Formation of unusual yellow Orapa diamonds

Suzette Timmerman*, Ingrid L. Chinn, David Fisher, Gareth R. Davies

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review

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Abstract

Twenty eclogitic diamonds from Orapa Mine (Botswana) with an unusual yellow colour are characterised for their growth structure, N systematics, and C isotope composition, and the major element composition of their silicate inclusions. The diamonds show complex luminescence with green, blue and non-luminescent zones and occasional sector zonation. All parts of the diamonds have low total N concentrations (<50 at.ppm, with one exception of <125 at.ppm) and a limited range in C isotope composition (−5.7 to −10.6‰). Fourier Transform Infrared spectra show bands at 1334, 1332, 1282, and 1240 cm−1 typical for Ib-IaA diamonds. Relict unaggregated N defects (Ns o and Ns +) are present and the preservation is likely caused by the low N concentrations and possible low mantle residence temperatures rather than young diamond formation (inclusion ages of 140, 1096, 1699 Ma; Timmerman et al. Earth Planet Sc Lett 463:178–188, 2017). Garnet and clinopyroxene inclusions extracted from 14 diamonds have an eclogitic composition with relatively low Ca contents and based on all characteristics, these diamonds form a distinct population from Orapa.

Original languageEnglish
Pages (from-to)209-218
Number of pages10
JournalMineralogy and Petrology
Volume112
Issue numberSupplement 1
Early online date21 Jun 2018
DOIs
Publication statusPublished - Dec 2018

Keywords

  • Carbon isotopes
  • Nitrogen
  • Silicate inclusions
  • Zimbabwe Craton

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