Diamond mines with a significant population of sublithospheric diamonds show a larger abundance of olivine xenocrysts coming from the base of the lithosphere and even extending beyond the Lithosphere-Asthenosphere Boundary (LAB), compared to diamond mines with little or no sublithospheric diamonds. However, it is not yet understood in what lithological host the sublithospheric diamonds are residing and if there is a direct connection between the olivine xenocrysts and sublithospheric diamonds or if they are simply only sampled from the same region but are not genetically related.
The aim of this project is to characterize micro-peridotitic xenoliths and xenocrysts from Large Diameter Drilling (LDD) samples from the Karowe diamond mine and determine how much mixing and disruption of diamond-hosting lithologies takes place during kimberlite eruption. The samples are from 12 meter depth intervals in the drill core and show a variation in mineral assemblages and textures. The diamond grades for lithospheric/sublithospheric diamond proportions are known (by De Beers) for each 12 meter depth interval. By connecting the chemistry of the xenoliths and xenocrysts to the diamond information, the following questions can be answered: i) is there a correlation between diamond grade and xenolith/xenocryst chemistry, ii) is there a correlation between lithospheric/sublithospheric diamond proportions and xenolith/xenocryst chemistry, iii) how much mixing is there in the kimberlite or are xenoliths/xenocrysts and diamonds partially staying together during ascent and eruption, iv) what is the density distribution of olivine with depth?
The project will include petrographic characterization of selected thin sections, electron microprobe, laser ablation ICP-MS on thin sections and mounts, and potentially Fe stable isotope analyses of selected samples.
In collaboration with Dr. Ingrid Chinn, De Beers Group of Companies
Advisors: Prof. Suzette Timmerman
University: BE