Japan Oil, Gas and Metals National Corporation (JOGMEC) acquired the right in January to earn up to an initial 50% of Lofdal by spending $20 million.

Namibia Critical Metals said the extra funding increased the term one joint venture expenditure from $3 million to $4.1 million by March 31, 2021, and the extra could be credited against the term two expenditure of $7 million.

"We are very pleased to see this additional injection of funds by our joint venture partner, which will enable us to further demonstrate the value in Lofdal as a long term, sustainable supply of heavy rare earths for Japan," president Don Burton said.

He said Lofdal was "one of only two primary xenotime deposits under development in the world" aside from Browns Range in Australia.

He said a second rig had been deployed to Lofdal and the company was aiming to deliver an updated resource for Area 4 and a maiden resource for Area 2B in the first quarter of 2021.

A 2014 preliminary economic assessment said Lofdal could produce an average 1,500 tonnes per annum of separated rare earth oxides (REO), and Burton said had demonstrated Lofdal had the potential for "significant production of dysprosium and terbium, the two most valuable heavy rare earths used in high powered magnets".

China's dominance of rare earths supply was in the spotlight again last year amid trade tensions with the US, and Japan has been seeking to shore up supplies after China restricted exports 10 years ago following a diplomatic dispute.

Namibia Critical Metals last month secured a 24-month, C$5 million drawdown equity financing with Alumina Partners (Ontario) to accelerate exploration at its projects other than Lofdal in Namibia.

Its shares closed down 6.8% yesterday to 20.5c, near the middle of a one-year range, capitalising it at $37.6 million (US$28.2 million).