Preliminary results on mineralogical and geochemical changes at the transition between oxidiation and primary (sulfide) zone in copper flotation tailings located in Chile are presented. The tailing Cauquenes (El Teniente) and Piuquenes (La Andina) were sampled down to a depth of 10,4 m with percussion drilling. In both tailings, results of sequential digestions analyses show a similar distribution. In the oxidation zone (jarosite zone) Cu, Ca, Co, Mg, Mn, Pb, Zn are almost completely leached out. Fe and Mo display relatively high values in the oxalic acid and H202 fractions of the oxidation zone indicating that they have been fixed in Fe(III)hydroxides subsequently to the breakdown of sulfides. K is fixed in jarosite. As, Al, and Ba show relatively high values in the oxalic acid fraction in the oxidation zone. The underlying precipitation zone (gypsum zone) is characterized by enrichment of elements leached from the oxidation zone in particular Cu, Co, and Mo. In the basal primary zone, carbonates (e.g. siderite) and sulfides are still stable and no secondary mineral formation is recognized