U.S. copper miner Freeport McMoRan will postpone its sales of refined copper from Indonesia until the second quarter of 2025 as a fire at its new smelter causes a further production delay, two sources with knowledge of the matter said.

Long production delays at the new Manyar smelter, with an output capacity of 480,000 metric tons of copper cathode a year, are likely to narrow an expected 2025 surplus of the metal and support prices.

Freeport said earlier on Tuesday it is investigating the cause of the fire at a sulphuric acid unit at Freeport's Manyar site, located in East Java province, which was extinguished late on Monday.

Its subsidiary running the plant, PT Freeport Indonesia (PTFI) is conducting damage assessments and root cause evaluations, a spokesperson told Reuters.

"The impact of this event on our planned ramp-up to full production also will be assessed," the company said.

The $3.7 billion Manyar copper smelter was completed in June and started output in September. However, production was delayed until November due to water and steam leakage during an initial test period, Reuters reported earlier this month.

The sources also said Freeport has been in talks with the Indonesian government to extend its export licence for copper concentrates which expires at the end of 2024 into the first quarter of next year.

A slow ramp-up at Manyar could mean lower consumption of copper concentrate feedstock and a potential release of output mined from its flagship Grasberg mine in Indonesia, the world's second biggest copper-gold mine, to an undersupplied market.

Indonesia's government is trying to discourage export of copper ores and concentrates. It wants miners to smelt metal locally to add value and increase state revenues.