Mineral inclusions of iron ores of Bakchar deposit (Western Siberia)

The results of studies of mineral micro-inclusions in the oolitic iron ores of the Bakchar deposit were shown. These inclusions are particles whose dimension does not allow to clearly identify them with traditional mineralogical methods. During research of the ore horizon of the Polynyanka site, three iron ore types were distinguished that differ in their structural-textural characteristics, mineral composition of the cementing mass, as well as in the specificity of their position within a section. The first type is goethite-hydrogoethite (oolitic), which are cemented or loose brown sediments. The second type of ore is glauconite-chlorite or clay with a poorly cemented dense structure and a greenish-gray colour. The third type of transitional ore carries features as goethite-hydrogoethite and glauconite-chlorite types. The main component of the iron ores is oolite, which concentrate iron hydroxides. Oolites of Bakchar iron ores are very diverse in form and colour. According to the results of scanning electron microscopy (SEM), oolites of Bakchar deposit have a complicated concentrically layered structure. The microlocal inclusions were studied by SEM (Tescan VEGA II LMU) combined with energy dispersive spectrometer INCA Energy. In the oolitic ores there were discovered mineral separations, consisting of sulfides, native silver and REE minerals. They are widely distributed, mainly in the oolitic units. The inclusions of oolites were divided into groups based on the composition and localization in ores - sulfide, phosphate and sulfide-phosphate. Association of sulfides involved small inclusions of pyrite, sphalerite, covellite and stibnite. Two distinct morphologies of pyrite were discovered. The first generation is framboidal and the second - euhedral. Phosphate association consists of calcium and REE minerals. Microinclusions of phosphates are mixtures of ultrafine minerals monazite and apatite. Native silver is present in the form of microlocal and hair-like segregations in oolites. The existence of sulfides, REE phosphates and native silver in oolites indicate unstable physical and chemical conditions. During the growth of oolites the redox potential changed, it had a pulsating character. This was reflected in the alternation of hydroxides of iron and clay component with the corresponding adsorbed complexes. Hydroxides sorbed phosphorus and REE, the clay matter sorbed metals. The research has been carried out in the Analytic Centre of Natural Systems Geochemistry of Tomsk State University. The study was funded by the Russian Ministry of Education and Science (Federal Program ''Scientific and Teaching Staff of Innovative Russia for 2009-2013'').

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