In the production of ground calcium carbonate (GCC) for the paper industry, any colouring contaminants must be removed during processing (usually flotation) to achieve sufficient GCC brightness. Flotation of GCC feedstock is characterised by the presence of both particulate and dissolved calcite (CaCO3), an alkaline pH and the use of amine collectors. This paper investigates the possibility of removing pyrrhotite and pyrite, under these conditions. Microflotation results show that the recoveries are highly dependent on pH. Pyrrhotite recovery decreases dramatically when going from pH 8 to pH 10. Pyrite display high recoveries at pH 8 and 9, and lower recoveries at higher pH. Recoveries were dependent on conditioning time. Pyrite floats considerably faster than pyrrhotite at all pH levels investigated, whereas pyrrhotite seems to be slow floating and could benefit from prolonged flotation times. Compared to the saturated CaCO3 system, flotation recoveries decreased when using deionised water or CaCl2 solution. The flotation results could not be fully explained by zeta potential. Bench scale flotation experiments on a sulphide bearing marble, confirmed the microflotation results at low collector concentrations (i.e. 200 g/t). By increasing the amine concentration, the flotation performance became independent of pH. (C) 2014 Elsevier Ltd. All rights reserved.