The DFS' post-tax net present value climbed 9.4% to US$197 million, with the internal rate of return up 23.9% to 119% and a payback period of under two years.
The life of mine (LOM) was increased by four years to 24 at 40,000 tonnes per annum of production, while LOM revenue was increased by 21.6% to $1.4 billion.
Development capital cost dropped 6% to $27.8 million.
The DFS determined operational costs of $347 per tonne of concentrate FOB at the port of Mtwara, and cash margins of over $1,000/t FOB.
Average annual free cash flow was estimated at $28.8 million, up 2.9% and the LOM EBITDA was forecast at $1.07 billion, climbing 21%.
Walkabout said the robust economics were based on current sales assumptions, with the weighted average basket price reduced to a $1,515/t.
Lindi Jumbo's reserves were increased in February by 10% to 5.5 million tonnes, with the total graphite content (TGC) up 22% to 987,000t and the life of mine grade up 11% to 17.9% TGC.
Executive director Allan Mulligan said the DFS demonstrated Lindi Jumbo's "compelling economics in spite of conservative sales assumptions".
"We have a high degree of confidence in the revised cost estimates which are derived from actual engineering drawings and negotiated contract prices.
"This mine has been designed to withstand potential start-up and ongoing risks. It continues to show outstanding economics with a payback period of less than two years," he said.
At A14c (US9.86c), Walkabout shares are close to the A15c level seen six months ago.