Abstract
Rutile-dominated nodules from the Kampfersdam and Jagersfontein kimberlite pipes in South Africa contain euhedral olivines and spinels, graphic intergrowths of olivine and rutile, and massive rutile. In a similar nodule from the Pulsator dump in Kimberley, rutile and ilmenite are graphically intergrown with enstatite. These are interpreted as having crystallized from a Ti-rich silicate magma. The Jagersfontein samples contain Ca-Cr-Nb- Zr-beaing armalcolite that may also be magmatic or, together with Nb-rich titanite and calcite, may have formed by metasomatic reaction of the rutile-dominated cumulate assemblage with a Ca-rich fluid, possibly the residue from the magma that precipitated the cumulate assemblage. Despite some similarities in paragenesis and mineral chemistry, there are important differencesb etweent he rutile-olivine nodulesa nd the MARID nodulemetasomatized peridotite group. These include the paucity of phlogopite and absence of K-richterite in the former, precluding a simple genetic relationship between the two groups.
