CHINA'S antitrust authorities removed the last obstacle to Glencore's US$30 billion takeover of miner Xstrata yesterday after the commodities trader agreed to sell a US$5.2 billion mining project to ease its grip on copper.

Xstrata's Las Bambas mine in Peru had been set to be sold to secure the approval of China's Ministry of Commerce, but Glencore also agreed eight-year commitments covering the supply of copper, zinc and lead to China.

Chinese regulators have rarely demanded asset sales to improve competition after a major tie-up, but the importance of the metals that Glencore mines and trades for China's economy meant the merger was unlikely to succeed without changes.

In particular, Glencore had already signaled that Chinese authorities were focused on its hold on the copper market, and specifically copper concentrate. Glencore and Xstrata combined account for roughly 7 percent of global copper supply.

Glencore, which is now on track to complete the industry's biggest-ever deal in two weeks, has to begin the process of selling Las Bambas within three months, and find a buyer by the end of August 2014.

If it does not find a buyer for the asset - a major mine expected to produce an annual 400,000 metric tons of copper for at least four years from 2015 - it will have to find alternatives.

Glencore, which has made no secret of its desire to slash the number of Xstrata mines being built from scratch, will have three months to offer up one of the miner's longer-dated projects instead - namely Tampakan in Peru, Frieda River in Papua New Guinea, El Pachon or Alumbrera in Argentina.

"Them being willing to sell Las Bambas shows there are no sacred cows in the eyes of the Glencore management. It shows they think a little differently - they've always shied away from greenfield projects," analyst Jeff Largey at Nomura said.

"If they can pull value forwards on Las Bambas by selling it - rather than taking on all the operational and execution risk associated with building it (and) bringing it to production - I think the market will reward them."

Glencore agreed to supply a minimum of 900,000 tons of copper to Chinese clients a year for eight years from 2013. The price for at least 200,000 tons will be priced in accordance with the benchmark level. It also agreed to supply zinc and lead concentrate on "fair and reasonable" terms.