South32's (ASX:S32) Groote Eylandt manganese mining and export operations in the Gulf of Carpentaria look set to remain offline for another year following Cyclone Megan, which devastated the area in mid-March.

In its March quarter production and sales report, South32 stated that the damage was extensive and would require considerable time to repair, bringing the affected mining and shipping areas back online.

The damage bill is expected to be substantial, potentially exceeding $US500 million in lost revenues for South32. The mine, one of the world's largest, generated sales revenue of $US688 million in the 2022-23 financial year from exports of just over 3.61 million tonnes of manganese ore (from 3.545 million tonnes mined).

The mine reported an EBITDA of $US369 million for 2022-23. The absence of this revenue will significantly impact South32's earnings over the next year.

"Engineering studies are currently underway for the restoration of wharf and haulage road bridge infrastructure. These studies will inform the final schedule and capital costs," the company announced on Monday.

"Based on our preliminary schedule estimate, we anticipate resuming wharf operations and export sales in Q3 FY25 (i.e., in the March quarter of next year).

"Alternative shipping options are being evaluated to mitigate the impact of the wharf outage. These options may establish partial ore export capability before the wharf restoration is complete."

The company noted that more detailed work and anticipated capital costs will be released "once the recovery plans are sufficiently progressed. Guidance for Australia Manganese remains withdrawn."

"Australia Manganese maintains property damage and business interruption insurance. We are working with our insurers to assess the impact of Tropical Cyclone Megan and expected insurance recoveries," South32 said.

During the March storm, a bulk carrier loaded with 41,000 tonnes of manganese ore collided with the wharf at Groote Eylandt, causing severe damage.

This means the vessel insurers will be involved in compensation talks, further complicating matters for South32.

South32 reported that saleable production from Groote Eylandt fell by 13% (or 352,000 wet metric tonnes - wmt) to 2.324 million wmt in the nine months ending in March, due to the impact of Tropical Cyclone Megan.

Apart from this issue, South32 had a reasonably good quarter and first nine months of the 2023-24 financial year, with a rebound in coal production from its mines in the Illawarra, although wet weather impacted operations at the Cannington mine in North Queensland due to a second cyclone.

"Cannington payable zinc equivalent production increased by 15% year-to-date, as the operation realized higher average metal grades, and mitigated the impact of heavy rainfall following Tropical Cyclone Kirrily," the company stated.

"Illawarra Metallurgical Coal saleable coal production increased by 60% in the quarter, as the operation completed two planned longwall moves in the prior quarter and delivered improved longwall performance at the Appin mine.

With Groote Eylandt shut down, the company's South Africa manganese business saw record production in the quarter, delivering an 8% uplift in year-to-date production.

South32 Chief Executive Officer Graham Kerr said in Monday's statement, "This quarter, we delivered improved operating results, highlighted by record year-to-date production at Hillside Aluminium and South Africa Manganese, and a 60 per cent uplift in quarterly volumes at Illawarra Metallurgical Coal.

The company announced the sale of the coal business for $US1.65 billion to Indonesian and Australian interests, but BlueScope Steel, the major customer, has a first right of refusal in its contract and is yet to make its decision regarding whether to enforce that right.

"With the exception of Australia Manganese, our FY24 production and operating unit cost guidance remain unchanged, placing us in a strong position to capitalize on strengthening market conditions for many of our key commodities," Kerr said in Monday's statement.