Arsenic speciation in fluid inclusions using micro-beam X-ray absorption spectroscopy
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Julianne James-Smith
Abstract
Synchrotron radiation X-ray fluorescence (SR-XRF) was used to characterize As speciation within natural fluid inclusions from three deposits with different hydrogeochemical and geological settings. The studied samples represent different compositions of Au-bearing fluids: typical orogenic Au deposit (low-salinity, ~6 mol% CO2 ± CH4; Brusson, Western Italian Alps); brines from a Proterozoic (Fe)- Cu-Au deposit (Starra, Queensland, Australia); and an As-rich magmatic fluid with a bulk composition similar to that typical of orogenic gold (Muiane pegmatite, Mozambique). Arsenic K-edge X-ray absorption spectra (XAS) were obtained from fluid inclusions at temperatures ranging from 25 to 200°C, and compared with spectra of aqueous As(III) and As(V) solutions and minerals. X-ray absorption near edge structure (XANES) data show that initially the fluid inclusions from all three regions contain some As in reduced form [As(III) at Brusson and Muiane; As-sulfide or possibly As(0) at Starra]. However, this reduced As is readily oxidized under the beam to As(V). Therefore, extended X-ray absorption fine structure (EXAFS) spectra for the As(III) aqueous complex could be collected only on the sample from the Muiane pegmatite containing large fluid inclusions with high As concentrations (>>1000 ppm). Analysis of these EXAFS data shows that As(OH)3(aq) (coordination number of 3.0 ± 0.2 atoms, bond length of 1.76 ± 0.01 Å) is the dominant arsenic aqueous species in the Muiane fluid inclusions at 100 °C, in accordance with predictions based on studies conducted using autoclaves. The As(V) complex resulting from photooxidation in the Muiane inclusions was characterized at 200 °C; the As-O bond distance (1.711 ± 0.025 Å) corresponds to that found in the arsenate group in minerals, and to that measured for the (HAsO4)2- complex at room temperature (1.700 ± 0.023 Å).
The extent of the XAS information that could be obtained for As in this study was limited by the rapid photooxidation that occurred in all inclusions, despite the relatively low photon flux density used (~4.4 × 106 photons/s/μm2). Photosensitivity was not observed in autoclave experiments and is the result of a complex interaction between redox-sensitive complexes in solution and the products of water radiolysis generated by the beam. Even under such challenging experimental conditions, the information gathered provides some precious information about As chemistry in ore-forming fluids
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Corundum–leucosome-bearing aluminous gneiss from Ayyarmalai, Southern Granulite Terrain, India: A textbook example of vapor phase-absent muscovite-melting in silica-undersaturated aluminous rocks
- Near infrared spectra of white mica in the Belt Supergroup and implications for metamorphism
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- The crystal chemistry and crystal structure of kuksite, Pb3Zn3Te6+P2O14, and a note on the crystal structure of yafsoanite, (Ca,Pb)3Zn(TeO6)2
- Chabazite-Mg: a new natural zeolite of the chabazite series
- Solution calorimetric investigation of fluor-chlorapatite crystalline solutions
- Pertsevite-(OH), a new mineral in the pertsevite series, Mg2(BO3)1–x(SiO4)x(F,OH)1–x (x < 0.5), from the Snezhnoye deposit in Sakha-Yakutia Republic, Russia
- Bitikleite-(SnAl) and bitikleite-(ZrFe): New garnets from xenoliths of the Upper Chegem volcanic structure, Kabardino-Balkaria, Northern Caucasus, Russia
- Silicon coordination in rutile and TiO2-II at ambient and high pressures: Si-29 NMR
- Spin orientation in a natural Ti-bearing hematite: Evidence for an out-of-plane component
- Theoretical determination of the Raman spectra of single-crystal forsterite (Mg2SiO4)
- Nitrogen and hydrogen isotope compositions and solubility in silicate melts in equilibrium with reduced (N+H)-bearing fluids at high pressure and temperature: Effects of melt structure
- In situ ultrasonic velocity measurements across the olivine-spinel transformation in Fe2SiO4
- The computation of equilibrium assemblage diagrams with Theriak/Domino software
- Determination of nanoparticulate magnetite stoichiometry by Mössbauer spectroscopy, acidic dissolution, and powder X-ray diffraction: A critical review
- Low-temperature behavior of natural kalsilite with P31c symmetry: An in situ single-crystal X-ray diffraction study
- First-principles simulations of MgO tilt grain boundary: Structure and vacancy formation at high pressure
- The effect of oxo-component on the high-pressure behavior of amphiboles
- Integral molar absorptivities of OH in muscovite at 20 to 650 °C by in-situ high-temperature IR microspectroscopy
- Principles of thermal expansion in the feldspar system
- A moissanite cell apparatus for optical in situ observation of crystallizing melts at high temperature
- Polezhaevaite-(Ce), NaSrCeF6, a new mineral from the Khibiny massif (Kola Peninsula, Russia)
- The interlayer structure of trioctahedral lithian micas: An AXANES spectroscopy study at the potassium K-edge
- Amorphous Materials: Properties, Structure, and Durability. Arsenic enrichment in hydrous peraluminous melts: Insights from femtosecond laser ablation-inductively coupled plasma-quadrupole mass spectrometry, and in situ X-ray absorption fine structure spectroscopy
- Letter. Partial high-grade alteration of monazite using alkali-bearing fluids: Experiment and nature
- Letter. A first-principles determination of the orientation of H3O+ in hydronium alunite
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- Letter. Kaolin polytypes revisited ab initio at 10 GPa
