Paper No. 7
Presentation Time: 1:30 PM-5:30 PM
USING STABLE ISOTOPES TO DISTINGUISH GROUND WATER AND SURFACE WATER CONTRIBUTIONS TO DRAINING MINE TUNNELS, SUGARLOAF MINING DISTRICT, SAWATCH MOUNTAINS, NEAR LEADVILLE, COLORADO
Water samples were collected for analysis of stable isotope ratios in water (delta 18Oxygen (&delta18O) and delta deuterium) to determine the source of water draining four mine tunnels in the Sugarloaf mining district, Colorado. Three tunnels within the district, the Bartlett, Dinero, and Siwatch, have elevations lower than Turquoise Lake (a large reservoir located between 0.3 and 1.5 kilometers north of the mine tunnels) and may be hydrologically connected to the lake. Results indicate distinct groupings of the isotope ratios. The lake water had the most enriched (heaviest) isotopic signature and a wide seasonal variation (&delta18O ranged from 17.8 to 16.3 per mil). Isotope ratios in samples from the mine tunnels (&delta18O ranged from 19.3 to 18.3 per mil) were lighter than lake water, had minimal seasonal variation, and were similar to values in ground water within the mining district indicating a ground-water origin for most mine-tunnel drainage, and little contribution from Turquoise Lake. Lake water mixed with infiltrating snowmelt could also explain the isotopic signatures of the mine drainage. However, the lack of seasonal variation in the isotope ratios of the mine-tunnel samples and the similarity of isotopic signatures from tunnels located below lake elevation to those from tunnels located above lake elevation do not support this hypothesis. Samples from the Bartlett tunnel, located closest to the lake, showed seasonal variation toward more enriched isotopic values that indicated a possible direct contribution of lake water to the Bartlett tunnel. A separate tracer study confirmed the hydrologic connection between the lake and the Bartlett tunnel. This result is significant because the reservoir may be enlarged in the future, which could increase drainage from the Bartlett tunnel and negatively affect water quality downstream from the reservoir.