Preliminary Assessment of Metals Partitioning in Soil and Vegetation in a Subalpine Wetland
The Bismark Mine is located near the headwaters of the South Boulder River in Madison County, Montana (Figure 1). The bedrock of the area is predominantly metamorphic rock of the Archean Pony series, intruded by a tongue of the Cretaceous quartz monzonitic Tobacco Root batholith. The gneiss and the granite are both weakly fissured and mineralized near the contact. The mine is located on several of these fissure veins near the granite-gneiss contact. Additionally, numerous small veins of pyrite, chalcopyrite, and molybdenite with quartz are present. During its operation, over 58,000 lbs. of copper, more than 7,000 lbs. of lead, and almost 1,200 oz. of silver and smaller amounts of gold were removed. The mine was abandoned by 1963. During the mining process mine tailings were discarded downslope from the mine adits. A wetland naturally developed on top of the tailings due to diffuse seepage of seasonal snowmelt from the surrounding area and discharge from the lower adit of the mine. Multiple unmapped seeps contribute flow to the wetland. The water emerging from the adit and seeps has a pH between 6.78 and 8.05 and contains measurable concentrations of major and trace elements, including Fe (up to 1.47 mg/L), Pb (up to 17.4 µg/L), Zn (15 – 36 µg/L), Cu (up to 116.7 µg/L), and As (up to 3.66 µg/L). The purpose of this study, which is part of a more extensive wetland characterization, was to investigate metal retention and accumulation within the wetland soils and vegetation and to evaluate potential for metal release from the soils.