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Contributions to Mineralogy and Petrology

, Volume 150, Issue 1, pp 54–69 | Cite as

Dissolution forms in Lac de Gras diamonds and their relationship to the temperature and redox state of kimberlite magma

  • Yana FedortchoukEmail author
  • Dante Canil
  • Jon A. Carlson
Original Paper

Abstract

The degree and character of diamond dissolution were compared to crystallization temperatures (T) and oxygen fugacities (fO 2) estimated from chromite inclusions in olivine phenocrysts in several kimberlites from Lac de Gras, Northwest Territories, Canada. The T and fO 2 values calculated at an assumed pressure of 1 GPa are in the range of 970–1,140±50°C and 2.8–4.4 log fO 2units below the nickel–nickel oxide (NNO) buffer. The T and fO 2 vary between kimberlites from northwest and southeastern clusters within 150°C and 1 log unit, respectively. A detailed description of morphological forms and surface dissolution features for diamond parcels from the Panda, Beartooth, Grizzly, Misery and Jay kimberlites (>7000 stones) show that an increase in diamond resorption in the kimberlites corresponds to increase in T. The development of various surface dissolution pits and structures correlates with higher fO 2 of kimberlites and therefore mainly happens in the magma. The two processes of diamond dissolution, volume resorption and surface etching, do not show a strong correlation with each other, since some of the resorption occurs in the mantle. We suggest that the fO 2 of the kimberlite magma plays an important role in both the processes. The proportion of plastically deformed brown diamonds does not correlate with the degree of volume resorption, but does correlate with the development of surface forms. The diamond grade is higher in kimberlites with lower fO 2, confirming that conditions of kimberlite crystallization can have notable effect on diamond dissolution.

Keywords

Olivine Chromite Olivine Phenocryst Kimberlite Pipe Monticellite 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgements

The diamond descriptions were completed by YF at BHP Billiton Diamonds Inc., whom we thank for generous access to drill core and diamonds, and for suggestions and permission to publish. We also thank T. Nowicki at Mineral Services Canada Inc., and M. Kopylova for providing some of the kimberlite samples, M. Kopylova and C. McCammon for the chromite ‘Fe3+ standards’, and M. Raudsepp for assistance with EMP analyses. We are grateful to J. Gurney for sharing his experience in diamond description, and M. Arima, C. Ballhaus and O. Navon for reviews. This research was supported by a Natural Sciences and Engineering Research Council of Canada Postgraduate Scholarship to YF and Discovery Grant to DC.

Supplementary material

410_2005_3_MOESM1_ESM.pdf (133 kb)
Supplementary material

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Yana Fedortchouk
    • 1
    Email author
  • Dante Canil
    • 1
  • Jon A. Carlson
    • 2
  1. 1.School of Earth and Ocean SciencesUniversity of VictoriaVictoriaCanada
  2. 2.BHP Billiton Diamonds IncKelownaCanada

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