Zeta-potential and settling rate were measured for galena and pyrite in the presence of Ca, Pb and Fe(II) ions, and in the presence of each other. The zeta-potential technique was modified to permit the influence of the minerals on each other to be included. Settling rate was measured by a conductivity-based technique with automated data acquisition, and was used to indicate the level of agglomeration. For the minerals individually, the pH of maximum settling rate (i.e., maximum level of agglomeration) generally, corresponded to the iso electric paint (iep). The added ions consistently increased the iep. The presence of calcium tended to reduce the settling rate of pyrite hut overall the effect of Ca and Pb on settling rate was minor. In contrast Fe(II) significantly reduced the settling rate of both minerals. This is tentatively attributed to hydrophilic surface Fe hydroxy species introducing a force of repulsion. In the case of the mineral mixture, the zeta-potential of the galena in particular was altered becoming more positive above pH 4.5 and more negative at lower pHs. This is attributed to galvanic interaction promoting oxidation products on the galena surface. The pH of maximum settling rate corresponded to the zeta-potential of both minerals approaching zero. When the minerals were oppositely charged the conditions remained (relatively) dispersing. Such studies may open new avenues to understanding the role of agglomeration in limiting mineral separation. Some observations on its role in flotation are offered.