Mineralogical characterization related to physicochemical conditions in the pyrite-rich tailings in Guryong Mine, Korea

The detailed characterization ofmineralogical changeswith depth in pyrite-rich tailings froman abandoned mine provides insight into the future geochemical progression of the tailings. Based on the pH and mineralogical characterization, the Guryong mine tailings can be divided into four zones: jarosite zone, iron (Fe)-sulfate zone, Fe-oxyhydroxide and gypsum-bearing pyrite zone, and calcite-bearing pyrite zone. The jarosite zone was approximately 50 cm deep from the surface and had secondary gypsum (CaSO₄·2H₂O) and jarosite [KFe₃ (SO₄)₂(OH)₆]. The pH of the jarosite zone ranged from 2.3 to 4.0, and the ratio of total Fe to total sulfur (S) ranged from 0.7 to 4.3. These results show that the solid phase, schwertmannite or jarosite, is associated with the total sulfate (SO₄) content. The Fe-sulfate zone had low pHvalues caused by strong pyrite oxidation and greatest amounts of the secondary minerals and acid-leachable heavy metals. The Fe-oxyhydroxide and gypsum-bearing pyrite zone reflects partial alteration of pyrite resulting in the coexistence of secondary gypsum and primary pyrite. The calcite-bearing pyrite zone had pH values exceeding 7.0 at greater depths and contained primary calcite (CaCO₃). However, the GS6 and GS10 profiles, which contained coarse particles near the water table, were the most acidic and their calcite contents were not dectected. The oxidation of pyrite is the most important factor in the mineral cycling of Guryong mine tailings, controlling the changes in pH, the precipitation of secondary mineral phases, and the behavior of heavy metals through the profile.