rubies

In this study, the oxygen isotope (δ 18 O) 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 δ 18 O values betweeñ 0 and +1 and represent one of only a few cases worldwide where δ 18 O signatures can be used to distinguish 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 δ 18 O 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 use of in-situ methods to determine the origin of gem-quality corundum and reconfirms its usefulness in geographic "fingerprinting".

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 distinguish 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 use of in-situ methods to determine the origin of gem-quality corundum and re-confirms its usefulness ...

Gem-quality (cabochon) ruby-bearing occurrences (here termed PAR-1 and PAR-5) located near Paranesti, north eastern Greece have been systematically studied for the first time in this paper. Tectonically, the occurrences are located within the Nestos Shear Zone (NSZ). The NSZ separates two distinct geological units. The Rhodope Terrane is a heterogeneous unit of gneisses, mafic, ultramafic, and meta-sedimentary rocks in the hanging wall. The footwall Pangaion-Pirin Complex consists of marbles and acid gneisses of a Mesozoic carbonate platform on pre-Mesozoic continental basement. In this paper, a range of petrographic and geochemical techniques were used to determine (1) any similarities and differences to other mafic-ultramafic hosted ruby deposits worldwide; (2) distinctive geochemical fingerprints for Paranesti; and (3) the likely P-T conditions of formation. Detailed petrographic and whole-rock analyses utilizing ICP-MS, XRF, and XRD have found the Paranesti corundum to be of a mafic/ultramafic protolith with approximately 40 wt.% SiO 2 , 16 wt.% Mg, 11000 ppm Cr, and 440 ppm Ni. EMPA major element analysis determined the mineral inclusions within the corundum grains to be picotite and hercynite spinels. Pargasite is the dominant amphibole within the corundum-bearing amphibole schist host. The surrounding non-corundum bearing chlorite schist mainly comprises clinochlore. Petrographic examination of the mineral assemblages within the corundum-bearing schists revealed strong fracturing and alignment (parallel to the main regional foliation) of the corundum grains and margarite reaction rims around the corundum. The surrounding non-corundum amphibolites also contain anorthite, along with relict sillimanite, kyanite, and chlorite/muscovite/epidote overprinting. Detailed LA-ICP-MS trace element analysis of the color range of corundum from the two occurrences showed the corundum to be mainly of metamorphic origin, though pale rubies from PAR-5 suggest some metasomatic influence.