The project, known as Cut 9, follows a $3 billion (£2.1 billion) expansion of the mine in 2010 to uncover 100 million carats of diamond and extend the life of the mine to 2024.

If approved by Botswana environmental authorities, the project will deepen the mine to 855 metres from 650 metres, the company said in a regulatory environmental impact assessment notice.

Debswana managing director Balisi Bonyongo told Reuters on March 27, 2018 that feasibility studies for Cut 9 will be completed before the end of the year which will inform the amount of funds required for the project.

De Beers is a unit of Anglo American . Botswana is the world's biggest diamond producer and Debswana says the Jwaneng Mine is the world's richest diamond mine by value.

(Writing by Tiisetso Motsoeneng. Editing by Jane Merriman)