Philex Mining Corp. expects the start of production at its Silangan copper-gold mine in the Philippines to be delayed by four years to 2022 amid a national ban on new open pit mining, Reuters reported March 22.

Production at Silangan was scheduled to start by 2018 but has been set back due to the ban introduced in 2017 as part of the government's efforts to improve environmental protection. Open pit extraction has been blamed for significant environmental damage in certain areas.

The company said it is working on an infrastructure design that would use underground mining to extract ore. CEO Eulalio Austin said Philex is trying to secure all requisite permits and approvals to operate the mine.

Silangan's development cost, based on open pit extraction, was estimated at US$1.2 billion, according to the newswire.

Philippine President Rodrigo Duterte has warned that he might declare a total ban on open pit mining.

Silangan has the potential to be Philex's largest source of revenue after its Padcal copper-gold mine closes in 2022, according to the report.