2011

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Geochemistry of  alkaline metasomatitic rocks and carbonatites from the Gremiakha-Vyrmes massif of the Kola Peninsula

Sorokhtina N.V.^*, Kogarko L.N.^*, Gredina I.V.^*, Roschina I.A.^*, Shpachenko A.K.^**

 ^*Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Moscow, Russia, ^**Geological Institute KSC RAS, Apatity, Russia

Gremiakha-Vyrmes is an Early Proterozoic multiphase alkaline-ultrabasic intrusive complex. According to the early publication (Arzamastsev et al., 2006) this massif includes 3 complexes. Our geological data and some publications (Kirnarsky, 1959, Polkanov et al., 1967,  Arzamastsev et al., 2006, Savatenkov et al., 1999) proposed that this massif includes four rock complexes (from old to young): 1 basic-ultrabasic; 2 alkaline rocks with ijolite-melteigites and foidolites; 3 alkaline-granites and granosyenites; 4 alkaline metasomatic rocks and carbonatites. Zr-Nb ore deposit has been found in metasomatic rocks of fourth complex. Rare-metal mineralization of Gremiakha-Vyrmes was discovered by the Geological service of Murmansk region (Sholokhnev et al., 1985). Location, description of metasomatic rocks and carbonatites, evolution of chemical composition of main Nb mineral pyrochlore have been published (Sorokhtina et al., 2010). Alkaline metasomatic rocks and carbonatites are located in the central part of massif and surrounded by the basic-ultrabasic, foidolitic and alkaline-granites rocks. The approximate area of rare-metal metasomatic rocks is 10 km². The metasomatic rocks consist of various albitites, aegirinites and nepheline-aegirine pegmatoids. The whole rocks form the lenses, sheet like bodies and veins. Thin carbonatite veins intersect metasomatic rocks.

The first geochemical dates of trace element abundances for the metasomatic rocks and carbonatites of the Gremiakha-Vyrmes are presented on the picture (fig.1,2). The chemical analysis of the major and minor elements have been carried out by XRF and ICP-MS analytical methods in the Vernadsky Institute RAS.

Fig. 1. Carbonaceous chondrite-normalized trace element abundances for the metasomatic rocks and carbonatites in the Gremiakha-Vyrmes, and global average composition of calcite carbonatites (Woolley & Kempe, 1989). K, Pb, P, Ti, Zr, Y, Nb for rare metal and average albitites presented by XRF, other elements by ICP-MS. Values of average albitites presented without rare metal albitite, normalizing values after (Mc Donough & Sun, 1995)

The chondrite-normalized trace element spectra for the albitites and aegirinites are rather uniform (fig.1). Rare-metal albitites are strongly enriched by U, Nb (up to 21712 ppm) and Ta. Average albitites and aegirinites are enriched Zr, which is concentrated in aegirinite up to 1 wt.%. The trace element spectra for the carbonatites and metasomatic rocks are different. Generally, distribution trace element patterns for the Gremiakha-Vyrmes calcite carbonatites are similar to those from average calcite carbonatites of the globe (Woolley & Kempe, 1989). The lower concentrations of Th, U, REE and higher Rb, K, Sr, Ti are observed in carbonatites of Gremiakha-Vyrmes massif. Rb, K, Sr and Ti are concentrated in accessory and mine minerals of carbonatite: Rb, K in feldspar, Sr in calcite (to 3 wt.%), Ti in titanite. The Gremiakha-Vyrmes carbonatites and metasimatites exhibit a negative Rb, K, P and Ti anomaly (fig.1).

Chondrite-normalized REE spectra for the metasomatic rocks and carbonatites are close to the average calcite carbonatites and characterized lower of concentrations of REE as compare to average calcite carbonatites of the globe (Woolley & Kempe, 1989) (fig.2).

Fig. 2 Carbonaceous chondrite-normalized rare earth element patterns of metasomatic rocks and carbonatites from the Gremiakha-Vyrmes, and global average composition of calcite carbonatites (Woolley & Kempe, 1989), normalizing values after (Mc Donough & Sun, 1995). Legend presented on fig.1.

The obtained age of metasomatic rocks and carbonatites is close to the average age of the formation of most rock of the massif ~1900 Ma (Savatenkov et al., 1999, Sorokhtina et al., 2010). Based on the isotopic data, as well as on physico-chemical parameters of the carbonatite and albitite formation, we suggest that carbonatites were formed synchronously with alkaline rocks (Sorokhtina et al., 2010). Probably the Gremiakha-Vyrmes carbonatites were the source of Nb, U, Th, Zr and REE. Albitites and aegirinites are accumulated rare metals and could be formed during the metasomatism triggered by intrusion of carbonatites into the alkaline and basic-ultrabasic complexes of the massif.

References

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