The federal government has told Energy Resources of Australia that it cannot resume processing uranium until regulators are happy with the integrity of the Ranger mine site at Kakadu following a massive leak of toxic slurry.
The Australian government suspended processing operations at the Northern Territory mine after a leach tank with a 1.5 million litre capacity burst and spilled out a radioactive and acidic slurry at 1am on Saturday.
ERA have not yet said how full the tank was at the time.
"I have told ERA that they cannot resume processing at Ranger until the company demonstrates the integrity of the processing plant to the satisfaction of the regulatory authorities," Industry Minister Ian Macfarlane said in a statement on Monday.
He said ERA must also prove that Kakadu National Park and human safety are protected.
"I understand the concerns of traditional owners and local residents and can assure them that governments will continue to ensure the mine operates to the highest standards."
About 30 people attended a snap rally at ERA's Darwin office on Monday, where the director of the Environment Centre NT accused ERA of covering up environmental damage caused by the spill.
"I think they're lying," Dr Stuart Blanch told AAP.
"It's clear there's contaminated water from the burst tank on soil."
The Environment Centre NT said the slurry spill overflowed levee banks designed to contain it and got into the mine's stormwater drain system, and want independent scientists to be permitted on-site to determine the damage.
The supervising scientist, who is the federal regulator of the site, has already begun a full investigation.
"Preliminary reports indicate that the spill was contained within the plant area and that there is no threat to the surrounding environment or human health outside the immediate area," Mr Macfarlane said.
But the Gundjeihmi Aboriginal Corporation (GAC), which represents the Mirarr traditional owners of the land, says it has no faith in regulators.
Supervising Scientist Richard McAllister was a water and environmental engineer for an ERA subsidiary for several years during the 1990s.
"There's historically been a revolving door of personnel between the Office of the Supervising Scientist (OSS), the NT government and the company, and it speaks to the need for a clear independent assessment," GAC CEO Justin O'Brien said.
He called Ranger "a hillbilly operation, run by a hillbilly miner with hillbilly regulators".
Bryan Wilkins, regional organiser of the Australian Manufacturing Workers' Union, said that during the tank's construction and installation in 1993 or 1994 the welding was not properly tested.
"I know it wasn't - I was there," he told AAP.
Mr Macfarlane has established a taskforce consisting of the NT Department of Mines and Energy, NT WorkSafe, the Supervising Scientist and the Department of Industry to manage the response to the leak.
There have been more than 200 safety breaches and incidents over the past 30 years at the site, according to the Environment Centre NT, and this is the third incident in the past month alone.