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High fluoride concentrations (up to 11 mg/L) have been reported in the groundwater of the Guarani Aquifer System (Santa Maria Formation) in the central region of the state of Rio Grande do Sul, Southern Brazil. In this area, dental fluorosis is an endemic disease. This paper presents the geochemical data and the combination of statistical analysis (Principal components and cluster analyses) and geochemical modeling to achieve the hydrogeochemistry of the groundwater and discusses the possible fluoride origin. The groundwater from the Santa Maria Formation is comprised of four different geochemical groups. The first group corresponds to a sodium chloride groundwater which evolves to sodium bicarbonate, the second one, both containing fluoride anomalies. The third group is represented by calcium bicarbonate groundwater, and in the fourth, magnesium is the distinctive parameter. The statistical and geochemical analyses supported by isotopic measurements indicated that groundwater may have originated from mixtures of deeper aquifers and the fluoride concentrations could be derived from rock/water interactions (e.g., desorption from clay minerals).

The high-grade gold mineralization at Fazenda Brasileiro occurs in quartz-albite-sulfide veins hosted by iron-rich metagabbros and forms the upper part of a differentiated mafic sill.The veins are enveloped by zones of hydrothermal alteration in which the metamorphic greenschist facies assemblage has been replaced by new mineral associations with a distinct zonation. Based on petrographic criteria these associations are classified into (1) parent rock, (2) zone of incipient alteration, (3) zone of advanced alteration, and (4) vein. The sequence of alteration is characterized by a major decrease in the chlorite content along with increases in albite, carbonates, pyrite, and arsenopyrite.Ore deposition resulted from the interaction between wall rocks and a low-salinity, H20-CO2-CH4-dominated hydrothermal fluid containing Na, S, and Au, which percolated through permeable zones developed during late-stage deformation. The deposit shows marked overall similarities with other greenschist facies gold deposits, such as Hunt, Sigma, and Kerr-Addison, in regard to the hydrothermal alteration pattern.

ResumoEste artigo analisa a experiência de convivência das populações do Vale do Itajaí com enchentes ao longo do último século e meio, mostrando como o processo de ocupação do território forjou situações que hoje explicam o porquê das tragédias ocasionadas pelas chuvas e enchentes. Também identifica que, desde o século XIX, a possibilidade em carrear recursos financeiros para resolver problemas imediatos decorrentes dos processos naturais foi uma (solução paliativa) encontrada pelas autoridades, cujos benefícios políticos parecem ter sido tão significativos que, até hoje, este tipo de solução é priorizada. A partir de registros escritos e revisão bibliográfica, os autores concluem que se pode pensar numa "indústria das enchentes", que se alimenta dos desastres e não envolve políticas efetivas de prevenção, onde se impõe a necessidade de rever os modelos de planejamento urbano e de uso do território, transferindo à população, notadamente a mais pobre, a responsabilidade pela mitigação dos danos e perdas. Palavras-chave: Desastres socioambientais; Rio Itajaí-Açu; Enchente.* Esse artigo é decorrente e parte da dissertação de mestrado escrita e orientada pelos autores deste artigo.