Australian company De Grey Mining has surrendered its permit to carry out low-impact exploration on a 6500 hectare block in the Russell State Forest.

The company still holds two active permits to investigate mining copper, gold, silver, lead and zinc on blocks in the Puhipuhi hills.

A change of conditions has been applied for and is pending on one of those permits, number 51985.

De Grey's permit 55058 for the "north Puhipuhi" block in the Russell forest was due to expire in 2018.

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However, the company applied to drop that permit in October and was given approval by the New Zealand Petroleum and Minerals (NZP&M, formerly Crown Minerals) on December 17. De Grey Mining declined to comment on why it dropped the 55058 permit, what changes the company is awaiting confirmation of on number 51985, or whether NZP&M-imposed timelines are behind the move.

Jenny Kirk, the co-ordinator of Puhipuhi Mining Action Group said that the ditching of the permit was "interesting".

"We are pleased that the Russell Forest permit has been surrendered because that is important and beautiful bush, and we did not want it disturbed. I imagine that De Greys would not have wanted the controversy surrounding exploration in a state forest," Ms Kirk said.

"But we are still really worried that De Greys continues to hold exploration permits for Puhipuhi. Our concerns about disturbance of the mercury in the Puhipuhi district are as valid as ever, it won't go away."

NZP&M requires annual summary reporting from permit holders and reporting at the completion of particular programmes of work, a ministry spokesman said.

"Compliance with work programme conditions is assessed retrospectively. If a company does not carry out the activity initially proposed in their work programme, NZP&M will assess whether there are valid reasons for this when determining whether they can retain their permit."

Companies may also submit an application for a change of permit conditions as De Grey Mining has done with permit 51985.