The New Massadou Diamondiferous Kimberlite Field in Guinea

Abstract

A new Massadou kimberlite field, was discovered in southeastern Guinea, near the town of Macenta. It consists of 16 poorly diamondiferous kimberlite dikes, ~1 m thick on average. The ore-controlling zone has a width of around 600 m, its orientation corresponds to the K-4 trend after S. Haggerty, and it is quite well detectable in satellite images. A thick laterite weathering profile has developed on the kimberlites. The main indicator minerals are pyrope, chromite, and ilmenite. Ilmenite grains have a zoned structure with a high-Fe core (hemoilmenite) overgrown by a parallel-columnar aggregate of Mg-ilmente rim resulting from interaction of the core phase with kimberlitic melt. The age of kimberlites is estimated as 140–145 Ma by analogy with those in adjacent areas. Dikes occur as an independent form of kimberlite magmatism in the Guinean–Liberian shield, rather than being roots of kimberlite pipes; therefore, the erosion cutout is relatively small and large-scale diamond placers should not be expected.