Mössbauer spectroscopy of ore-forming chromium spinels of the Polar Urals

• Published in: Litosfera (Ekaterinburg. Online) Vol. 24; no. 6; pp. 1046 - 1059
• Main Authors: Shiryaev, P. B., Vakhrusheva, N. V.
• Format: Journal Article
• Language: English
• Published: 15.01.2025
• ISSN: 1681-9004; 2500-302X
• DOI: 10.24930/2500-302X-2024-24-6-1046-1059

Research subject. The work studied the heterogeneity of the chemical and phase composition of chromitites and ore-forming chromium spinels of the Polar Ural massifs Rai-Iz and Voikaro-Syninsky. Its influence on the value of the oxidation state of iron (Fe# = Fe 3+ /(Fe 3+ + Fe 2+ )), determined by the calculation method, from the stoichiometric formula of the mineral, and using Mössbauer spectroscopy, is analyzed. The purpose of the study is to determine the degree of influence of various manifestations of the heterogeneity of the chemical composition of spinel on the results of determining Fe 3+ /(Fe 3+ + Fe 2+ ) using Mössbauer spectroscopy. Methods and materials. Monofractions of ore-forming chromium spinels were studied by Mössbauer spectroscopy (SM2201 spectrometer). The study of the heterogeneity of chromium spinel grains was carried out using microprobe analysis (electron probe microanalyzer Cameca SX-100) in polished sections and blocks, as well as X-ray phase analysis (powder diffractometer SHIMADZU XRD-6000) in samples analyzed on a Mössbauer spectrometer. Results. The studied ore-forming spinels exhibit three types of compositional heterogeneity, which determine the Fe# Möss – Fe# stoich discrepancy and influence its value: 1) chemical zoning of grains; 2) multiphase, associated with the presence of two generations of mineral grains with varying degrees iron oxidation; 3) hidden multiphase, manifested in broadening of diffraction peaks. In all cases, there is variability in the degree of iron oxidation in the mineral grains. Conclusions. The studied ore-forming spinels of the main ore bodies of the Rai-Iz massif and the northern part of the Voykar-Synya massif have a normal, unconverted structure, and the distribution of cations over its positions corresponds to the crystal chemical formula. Deviations in the distribution of iron cations, established during the study of the mineral by Mössbauer spectroscopy, are associated with the chemical heterogeneity of its grains and the presence in the ore of several spinel phases of different compositions.