Minerals associated with diamonds from the Roberts Victor mine

Olivine and associated minerals predominate as inclusions in diamonds from the Roberts Victor mine, near Kimberley, South Africa. The most abundant paragenesis is olivine-orthopyroxene-chromite, followed by olivine-orthopyroxene-garnet; there is a minor olivine-orthopyroxene-garnet-clinopyroxene field. Less than 15% of the minerals in diamond are eclogitic. These relative abundances are at gross variance with the xenolith suite which is >95% eclogite. Sulphides are found with both associations. Co-existing mineral pairs from both parageneses give calculated equilibration T >1250oC. The eclogitic inclusion pairs have lower K_D ratios than diamondiferous eclogites from the same locality. It is inferred that the xenoliths have cooled by at least 200oC in the mantle prior to sampling by the kimberlite. The inclusion suite shows many characteristics similar to inclusions in diamonds from the Finsch pipe, South Africa. -J.M.H.