Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (11) Citing Articles via Google Scholar Google Scholar Articles by Utsunomiya, S. Articles by Ewing, R. C. Search for Related Content GeoRef GeoRef Citation

Nanoscale mineralogy of arsenic in a region of New Hampshire with elevated As-concentrations in the groundwater

Satoshi Utsunomiya, Stephen C. Peters^*, Joel D. Blum and Rodney C. Ewing

Department of Geological Sciences, University of Michigan, Ann Arbor, Michigan 48109-2104, U.S.A.

Correspondence: E-mail: rodewing{at}umich.edu

Bedrock samples were examined from a region in south-central New Hampshire in order to understand the factors responsible for elevated As-concentrations (up to 180 ppb) in the groundwater. Although the As is predominantly from natural sources, the precise mineralogy of the As-bearing phases was unknown. As-bearing samples were examined in detail using advanced electron microscopy techniques, including high-angle annular dark field scanning electron microscopy (HAADF-STEM), STEM elemental mapping, and high resolution TEM. Numerous As-bearing minerals were observed, predominantly arsenopyrite (FeAsS) with some westerveldite (FeAs). The arsenopyrite was partially altered to nanocrystalline (~20 nm) magnetite and westerveldite, most likely during hydrothermal circulation of fluids following the emplacement of a nearby granitoid pluton. A reaction rim surrounds the pristine cores of arsenopyrite, with compositionally variable amorphous zones (containing Fe, As, K, and O), a Cu-sulfide, and a uranium-bearing phase, suggesting at least three distinct fluid compositions during alteration. Because the K-Fe-As-oxide is amorphous and the nanocrystalline FeAs has a high surface area per unit mass, the dissolution rate of As-bearing phases during recent low-temperature weathering is increased. The rapid dissolution of the reduced As phase (FeAs), which is unstable under oxidizing conditions, may be an important factor in the elevated As-concentrations in the groundwaters of this region.

This article has been cited by other articles:

				N.K. Foley and R.A. Ayuso Mineral sources and transport pathways for arsenic release in a coastal watershed, USA Geochemistry: Exploration, Environment, Analysis, February 1, 2008; 8(1): 59 - 75. [Abstract] [Full Text] [PDF]