Chilean antitrust watchdog FNE and Tianqi had presented the agreement, intended to limit the exchange of commercially sensitive information between the two companies, to Chile's antitrust court in September.

It was approved by the five-member court without conditions.

"The approval of this extrajudicial agreement does not prevent third parties with a legitimate interest, who think that the facts in this agreement ... affect free competition, from taking whatever action they feel is most appropriate," the court said in a statement emailed to Reuters.

The agreement stipulates that Tianqi cannot name any of its executives or employees to SQM's board, and requires that the Chinese miner notify regulators of any future, lithium-related deal struck with either SQM or rival Albemarle.

In a statement, Tianqi said the deal ensured competition in the lithium market would be maintained.

"With this resolution, and considering the timeline, we anticipate the transaction will be completed in the last quarter of 2018," Tianqi said.

SQM, which had objected to the deal on the grounds it did not go far enough to limit Tianqi's access to corporate secrets and sensitive information, did not immediately reply to a request for comment.

Chile's antitrust regulator launched an investigation in June, shortly after Tianqi said it would buy 24 percent of SQM for $4.1 billion, giving it a coveted stake in one of the world's top producers of lithium, a key component in the batteries that power everything from cellphones to electric vehicles.

Beijing is aggressively promoting electric vehicles to combat air pollution and help China's domestic carmakers leapfrog the combustion engine to build global brands.

(Reporting by Dave Sherwood; Editing by Steve Orlofsky and Rosalba O'Brien)