High-temperature Silicate Melts Research Articles

Contrasting Diamond Potentials of Kimberlites of the V. Grib and TsNIGRI-Arkhangelskaya Pipes (Arkhangelsk Diamondiferous Province) as a Result of the Different Compositions and Evolution of the Lithospheric Mantle: Data on the Contents of Major and Trace Elements in Garnet Xenocrysts

Abstract —The paper presents data on the contents of major and trace elements in garnet xenocrysts from kimberlites of the highly diamondiferous V. Grib pipe (1100 grains) and weakly diamondiferous TsNIGRI-Arkhangelskaya pipe (446 grains). We have established that the high diamond potential of the V. Grib kimberlite pipe is due to several factors related to the composition and structure of the lithospheric mantle represented by kimberlite: (1) a “cold” regime, with a heat flow of 36–38 mW/m2; (2) a thick “diamond window” (70–102 km), with the depth level of the lower boundary of the lithospheric mantle estimated at >200 km; (3) the high degree of preservation of diamondbearing peridotites under the P–T conditions of diamond stability despite the high degree of impregnation of the lithospheric-mantle rocks by high-temperature silicate melts. The low diamond content of the TsNIGRI-Arkhangelskaya kimberlite pipe as compared with the V. Grib pipe is due to the following factors: (1) a more intense heat flow in the lithospheric mantle, 38–42 mW/m2; (2) a thinner “diamond window”, 10–60 km, with the depth level of the lower boundary of the lithospheric mantle estimated at <200 km; (3) weak impregnation of the rocks of the middle and lower lithospheric mantle by CHO fluid/melt, which might have induced diamond formation; (4) minimum preservation of diamond-bearing peridotites in the lower lithospheric mantle, partly because of the possible impregnation of this zone by high-temperature silicate melts.

The Earliest Generation of Diamond: The First Find of a Diamond Inclusion in Kimberlitic Olivine

Today, it is known that the majority of diamonds are crystallized mostly from a metasomatic agent close in the main characteristics to carbonatite melts acting upon mantle rocks, and therefore, diamonds are located in the interstitial space of these rocks. So far, diamond has never been found included in other kimberlitic or xenolithic minerals. We have found a diamond inclusion inside the kimberlitic olivine grain, which is the first find of its kind. The diamond crystal is to have been captured by the growing olivine at quite high temperatures (more than 1400 °C) early in the history of the cratonic lithospheric mantle formation. The event had taken place long before the depleted peridotite cooled down to the temperature of the Middle Archean cratonic geotherm corresponding to the diamond stability field at depths where carbonatite melts can react with depleted peridotite, making it a diamond-bearing rock. On the one hand, this find provides evidence that diamonds can crystallize from the high-temperature silicate melt with some carbonate component. On the other hand, the diamond was found coexisting with a sulfide inclusion in the same olivine, i.e., crystallization from a sulfide melt may be another way of diamond formation.

Whole-rock geochemistry and mineral compositions of gabbroic rocks and the associated Fe–Ti (–V) oxide deposit in the Gonamsan intrusion, South Korea

The NS trending sill-like Gonamsan gabbroic intrusion in the central region of the Korean Peninsula intruded Neoproterozoic metasedimentary rocks composed of schists intercalated with gneisses, marbles, and quartzites. The intrusion has an east zone (EZ) composed of diorite–monzodiorite, diorite–gabbro, and oxide gabbro–monzodiorite, and a west zone (WZ) composed of quartz monzodiorite. These silicate rocks have similar primitive-mantle normalized trace elements and chondrite-normalized REE patterns, suggesting that they are co-magmatic. Plagioclase anorthite (An) contents (1.9–54.0), pyroxene MgO/ (MgO + FeO) (Mg#) (35.4–73.7), and olivine forsterite (Fo) values (14.5–20.9) show a wide range through the intrusive silicate suite, but each unit has narrow ranges, and reverse fractionation is absent. The Fe–Ti (–V) oxide mineralization only occurs in the EZ and is characterized by variations in morphology, size, mineral assemblages, and chemical compositions of the Fe–Ti oxide minerals. Stratiform Fe–Ti (–V) oxide mineralization interlayered with diorite–monzodiorite is restricted to metasedimentary host rocks in the central region of Gonamsan and comprises magnetite and ilmenite with lesser amount of olivine, tschermakite, apatite, spinel, pyroxene, and plagioclase. Lenticular mineralization occurs along the western margin of the diorite–gabbro and consists of magnetite and ilmenite with minor hornblende, apatite, chlorite, and spinel. Oxide gabbro interlayered with relatively thin monzodiorite bands forms cyclical units irregularly distributed throughout the EZ and consists of olivine and pyroxene with minor interstitial magnetite, ilmenite, and apatite. Magnetite is the principal Fe–Ti oxide mineral, and varies in chemical composition and microtextures in different ore zones. Overall, the compositions of magnetite from all mineralized zones fall in the compositional fields for magmatic Fe–Ti, V deposits defined by Dupuis and Beaudoin (2011). Magnetite from the stratiform Fe–Ti oxide mineralization is compositionally consistent with those from high-temperature silicate melts and displays complex ilmenite and spinel exsolution textures that resulted from re-equilibration of ulvöspinel–magnetite solid solution during cooling. In contrast, magnetite from the lenticular ore and oxide gabbro are compositionally consistent with being derived from evolved low-temperature melt. Based on the whole-rock geochemistry, mineral composition, and mineralization distribution, the Fe–Ti (–V) oxide mineralization in the Gonamsan intrusion seems to be related to Fe–Ti-rich melt formed from magmatic fractionation and migration along a relatively permeable zone, rather than other magmatic and post-magmatic processes.

Experiments to understand crystallization of levitated high temperature silicate melt droplets under low vacuum conditions

We report experiments on crystallization of highly undercooled forsterite melt droplets under atmospheric and sub-atmospheric pressure conditions. Experiments have been conducted under non-contact conditions using the principles of aero-dynamic levitation. Real time dynamics of solidification, along with the transient evolution of surface textures, have been recorded using high speed camera for three cooling rates. These images have been matched with the time-tagged temperature data to understand the effect of pressure conditions and cooling rates on the crystallization dynamics. Compared to normal pressure, relatively higher levels of undercooling could be achieved under sub-atmospheric conditions. Results showed a strong dependence of surface textures on pressure conditions. For any externally employed cooling rate, relatively small length scale morphological textures were observed under sub-atmospheric conditions, in comparison to those achieved under ambient conditions. The observed trends have been explained on the basis of influence of pressure conditions on recalescence phenomenon and the rate at which latent heat of crystallization gets dissipated from the volume of the molten droplet. Sub-atmospheric experiments have also been performed to reproduce one of the classical chondrule textures, namely the rim + dendrite double structure. Possible formation conditions of this double structure have been discussed vis-à-vis those reported in the limited literature. To the best of our knowledge, the reported study is one of the first attempts to reproduce chondrules-like textures from highly undercooled forsterite melt droplets under sub-atmospheric non-contact conditions.

Precious metals in magmatic Fe-Ni-Cu sulfides from the Potosí chromitite deposit, eastern Cuba

The Moa-Baracoa ophiolite in eastern Cuba is one of the few known ophiolites that display sulfide mineralization attributable to a magmatic origin in association with podiform-chromite ores hosted in the mantle-crust transition. These sulfide ores chiefly consist of Fe-Ni-Cu sulfides, namely pyrrhotite, pentlandite, chalcopyrite and cubanite partly altered to valleriite. The sulfide mineralization is located along the contact between the podiform-like chromite ores and intruding pegmatitic gabroic dykes. The detailed mineralogical study of the sulfide mineralization coupled with the first ever laser ablation ICP-MS analysis reveals that this sulfide mineralization show contents of the precious metals (Os, Ir, Ru, Pt, Re, Au, Ag) and other (semi)-metals (Co, Ni, Cu, Se, Te, Bi, Pb, As Sb) comparable to those sulfides from the magmatic sulfide deposits associated with mafic complexes hosted in the continental crust. The results obtained from this study confirm that Fe-Ni-Cu sulfides at Potosí are magmatic in origin, and very likely derived from the solidification of droplets of sulfide melt segregated by immiscibility from the intruding mafic melts once they interacted with the pre-existing chromitite at the mantle-crust transition zone of the ophiolite. The immiscibility of sulfide melt was achieved as a result of a progressive increase of fS2, very likely triggered by a set of circumstances, including the progressive fractionation of the intruding mafic melt leading to increase of aSiO2 and accumulation of volatiles as well as the crystallization of oxides. Two main generations of pentlandite were observed. One generation is primary in origin and it was locally exsolved along with pyrrhotite from monosulfide solid solution (MSS) during low-temperature cooling. The second type of pentlandite resulted from the reaction of MSS with coexisting droplets of Cu-and Ni-rich sulfide melt. LA-ICP-MS analysis reveals that most precious metals (Ru, Os, Ir, Re, Au, Ag) were concentrated along with the base-metal sulfides (BMS), although their distribution among the different BMS (pyrrhotite, pentlandite, chalcopyrite and cubanite) does not strictly follow the expected distribution according to the known melt-solid and solid-solid partition coefficients. Unlike the other analyzed PGEs, Pt was not preferentially concentrated in BMS but as discrete micrometer-sized sperrylite grains. The crystallization of sperrylite took place before and contemporaneous to sulfide segregation, and Pt-As nanoparticles probably played an important role in the Pt uptake as nucleation seeds for the formation of micron-sized sperrylite grains. These observations highlight the open-system nature of the ore forming system as well as the important role of arsenic in concentrating PGE in high-temperature silicate and sulfide melts.

Electroplasma installation for producing high-temperature silicate melts

The paper presents the design of an electroplasma installation for producing the high-temperature silicate melts. The optimal operating modes of the screw feeder (from 12.3 kg·h−1 to 25.4 kg·h−1) were established to ensure the production of a homogeneous high-temperature silicate melt. The design of electroplasma installation with a closed volume to produce highly viscous melts with the viscosity values of more than 105 Pa·s is proposed.

Theoretical calculation of equilibrium Mg isotope fractionation between silicate melt and its vapor

Isotope fractionation during the evaporation of silicate melt and condensation of vapor has been widely used to explain various isotope signals observed in lunar soils, cosmic spherules, calcium–aluminum-rich inclusions, and bulk compositions of planetary materials. During evaporation and condensation, the equilibrium isotope fractionation factor (α) between high-temperature silicate melt and vapor is a fundamental parameter that can constrain the melt’s isotopic compositions. However, equilibrium α is difficult to calibrate experimentally. Here we used Mg as an example and calculated equilibrium Mg isotope fractionation in MgSiO3 and Mg2SiO4 melt–vapor systems based on first-principles molecular dynamics and the high-temperature approximation of the Bigeleisen–Mayer equation. We found that, at 2500 K, δ25Mg values in the MgSiO3 and Mg2SiO4 melts were 0.141 ± 0.004 and 0.143 ± 0.003‰ more positive than in their respective vapors. The corresponding δ26Mg values were 0.270 ± 0.008 and 0.274 ± 0.006‰ more positive than in vapors, respectively. The general $$\alpha - T$$ equations describing the equilibrium Mg α in MgSiO3 and Mg2SiO4 melt–vapor systems were: $$\alpha_{{{\text{Mg}}\left( {\text{l}} \right) - {\text{Mg}}\left( {\text{g}} \right)}} = 1 + \frac{{5.264 \times 10^{5} }}{{T^{2} }}\left( {\frac{1}{m} - \frac{1}{{m^{\prime}}}} \right)$$ and $$\alpha_{{{\text{Mg}}\left( {\text{l}} \right) - {\text{Mg}}\left( {\text{g}} \right)}} = 1 + \frac{{5.340 \times 10^{5} }}{{T^{2} }}\left( {\frac{1}{m} - \frac{1}{{m^{\prime}}}} \right)$$ , respectively, where m is the mass of light isotope 24Mg and m′ is the mass of the heavier isotope, 25Mg or 26Mg. These results offer a necessary parameter for mechanistic understanding of Mg isotope fractionation during evaporation and condensation that commonly occurs during the early stages of planetary formation and evolution.

Studying regimes of convective heat transfer in the production of high-temperature silicate melts

The article presents the results of theoretical and experimental studies of the production of high-temperature silicate melts using the energy of low-temperature plasma in a conceptually new setup. A mathematical model of unsteady regimes of convective heat and mass transfer is developed and numerically implemented under the assumption of non-Newtonian nature of flow in the melting furnace with plasma-chemical synthesis of high-temperature silicate melts. Experiments on melting silicate containing materials were carried out using the energy of low-temperature plasma. The dependence of dynamic viscosity of various silicate materials (basalt, ash, waste of oil shale) was found experimentally.

Joule heating effects on quartz particle melting in high-temperature silicate melt

This work is mostly focused on the melting process model simulation of quartz particles having the radius within the range of 10-6-10-3 m. The melting process is simulated accounting for the heat generation at an electric current passage through a quartz particle.

Investigation of the Melting of Quartz Sand by Low-Temperature Plasma

The possibilities of producing high-temperature silicate melt of quartz sand from the Tuganskoe deposit (Tomsk Oblast) by means of low-temperature plasma are investigated.

A theoretical model of isotopic fractionation by thermal diffusion and its implementation on silicate melts

When a homogeneous system is placed under a temperature gradient for a sufficient time, both its chemical and isotopic compositions will differentiate between the hot and the cold ends. Molecular-level knowledge of this process is of critical importance to understanding concentration and isotopic distributions in many geologic systems. Recently, different theoretical models have been proposed to explain isotopic fractionations observed in laboratory experiments under high temperatures, but there is still a lot of debating. Here we provide a unified theory based on local thermodynamic equilibrium approach to evaluating thermal isotope fractionations under a wide range of temperatures. For high temperature silicate melts, our theory offers a simple equation for calculating isotopic fractionations of all isotope systems: ΔXM=−(3/2)ln(m∗/m)ln(T/T0). The results from this equation agree with observed data for the most of network modifiers and resolve existing discrepancies among different interpretations. It can also explain O and Si isotope results if consider their diffusing species not as a single ion but a larger unit (e.g., [SiO3] or [SiO4]). The simplicity of the equation support a classical mechanical collision model for high-temperature diffusing particles in silica melts.

Resource Saving Technology for Plasma Treatment of Molybdenum Ore Tailings

In the production of mineral fibers it is possible to synthesize high-temperature silicate melts from molybdenum ore tailings using low-temperature plasma. Physicochemical research was carried out in relation to raw materials and melt products.

The solvation radius of silicate melts based on the solubility of noble gases and scaled particle theory.

The existing solubility data on noble gases in high-temperature silicate melts have been analyzed in terms of Scaling Particle Theory coupled with an ab initio assessment of the electronic, dispersive, and repulsive energy terms based on the Polarized Continuum Model (PCM). After a preliminary analysis of the role of the contracted Gaussian basis sets and theory level in reproducing appropriate static dipole polarizabilities in a vacuum, we have shown that the procedure returns Henry's law constants consistent with the values experimentally observed in water and benzene at T = 25 °C and P = 1 bar for the first four elements of the series. The static dielectric constant (ɛ) of the investigated silicate melts and its optical counterpart (ɛ(∞)) were then resolved through the application of a modified form of the Clausius-Mossotti relation. Argon has been adopted as a probe to depict its high-T solubility in melts through an appropriate choice of the solvent diameter σs, along the guidelines already used in the past for simple media such as water or benzene. The σs obtained was consistent with a simple functional form based on the molecular volume of the solvent. The solubility calculations were then extended to He, Ne, and Kr, whose dispersive and repulsive coefficients are available from theory and we have shown that their ab initio Henry's constants at high T reproduce the observed increase with the static polarizability of the series element with reasonable accuracy. At room temperature (T = 25 °C) the calculated Henry's constants of He, Ne, Ar, and Kr in the various silicate media predict higher solubilities than simple extrapolations (i.e., Arrhenius plots) based on high-T experiments and give rise to smooth trends not appreciably affected by the static polarizabilities of the solutes. The present investigation opens new perspectives on a wider application of PCM theory which can be extended to materials of great industrial interest at the core of metallurgical processes, ceramurgy, and the glass industry.

Unsteady regimes of hydrodynamics and heat transfer at production of high-temperature silicate melts

An absolutely new setup for production of high-temperature silicate melts with application of energy of low-temperature plasma is considered in this paper. The mathematical model “stream function — vorticity” was developed and numerically implemented in transformed variables. This model describes the unsteady regimes of convective heat transfer in the melting furnace. The effect of time and electric current density on the flow structure and heat transfer was studied. The features of hydrodynamics caused both by unsteady character of the process and significant dependence of thermal-physical characteristics on temperature were identified.

Effect of cavitation on high-temperature silicate melts

The effect of acoustic vibrations in the cavitation regime on high-temperature high-viscosity slag melt is evaluated experimentally. It is determined that ultrasonic treatment greatly increases the crystallization power of melt; this could be due to depolymerization of the silicon-oxygen framework of silicate melt and the creation of an extended interface between the gaseous and liquid phases in the melt. It is shown that acoustic treatment promotes dispersion of a refractory solid phase in the melt.

The Soret effect and isotopic fractionation in high-temperature silicate melts

Diffusion in condensed phases is a ubiquitous but poorly understood phenomenon. For example, chemical diffusion, which is the transport of matter associated with chemical concentration gradients (Fick's law), is treated as a separate process from thermal transport (the Soret effect), which is mass transport induced by temperature gradients. In the past few years, large variations in the proportions of isotopes of Mg, Ca, Fe, Si and O found in silicate melts subject to thermal gradients have been found, but no physical mechanism has been proposed. Here we present a model of diffusion in natural condensed systems that explains both the chemical and isotopic fractionation of Mg, Ca and Fe in high-temperature geochemical melts. Despite the high temperatures associated with these melts (T>1,000 °C), we find that consideration of the quantum-mechanical zero-point energy of diffusing species is essential for understanding diffusion at the isotopic level. Our model explains thermal and chemical mass transport as manifestations of the same underlying diffusion mechanism. This work promises to provide insights into mass-transport phenomena (diffusion and evaporation) and associated isotopic fractionations in a wide range of natural condensed systems, including the atmospheric water cycle, geological and geochemical systems and the early Solar System. This work might also be relevant to studies of mass transport in biological and nanotechnological condensed systems.

Two-step nucleation process of silicate interplanetary dust particles at the vicinity of silicate melt

Abstract The condensation processes of interplanetary dust particles (IDPs) around a high temperature silicate melt droplet were investigated in situ by a newly developed flash heating technique under microgravity using a drop tube facility. Two-step nucleation process was captured in the vicinity of the MgSiO 3 melt by a CCD camera. The first nucleation was observed at a distance of 7 mm from the vapor source at 0.3 s and the second nucleation was observed 1.4 s after the MgSiO 3 melt evaporated. The first nucleated particles were irregularly shaped amorphous silica with a diameter of 100–500 nm. The amorphous enstatite particles with a diameter of 70 nm nucleated 1.1 s later. The observed condensation sequence was silica and then enstatite . The difference of these condensations sequence with the chemical equilibrium was showed through the present experiment. The present in situ observation under microgravity was found to be a very useful technique to judge the nucleation sequence of various phases in very short duration within 3.0 s.

Electrochemistry of cations in diopsidic melt: Determining diffusion rates and redox potentials from voltammetric curves

We have used Linear Sweep Voltammetry to measure properties of selected ions in diopsidic melt. In general, the redox reactions studied are complicated by such factors as slow reaction kinetics, monomerizations, and dimerizations, or presence of multi-step reductions that overlap on voltammetric curves. Criteria for recognizing these complications are gleaned from the literature and their application to reductions in high temperature silicate melts is discussed. Criteria that establish whether the reduction potentials obtained from the curves represent equilibrium conditions are also discussed. Diffusion coefficients were measured in diopsidic melt for cations of Eu, Mn, Cr and In. We observe that diffusion rates decrease as the size of the diffusing cation increases. Diffusional activation energies are similar to those reported for other silicate melt compositions. Enthalpies and entropies of reduction were determined for the cations V(V), Cr 3+, Mn 2+, Mn 3+, Fe 2+, Cu 2+, Mo(VI), Sn(IV) and Eu 3+. The free energies can be used to compute relative proportions of multivalent cations in various valence states as a function of temperature and fO 2. Reduction potentials also provide a means for studying the structural state of cations in the melt. Free energies of reduction in melts of different compositions cannot be modeled solely by changes in oxide ion activity, but must include contributions from changes in the activities of the cations as well.

Dissolution of Mafic Minerals and its Implications for the Ascent Velocities of Peridotite-Bearing Basaltic Magmas

Crystal dissolution in high temperature silicate melts is typically controlled by diffusion across a boundary layer in the melt next to the crystal. Experimental studies on basaltic systems show a decreasing rate of dissolution from garnet, clinopyroxene, orthopyroxene, to olivine, with the dissolution rate of garnet about 10 times that of olivine at pressures up to 20 kbars. Preferential dissolution is exhibited by many upper mantle-derived spinel peridotite xenoliths in which embayment of orthopyroxene relative to the juxtaposed olivine grains occurs at the xenolith-host basalt contacts. By combining the data on dissolution rates as a function of pressure, the relationship between the path of adiabatic ascent and the liquidus, and the density and viscosity of basaltic melt, we establish here formulations relating the amount of peridotite dissolution to the ascent times and velocities of alkali basalts in continental and oceanic settings. The results show that alkali basalts may ascend at velocities of u...