Isotopic and elemental evidence for a relationship between kimberlite and Zaire cubic diamonds

Cubic diamonds from Zaire contain fluid inclusions which may record the conditions under which the diamonds formed-either in the mantle or in the kimberlite magma which transported them to the surface. Here we present Sr isotope ratios for whole cubic diamonds, and abundances of rare-earth elements, K, Rb, Sr and Ba for both whole cubic diamonds and the leachings from crushed cubic diamonds. The ⁸⁷Sr/⁸⁶Sr ratios of the diamonds range from 0.7038 to 0.7052, which is almost identical to that of Mbuji Mayi kimberlite¹. The chondrite-normalized elemental abundance patterns of the diamonds roughly resemble that of kimberlite but show more enrichment in incompatible elements. The bulk of the impurities are soluble in water. The results of the present study support the genesis of fluid inclusions in diamond in the kimberlite or in the source of kimberlite magma.