English

Abstract

A study of an acidic lake (pH ~1) resulting from the deposition of copper leaching spoil waters and acid mine drainage of the Zn-Pb (-Ag-Bi-Cu) deposit Cerro de Pasco is presented. The data shows for the lake water concentration ranges and mean values of 1440-7180 (4330) mg/L Fe, 33.5-105 (87) mg/L Cu, 180-746 (493) mg/L Zn, 13-63 (48) mg/L As, 2.2-5.3 (2.9) mg/L Pb, 11205-42300 (29250) mg/L SO4 −2 and an acidity of 14480-21440 (16775) mg/L CaCO3. Lake water mean values did not differ significantly from values measured for discharge water. Within the lake water body most element concentrations increased with water depth. Infiltrated acidic waters dissolved the limestone bedrock under formation of argillaceous gypsum, overlying dissolving calcite. In the precipitating gel-like matter and upper parts of dissolved bedrock, heavy metals enriched in composition to the lake water. X-ray fluorescence data show for this kind of sediment concentration ranges and mean values of 0.76-12.38 (5,98) wt% Fe2O3, 51-3980 (1301) mg/kg Cu, 275-8034 (3822) mg/kg Zn, 43-5781 (898) mg/kg As, 21-1310 (261) mg/kg Pb, 0.7-11 (6.2) wt% S. Heavy metals are most likely fixed by organic matter (15 wt% TOC) in form of chelate complexes. The high amounts of organic carbon in the upper part of the sediments most likely results from the discharged spoil waters of the Cu extraction plant. Hydroxides formed during first steps of the infiltration of the bedrock dissolve during later steps of the lake water bedrock interaction.