Известия Томского политехнического университета: Инжиниринг георесурсов (May 2019)
The Kalninsky ultramafic massif of Western Sayan: ore mineralization and its genetic nature
Abstract
Relevance of the work is caused by the need of detailed petrological studies of ultrabasic massifs of Amylsky chromite-bearing area of the Western Sayan in terms of their potential for chromite ore and associated precious metal mineralization. The main aim of the study is to characterize mineralization in Kalninsky ultramafic massif for reconstructing the evolution of the material composition of chromites and sulfides associating with them at massif rocks formation and their subsequent metamorphic changes. The methods used in the study: characteristics of mineralization in transparent and polished sections on the polarizing microscope AxioScope Carl Zeiss; evaluation of chemical composition of chromospinelides and sulfides on scanning electron microscope Tescan Vega II LMU, equipped with energy-dispersive spectrometer (detector Si (Li) Standard) INCA Energy 350 and wave-dispersive spectrometer INCA Wave 700; content of Au and PGE in chromites on quadrupole ICP MS - Agilent 7500 series spectrometer. The results. The author has studied the features of ore mineralization of the Kalninsky ultramafic massif. The paper introduces minerals tipomorfizm and chemical compound. The resulted data allowed determining the degree of partial melting of the initial substrate and the temperature of its metamorphic transformation when moving and consolidating in the earth's crust. The author could trace the evolutionary direction in change of chromospinelide and associated sulphides chemical composition. It was determined by the conditions of their depletion in the upper mantle and subsequent metamorphic transformations. The chemical composition of chromospinelides correspond to minerals of upper mantle substrate with a high degree of partial melting (28…41 %) and to chromospinelides from ultramafites of oceanic trenches. The substrate has undergone plastic metamorphism at temperatures from 844 to 746 °C. Sulphidic mineralization represented by scattered impregnation of heazlewoodite was formed during low-temperature hydrothermal process. The latter contributed to nickel redistribution released from the olivine and orthopyroxene and to its localization as independent mineral phases.
