ENVIRONMENTAL GEOCHEMISTRY OF METAL CONTAMINATED SEDIMENTS OF THE BIG RIVER IN SOUTHEASTERN MISSOURI
Inductively Coupled Plasma analysis of partially digested silt- and clay-sized fraction sediments collected three different dates at locations 2.5 and 12.5 nautical miles downstream from the Desloge tailings pile have mean Pb concentrations of ~5200 +/-1300 and 2400 +/- 400 ppm, respectively. Average Zn concentrations at 2.5 and 12.5 nautical miles downstream from the tailings are ~4600 +/-1500 and 1400 +/-200 ppm, respectively. The large standard deviations are likely due to a heterogeneous metal distribution. By comparison, background metal contents from a control site located upstream from the mines contained ~70 ppm Pb and 80 ppm Zn. The river area of primary sampling cuts through calcareous shale and dolomite of Paleozoic age which causes the Big River to have a pH of 7.2-8.3. Scanning Electron Microscopy and Energy Dispersive Spectroscopy analysis of individual metallic sediment particles collected at intervals downstream from the Desloge tailings indicate that pyrite (FeS2) and sphalerite (ZnS) phases survive only ~2 nautical miles downstream. Galena (PbS) is more durable than the other sulfides and is found up to ~8 nautical miles downstream from the tailings. Attrition of the sulfide particles occurs by a combination of mechanical and chemical processes. No sulfide phases have been found further than ~8 nautical miles downstream. Analysis of sedimentary particles collected further downstream indicates that contaminant metals tend to adsorb onto Si, Fe and Mn oxide and/or oxyhydroxide phases.