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Geochemical
peculiarities of Chernigovka carbonatitic massif (Ukraine, Azov area)
Kryvdik
S.G.*,
Dubyna A.V.*,
Kogarko L.N.**
*N.P.
Semenenko Institute of geochemistry, mineralogy and ore formation NAS of
Ukraine, Kyiv, Ukraine
kryvdik@ukr.net
**V.I. Vinogradov Institute
geochemistry and analytical chemistry RAN
kogarko@geokhi.ru
Chernigovka (Novo-Poltavka)
carbonatitic massif in
Azov area is
considered one of the most studied in the mineralogical and petrological
aspects. However, many questions of geochemistry and formation
conditions of this massif remain unclear. Although in general massif has
a typical rock suite (alkaline pyroxenites, ijolite-melteigites,
nepheline and alkaline syenites, carbonatites, fenites), it has an
"anomalous" features of the chemical composition of carbonatites and
alkaline rocks [1, 6].
The ICP MS data obtained in recent years, as well as analysis of the
results of previous researchers [5, 8]
allowed identifying some geochemical features of the Chernigovka massif
that distinguish it from other carbonatitic complexes.
In the early calcite
carbonatites (sovites) of this massif is often fixed a quite high Ta
content (200 ppm) relative to Nb (Nb/Ta ratio about 3,9-6,9). In earlier
publications [5, 8],
there are analyzes of carbonatites with Nb/Ta up to 6,6, in rare cases -
3.6. In Malosayan massif have been also reported carbonatites with the
Nb/Ta ratio - 2,7-4,5 at 422 ppm Ta [7].
A higher Ta content (262
ppm) was recorded in the biotite-albite nepheline syenite (canadite)
with the Nb/Ta ratio to 3,9. Lower Nb/Ta ratio (2,8) at 421 Nb ppm and
152 ppm Ta content was found in the apatite-magnetite foskorites of this
massif. At the same time in the later calcite-dolomite and significantly
dolomite (ankerite) carbonatites of Chernigovka massif Nb/Ta ratio is
quite high (28-38), i.e. customary for the carbonatites.
Such discriminate Nb/Ta
from the different rock types of this massif are due to a different
mineral forms of these elements. In sovites among the main niobates
hatchettolite with Nb/Ta ratio 2,5-3,0 is typically or predominant.
Therewith in this mineral is quite high, but not characteristic for
typical carbonatites, uranium content (9-12% U3O8)
[2, 4].
Probably observed in kanadites minerals of the pyrochlore group also
belongs to hatchettolite.
In beforsites mainly
niobates are columbite and cerium fergusonite by subordinate role of
conventional pyrochlore.
Several unusual in this
massif are nepheline syenites - canadites (nepheline + albite + biotite
± microcline). Except mentioned increased or high Nb and Ta
concentrations (low Nb/Ta) there is a high content of Zr (0,1-0,3%). In
comparition to more melanocratic rocks of the massif - alkaline
pyroxenes and ijolite-melteigites, kanadites are characterized
significantly more Zr content, and as much or even more Nb, but lower
REE and Y. In overwhelming majority of the well-known carbonatitic
complexes nepheline syenite are depleted in REE, Zr, Nb and Ta in
comparison with the earlier melanocratic rocks (jakupirangites,
ijolite-melteigites, melilitites).
In addition, nepheline from
nepheline syenites and melteigites are more sodium than in the most
similar of alkaline rocks [3].
These geochemical and
others (petrological, mineralogical) features of Chernigovka
carbonatitic massif that distinguish it from most of the known
carbonatitic complexes, are due to by abyssal conditions of its
formation. This massif belongs to one of their most deep eroded [1,
6]. Abyssal conditions of its formation
are reflected in the untypical distribution of rare earths (Nb, Ta, Zr,
Hf, TR, Y) between the silicate and carbonatitic differentiates, that
confirm by experimental data [9].
1.
Glevassky
E.B., Kryvdik S.G.
Precambrian carbonatitic
complex of Azov area. Kyiv: Naukova Dumka, 1981. 228 p. (in Rassia)
2.
Kapustin
U.L., Lapitsky E.M., Pogrebnoy V.T. et al.
Carbonatite zone of the Ucrainian Shield. Sovet. Geol. 1977. №9. P.
80-92. (in Rassia)
3.
Kononova
V.A.
Jacupirangite-urtite series of alkaline rocks. Moscow: Nauka, 1976. 214
p. (in Rassia)
4.
Kryvdik
S.G., Tkachuk V.I.
Petrology of alkaline rocks
of the Ukrainian Shield. Kyiv. Naukova Dumka, 1992. 212 p. (in
Rassia)
5.
Rare elements of the Ukrainian Shield. Kyiv. Naukova dumka, 1986.
256 p. (in
Rassia)
6.
Ryabchikov
I.D., Kogarko L.N., Krivdik S.G., Ntaflos T.
Formation conditions of carbonatites of Chernigovka massif (Azov area,
Ukraine) // Geol. ore depos. 2008. v.50. №6. P. 483-493. (in Rassia)
7.
Samoylov
V.S.
Geochemistry of carbonatites. Moscow: Nauka, 1984. 193 p. (in Rassia)
8.
Shramenko
I.F., Stadnik V.A., Osadchiy V.K.
Geochemistry carbonatites
of the Ukrainian Shield. Kyiv: Naukova Dumka, 1992. 212 p. (in Rassia)
9.
Bell K.
Carbonatites – Genesis and Evolution. Boston, Mass, Unwin Hyman Ltd.,
618 p. |