Abstract
ABSTRACT: This work presents the investigation in an environment that contains uranium deposits by using Pb isotope signatures. The study area, southeast of Brazil, is characterized by the lack of surface water and, as a consequence, the groundwater plays an important role in the economy of the region, such as the supply to the uranium industry and, above all serving the needs of the local population. The objective of the present investigation is the determination of the signatures of Pb in groundwater and sediments as well as the identification of environments under influences of geogenic and/or anthropogenic sources. It was determined that the Pb in the majority of sediments was geogenic in origin. Although data from the literature, related to the environmental studies, consider 206Pb/207Pb isotopic ratio values below or close to 1.2 as an indicative of anthropogenic Pb, the 206Pb/ 207Pb determined for the majority of groundwater samples ranged from 1.14 to 1.19, and are similar to the data reported for rocks samples (1.09 to 1.96) from area with U mineralization. It was also determined that the anthropogenic influence of the uranium was restricted to a single sampling point within the mining area.
Highlights
IntroductionLead isotopic studies provide a convincing approach to studying and tracing the geogenic and/or anthropo‐ genic sources of Pb in different environmental matrices, i.e., waters, soils, sediments, rocks, aerosols, peat deposits, tree rings (plants) etc (Bollhöfer et al 1999, Bollhöfer & Rosman 2000, 2001, Chen et al 2005, Gioia et al 2006, 2010, Gulson et al 2007, Komárek et al 2008, Rosman et al 1993, 2000, Rosman & Taylor 1998)
The majority of the sediment values are close to the geogenic reference data reported by Cordani et al (1992) for this U‐mineralized area, which indicates a geogenic behavior of these signatures
The use of the 206Pb/207Pb versus 208Pb/207Pb and the 208Pb/204Pb vs 206Pb/204Pb diagrams and the association with the 206Pb/207Pb ratios makes it possible to determine areas with anthropogenic U, as well as areas with Pb originated from geogenic sources
Summary
Lead isotopic studies provide a convincing approach to studying and tracing the geogenic and/or anthropo‐ genic sources of Pb in different environmental matrices, i.e., waters, soils, sediments, rocks, aerosols, peat deposits, tree rings (plants) etc (Bollhöfer et al 1999, Bollhöfer & Rosman 2000, 2001, Chen et al 2005, Gioia et al 2006, 2010, Gulson et al 2007, Komárek et al 2008, Rosman et al 1993, 2000, Rosman & Taylor 1998). In addi‐ tion, it is useful to demonstrate and iden‐ tify the anthropogenic input from different sources of Pb from various mining activities, such as uranium/thorium mining and others with potential to generate Naturally Occurring Radioactive Materials (NORM) (Chow et al 1975, Gulson et al 1989, 1992, Bollhöfer & Martin 2003, Moraes et al 2004, Ketterer et al 2010, Vecchia 2015, Vecchia et al 2015). In contrast the uranogenic Pb signature, derived by radio‐ active decay from U, is characterized by higher 206Pb/204Pb, 207Pb/204Pb and 207Pb/206Pb ratios and little or no relative increase in 208Pb/204Pb or 208Pb/207Pb
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