Geochemical and lead-isotope data from stream and lake sediments, and cores from the upper Arkansas River drainage; effects of mining at Leadville Colorado on heavy-metal concentrations in the Arkansas River

Abstract

Geochemical studies of minus-80-mesh size fraction of streamsediment samples collected from the upper Arkansas River drainage basin in Lake County, Co. , show that the effect of mining activity, both past and present, on heavy-metal concentrations in the river can be readily documented. Application of geochemical leaching procedures often used in mineral exploration enhances the effect of acid-weathering caused by the oxidation of pyrite. Lead-isotope measurements of leaches of irregularly spaced stream-sediment samples clearly delimit the extent of elevated heavy-metal concentrations in the upper Arkansas River caused by mineralization at Climax, Leadville, and to a lessor extent, at St. Kevin Gulch. All leaches of the stream-sediment samples collected from either tributaries of Arkansas River, or from the Arkansas River itself within the boundaries of the Leadville mining district, have leadisotopic compositions that match those of published lead-isotope data from the ores at Leadville. In contrast, leaches of all stream-sediment samples collected outside the district within the upper Arkansas River drainage basin do not match the lead-isotopic signature of ores from the Leadville mining district. Detailed studies of the stratigraphy of four cores taken in the Arkansas River flood plain near the confluence with California Gulch in the Leadville mining district document high metal concentrations in an area immediately south of the confluence where heavy-metal-laden tailings from the Leadville mining district have been deposited. 210Pb geochronological studies of these cores show that the tailings in the Arkansas River were deposited over a twenty-year period. Further work is required, however, before definite dates can be assigned to the age of deposition of these tailings. The lead-isotope data and the 210Pb studies allow determination of the heavy-metal concentrations present in the Arkansas River drainage prior to mining at Leadville. Pre-mining concentration of lead in minus-80-mesh stream sediments was about 39 ppm, in sandy sediments about 29 ppm, and in soil samples collected from beneath the tailings deposit, about 38 ppm. Premining concentrations of zinc were 158 ppm, 64 ppm, and about 200 ppm in these sample media. Pre-mining concentrations of copper were about 14 ppm, 10 ppm, and 17 ppm, respectively. Enrichment of various heavy metals in the stream sediments from the Leadville mining district range from 2 to 215 times normal crustal abundance with lead being the most enriched. Core samples of sediments in the Arkansas River drainage derived from tailings from the Leadville mining district have enrichments of heavy metals ranging from 63 to 944 times crustal abundance. The field and analytical methods used in this study demonstrate methods applicable to environmental geochemical perturbations caused by mining and industrial activity worldwide.

Geochemical background - an environmental perspective

“…For instance, the comparison of stable sulfur isotopes in different environmental samples with those in industrial samples allows to estimate the influence of local pollution sources on the environment (Górka et al 2008;Krouse, Grinenko 1991). Stable lead isotopes 205 Pb/ 204 Pb are often used in the study of anthropogenic pollution (Jaakkola et al 1983;Church 1993;Church et al 1999). Differences in the ratio 53 Cr/ 52 Cr in environmental samples are determined to identify Cr from anthropogenic sources (Izbicki et al 2008).…”

Legacy Lead from Past Mining Activity and Gasoline Additives: Evidence from Lead Isotopes and Trace Element Geochemical Studies in the White River Basin, Southern Ozark Region, USA

“…The above-mentioned extraction technique releases the labile metals, defined as those metals released by a weak, warm-acid leach (2N HCl-H 2 O 2 ). The concentrations of the labile metals, including Pb, Zn, Cu, Co, and Ni, that were deposited on the grain coatings of the stream sediments represent weakly-bound metals that are associated with the organic, carbonate, and Fe-and Mn-oxide phases or adsorbed onto clay surfaces [9,40,41]. Acid mine drainage that was caused by the weathering of pyrite triggers the precipitation of Fe-oxide coatings on sediment grains, and therefore the precipitation of metals carried in the streams is a grain-surface phenomenon [9].…”

Biogeochemistry of lichens and mosses in and near Mt. Zirkel Wilderness, Routt National Forest, Colorado; influences of coal-fired power plant emissions

“…Ratios of lead isotopes in lichens also offer the potential for unique identifiers of pollutant sources. Church (1993) has used the ratios of 208Pb/204Pb and 206Pb/204Pb to conclusively identify the source of lead in stream sediments in the Leadville mining district. Similar techniques have been used by Jaakkola and others (1983) to estimate the relative contribution from gasoline and incinerator ash to lead in lichens.…”

“…Lead isotope ratios for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb, were determined in selected samples of Xanthoparmelia, Tortula, and two whole coal composite samples by the U.S. Geological Survey with a method similar to the procedure outlined by Church (1993). The lichen and moss samples were wet ashed, whereas the coal samples were dry ashed at 500 °C prior to acid digestion.…”