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Vol. 1 (1998 year), No. 3

Liferovich R.P., Bayanova T.B., Gogol O.V., Sherstenikova O.G., Delenitsin O.A.
The Genesis of Postcarbonatite Phosphate Mineralization of the Kovdor Phoscorite - Carbonatite Complex

⁸⁷Sr/⁸⁶Sr isotopic ratios were studied in carbonates and phosphates from postcarbonatite hydrothermal mineral assemblages occurring in the phoscorite-carbonatite complex of the Kovdor alkaline-ultrabasic massif. The obtained results compared with those published earlier for the Kovdor carbonatites and phoscorites show that the hydrothermal phosphatic mineralization in cavities of dolomitic carbonatites and phoscorites was formed by juvenile solutions. The latter were not derived from drainaged rock (i.e. from dolomitic carbonatites), but were fluids produced by a magmatic chamber, which was generating phoscorite-carbonatite series during a calcitic stage of formation of the Kovdor complex. The following fact is of interest: mineral-forming solutions, despite being formed in the crust, have a mantle ⁸⁷Sr/⁸⁶Sr ratio, which can be explained by their relation to a mantle-derived carbonatite. Data obtained on Sr isotopic composition of carbonate-fluorapatite, which is a cement-forming mineral in apatite-francolite breccias of the central area of phoscorite-carbonatite complex, suggest an explosive origin for these rocks, followed by significant hydrothermal alteration. The role of exogenic processes in the formation of present-day apatite-francolite breccia composition rises toward the marginal area of the Kovdor phoscorite-carbonatite complex.

(in Russian, стр.8, fig. 1, tables. 1, ref 21, MS Word 95, MS Word 95 85 Kb)