Age, origin and emplacement of diamonds: a review of scientific advances in the last decade

CIM Bulletin, Vol. 85, No. 956, 1992

M.B. Kirkley, J.J. Gurney, Department of Geochemistry, University of Cape Town, South Africa, and A.A. Levinson, Department of Geology and Geophysics, University of Calgary

Scientific advances in the past decade have greatly clarified our understanding of certain concepts relating to the age and origin of diamonds. These advances are largely the result of geochemical studies of mineral inclusions in diamonds, made possible by modem analytical techniques which enable the accurate chemical analysis of micro-sized particles of the order of 200 microns in maximum dimension. As a generalization, the inclusions indicate that most diamonds formed from either of two rock types, peridotite and eclogite. Peridotitic diamonds have yielded ages of 3300 million years, whereas eclogitic diamonds are younger and range in age from approximately 1000 to 1600 million years. Kimberlite and lamproite, the two rock types usually associated with diamonds, typically are much younger than the diamonds they contain. Thus, it is now clear that kimberlites and lamproites are only the transporting mechanisms which brought diamonds to the surface and are in no way related to the formation of most diamonds. The latest concepts which developed during the past decade regarding the sources of carbon for the crystallization of diamonds from peridotite and eclogite, and the mechanisms of kimberlite and lamproite emplacement, are also discussed.

Keywords: Industrial minerals, Diamond mining, Kimberlites, Lamproites.