MSCC3 3rd MINERAL SCIENCES IN THE CARPATHIANS ...

Acta Mineralogica-Petrographica, Abstract Series 5, Szeged, 2006SAPPHIRE-BEARING SYENITE XENOLITH FROM GORTVA, CEROVÁ MOUNTAINS,SLOVAKIAUHER, P. 1 , GREGÁŇOVÁ, G. 2 & SZAKÁLL, S. 31 Department of Mineral Deposits, Comenius University, Mlynská dolina G, 842 15 Bratislava, SlovakiaE-mail: puher@fns.uniba.sk2 Department of Mineralogy and Petrology, Comenius University, Mlynská dolina G, 842 15 Bratislava, Slovakia3 Department of Mineralogy and Petrology, University of Miskolc, H-3515 Miskolc-Egyetemváros, HungaryA blue corundum (sapphire) crystal, 7 mm large, in basaltfrom Hajnáčka maar near Fiľakovo, Cerová Mts., southernSlovakia, was first described by SZÁDECZKY (1899); thelocality was re-discovered during extended paleontologicalresearch (UHER et al., 1999). Numerous blue or pale violetsapphire crystals, 1–5 mm in size, were separated from Pliocenesand filling of the Hajnáčka maar together with otherheavy-mineral assemblage (spinel, magnetite, magnesiochromite,ilmenite, titanite, forsterite, zircon, almandine,allanite, augite, diopside, enstatite, pargasite, kaersutite) andplagioclase with Ab 69–74 An 18–25 Or 06–08 composition (UHER etal., 1999; GREGÁŇOVÁ, 2002). Locally, sapphire containsinclusions of zircon, monazite-(Ce), spinel, pyrrhotite (?) andan Y-U-Th-Nb-Ta phase (euxenite-(Y)?). Recently, 9 and7 mm large, blue sapphire crystals were discovered in sands.However, all these recent finds of sapphire were describedfrom secondary alluvial deposits and the primary rock ofHajnáčka sapphire was unknown up to now. On the basis ofgeological settings and rare corundum occurrence in syeniticxenoliths from Pinciná maar, 23 km NW of Hajnáčka(HURAI et al., 1998), analogous syenites were assumed asthe most probable parental rock for Hajnáčka sapphire(UHER et al., 1999).Fortunately, a photography of blue sapphire in host-rockfrom Gortva near Hajnáčka, to be found in the Herman OttóMuseum, Miskolc (inv. No. 14035), appeared in the Mineralsof the Carpathians monograph (SZAKÁLL ed., 2002) andstudied now in detail by EMPA. Sapphire forms 2–4 mmcrystals in white coarse-grained syenitic host rock. The wholedescribed syenite forms a several cm large xenolith in blackalkali basalt with pyroxene phenocrysts and feldspar-richgroundmass with ilmenite and titanian magnetite. Alkalifeldspar of oligoclase composition (Ab 63–67 An 24 Or 10–13 ) is thedominant mineral of the syenite. Fibrolitic sillimanite forms a0.1–0.4-mm thick contact zone between sapphire and feldspar.Fillimanite probably formed as a product of later, postmagmaticcontact re-equilibration between corundum andfeldspar, possibly during the thermal event connected withtrapping of the syenite xenolith by the hot basalt lava. Leuciteoccurs as subhedral crystals (0.1–0.5 mm in size) in associationwith feldspar, pyroxene and Ti-rich magnetite. Pyroxeneforms 0.02 to 0.15-mm long columnar crystals of augite todiopside composition (Wollastonite 47–51 Clinoenstatite 34–43Clinoferrosilite 09–18 ). Feldspar composition in leucite- andpyroxene-rich areas changes to Na,K-rich, anorthoclase orsanidine-like member (Ab 51–59 An 02–07 Or 34–46 ), enriched in Ba(0.5–1.3 wt% BaO). Locally, ca. 1 mm large irregular zone ofmonomineralic analcime forms a matrix for pyroxene andleucite. Analcime formed as an in situ replacement productby solid-state ion exchange from leucite (X-type analcime;LINE et al., 1995).The studied sapphire and other minerals solidified from afelsic melt, probably in the lower crust and later they havebeen transported to the surface in syenite xenoliths orxenocrysts by alkali basalt lava. Analogous felsic syeniticxenoliths from the Pinciná maar, Slovakia crystallized undera pressure around 6 kbar (ca. 22 km of lithostatic load) andliquidus temperature of inclusion melts at 1080 °C(HURAIOVÁ et al., 1996). Similar models for corundumorigin from lower crustal felsic magma and their later upliftas xenoliths or xenocrysts in alkali basalt are widely acceptedalso for large sapphire occurrences in Thailand and Australia(e.g. COENRAADS et al., 1995, SUTHERLAND et al.,1998).ReferencesCOENRAADS, R. R., VICHIT, P. & SUTHERLAND, F. L.(1995): Mineralogical Magazine, 59: 465–479.GREGÁŇOVÁ, M. (2002): . PhD. Thesis, Manuscript,Comenius University, Bratislava, 75 p.HURAI, V., SIMON, K., WIECHERT, U., HOEFS, J.,KONEČNÝ, P., HURAIOVÁ, M., PIRONON, J. &LIPKA, J. (1998): Contributions to Mineralogy and Petrology,133: 12–29.HURAIOVÁ, M., KONEČNÝ, P. KONEČNÝ, V., SIMON,K. & HURAI, V. (1996): European Journal of Mineralogy,8: 901–916.LINE, C. M. B., PUTNIS, A., PUTNIS, C. & GIAMPAOLO,C. (1995): American Mineralogist, 80: 268–279.SUTHERLAND, F. L., HOSKIN, P. W. O., FANNING, C.M. & COENRAADS, R. R. (1998): Contributions toMineralogy and Petrology, 133, 356–372.SZÁDECZKY, GY. (1899): Földtani Közlöny, 29: 240–252.SZAKÁLL, S. (ed., with the contributions of UDUBAŞA,G., ĎUĎA, R., SZAKÁLL, S., KVASNYTSYA, V.,KOSZOWSKA, E. & NOVÁK, M.) (2002): Minerals ofthe Carpathians. Prague: Granit.UHER, P., SABOL, M., KONEČNÝ, P., GREGÁŇOVÁ,M., TÁBORSKÝ, Z. & PUŠKELOVÁ, Ľ. (1999): SlovakGeological Magazine, 5: 273–280.124www.sci.u-szeged.hu/asvanytan/acta.htm