Περίληψη:
Greece contains several gem corundum deposits set within diverse
geological settings, mostly within the Rhodope (Xanthi and Drama areas)
and Attico-Cycladic (Naxos and Ikaria islands) tectono-metamorphic
units. In the Xanthi area, the sapphire (pink, blue to purple) deposits
are stratiform, occurring within marble layers alternating with
amphibolites. Deep red rubies in the Paranesti-Drama area are restricted
to boudinaged lenses of Al-rich metapyroxenites alternating with
amphibolites and gneisses. Both occurrences are oriented parallel to the
ultra-high pressure/high pressure (UHP/HP) Nestos suture zone. On
central Naxos Island, colored sapphires are associated with desilicated
granite pegmatites intruding ultramafic lithologies (plumasites),
occurring either within the pegmatites themselves or associated
metasomatic reaction zones. In contrast, on southern Naxos and Ikaria
Islands, blue sapphires occur in extensional fissures within Mesozoic
metabauxites hosted in marbles. Mineral inclusions in corundums are in
equilibrium and/or postdate corundum crystallization and comprise:
spinel and pargasite (Paranesti), spinel, zircon (Xanthi), margarite,
zircon, apatite, diaspore, phlogopite and chlorite (Naxos) and
chloritoid, ilmenite, hematite, ulvospinel, rutile and zircon (Ikaria).
The main chromophore elements within the Greek corundums show a wide
range in concentration: the Fe contents vary from (average values) 1099
ppm in the blue sapphires of Xanthi, 424 ppm in the pink sapphires of
Xanthi, 2654 ppm for Paranesti rubies, 4326 ppm for the Ikaria
sapphires, 3706 for southern Naxos blue sapphires, 4777 for purple and
3301 for pink sapphire from Naxos plumasite, and finally 4677 to 1532
for blue to colorless sapphires from Naxos plumasites, respectively. The
Ti concentrations (average values) are very low in rubies from Paranesti
(41 ppm), with values of 2871 ppm and 509 in the blue and pink sapphires
of Xanthi, respectively, of 1263 ppm for the Ikaria blue sapphires, and
520 ppm, 181 ppm in Naxos purple, pink sapphires, respectively. The blue
to colorless sapphires from Naxos plumasites contain 1944 to 264 ppm Ti,
respectively. The very high Ti contents of the Xanthi blue sapphires may
reflect submicroscopic ruffle inclusions. The Cr (average values) ranges
from 4 to 691 ppm in the blue, purple and pink colored corundums from
Naxos plumasite, is quite fixed (222 ppm) for Ikaria sapphires, ranges
from 90 to 297 ppm in the blue and pink sapphires from Xanthi, reaches
9142 ppm in the corundums of Paranesti, with highest values of 15,347
ppm in deep red colored varieties. Each occurrence has both unique
mineral assemblage and trace element chemistry (with variable Fe/Mg,
Ga/Mg, Ga/Cr and Fe/Ti ratios). Additionally, oxygen isotope
compositions confirm their geological typology, i.e., with, respectively
delta O-18 of 4.9 +/- 0.2%o for sapphire in plumasite, 20.5%o for
sapphire in marble and 1%0 for ruby in mafics. The fluid inclusions
study evidenced water free CO2 dominant fluids with traces of CH4 or
N-2, and low CO2 densities (0.46 and 0.67 g/cm(3)), which were probably
trapped after the metamorphic peak. The Paranesti, Xanthi and central
Naxos corundum deposits can be classified as metamorphic sensu stricto
(s.s.) and metasomatic, respectively, those from southern Naxos and
Ikaria display atypical magmatic signature indicating a hydrothermal
origin.
Greek corundums are characterized by wide color variation, homogeneity
of the color hues, and transparency, and can be considered as potential
gemstones.
Συγγραφείς:
Voudouris, Panagiotis
Mavrogonatos, Constantinos
Graham, Ian and
Giuliani, Gaston
Melfos, Vasilios
Karampelas, Stefanos and
Karantoni, Vilelmini
Wang, Kandy
Tarantola, Alexandre
Zaw,
Khin
Meffre, Sebastien
Klemme, Stephan
Berndt, Jasper and
Heidrich, Stefanie
Zaccarini, Federica
Fallick, Anthony and
Tsortanidis, Maria
Lampridis, Andreas
