Fifty-four kimberlite pipes and dykes cut Precambrian granite in the Singida region of Tanganyika. The pipes range from 60 to 2500 feet in diameter, and occur in clusters and lines. The lines follow fracture zones. In addition to intrusive kimberlite, the pipes contain massive to stratified kimberlite tuff and sedimentary-tuffaceous beds. Some pipes have jackets of explosion breccia. The Singida pipes represent the upper parts of kimberlite volcanoes. The kimberlite consists mostly of serpentine which has replaced olivine. Magnesium ilmenite, pyrope, dark green diopside and perovskite are characteristic accessory minerals. After consolidation, the kimberlite was entirely serpentinized, and partly carbonatized and silicified. The absolute age of the pipes is not known. Indirect evidence suggests an early Tertiary age. The Singida kimberlites may have been emplaced during an early ultrabasic phase of Tertiary-Recent alkaline volcanism of the Eastern Rift Valley.

Stevenson, J. S. (Supervisor)