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Vol 33, No 5 (2025)
Articles
3-4
Experimental Modeling of the Process of Formation of Native Metals (Fe) in the Earth's Crust in the Restorative Conditions
Abstract
The work presents the results of the experimental modeling of the process of formation of native Fe in the earth's crust when the basalt melts interacting with fluid (H2, H2+CH4) at temperatures (1100-1250°C), fluid pressure (1-100 MPa) in strongly restored conditions - fO2 = 10-12-10-14 bar. The experiments were carried out using the installation of a high gas pressure equipped with a unique device that provides long-term experiments at high temperatures and fluid pressure. In the experiments, natural samples of magmatic rocks were used: the magnesian basalt of the northern breakthrough of the volcano Tolbachik (Kamchatka), as well as a magnesian basalt, enriched with nickel and cobalt oxides. Based on the experimental modeling, the following features of the process of interaction between the recovery fluid with basalt melts are established: 1. Despite the high restoration potential of the H2 system or the mixture (H2+CH4) - a magmatic melt, hydrogen oxidation reactions and the complete restoration of metals oxides in the melting do not go to the end. The cessation of redox reactions in the basalt melt occurs due to the formation of H2O in the melt, buffering the restoration potential of hydrogen or mixture (H2+CH4). 2. Initially, the homogeneous magmatic melt becomes heterogeneous: the formed H2O dissolves in the melt and, partially, in the fluid phase, while melts of more sour composition and small metal isolations of the liquidation structure are formed. 3. The process of metal-silicate liquidation in magmatic melts in their interaction with a restorative fluid can be carried out at real temperatures of the magmas in nature (≤1250°C), significantly lower corresponding melting temperatures of iron and its alloys with nickel and cobalt. 4. Carbon, which is formed in experiments due to pyrolysis CH4, dissolves in the metal phase. Thus, the mechanism responsible for the presence of carbon in a native basalt in nature is experimentally substantiated. 5. The structure and sizes of experimentally installed metal isolations are well consistent with natural data on finds of native metals, primarily iron and its alloys with nickel and cobalt, in magmatic rocks of various composition and genesis.
5-17
Experimental Study of Cation-Exchange Equilibriums of Solid Solutions of Gallium Feldspars (K,Rb)GaSi3O8 with Water-Salt Fluid (KCl-RbCl-H2O) at 550°C and 1.5 kbar and Application to the Description of the Properties of Solid Solutions with a Feldspar Structure
Abstract
Feldspars of the KGaSi3O8-RbGaSi3O8 series were synthesized at a temperature of 550°C and a pressure of 1.5 kbar, and cation-exchange reactions feldspar - solution (1M KCl + 1M RbCl) were studied. The parameters of the unit cells of the solid solutions were specified, and the excess mixing functions were calculated. A comparison with previously studied feldspars was made. Empirical dependencies for calculating the energy parameters of the Margules model and the volumes of unit cells of various feldspars were proposed.
18-39
Formation of Cryolite in Granites of the Katugin Deposit from the Position of the Results of Experiments in a Fluorine-Lithium-Containing Granite System
Abstract
The parageneses of cryolite-containing granites of the rare-metal Katugin deposit are studied and compared with the experimental results for the fluorine-lithium-containing granite system. According to the experiment, cryolite crystallization begins from the salt melt, which is in equilibrium with the aluminosilicate melt, at 700°C and 1 kbar. In the temperature range of 500-600°C and a pressure of 1 kbar, cryolite crystallizes together with quartz from the aluminosilicate melt. Rare earth elements are distributed in the fluorine-lithium-containing granite system mainly in favor of the salt alkali-aluminofluoride melt. It is shown that the formation of cryolite and associated rare earth minerals is possible at the magmatic stage of the Katugin deposit formation due to silicate-salt immiscibility in granite melts at late stages of differentiation.
40-57
Trace Elements Partitioning in the System P2O5–CaO–Na2O ± (SiO2 + Al2O3)–F–H2O–CO2 at 500 MPa
Abstract
The distribution of Ti, Zr, Nb, La, Sm, Yb, and Y was experimentally studied between phosphate-carbonate melts, silicate-bearing melts (at addition of silicate in starting mixtures) and minerals – apatite (Ca₅(PO₄)₃F), fluorite (CaF₂), and nacaphite – (CaNaPO₄F). Four experimental series were carried out in an internally heated gas pressure vessels at a pressure of 500 MPa using four types of starting melts: (1) Ca₅(PO₄)₃F + CaCO₃ + Na₂CO₃ + NaAlSiO₄ at 1100–750 °C;
(2) Ca₅(PO₄)₃F + CaCO₃ + NaF + NaAlSiO₄ at 950 °C; (3) NaPO₃ + CaCO₃ + CaF₂ + NaF + NaAlSiO₄ at 900 °C; and (4) NaPO₃ + CaCO₃ + NaF + NaAlSiO₄ at 900 °C with variable proportions of P₂O₅, CaO, Na₂O, and SiO₂. H₂O, H₂C₂O₄, as well as a mixture of trace element oxides were added in equal mass proportions to all starting compositions. The experimental products were analyzed by electron probe microanalysis. Depending on the CaO and P₂O₅ proportion, the silicate-free starting mixtures in three former series yielded two types of quenched melts: calcite-rich melt with 20 mol % Na₂O at lower P₂O₅ content and sodic-carbonate-phosphate melt with low CaO at higher P₂O₅ content. The solubility of ZrO₂, TiO₂, and Nb₂O₅ in the obtained calcite-rich quenched melts at 650 °C is low and constrained by the crystallization of Zr, Ti, and Nb oxides. At 1000 °C, these oxides are not formed, and the concentrations of ZrO₂, TiO₂, and Nb₂O₅ increase in melts with increasing P₂O₅/(P₂O₅ + CaO) ratio. The REE partition coefficients between apatite and coexisting Ca-rich carbonate melt increase with increasing P₂O₅ content from 0.2 to 0.9 for La₂O₃, from 0.25 to 0.75 for Sm₂O₃, from 0.2 to 0.6 for Yb₂O₃, and from 0.2 to 0.4 for Y₂O₃, reaching in a single case 0.5. In runs of series IV the silicate-bearing starting mixtures yielded two immiscible melts: SiO₂-free phosphate-rich melt with apatite and nepheline, and aluminum-silicate melt in run IV-7. Run IV-8 produced two immiscible melts, sodic-phosphate and silicate, with P₂O₅ content no more than 25 wt %. The concentrations of TiO₂, ZrO₂, Nb₂O₅ are much higher in the phosphate-rich melt than in the silicate melt with the lower phosphorus content. Their partition coefficients in run IV-7 are dTiO₂ = 13.9, dZrO₂ = 2.46, dNb₂O₅ = 3.01, and are less, but still more than one in run IV-8: dTiO₂ = 1.29, dZrO₂ = 2.04, dNb₂O₅ = 1.24.
58-78
Behaviour of Trace Elements at Shock Transformation of Zircon to Reidite
Abstract
Large single crystals of natural zircon were shock-loaded at 13.6 and 51.3 GPa in planar geometry. No structural transformations are observed after the loading at 13.6 GPa. In the experiment at 51.3 GPa zircon transforms to its denser polymorph – reidite, with sheelite-like structure. Investigation of the reidite sample using X-ray diffraction, Raman spectroscopy, photo- and cathodoluminescence revealed segregation of some trace elements cations (such as REE) on planar defects. Importantly, the segregation has occurred in a laboratory-scale experiment without long-term annealing of the sample after the shock loading. Plausible mechanism of segregation of three-valent trace elements implies local violation of charge balance in course of reconstructive transformation of zircon to reidite. As a result of related changes in topology of polyhedra and in second (Si–Zr) coordination sphere, a fraction of trace elements is expelled into energetically expensive interstitial positions with high diffusivities even at low temperatures.
79-93
Oxygen and Carbon Isotope Composition of Vitim Nephrite Province Rocks
Abstract
The oxygen isotopic composition of dolomite type nephrite, contact and host regional rocks of Kavokta, Voimakan and Nizhne-Ollomi deposits of Vitim province was studied. The nephrite is characterized by an anomalously light oxygen isotope composition δ18O −21.5 ÷ −15.8‰. Contact metasomatic rocks showed wider variations, including also anomalously light isotope ratios −21.5 ÷ +9.2‰. The country rocks of the deposit area are characterized by heavier oxygen isotope compositions: granite and granodiorite −7.51 ÷ −0.71‰, amphibolite −8.38 ÷ +9.60‰, dolomitic marble +20.8 ÷ +26.1‰. The anomalously light isotopic composition of nephrite, is thus explained by the meteoric origin of the fluid from melt water and the removal of isotopically heavy oxygen by carbon dioxide in the process of decarbonatization of dolomitic marble. The granite mainly provided the regional heating that activated the fluid. The analyzed dolomite is characterized by a heavier carbon isotopic composition +3.2 ÷ +5.2‰ δ13C, explained by fermentation of organic matter and methane formation in the basin in which the dolomite was formed. Calcite from calcite-tremolite skarn is characterized by lighter carbon isotopic composition −6.4 ÷ +0.7‰ δ13C as a result of metasomatic process.
94-116