Nepheline Syenite-Porphyry of the Azov Area — a New Type of Rocks in the Ukrainian Shield

UDC 550.42 (477)

S.G. Kryvdik (1), O.V. Dubyna (1), Yu.A. Amashukeli (2), O.A. Vyshnevskyi (1)
(1) M.Р. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladina Pr., Kyiv-142, Ukraine, 03680
(2) SSPO "State information geological fund of Ukraine"
16, Eugène Pottier Str., Kyiv, Ukraine, 03680
Nepheline Syenite-Porphyry of the Azov Area — a New Type of Rocks in the Ukrainian Shield
Language: Ukrainian
Mineralogical journal 2015, 37 (4): 78-84

Abstract: The mineral composition and geochemical characteristics of dike nepheline syenite-porphyry of the Azov area in detail are first described. This type of rocks is new for Ukraine and belongs to the family of alkaline basic rocks. This rock consists of phenocrysts of biotite, nepheline and alkali feldspar and a matrix of alkali feldspar, aegirine-hedenbergite, andradite, nepheline (partly substituted by cancrinite and sodalite), biotite and apatite. The crystallization sequence of minerals in nepheline syenite-porphyry indicates the agpaitic trend of evolution. Some differences in the composition of phenocrysts of biotites (more magnesian) and main mass are revealed. In pyroxenes of studied rocks as in ones of nepheline syenites of the Oktyabrsky massif the aegirine (66—71 %) component prevails while hedenbergite (12—15 %) and diopside (5—11 %) ones are subordinate. By content of salic and femic minerals, widespread sodalitization and cancrinitization of nepheline, syenite-porphyry is similar to nepheline syenite of the Oktyabrsky massif but differs from the latter by andradite availability. It is caused by as result of decreased SiO2 (48—49 %) content and hipabyssal condition of crystallization. The nephelinesyenite porphyry belongs to miaskite or to intermediate between miaskite and agpaitic type and is characterized by high content of phosphorus (compared to most rocks of the Oktyabrsky massif), REE, Nb (90—235 ppm) and Zr, while it is significantly different from dyke aegirine microfoyaites of the Oktyabrsky massif. By Р2О5 content and magnesity they are similar to pulaskites as the most primitive syenitic rocks of the Oktyabrsky massif. In addition in the REE pattern from the nepheline syenite-porphyry a negligible negative Eu/Eu* (0.86) is presented that makes them similar to the mentioned rocks from this massif. This nepheline syenite-porphyry is supposed to belong to the Oktyabrsky alkaline complex, although it may represent the least differentiated rocks among all known alkaline rocks of this massif.

Keywords: syenite-porphyry, nepheline, alkaline rocks, Oktyabrsky massif, Azov area.

1. Amashukeli, Yu.A., Dubyna, O.V. and Kryvdik, S.G. (2011), Mineral. Journ. (Ukraine), Kyiv, Vol. 33 No 4, pp. 53-66.
2. Dubyna, O.V., Kryvdik, S.G. and Sharygin, V.V. (2014), Geochemistry, Moscow, No 10, pp. 907-923.
3. Kryvdik, S.G. and Tkachuk, V.I. (1990), Petrology of alkaline rocks of the Ukrainian Shield, Nauk. dumka, Kyiv, 408 p.
4. Kryvdik, S.G. and Tkachuk, V.I. (1998), Geochemistry, Moscow, No 4, pp. 362-371.
5. Kryvdik, S.G., Amashukeli, Yu.A. and Dubyna, O.V. (2011), Tez. XXVIII of Intern. conf. "Ore potential of alkaline, kimberlite and carbonatite magmatizm", Sept. 9-16th, M.-Minsk, pp. 107-109, available at:
6. Kryvdik, S.G., Voznyak, D.K., Sharygin, V.V. and Dubyna, O.V. (2012), Proc. of Ukr. mineral. soc., Kyiv, Vol. 9, pp. 7-34.
7. Kryvdik, S.G., Tsymbal, S.M. and Razdorogniy, V.F. (2006), Mineral. Journ. (Ukraine), Kyiv, Vol. 28 No 2, pp. 5-40.