Известия Томского политехнического университета: Инжиниринг георесурсов (Sep 2017)
Petrocrafical and mineralogical features of ultramafits from Kirelsk fragment of Kansk greenstone belt (NW of the East Sayan)
Abstract
Ultramfits of the studied territory are perspective on detection of Cu-Ni with platinum-group elements deposits that causes the relevance of their research. The main aim of the study. Petrologic researches were directed to establishing the formational accessory of ultramafits of Kulibinskaya area, extraction of the main petrographic varieties and identification of potentially ore-bearing types of rocks. The methods used in the study. Detailed petrographic studying of ultramafits realized on a polarisation microscope «AxioScop 40» (Carl Zeiss) that allowed revealing their main varieties and determining their formational accessory by structural features. Composition of minerals and rocks was generally studied in the Center of collective use «Analytical center of a geochemistry of natural systems» at Tomsk State University. Chemical composition of rock-forming minerals was estimated on the electronic scanning microscope «Tescan Vega II LMU» equipped with the energy-dispersion spectrometer INCA Energy 350 and the wave-dispersion spectrometer INCA Wave 700. Contents of rare and rare-earths elements was defined by the ICP-MS method on a spectrometer of the Agilent 7500 series. Bulk chemical composition was defined by the quantitative chemical analysis in the laboratory of the «Minusinsk GRE» (Minusinsk). The results. It was ascertained that ultramafits in the explored territory are divided into two formational types and united in two complexes: kingashsk magmatic dunite-verlite-picritic and idarsk restite dunite-harzburgitic. The ultramafits of a kingashsk complex composing bodies of the subvolcanic facies are the subject of the greatest practical interest. They are presented by dunites, verlites, their serpentinised varieties and picrites with various structures, which are derivants of primary high-magnesian pikritic magma. Cumulative or porphyryc structures are tipical for them. They form a persistent trend of a variation of chemical composition of minerals, which reflects serial magmatic differentiation of an initial high-magnesian picritic melt. It is established that ore components stand apart, mainly, in the interstices, or in a groundmass. Cumulative dunites and their serpentinised varieties which form ore-bearing Kingashsk massif are optimum for Cu-Ni-PGE mineralization. The subsequent more differentiated varieties are depleted by valuable components. Restite ultramafits are presented by the rocks of dunite-gartsburgitic association with the reference metamorphic granoblastic structures. They differ in more homogeneous high-magnesian chemical composition of minerals caused by intensive depletion of initial mantle substratum.
