Throughput decline reversed, and revenue increased by $150M through the application of SMC-Test-related technology.
The Batu Hijau mine, formerly owned by Newmont but now run by Amman Minerals, is the second largest copper and gold mine in Indonesia. Since its start up in 2000 it has produced over 3.6 million tonnes of copper and 8 million ounces of gold. Its concentrator has a grinding circuit comprising 2 parallel lines in SABC configuration. Nominal treatment capacity is 120,000 tonnes per day.
Batu Hijau has a long history of applying geometallurgical techniques to consistently estimate long term mill throughput, normally to within ±2% accuracy. This predictive ability had provided mine management with a solid foundation for identifying operating and design criteria for short term grinding circuit optimisation and future expansions. However, early in 2008 their grinding circuit throughput forecast model began to show signs that it was predicting higher throughputs than the mine was able to deliver in practice, a problem that by the end of 2008 led to a production shortfall of 6 million tonnes of ore (Wirfiyata and McCaffery, 2011). At 2008 copper and gold prices this is equivalent to a loss in annual revenue of an estimated $US150 million.
A review of the model was therefore undertaken. One of its principal findings was that the point load index, which had historically been used to characterise the SAG mills’ response to changes in ore hardness, was failing to identify that the SAG mill throughput was reducing as the mine progressively developed a new, lower copper grade zone in the pit. An extensive ore characterisation campaign was therefore mounted using the SMC Test. The results confirmed that the lower grade ore was indeed significantly harder from a SAG mill grinding perspective. The grinding circuit throughput forecast model was therefore modified such that the point load index was replaced with the SMC Test’s ore strength parameter – DWi. The result was that the following years mine plans were modified such that the grinding circuit was able to meet budget throughput targets to within an average of 1.2%, thereby avoiding the previous revenue losses.
Wirfiyata, F and McCaffery, K. 2011. Applied geometallurgical characterisation for life of mine throughput prediction at Batu Hijau. SAG 2011, Vancouver. University of British Columbia: Vancouver.