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Published September 1969 | public
Journal Article

O¹⁸/O¹⁶ and C¹³/C¹² Ratios of Coexisting Minerals in the Oka and Magnet Cove Carbonatite Bodies


Oxygen isotope analyses were obtained for five magnetites (δ = +1.1 to +2.9), three biotites (+4.2 to +5.2), two melilites (+4.7 to +5.2), one apatite (+5.6), one niocalite (+4.2) and one pyrochlore (+1.2) from five samples of okaite and carbonatite in the Oka, Quebec, and Magnet Cove, Arkansas, complexes. Calcites from these and three other samples were analyzed for both O¹⁸/O¹⁶ and C¹³/C¹² (δO¹⁸ = +6.6 to +7.6, δC¹³ = -5.8 to -5.2). The order of increasing O¹⁸ concentration among minerals is consistent in all samples. Calculated whole-rock δO¹⁸ values (+4.7 to +5.9) are similar to those of mafic and ultramafic igneous rocks, and the δO¹⁸ and δC¹³ values of the calcites fall within the range previously suggested as being characteristic of primary igneous carbonatites. Crystallization temperatures, calculated from O¹⁸ fractionations for the pair calcite-magnetite, demonstrate that the okaites and carbonatites crystallized at about the same temperatures as, respectively, gabbros and "granitic" igneous rocks.

Additional Information

Appreciation is expressed to P. Yanagisawa for performing some of the fluorine extractions of oxygen, and to G. J. Wasserburg, M. Bass, A. R. Philpotts and A. E. Bence for supplying samples. Financial support for this research was provided by the National Science Foundation, grant no. GA 992.

Additional details

August 19, 2023
October 24, 2023