M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of NAS of Ukraine

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Ore bearing of hypersolvus syenite intrusions as prospective rare metal objects on the Ukrainian Shield

ABSTRACT

Report on the scientific research work: 102 p., 72 figures, 12 tables, 49 references.

The objects of the research are the syenite massifs of the Ukrainian shield: Yastrubets, Davydkiv, Velyka Vyska, Azov.

The purpose of the work is to draw a conclusion about the ore-bearing prospects of the Davydkiv, Velyka Vyska, and Yastrubets syenite massifs, comparing their mineralogical features with those of the Azov syenite stock.

Research methods: X-ray phase analysis, electron microprobe analysis, X-ray fluorescence analysis, optical microscopy analysis, thermometry analysis, cryometry analysis, IR-spectrometry analysis.

The discovery in the Azov megablock of the Ukrainian Shield of a promising Azov deposit with an unconventional ore composition (brytholite+zircon+fluorite) made us pay attention to other megablocks of the shield in order to look for signs of mineralization of a similar type. The atypicality of the Azov Zr-REE deposit is caused by the special composition of the magma and the conditions of formation of the Azov intrusion. It is confined to the eponymous stem of alkali feldspar syenites, called hypersolvus, which are formed in conditions of high temperature, relatively moderate pressure and are characterized by a specific composition of rock-forming minerals.

The results of the comparison showed that the syenites of the Yastrubets, Davydkiv, and Velyka Vyska massifs, as well as the syenites of the Azov stock, were formed from melt. All four arrays are intrusions of the hypersolvus type. The crystallization temperature of syenite rocks ranged from >700 to 1000-1200 °С and decreased in the series: Velyka Vyska → Azov → Davydkiv → Yastrubets intrusions. In Yastrubets, the final crystallization of alkali feldspar took place under subsolvus conditions. The hypersolvus spar of the Velyka Vyska intrusion is enriched in potassium and corresponds to the composition of sanidine, in other intrusions the mineral of anorthoclase composition prevails. Crystallization of syenite melt was accompanied by heterogenization of melts - separation of salt melts from silicate melts and separation of the latter into salic and femic parts. The decisive role of salt liquefies in the formation of phosphate (with britholite, apatite) ores, as well as the indicator value of magmatic fluorite, was noted. The melts from which the syenites crystallized are the product of magma differentiation according to the Fenner trend, which was accompanied by the accumulation of ferrum in the residual melt. The Azov and Yastrubets syenites, the bodies of which are located in deep fault zones, were formed from melts of a higher level of differentiation than the Davydkiv and Velyka Vyska syenites, the bodies of which are confined to the margins of anorthosite-rapakivigranite plutons. A predictive assessment of the ore-bearing capacity of hypersolvus intrusions is given. The closest analogue of the Azov intrusion in terms of formation conditions is recognized as the Velyka Vyska intrusion.

Authors:

Kulchetska Hanna Oleksandrivna

Kryvdik Stepan Hryhorovych

Hrechanovska Olena Yevhenivna

Belskyi Volodymyr Mykolaiovych

Chernysh Dariia Serhiivna

Kurylo Serhii Ihorovych

Herasymets Iryna Mykolaivna

Other authors:

Keywords:

britholite, allanite, zircon, chevkinite, fluorite, liquation, melt, differentiation

Head of the research: