The question of ultimate recovery in heap leaching operations is always of particular concern with respect to economic considerations. Of course, the particle size distribution is a critical factor which determines ultimate recovery and which must be established based on a balance between the extent of mineral exposure and transport phenomena. Now it seems that the ultimate recovery for a given particle size distribution can be established from mineral exposure analysis by X-ray microtomography (XMT). Using recently developed software, micro-computed tomography (CT) data can be used to determine the fraction of mineral exposed and thus the ultimate recovery. Examples of mineral exposure analysis are given for the copper heap leaching operation at Zaldivar, Chile. (C) 2003 Elsevier B.V. All rights reserved.