Wellington, Oct 21 NZPA - Environment Minister Nick Smith has acknowledged a potential problem with outdated mining licences that the Environment Commissioner says could cause major environmental damage.

Environment Commissioner Jan Wright released a report today recommending the Government tighten up "weak and unenforceable" environmental regulations on 111 mines around the country.

Dr Smith accepted it was a major issue.

"I have asked officials to go away and consider whether we have to have a re-look at those provisions and the way those mining licences work," he said.

"The Government is looking at reviewing that underlying principle that says that with a old mining permit you can't change the provisions, I think there does become a time where changing the conditions does become a problem."

Dr Wright said during her independent inquiry, she discovered the licences were still operating under old mining legislation, so were exempt from environmental regulations under the Resource Management Act.

Some of the licences were granted for up to 100 years with the longest not due to expire until 2062 .

Conservation land is being used on at least 55 of the 111 licences, which include mining for coal, brown coal, gold, silver, gravel and aggregates.

The amount of land covered by the mines totalled 20,734 hectares, including 3019ha of Department of Conservation (DOC) land.

The Green Party was scathing of the report and said it did not address the elephant in the room, which was the environmental impact, particularly of coal as a climate change pollutant.

"Mining has a massive impact on the environment: coal is the dirtiest fuel, large mines leave weeping wounds and scars on the landscape, and mining our conservation lands is incompatible with protecting them and our tourism industry," Green Party MP Jeanette Fitzsimons said.

"Mining more and more coal is disastrous for the climate -- our children will not thank us."

However, Ms Fitzsimons welcomed Dr Wright's recommendation to review the 111 licences that were described as "weak", "outdated" and "often unenforceable".

"Reviewing these licenses is long overdue, and has been ignored by successive governments for decades. However, even modern mining laws give mining special privilege, and this Government is keen to give away more conservation land to mining."

Ms Fitzsimons said the report did not consider the impact of the mine on endangered species such as the rare giant snail, Powelliphanta augusta.

Dr Wright said that topic was too large for the report she undertook to write and would need to be researched separately.

Forest and Bird advocacy manager Kevin Hackwell while the organisation supported the commissioner's view the Government must act to address the problem of old licences, it was disappointed her report failed to address the threat to the giant snails due to mining of their habitat by State-owned Solid Energy at the Stockton Mine on the West Coast.

The report commended Solid Energy for reducing its pollution of water running off the mine, but Dr Wright said it was too early to tell if soil and vegetation rehabilitation was likely to be successful.

Solid Energy chief executive officer Don Elder said the report was an endorsement of the commitment and work to bring about a demonstrable improvement in the company's environmental management over the last five years.

Energy Minister Gerry Brownlee said Solid Energy's improvements to their environmental impact since 2005 showed a " high degree of environmental sensitivity".

"I think it's even better when we consider that that operation has been there for over 100 years and so that's 100 years of degradation of the rivers and in the last few years they've got things back so the whitebait's back in the river, fantastic."