Rio Tinto PLC's (RTP) $19.5 billion agreement with Aluminum Corp. of China would see the Chinese company take a 15% stake in the Escondida copper mine but won't alter the participant agreement with BHP Billiton Ltd. (BHP), a Rio Tinto spokeswoman said.

BHP Billiton owns 57.5% of the mine and has pre-emptive rights to buy Rio Tinto's stake. Rio controls 30% of Escondida but is selling half of that to Chinalco under terms of a broad deal announced Thursday.

"We have structured it to ensure it fully respects all our obligations under the participant agreement," a Rio Tinto spokeswoman said Thursday.

Company Web site: www.riotinto.com

-By Jeffrey Sparshott, Dow Jones Newswires; +44 (0)207 842 9347; jeffrey.sparshott@dowjones.com