Project is expected to extend the mine’s life for 20 years, until 2040, allowing Lucara to exploit the highest value part of the orebody.

The world’s top producer by value sold $515 million worth of rough diamonds, the largest figure for this time of year since 2016.

The buyer is a partnership between Petra itself and the South African subsidiary of Stargems Group, which will cut and polish the stones locally.

New research shows that some diamonds are made up of former living organisms that have been recycled more than 400 kilometres below the surface.

The company's main asset in Botswana is the mothballed Ghaghoo imine, which it acquired from De Beers in 2007.