Stable isotopes (H, O, S) signatures evidencing evolutionary trends of Brazilian spas groundwaters

Autor(es)

Soler, Albert ^[1] ; Bonotto, Daniel Marcos ^[2]

Afiliação do(s) autor(es)

^[1] Univ Barcelona, Fac Ciencies Terra, Dept Mineral Petrol & Geol Apl, Res Grp Mineral Aplicada & Medio Ambiente MAiMA, Grup MAiMA SGR Mineral Aplicada Geoquim & Geomicr, C Marti I Franques S-N, E-08028 Barcelona - Spain

^[2] Univ Estadual Paulista, IGCE, UNESP, Av 24-A 1515, POB 178, BR-13506900 Rio Claro, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: JOURNAL OF GEOCHEMICAL EXPLORATION; v. 210, MAR 2020.
• Citações Web of Science: 0

Resumo

This paper reports a stable isotope (H, O, S) study of groundwater samples (25) in 10 spas from southeast Brazil. They are cold (25 degrees C, 36%), hypothermal (25-33 degrees C, 60%) and mesothermal (33-36 degrees C, 4%) waters; and are predominantly composed of bicarbonate, carbonate and sodium. Dissolved sulfate is the dominant anion in one water sample and its concentration increased with increase in pH, electrical conductivity (EC) and total dissolved solids (TDS) values in the samples. H-2 and O-18 data reported in the literature for circa 700 rainwater samples collected in Sao Paulo State and Brasilia airport, Brazil, were used to construct the following regional meteoric waterline (RMWL): delta H-2 V-SMOW (parts per thousand) = 8.06 delta O-18(water) V-SMOW (parts per thousand) + 12.85. The H-O isotopes of the studied groundwater samples show a delta O-18(water) variation of -14.1 to -5.3% V-SMOW, whereas the delta H-2 range was -66.5 to -31.7% V-SMOW, which was plotted on or near the RMWL, suggesting a meteoric origin for them. However, one hypothermal water sample (29 degrees C) plotted away from this RMWL, and is from a deep fractured aquifer which mainly occurs in fenitization aureole rocks surrounding the carbonatite complex at Araxa spa, Minas Gerais State, and a magmatic hydrothermal water may contribute to this water sample. The use of both delta S-34(sulfate) and delta O-18(sulfate) values in the selected sites permitted the plotting of a mixture line of the dissolved sulfate in the different aquifer systems of this study, considering two major sources as endmembers: sulfide oxidation, SOX (delta S-34(sulfate)=+1% and delta O-18(sulfate)=+1 parts per thousand) and sulfates possessing delta S-34(sulfate)=+9 parts per thousand and delta O-18(sulfate) = +21% (OSW). This is an unusual isotopic composition opposite from that of sea water. The delta S-34(sulfate) and delta O-18(sulfate) values tend to increase with increase in dissolved sulfate concentration. The OeS isotopes signatures that deviated from the general mixture line could be due to several processes, including atmospheric deposition, SO2 oxidation in the atmosphere, soil-derived sulfate, sulfide oxidation, evaporites dissolution and the presence of dissimilatory sulfate-reducing bacteria. Three sulfate isotope composition of spring waters from Aguas da Prata spa in the Pocos de Caldas alkaline massif (PCAM) represented endmember sources that defined a triangle around the remaining PCAM samples, as well as the samples from the crystalline basement, Sao Francisco craton, and Alto Paranaiba igneous province (APIP). Such triangle allows for estimation of the relative isotopic contribution in the different spas groundwaters, which is a new approach that focuses on the use of delta S-34(sulfate)-delta O-18(sulfate) pair in environmental studies, and shows its usefulness in addition to other conventional hydrogeochemical fingerprints. (AU)

• Processo FAPESP: 16/03054-2 - Estudo radiométrico integrado em estâncias hidrominerais dos estados de São Paulo e Minas Gerais
• Beneficiário: Daniel Marcos Bonotto
• Modalidade de apoio: Auxílio à Pesquisa - Regular