Bafertisite and jinshajiangite from the Gremyakha-Vyrmes alkaline complex, Kola Peninsula

Lykova I.S.*, Pekov I.V.*,*, Kononkova N.N.**, Shpachenko A.K.***

*Lomonosov Moscow State University, Moscow, Russia;

**Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Moscow, Russia;

***Geological Institute of Kola Science Centre RAS, Apatity, Russia

 

The layered titanosilicates bafertisite, Ba2Fe4Ti2O2(Si2O7)2(OH)4, and jinshajiangite, NaBaFe4Ti2O(Si2O7)2(OH)3F, have been identified in 2007 by us in the Gremyakha-Vyrmes alkaline complex, NW part of Kola Peninsula, Russia.

Minerals of the bafertisite group were not reported from Gremyakha-Vyrmes before. For jinshajiangite, it is first find in Russia. The data on two finds of jinshajiangite were published. It was first described in an arfvedsonite dike in alkali syenites near the Jinshajiang River, western Sichuan province, SW China (Hong Wenxing, Fu Pinqiu, 1982). Second locality of jinshajiangite is Norra Karr alkaline massif, Sweden. The crystal structure of jinshajiangite was studied by Rastsvetaeva et al. (2008) on Swedish sample. Bafertisite is more widely spread in nature than jinshajiangite. One find of bafertisite in Russia, namely in the Burpala alkaline complex, Northern Baikal Region, was reported (Ganzeev et al., 1971). Note that iron in the Burpala sample, analysed using wet chemical methods, was detected in both bivalent and trivalent states. In its empirical formula, (Fe2++Fe3+) > Mn2+ but Mn2+ > Fe2+ as well as Mn2+ > Fe3+. Thus, if its analysis is correct in part of the quantitative determination of the Fe2+/Fe3+ ratio then, within the bounds of modern mineralogical nomenclature, this mineral should be defined as hejtmanite, a Mn-dominant analogue of bafertisite with the idealized formula for the end-member: Ba2Mn4Ti2(Si2O7)2O2(OH)4. In this case, our find of bafertisite could be also considered as the first in Russia.

The described minerals were found in a pegmatite related to alkaline granites at northern coast of the Gremyakha lake. Jinshajiangite occurs as needle-shaped crystals up to 2 mm long. The crystals typically form chaotic aggregates up to 7 mm across. Jinshajiangite is golden-brown with red to yellowish-red tint. Bafertisite forms yellowish-red lamellar crystals up to 1 x 3 x 4 mm. Associated minerals include albite, microcline, quartz, arfvedsonite, zircon, and apatite.

Bafertisite and jinshajiangite have been identified by chemical, X-ray diffraction and infrared spectroscopy data.

The X-ray powder patterns of bafertisite and jinshajiangite from Gremyakha-Vyrmes are similar to ones of these minerals studied earlier (Kuan Ya-Hsien et al., 1963; Hong Wenxing, Fu Pinqiu, 1982). The main basal reflection (002) of Kola jinshajiangite is characterized by the interplanar spacing 10.40 Å, the 001 reflex of Kola bafertisite is 10.95 Å.

The chemical composition of bafertisite and jinshajiangite was studied using the electron microprobe. Formulae were calculated basing on 4(Si+Al). All iron was considered as bivalent, the O/OH ratio was calculated by charge balance. The empirical formulae (cations have groupped according to structural data for the minerals) are:

bafertisite:

(Ba1.98Na0.04K0.03)Σ1.05(Fe3.43Mn0.37Mg0.03)Σ3.83(Ti2.02Nb0.03)Σ2.05(Si3.92Al0.08O14)(O1.84OH0.16)Σ2.00(OH2.39F1.61)Σ4.00;

jinshajiangite:

(Na0.57Ca0.44)Σ1.01(Ba0.57K0.44)Σ1.01(Fe3.53Mn0.30Mg0.04Zn0.01)Σ3.88(Ti1.97Nb0.06Zr0.01)Σ2.04(Si3.97Al0.03O14)O2.00

(OH2.25F0.73O0.02)Σ3.00.

The Kola jinshajiangite differs from the original Chinese sample in higher value of the Mn/Fe ratio and lower value of the Nb/Ti ratio and lower F content. The Swedish mineral occupies intermediate position in its Mn/Fe ratio.

In its chemical composition, bafertisite from Gremyakha-Vyrmes is similar to bafertisite from its type locality, the Bayan Obo alkaline complex, Inner Mongolia, China (Semenov, Chang Pei-Shan, 1959).

Chemically, bafertisite and jinshajiangite from Kola differ one from other not only in part of species-defining sodium and barium cations but also in subordinate constituents. Bafertisite is characterized by higher content of fluorine and lower content of niobium. Concentration of calcium in Kola bafertisite is below detection limit whereas in our jinshajiangite, Ca, undoubtedly replacing Na, is significant admixture.

Barium minerals were not found in the Gremyakha-Vyrmes alkaline granites and their derivatives before (Polkanov et al., 1967; Bulakh, 1997). Ba was accumulated probably because of its mobilization from potassium feldspar as a result of albitization of granite interacted with feldspathoid rocks, namely nepheline syenites and ijolites.

This study was supported by grant of President of Russain Federation No. 863.2008.5 and grant of Russian Science Support Foundation (I.V.P.).

 

References:

Bulakh A.G. On the mineralogy of alkaline granites of the Gremyakha Tundra, Kola Peninsula // Vestnik SPbGU. 1997, ser. 7, issue. 3, p. 18-28 (in Russian).

Ganzeev A.A., Efimov A.F., Lyubomilova G.V. Manganese bafertisite from Burpala massif (Northern Baikal Region) // Proc. of Fersman Mineralogical Museum of AN USSR. 1971, vol. 20, p. 195-197 (in Russian).

Hong Wenxing, Fu Pinqiu. Jinshajiangite a new Ba-Mn-Fe-Ti-bearing silicate mineral // Geochemistry (China). 1982, 1, p. 485-464.

Kuan Ya-Hsien, Simonov V.I., Belov N.V. Crystal structure of bafertisite, BaFe2TiO[Si2O7](OH)2 // Doklady AN USSR. 1963, vol. 149, 6, p. 1416-1419 (in Russian).

Polkanov A.A., Eliseev N.A., Eliseev E.N., Kavardin G.I. Gremyakha-Vyrmes Massif on Kola Peninsula. M.-L.: Nauka, 1967, 236 pp. (in Russian).

Rastsvetaeva R.K., Chukanov N.V., Rozenberg K.A. Crystal structure of jinshajiangite from Norra Karr massif (Sweden) // Kristallografiya. 2008, vol. 53, 4, p. 593-596 (in Russian).

Semenov E.I., Chang Pei-Shan. New mineral bafertisite // Science Record. 1959, vol. 3, 12, p. 652-655 (in Russian).


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