2009-05-19_REVISION - M1981021 (32)

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Section 2 Methodology 2.1 Overview Analyses on a single grain of soil or -- { a single crystal of a precipitate r =r r- were accomplished using an EMP. =? = Not only can analyses be made on " particles as small as 1 micron, but the EMP also provides a visual , 3? "`?- picture of the soil at magnifications ranging from 40 to 90,000 times.: The visual mode is referred to as the "backscatter mode.'' Information about the relative 4 ' atomic number of the compounds can be obtained in the backscatter mode due to the contrast in brightness bettver-n tht• low atomic number compounds and the compounds with high atomic numbers. For example, arsenic and iron compounds, which have high mean atomic numbers, tend to be bright white in backscatter mode, while silica compounds, with lower mean atomic numbers, are gray and organic carbon is nearly black. Direct visual inspection of the soil also provides information on the associations, morphology, and any reaction rims on the particles, all of which provide insight into the geochemical history of the sample. Soil samples were analyzed on a JEOL 8600 Superprobe located in the Department of Geological Sciences, University of Colorado, Boulder, Colorado. 2.2 Sample Preparation Samples were air dried, homogenized, and sieved through US Sieve No. 60 (0.25 mm). The <0.25 mm fraction was sent to the University of Colorado for magnetic separation, analysis, and preparation of the EMP grain mounts. 2.2.1 Arsenic and Iron Analyses Arsenic and iron analyses were performed at the University of Colorado by diegesting the samples using I-IF/HCI/HN03 (USBM Method) followed by analysis using USEPA Method 6010 (ICP/MS). 2.2.2 Magnetic Separation 40 • 11 5 T.'.b4986-Dcniwn Mincslask Order 1 - DMO Smnphng and Analysi Plan\Taxk 3 _ 12 . SuJ, Ore. Rt" Data Acvc"rnent RerKwl'$joavatlab8it-v'%DrnwtnBMPTcxt021709(2)."-