A simple method for predicting equilibrium composition of leaching systems in hydrometallurgical processing of ores has been developed with the use of spreadsheet. Based on the minimum Gibbs energy principle, the mathematical basis together with a calculation algorithm is described. Example calculations are illustrated for chemical equilibrium of Cu+-CN--H2O systems involving fluid and solid species. The calculated results are consistent with those reported in the literature. The ability to carry out the calculations within a spreadsheet environment is the main advantage of the proposed method and algorithm. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.