Authors / CoAuthors
Kirste, D. | de Caritat, P. | Welch, S.
Abstract
Introduction Developing predictive numerical models of hydrogeochemical systems requires an understanding of the physical and chemical processes affecting the composition of the water. Physical processes like mixing and evaporation can be reasonably well defined using the chemical data but redox sensitive chemical processes are more difficult to quantify. Applying the isotope chemistry of dissolved sulfate to characterise and even quantify these redox processes enhances the capabilities of numerical modelling, in particular those associated with acid mine drainage, acid sulfate soils and sulfide mineral exploration. This work describes how the stable isotopes of sulfur and oxygen in sulfate can be used to better characterise geochemical processees and thereby improve reactive transport models. Discussion Groundwater, pore water and surface water from a number of areas in Australia have been used to determine the sources of sulfur in acid sulfate susceptable systems. Several trends become apparent, sulfate reduction, and sulfide oxidation commonly dominate the chemical processes controlling sulfur in a groundwater system. Bacterial sulfate reduction (BSR) can be recognised by the affect on the 34S and 18O of sulfate. Both ratios increase as the lighter isotope is removed through dissimilatory bacterial reduction, leaving behind the heavier isotopes. Oxidation of sulfides occurs through 2 processes, one involving molecular oxygen (O2) and the other involving oxidised iron (Fe3+). The different pathways result in considerable differences in the oxygen isotopic composition of the product sulfate. Surface water and some groundwater from the Loveday basin in SA show evidence of evaporation and BSR while the near surface pore waters, although similarly evaporated, contain sulfate that predominantly originates from sulfide oxidation. Sulfate in groundwater from several other regions has stable isotopic compositions that indicate sulfide oxidation involving either the O2 or the Fe3+ pathways. The implications of are that the sulfate history can be understood through isotopic analysis and that this can be used in geochemical models to trace
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nonGeographicDataset
eCat Id
64967
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
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Keywords
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- External PublicationAbstract
- ( Theme )
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- groundwater
- ( Theme )
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- geochemistry
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2006-01-01T00:00:00
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geoscientificInformation
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70
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