A seabed mining company will be forced to reveal hundreds of pages of blacked-out information following a ruling by the Environment Court.

Trans Tasman Resources has applied to mine a section of seabed off the coast of South Taranaki of 50 million tonnes of sand per year, and extract the iron ore using a giant magnet.

The company applied to the Environmental Protection Authority (EPA) for permission to conduct the mining and has submitted a lengthy application, some of which the EPA withheld from the public on the grounds it was commercial sensitive.

Jonathan Cameron Kasm chair Phil McCabe said it was a big win for the group.

However, conservation group Kiwis Against Seabed Mining, Taranaki iwi Ngati Ruanui and Talleys Fisheries Group took the authority to the Environment Court, claiming that the public could not make a submission on the proposal without having unfettered access to the whole application.

On Tuesday in Wellington the court ruled in favour of Kasm, Ngati Ruanui and Talleys, meaning the blacked-out sections of the application will be made public.

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Robert Charles Debbie Ngawera-Packer said TTR should have done the right thing a long time ago.

In his decision, Judge Brian Dwyer said he did not consider the information a trade secret and the public interest outweighed that of Trans Tasman Resources.

The company said it would release all the redacted information as soon as possible.

The EPA had already bowed to pressure from Kasm and Ngati Ruanui and extended the submission period on the application by two weeks, but they declined to release the redacted information in October, which sparked the legal action.

TTR The 66 square kilometres off the South Taranaki coast where Trans Tasman Resources have applied to mine iron ore.

Kasm's chairman Phil McCabe said the decision was a massive win for the group.

"The court ruled that public interest outweighed any trade secret by a considerable margin," he said.

"Yes having this information is important but I think the bigger win is confronting the issue of transparency."

McCabe said TTR had bullied the EPA into allowing certain parts of its application to remain secret.

"Secrecy is not okay particularly in a public process about a publicly owned resource," he said.

Ngati Ruanui general manager Debbie Ngarewa-Packer said Environment Court had "done the right thing".

"To be honest it was quite a nerve-racking process, we didn't know which way the judge would go," she said.

"TTR should have done the right thing a long time ago, they shouldn't have forced three parties to come together and oppose this."

Ngarewa-Packer said the iwi wasn't opposed to big business - they've worked with oil and gas companies for years - but transparency was lacking in TTR's application.

However, Kasm and Ngati Ruanui aren't stopping the fight there, they're going to petition the EPA to again extend the submission period so the public had more time to view the newly released information.

A TTR spokesperson said it was inappropriate to comment on the EPA process and could not confirm whether they would appeal the court's decision or not.