Evolution Mining’s Cowal Gold Operations, located in New South Wales, Australia, operates a large-scale gold processing facility with a conventional comminution circuit consisting of primary crushing followed by semi-autogenous grinding (SAG) and ball milling. The circuit is configured to process a blend of open pit and underground ores and feeds downstream flotation and leaching processes.
Due to the relatively coarse grind size requirement of approximately 180-200 µm, the processing plant is not highly sensitive to grind size variations. Instead, plant performance is strongly dependent on maximising throughput through efficient utilisation of installed milling capacity.
A challenge at Cowal has been the optimisation of SAG mill performance following relining events. During these periods, conservative operating strategies are typically employed to minimise the risk of liner damage. While such strategies are effective in mitigating mechanical risk, they can result in sub-optimal breakage conditions, reduced power draw, and extended ramp-up periods.
Lost throughput during ramp-up directly translates to reduced gold production and economic loss. As a result, improving ramp-up efficiency represents a high-value opportunity for operational optimisation. Following a major shutdown and relining campaign in March-April 2025, an initiative was undertaken to implement a structured, data-driven ramp-up strategy aimed at accelerating recovery to steady-state performance while maintaining liner integrity.
Molycop’s MillROC provided real-time monitoring of key process variables, centralised data visualisation and trend analysis of load, power and throughput. MillSlicer enabled detailed analysis of conditions in which slurry pooling was suspected to be more prevalent with certain parameters, distribution of liner strikes, and charge behaviour dynamics. This information was critical for ensuring that increased operating intensity did not result in excessive liner stress. Ball charge was tracked using power-based estimation models and steel consumption rates. This allowed for accurate and proactive control of charge levels.
Progressive increases in ball charge and mill load resulted in measurable improvements over the first four weeks post-reline. Throughput increased by approximately 14% during the ramp-up period. This improvement was driven primarily by increased power utilisation, improved impact efficiency and enhanced steel-to-rock interaction. The increase in SAG power resulted in improved energy transfer to the ore, higher breakage rates and more efficient comminution.
The structured ramp-up approach resulted in reduced fluctuations in mill load improved control response and more stable circuit operation. Despite increased operating intensity, no abnormal liner damage was detected, and impact levels remained within acceptable limits, while monitoring enabled proactive intervention where required.
The results demonstrate that ramp-up optimisation is an ongoing process. Further opportunities for improvement include refinement of operating parameters for different ore types, integration of ore competency data into control strategies, continued use of advanced analytics tools, and ongoing collaboration between operational and technical teams.
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