International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Sapphires related to alkali basalts from the Cerova Highlands, Western Carpathians (southern Slovakia): composition and origin

Pages: 71 - 82

Authors: PAVEL UHER, GASTON GIULIANI, SANDOR SZAKALL, ANTHONY FALLICK, VLADIMIR STRUNGA, TOMAS VACULOVIC, DANIEL OZDIN, MARGARETA GREGANOVA

Abstract: Blue, grey-pink and pink sapphires from the Cerova Highlands, Western Carpathians (southern Slovakia) have been studied using CL, LA-ICP-MS, EMPA, and oxygen isotope methods. The sapphire occurs as (1) clastic heavy mineral in the secondary sandy filling of a Pliocene alkali basaltic maar at Hajnacka, and (2) crystals in a pyroxene-bearing syenite/anorthoclasite xenolith of Pleistocene alkali basalt near Gortva. Critical evaluation of compositional diagrams (Fe, Ti, Cr, Ga, Mg contents, Fe/Ti, Cr/Ga, Ga/Mg ratios) suggests a magmatic origin for clastic blue sapphires with lower Cr and Mg, but higher Fe and Ti concentrations in comparison to the grey-pink and pink varietes, as well as similar compositional trends with blue sapphire from the Gortva magmatic xenolith. Moreover, blue sapphires show similar δ18O values: 5.1 ‰ in the Gortva xenolith, 3.8 and 5.85 ‰ in the Hajnacka placer, closely comparable to mantle to lower crustal magmatic rocks. On the contrary, pink and grey-pink sapphires show higher Cr and Mg, but lower Fe and Ti contents and their composition points to a metamorphic (metasomatic) origin.

Keywords: Western Carpathians, Slovakia, Hajnacka, Gortva, CL, LA-ICP-MS, EMPA, oxygen isotopes, placer, alkali basalts, anorthoclasite xenolith, corundum, sapphire

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