MANILA, Philippines - The southern province of South Cotabato is likely to ban open pit mining due to environmental concerns, its governor said on Thursday, a move that could halt Xstrata Plc's $5.2 billion copper-gold project.

The province's legislative council approved the ban on third reading earlier this week and the measure will soon be endorsed to the governor.

"The vote by the provincial council was unanimous so how can I veto it?," Daisy Avance-Fuentes, governor of South Cotabato province, told Reuters in a phone interview.

The state's Mines and Geosciences Bureau said in position paper a looming ban "effectively means a ban on the development of the Tampakan copper-gold mine," considered Southeast Asia's largest undeveloped copper-gold prospect.