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up metals and acid while percolating through sulfide-bearing dumps. However, the presence of <br /> iron bogs away from old workings proves that natural seeps also carried anomalous loads of <br /> metals (and probably acid). Th`✓ iron bogs located near old mine workings probably pre-date <br /> the workings. Prospectors consider iron staining to be a good indication of mineralization and <br /> often drove test tunnels into limonite-stained rock. <br /> Iron bogs are formed as a result of iron-laden ground water discharging as springs and seeps. <br /> The relatively low redox potential of ground water allows iron to remain in solution in the <br /> subsurface. When iron-laden gr�und water is discharged to the surface, the iron is oxidized and <br /> precipitates as hydroxides and/o� oxyhydroxides. Many other heavy metals tend to be adsorbed <br /> onto the iron precipitate and are removed from solution. The precipitation process is <br /> accompanied by the release of h drogen ions (Garrells and Christ, 1965, p. 189) which lowers <br /> pH. The net effect is that a siinificant part of the dissolved metals load of ground water is <br /> i <br /> removed from solution soon aftdr the water surfaces, but the water becomes more acidic. <br /> A pH of 4.5 was measured at a'sizable natural discharge zone near the Mogul Mine portal on <br /> July 31, 1991 by Simon Hydro-Search staff. A pH of 4.24 was measured at the same discharge <br /> zone on October 17, 1991 by SJCMV staff. The pH measurements were made at a location <br /> which was upstream of the waters flowing from the Mogul Mine portal. This discharge zone <br /> appears to be localized by the Bonita fault (see Figure 4). The Bonita fault is perpendicular to <br /> the dominant northeast/southwes fracture trend and is expected to intercept ground water from <br /> such fractures. A low pH may be typical of water which has traversed the full extent of the <br /> snnjusn\sunny\110361\ocl91.Itp[ 25 <br /> e�� simonWEDINO-HROINCH <br />