Using Resistivity to Map Acidic Waters at the May Day Mine Dump, Silverton, Colorado.
The May Day Mine dump is located on a mountainside above Cement Creek, north of Silverton, CO. As Cement Creek flows past the May Day Mine, dissolved metal loads increase in the stream, though no tributaries enter the stream reach. Induced polarization studies show local pockets in the upper bench of the May Day Mine dump with acidic pore waters. The pore water appears to get less acidic as it migrates through the dump; however, water samples from a well located at the toe of the dump are highly acidic and contain large concentrations of dissolved metals. An airborne EM survey flown over the area shows a linear conducting feature that enters Cement Creek just south of the May Day Mine dump. The airborne survey was followed with ground geoelectrical surveys, which confirm the existence of the conducting feature and suggest that it dips steeply and extends to a depth of at least a few tens of meters. This conductor may reflect a fissure zone that carries water, a potential source of some of the water that enters Cement Creek near the May Day Mine, which suggests that the metals dissolved in that water might originate through natural processes.