Advances in kimberlite geology

Over the past fifteen years the original data on the kimberlites of South Africa have been supplemented with a wealth of information on the kimberlites of the U.S.S.R., the U.S.A., and various parts of Africa. From their distribution pattern, it can now be shown that kimberlites are virtually confined to the old Precambrian cratons and that the diamond-bearing kimberlites exist on the older cratonic nuclei that have not been deformed for the past 2,500 m years. The kimberlite dykes infill major, deep-seated fractures that cross the cratons on a geometrical pattern. The kimberlite that infilled these fractures was a hot fluid that penetrated to within 2–3 km of the surface before there was explosive breakthrough to the surface with subsequent formation and infilling of the high-level diatremes by a gas-solid fluidisation process. The kimberlites can vary widely texturally, from the fragmental variety found in the diatremes, to massive varieties found within the hypabyssal dykes or skills.