(IDEX Online) - The planned expansion of Botswana's flagship Jwaneng mine should help to create over $920m of extra revenue in the next four years, said operator Debswana.The company, a joint venture between De Beers and the government, will begin underground mining after 50 years of open-cast operations at Jwaneng, the richest diamond mine in the world by value."Early access is expected by 2023 with full production from 2034. At full operation, Jwaneng will be the world's largest underground mine with a more than 360 km of tunnel network," Thabo Balopi, Debswana's head of transformation and innovation, told a briefing with investors and media.Debswana was hard hit by the pandemic. Exports fell 30 per cent in 2020 from $3.05bn in 2019 to $2.02bn and VAT was increased from 12 per cent to 14 per cent.The miner says a five-year strategy, including a restructuring, greater efficiencies and the closure of a smaller low-grade mine, should boost revenues. It said the initial cost of the Jwaneng expansion was $6bn.Pic shows Jwaneng mine