The absence of tin in the bed sediments would suggest that this is not likely from particulate brass contamination. The source of this urban metal signature is unknown. Furthermore, the lead-isotopic compositions in the two samples from Junction Creek differ, probably reflecting lead added to the environment by the combustion of gasoline. These urban metal sources contribute only small amounts of metals to the Animas River. Although the diagram contains many data points, the most important feature of the plot is the small variation in the data set as a whole.
Selenium is isochemical with sulfur and substitutes for sulfur in the sulfide minerals.
It is not surprising that the sediments derived from the area above Silverton contain 1-2 ppm selenium and that the bed sediments of the Animas Canyon reach contain about 1 ppm selenium. Sediments from Lightner Creek are characterized by a large component of Mancos Shale and contain 2.7 ppm selenium. All of these sites, except the Kittimac Mill site, are from the headwaters of the respective drainages where early mining activities took place. We cannot distinguish from these data and published geochemical data on the mineral deposits whether these elevated mercury concentrations are related genetically to the epithermal vein mineralization or to early gold recovery practices by individual miners. The surface expressions of these veins in Prospect Gulch may have been overprinted by the later intrusion and alteration associated with the chimney deposits of the Red Mountain district.