Works paused at contentious Tas mine site

A company behind a controversial mine expansion plan in Tasmanian wilderness has stopped works at the site after legal threats from conservationists.

Majority Chinese government-owned Minerals and Metals Group (MMG) wants to build a new tailings waste storage dam in the Tarkine rainforest.

The federal Environment Department ruled earlier this week that the proposal must undergo a full assessment under the Environment Protection and Biodiversity Conservation Act.

It prompted the Bob Brown Foundation and state and federal Greens members to call on MMG to cease all preparatory works at the site.

Dr Brown said any continued works at the site would be against the law given the assessment ruling.

"We reject any suggestion we have acted unlawfully and our works at the proposed tailings storage site have been limited to track work without any impact to 'old-growth' forest," MMG said in a statement issued on Wednesday.

"However, we have been forced to pause our works at South Marionoak whilst we deal with unwarranted legal threats from the Bob Brown Foundation.

"Our current approvals cover this work under state legislation and are necessary for compliance with Commonwealth assessments.

"We will continue to work with the government in relation to the approval requirements for the project."

In a letter sent to MMG on Tuesday, the Bob Brown Foundation says the company's track upgrades include road grading and cutting trees at the side of the road.

The foundation questioned whether such work is legal considering the assessment ruling and threatened to take the matter to the Federal Court.

"(MMG's) sudden cessation of work after receiving our letter indicating we would take court action indicates that their own legal advice concurs with ours," Dr Brown said in a statement.

More than 60 activists have been arrested at protests at the site in the state's northwest over the past seven weeks.

The planned dam would involve piping mining waste some 3.5 kilometres to a proposed 140-hectare reservoir. In the process, as much as 285ha of wilderness, including rainforest, would be cleared.

"Our intent has always been to find the most balanced solution for Tasmanians, our 500 employees and the township of Rosebery," MMG's statement said.

"We believe decisions need to be made based on the best of science and proper analysis and not any one view."