Shares of the company were up 17.3% at $9.49.
The Pentagon-backed mine, which would be the country's first antimony project, has an estimated reserve of 148 million pounds of the metal used in bullets and tanks, as well as in flame retardants and alloys for electric vehicle batteries.
The move comes against the backdrop of China, the world's largest antimony producer with about 50% market share, planning to restrict exports of the metal and related elements from Sept. 15, citing national security reasons.
Earlier this year, Perpetua had received a letter of interest from the U.S. Export-Import Bank, the government's export credit agency, for a loan worth up to $1.8 billion.
The Stibnite mine also has 4.8 million ounces of gold reserves.
