A comparative trace element study of diamonds from Premier, Finsch and Jagersfontein Mines, South Africa

ABSTRACT Neutron activation studies of the impurity chemistry of more than 1500 natural diamonds from three South African kimberlite sources: Premier, Finsch and Jagersfontein, provide evidence for the presence of sub-microscopic inclusions of a quenched or temperature-re-equilibrated melt from which these diamonds crystallized. These micro-inclusions of parental magma contain variable amounts of H 2 O–CO 2 -rich fluids and Fe–Ni–Cu–Co sulphides in addition to a major silicate phase which is relatively constant in composition irrespective of the source of the diamonds and the age of emplacement of their host kimberlite. These micro-inclusions are present in varying amounts in all diamonds analyzed and may even dominate the impurity chemistry of diamonds with observable mineral inclusions. An estimate of the major element composition of the silicate melt inclusions indicates that the diamonds investigated crystallized from an H 2 O–CO 2 -rich picritic magma in the presence of immiscible Fe–Ni–Cu–Co sulphides.