(Adds detail and update on Caserones mine)
TOKYO, March 26 (Reuters) - JX Holdings Inc, Japan's top oil refiner by sales, widened its group net loss estimate for the year ending March 31 as it wrote down $420 million on its investment in Chile's Caserones mine.
The company said on Thursday it would likely post 50 billion yen ($420 million) in impairment losses for copper assets, as the planned ramp-up at its Caserones mine in Chile has been delayed due to the time needed to develop a deposit site for waste.
Also affected by weaker oil prices, the group's net loss estimate rose by 110 billion yen to 320 billion yen for the year.
This marks the first net loss for JX, formed in 2010 via the merger of Nippon Oil Corp and Nippon Mining Holdings Inc.
Caserones has had a troubled start to operations.
Construction delays, bad weather and other factors led it to postpone its first shipment from January to July 2014 and pushed up costs.
Last week, it was fined $12 million for violating environmental regulations.
And, alongside other mines, operations are currently suspended due to unusually heavy rainfall in Chile. Caserones is located in Atacama, the worst-hit area.
Worries about a global oversupply in oil led to a 60 percent slide in crude prices between June and late January, though Brent crude has recovered to nearly $60 a barrel.
The company said it would likely post 25 billion yen in impairment losses for oil and natural gas development projects, reflecting weaker oil prices, while also projecting a 25 billion-yen loss from re-evaluation of its coal development projects.
It narrowed its estimate for inventory losses by 10 billion yen to 420 billion yen, because of a slight recovery in oil prices since its February outlook.
As well as forcing cutbacks in investment among global oil companies, the oil price decline is likely to force Japan's five biggest refiners to book more than $4 billion in inventory losses, two analysts have said. ($1 = 119.0500 yen) (Reporting by Osamu Tsukimori, additional reporting by Rosalba O'Brien in Santiago; Editing by Prateek Chatterjee and Jonathan Oatis)