Hydrothermal synthesis and morphology of Ga-bearing tourmaline

Ga-bearing tourmaline was originally synthesized in boron, boron–alkaline, and boron–fluorine hydrothermal solutions at a temperature of 600–650°C and pressure of 100 MPa as crystals of spontaneous growth and on seeds. The maximal concentration of Ga₂O₃ in synthetic crystals reaches ~24.5 wt %. In addition to Ga-bearing tourmaline, Ga-bearing topaz crystallizes in boron–fluorine solution. Ga-bearing albite crystallizes in boron–alkaline solutions, whereas no additional phases are formed in pure boron solutions.     

Phase states of hydrous–hydrocarbon fluids at elevated and high temperatures and pressures: Study of the forms and maximal depths of oil occurrence in the Earth’s interior

Based on synthetic fluid inclusions in quartz grown at 240–490°C and 7–150 MPa in aqueous–oil solutions, the behavior, composition, and phase states of liquid, gaseous, and solid hydrocarbons (HC) were studied. Investigations were performed using common and fluorescent microscopy, microthermometry, local common and high-temperature IR Fourier spectroscopy, Raman spectroscopy, chromatography, and X-ray and microprobe analysis. The data obtained allowed us to understand the influence of thermobaric conditions and volume proportions of the oil, aqueous, and gaseous phases on the composition, phase state, and behavior of hydrous–hydrocarbon fluids and estimate the forms and probable maximal depths of the origin of oil in the Earth’s interior.     

Influence of crude oil cracking on distribution of hydrocarbons in the Earth’s interior (experimental data)

The compositions and phase conditions of water-hydrocarbon fluids in synthetic quartz inclusions were studied by the methods of microthermometry, local IR spectroscopy, and gas-liquid chromatography. Synthetic quartz was grown in near-neutral fluoride, low-alkali bicarbonate, and alkali carbonate solutions with crude oil and its major fractions. The crystals with fluid inclusions were grown under thermal gradient conditions at relatively low temperatures (240–280°C) and pressures (6–45 MPa). After the study, the inclusions of grown crystals were subject to thermal processing in autoclaves at 350–380°C and 80–125 MPa. As a result, the initial water-hydrocarbon inclusions underwent significant changes. Hydrocarbon gases, largely methane and residual solid bitumens, appeared in their composition; the gasoline-kerosene fraction content increased substantially in liquid hydrocarbons (HCs). These changes are caused, first of all, by crude oil cracking, which is manifested already at 330°C and attains its maximum activity at 350–500°C (pressure of saturated vapor and higher). In natural conditions with increase in depths and, thus, the thermobaric parameters, this process is inevitable. According to the obtained experimental data, this very phenomenon and the existence of real thermal and baric gradients in the Earth’s interior provide for the formation of vertical zoning in the distribution of hydrocarbon deposits of different types.     

Experimental study of the interaction of mineral-forming hydrothermal solutions with oil and their joint migration

Interaction between oil and hydrothermal solutions of different compositions was experimentally studied in a wide range of temperature (260–490°C) and pressures (8–150 MPa). This study was based on a new technique involving simultaneous occurrence of water-hydrocarbon interaction and growth of quartz, calcite, and fluorite crystals with fluid inclusions from the same solution. Fluid inclusions were studied to characterize the behavior of oil and aqueous solutions at elevated and high temperatures and pressures. It was shown that, owing to interaction with hydrothermal solutions, oil is intensely removed from the source rock and accumulated in the frontal part of hydrothermal convective flow. During this process, the oil is partially transformed into hydrocarbons, light oil, semiliquid and solid bitumens. At temperatures of 300–350°C and pressures of 50–100 MPa, oil and its fractionation products migrate in hydrothermal solution mainly in a drop-liquid state. At higher temperatures (360–395°C), when the oil/water ratio in the initial mixture is no higher than 1/70–1/35, liquid and gaseous hydrocarbons are completely dissolved in hydrothermal solutions forming a complex homogenous water-hydrocarbon fluid. The fluid can exist and migrate in this state, but it becomes heterogeneous with decreasing P-T parameters. Under favourable structural and lithological conditions, this can lead to the formation of displaced oil-and-gas deposits, with oil enriched in light components. The experiments unambiguously confirmed the concept that bitumen inclusions in minerals can serve as indicators of hydrocarbon migration paths in the Earth’s crust.     

The amethyst-citrine dichromatism in quartz and its origin

The occurrence of the amethyst-citrine dichromatism in natural and mainly synthetic quartz crystals was studied as a function of their growth conditions. It has been found experimentally that the origin of the coloration is related to the variable dependence of the incorporation of the amethyst- and citrine-producing impurities on the crystallographic direction and growth rates of the faces and also to the effect the charge compensators have on the thermal stability of the amethyst color centers.     

Silica and alumina transfer in supercritical aqueous fluids and growing of topaz monocrystals in them

Silica and alumina transfer during the dissolution and growth of quartz, corundum, and topaz in supercritical aqueous fluids have been experimentally studied under a direct temperature gradient, and the possibility for growing of topaz monocrystals in them have been determined. It was demonstrated that the directions of silica and alumina transfer shows no unambiguous correlation with the composition, PT conditions, pH, and density of the fluids, and, in some cases, can be opposite. This defines simultaneous spatially associated or separated growth of quartz and topaz, as is often observed in camera pegmatites. Our experimental data made it possible to develop a reproducible seed growth of topaz monocrystals and to study their structure, morphology, and physical properties.     

Growth and morphology of high-germanium single crystals

Experimental data on the growth and study of high-germanium single crystals with better piezoelectric characteristics and with a working capacity at higher temperatures and pressures in comparison with pure quartz are reported.