Tasmania's resources minister has blamed a lodging error for his incorrect granting of a lease at the site of a contentious mining proposal.
Chinese-owned company MMG was granted the lease on an access track in the state's northwest, near where it wants to build a new heavy metals tailings dam.
Resources Minister Guy Barnett sent a letter to the Bob Brown Foundation after the conservation group, which has stridently opposed the dam, questioned the lease.
"Following due consideration, I was not empowered to make the decision," the letter, dated September 24, reads.
"In consequence, there has been no valid grant of that lease. MMG has been informed."
The Bob Brown Foundation claims the lease was granted with the goal of shutting down protests.
"This was an attempt to ... lock the community out of an area that MMG and the minister did not want them seeing," campaigner Scott Jordan said.
"Without our intervention, this illegal lease would have done just that."
Minister Barnett said the Bob Brown Foundation continued to muckrake and misinform the community about mining.
He said MMG recently made the application for the mining lease over an existing access track to its South Marionoak site under the Mineral Resources Development Act 1995.
"The application was assessed by Mineral Resources Tasmania, which recommended it be approved - a recommendation I subsequently accepted," Minister Barnett said.
"A lodging error in the application was then found by the department and immediate action was taken. MMG were advised and submitted a new application."
The new application is currently being assessed and Mr Barnett said a comprehensive review of the tenement application would be undertaken.
"I'm further advised that the act allows for mining lease applications to be made to allow for access purposes and that this is not uncommon practice," he said.
Acting Premier Jeremy Rockliff brushed aside suggestions from the state Greens that Mr Barnett should resign.
"This is a minor administrative error ... Mr Barnett is an outstanding hard-working minister and will continue to be so," he told reporters.
MMG was forced to halt preparatory works at the site in July after court threats by the Bob Brown Foundation over their legality.
The federal Environment Department in July ruled the dam must undergo a full assessment under the Environment Protection and Biodiversity Conservation Act.
The proposal would involve piping mining waste some 3.5 kilometres to a 75-hectare dam. At least 140ha, and as much as 285ha of wilderness, would be cleared.