The US$2 billion investment at Jwaneng, which the companies consider one of the world's most valuable diamond operations, will allow operations to 2035 - and could yield 53 million carats of rough diamonds from 44 million tonnes of treated material.
Cut-9's diamond mining services will be provided by Majwe Mining, a joint venture of Bothakga Burrow Botswana and Thiess Botswana, under a US$1.2 billion contract. About 1,000 jobs will be created at the peak of the work.
"The extension of Jwaneng mine secures Botswana's rightful place as a leading diamond-producing nation for years to come," Debswana chairman Bruce Cleaver said.
"With global consumer demand for diamonds reaching record levels in 2018, the extension will enable us to continue to meet the needs of our consumers all over the world. We are deeply proud of the central role Jwaneng mine has played in Botswana's remarkable development story and of the role this investment will play in its future."
Debswana managing director Albert Milton added that it is committed to safety and to delivering on the citizen economic empowerment (CEEP) goals: "[We] will focus on training our people, developing their skills and harnessing technology to create further safety and efficiency improvements."
The government of the Republic of Botswana and De Beers Group hold Debswana 50-50.
The Jwaneng mine contributes approximately 70% of Debswana's total revenue, and its diamonds, in turn, contribute half of public revenue, 33% of GDP and over 80% of foreign earnings to the country.
Debswana operates a total of four diamond mines in Orapa, Letlhakane, Damtshaa and Jwaneng.