two-volume cell technology, was coupled to an ELEMENT 2 double-focusing single-collector magnetic sector field-ICP-MS from Thermo-Fisher Scientific to run the analyses.

Trace elements were also investigated with micro-X-ray fluorescence analyses (µXRF) at Roskilde University (now at the National History Museum of Denmark) applying a Bruker M4 Tornado. The investigation concentrated on O, Mg, Al, Si, Ti, V, Cr ,Fe, Ga, and Zr.

The third method to investigate for trace elements was Laser-induced breakdown spectroscopy (LIBS) applying equipment from the Department of Plant and Environmental Sciences at Copenhagen University. Samples were investigated for all trace elements and a range of trace elements was observed.

Oxygen isotope values were determined for ruby minerals at the University of Lausanne on a Finnigan MAT 253 isotope ratio mass spectrometer. Oxygen isotope compositions are given in the standard notation, expressed relative to VSMOW in permille (‰).

Mineral and fluid inclusions together with growth feature characteristics were studied, and images were taken with a Leica DFC295 camera and Leica Application Suite 3.7 software at the Geological Survey of Denmark and Greenland. Investigations show solid and fluid inclusions and growth features that are typical for the investigated samples from the Fiskenæsset Complex.

Scientific reporting

More information on the project can be obtained from the following contributions:

Formation, origin and geographic typing of corundum (ruby and pink sapphire) from the Fiskenæsset complex, Greenland. Link
Meso- and Neoarchaean geological history of the Bjørnesund and Ravns Storø Supracrustal Belts, southern West Greenland: Settings for gold enrichment and corundum formation. Link
Fingerprinting of corundum (ruby) from Fiskenæsset, West Greenland. Link

Nattivit

Nattivit ruby

Nattivit

Aappaluttoq ruby

Contact

Nynke Keulen

Senior researcher

Phone: 91 33 38 73
E-mail: ntk@geus.dk

Ruby occurrences in Greenland

Main Greenlandic Ruby Occurrences

Geochemical and optical characterisation of rubies

Scientific reporting

Nattivit

Nattivit ruby

Nattivit

Aappaluttoq ruby

Contact

eng.geus.dk