The study of the effect of long-term water cover on the mill tailings of Silver Lake Mill # 1, near Silverton, Colorado

Abstract

Mining and milling of metals were the primary industries in the study area for most of the late 1800’s into the early 1900’s. Wastes from the mining and milling processes are abundant in the area and present significant threats to the environment. Abandoned in 1900, the Silver Lake Mill is located on Silver Lake, southeast of Silverton, CO. Tailings (mill wastes) are located above and below the lake level providing an excellent location to study long term water cover of mill tailings. The project included water samples from the lake, its outlet and inlets plus tailings samples above and below water level. These samples were used to determine if the lake was contaminated and if so, its source. Field parameters of pH, conductivity, temperature, and dissolved oxygen were observed. Samples were analyzed for Al, Fe, Cu, Ni, Zn, Cd, and Pb. All parameters except Ni were found in the lake, but neither the inlets nor the outlets had high enough metals concentrations to be the sole contributor. Examination of these results show that the lake holds contaminated water with an increasing metal concentration at depth. It also appears that the submerged mine and mill wastes contribute most of the metal contamination found in the lake. Lastly, the study has shown that the contamination is generally contained within the lake.