T. G. Shumilova

Diamond formation from CaCO3 at high pressure and temperature

We studied the decomposition of CaCO3 by laser heated diamond anvil cell experiments at pressures between 9 and 21 GPa up to 4000 K. The quenched samples were characterized by micro-Raman spectroscopy. From the results we conclude that calcite decomposes into CaO + O2 + C across the whole pressure range investigated at temperatures around 3500 K, initially forming graphite nanoparticles with dimensions around 3–11 nm. The graphite particles may aggregate and transform into diamond with dimensions around 20 nm if the sample is annealed in the diamond stability field. We therefore conclude that diamond can be crystallized directly from carbonatitic melts by decomposition of CaCO3 at high pressures and temperatures, and that phase diagrams showing a decomposition into CaO + CO2 in this P , T -range need to be reevaluated.

Natural monocrystalline lonsdaleite

The existence of a new type of natural lonsdaleite confined to regionally metamorphosed and metasomatically modified rocks is verified based on complex data obtained by high resolution microscopy and spectroscopy. The structural and spectroscopic characteristics of isolated lonsdaleite particles that have a relatively large size and monocrystalline structure are given for the first time. The results of these studies can be used not only for simulating the processes of natural diamond formation, but also for designing superhard materials with allowance for the fact that lonsdaleite is the hardest material on Earth.

Onion-like carbon in impact diamonds from the Popigai astrobleme

Phase composition and nanostructure of layered and irregular massive impact diamond grains from the Popigai astrobleme have been investigated by Raman spectroscopy and high-resolution electron microscopy and the conditions of phase transformations are discussed. Several coexisting carbon phases forming tight aggregates have been found, including cubic and hexagonal diamond polymorphs, graphite, amorphous carbon, fullerene-like/onion-like carbon. The latter is described within impact diamonds for the first time. It is proposed that the formation of onion-like carbon, in both layered and massive impact diamond grains, is connected with high-pressure graphite transformation or post-pressure stress cooling which causes the partial back transformation of diamond nanocrystallites to sp2 carbon. However, a possible relict origin of the fullerene-like carbon from the impacted initial sedimentary rocks with fullerenes and fullerene-like substances, like shungite or coal, can not be excluded. The difference between micro- and nanostructures of layered and irregular massive impact grains is presented.

Conditions and formation mechanism of carbon phases in late quarternary geyzerites and travertines of Ol???khon area and Ol???khon Island (Baikal rift zone)

Late Quaternary geyserite and travertine in Ol’khon Area and Ol’khon Island contain a recently discovered high-temperature association of hydrocarbon and carbonaceous phases, including highly crystalline graphite, α-carbyne, and bitumen, which were produced at temperatures no lower than 400°C. A carbon modification α-carbyne, which was previously found only among experimental products, was first identified in geyserite from the Ol’khon area. Nanometer-sized morphostructures and crystallites were detected on the surface of highly crystalline graphite from the geyserite and travertine. No such structures and crystallites have ever been found on graphite of magmatic, metamorphic, metasomatic, or pneumatolytic origin. The newly formed nanometer-sized morphostructures and crystallites should be regarded as typomorphic features of carbonaceous phases in high-temperature hydrothermal rocks. Graphite was likely produced in the geyserite and travertine by low-pressure polycondenssation of hydrocarbons, at free growth in open space from oversaturated solutions and/or a gas phase.

Experimental modeling of native carbon formation in a C–O–H fluid system

Integrated data are presented on structure–morphology features, as well as on the material and phase composition, of a fluid-produced carbonaceous substance (CS) formed under known thermodynamic conditions of the experiment (C–O–H system, 500–800°C, and 500–1000 atm). Solid products of the synthesis were examined by means of X-ray phase and thermal analyses, scanning electron microscopy combined with microprobe analysis, transmission electron microscopy, high-resolution Raman spectroscopy, IR spectroscopy, and CHN-analysis. The characteristics of the experimental CS may be applicable in genetic modeling of natural ore-bearing fluidal carbonaceous systems.

Ultrahigh-Pressure Liquation of an Impact Melt

Liquation structures were described in ultrahigh-pressure impact glasses of the Kara astrobleme (Pay-Khoy) with differentiation into the bisilica, aluminosilicate, and ore components for the first time. The sequence of differentiation of mineral phases upon solidification of an ultrahigh-pressure impact melt was established: coesite, silicate glass, augite, aluminosilicate glass of albite composition, and pyrite. The discovered impact glasses are highly resistant to postimpact alterations.

Transport and Crystallization of Noble Platinum in Supercritical C–O–H Fluid

Experimental data is provided for the transport of platinum in a supercritical C–O–H fluid system. The transfer of platinum in space with its condensation on the surface of native carbon (diamond and amorphous carbon) in the form of micro- and nanocrystals, shapeless particles, and filamentous formations is established for the first time. The dominant participation of platinum in the formation of carbon micro- and nanotubes is demonstrated. The results are important in modeling the formation of noble metal deposits with deep fluid carbon systems.

NEW DATA ON AGE AND NATURE OF CARBONIZATION WITHIN SOUTHERN FLANK OF THE BAIKAL LEDGE OF THE SIBERIAN CRATON BASEMENT

The Baikal ledge rock formations in the Siberian craton structure are included in the Akitkan mobile belt which is considered as the Late Paleoproterozoic independent island arc system moved up to the ancient basement during the terrains amalgamation 1.91–2.00 Ga ago (Fig. 1) [Rosen, 2003; Gladkochub et al., 2009; Didenko et al., 2013].

Metal concentrations and carbonaceous matter in the black shale type rocks of the Urals

Here, the results of examination of black shale type rocks from the Urals for noble metal mineralization are presented for the first time: they have been obtained using atomic–absorption spectrometry along with data of a complex analysis of a carbon mineralization applying a complex of high-resolution techniques. The data acquired demonstrate anomalously high Au concentrations in all the rocks examined. The carbon matter occurs in a wide range of phase states, including nanocrystalline graphite, carbon nanofiber, nanoglobules, diamond-like carbon, and bitumens. The black shale type rocks were found to be promising for further studies in order to seek industrially valuable objects including in areas of the northern part of the Urals.

Gas–oil fluids in the formation of travertines in the Baikal rift zone

Active participation of gas–oil fluids in the processes of mineral formation and petrogenesis in travertines of the Arshan and Garga hot springs is substantiated. The parageneses of the products of pyrolytic decomposition and oxidation of the gas–oil components of hydrothermal fluids (amorphous bitumen, graphite-like CM, and graphite) with different genetic groups of minerals crystallized in a wide range of P–T conditions were established. Travertines of the Baikal rift zone were formed from multicomponent hydrous–gas–oil fluids by the following basic mechanisms of mineral formation: chemogenic, biogenic, cavitation, fluid pyrometamorphism, and pyrolysis.