The Mothae kimberlite intrusion is a kimberlite diatreme, or pipe, which was the feeder to a now eroded kimberlite volcano.
The Mothae kimberlite is situated on the southern edge of the Kaapvaal Craton, which extends through central, eastern and north-eastern South Africa, into southern Zimbabwe and southeastern Botswana, and incorporates most of Swaziland.
As the diamondiferous Northern Lesotho Kimberlite Field is in the Kaapvaal Craton, it conforms to ‘Clifford’s Rule’, which states that diamondiferous kimberlites tend to occur in geological regions that have been tectonically stable since the Archaean.
The Archaean basement in Lesotho is entirely covered by the flat-lying Paleozoic to Mesozoic Karoo Supergroup which reaches a thickness of approximately 4 km in Lesotho.
The surface geology within the Mothae license area comprises amygdaloidal and nonamygdaloidal Mesozoic (180 Ma) Drakensberg Group flood basalt, into which the Mothae kimberlite has intruded. The average elevation of the Mothae kimberlite is approximately 2,900 mamsl and the thickness of the basalt into which it is emplaced is estimated to be of the order of 1,000 m, although basalt thickness on the property may locally reach up to 1,400 m. Basalts are underlain by Beaufort Group sediments of the Karoo Supergroup.
Kimberlite emplacement during the Cretaceous Period was widespread throughout southern Africa and was probably associated with tectonic trigge ........
