2011

Òåçèñû ìåæäóíàðîäíîé êîíôåðåíöèè

Ðóäíûé ïîòåíöèàë ùåëî÷íîãî, êèìáåðëèòîâîãî

 è êàðáîíàòèòîâîãî ìàãìàòèçìà

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

A new type of alkaline metasomatites in Azov area

Morgun V.G.

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

morhungeol@rambler.ru

The Azov geoblock of Ukrainian shield (USh) (specially his eastern part), is characterized by wide-spread of alkaline rocks. In this region also alkaline metasomatites are spread enough (v. Dmytrivka, Khlibodarivka, Petrovo-Hnutovo ore occurrence, g. Chernecha, Verbova, Kalmyts’ka, etc) and were described in numerous publications. These metasomatites were formed mostly after granitoides of different composition (biotite-amphibole granites and enderbites). But in last times a new type of alkaline metasomatites (Tunikova gully) was exposed, which were formed on significant quartz rocks (quartzite).

Disposition of alkaline metasomatites in gully Tunikova are shown on scheme (fig 1). Metasomatites Tunikova gully are found in south from Oktyabrs’ky massif. Similar metasomatites are known near this massif ((Dmytrivka and Khlibodarivka careers). On the scheme the numerals 1 and 2 show the places of finding of alkaline metasomatites including  albitites and significant quartz rocks, with were country rocks for alkaline metasomatites of this area.

 The finding of similar alkaline metasomatites were noted on the banks of Vali-Tarama gully, where Tunikova gully flown into. It gives the grounds to believe these rocks to be related. Metasomatitic processes in this zone were influenced on the all country rocks.

This occurrence of apoquartzitic alkaline metasomatites in Tunikova gully is unusual not only for Azov area but also for the whole USh. The main minerals of apoquartzitic alkaline metasomatites are, except quartz (probably recrystallizational), aegirine and alkaline amphiboles, under subordinated part of albite and alkaline feldspars. Accessory minerals of these metasomatites are bastnesite, rutile, ilmenite, sphene, monazite, zircon, probably britholite.

In these apoquartzitic metasomatites enough thick veins of alkaline amphiboles (5-10 cm), sometimes aegirine are formed, besides these minerals. Other, typical mineral of alkaline metasomatites, aegirine is found mostly as a dispersion in the rock and often near biotite. This is due, most likely, so that the response of silica and biotite occurred peculiar process of exchange of components, together with the receipt of alkaline solution forms an alkali pyroxene.

In another location in gully Tunikova (upstream) was found apogranitoid aegirine alkaline metasomatites and albitites that are very similar to ones in the Dmytrivka career. In these metasomatites new formed zircon, rare-earth carbonate and minor mineral alike pyrochlore are founded, increased or high contents of Zr, Ce, La, Y and Nb are determined in the rocks

We can assume that alkaline apogranitoid or apoquartzitic metasomatites are of considerable thickness and with rare-mineralization can represent complex deposits of such metals as Nb, Ce, La, Y, Zr, and Mo (it has a place in Dmytrivka career). In addition, the findings of such metasomatites may indicate the presence of carbonatites with apatite and pyrochlore mineralization (Khlibodarivka career).

The amphiboles of metasomatites gully Tunikova are similar by composition to the amphiboles of Dmytrivka, Khlibodarivka and Berezova Gat’ occurrences. They are represented by riebeckite, arfvedsonite and intermediate varieties, as it’s shown on the diagram (fig 2).

You can see two separate fields.  The amphiboles of Oktyabrs’ky and Chernihivka massifs are situated in the first field. They are characterized by high alumina and low alkaline content. In the field ¹ 2 (high content of alkaline and low alumina) there are the amphiboles from metasomatites of Dmytrivka, Khlibodarivka and Berezova Gat’ villages and also some amphiboles of metasomatites from r. Kal’mius and gully Tunikova. Others amphiboles, which are shown on the diagram, take an intermediate position.

Pyroxenes are also represented by alkaline varieties (aegirine, aegirine-salite) and are typical for rocks of this kind. Most likely, alkaline pyroxenes have been formed by reaction between quartz and biotite and interaction with introducing of alkaline solutions.

Plagioclase is mainly represented by albite (sometimes oligoclase). K-feldspar is usually represented by pertiteless microcline (sometimes with minor perthite), and micas – by biotite [2].

Somewhat different composition have albitites from gully Tunikova. This is essentially albite rock of apogranitoid origin with relics (at the initial and intermediate stages) of minerals of the country rocks (biotite, quartz, orthoclase, and microcline) and new formed aegirine. Albitites are situated in the local field of two-feldspar granites.

These alkaline metasomatites are considered as fenites. Despite the different composition and structure the initial rocks, of the process of their fenitization is similar to one in all discovered areas. But this is only true for rock-forming minerals (albite, microcline, aegirine and alkaline amphiboles). By comparing the accessory minerals such regularity is not clear, since several of them and their prevalence is not constant. That is, if an assemblage of rock-forming and partially secondary minerals is the same, and their composition is close, the accessory minerals in different types of fenites may substantially differ from each other. Apoquartzitic fenites are characterized by rutile and monazite, while albitites from Dmytrivka –  by astrophyllite and pyrochlore,  and in metasomatites of Khlibodarivka and Kaplany villages – apatite

These differences may be due to such causes: the composition of initial rocks which had been fenitizated composition rocks which fenitizate (carbonatites, nepheline syenites, jacupirangite-ijolites, etc.), the composition of alkaline solutions, remoteness from magma chamber causing fenitization and the level of erosional cut.

Literature:

1. Eliseev N.A., Kushev V.G., Vynogradov D.P. Proterozoic intrusive complex of East Azov area. – M., L: Nauka, 1965 – 202 c. (in Russian).

2. Kryvdik S.G., Morgun V.G., Sharygin V.V. Micas from fenites and alkaline metasomatites of eastern Azov region // Mineralogical Journal (Ukraine). 2010. V. 32. No. 4, P. 3-11. (in Ukrainian).

3. Krivdik S.G, Tkachuk V.I. Petrology of the alkaline rocks of the Ukrainian shield - Kiev: Naukova Dumka, 1990. – 408 (in Russian).