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.

This content is PDF only. Please click on the PDF icon to access.

First Page Preview

First page PDF preview
You do not have access to this content, please speak to your institutional administrator if you feel you should have access.