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The origin of a new pargasite-schist hosted ruby deposit from Paranesti, Northern Greece

Wang, K.K. ; Graham, I.T. ; Lay, A. ; Harris, S.J. ; Cohen, D.R. ; Voudouris, P. ; Belousova, E. ; Giuliani, G. ; Fallick, A.E. ; Greig, A.

The origin of a new pargasite-schist hosted ruby deposit from Paranesti, Northern Greece

Wang, K.K. ; Graham, I.T. ; Lay, A. ; Harris, S.J. ; Cohen, D.R. ; Voudouris, P. ; Belousova, E. ; Giuliani, G. ; Fallick, A.E. ; Greig, A.

Canadian Mineralogist, 2017, 55, 535-560

Abstract :

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.% SiO2, 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.

Voir en ligne : http://dx.doi.org/doi:10.3749/canmi...




publié lundi 21 août 2017