ABSTRACT

Fifteen major components and 21 trace elements (Li, F, S, Cl, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Cd, Ba, Hg, Tl, Pb and Bi) were analyzed for 11 kimberlites and 3 xenoliths (garnet peridotite, eclogite and gabbro) from South Africa. Selected major and trace element contents of olivine, serpentine, pyroxene, phlogopite, perovskite, spinel, magnetite, Fe-Ni-Cu-S ores and native copper in several kimberlites were also measured. Sulfur isotope compositions of 5 kimberlites and a garnet peridotite range from δ³⁴S -3 to +9.6‰. The concentrations of major elements and Cr, Co, Ni, Zn, Hg have a small, but those of Li, Na, K, Rb, Cl and Tl a wide range of variation. Good correlations of K-Rb have to be mentioned. Large Fe₂O₃/FeO ratios indicate relatively high oxygen fugacities during eruption. Additional data on about 60 elements in bulk kimberlites have been compiled from the literature to estimate the average chemical composition of kimberlites. In order to know the accumulation and depletion of elements during magma formation, the elemental abundances of kimberlites were compared with those of undepleted mantle rocks. Kimberlites are characterized by very high concentrations of incompatible and volatile elements such as La, Ce, C, Nd, Th, U, F, Cs, Nb, Sm, Ta, Rb, Ba, K, P, Pb and Sr, and low concentrations of Si, Na, Al and heavy REE. Concentrations of the former elements suggest that kimberlite magmas are produced by a small degree of partial melting in the presence of CO₂ and H₂O under upper mantle conditions.