High-density fluid microinclusion-bearing diamonds from the De Beers Pool and Finsch mines, South Africa

Abstract: Fifteen microinclusion-bearing fibrous diamonds from the De Beers Pool and Finsch kimberlites, South Africa, were analyzed for their major and trace element, He isotopic compositions, and nitrogen content and aggregation state. High-density fluid (HDF) microinclusions of saline compositions were found in 9 of the diamonds, silicic compositions in 1 diamond and carbonatitic in 4 diamonds. Some of the diamonds encapsulate also micro-mineral inclusions, and one diamond did not contain HDFs but rather only micro-mineral inclusions. All HDFs are enriched in incompatible elements; the fractionated nature of these patterns is more pronounced in the carbonatitic HDFs. 3He/4He isotopic ratios in the saline HDFs are 2.66-4.43 (Ra normalized) compared to 0.07-0.69 in the diamonds with silicic and carbonatitic HDF compositions.

Other Description: Yaakov Weiss, Steven L. Goldstein, Cornelia Class, Yael Kiro, Gisela Winckler, Jeff W. Harris; Helium in diamonds unravels over a billion years of craton metasomatism; under review.

Weiss, Y., Goldstein, S.L., 2018. The involvement of diamond-forming fluids in the metasomatic ‘cocktail’of kimberlite sources. Mineralogy and Petrology, 1-19.

Weiss, Y., Navon, O., Goldstein, S.L., Harris, J.W., 2018. Inclusions in diamonds constrain thermo-chemical conditions during Mesozoic metasomatism of the Kaapvaal cratonic mantle. Earth and Planetary Science Letters 491, 134-147.