Factors related to the genesis of the fine fraction of till were investigated by means of grinding experiments. Eleven 40 kg till samples were sized into the < 0.06 mm and 0.06–8 mm fractions using plastic sieves. Grinding experiments were carried out on the coarser fraction using a centrifugal ball mill with a zircon oxide mill chamber. For sandy till, the method was considered to be a valid simulation of till genesis because grinding the coarser fraction produced an artificial fine fraction (AFF) similar in chemical composition to the natural fine fraction (FF). The same was not found for till rich in clay because a considerable part of the natural fines in clayey till has not been generated through comminution but is actually resedimented preglacial material. The first part of the study investigated the effect of mechanical processes on the composition of the FF. Differences in degree of grinding were intended to simulate differences in transport distance. An increase in the degree of grinding increased the production of the AFF. As the degree of grinding increased, the concentrations of Co, Cu, Fe, Mn, Ni and Zn in the AFF decreased as a negative exponential function towards the overall composition of the coarser fraction (0.06–8 mm). The change in the chemical composition reflected the comminution of the component minerals in the order: mica, amphibole, feldspar, quartz. The entrainment of debris by a glacier was modelled by coarsening the grain size of the feed. The concentrations of Co, Cu, Fe, Mn, Ni and Zn were greater in the AFF produced from the coarsened relative to the normal feed because mica and amphibole were enriched relative to feldspar and quartz. The second part of the study consisted of an investigation of the effect of chemical additives on the grinding of till. Treatment with H 2O 2 before grinding increased the production of AFF; under oxidizing conditions, mica in particular was corroded more effectively than quartz and feldspar, so that the AFF produced from the oxidized sample was enriched in mica relative to the AFF procuded under normal condition. This mineralogical fractionation was reflected in the larger Co, Cu, Fe, Mn, Ni and Zn concentrations in the treated fraction. Oxidation also increased the proportion of plagioclase over K-feldspar in the AFF. Corresponding changes in concentration were not found when H 2SO 4 and NaCl were added during the grinding; rather, through a chemomechanical effect these additives merely increased the mobility of the particles in the mill chamber and thereby markedly increased the production of AFF. On the basis of the results, a model is proposed in which zones in a till that are characterized by high Co, Cu, Fe, Mn, Ni and Zn concentrations and aligned in the direction of glacial transport are areas where the entrainment of basal debris has been dominant over transport and comminution, and vice versa. Regional differences in the strength of the processes are reflected as fluted patterns on geochemical maps.