The new Massadou diamondiferous kimberlite field in Guinea

Abstract

A new kimberlite field, called Massadou, has been discovered in southeastern Guinea near Macenta city. The field consists of numerous ~1 m thick kimberlite dikes with low diamond contents; altogether 16 dikes have been found so far. Mineralization occurs along a 600 m wide zone distinct in satellite images, which is oriented in the same way as the K4 kimberlite reported by Huggerty. The Massadou kimberlite is covered by a thick laterite weathering profile. Main kimberlite indicator minerals found in the area are pyrope, chromite, and ilmenite. The latter occurs as zoned grains with a high-Fe core (hemoilmenite) surrounded by a parallel-columnar aggregate in the rim. The aggregate has a composition of ordinary kimberlitic Mg ilmenite and results from interaction of hemoilmenite with the kimberlite melt. The kimberlite age is estimated as 140—145 Ma by analogy with the surrounding fields. The dikes independent products of kimberlite magmatism in the Guinea-Liberia shield rather than being roots of pipes as interpreted by Skinner (2004). Therefore, the erosion cutout is moderate, and there are no reasons to expect the presence of large and rich diamond placers.