Kimberlite exploration in Tanzania

Abstract

In 1979 an aeromagnetic survey covering approximately 9 500 sq kms was conducted in the Shinyang Region of Tanzania. Ground follow-up work in the Mwadui Diamond field (1 700 sq km) showed about 100 magnetic anomalies (interpreted by Geosurvey International Ltd) that were possible targets for kimberlites. Twelve of these anomalies coincided with previously discovered kimberlites and fifteen of them were proved to be new kimberlite pipes. Bulk tests showed that four of the discovered kimberlites were diamondiferous but none proved to be economic. The remaining plug-like anomalies were either dolerites, diorites or gabbros. Orientation surveys were done to test ground geophysical techniques namely Magnetometry, Pulse EM, Induced Polarisation and Resistivity over known pipes. Helicopter EM33/2 survey was also tested in an area of 100 sq. kms occuring some 25 km SE of Mwadui Mine. It was found that a combination of Heavy Mineral (HM) surveys and Electromagnetic (EM) surveys were important in locating non-magnetic kimberlite pipes that are filled with epiclastic material. The magnetic method however, has a tendency to give many plug-like anomalies that may not necessarily be kimberlites. A geochemical orientation survey showed that Nb and Ni are most promising indicators of kimberlites in the metasedimentary and granitic environment of the Shinyanga Region.