1. The Redox State of Chromium Ores of the Polar Urals.
- Author
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Shiryaev, P. B. and Vakhrusheva, N. V.
- Abstract
The redox state of chromium ores of the main industrially significant types, developed in ultramafic rocks of the Rai-Iz–Voykar complex of the Polar Urals, was studied. The chromitites occurring in various geological settings—dunite–harzburgite complex and large dunite bodies metamorphosed to different degrees—have been investigated. For the first time, oxygen fugacity and temperature of the formation of chromium ores, based on olivine–spinel equilibrium, were studied in more than representative samples from the Rai-Iz and Voikar–Synya massifs. The Fe/(Fe + Mg) of minerals increases linearly from chromitites to their host ultramafic rocks at each of the studied objects. The temperature of olivine–spinel equilibrium in chromitites varies within 550–800°С. The oxygen fugacity in aluminous chromitites averages FMQ +0.5–1.5 log units; in medium chromium, FMQ +1.5–2.5 log units; in high-chromium ones, more than +2.5 log units relative to the FMQ buffer. The oxygen fugacity in densely disseminated chromitites is 0.5–1 log units higher than in poorly disseminated and rarely disseminated ones. The T–fO
2 values correspond to the crustal conditions and are close to those established in the metaultramafic rocks of the studied massifs. The data obtained may indicate that the concentration of the ore component and the formation of chromium ore deposits occur not only in mantle or lower crustal conditions, characterized by fO2 values close to the FMQ buffer, but also as a result of ultramafic crustal metamorphism occurring in an oxidizing environment. [ABSTRACT FROM AUTHOR]- Published
- 2024
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