Abstract

The garnet Iherzolite nodules in kimberlite from South Africa consist essentially of oh vine, orthopyroxene, garnet, clinopyroxene, and serpentine with minor amounts of phlogopite and opaques occurring in some samples. The average chemical compositions of 41 samples are: SiO2 44.66%, Al2O3 1.22%, total Fe as FeO 7.87%, MgO 42.94%, CaO 0.81%, Na2O 0.155%, K2O 0.123%, TiO2 less than 0.10%, MnO 0.113%, Cr2O3 0.352%, NiO 0.370%, Co 89 ppm, Sr 31 ppm, and Zn 42 ppm. The MgO/(total Fe as FeO) ratios of the rocks range from 4.63 to 6.14. Al2O3, CaO, Na2O, MnO, Cr2O3, Sr, and Zn decrease while NiO increases with increasing Mg/(total Fe as FeO) ratios. The systematic chemical variations in the garnet lherzolites may be interpreted as due to different degrees of partial fusion of the undepleted upper mantle materials consisting of some members of the garnet lherzolites with relatively low MgO/(total Fe as FeO) ratios.

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