The federal environment department ruled earlier this week that the proposal must undergo a full assessment under the Environment Protection and Biodiversity Conservation Act.
The Bob Brown Foundation – which has staged a rolling protest against the proposal for two months – and Greens MPs called on the company to stop works at the site until the assessment was complete.
MMG initially rejected the call, saying it had approval to undertake preparatory works for the tailings dam, but ceased work after receiving a legal letter from the conservation group.
Brown said its legal advice showed MMG had “flouted the provisions of federal environment law” by continuing work before the assessment was complete.
“Its sudden cessation of work after receiving our letter indicating we would take court action indicates that their own legal advice concurs with ours,” he said. “The arrogance of this company proceeding as it has is monumental.”
The company rejected the suggestion it had acted unlawfully, or that its works at the proposed tailings dam site affected old-growth forest. It said it had been limited to trackwork. It had been forced to “pause” its operation while it dealt with what it described as “unwarranted legal threats”.
“Our current approvals cover this work under state legislation and are necessary for compliance with commonwealth assessments,” it said. “We will continue to work with the government in relation to the approval requirements for the project.”
The company did not say how long work would be paused.
MMG said a new tailings dam was needed to extend the life of the 85-year-old Rosebery zinc, copper and lead mine that employs about 500 staff and contractors in Tasmania’s remote north-west.
If the dam is approved, the company expects to clear up to 285ha – roughly equivalent to 350 football pitches – of rainforest and other terrain for both the South Marionoak dam and a 3.5km pipe that would carry toxic waste from the mine across the Pieman River.
The plan is supported by the Tasmanian Liberal government and the local mayor. Opponents say crossing the river would place the tailings dam inside the takayna/Tarkine, a vast and environmentally diverse area that the Australian Heritage Council has recommended should be protected.
The Tarkine’s boundaries remain loosely defined and contested, but based on the heritage council’s assessment nine years ago it covers at least 439,000ha. It includes beaches, buttongrass moorland, wild rivers and unique cave formations, but is best known as home to the world’s second-largest temperate rainforest and Aboriginal shell middens.
Some parts have been mined and logged over a long period, but significant sections remain untouched.
Opponents say there are other options for a tailings dam outside the Tarkine. MMG has said it would “never stop looking at other options” for waste storage, but the proposed site was the only viable option to replace two dams that would be full by 2024.
More than 60 protesters have been arrested in the forest attempting to stop preparatory works for the tailings dam.
The environment minister, Sussan Ley, visited the site last month and had meetings with both the company and Brown before the project was declared a “controlled action” this week that would require a full assessment.