Porcupine Flat Mill centennialminingPorcupine Flat Mill The Porcupine Flat Gold Processing Facility is located adjacent to the Maldon town site 140 kilometres northwest of Melbourne in central Victoria The 150 000tpa CIP plant was originally constructed and commissioned in 1989 by Triad Minerals to treat oxide material from the nearby Union Hill open cut with subsequent milling campaigns including underground sulphide ore