Controls on As, Pb, and Mn distribution in community soils of an historical mining district, southwestern Colorado
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Rico, Colorado is a small mountain community that was developed before the turn of the century around and near underground lead-zinc-silver mines. Today, US regulatory concerns in such communities focus on the metal content, particularly of lead, in community soils. This study integrates bedrock geology, surficial geology, mineralogy and geochemistry in order to define the controls on metal distribution in Rico community soils. The principal constituents of concern are As, Pb, and Mn. The results show that mining-related sources are discrete and localized whereas natural sources, including bedrock (mean Pb content of 3 500 ppm), colluvium (mean Pb content of 1 410 ppm), and older alluvium (mean Pb content of 744 ppm) are wider spread and are the principal sources of metals in Rico community soils. Historical mining sites like Rico should be expected to have significant surficial expressions of mineralized bedrock. In these communities, it is important to accurately define the role of all metal sources as a foundation for determining environmental liabilities, cleanup guidelines, and health risk assessments. The application of geology and mineralogy in support of geochemical characterization is necessary to accurately define the origin and distribution of both anthropogenic and natural metal sources at such sites.
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