Mali had previously proposed a 10-year stability period. But that came under criticism for being too short and likely to discourage investors.

"We have to consider that the research phase can take at least seven, eight or nine years," said Mines Minister Lelenta Hawa Baba Bah. "So we've gone for... a 20 years stability period."

Companies operating in the country include Barrick Gold Corp, B2Gold, Hummingbird Resources and AngloGold Ashanti.

(Reporting by Tiemoko Diallo; Writing by Juliette Jabkhiro; Editing by Alex Richardson)