State-owned firm China Finance National Co Investment signed a contract with a Canadian company to buy a 50 percent share and mining rights for 25 years in Asia's biggest sylvite mine in Thailand.
The company will use the sylvite to make potash fertilizer and hopes to increase its stake to 90 percent in the future.
The mine has known deposits of 900 million tons. The firm plans to extract one to two million tons a year and ship most of it to China but declined to give further details of the deal.
China was the world's second-largest sylvite importer last year, with imports of six million tons.