Abstract
Whole-rock magmatic compositions of hypabyssal-facies samples from on-craton kimberlites predict diamond prospectivity. Within a database of some 100 kimberlites worldwide, 88% of occurrences are correctly assigned using Ti, Cr, Ni and Y whole-rock concentrations. Prospective occurrences show lower Ti, Y, Ga, Mn, Fe, Sc, Zn, V and Cu, and higher Ni and Cr than non-prospective, otherwise similar rocks. Magnesium, more abundant in prospective occurrences, can also be used to distinguish these two groups, although to a lesser extent. Similar differences, excepting Ti, are observed between diamondiferous (prospective) and non-diamondiferous (non-prospective) lamproites. These distinctions result from differences in both groundmass and suspended-load compositions of these rocks. Differences in oxygen fugacity attending the genesis and evolution of kimberlitic magma most likely contribute to these distinct compositions, although other factors such as diamond presence in source regions and pressure and temperature conditions probably contribute as well.
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