EFFECTS OF MINE REMEDIATION ON WATER QUALITY AND BENTHIC MACROINVERTEBRATES IN THE UPPER ANIMAS RIVER WATERSHED, SOUTHWESTERN COLORADO

摘要

Tributary to the San Juan River, that is a tributary of the Colorado River, the headwaters of the Animas River are located in the San Juan Mountains of southwestern Colorado near the mining town of Silverton. The upper Animas watershed includes three major drainages covering 146 square miles: Animas River above the confluence with Cement Creek, the Cement Creek basin, and the Mineral Creek basin (Figure 1). The watershed has over 2,600 mine sites (including prospects). The upper Animas watershed lies within a highly mineralized Tertiary volcanic caldera where hydrothermal activity has resulted in "acid-sulfate" alteration in parts of the watershed. Mineralization that accompanied the hydrothermal alteration attracted gold and silver miners to the area in the 1870s. Although most of the mines closed during the first half of the 20th Century, one mine continued to operate in Cement Creek basin until 1991. Waters draining the areas affected by hydrothermal alteration are sources of acid and metal loading to the Animas River (Bove et al., 1999).