19 Jul Mount Carlton SAG Mill Optimisation
The Mount Carlton gold mine in Queensland’s North East, 150km from Townsville, sits on a high-sulphidation epithermal style deposit rich in gold, copper, and silver. Mt Carlton is an open pit mining operation with ore processed using a primary crusher, single stage SAG mill and flotation to produce a concentrate for sale.
OMC was involved in the original design of the comminution circuit and the project was commissioned in late 2012 with first concentrate shipped in March 2013. The circuit was started up and achieved design targets. When Evolution sort to optimise the project in late 2015, OMC was invited to assist the team by undertaking a circuit review to identify opportunities and set goals for the optimisation.
During 2016 site personnel did excellent work implementing most of the optimisation strategies developed with OMC, which had a significant impact on plant performance.
Pebble ports where removed from the grates, reducing the average ball size diameter and consumption in the mill. The smaller ball diameter reduced impact breakage, allowing the mill to operate at higher speed and under more autogenous conditions. This increased efficiency and utilised more installed SAG mill power. The cyclone operation was changed to constant pressure and the vortex finder size was decreased improving cyclone performance.
The removal of the pebble ports has facilitated a change in the mill operating speed to hyper-synchronous from sub-synchronous prior to the change. This allows higher SAG mill power utilisation. Before the change, the SAG mill power utilisation was about 65.1%. This increased to 72.4% post the grate change. An analysis of production data following the change in 2016 showed 80% SAG mill power utilisation.
Comparing pre and post optimisation production datasets, the impact of the changes became apparent. Removing the pebble ports has reduced the average ball size in the mill, preserving rock media, which has allowed the mill to run 12.7% faster with an 11.3% increase in power draw when combined with a slight reduction in ball charge. This additional power has been used to increase throughput by 2.4% while achieving a 27 µm reduction in product size. This reduction in grind size has been achieved with only a 6.8% increase in specific energy consumption because of a 6.5% average increase in grinding efficiency. The circuit product size also became much more consistent. The changes also lead to a decrease in ball consumption, saving hundreds of thousands of dollars a year in operating cost.
The SAG mill is currently not the circuit bottleneck, achieving the design capacity at a finer than design grindsize. Under the current conditions, ball consumption and energy efficiency has been optimised at the target plant capacity with flow on effects in downstream processing recovery benefits.
The Mount Carlton comminution circuit optimisation was a great success through the teaming of Orway Mineral Consultants with the dedicated staff at Mt Carlton.
Primary Crusher, Stockpile and Pebble Crushers
SAG mill and Flotation Circuit
For more information about SAG mills or communition, contact Orway Mineral Consultants today.