McArthur River Mining is facing a maximum $1 million fine following the leak of thousands of litres of fuel from a storage tank on site.
AAP reports the Xstrata subsidiary notified the NT Government of the spill at its McArthur River zinc mine last year.
The leak was detected from a pipe connected to a storage tank, and according to AAP the Government said the valve had been open for two days and 27,000 litres of fuel had escaped.
Xstrata also recently announced plans to resume operations at its Blakefield South coal mine in NSW.
The project was closed last year due to a fire, which union officials said was the result of an explosion or ignition of methane.