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During the summer of 1989,172 surface sediment sample sites were occupied in Lake Coeur d'Alene, the Coeur d'Alene River, and the St., Joe River, Idaho, at a density of approximately I/km2. Additional samples were collected from the banks of the South Fork of the Coeur d'Alene and the Coeur d'Alene Rivers in 1991. All the samples were collected to determine trace element concentrations and distribution patterns and to relate them to mining, mining-related, and discharge operations that have occurred in the Coeur d'Alene district since the 1880's, some of which are ongoing. \ The majority of the surface sediments in Lake Coeur d'Alene north of Conkling Point and Carey Bay are substantially enriched in Ag, Cu, Pb, Zn, Cd, Hg, As, and Sb relative to unimpacted sediments in the southern portion of the lake near the St. Joe River. All the trace element-enriched sediments are extremely fine grained (mean grain sizes <63 urn). The majority of the enriched trace elements, based on both the chemical analyses of separated heavy and light mineral fractions and a two-step sequential extraction procedure, are associated with an operationally defined Fe oxide phase; much smaller percentages are associated either with operationally defined organics/sulfides or refractory phases. The presence, concentration, and distribution of the Fe oxides and heavy minerals indicates that a major portion of the enriched trace elements probably are coming from the Coeur d'Alene River, which is serving as a point source. Within the lake, this relatively simple pattern is complicated by a combination of (1) formation of trace element-rich authigenic Fe oxides that appear to have reprecipitated from material solubilized from anoxic bed sediments and (2) physical remobilization by currents and wind-driven waves. The majority of the enriched trace elements associated with "Fe oxides" may become environmentally available upon burial in the anoxic lake bottom sediments. Fewer trace elements are associated with sulfide minerals; these trace elements may become environmentally available only if they are exhumed and exposed to an oxic environment. The processes that have caused the trace element enrichment in the surface sediments of Lake Coeur d'Alene are likely to continue for the foreseeable future.

Effect of mining-related activities on the sediment-trace element geochemistry of Lake Coeur d'Alene, Idaho, USA; Part 1, surface sediments