In this study, the effect of bentonite and kaolinite minerals with low and high crystallinity on pulp rheology and the flotation of copper and gold minerals was investigated. It was found that clay minerals modified the pulp rheology depending on the type of clay minerals present. Bentonite, a 2:1 structured clay mineral increased pulp viscosity more significantly than kaolinite, a 1:1 structured clay mineral, and poorly crystallized kaolinite increased pulp viscosity more than well crystallized kaolinite. It was also found that pulp rheology modified by clay minerals was strongly correlated with copper and gold flotation. The higher pulp viscosity corresponded to the lower copper recovery. While high pulp viscosity was related to the decreased gold flotation, slightly increased pulp viscosity by clay minerals enhanced gold flotation. (C) 2014 Elsevier Ltd. All rights reserved.