The Costerfield operation is located in Victoria, Australia, within the Costerfield mining district, approximately 10 km northeast of the town of Heathcote, Victoria. Purchased in 2009, Mandalay Resources immediately restarted capital development and mining. By 2013, through extensive improvements and investments in mining and processing methods, the processing plant's capacity was expanded to approximately 13,000 tonnes per month from 5,000.
The Augusta mine has been operational since 2006 and was the sole ore source for the Brunswick processing plant until December 2013, when ore production started from the Cuffley deposit located approximately 500 m to the north of the Augusta mine workings. The Brunswick deposit is being mined in conjunction with the Youle deposit, which produced its first ore in August 2019. Mandalay Resources expects Youle to be the sole ore source by the third quarter of 2020.
The mining method employed is long-hole stoping with cemented rock fill. Ore is accessed by a primary spiral ramp. Level spacing is at 10 m centers and horizontal development is advanced in a minimum of 1.8 m wide drives in both directions of the deposit. Levels are then mined out on retreat with long hole stopes drilled to a minimum width of approximately 1.5 m. The stopes are subsequently backfilled with cemented rock fill to supply stability, reduce dilution, and allow for mining above and below developed levels.
Ore is trucked on the surface from the Augusta mine portal to the Brunswick processing plant, where it is stockpiled and blended into the processing circuit. Costerfield is currently planning a second mine portal at Brunswick. The circuit includes primary mobile crusher, primary and secondary ball mills, rougher, scavenger, cleaner flotation, gravity circuit, and filtering. Gravity gold concentrate is sold to a refinery in Melbourne, Victoria, and gold-antimony flotation concentrate is trucked to the port of Melbourne and shipped to a smelter in China.