Author: Steven Lange
Conference: Mine Closure 2019
Date: September 3-6, 2019

ABSTRACT
The Animas River in the area around Silverton, San Juan County, Colorado has been adversely impacted by high loading of iron, aluminium, cadmium, copper, lead, zinc, arsenic, and nickel. Metals loading in the Animas River has limited aquatic life, including the trout fishery downstream from Silverton. The metals concentrations in the Animas River is due to acid rock drainage formed from a combination of natural weathering of mineralised rocks and residues from over 100 years of historic mining. Sunnyside Gold Corporation (SGC) was formed and acquired the Sunnyside Mine in the Upper Animas basin in 1985. SGC operated the mine from 1986 until 1991 using modern techniques and under strict environmental regulation, and has engaged in more than 30 years of reclamation and remediation in the Silverton Caldera. This included removal of mine waste from owned and other area mines, treatment of water discharged from mine portals, seasonal treatment of the flow in Cement Creek, installation of bulkheads in mine workings, and stabilisation of tailings deposits. Evaluation of long-term monitoring results demonstrates that SGC’s actions have substantially reduced acid rock drainage and metals loading in the Animas River compared to what would have otherwise been the case.

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