The project has 19 identified pegmatite zones over its 2,750-hectare licence area in southern Rwanda.
Rio will have the option to invest $7.5m in two stages to earn a stake of up to 75% in the licence to explore lithium. Stage one exploration costs are estimated at $3m and will be invested over a period of up to two years which will earn a 51% interest.
Stage two exploration costs are expected to be $4.5m and will be invested over a follow-on period of up to three years, which will earn an additional 24% stake in the licence.
Cash consideration for the two stages is $300,000, along with a 2% net smelter return (NSR) over the project, capped at $50m.
In addition, Rio is being presented with an option to add two other Aterian projects in Rwanda, pending approval from authorities.
Aterian chairman Charles Bray said: “This is a transformative deal for Aterian and highlights our ability to identify potential world-class deposits in critical minerals such as lithium. We have identified 19 separate LCT (lithium-caesium-tantalum) pegmatite zones across the 2,750-hectare project offering the prospective scale necessary to attract such a major partner as Rio Tinto.
“I am very proud of the Aterian team and their work to identify and unlock strategic mineral assets in Africa and to make this transaction possible. I would like to thank Rio Tinto for their time working with us to enable this investment in the significant lithium potential in Rwanda.”
The HCK licence is held by Aterian in a joint venture with HCK Mining, a private, Rwandan-registered entity.
Aterian holds a 70% stake in Kinunga Mining, which holds the project licence, while HCK Mining owns the remaining 30% stake.