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sulfur isotope, and precipitation or removal of that reduced sulfate as pyrite or other <br />sult3des, a yellowish color, which has been observed in the seep water, and which could <br />indicate the presence oi' iron, supports this nation because such pyrite precipitation would <br />not be expected [o be 160 percent ef6eient, so some iron should still be in solution. <br />Values for SD and S'"O lie remarkably close to the meteoric water sine. With the <br />possible exception of values which are more [ban about 3 per mil from the meteoric water <br />line, most of these values could represent local meteoric water. Even the isoti~pically <br />lightest samples, which are from the fault waters. are only about S per mil tighter, in SD, <br />than Colorado meteoric waters reported in Lawrence and Taylor (1971; Deuterium and <br />oxygen-18 correlation: Clay Minerals and hydroxides in Quaternary soils compared to <br />meteoric waters. Geochimicu et Cosmochimica Acta, v. 3i, p. 993-1003). The close <br />correlation with the meteoric water line indicates minimal exchange of oxygen isotopes <br />between waters and rock, and points to a relatively young age for the waters, although <br />young in this case could he thousands of years as opposed to tens of thousands. Older <br />ages imply longer residence times and greater amounts of isotopic exchange between the <br />waters and rocks. Overall, the values argue for relatively rapid recharge of the <br />groundwater {thousands of years j. Nevertheless, there is good evidence that some of the <br />fault waters, notably a few from the Southeast Nead gate fault and the 6 Fast Mains fault, <br />have undergone some water:rock exchange prior to discharge in the mtderground mine. <br />Variable mixtures of local meteoric water and fault water can readily explain the <br />range of SD and S'kO values in alt of the waters. Che SD and S'YU values of the NW <br />panels sump and the Edwards mine portal are identical within analytical uncertainty. <br />htsofar as the N W Panels sump water may represent the Edwards Portal seep water, is is <br />clear that meteoric water mixing occurs within the sump. and that no further mixing is <br />needed to explain the seep water compositicm, at least in terms of SD and fit8O values. <br />There is a significant shift in S"G between the fault waters and the seep water. {a <br />value of+24, which tvas reported for the 13-seam sample, is probably a misprint, and that <br />value is more likely -24 err perhaps + or - 2.4 per mil, which could significantly affect <br />other interpretations. This analysis was disregarded.) Fault waters are signiteantly <br />heavier (-2.7 to +10.7) than the seep water {-12.9). Interactions with meteoric water can <br />he called on to explain part of this shift as atmospheric CU, has a S"C of about -7 per <br />mil, but obviously cannot account for all of it. Soil gas CO_ is considerably lighter, <br />ranging liom about -] 0 to -30 per mil (see values in P. Defines, "The Isdtopic <br />Composition of 12educed Organic Carbon" in P. Fritz and J.Ch.Fontes, 1980, }{andbook <br />of Environmental Isotope Geochemistry, Elsevier, p. 329-434). Variations between the <br />sump water (S"C' = -5.4j and the seep water (S''C - -12.9j require some further dilution <br />with meteoric water containing soil gas CO, to explain this shift totally. <br />Radioisotope Ages. <br />Owing to the presence of me[hane and other carbon compounds, the "C age <br />infi~rrnation is rather sketchy. What can he said from the data is that the Sump water and <br />the Edwards Mine water stave a relatively high percent of modem carbon (pmc) evhereas <br />6 <br />