Regolith and diamond deposits around Tortiya, Ivory Coast, West Africa

The diamond deposits of the Tortiya region are polygenetic, with placer concentration probably taking place in both the Precambrian and the Quaternary. Geomorphological, sedimentological, and micromorphological studies of regolith have been carried out, covering major depositional environments in the diamondfields. The bulk of the diamonds occurs in colluvial deposits that are less than 10 m thick and of probable Quaternary age, formed by the weathering, erosion, and reconcentration of earlier deposits. The richest diamond deposits are towards the base of what appears to be ferruginised mudflows. Studies of regolith micromorphology and mineralogy have given insights into the processes that could have concentrated the small (0.2–2.5 mm) diamonds typical of Tortiya. These include: (i) desiccation fractures in exposed saprolite, producing diamond-trapping cracks; (ii) possible settling of heavy minerals at the base of mudflows; (iii) disintegration and dissolution of quartz during ferricrete formation, which diamonds probably survive; (iv) the downward movement of small clasts in ferricrete, along passages of up to 2 mm wide; (v) the dissolution of ferricrete in hydromorphic zones, resulting in a relative concentration of diamonds.