Greenland ruby and corundum occurrences with geochemistry
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:
Interactive GIS-map of Ruby Occurrences
Main Greenlandic Ruby Occurrences
Aappaluttoq is part of the Fiskenæsset complex, where rubies occur in ultramafic rocks that are in contact with anorthosites and leucogabbroic rocks (both aluminium-rich rocks). The ruby forming reaction is triggered by felsic sheets intersecting these rocks that intruded c. 2.7 billion years ago. This probably makes the Fiskenæsset complex rubies the oldest rubies in the world. Over 40 localities have been discovered in the Fiskenæsset complex so-far and occurrences vary largely in size and quality.
In the fjord-system inland from the Greenlandic capital Nuuk, several smaller ruby and corundum occurrences have been found. Most occur on the island of Storø, where ultramafic rocks are found in contact with aluminium-rich metasediments. The rubies and corundum observed here are often large and included, but show nice barrel-shaped crystal forms which are attractive for mineral collectors. A large, geologically similar, occurrence is found near the town Maniitsoq in the Kangerluarssuk fjord.
In the area around the East-Greenlandic town Tasiilaq rubies and corundum have been discovered in several small localities. The most important outcrops are found north and south of the fjord at Nattivit Kangertiva. Most rubies are of the plumasite type (ultramafic rock cut by a felsic sheet).
Methods for geochemical and optical characterisation of rubies
The Greenlandic rubies and corundum have been investigated with a range of laboratory techniques, were the most important techniques, of which the results are also included in the interactive map, are described here.
Trace elements were analysed with laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS) 22 elements were investigated, but the best results for characterisation of ruby 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 permil (‰).
Mineral and fluid inclusions and 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.
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