Mineral surveying in world heritage sites on the West Coast will go ahead – but Prime Minister John Key has ruled out mining there.

As revealed by The Dominion Post yesterday, aeromagnetic surveying will be conducted in the South Island from Haast to Karamea, including large chunks of Te Wahipounamu South West New Zealand world heritage area, which takes in Aoraki-Mt Cook and Fiordland.

It follows a similar project in Northland last year, when more than 13,590 square kilometres were surveyed.

A competitive tender process for exploration permits for metallic minerals in Northland has since been announced.

Forest & Bird Far North branch chairman Dean Baigent-Mercer said the assurances being given now were the same as those used in the north two years ago.

Northland was now being marketed to international mining companies, he said.

"One of my personal great regrets is that we didn't get ahead of this issue and prevent the survey plane from going up, because now it's compounding into a really massive social and environmental problem."

The surveying went on without consent on private land and areas subject to Treaty claims. "These people don't spend a huge amount of taxpayers' money for nothing to happen."

Parts of Te Wahipounamu, a world heritage area as designated by the United Nations Educational, Scientific and Cultural Organisation (Unesco), will be included in the West Coast surveys.

There was public outrage when plans to look for minerals in areas protected by Schedule 4 of the Crown Minerals Act were announced in 2010.

The Government backed down and eventually ruled out mining in areas protected under the schedule.

Mr Key yesterday made the same pledge for world heritage areas. "I can give you an assurance we won't be mining on world heritage sites."

The survey was being undertaken in world heritage areas because there were other benefits from gathering the information, he said.

But Schedule 4 land would not be surveyed. "What we are doing is gathering information for a variety of other reasons."

Unesco's natural sites advisory body, the International Union for Conservation of Nature, called on the Government last year to prevent mining in world heritage areas.

The Greens also want world heritage sites made off limits for mining, and Labour Party conservation spokeswoman Ruth Dyson said such areas should be out of bounds.