The invention relates to a reverse froth flotation process for treating a calcium carbonate ore containing silicates. The process comprises the use of two collectors selected from the group consisting of fatty tri-lower-alkyl quaternary ammonium compounds, fatty di-lower-alkyl benzyl quaternary ammonium compounds, fatty lower-alkyl di-benzyl quaternary ammonium compounds, di-fatty di-lower-alkyl quats, di-fatty lower-alkyl benzyl quats, and fatty bis-imidazoline quats. The use of a combination of different quats was found to result in a synergetic performance of the collectors.