The environment minister personally killed off Clive Palmer's coal mine but allowed a delegate to decide on another mine that got the green light.
Tanya Plibersek rejected Mr Palmer's central Queensland coal mine earlier this year under federal environment laws, finding it posed a real risk of causing irreversible damage to the Great Barrier Reef less than 10km away.
But she did not intervene in the decision-making process for the Isaac River coal mine in central Queensland.
A departmental delegate was responsible for provisionally approving that project, the first new coal mine to get the go-ahead since Labor won office.
"Why did the minister delegate that decision rather than making the decision herself?" Greens senator Sarah Hanson-Young asked departmental officials during a budget estimates hearing on Tuesday.
Department of Climate Change, Energy, the Environment and Water secretary David Fredericks said there was a standing delegation from the minister.
"At the end of the day that was the delegation that was relied upon by the department to make a decision," he said.
The hearing was told the decision to stop Mr Palmer's mine was not a delegated decision and the minister decided herself to refuse it.
"Oh, so she makes the ones she wants to make and delegates the ones she doesn't want to make. Is that how it goes?" Senator Hanson-Young said.
Bruce Edwards, the division head for environmental replied: "That's not how it works.
"The minister of course has the power under the legislation. We are her delegates and so we engage with her on a case-by-case basis about whether she wants to take particular decisions.
"The minister, in this case, there's been no indication that she's asked to do that directly so we've proceeded as delegates for that project."
The hearing was told the Isaac River mine was assessed under all tests set out under federal environment laws. It's yet to receive final approval.
