Compania Minera Doila Ines de Collahuasi SCM initiated the development of a new geometallurgical model to characterize its Rosario deposit in terms of its comminution circuit capacity and flotation performance. The comminution component of the model is now complete and is described in detail in this article. The model uses a combination Of Simulation and power-based approaches to relate ore hardness and flotation feed size to grinding circuit throughput. Ore hardness values are provided by Collahuasi's block model which has been populated with ore characterisation data derived from Bond ball work index tests, JK drop-weight tests and SMC Tests (R) on diamond drill cores. The influences of planned and unplanned maintenance downtime are taken into account both in terms of frequency and duration. The accuracy of the model is demonstrated using weekly production data taken from the period January-December 2008, showing an average relative error of 5.2% and an R(2) value of 0.95. The model is now in successful routine use at the mine for planning purposes and is currently in the process of being further developed to incorporate the response of the flotation circuit. (C) 2009 Elsevier Ltd. All rights reserved.