Queensland miners may downplay the true cost of mine rehabilitation after a recent court ruling, activists warn.
In 2018, laws were introduced to establish a standardised rehabilitation financial assurance calculator, created by the government, to stop mining companies underestimating the cost by using their own calculators.
Earlier this year a successful appeal in the Land Court of Queensland by Century Mining tested the laws.
The estimated rehabilitation cost (ERC) was $230,465,718 for its Century Mine in northwest Queensland but Century argued its own estimates suggested rehabilitation would cost much less, at $173,271,205.71.
The court ruled the ERC would be $183,916,150.06, saying there was no requirement to "slavishly" comply with the approved calculator and that the department's estimate was merely a guideline.
Activists believe the decision of the Land Court effectively opens the door to mining companies once again calculating their own costs of rehabilitation.
They argue companies will consistently use the ruling to underestimate the costs and improve their bottom line for the benefit of their shareholders.
"This ruling has serious implications for the Palaszczuk government's recent mine rehabilitation reforms," Lock the Gate Alliance spokesperson Ellie Smith said.
"This key reform was in response to documented evidence that mining companies had consistently underestimated the cost of mine rehabilitation when applying their own calculation methodologies."
In a letter to Environment Minister Meaghan Scanlon signed by five conservation groups, activists are calling for urgent action to enact legislative change and ensure mining companies cannot determine their level of financial assurance with regard to mine rehabilitation.
Mackay Conservation Group co-ordinator Peter McCallum says the implications for farmland and the environment also need to be considered.
"If mining companies are allowed to get away with failing to properly rehabilitate mine sites then our environment and farmland in Queensland will be damaged forever," he said.
"There are billions of dollars worth of rehabilitation necessary on Queensland's existing mines. This work creates jobs, so there are tens of thousands of jobs at risk if mining companies fail to rehabilitate properly."
Ms Scanlon has been contacted for comment.