The use of zinc as a cementation agent for gold from ammoniacal-thiosulphate solutions has been studied. The experimental variables investigated were: (i) pH (9-10.5), (ii) thiosulphate concentration (0.05-0.4 M), (iii) temperature (5-50 degreesC), (iv) presence of zinc in the system (both as cementation agent and in the gold solution), (v) presence of Cu(II) (0-0.05 M) in the solution, and (vi) [NH3]/[S2O32-] molar ratio in the aqueous solution. The cementation process was considered to be under diffusion control. A generalmechanism for gold cementation is proposed. (C) 2004 Elsevier Ltd. All rights reserved.