WATER MANAGEMENT FOR ACID MINE DRAINAGE CONTROL AT THE POLYMETALLIC DEPOSIT OF CERRO DE PASCO, PERU

The geochemical and mineralogical study of the Quiulacocha tailings impoundment has shown that the hydrological connection of the three mine-waste systems at Cerro de Pasco (Excelsior, Quiulacocha, Ocroyoc) is the most critical concern for the waste management. The Quiulacocha tailings cover 114 ha, comprising 79 Mt of tailings, which contain ~ 50 wt % pyrite. The tailings are located at 4340 m altitude in a tropical puna climate with about 1025 mm/a rainfall. The tailings are partially overlain by the Excelsior waste-rock dump, which contains about 26,400,000 m3 of waste rocks that cover 94 ha and contain ~60 wt % of pyrite. In the Quiulacocha impoundment there are two different types of tailings recognized: 1) Zn-Pb-rich tailings and 2) Cu-rich tailings. During the sampling campaign, the Zn-Pb-rich part of Quiulacocha was not producing important excess of acid mine drainage (AMD) from the oxidation zone, where pH is increased to near neutral values at 1 m depth. The underlying tailings were still able to neutralize the acidity, produced in the oxidation zone through sulfide oxidation, by the underlying carbonates (dolomite and siderite). The main source of AMD in this mine-waste system is from the Excelsior waste-rock dump. Its acid seepage infiltrates into Quiulacocha forming a Fe-Zn-Pb plume with a pH 5.5 – 6.1 and containing up to 7440 mg/L Fe, 627 mg/L Zn, and 1.22 mg/L Pb. The plume was detected between 10 m to 13 m depth in the stratigraphy of Quiulacocha. Additionally, the AMD seepage fro