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MPM-01 General contributions to mineralogy

New data for minerals of CaZrO₃-CaSnO₃-CaTiO₃ system

Evgeny Galuskin, University of Silesia (Poland)
Irina Galuskina, University of Silesia (Poland)
Viktor Gazeev, Institute of Geology of Ore Deposits, Geochemistry, Mineralogy and Petrography (IGEM) RAS (Russian Federation)
Nikolai Pertsev, Institute of Geology of Ore Deposits, Geochemistry, Mineralogy and Petrography (IGEM) RAS (Russian Federation)
Antoni Winiarski, University of Silesia (Poland)
Aleksander Zadov, OOO "TEPLOHIM" (Russian Federation)
Piotr Dzierzanowski, Warsaw University (Poland)
 

Lakargiite - a new mineral of the perovskite group with an ideal formula CaZrO₃ (IMA-2007-014, Pbmn, a = 5.55, b = 5.70, c = 7.93Å), was found in altered carbonate xenoliths in Pleocene ignimbrites of the Verkhny Chegem volcanic structure, located in a upland part of Kabardino-Balkaria, Caucasus, Russia. Lakargiite, represented by Ca(Zr,Sn,Ti)O₃ solid solution, from different skarn zones shows significant variations of composition. Dendritoids and spherulites of lakargiite up to 200 m in size and maximum content of CaZrO₃ molecule reaching 93 mol.% occur in cuspidine, larnite, calcio-olivine and reinhardbraunsite zones. Pseudocubic crystals of lakargiite up to 30 m in size and mean contents CaTiO₃ of about 13-15 mol.% and CaSnO₃ of about 10-12 mol.% often appear in spurrite zone together with wadalite and hydrocalumite. High stannian lakargiite with approximate formula Ca(Zr_0.65Sn_0.28Ti_0.07)O₃ are very rarely noted in spurrite zone with ellestadite group minerals. Intermediate phase between perovskite and lakargiite with formula Ca(Zr_0.36Ti_0.35Fe³⁺_0.12Sn_0.1Nb_0.07)O_2.98 forming intergrowths with a potentially new mineral Ca₃Fe³⁺₂TiO₈ was discovered in skarn zones with high concentration of rondorfite. In some lakargiite crystals high content of U, Nb, Fe, Th, Ce, La, Sc, Hf, Cr are noted. Uranium in lakargiite is most likely in six-valent form and occupies an octahedral Zr-site according to the scheme 3Zr = 2(Fe³⁺, Sc, Cr) + U⁶⁺. The formula of U-bearing lakargiite is as follows: Ca(Zr_0.52Ti_0.18Sn_0.10Fe³⁺_0.11Sc_0.04U⁶⁺_0.05)O₃. Polymineral pseudomorphs after zircon showing the next zonality from the center to the edge: zircon - baghdadite-like mineral - lakargiite, were found in cuspidine zones together with relics of volcanic glass. Sn-bearing kimzeyite has been detected between lakargiite and baghdadite-like mineral. Lakargiite crystallization took place at sanidinite facies conditions of contact metamorphism (>800°C) at shallow depth