Use of an intact core and stable-metal isotopes to examine leaching characteristics of a fluvial tailings deposit.

The upper Arkansas River south of Leadville, Colorado, contains deposits of fluvial tailings from historical mining operations. A stable-metal isotope (111Cd) was used to study metal retention and release mechanisms affecting metal transport from the deposits to shallow groundwater systems. An intact core was excavated from a small deposit and subjected to column experiments to examine the amount of metals leaching through the core. Deionised water was continuously applied to the top of the core and effluent collected from the bottom for a period of about two months. Unsaturated, partially saturated and fully saturated conditions were studied. Partial and complete saturation of the core resulted in the development of reducing conditions. During the unsaturated leaching phase, core effluents were acidic (pH 2.8-3.5) and contained elevated metal concentrations. During a portion of the unsaturated leaching phase isotope spikes and conservative tracers were simultaneously applied to the top of the core. During the unsaturated leaching phase, the isotope spikes did not exhibit breakthrough with the simultaneous addition of conservative tracers. However, some of the isotope spikes did break through when reducing conditions occurred in the core under partial and complete saturation conditions. The results indicate that there is a large reservoir of water-soluble material within the fluvial tailings deposit, which yields elevated metal concentrations and high acidity and which may degrade adjacent ground- and surface-water quality.
The upper Arkansas River south of Leadville, Colorado, contains deposits of fluvial tailings from historical mining operations. A stable-metal isotope (111Cd) was used to study metal retention and release mechanisms affecting metal transport from the deposits to shallow groundwater systems. An intact core was excavated from a small deposit and subjected to column experiments to examine the amount of metals leaching through the core. Deionised water was continuously applied to the top of the core and effluent collected from the bottom for a period of about two months. Unsaturated, partially saturated and fully saturated conditions were studied. Partial and complete saturation of the core resulted in the development of reducing conditions. During the unsaturated leaching phase, core effluents were acidic (pH 2.8-3.5) and contained elevated metal concentrations. During a portion of the unsaturated leaching phase isotope spikes and conservative tracers were simultaneously applied to the top of the core. During the unsaturated leaching phase, the isotope spikes did not exhibit breakthrough with the simultaneous addition of conservative tracers. However, some of the isotope spikes did break through when reducing conditions occurred in the core under partial and complete saturation conditions. The results indicate that there is a large reservoir of water-soluble material within the fluvial tailings deposit, which yields elevated metal concentrations and high acidity and which may degrade adjacent ground- and surface-water quality.