This paper reports the results of a study of two tailings, under desert conditions in the III. Region of Chile. Both tailings received significant amounts of man controlled water from the hill side above, after operation had ceased. Sampling was undertaken with a soil sampling equipment up to a depth of 8 metre. The samples were analyzed by x-ray diffraction and ICP-MS. Sampling observation in the field showed a zonation inverse, known in humid climates zones, in which the oxidation zone lies above an accumulation zone and a basal primary zone. In the studied tailings the stratigraphic column changes from a homogenous primary zone at the top, to an inhomogenous zone with intercalations of oxidized layers, to a very homogenous oxidation zone at 5-8 metre depth. The pH changes from 7-8 to 4 and the grain size from fine sandy to clayey between the primary and the oxidation zone. These zones are directly related to the water level in the tailings. X-ray diffraction analysis has confirmed that sulphides such as pyrite are only present in the primary zone; whereas gypsum and jarosite are present in the oxidation zone. The latter indicate the influence of sulphate rich acid solutions, resulting from the oxidation of pyrite (known as acid mine drainage - AMD). The element distribution indicates also a sulfide oxidation zone. The distribution of environmentally unhealthy heavy metals shows an accumulation at the uppermost parts of the oxidation zone, as a result of "unspecified" adsorption (surface) on the Fe(IIl)hydroxides and / or of sulphide precipitation. Below in the homogenous oxidation zone, heavy metal distribution is also homogenous and the metal contents are much higher than in the primary zone, which indicates a "specified" adsorption (incorporation in the crystal system, stable at low pH) and a geochemical equilibrium. The results show clearly that the geochemical processes in the studied tailings are directly related to the man controlled water input. The detected processes are related to pyrite oxidation and show a strong mobilization of all types of elements. The distribution of elements is interpreted to indicate an upwards migrating oxidation zone, characterized by the precipitation of Fe(IIl)hydroxides from Fe(II), metal rich solutions, and a water flow confined to the top of the oxidation zone.