Abstract:Lead isotope compositions and Pb, Cu, Zn, and As concentrations in stream sediment leachates in the White River Basin, southern Ozark Region, have been determined to discriminate between natural and anthropogenic sources of Pb and to assess the metal loads that are transported by streams draining the Mississippi Valley-type (MVT) Zn-Pb mines in the Northern Arkansas district. The samples that were collected downstream of and closest to the mines have trace element concentrations well above those in soils from Arkansas. The trace element concentrations are lower in samples that were collected upstream of the mines. Most of the analyzed samples have trace metal concentrations above the United States Environmental Protection Agency (USEPA) Sediment Quality Guidelines Threshold Effects Level. The Pb isotope values of the downstream samples and the MVT ores are similar, suggesting a similar Pb source. The Pb isotope values of the upstream samples are similar to those that were defined by soils from the Ozark Plateau, suggesting that Pb from historic mining does not dominate upstream sediments. However, a linear regression line through the leachate data indicates that mixing between two end-members represented by leaded gasoline and ores could generate the Pb isotope ratios that were noticed in the upstream leachates.
High concentrations of Ga and Ge, two strategic metals vital to modern technology and industry, have been noticed in ores from various Mississippi Valley-type deposits in midcontinent U.S.A. [1]. These deposits also account for a substantial amount of worldwide Pb and Zn resources. A variety of crustal rocks, including basement rocks, shales, and carbonate aquifers, have been suggested as potential source(s) of ore metals [2, 3, 4, 5, 6]. MC-ICP-MS Pb isotope analysis of ores and rocks have been carried out to re-evaluate these source(s). Lead isotope values of ores define two collinear, parallel trends: Tri-State (TS) and Central Missouri (CM) ores are collinear with Southeast Missouri (SM) and Northern Arkansas (NA) ores; Upper Mississippi Valley (UMV) and Illinois-Kentucky (IK) ores are collinear with Central Appalachian (CA), Southern Appalachian (SA), East Tennessee (ET), Central Tennessee (CT), and South-Central Kentucky (SCK) ores (Figs. 1, 2). Ores from Ozark region (CM, SM, TS, and NA districts) are characterized by 208 Pb-depleted Pb compared to Pb in UMV,
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