O.V. Dubyna 1, 2
https://orcid.org/0000-0002-6003-4873
S.G. Kryvdik 1
https://orcid.org/0000-0002-8356-1115
O.A. Vyshnevskyi 1
https://orcid.org/0000-0002-7206-2185
1 M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine 34, Acad. Palladin Ave., Kyiv, Ukraine, 03142
2 Taras Shevchenko National University of Kyiv, Institute of Geology 90, Vasylkivska Str., Kyiv, Ukraine, 03022
https://doi.org/10.15407/gof.2024.45.021
The results of mineralogical studies of melanocratic apatite-enriched albite-pyroxene rocks of the Chernihivka carbonatite massif are presented. The studied rock was discovered by drilling among alkaline syenites. This rock is represented by vein- like body (thickness up to 30-50 cm). The rock-forming minerals are aegirine-diopside, albite, ferruginous phlogopite, amphibole (edenite-katophorite series) and apatite (up to 20%); accessory — calcite, allanite and pyrite. The studied rock is similar by mineral composition and high apatite content to tvaitosites and tvaitosite-pyroxenites of the massif, which are more distributed in the northern and central parts. However, it differs from them in the composition of phlogopite and amphibole. The latter is not characteristic for typical tvaitosites and tvaitosite-pyroxenites. The obtained preliminary data make it possible to put forward only hypothetical considerations regarding the genesis of this rock. Quit possible their origin could be related with separation of alkaline essentially aqueous fluids from the primary carbonatite melt with subsequent migration into hosted alkaline syenites. The subsequent reaction of these fluids with hosted rocks could lead to the recrystallization of initial feldspar to albite and appearance of secondary calcite, phlogopite, amphibole, and apatite. At the same time, it is assumed that tvaitosites – tvaitosite-pyroxenites series were formed as result of syenite melt differentiations (pyroxene fractionation), since they are composed of the same minerals as the hosted alkaline syenites and main difference between these rocks is only in proportion of pyroxene.
Key words: tvaitosite, aegirine-diopside, edenite-katophorite amphibole, carbonatites.
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