Using a modern microprobe, we have thoroughly studied the structure and phase composition of polymictic rims on picroilmenites sampled from modern alluvial deposits and from eluvium of the Khorkich pipe in the Taigikun-Nemba kimberlite field. Data obtained helped to refine the composition and genesis of similar rims. We have established that their formation was a long process, which included both reactionary replacement of picroilmenite by neogenic mineral phases at the magmatic stage as a result of the long-term interaction of its grains with kimberlitic melt and the subsequent postmagmatic replacement (corrosion) of these phases by secondary minerals. At the magmatic stage, perovskite and titanomagnetite were the major minerals that developed after the picroilmenite grains. At the postmagmatic stage, both picroilmenite and neogenic mineral phases were replaced by leucoxene and serpentine. The formed surfaces are primary in the context of the processes of formation of heavy-concentrate aureoles, and the relief itself is more correct to be called reactionary-corrosive. We suggested that the development of a rather intensive reactionary-corrosive relief on picroilmenites can exert a negative effect on the diamond potential of kimberlite bodies.

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