In the course of ore mineral treatment large amounts of mineral residues will be deposited in tailings
dams. The spilled material might contain some amount of valuable as well as hazardous material. The spilling process generates vertical and lateral mineral and grain size fractionation. Mine tailings therefore show distinct chemical and mineralogical pattern along the spilling path and across the same, completely different from the initially spilled material. Spilling pulses and migrating spilling points cause local enrichment of individual phases such as sulfides, micas, etc. After deposition these finely laminated mine tailings are exposed to alteration. Alteration is not homogeneous. The variable degree of water saturation and the position of the oxidation front are basically due to inclination of lamina, and to changes in grain size along the transport path. But even at the relatively coarse rim intercalated fine grained lamina change the hydraulic properties creating capillary barriers, lamina with enhanced water retention capacity etc. Alteration occurs in microenvironments at the boundaries of lamina contrasting in grain size, porosity, saturation, mineralogy redox, pH, and chemistry. The dissolution, oxidation, and hydration of minerals cause a loss and gain of volume, , generating micro-porosity within minerals and clogging pores at different positions respectively. In this paper, optical microscopy, automated mineralogy using a FEI-ESEM based mineral liberation analyser (MLA) system on dry polished thin sections, and image analysis are combined to define characteristic features such as porosity, primary and secondary phases, grain size, and mineral assemblages for individual lamina to highlight boundaries of contrasting features being responsible for the development of micro-hardpans. The aim is to develop new strategies for auto-remediation, and to localize zones of anomalous enrichment of potentially valuable metals.