Grinding Circuit Improvements at Gold Fields’ Granny Smith Operation
The Gold Fields Granny Smith mine in Western Australia has a long history of collecting high quality grinding survey data from which to make circuit improvements. This started when the semi-autogenous grinding (SAG) mill was originally operating at the Placer Dome Kidston mine, after being relocated to Granny Smith for Barrick Gold and continuing now under Gold Fields Australia ownership.
With the assistance of SRK, Granny Smith achieved incremental crushing and grinding circuit improvements based on frequent survey data as well as stabilising/optimising control methods. They have operated their circuit under a wide variety of configurations, tonnages, and feed sizes over the past eight years and met expectations when benchmarked against theoretical specific energy estimates.
To date, they can directly attribute an increase in gold recovery to these grinding circuit changes, while having to operate within a limitation on the cyclone overflow % solids (due to a lack of pre-leach thickening). One of the reasons for their circuit stability is the very fine secondary crushed product size they are sending to their grinding circuit. This allowed them to reduce the SAG mill media size and operate at a slower speed without the rock load building and destabilising the mill. In turn, this provided spare mill capacity which can be used to assist the ball mill. One of SRK’s recommendations under consideration is returning a portion of the cyclone underflow back to the SAG mill. The spare mill capacity can then be applied to the material without the need for dilution water – and maintaining the required leach feed % solids.
After each stage of optimisation, SRK conducted full surveys of the grinding circuit to confirm the improvements and to benchmark current operational efficiency against historical performance. It is safe to say that the Granny Smith comminution circuit has a well documented history with further plans for improvements in the future.
