Nitrogen and carbon isotopic composition in the diamonds of Mbuji Mayi (Zaïre) |
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| Authors: | M Javoy F Pineau D Demaiffe |
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| Institution: | 1. Laboratoire de Géochimie des Isotopes Stables, LA 196 C.N.R.S., Universitéde Paris VII, 2, Place Jussieu, 75251 Paris Cédex 05France;2. Laboratoire Associéde Géologie-Pétrologie, UniversitéLibre de Bruxelles, 1050 Bruxelles Belgique |
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| Abstract: | The concentration and isotopic composition of nitrogen, measured in large diamonds (gram size) from the Mbuji Mayi kimberlite district (Zaïre) show a large range of variation (100<N<2100 ppm, ?11.2<δ15N< +6.0). The15N-depleted nitrogen is associated with the higher nitrogen concentrations. The large diamonds are individually rather homogeneous in13C (range ofδ13C < 0.9‰) while variations occur within small octahedral diamonds from the same district (range up to 5.8‰). The total range ofδ13C variation is about the same for the large diamonds (?10.5 <δ13C < ?5.5), the small octahedral diamonds (?10 <δ13C < ?4.6), and the carbonates from local kimberlites (?11.8 < δ13C < ?5.5). The diamond carbon isotopic data could indicate a complex story of crystallization within a deep-seated system fractionating its carbon isotopes.The nitrogen results indicate that nitrogen in diamonds is, on the average, markedly depleted in15N (weighted average ?5.15‰) relative to atmosphere, sediments and upper mantle. |
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