The Use Of Pb Isotopes To Characterize The Fate And Transport Of Pb In An Interrupted Stream, Aravaipa Creek, Graham County, Arizona

Abstract

This study identifies the probable sources of Pb pollution in the perennial reach of Aravaipa Creek using 208pb/204pb, 206pb/204pb and 207pb/204 Pb ratios, 87Sr/86Sr isotope ratios, total metals analysis, metals ratios and sequential extractions. Comparison of these data in local ores, minewaste, crystal specimens, and streambed sediments establishes two Pb isotopic ratio groupings. Pb isotope ratios show one source, the flotation mill at Klondyke, Arizona, is a major contributor to Pb in the perennial reach, and are consistent with mines from the reduced end of the deposit as sources of ores processed on-site. Differences between ephemeral and perennial reach Sr ratios is consistent with in-stream Sr/Ca re-equilibration. Sequential extraction data reveal carbonate grain coatings as the controlling phase for Pb fate in streambed sediments. Spatial trends of metals, Pb and Sr isotope ratios, and sequential extraction data are consistent with atmospheric deposition as the probable mechanism for offsite Pb transport.