Mechanisms involved in bioleaching of an aluminosilicate (95% of spodumene) by heterotrophic microorganisms were investigated. Two moulds (Aspergillus niger and Penicillium purpurogenum) and a yeast (Rhodotorula rubra), all isolated from the mineral, were assayed. The mineral was put into the bioleaching medium under two different conditions: free or into a dialysis tube. The bioleaching mechanism for A. niger or P. purpurogenum was related to the production of low molecular weight metabolites, mainly organic acids. In contrast, bioleaching by R. rubra was related to its metabolic activity and to structural macromolecules of the capsule and the cell wall. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.