The chaotic behaviour of particle drift orbits ending on the target plates in a poloidal divertor tokamak is studied. The source of the chaotic motion is taken to be the non-axisymmetric magnetic field perturbations. As is well known from the Chirikov-Taylor-map studies, near the separatrix, the perturbed magnetic field lines also develop a structure with various islands immersed in a chaotic sea. Following ion drift orbits across such a separatrix layer, it is shown here that particle orbits also develop both chaotic and coherent layers. Hence, the ion heat flux transported along such orbits displays a corresponding inhomogeneous distribution over the divertor plates. (C) 1999 Elsevier Science B.V. All rights reserved.