Petrology of some melilite-bearing rocks from Cape Province, Republic of South Africa: relationship to kimberlites.

Abstract

'Olivine melilitites' from 4 occurrences in the Cape Province, South Africa, were studied: 2 are satellite plugs of the Saltpetre Kop volcano; 2 are plugs from the Bitterfontein region at Biesiesfontein and Zandkopsdrift. Differences in the bulk chemistry and normative character do not suport the view that olivine melilitite is a derivative of kimberlite magma: 1) kimberlites are enriched in Mg and depleted of Ca and Na relative to olivine melilitites; 2) phenocrystic phases in kimberlite are enriched in Mg (olivine and phlogopite) and depleted of Ba (phlogopite) relative to those of olivine melilitites; and 3) there are differences in groundmass mineralogy between kimberlites (calcite, phlogopite, serpentine) and olivine melilitites (zeolites, nepheline, melilite, Ti-garnets).-from Authors