4.2 SOBOLEV Nikolay

Composition of Volatile Components in Russian Diamonds and Associated Minerals

N.V. Sobolev (sobolev@igm.nsc.ru), A.A. Tomilenko, T.A. Bulbak and A.M. Logvinova

V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, 630090, Novosibirsk, Russia

Diamond inclusion studies established two main types of Earth’s mantle environment for diamond formation within subcratonic lithosphere, peridotitic and eclogitic. For Russian diamonds of any size, from micro (< 1 mm) up to large crystals (> 10.8 cts) peridotitic type dominates for kimberlites (> 90%) and is lower (< 30%) for placers of the north of Siberia and the Urals.

Volatile components in diamonds, their polycrystalline aggregates (PA) and associated garnet and olivine were analysed by GC-MS using a Focus GC/DSQ II MS (Thermo Scientific, USA). Microdiamonds (Type IIa, the d13C is -22.9 ‰ PDB) from diamondiferous peridotite, PA as well as other diamonds and minerals contain hydrocarbons and their derivatives, represented by aliphatic (paraffins, olefins), cyclic (naphthenes, arenes) and oxygenated hydrocarbons, nitrogenated and sulfonated compounds, CO2, H2O.

One typical dodecahedral diamond from Uralian placers was found to contain abundant primary, oriented (< 0.1 µm) octahedral fluid inclusions caused a milky color of the whole crystal. Its d13C is – 8.5‰ PDB. Nitrogen in solid state, confirmed by Raman spectroscopy (40% rel.) along with H2O (26%), CO2 (3%) and hydrocarbons (31%) are identified in this diamond, most probably having superdeep origin. Methane is found in negligible amount, less then 0,03% and was completely absent in PA.

This work was supported by RSF grant 14-17-00602П.