The scope of work for Ok-Tedi was to conduct modelling of the grinding circuits to assess the benefits of adding recycle pebble crushing to the existing SAB circuits and to conceptualize and estimate, to a scoping level, the cost of implementing the upgrade.
Traditionally processing very soft ore types, recycle crushing was not necessary to the success of the Ok Tedi grinding circuits. However, with future ore types becoming more competent, it was envisaged that the circuits would become SAG mill limited in the future with a corresponding reduction in throughput. It was anticipated that recycle crushing would relieve the SAG mill restriction, allowing throughput to be maintained and ensure that good energy efficiency could be maintained.
When the modelling was completed, the existing circuit was found to swing between being SAG mill limited and ball mill limited, depending upon the ore blend being treated. The high variability in the ore competency and ore SG contributed to the power imbalances in the circuit. The power balance was also highly dependant upon the product size being targeted
Due to the challenging site location and layout, the capital costs involved with this project were found to be significant when compared with the modest throughput increases predicted by the modelling with the addition of a recycle crusher. In order to achieve significant throughput increases, the overall power available in the circuit would need to be increased substantially, by way of more grinding power