2009-05-19_REVISION - M1981021 (32)

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• A magnetic separation was performed at the University of Colorado on the dried and sieved samples using a Franz Model L1 magnetic separator set at 1.5 amps ans a 20 degree tilt. 2.2.3 Preparation of Grain Mounts A 1 gram split of each dried and sieved sample was used to prepare epoxy grain mounts. The procedure for preparing the mounts included pouring the sample into a 1- inch diameter mold and covering with a thin layer of air-cured epoxy. The grains were then blended with the epoxy using a disposable wood stirring rod and additional epoxy was added. After curing at room temperature, the mount was ground flat, forming a cross sectional cut through the grains. Polishing of the mount was performed using successively finer grades of oil-based diamond paste. The final step in the preparation of the grain mounts was to apply a thin carbon coating to the surface of the mount or "puck" in order to allow proper conduction during microprobe analysis. 2.3 Operating Conditions Operating conditions included a 15 KeV accelerating voltage, 17 NanoAmp cup current, and a 1 to 2 micron beam size. Certified pure element standards were used to determine phase compositions. Wavelength spectrometer crystals TAP for arsenic, PET for iron and sulfur and LDE1 for oxygen were used for the WDS analyses. 2.4 Analytical Procedure • Sample pucks were scanned for arsenic-containing minerals using backscattered electron images. The scanning was done manually by systematically traversing from left to right until the edge of the mount was reached. The puck was then moved up one field of view and scanned from right to left. This process was repeated until the whole mount was scanned. Typically, the magnification used for scanning samples was 40-10OX and 300-600X, depending on the individual sample's grain size distribution. The last setting allowed the smallest identifiable (1 to 2 pm) phases to be found. Once a candidate particle was identified, then the backscatter image was optimized to discriminate any different phases within the particle or its association. Identification of the arsenic-bearing phases was done using both energy-dispersive and wavelength-dispersive spectrometers set for analyses of arsenic, sulfur, iron, and oxygen. 2.5 Samples Analyzed A summary of the samples analyzed by EMP are summarized in Table 2-1. 6 TA64986-Denison Mine Umic Order 3 - DMO Sampling and Analysis Plan\Task 3.12 - Soil, Oro, Rock Data Assessment Report\Bioavailability\DcnisonEMPTutO21709 (2).doc