The Tampakan mine is cutting costs while it undergoes "an extremely complex and uncertain pathway to ultimate project approval", spokesman John Arnaldo of Glencore Xstrata unit Sagittarius Mining said on Tuesday.
"At present, the project faces substantial development challenges . . . no investment decision can be made until the current project challenges are resolved and necessary approvals obtained," he told AFP.
He said the hurdles include a local government ban on open-cut mining, while the company must also still obtain a substantial number of community and government permits.
Out of 1,060 workers, the company is dismissing 300 regular and project employees and about 620 contract workers, said Arnaldo.
Under its revised work plan, the company will still be spending about $1 million a month, down from its previous 2013 work plan of $4 million a month, he added.
Sagittarius describes the Tampakan project, on the major southern island of Mindanao, as one of the world's largest undeveloped copper and gold deposits.
The project would be the Philippines' largest ever foreign investment but it has been opposed by anti-mining activists, tribal groups and even church leaders.
Arnaldo said the company has so far invested more than $500 million in developing Tampakan, and had hoped early approvals would allow it to start commercial production by 2019.
The Philippines is believed to have some of the world's biggest mineral reserves — the government estimates the country has at least $840 billion in gold, copper, nickel, chromite, manganese, silver and iron ore deposits.
However, the minerals have been largely untapped, partly because of a strong anti-mining movement led by the influential Catholic Church.
Poor infrastructure and security concerns have also kept investors away.