Abstract
Relevance of the work. The conditions for the formation of chromium ores in alpine-type ultramafites remain a topical subject of research. In recent years, scientific papers have focused on the issue of changing the chemical composition of ore-forming minerals and chromium ores under the influence of deformation and dynamic recrystallization processes accompanying metamorphism. The results of such studies make it possible to formulate a new model of the formation of chromium mineralization taking into account a significant amount of geological data indicating that alpine-type ultramafic rocks are “mantle tectonites”. In our work, we have studied zonal ore-forming spinels from chrome ores of the Polar Urals. The results of the study make it possible to associate the formation of chemical zoning in minerals and ore bodies with recrystallization under the influence of stress tension. Purpose of the work – study of the conditions for the formation of chemical zoning of chromium spinels from alumina and medium chromium ores of the Voikaro-Syninsky massif. Results. Zonal ore-forming spinels from medium-chromium and aluminous chromitites of the Voikaro-Syninsky massif (Polar Urals) have been studied. It was found that replacement rims are developed along the grains of oreforming spinels with an increased content of Cr2 O3 and an oxidation state of iron in relation to the core, as well as a reduced content of Al2 O3 . The oxidation state of iron in the rims of most grains does not exceed the values typical for unaltered ore-forming spinels. T–fO2 parameters of zoning formation in spinels were determined by oxythermobarometry. Comparison with zoned chrome spinels of the Golyamo Kamenyane massif (Bulgaria). Conclusion. Metamorphic transformations of alumina and medium-chromium chromitites of the Voikaro-Syninsky massif, occurring under subcrustal conditions under the action of directional stress at relatively constant T–fO2 parameters, lead to an increase in the chromium content of the ore mineral.
Highlights
The zoning of ore-forming and accessory chrome spinels from alpine-type ultramafic rocks is the subject of numerous studies
Researchers have found that the formation of a replacement rim for high-chromium, and relatively ferrous spinels for medium-chromium, is associated with regressive water metamorphism that took place under reducing conditions [4]
Ore body 3415 of the Arkashorkoye ore occurrence consists of two blocks, the spinels of which differ in composition
Summary
The zoning of ore-forming and accessory chrome spinels from alpine-type ultramafic rocks is the subject of numerous studies. The Cr2O3 content in spinels from the ores of the Tsentralnoye deposit and the Yengayskoye-1 ore occurrence varies from the centre to the edge of the grain in different ways: in the first case, it increases, in the second – decreases. This may be due to the different pressures at which the zoning of the mineral was formed. It is noted that spinels have either a homogeneous internal structure, or zonal, with a later rim of ferrichromite and magnetite [12, 13]
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