ИСТИНА

Mesozoic Sr-Ba carbonatites from the Murun alkaline massif (Irkutsk district, Russia) are related to the unique in the world charoite deposit. These carbonatites form intrusive bodies inside of multistage magmatic alkaline complexes. These endogen carbonate rocks (carbonate component counts at least 50%) contain Na-pyroxen (aegirine-augite), feldspar, amphibole, phlogopite, forsterite, apatite, magnetite and occasionally, in contact zones, quartz. The quartz contains two types of primary fluid inclusions: 1) multiphase inclusions with carbonate water-saturated melt presented by multiple anisotropic solid phases, vapor bubble and interstitial aqueous solution; and 2) single-phase gas inclusions. Homogenization temperature of multiphase inclusions is 650-610°C. Gaseous inclusions consist of dense nitrogen and homogenize into liquid phase at temperatures from -164.5 to -149.5°C that corresponds to nitrogen density 0.64-0.48 g/cm3. At 650-610°C the pressure of nitrogen inside these gaseous inclusions arrives up to 5.5-2.4 kbar. Composition of the multiphase fluid inclusions was studied by FIB-SEM and confocal Raman spectroscopy methods in Lithosphere Fluid Research (Budapest, Hungary) and GeoRessources (Nancy, France) Laboratories, correspondingly. Among solid phases we identified nahcolite, barite (with some Sr amounts), siderite, anhydrite, pyrite and sphalerite. Moreover, two rare phases containing Fe-S and K-Al-(S) were detected. The one of them was identified as ferrotychite, Na6Fe(II)2 (SO4) (CO3)4. The other K-Al-(S) phase was not identified. The composition of the gas bubble inside multiphase inclusions (in mol%) is N2 98–92, CH4 1–7 and CO2 0.5. Using high-resolution Raman spectroscopy we identified also calcite among solid phase, and traces of graphite, ions SO42-, H2S, HS- and NH3*H2O0(aq) in the aqueous phase. Our results confirm the nonordinary chemical composition of these rocks and provide new insights into volatile composition of carbonatite melt containing high concentrations of nitrogen and sulfur in various states.