Mineralogical and geochemical features of magnesia-ferruginous carbonates of the Avzyan ore region of the Southern Ural in connection with metasomathosis regularities

Abstract

The authors conducted a detailed mineralogical-geochemical study (thermogravimetric, X-ray diffraction, chemical analysis and ICP-MS) of the Magnesium-ferruginous metasomatites of the Avzyan ore region, represented by ferruginous magnesites of the Ismakaevo deposit and the brejnerites of the Bogryashka manifestation. Metasomatites are confined to the primarily limestone Minyak subsuite of the Suran Suite of the Lower Riphean. Iron magnesites contain up to 4% by weight of FeO, braunerites up to 20.5% by weight of FeO, which the calculation method confirms according to diffractometry data. The authors established significant correlations between elements of the iron group and chalcophile elements, reflecting their increased concentrations in pyrite, widely represented in metasomatites. In addition, the authors noted a strong correlation of thorium with light lanthanides, which happens due to accessory impregnation of monazite. Correlation of carbonate metasomatites with their trace element composition appears in the interrelation of dolomite with strontium, yttrium and lanthanides of the middle-heavy group (Sm-Lu). The article shows three types of distribution of rare-earth elements: dolomite, magnesite and mixed, characterized by a different ratio of light, medium and heavy lanthanides, depending on the position in the metasomatic column. Weak positive values of cerium and europium anomalies in most of the examined groups of metasomatites to some extent confirm the highly reducing nature of the fluids. Geochemical data together with the analysis of the geological structure and development of the region make it possible to associate magnesian-ferruginous metasomatism in the carbonate rocks of the Suran Suite with the processes of remobilization of evaporite brines buried in the Lower Riphean deposits. Intensive interaction of brines with sedimentary and volcanogenic rocks in the tectonically active zone of the Mashak riftogenic graben resulted in their enrichment with various ligands, increase in basicity and more active hydrothermal redeposition in the metasomatic products of the lanthanides of the middle and heavy groups.