The Minister for the Environment has been urged to rule on a "cunning" bid to prospect and possibly mine a vast area of seabed directly off the West Coast.

Trans-Tasman Resources, which spent $65 million in a failed bid to mine ironsands from the South Taranaki seabed, has shifted focus to now apply for a prospecting permit here.

But because the permit area falls within the 12-mile nautical limit, it will not need a marine consent from the Environmental Protection Agency (EPA) if it proceeds to the mining stage.

The EPA has previously rejected two applications for seabed mining within the exclusive economic zone, one from Trans-Tasman and another from Chatham Rock Phosphate.

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By coming in under the 12-mile limit, Trans-Tasman would only need resource consent from the West Coast Regional Council.

For now, Trans-Tasman is in the initial stage of getting the exploration permit.

"They are being cunning by only applying for an area within 12 nautical miles (limit), which is within West Coast Regional Council jurisdiction under the RMA," Green Party mining spokeswoman Eugenie Sage said today.

The Minister for Environment could rule and have it dealt with by the EPA "given (the regional council's) lack of expertise and the EPA's much greater expertise on the impacts of the proposal and its high risk," Ms Sage said.

EPA spokeswoman Tanya Piejus confirmed the authority was responsible for managing the effects of specified restricted activities on the environment in the exclusive economic zone and continental shelf. That started at the 12 nautical mile mark and extended to 200 nautical miles offshore.

The prospecting permit Trans Tasman has applied for covers 4436 square kilometres, extending from Karamea to Ross, from 1km offshore.

Trans-Tasman said in a statement it would focus on developing offshore mineable resources of iron rich mineral sands known to host ilmenite, zircon, garnets and gold. Ilmenite can be used for paint, and garnets for sandblasting.

Andrew Stewart, from Tran-Tasman, said they were in the very early stages of resource investigation.

Getting the prospecting permit

would allow them to undertake activities for the purpose of identifying areas likely to contain deposits of heavy minerals and potentially precious metals.

"As such, it is impossible to say at this stage what the potential type and scale of operations and economic outcomes -- including jobs -- could be."

Prospecting would be undertaken over a two-year period and include activities such as collating relevant information, literature reviews, undertaking geological modelling and potentially conducting surveys such as sampling and geophysics surveys.

"As such, these prospecting activities would have almost no impact on the environment," Mr Stewart said.

Beyond the 12 nautical mile mark, the water was too deep anyway.

The company would "actively work with West Coast Regional Council and other key stakeholders prior to the commencement of any field work," Mr Stewart said.