Trans-Tasman Resources (TTR) is making another bid to get consents to mine ironsands from the seabed off Patea coast.

It's initial application was turned down by a committee appointed by the Environmental Protection Authority (EPA), which said the science involved in the application was too uncertain about the potential impact of the planned undersea mining process.

But now TTR said it has fresh scientific data and other evidence it hopes will persuade the regulators to change their minds.

The project would involve suction-dredging about 50 million tonnes of ironsand a year from a 66 square kilometre area of the sea floor off the coast of Kakaramea and Manutahi in water between 20m and 42m deep.

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The company, which has a majority of Australian shareholders, spent more than $60 million and seven years prior to the 2014 rejection and appealed the decision unsuccessfully.

The initial application was made to a decision-making committee (DMC) appointed by the EPA, but now TTR says it is preparing its case to be heard by a new DMC.

In a statement, TTR executive chairman Alan Eggers said the company had undertaken a comprehensive programme of additional science and engineering work to update and refine the environmental assessments of its application and how it can be successfully undertaken.

"We are confident this programme addresses all the previous DMC's concerns," Mr Eggers said.

TTR argues its extraction methods are far lower-cost than on-land mining as they involve vacuuming up iron-rich sands and returning around 90 percent of the sand, with iron ore extracted, to the ocean floor. Specialised bulk freighters would then transport the extracted titano-magnetite ore to steel mills, most probably in Asia.

The company said the project would bring some generate around $300 million a year in royalties, tax paid, and export earnings and could support around 1650 jobs in New Zealand.

Key issues dealt with at the two months of hearings in 2013 was the potential environmental impact of sand plumes in the ocean and the impact on the limited range of sea-life capable of surviving in the relatively barren marine environment the consent covered.

Environmental groups were also concerned about whales' migratory habits through the area and possible impact on endangered dolphins.

Kiwis Against Seabed Mining, the principal lobby against the proposal said it was disappointing TTR was making a fresh application.