2010

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Alkaline metasomatites of East Azov area

 Morgun V.G.

Semenenko Institute of Geochemistry, Mineralogy and Ore Formation, Kyiv, Ukraine

morhungeol@rambler.ru

In Eastern Azov area, on the territory of Ukrainian Shield (USh) alkaline metasomatites   are wide-spread. They consist of alkaline feldspars, aegirine, & amphiboles rich in fluorine (riebeckite-arfvedsonite), sometimes they contain Mn-astrophyllite. In one case they attend the veins of carbonatites (Khlibodarivka), in other they associated with calcitic & fluorite-calcitic veins with parisite (small ore occurrence Petrovo-Hnutovo, near v.Kaplany on the Kalmius river). By geochemical peculiarities alkaline metasomatites of the Eastern Azov area are various enough. In Dmytrivka career TR-Zr-Nb mineralization is typical for this rocks (zircon, pyrochlorine, britholite) or rich impregnation of molybdenite; often occurrence of metasomatites on the Kalmius river, is interested of their high TR & fluorite mineralization. Available data of isotopic age (K-Ar, Pb-Pb U-Pb methods) of some occurrence of metasomatites (Khlibodarivka, Dmytrivka) show that, they are more ancient (1,835 1,935 M.a) than alkaline rocks of Oktyabrskyj massif (1,800 M.a.). Author suppose that this metasomatites is of fenitic nature. They are related to eroded alkaline rocks of carbonatitic complex (in Khlibodarivka they attend the veins of carbonatites).

                Alkaline metasomatites of East Azov  area are known since the time of J.A. Morozewicz and L.F. Einberg, that usually belong them to alkaline syenite. These rocks were probably first named by V.I. Kuzmenko as metasomatites during the research of Petrovo-Hnutovo ore parasite occurrence. The most complete description of these metasomatites was given in the monograph of M.L. Yeliseyev et all. At that time, alkaline metasomatites were already known in many places, mainly in outcrops on the river Kalmius (Petrovo-Hnutovo ore occurrence, gullies of Chernecha, Verbova, Kalmytska, etc.).. Author treats mentioned alkaline metasomatites as vein formation or as fenites. Specific meaning of "fenite wasnt determined. I.D. Tsarovskyy believed that these metasomatites related to alkaline rocks Oktiabrs'ky massif, but the researcher did not published the results of their observations on these metasomatites. Later these were found metasomatites among enderbites in Khlibodarivsky career. Association of alkaline metasomatites veins with carbonatites (as exocontactic metasomatites) in this career,  permits consider the rest metasomatites as fenites. The same considerations cited in an article Ye.Ya. Marchenko et all, about aegirine metasomatites at Petrovo-Hnutovo parisite-fluorite ore. Later  alkaline metasomatites with TR-Zr-Nb mineralization were identified in the quarry near Dmitrivka (to north) from Oktyabrsky massif. Available results of age determining of alkaline metasomatites and accompanying carbonate rocks have shown that they are more ancient (1,850 2,000 M.a.) than alkaline rocks in Oktiabrs'ky massif (1,800 M.a.). All these, and some peculiarities of the mineral composition of the investigated alkaline metasomatites allowed us to come to a definitive conclusion about their belonging to fenites, i.e. metasomatites, genetically relate to unexposured carbonatites by erosion  (in Khlibodarivka  ).

 Alkaline metasomatites distributed close to Oktyabrsky massif (Dmytrivka, Khlibodarivka, Vali-Tarama gully) and far from it mainly occur in outcrops at the river Kalmius (Figure). Obviously, alkaline metasomatites spread much wider than it shown in the scheme. They are described only in natural outcrops on the boards of gullies on the Kalmius and are opened with two quarries ( Dmytrivka and Khlibodarivka villages). We can assume that such metasomatites  available in the areas where the country rocks are usually covered with weathering crust. However, we note that on a good expose territory of South-Kalchyk, including current Kalchyk (Kremenivskyy) career, and intensely out-drilling Azov area (with the same TR deposits) alkaline metasomatites are not found . It may be, to some extent, indirect evidence that the investigated alkaline metasomatites is earlier than granite and syenite of South-Kalchyk massif (by 1.800 M.a.).

This metasomatites are obviously more thickness and they are somewhat in remote areas of the Oktiabrs'ky massif (r. Kalmius). The exception may serve only quarry in the village Dmytrivka, where the thickness of metasomatites can reach to several meters. However, these metasomatites are some different comparated with similar species at other points of East Azov - they are strongly enriched in Zr, Nb, and especially in Mo. Note that on the river Kalmius (left bank), opposite v.Orlivske, we found apobasitic metasomatites of other rocks with rich Zr mineralization. Mostly alkaline metasomatites lie among the various granitoids in the zones of fissuring (because they were named as vein metasomatites). There are usually small vein-like segregations, their thickness rarely reaches first or more meters. Their strike is often north-west and north-east, the fall - mostly steep to the vertical. Country rocks are biotitic, biotite-amphibole granites, pegmatites (Dmytrivka, Kalmius) enderbites (Khlibodarivka), granite-gneisses (Vali-Tarama gully). As mentioned above, in Khlibodarivsky career alkaline metasomatites occurre along exocontacte of carbonatitic veins that lie among enderbites. These metasomatites consist of albite, microcline, alkaline amphibole, aegirine, whose content varies widely. This gave us reason to believe that all available in career alkaline metasomatites genetically and spatially are related to the carbonatites (or other rocks of carbonatitic complex). At this the thickness of metasomatites and carbonatites, are almost identical to 30 cm. Pyrochlore and monazite were found in this carbonatites. It is interesting to note another feature - alkaline metasomatites accompanied carbonatite veins usually occurr everywhere,  in exocontactic zone only quartsbearing country rocks which are often granitoides, but not in those rare cases when they across the xenolith of twopiroksenic crystal lines. The basic rocks are hardly exposed to fenityzation (these observations are described in Chernihivka carbonatitic massif and in many other carbonatites areas).  

K-Ar age of Mg-ribekite of carbonatites in Khlibodarivsky career is 1,850 M.a., i.e. carbonatites are some older rocks than Oktiabrs'ky massif (1.8 billion).Owing to the value of K-Ar method is often underestimated, we can consider more ancient the formation of carbonatite and fenites of the career of Khlibodarivka. Khlibodarivka quarry is also interesting because of long known dikes of kamptonites (of subalkaline gabbroides with megacrystals of kaersutite, augite, biotite, anorthoclase).

 Thus, in the East Azov area are many localities of alkaline metasomatites. The overwhelming majority of this rocks was found in coastal outcrops localities in Kalmius river. They are available in the vicinity of Oktiabrs'ky alkaline massif (Dmytrivka, Khlibodarivka), although in this massif such metasomatites arent available. Moreover, the available geologic dating of these metasomatites are more ancient than the alkaline rocks of Oktiabrs'ky massif (50-200 million years by K-Ar i U-Pb methods). Most of these metasomatites (where are thick bodies) accompany (or directly connected) with endogenous carbonate or carbonate-fluorite veins. In Hlabodarivsky career these carbonate (calcite) have all features characteristic of typical carbonatites - presence of apatite, pyrochlore, monazite. Moreover, these veins are surrounded by exocontactic aureole of alkaline metasomatites.

In other forms of alkaline metasomatites (Petrovo-Hnutovo, Kaplany), according to isotope characteristic of C, O and Sr, carbonate veins are also deep seated origin, although the conclusions of their belongings to carbonatites not is get clear. However, in Dmitrivsky career, carbonate and fluorite-carbonate rocks among species are not found, although in thinsections of metasomatites fluorite occurs quite often. The authors tend to treat these hydrothermal-metasomatic rocks. They certainly spatially and genetically are related to metasomatites. There is a reason to believe that alkaline metasomatites and these carbonate and fluorite-carbonate veins are genetically related to carbonatites and other alkaline ultrabasic rocks, i.e. alkaline metasomatites are fenites in its original sense of the term.

Figure. Scheme of alkaline metasomatites of East Azov area.
1 - tectonic dislocations 2 -  the border of East Azov batholith by P.S. Karmazin [1970], 3 - Archean and Proterozoic migmatites and granites, 4 main zones of the linear folding granulite complexes, 5 - formation superimposed of protoriftogenic structures 6 - ferruginous silicon formations; 7 - intrusive-magmatic rocks of the platform stage, 8 - ultrabasic alkaline rocks and carbonatites of the Chernihivka massif, 8 - locations of alkaline metasomatites; 9 granites of Kam'yanomohyly type, 10 - dikes and small bodies of basic rocks, 11 dikes of metajacupirangites, 12 the massifs of alkaline ultrabasic complexes , 13 Kalmius river. The numbers on the scheme: 1 - Khlibodarivsky career 2 - Dmytrivka quarry, 3 -  gully Chernecha (v. Orlivs'ke), 4 - gully Verbova, 5 - Petrovo-Hnutovo ore occurrence, 6 - gully Kalmytska, 7 - v. Kaplany, 8 - v.Mykolayivk
a, 9 gully  Vali-Tarama.