Mineralogical and petrographic features of metakomatiites of the Kostomuksha greenstone structure (Karelia)

Object of study. The paper presents the mineralogical and petrographic study results of metamorphosed and metasomatized komatiites and komatiitic peridotites from the Ozerki soapstone deposit and Pentinsuo prospect, located in the Kostomuksha greenstone structure of the Karelian Craton, Fennoscandian Shield. Material and methods. Surface and drill core samples of various mineral and structural-textural varieties of altered komatiites were studied by optical microscopy, electron microscopy with an attachment for microanalysis, XRD phase, thermogravimetric and chemical analysis. Results. Soapstone formation in the investigated localities displays a multistage alteration and associates with the superimposed alteration of Mg-rich metakomatiite flows and olivine cumulates due to influx of carbon dioxide bearing fluids enriched in calcium and potassium. The chemical composition of initial komatiite (MgO content of the rock) and the degree of its fracture intensity are the main factors controlling soapstone formation. In differentiated lava flows soapstone is formed mainly in high-magnesium cumulate zones characterized by a high content of serpentine. In the flow top and spinifex zones an early amphibole-chlorite-magnetite mineral association is preserved in varying degrees. Talc and carbonate are formed by the decomposition of serpentine and amphibole. The chlorite content in soapstone is controlled by the Al2O3 concentration in the respective flow zones. Conclusion. The carbonate-chlorite-talc is the general natural type of soapstone associated with thin komatiite lava flows of distal volcanic facies. In more thick proximal lava flows the formation of soapstone of chloritecarbonate-talc and talc-carbonate composition is possible. The most prefered prospecting areas for soapstone are fields proximal to the eruptive vent, main lava conduits and subvolcanic analogues of komatiites.

1. Anovitz L.M., Essene E.J. (1987) Phase equilibria in the system CaCO3–MgCO3–FeCO3. J. Petrol., 28(2), 389-414.

2. Arndt N.T., Lesher C.M., Barnes S.J. (2008) Komatiite. Cambridge, Cambridge University Press, 467 p.

3. Frolov P.V. (2003) Karelia’s talc. Distribution of occurrences, some geological and mineragenic characteristics of economic ore deposits. Geologo-tekhnologicheskie issledovaniya industrial’nykh mineralov Fennoskandii [Geological-technological study of Fennoscandia’s indusrial minerals]. Petrozavodsk, Kar. filial Akad. Nauk SSSR, 38-51. (In Russian)

4. Frolov P.V., Furman V.N. (2003) The Svetloozero ferrous talc ore occuerence – the reference object of complex deposits in greenstone belts of Karelia. Geol. Polezn. Iskopaemye Karelii, 6, 58-66. (In Russian)

5. Furman V.N. (1995) Otchet o rezul’tatakh poiskov tal’kovykh rud i tal’ko-khloritovogo kamnya v Respublike Kareliya v 1990–1994 gg. [Report on the results of 1990–1994 talc ore and talc-chlorite stone prospecting in the Republic of Karelia]. Karel’skii TFGI, Petrozavodsk. (In Russian, unpublished)

6. Furman V.N. (2001) Otchet o rezul’tatakh poiskovykh rabot na zoloto, provedennykh v yuzhnoi chasti Kostomukshskoi zelenokamennoi struktury v 1988–2001 gg. [Report on the results of 1998-2001 gold prospecting in the southern Kostomuksha greenstone structure]. Karel’skii TFGI. Petrozavodsk. (In Russian, unpublished) Geologiya i metamorfizm zhelezisto-kremnistykh formatsii Karelii [Geology and metamorphism of cherty ironformations of Karelia]. (1991) Leningrad, Nauka Publ., 173 p. (In Russian)

7. Gor’kovets V.YA., Raevskaya M.B. (1983) Effusives of ultrabasic composition of the Kostomuksha iron ore deposit area. Magmatizm i metallogeniya dokembriiskikh obrazovanii Karelii [Magmatism and mttallogeny of of Karelia’s Precambian]. Petrozavodsk, Kar. filial Akad. Nauk SSSR, 34-37. (In Russian)

8. Gor’kovets V.YA., Raevskaya M.B. (1988a) GimolaKostomuksha greenstone belt. Komatiity i vysokomagnezial’nye vulkanity rannego dokembriya Baltiiskogo shchita [Komatiite and high magnesial volcanits of Early Precambrian of Baltic Shield]. Leningrad, Nauka Publ., 136-148. (In Russian)

9. Gor’kovets V.YA., Raevskaya M.B. (1988b) Reconstruction of the centers of ultrabasic volcanism (Kostomuksha iron ore deposit area). Geologiya i metamorfizm arkheiskikh zelenokamennykh poyasov [Geology and metamorphism of Archean greenstone belts]. Petrozavodsk, KNTs RAN, 57-66. (In Russian)

10. Hill R.E.T., Barnes S.J., Gole M.J., Dowling S.E. (1995) The volcanology of komatiites as deduced from field relationships in the Norseman-Wiluna greenstone belt, Western Australia. Lithos., 34, 159-188.

11. Huhta A., Kärki A. (2018) A proposal for the definition, nomenclature, and classification of soapstones. GFF, DOI: 10.1080/11035897.2018.1432681.

12. Johannes W. (1969) An experimental investigation of the system MgO–SiO2–H2O–CO2. Amer. J. Sci., 267, 1083- 1104.

13. Karlsen T.A., Rian E., Olesen O. (2000) Overview of talc resources and reserves in the Altermark talc province, northern Norway and possible uses of the talc ore. Norges geologiske undersøkelse Bull., 436, 93-102.

14. Klimovskaya E.E., Klimovskij A.V. (2012) Geological nature of the Ozerky soapstone deposit magnetic anomalies (Kostomuksha greenstone belt)]. Trudy Karel’skogo nauchnogo centra RAN [Proc. Karelian Research Centre of RAS], 3, 78-86. (In Russian)

15. Korenbaum S.A. (1967) Mineral’nye paragenezisy tal’kovykh mestorozhdenii [Mineral assemblages of talc deposits]. Moscow, Nauka Publ., 455 p. (In Russian)

16. Kozhevnikov V.N. (1982) Usloviya formirovaniya strukturno-metamorficheskikh paragenezisov v dokembriiskikh kompleksakh [Conditions of formation of structuralmetamorphic parageneses in Precambrian complexes]. Leningrad, Nauka Publ., 184 p. (In Russian)

17. Kozhevnikov V.N. (2000) Arkheiskie zelenokamennye poyasa Karel’skogo kratona kak akkretsionnye orogeny [Archean greenstone belts of the Karelian craton as ac cretionary orogens]. Petrozavodsk, KNTs RAN Publ., 223 p. (In Russian)

18. Kuleshevich L.V. (1984) Listvenites in the greenstone belts of Eastern Karelia. Geol. Rudn. Mestorozhd., 26(3), 112- 116.

19. Kuleshevich L.V. (1992) Metamorfizm i rudonosnost’ arkheiskikh zelenokamennykh poyasov yugo-vostochnoi okrainy Baltiiskogo shchita [Metamorphism and ore content of the Archaean greenstone belts in the southeastern Baltic Shield]. Petrozavodsk, KNTs RAN Publ., 267 p. (In Russian)

20. Kuleshevich L.V. (2004) Evolution of endogenic regimes and stages of gold ore formation in the Kostomuksha greenstone belt, Karelia. Dokl. Earth Sciences, 397(5), 672-676.

21. Kuleshevich L.V., Furman V.N. (2009) The Taloveis gold deposit in the Precambrian Kostomuksha greenstone belt, Karelia. Geol. Ore Deposits, 51(1), 58-76.

22. Lobach-Zhuchenko S.B., Arestova N.A., Mil’kevich R.I., Levchenkov O.A., Sergeev S.A. (2000) Stratigraphy of the Kostomuksha belt in Karelia (Upper Archean) as inferred from geochronological, geochemical, and isotopic data. Stratigr. Geol. Correl., 8(4), 319-326.

23. Niemelä M. (2001) Talc-magnesite deposits in Finland. Mineralia Slovaca, 33, 561-566.

24. Puchtel I.S., Hofmann A.W., Mezger K., Jochum K.P., Shchipansky A.A., Samsonov A.V. (1998) Oceanic plateau model for continental crustal growth in the Archaean: a case study from the Kostomuksha greenstone belt, NW Baltic Shield. Earth Planet. Sci. Lett., 155, 57-74.

25. Raevskaya M.B., Gor’kovets V.YA. (1986) Archean ultrabasic volcanism of Western Karelia. Izv. Vyssh. Uchebn. Zaved. Geol. i Razvedka, 5, 20-28. (In Russian)

26. Rannii dokembrii Baltiiskogo shchita [Early Precambrian of the Baltic shield]. (2005) (Ed. V.A. Glebovitskii). St.Petersburg, Nauka Publ., 711 p. (In Russian)

27. Romanovich I.F. (1973) Mestorozhdeniya tal’ka SSSR [Talc deposits of USSR]. Moscow, Nedra Publ., 224 p. (In Russian)

28. Sazonov V.N. (1975) Listvenitizatsiya i orudenenie [Listvenitization and mineralization]. Moscow, Nauka Publ., 172 p. (In Russian)

29. Shekov V.A. (2009) Otchet o rezul’tatakh poiskovo-otsenochnykh rabot na mestorozhdenii tal’kovogo kamnya Ozerki (oblitsovochnyi kamen’) v 2005–2008 gg. [Report on the results of the 2005–2008 prospecting and appraisal of the Ozerki soapstone deposit (dimension stone)]. Karel’skii TFGI. Petrozavodsk. (In Russian, unpublished) Stratigrafiya dokembriya Karelii. Opornye razrezy verkhnearkheiskikh otlozhenii [Precambrian stratigraphy of Karelia. Key sections of Upper Archean deposits]. (1992) Petrozavodsk, KNC RAN Publ., 190 p. (In Russian)

30. Talantsev A.S. (1981) Geotermobarometriya po dolomitkal’tsitovym paragenezisam [Geothermobarometry on dolomite-calcite mineral assemblages]. Moskow, Nauka Publ., 136 p. (In Russian)

31. Trommsdorff V., Evans B.W. (1977) Antigorite-ophicarbonates: phase relations in a portion of the system CaO–MgO– SiO2–H2O–CO2. Contrib. Mineral. Petrol., 60, 39-56.

32. Vesasalo A. (1965) Talc schists and soapstone occurrences of Finland. Bull. Comm. Geol. Finl., 216, 75 p.