UNDERSTANDING THE MOBILIZATION OF METAL POLLUTION ASSOCIATED WITH MINE WASTE MATERIAL FROM A HISTORICAL SILVER MINE IN PERU

Heavy metals in aquatic environments have received considerable attention around the world due to their potential accumulation producing environmental toxicity. Further, many previous studies have shown that the most critical contributor to heavy metal pollution in river basins is mining activity.

This study mainly aims to understand the metal occurrence and mobilization into the surrounded streams from mine waste deposits to propose remediation alternatives in the future. The mine deposit of study is a high sulfidation epithermal deposit that exploits silver from the early 20th century until now. Monitoring programs considered water, sediment, and mine waste samples to describe the effects of historical mining activities in the surrounding creeks and to predict future leaching behavior. The hydrogeochemistry characterization considered the next tests: ICP mass, ABA, SPLP, WRA, Mineralogy, Humid cells, and Phreeqc modeling.

As preliminary results, mine waste material contained high concentrations of sulfide, mainly as pyrite, marcasite, sphalerite, and galena, being the responsible for acid mine drainage generation, and carbonates (primarily limestone). Weathering cell tests carried out on various mine waste materials produced two types of contaminated drainage: acidic and neutral. The most abundant trace elements found in the leachate test were As (0.81 mg/L), Cd (0.1 mg/L), Fe (5.45 mg/L), Mn (34.43 mg/L), Zn (12.83 mg/L), and Pb (0.84 mg/L). Kinetic tests allowed us to identify four geochemical processes; the fourth determined the continuity of acid production, sulfide oxidation such as pyrite, chalcopyrite, and goethite, increasing sulfates, Fe, Cu in leachates. Additionally, water samples presented maxim concentration of Fe, Cd, Pb, and Mn higher than environmental standards. The geochemical modeling results show rivers water quality was only slightly changed with a variation for change in weather season after ten years (mine life remaining) of model simulation.

Finally, the study demonstrates an impact from the leaching of mine waste material to the surrounding streams, mainly due to sulfidic oxidation. Furthermore, it identified geochemical processes that govern the mobility of different metals. This information is useful to propose remediation alternatives in the next stage of the study.