Известия Томского политехнического университета: Инжиниринг георесурсов (Sep 2016)

Chromitites of Kharcheruz block of Syum-Keu massif: ore composition and genesis (Polar Ural)

  • Alexey Nikolaevich Yurichev,
  • Alexey Ivanovich Chernyshov

Journal volume & issue
Vol. 327, no. 8

Abstract

Read online

The relevance of the work is caused by the need of detailed petrological studies of poorly studied ultrabasic massifs of Russia in terms of their potential on chromite ore, which are currently the raw materials in very short supply for the state. The main aim of the paper is to characterize petrographic features and chemistry of chromitites from Kharcheruz block of Syum-Keu massif to reconstruct the evolution of material composition of ore chromosphinelides at formation of rocks and their subsequent metamorphic changes, geodynamic conditions of formation of the investigated object. The methods used in the work: study of silicate and ore minerals in transparent sections and polished sections on the polarizing microscope AxioScope Carl Zeiss; evaluation of chemical composition of chromosphinelides 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. The results. The authors have made the first attempt to describe in detail chromitites identified among dunites within poorly studied Kharcheruz block of Syum-Keu massif. By quantifying role of chromosphinelides they are divided into three types: interspersed, thickly interspersed and drain. By textural features the schistose chromitites, which are the product of plastic flow, are marked. By chemical composition ore chromosphinelides are presented by chromites and chromohercynites and exhibit a single linear evolutionary trend, reflecting the transformation of their material composition under influence of high-pressure dynamometamorphism. This process was accompanied by magnesium and aluminum removal from chromosphinelides and increase of chromium, which led to the natural «beautification» of the latter. The second conversion step, associated with the later processes of superimposed regional metamorphism, did not affect significantly the chemical composition of ore chromosphinelides and it is associated with a slight shift of ferrous iron to ferric. The investigated chromosphinelides meet the minerals of upper mantle substrate with a high degree of partial melting (29...40 %), which occurred in spreading zone, adjacent to the hot spot. Later, in the island arc system, this anomalous oceanic lithospheric mantle underwent interaction with boninite melts, initiated by subduction, that led to occurrence of dunite and chromitites with obvious characteristics of above-subduction peridotites.

Keywords