ENERGY DISPERSIVE SPECTROSCOPY OF BIG RIVER SEDIMENTS

Energy Dispersive Spectroscopy of Big River Sediments. McBurnett, J. D., Wronkiewicz,D., Faeth, A., Department of Geology and Geophysics,University of Missouri, Rolla The objective of this study was to identify heavy metal minerals in the sediment of the Big River, St. Francois County. A five-mile stretch of the Big River, downstream of the Bonneterre tailings pile was sampled at one half mile intervals. Samples were collected by panning to concentrate dense particles. Individual particles were selected under an optical microscope for energy dispersive spectroscopy on a Hitachi S570 SEM. Sphalerite grains were identified based on the presence of a sulfur Ka peak and zinc K and L peaks. Standardless quantitative analyses of sphalerite particles gave an average atomic ratio of Zn:S of 1:1.2. Iron sulfide grains were identified based on sulfur Ka and iron K and L peaks. Standardless quantitative analyses of a iron sulfide particles gave an atomic ratio of Fe:S of 0.63:1. Cubic lead bearing particles, presumably sulfides, were identified but standards based quantitative analyses failed to show any sulfur. The sulfur Ka at 2.307 keV, seen in the other mineral grains overlaps with the lead Ma at 2.346 keV. The presence of lead in the particles can be confirmed by the lead La peak at 10.549keV. Quantitative analyses of lead bearing particles found up to 70 atomic % Pb. Lead bearing particles from each site were imaged and show increased surface dissolution features downstream. The addition of sulfide minerals from the Flat River is evident from an increase in the abundance and range in the degree of weathering of sulfide particles below the confluence of the Big and Flat River.