minerals Article Fingerprinting Paranesti Rubies through Oxygen Isotopes Kandy K. Wang 1,*, Ian T. Graham 1, Laure Martin 2, Panagiotis Voudouris 3 , Gaston Giuliani 4, Angela Lay 1, Stephen J. Harris 1 and Anthony Fallick 5 1 PANGEA Research Centre, School of Biological, Earth and Environmental Sciences, University of NSW, 2052 Sydney, Australia; [email protected] (I.T.G.); [email protected] (A.L.); [email protected] (S.J.H.) 2 Centre for Microscopy Characterisation and Analysis, The University of Western Australia, 6009 Perth, Australia; [email protected] 3 Faculty of Geology and Geoenvironment, National and Kapodistrian University of Athens, 157 84 Athens, Greece; [email protected] 4 Université de Lorraine, IRD and CRPG UMR 7358 CNRS-UL, BP 20, 15 rue Notre-Dame-des-Pauvres, 54501 Vandœuvre-lès-Nancy, France; [email protected] 5 Isotope Geosciences Unit, S.U.E.R.C., Rankine Avenue, East Kilbride, Glasgow G75 0QF, UK; [email protected] * Correspondence: [email protected]; Tel.: +61-411418800 Received: 1 December 2018; Accepted: 30 January 2019; Published: 3 February 2019 Abstract: In this study, the oxygen isotope (δ18O) composition of pink to red gem-quality rubies from Paranesti, Greece was investigated using in-situ secondary ionization mass spectrometry (SIMS) and laser-fluorination techniques. Paranesti rubies have a narrow range of δ18O values between ~0 and +1 and represent one of only a few cases worldwide where δ18O signatures can be used to distinguishh them from other localities. SIMS analyses from this study and previous work by the authors suggests that the rubies formed under metamorphic/metasomatic conditions involving deeply penetrating meteoric waters along major crustal structures associated with the Nestos Shear Zone. SIMS analyses also revealed slight variations in δ18O composition for two outcrops located just ~500 m apart: PAR-1 with a mean value of 1.0 ± 0.42 and PAR-5 with a mean value of 0.14 ± 0.24 . This work adds to the growing useh of in-situh methods to determine the origin of gem-qualityh corundumh and re-confirms its usefulness in geographic “fingerprinting”. Keywords: rubies; corundum; in-situ oxygen isotopes; Paranesti Greece; Nestos Shear Zone; Secondary ion mass spectrometry (SIMS) 1. Introduction 1.1. Oxygen Isotopic Studies in Corundums Oxygen is an abundant element in the Earth’s crust, mantle and fluids. Oxygen consists of three naturally-occurring stable isotopes: 16O (99.76%), 17O (0.04%) and 18O (0.2%). δ18O expressed as Vienna standard mean ocean water (VSMOW) in per mil is the standard for the oxygen isotopic composition which is a measure of the ratio of the stable isotopes oxygen-18 (18O) and oxygen-16 (16O). There are numerous applications of oxygen isotope geochemistry including paleoclimatology, urban forensics, geological genesis and many more [1–3]. Oxygen isotope fractionation is a function of the initial Rayleigh evaporation-precipitation cycle, temperature of the system and degree of water-rock interaction and therefore great care must be taken when interpreting oxygen isotope values [4–7]. Minerals 2019, 9, 91; doi:10.3390/min9020091 www.mdpi.com/journal/minerals Minerals 2019, 9, 91 2 of 14 Minerals 2019, 9, x FOR PEER REVIEW 2 of 14 AlthoughAlthough worldwide worldwide corundumcorundum oxygen isotope va valueslues have have been been found found in in a awide wide range range from from - 27‰ (Khitostrov, Russia) to +23‰ (Mong Hsu, Myanmar), most are in the range of +3‰ to +21‰ [8– -27 (Khitostrov, Russia) to +23 (Mong Hsu, Myanmar), most are in the range of +3 to +21 [8–10]. 10]. This criterion has often been used to determine the geological origin of coloured corundum and Thish criterion has often been usedh to determine the geological origin of colouredh corundumh and especially the gem corundums, rubies and sapphires. δ18O has been particularly useful in determining especially the gem corundums, rubies and sapphires. δ18O has been particularly useful in determining the likely primary geological origin of placer corundums where the primary origin is uncertain [11]. the likely primary geological origin of placer corundums where the primary origin is uncertain [11]. As isotopic fractionation is a function of both temperature and geological processes, oxygen isotope As isotopic fractionation is a function of both temperature and geological processes, oxygen isotope data need to be treated with some degree of caution Thus, there are very few examples where oxygen data need to be treated with some degree of caution Thus, there are very few examples where oxygen isotopes have been used to “fingerprint” the geographic location [12]. isotopes have been used to “fingerprint” the geographic location [12]. 1.2.1.2. Geological Geological Setting Setting and and SampleSample BackgroundBackground The Paranesti rubies are found within the Nestos Shear Zone (NSZ) of the Rhodope Mountain The Paranesti rubies are found within the Nestos Shear Zone (NSZ) of the Rhodope Mountain Complex (RMC) in north-eastern Greece (Figure 1). The tectonic and polymetamorphic record of this Complex (RMC) in north-eastern Greece (Figure 1). The tectonic and polymetamorphic record of Northern Aegean region (including the RMC) reflects the Middle Jurassic to Neogene northeast this Northern Aegean region (including the RMC) reflects the Middle Jurassic to Neogene northeast dipping subduction and convergence of the African-Eurasian plates which resulted in the closure of dipping subduction and convergence of the African-Eurasian plates which resulted in the closure of the the Tethys Ocean [13,14]. The NSZ is thought to be a one of the syn-metamorphic thrusts in the RMC Tethys Ocean [13,14]. The NSZ is thought to be a one of the syn-metamorphic thrusts in the RMC that that are responsible for regional metamorphic inversion, placing higher amphibolite-facies are responsible for regional metamorphic inversion, placing higher amphibolite-facies intermediate intermediate terranes onto upper-greenschist to lower amphibolite-facies rocks of the lower terrane terranes onto upper-greenschist to lower amphibolite-facies rocks of the lower terrane [15,16]. [15,16]. FigureFigure 1. 1.Geological Geological map map of theof the Rhodope Rhodope Mountain Mountain Complex, Complex, with with Paranesti Paranesti located located within within the Nestos the ShearNestos Zone Shear (red Zone star) (red (Adapted star) (Adapt fromed Moulas from etMoulas al, 2017 et al, [17 2017]). [17]). BasedBased onon an earlier earlier systematic systematic study study on onParanesti Paranesti [18], [the18], ruby-bearing the ruby-bearing occurrences occurrences were found were foundto be hosted to be in hosted pargasite in pargasite schist with schist a mafic/ul withtramafic a mafic/ultramafic protolith. The protolith.surrounding The non-corundum- surrounding non-corundum-bearingbearing chlorite schist was chlorite found schistto mainly was be foundcomprised to mainly of clinochlore. be comprised The ruby-bearing of clinochlore. occurrence The ruby-bearingfound on the occurrencehillside is referred found onto as the PAR-1 hillside (Figure is referred 2a) and to the as road-side PAR-1 (Figure occurrence2a) and is termed the road-side PAR- 5 (Figure 2b). Not all of the pargasite boudins nor the pegmatite intrusion found within the vicinity of the two sites contained corundum (Figure 2c,d). Minerals 2019, 9, 91 3 of 14 occurrence is termed PAR-5 (Figure 2b). Not all of the pargasite boudins nor the pegmatite intrusion found within the vicinity of the two sites contained corundum (Figure 2c,d). Minerals 2019, 9, x FOR PEER REVIEW 3 of 14 (a) (b) (c) (d) FigureFigure 2.2. LocalityLocality diagramdiagram ofof thethe rubyruby occurrences.occurrences. ((aa)) PAR-1PAR-1 locationlocation onon toptop ofof thethe hill.hill. ((bb)) PAR-5PAR-5 locationlocation on on the the roadside.roadside. ((cc)) PargasitePargasite schistschist boudinboudin foundfound approx.approx. 500500 mm northnorth ofof PAR-5PAR-5 withoutwithout anyany corundum.corundum. ((dd)) PegmatitePegmatite onon toptop ofof thethe ruby-bearingruby-bearing pargasite pargasite schist schist at at PAR-1. PAR-1. AA summarysummary of of the the main main findings findings from from this this previous previous study study is listedis listed in Tablein Table1. Detailed 1. Detailed LA-ICP-MS LA-ICP- traceMS trace element element analyses analyses showed showed that the that rubies the rubies are of are metamorphic of metamorphic origin (Figureorigin (Figure3a) with 3a) minor with partial minor metasomaticpartial metasomatic influences influences (Figure (Figure3b). The 3b). high The Rhigh2 value R2 value based based on theon the Fe/Mg Fe/Mg vs vs Ga/Mg Ga/Mg elemental elemental discriminationdiscrimination diagram diagram shows shows both both PAR-1 PAR-1 and and PAR-5 PAR- rubies5 rubies to contain to contain highly consistenthighly consistent trace element trace compositionselement compositions (Figure 3 a).(Figure 3a). Minerals 2019, 9, x FOR PEER REVIEW 4 of 14 Table 1. Summary of prior Paranesti ruby results (Wang et al. 2017 [18]). Minerals 2019, 9, 91 4 of 14 Attributes PAR-1 PAR-5 Physical Characteristics Site TableHillside 1. Summary surface of prior outcrop Paranesti rubyRoadside results (Wang surface et al. outcrop—500 2017 [18]). m east of PAR1 Grain-sizeAttributes 10 mm–20PAR-1 mm 5 mm–10PAR-5 mm Colour Deeper red than PAR-5 (generally) Medium red Physical Characteristics InclusionsSite HillsideSpinels surface outcrop Roadside