South Africa’s Sibanye Gold will pay $2.2 billion for U.S.-based Stillwater Mining, Sibanye said on Friday, extending its push into platinum group metals.

Sibanye has entered into a definitive agreement to acquire all of the outstanding common stock of Stillwater Mining for $18.00 per share in cash, a 23 percent premium on the firm’s closing price on Thursday, the South African firm said in a statement.

Sibanye, a bullion miner that was spun off from Gold Fields in 2013, last year bought Aquarius Platinum and Anglo American Platinum’s mines in Rustenburg, but the Stillwater deal will be its first venture beyond South Africa.

Stillwater, which operates in the state of Montana, is the only U.S. miner of platinum group metals (PGM) and the largest primary producer of PGMs outside South Africa and Russia.

“The transaction represents a transformational opportunity for Sibanye to acquire high-quality, low-cost, PGM assets at a favourable point in the cycle,” said Sibanye Chief Executive Neal Froneman.