The fine was handed down by the New South Wales Land and Environment Court.
Moolarben was found to have failed to implement appropriate erosion and sediment controls, which in turn led to the pollution leak.
The company pointed out the discharge occurred while the mine was under the control of the mine’s previous owner Felix Resources.
The Bylong Valley Protection Alliance says the court judgement gives them “cold comfort”, particularly in light of Moolarben’s argument about the discharge happening on Felix’s watch.
BVPA secretary Craig Shaw said: “In particular, key consultancy personnel and some Felix Resources directors associated with the inadequate controls that led to the fine for Moolarben are the very same people and entities involved in the proposed Mt Penny project here in Bylong”