Vol 69, No 3 (2024)

Experimental data were analyzed on the partitioning of trace elements between minerals (olivine, orthopyroxene, clinopyroxene, and feldspars) and silicate melts. The data span over a wide range of conditions (from 1 atm to 10 GPa and ~1000–2000 °C) and compositions of melt (from ultrabasic to ultrasilicic) and minerals. The dependence of logarithms of partition coefficients (lnD_i ) on conditions and compositions was approximated by linear functions of 1/T, P/T (P is pressure, and T is absolute temperature) and compositional parameters of mineral and melt. It was found that D_i /D_j values for a number of element pairs are independent of experimental parameters and vary within narrow ranges. The coefficients of D_i dependencies on conditions and compositions were estimated by minimization of quadratic deviations of model D_i and D_i /D_j values from experimental values. The obtained equations can be used to calculate D_i values for a number of elements with an accuracy of approximately a factor of 1.2–2.0. The obtained values were applied as an example for a model of formation of mafic melts of mid-ocean ridges through melting of a peridotite source and crystallization of primary magmas under crustal conditions.

Three variably old groups of banded iron formation (BIF) are known in the Kostomuksha Greenstone belt (KGB) of the Karelian Craton. This paper deals with the earliest of them, Mesoarchean (2.87–2.81 Ga) – BIF-1. BIF-1 occurs among the komatiite-basalt unit of the KGB. BIF-1 consists mainly of quartz and magnetite, with varying amounts of amphibole, biotite, and garnet; they contain 48.3-58.6 SiO₂ and 21.34–33.82 wt. %, Fe₂O₃^T, suggesting that the rocks are BIF. BIF-1 of the KGB, as well as most Archean BIFs, contain high Fe₂O₃^T, concentration, display a contrasting positive Eu anomaly, lost of Ce anomaly, the depletion of LREE relative to HREE. However, they stand out among other BIFs with high Al₂O₃, TiO₂, MgO, K₂O, Cr, Ni, Zr, Ba, Cu and Zn concentrations. BIF-1 was formed in a marine basin in an anoxic atmosphere due to hydrothermal fluids, the proportion of which varies from 20 to 80 %, and a terrigenous component derived mainly from basalts, komatiites, and dacites in host rocks. Mesoarchean BIF-1 of the KGB s was formed in a small rift within an oceanic volcanic plateau, the formation of which is associated with the influence of a mantle plume on the oceanic lithosphere.

Destinezite (Fe³⁺ Al_0.02)(PO₄)_0.99(SO₄)_0.90(OH)_1.20 ⋅ 5.97H₂O (Czech Republic) has been studied by thermal and electron-microprobe analyses, X-ray powder diffraction, IR, Raman, and Mössbauer spectroscopy. The enthalpy of formation of destinezite Fe^{3 +}(PO₄)(SO₄)(OH)⋅6H₂O from the elements ∆_fH⁰(298.15 K) = −4258 ± 12 kJ/mol was determined by the method of solution calorimetry in melt lead borate 2PbO ⋅ B₂O₃ on a Calvet microcalorimeter Setaram (France). The value of its absolute entropy S⁰(298.15 K) = 462.0 J/(mol⋅K) was estimated, the entropy of formation ∆_fS⁰(298.15 K) = −2054 J/(mol⋅K) and the Gibbs energy of formation from the elements ∆_fG⁰(298.15 K) = −3646 kJ/mol.

On April 11-12, 2023, Vernadsky Institute of Geochemistry and Analytical Chemistry and the Korzhinsky Institute of Experimental Mineralogy of the Russian Academy of Sciences held the commemorative All-Russian annual seminar on experimental mineralogy, petrology, and geochemistry in Moscow (RASEMPG-2023). The seminar discussed the latest results of experimental research in the following key areas: phase equilibria under high P-T conditions; formation and differentiation of magmas; interactions in fluid-melt-crystal systems; hydrothermal equilibria and ore formation; mineral synthesis; thermodynamic properties of minerals, melts, and fluids; planetology, meteoritics, and cosmochemistry; physicochemical properties of geomaterials; experimental geoecology; methods and techniques of experiment. Around 250 scientists from 37 Russian research institutes and seven foreign organizations participated in the seminar, delivering over 160 reports.