A landscape ecotoxicology approach was used to assess the spatial distribution of copper in the recent bottom sediment (surficial sediment) of a Brazilian subtropical reservoir (the Guarapiranga reservoir) and its potential ecotoxicological impacts on the reservoir ecosystem and the local society. We discuss the policies and procedures that have been employed for the management of this reservoir over the past four decades. Spatial heterogeneity in the reservoir was evaluated by means of sampling design and statistical analysis based on kriging spatial interpolation. The sediment copper concentrations have been converted into qualitative categories in order to interpret the reservoir quality and the impacts of management policies. This conversion followed the Canadian Water Framework Directive (WFD) ecotoxicological concentration levels approach, employing sediment quality guidelines (SQGs). The SQG values were applied as the copper concentration thresholds for quantitative-qualitative conversion of data for the surficial sediment of the Guarapiranga. The SQGs used were as follows: a) interim sediment quality guideline (ISQG), b) probable effect level (PEL), and c) regional reference value (RRV). The quantitative results showed that the spatial distribution of copper in the recent bottom sediment reflected the reservoir's management policy and the copper application protocol, and that the copper concentrations varied considerably, ranging from virtually-zero to in excess of 3g/kg. The qualitative results demonstrated that the recent bottom sediment was predominantly in a bad or very bad condition, and could therefore have impacts on the local society and the ecosystem. It could be concluded that the management policy for this reservoir was mainly determined by the desire to minimize short-term costs, disregarding long-term socioeconomic and environmental consequences.

No abstract

Stable isotope analyses were carried out on sulfides from three mesothermal gold deposits of the Rio Itapicuru greenstone belt (Fazenda Brasileiro, Maria Preta, and Ambrosio mines) to constrain the source of the hydrothermal solutions. The ores are hosted in a volcanic-sedimentary sequence that evolved in an Archean cratonic area reworked during the Transamazonic event (ca. 2.1 Ga). The ore bodies were deposited by hydrothermal solutions in polycyclic shear zones generated by Paleoproterozoic dynamothermal metamorphism. In the Fazenda Brasileiro deposit, δ 34 S values for arsenopyrite from mineralized quartz veins range from 5.5‰ to +1.0‰; pyrites from Au-rich mineralized veins from the Maria Preta deposit yielded δ 34 S values ranging from +8.9‰ to +6.9‰, in agreement with published δ 34 S data (+0.1‰ to +6.6‰). A narrow spread in the δ 34 S values for Au-rich sulfides from both deposits indicates that gold deposition occurred under conditions involving a small range of fO 2 and fH 2 O. A barren, galena-rich vein from the Ambrosio deposit yielded δ 34 S values in the -7.6‰ to -9.9‰ range, probably reflecting mixing of different sources. These results, compared to stable sulfur isotope modeling of lode gold deposits, indicate that the studied deposits formed from hydrothermal solutions of metamorphic origin followed by duluite solutions of magmatic origin.