Geological Survey of Denmark and Greenland Bulletin 28, 2013, 53-56 53 Fingerprinting of corundum (ruby) from Fiskenæsset, West Greenland Nynke Keulen and Per Kalvig Since the late 1960s, it has been known that pink and red corundum occur in the area near Fiskenæsset (Qeqertarsuat- siaat) in southern West Greenland. Corundum is hosted in the Fiskenæsset complex, which is part of the Archaean base- ment of the North Atlantic Craton. To date, c. 40 corundum localities with a wide range of quality are known in the area – a few localities yield stones of gem quality. The most prom- ising locality, Aappaluttoq, is likely to be mined in the fore- seeable future by the Canadian company True North Gems (Figs 1, 2A). Red corundum of gem quality is called ruby; gem quality corundum of other colours (e.g. pink, yellow or blue) is called pink sapphire, yellow sapphire etc., while the blue gem corundum is sapphire. Red, pink and blue corun- dum are also known in smaller quantities from other areas in Greenland. The Fiskenæsset complex The Fiskenæsset complex (Fig. 1) comprises a series of in- trusive sheets of anorthosite, leucogabbro, gabbro and ultra- mafic rocks (Myers 1985), and is interpreted as derived from a supra-subduction setting, while the associated amphibolites stem from a mid-oceanic ridge to island arc basalt precursor (Polat et al. 2009). The greater Fiskenæsset region was meta- morphosed c. 2.85–2.80 Ga ago at mid- to upper amphi- bolite-facies temperatures and pressures, reaching granulite facies conditions near the village of Fiskenæsset (McGregor & Friend 1992; Schumacher et al. 2011). At least one genera- tion of the c. 2.71 Ga felsic pegmatite sheets cuts the anor- thosite, ultramafic rocks, amphibolite and gneisses and cre- ated reaction zones that developed aluminium-rich mineral assemblages derived from the aluminium in the anorthosite rocks (Schumacher et al. 2011; Fig. 2B). These reaction zone assemblages, associated with pegmatitic felsic sheets and the ultramafic bodies, include very coarse-grained, radial antho- phyllite ± green pargasite ± green or red spinel ± sapphirine ± cordierite (up to 30 cm single crystals) ± pink corundum, and ± phlogopite (Schumacher et al. 2011). This study is a first attempt to find geochemical and min- eralogical characteristics that can be used to tie the Green- landic rubies to their area of origin. This may have practical implications if an operation of rubies and pink sapphires is established in Greenland. Here, we present Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP- MS) trace-element geochemical and oxygen isotope data of samples from the Fiskenæsset area and other known locali- ties in Greenland (Storø, Maniitsoq, Kapisillit and Nattivit). © 2013 GEUS. Geological Survey of Denmark and Greenland Bulletin 28, 53–56. Open access: www.geus.dk/publications/bull Fig. 1. Simplified geological map of the Fiskenæs- set area in southern West Greenland showing the investigated pink and red corundum (ruby) localities in the Fiskenæsset complex. Map after Keulen & Kokfelt et al. (2011). M: Maniitsoq, S: Storø, K: Kapisillit, F: Fiskenæsset, N: Nattivit. ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; 63°N63°N GreenlandGreenland NNKKSS MM FF 50°W50°W 10 km10 km Qororssuaq EastQororssuaq East PiqinikPiqinik Rubin Ø (Tasiusarsuaq)Rubin Ø (Tasiusarsuaq) Qaqat AquleritQaqat Aqulerit Bjørnesund 2008Bjørnesund 2008 QaqqatsiaqQaqqatsiaq SiggartartulikSiggartartulikKigutilikKigutilik Lower AnnertusoqLower Annertusoq Upper AnnertusoqUpper Annertusoq AappaluttoqAappaluttoq Bjø rne sun d Bjø rne sun d Fiskenæ sfjorde n Fiskenæ sfjorde n GrædefjordGrædefjord GneissGneiss AmphiboliteAmphibolite GraniteGranite DoleriteDoleriteAnorthosite (Fiskenæsset complex)Anorthosite (Fiskenæsset complex) FiskenæssetFiskenæsset 5454 Trace-element geochemistry Corundum has the chemical formula Al2O3 and like most other minerals usually includes very small quantities of other elements in its crystal structure. The amounts of these trace elements and their ratios may depend on the geological con- ditions during the formation of the corundum and therefore usually vary between individual corundum deposits. Twen- ty-four different elements were analysed for by means of LA- ICP-MS; however most of them were not detected, includ- ing Sn, Nb, and Ta. Our investigations of the Greenlandic corundum were concentrated on the elements Mg, Si, Ti, V, Cr, Fe, and Ga, as these elements are present in significant amounts and are also the most widely documented. We used Fig. 2. A: Aappaluttoq, Fiskenæsset, seen from a helicopter towards the north. The white-grey rock is anorthosite. B: Rubies in their host rock at Tasius- sarsuaq, Fiskenæsset, Greenland. Fig. 3. Normalised trace-element distributions for A: Ti-Cr-Ga, B: Fe-Cr-Ga, C: Fe-Si-Ga and D: Fe-Cr-Ti in corundum from Fiskenæsset. The data are compared with data on interna- tional and Greenlandic corundum occurrences (Calligaro et al. 1999; del Castillo et al. 2009; Kalvig & Frei 2010; Pornwilard et al. 2011; Ra- kontondrazafy et al. 2008; Schwarz et al. 2008; Thirangoon 2008). Different colours show different countries. Initials of the authors’ names were used where more than one study of the same locality exist. Diagrams were created with WxTernary (Keulen & Heijboer 2011). A B Aappaluttoq Upper Annertusoq Lower Annertusoq Bjørnesund 2008 Siggartartulik Rubin Ø Kigutilik Intex Qororssuaq East Qaqqatsiaq Aappaluttoq (T) Aappaluttoq (KF) Annertusoq (KF) Qaqat Aqulerit (KF) Bjørnesund 2008 (KF) Rubin Ø (KF) Siggartartulik (KF) Piqinik (KF) Maniitsoq Storø Kapisillit Nattivit Winza Umba Tunduru Sahabano Zazafotsy Jagdalek Jaipur & Mysore John Saul Tsavo Ratnapura Luc Yen Macedonia 80% Fiskenæsset best Aappaluttoq Soamiakatra Ilakaka Andilamena Pailin (P) Pailin (C) Bo Rai Chanthaburi Mong Hsu Mogok Ti* Fe* Cr* Ga* Cr* Ga* Si* Fe* Ga* 80 Ti* Fe* Cr* 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 60 40 20 80 204060 80 20406080 204060 80 204060 A B C D 55 the Laser Ablation Sector-Field Inductively Coupled Plasma Mass Spectrometer (LA-SF-ICP-MS) at the Geological Sur- vey of Denmark and Greenland (Frei & Gerdes 2009), em- ploying an ELEMENT 2 instrument from Thermo-Fisher Scientific and a UP213 frequency-quintupled Nd:YAG solid state laser system from New Wave Research. Data reduction and determination of concentrations were calculated off-line through the software Iolite using the Trace_Elements_IS routine (Hellstrom et al. 2008). Further details on the meth- ods are found in Keulen & Kalvig (2013). Results on the trace-element investigations of corundum grains separated from 21 hand specimens from ten locali- ties in the Fiskenæsset complex are shown with red symbols in the ternary diagrams of Fig. 3. The data for corundum from the Fiskenæsset complex are in good concordance with earlier data from the area (Kalvig & Frei 2010; Thirangoon 2008). In Fig. 3 they are compared with data from other lo- calities in Greenland and from internationally, well-known, ruby occurrences. Samples from Fiskenæsset show a consid- erably higher amount of Cr (up to 14000 ppm) than samples from other areas in Greenland and most international sam- ples. The Fiskenæsset rubies are relatively rich in Fe and Si, but relatively poor in Ti and Ga, while V and Mg do not show very distinctive values compared to samples from other areas (Kalvig & Keulen, 2011). In order to use trace-element investigations as a finger- printing tool for rubies it is necessary to investigate the amount of overlap between samples from Fiskenæsset and other localities. The blue lines in Fig. 3 include 80% (26 out of 32) of the samples from the Fiskenæsset area, based on sample distribution density contouring. Most samples from other localities plot outside the blue line, but an overlapping chemistry is found with samples from Soamiakatra, Ilakaka, and Andilamena in Madagascar, Bo Rai and Chanthaburi in Thailand, Pailin in Cambodia and Winza in Tanzania. Ru- bies from all these localities are hosted by ultramafic to mafic rocks or are found as placer deposits. This indicates that the trace elements in the rubies derive from the ultramafic rocks that are associated with the anorthosite. However, if only the four handspecimens with the most transparent and most intensively red-coloured corundum grains from Aappaluttoq, Fiskenæsset, are taken into ac- count, no overlap between these handspecimens and sam- ples from other known ruby occurrences is seen. Corundum from these handspecimens is closest in transparency and col- our to the stones that would be sold from a potential mine and therefore represent the Aappaluttoq signature. As these corundum grains have a distinct composition, it can be con- cluded that trace-element geochemistry with ICP-MS is a helpful tool in fingerprinting rubies from Greenland. Oxygen isotope geochemistry Oxygen isotopic composition measurements were performed on ten samples from Greenland at the University of Laus- anne, Switzerland using an isotope ratio mass spectrometer, employing a method similar to that described by Kasemann et al. (2001), see Kalvig & Keulen (2011) for details. Six of the samples come from the Fiskenæsset complex. Their δ18O values vary between 1.62 and 4.20‰ for the Fiskenæsset area, which is low compared to the other areas in Greenland (up to 10.03‰ for Maniitsoq) with the exception of one sample from Nattivit (2.41‰; Fig. 4). The δ18O values are also low compared to most other investigated corundum deposits worldwide (Giuliani et al. 2007). The lowermost values (δ18O <3‰) are nearly diagnostic for the Fiskenæs- set area – worldwide only the placer deposits at Andilamena and Ilakaka in Madagascar and gem-corundum in a cordieri- tite from Iankaroka, Madagascar have lower reported δ18O values. Low δ18O values (≤4‰) generally ref lect rock types such as mafic rocks, mafic gneiss, basalts, and desilicated pegmatite in mafic rocks (Giuliani et al. 2005), which is in excellent agreement with the mafic to ultramafic setting of the Fiskenæsset rubies. The values for samples from Nat- tivit, Kapisillit and Storø are also low (2.4, 4.5 and 6.0‰ respectively) and also plot in the mafic–ultramafic field. Un- fortunately, no further geological information is available for these specimens and the data can thus not be validated Fig. 4. δ18O values for six samples from Fiske- næsset and four other localities in Greenland. The values are relative to VSMOW (Vienna standard mean ocean water). Colours indicate the approximate colour of the stones. Red boxes and classification as mafic-ultramafic, John Saul mine, and marble after Giuliani et al. (2007). Mafic-ultramafic John Saul Mine Aappaluttoq Annertusoq Bjørnesund 2008 Rubin Ø Siggartartulik Pikiniq Nattivit Maniitsoq Kapisillit Storø Marble δ18O corundum (‰, V-SMOV) 497395 078667 513743 497393 497392 497383 497397 289933 224779 497396 0 6 16108 18 202 4 221412 24 GGU no. 5656 against field observations. The value for Maniitsoq with δ18O =10.03‰ is typically related to skarns in marble, or to biotitite in gneiss related to shear zones with high f luid activity. The rubies in the investigated sample are assumed to stem from sapphirine-bearing hornblendite. The horn- blendite was probably formed in a shear zone with high f luid activity (like the biotitites in Madagascar). The low δ18O values are a potentially useful tool for fin- gerprinting Greenlandic rubies, especially the very low val- ues for the Fiskenæsset complex and Nattivit, as only few other international occurrences have such low values. Conclusions High confidence fingerprinting of rubies requires a com- bination of independent analytical methods such as trace- element analyses, oxygen isotope analyses and other studies. The two methods discussed here are efficient in characteris- ing the Fiskenæsset rubies. The ongoing research focuses on optical and physical characteristics, spectroscopy methods and scanning XRF. Acknowledgements This study is part of a collaboration project between the Bureau of Min- erals and Petroleum in Nuuk, Greenland and the Geological Survey of Denmark and Greenland. The authors wish to thank Kerstin Bauer and Torsten Vennemann for help with the oxygen isotope analyses. References Calligaro, T., Poirot, J.-P. & Querré, G. 1999: Trace element fingerprint- ing of jewellery rubies by external beam PIXE. Nuclear Instruments and Methods in Physics Research B 150, 628–634. 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