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Amphibole forensics: Using the composition of amphiboles to determine their source, the Libby, Montana, example

¹ Geological Sciences, University of Idaho, Moscow, Idaho 83844, U.S.A.
² RJ Lee Group Inc., 350 Hochberg Road, Monroeville, Pennsylvania 15146, U.S.A.

View larger version (106K): [in this window] [in a new window]   FIGURE 1. A section of a 7.5 min topographic map of Libby, Montana. The blue lines are the approximate boundary of glacial Lake Kootenai. The numbers are sample collection locations keyed to Figures 2–5.

View larger version (23K): [in this window] [in a new window]   FIGURE 2. Three sets of SEM images and associated EDS spectra obtained on polished samples of amphiboles from the former vermiculate mine near Libby, Montana: (a) Butte 2, (b) float, and (c) Harvard 1. (Names correspond to those used in Sanchez et al. 2008.) For each, the left image is at lower magnification and contains a box that represents the higher magnification image to the right. The small box on the right image coincides to the locations of the SEM beam, and in turn, the area analyzed in the EDS spectra immediately below the images. Note how the Na and K contents increase from a to b to c.

View larger version (38K): [in this window] [in a new window]   FIGURE 3. Two sets of SEM images and associated EDS spectra obtained on amphibole particles collected in road cuts of lake sediments located at 3a and 3b on the map in Figure 1. Note the upper EDS spectra is Na and K free, while the lower one contains Na and K, and resembles the EDS spectra shown in Figure 2.

View larger version (56K): [in this window] [in a new window]   FIGURE 4. Two sets of SEM images and associated EDS spectra obtained on amphibole particles occurring at 4a and 4b on the map in Figure 1. These samples have similar EDS spectra to those shown in Figure 3, but the particles are wider. The upper EDS spectra is Na and K free, while the lower one contains Na and K and resembles the EDS spectra shown in Figure 2.

View larger version (46K): [in this window] [in a new window]   FIGURE 5. Two sets of SEM images and associated EDS spectra obtained on amphibole particles collected at location 5a and 5b on the map in Figure 1. The upper amphibole is not associated with the vermiculite deposit, while the bottom one is, based on the Na and K contents.