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Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation ;}~ <br />and represent the relative difference in abundance of the isotope in the sample per mil (parts per thousand) <br />compared to standard mean ocean water (SMOW). <br />The isotopic composition of water samples was evaluated using the standard format which plots S'RO <br />against 8D and compares the resultant position against the meteoric water line (Figure 26). The meteoric <br />water line is described by the equation dD=Bo'~0+10 and represents isotopic fractionation by atmospheric <br />processes (Drever 1988). Waters that differ significantly from the isotopic compositions observed for <br />meteoric waters are generally interpreted to have had lung residence tunes as groundwater. <br /> Stable Isotope Analysis <br />t rp <br />tos <br /> • • <br />a,o • f / <br />~ Meteonc Water Une t 9Q-Dh~4° <br />,` 115 <br />y = 8x • 10 <br /> t 9D-DM <br /> \ <br /> JoM aon pre Shoot <br />-110 . <br /> / <br />~ <br />• Rateton Cr <br /> -co ~eki vai ~ ~se nr~n <br />725 ~ <br /> <br />-17 t65 -te 15S ~t5 -145 -14 <br /> ,S 1°p <br />Figure 26. Stable Isotope Evaluation of Water Samples <br />All of the water samples plot close to the meteoric water line which indicates a meteoric origin tier the <br />infiltrating mine water. In general the isotopic composition of the water has been relatively unaffected by <br />its transit through the rock mass suggesting that the water infiltrated quickly and moved to depth from <br />surface recharge areas. <br />Mine water samples are isotopically lighter than water from Ralston Creek. This fractionation could occur <br />ti•om differences in elevation hehveen source areas for the mine water and Ralston Creek. by evaporation of <br />the lighter Inactions from the stream, or by contact of Ralston Creek Water with atmospheric carbon <br />monoxide and carbon dioxide (Drever. 19881. All of these mechanisms work to increase the isotopically <br />heavier fraction in surface water. In general, the isotopic composition of precipitation at a given location is <br />approximately constant, but it varies from season to season and from one rainstorm to another. An <br />alternate explanation for the fractionation observed between mine water samples and Ralston Creek would <br />he that water in the mine is derived from infiltration of meteoric water that tell during a different season <br />than the water in the creek. <br />Although the stable isotope analyses indicate that mine water is of certain meteoric origin, isotopic <br />differences behveen the mine water and water in Ralston Creek suggest that Ralston Creek is not the direct <br />source of the underground water. In particular, the isotopic composition of water sampled from the 70U <br />and 1,700 level arc notably lighter than water in Ralston Creek. Samples collected fro-n the 1900 level and <br />the .lohnson Ore Shoot are less definitive. <br />1 I i Its 13-u' I I I (' Whetstone Associates • <br />