This paper deals with a weathering profile of carbonate-type tailings (sulfide-bearing carbonate-rich tailings) in Bali tailings storage of the Dahang tin-polymetallic orefield in Guangxi. The storage was closed about 20 years ago. Based on studying the profile using composite geological-geochemical methods such as investigation of fabrics and contents, XRD analysis, Sobek-ABA and NAG test, the authors have reached the following conclusions: ① oxidation of tailings increased from bottom to top of the profile, associated with gradually increasing acidity of tailings, resulting in a layering (zoning) structure: C layer at the bottom was a reduction and primary zone (incoherent tailings without alteration); B layer in middle profile was a suboxidation and base-buffer zone (incoherent tailings with partial alteration); A layer at the top was a oxidization and acidification zone (coherent hardpan, 1～1.5 m in thickness). An acidic-base buffer interface was located between A layer and B layer, higher than the oxidation-reduction interface at the bottom of B layer. ② Acidic-base buffering occurred in B layer, and the base materials were mainly derived from calcite. ③ Neutral efficiency (or real-consumption rate) of carbonate (CaCO3) was about 80%. These phenomena might be attributed to the following reasons: the armor formed by secondary minerals such as lepidocrocite and gypsum during the acidification of tailings caused the development of the rest of carbonate particles and then blocked the neutral reaction of carbonate in tailings. Therefore, it is inferred that the metal-sulfide tailings, even if containing excessive carbonate (base materials), still possess a potential of acidifying and generating acid mine drainage.