GENESIS OF GREY "HAWK’S EYE" OF THE KRYVYI RIH BASIN

UDC 549 : 553.8 : 353.31 (477.63)        

https://doi.org/10.15407/mineraljournal.38.02.046

V.A. Andreichak, V.D. Evtekhov, A.V. Evtekhova

State institution of higher education "Kryvyi Rih National University"

11, XXII Party Congress Str., Kryvyi Rih, Ukraine, 50002

E-mail: mineralogia.knu@gmail.com; evtekhov@gmail.com; eva_anna@mail.ru

GENESIS OF GREY "HAWK’S EYE" OF THE KRYVYI RIH BASIN

Language: Ukrainian

Mineralogical journal 2016, 38 (2): 46-51

Abstract: Results of complex mineralogical studies of the grey "hawk’s eye" (as its most common variety occurring in iron ore rock mass of the Kryvyi Rih basin) have been presented in the article. The eye manifestations take place in productive iron ore and enclosing rocks of practically all iron ore deposits of the Kryvbas, but they are the most typical of the Gleyuvatka deposit. Coloring and gemological value of the grey "hawk’s eye" are determined by mineral composition, structure, texture which depend on the conditions of the gem formation. Cummingtonite asbestos of metamorphogenic alpine veins among magnetite-cummingtonite quartzites was the initial material for the "eye" formation. It was silicified at the regressive stage of dynamothermal metamorphism, which caused the gem formation. The grey "hawk’s eye" of the highest quality is characterized by parity proportion of primary cummingtonite and epigenetic quartz. Further increase in silification process resulted in negative consequences: the "hawk’s eye" was gradually replaced by the monomineral granoblastic quartz aggregate, the gem was loosing its iridescence. The "tiger’s eye" is a product of hypergene changes of grey, light blue and blue "hawk’s eye" accompanied by formation of complex pseudomorph of dispersed goethite and hypergene quartz with inclusions of montmorillonite in fibrous individuals of amphiboles. Practically every geological process manifested in Kryvyi Rih structure: sedimentation, dynamo thermal metamorphism, sodium metasomatosis, tectogenesis and hypergenesis took place in the formation of "hawk’s" and "tiger’s" eyes of the Kryvbas. Crystallochemical, morphological, anatomical changes of the "eye" were confirmed by X-ray diffraction, X-ray fluorescence, magnetometric analyses.

Keywords: iron-banded formation, Kryvyi Rih basin, grey "hawk’s eye", localization, individuals and aggregates morphology, mineral composition.

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