Periodic Reporting for period 1 - KimberliteNewApproach (A new approach to revealing the composition of kimberlite melts and their deep mantle source)
Reporting period: 2016-07-01 to 2018-06-30
Diamonds are not generally produced by the crystallisation of kimberlite melts, but are xenocrysts entrained from mantle wall-rocks during ascent of kimberlite magmas. The project investigates barren kimberlites and diamondiferous kimberlites showing different grades. This project could have a major impact on diamond industry if it identifies significant differences in the composition of the kimberlite melts that generated the different diamond deposits.
Some of these results have been already published in the highly regarded international peer-reviewed journal Chemical Geology (Giuliani et al., in press). This article reports details of the mineralogy and petrology, including olivine and fluid/melt inclusion compositions, of the Bultfontein kimberlite in the Kimberley area (i.e. the kimberlite type locality). The results of this research will be included in the keynote presentation that Dr Giuliani will deliver at the prestigious International Kimberlite Conference (Botswana; September 2017), and subsequently published in the conference proceedings.
The major breakthrough of this project is that, for the first time, we have identified a direct relationship between the composition of olivine xenocrystic cores (i.e. derived from mantle wall-rocks) and that of magmatic olivine rims in kimberlites worldwide. This evidence provides the ""smoking gun"" that the composition of kimberlite magmas is a direct function of the characteristics of the mantle the magma ascends through. This is a radically new inference of possible wider applicability to the field of geochemistry and igneous petrology because it is commonly assumed that the composition of most of mantle-derived magmas reflects of the mantle source."