The invention relates to a process for the preparation of coating dispersions for use in the paper industry by co-grinding natural calcium carbonate (GCC) and precipitated calcium carbonate (PCC), characterized in that powdery GCC is co-ground with a slurry containing from 5 to 70% by weight of PCC to obtain a particle size distribution of the calcium carbonate with at least 90% by weight of smaller than 5 μm, at least 70% by weight of smaller than 2 μm, and at least 20% by weight of smaller than 1 μm, with a weight average particle size within a range of from 0.7 to 3 μm.