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from this investigation for a comparative study as part of a larger effort to see whether differences can be <br />seen in the geochemical characteristics and time trends of the mine-waste leachates from the various basins. <br />Specifically, observations and data were compiled and compared to see if changes in leachate pH, specific <br />conductance, and metal concentrations change over time from the 5-minute leach to the 18-hour leach in <br />order to see whether these trends reveal potential reasons for water-quality differences in streams draining <br />these basins. Net-acid production (NAP) (Lapakko and Lawrence, 1993) was performed on a split of the <br />solid portion of all 13 mine-waste samples in order to determine if a correlation can be made between NAP <br />and other geochemical data produced by leaching. Thirdly, after compiling and analyzing the leachate <br />geochemical data from all the sites, this investigation presents a ranking scheme for use in predicting which <br />historical mine-waste piles have the greatest potential for negative impact as a point source of acid and <br />metals into a watershed. <br />Acknowledgments <br />I thank Dana Bove for insight and interpretation of the geology for this study and Greg Lee for <br />help with GIS applications. <br />Montezuma Mine-Waste Piles: Geologic Perspective <br />The mine-wastes included in this study represent workings from mesothermal, fissure-filling lead- <br />zinc-silver vein deposits (Lovering, 1938). Galena, sphalerite, pyrite, and quartz are present in most of the <br />veins in the Montezuma mining district and surrounding area and are much more abundant than other vein- <br />related minerals. Copper sulfides are the most abundant of the minor constituents of these ores and were <br />found in most of the vein deposits. Silver, when present in these veins, was generally associated with <br />chalcopyrite and tetrahedrite-tennantite (Lovering, 1935); however, most of the silver in the ores formed as <br />discreet minerals, typically as silver sulfantimonides or sulfarsenides. Quartz is the dominant gangue <br />mineral associated with the Montezuma vein deposits. Ankerite and barite are also common. Ankerite, <br />when present, is reported to contain variable amounts of manganese, iron, and magnesium and weathers <br />black due to high manganese content (Lovering, 1938). Although ankerite is reported in relative abundance <br />in a number of the Montezuma mines (including the Lower Chautauqua, Wild Irishman, and Santiago), <br />when present in mine-waste material, its abundance was probably on the order of 1 percent or less (D. <br />Bove, written commun., 2003). Overall, vein deposits of the Montezuma and surrounding areas are typical <br />of polymetallic vein deposits hosted in noncarbonate rocks, as summarized by Plumlee and others (1995) in <br />a compendium on the geoenvironmental signatures of ore deposits (du Bray, 1995). <br />Mines west of the upper Snake River drainage basin-i.e., Deer Creek and Sts. John drainage <br />basins-are hosted in hornblende gneiss or amphibolites (Lovering, 1938). Rocks west of the upper Snake <br />River basin are generally unaltered and lacking in pervasive pyritization except locally around vein <br />deposits (D. Bove, written commun., 2003). In contrast, rocks in the eastern part of the upper Snake River <br />basin are dominantly biotite-quartz-sillimanite schist and gneisses that have been strongly affected by <br />hydrothermal alteration related to Tertiary-age intrusions (Neubert and others, 2004). The most intense <br />alteration and pyritization is focused in the Webster Pass and Handcart Gulch areas. <br />Clinochlore is present in many of the metamorphic rocks in the Montezuma area and also formed <br />as a replacement of biotite and other iron-magnesium silicates during hydrothermal alteration. Calcite is <br />Hageman_SIR_2508.doc 3 7/21/2004 2:50 PM