The JKMRC has been studying and modelling industrial AG and SAG mills for over 40 years, but the ability to simulate the effects of blending hard and soft components on mill performance remains quite limited. In an effort to quantify these effects for modelling purposes, a series of laboratory, pilot scale and full scale tests, using multi-component feeds were conducted under the AMIRA P9O project. The obtained data shows a non-linear trend between the measured mill throughput and the proportion of soft component in the feed, as well as the effect of fresh feed composition in mill product size distribution and load. Therefore, a new multi-component AG/SAG mill model structure was developed to account for these observed effects, and it was validated using pilot and full scale data. (C) 2012 Elsevier Ltd. All rights reserved.