The sulphides in griquaite and garnet-peridotite xenoliths in kimberlite

The sulphides in the garnet-peridotite and griquaite xenoliths in kimberlite were investigated microscopically, and the mineral assemblages and textural relationships are discussed. The results of a geochemical investigation of the K₂O, Na₂O, Cu, Co, Ni, and Zn contents of these nodules are discussed.It is concluded that the massive basaltic kimberlites (Frick, 1970) are the only kimberlites on which meaningful geochemical investigations could be attempted. It was also found that, owing to the amount of contamination induced by the kimberlite magma, neither the xenoliths nor the mineral separates derived from them can be used for a meaningful geochemical investigation. In an investigation of the upper mantle most of the geochemical work on these inclusions can therefore be disregarded.Two stages of sulphide mineralization can be distinguished in the garnet-peridotite xenoliths, and at least one stage of sulphide mineralization in the griquaite inclusions. The textural evidence supports a cumulate origin for the garnet-peridotite xenoliths, and strongly contradicts such an origin for the griquaite inclusions. It appears that the sulphides in the griquaite xenoliths form during the partial melting of the griquaite, as an immisible sulphide liquid. Although inconclusive, evidence does exist that the sulphur is disseminated in the lattices of the griquaitic clinopyroxenes.