Geological Sciences

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Analytical formulas for geometrical factor and sensitivity for long electrodes
(Wiley, 2024-11-22) Butler, S.L.
In the electrical resistivity method, electrodes are usually modelled as point current sources and point voltage measurements. If the burial depth of the electrode is significant compared with the spacing between electrodes, this point approximation may not be accurate. Common situations employing long electrodes include the use of metal-cased boreholes as electrodes and small-scale, high-resolution environmental, engineering and archaeological surveys where electrode spacings may be very small. In this contribution, I present analytical expressions for the mutual resistance between long electrodes modelled as line current sources. Mutual resistances are then used to calculate geometrical factors. Additionally, I present an expression for the current density and use it to derive an analytical expression for the sensitivity of electrode arrays with long electrodes. The sensitivity is, in turn, used to calculate the mean depth and position which can be used as estimates of depth and position of investigation and as pseudosection plot points. Example calculations using the geometrical factor, sensitivity and mean depth are shown, and comparisons are made with simulations and lab-scale experiments.
Paleobotanical Evidence for Mediterranean Climates in the Western Canadian Paleoarctic During the Late Middle Eocene
(Paleoceanography and Paleoclimatology, 2024-10) West, Christopher K.; Reichgelt, Tammo; Reyes, Alberto; Buryak, Serhiy D; Staniszewska, Kasia; Basinger, James
Paleogene age deposits east of the Fifteenmile River, northwest of Dawson City, Yukon, Canada preserve a diverse high-latitude fossil flora. Here, we provide new data on the age of the fossil site based on laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) U-Pb dating of tephra zircons, paleobotanical paleoclimate reconstructions, and growing season length estimates based on photoperiod. These new data indicate an age of the Fifteenmile River fossil locality as late middle Eocene and likely within the Middle Eocene Climatic Optimum episode. The paleoflora-based paleoclimate reconstruction indicates the region was relatively wet and warm with non-freezing winters, but also experienced seasonal dryness, with an approximate 7 months long growing season as suggested by photoperiod. We interpret this paleoclimate as summer dry and winter wet—a climate analogous to modern day warm Mediterranean climates in the Köppen-Geiger climate classification system. These findings provide a new perspective on the past climate and environment of high-latitude ecosystems during warm greenhouse intervals and contribute to our understanding of the Earth's climate history and its potential future changes.
Trace element analysis and luminescence behavior of quartz in pegmatites of the Tørdal Region, Norway
(Chemical Geology, 2024-09-29) Sittner, Jonathan; Götze, Jens; Müller, Axel; Renno, Axel D.; Ziegenrücker, René; Pan, Yuanming
This publication presents a study on the mineral chemistry and luminescence properties of quartz samples from pegmatites of the Tørdal region in Norway. A total of 12 samples were analyzed using Secondary Ion Mass Spectrometry (SIMS), Electron Paramagnetic Resonance Spectroscopy (EPR), and Cathodoluminescence (CL) to gain insights into their trace element concentration and distribution as well as their luminescence behavior. The samples are characterized by different Cl emissions at 450 nm, 500 nm 650 nm and an additional shoulder at 390 nm, which is only partially visible due to the absorption of the glass optics. Of these luminescence bands, the 500 nm band is the most dominant in most samples and it is characterized by an initial blue-green luminescence, which is not stable under electron irradiation. Moreover, it is characterized by a heterogeneous distribution within the samples. This luminescence can be mostly assigned to [AlO4/M+]0 defects, with charge compensation mostly achieved by Li+. Analyses by EPR spectroscopy prove the dominance of structurally bound Al, Li, and Ti ions in the investigated samples. Further analyses using SIMS mapping demonstrate that Na and K are mainly bound to micro fractures or inclusions, suggesting a limited role in the compensation of the luminescence centers. Additionally, the SIMS mappings show that some samples contain Al-rich clusters of 10 to 20 μm in diameter, whereas other trace elements are characterized by a homogeneous distribution. These clusters correspond to bright luminescence areas in size and shape and could potentially indicate H+ compensated [AlO4/M+]0 defects.
Uranium mineralization in the Thrace Basin, NW Türkiye: Evidence from radiation-induced defects in detrital quartz and synchrotron XRF/ XANES analysis
(Journal of Geochemical Exploration, 2024-06-30) Tunc, Ayetullah; Yakup, Çelik; Feng, Renfei; Inanç, Olcay; Pan, Yuanming
The Paleogene-Neogene Thrace Basin in northwestern Türkiye has long been known to host economic gas and oil resources and has recently been reported to potentially host sandstone-type uranium deposits in the Oligocene Sülog ̆lu Formation. The latter discovery raises questions about the source and deposition mechanism of uranium mineralization in the basin. This contribution reports on the results of a detailed electron paramagnetic reso- nance (EPR) spectroscopic study of detrital quartz from four sandstone and one mudstone samples in the Sülog ̆lu Formation and documents the distribution and speciation of uranium using combined microbeam synchrotron X- ray fluorescence maps (μsXRF) and microbeam X-ray near edge structure spectroscopy (μsXANES). The EPR spectra of quartz separates are characterized by the presence of diagnostic radiation-induced defects (i.e., silicon- vacancy hole centers H′3, H′4, and H′7 with gmax = 2.049, 2.034, and 2.018, respectively, and the oxygen-vacancy electron center E′1), formed by the bombardment of alpha particles emitted from uranium, thorium, and their unstable progenies. Moreover, notable decreases in the intensity of silicon-vacancy hole centers in the EPR spectra of quartz separates after partial dissolution with hydrofluoric acid, provide compelling evidence for the circulation of uranium-bearing fluids in the Thrace Basin. The μsXRF and μsXANES data reveal the occurrences of mixed U6+ and U4+ species in hematite partially replacing pyrite aggregates but dominantly U4+ in disseminated pyrite and illite in sandstones of the Sülog ̆lu Formation. These results provide new insights into uranium transport, reduction, and deposition mechanisms, with important implications for better understanding sandstone-type uranium deposits in general and further exploration in the Thrace Basin.
Bellerophontid molluscs in the Grimsby Formation (Llandovery, lower Silurian), Hamilton, Ontario, Canada and their paleoecological and taphonomic implications
(Canadian Science Publishing, 2024-08-01) Pratt, Brian R.; Hopkins, Graeme J.; Hopkins, Richard J.
Specimens of a small bellerophontid mollusc, considered conspecific with Planorbis bilobatus Conrad 1839 from coeval strata in New York State, were recovered from the Grimsby Formation (lower Llandovery, lower Silurian), exposed in the Niagara Escarpment of western Hamilton, Ontario. Because Conrad’s species name is pre-occupied and is a secondary homonym, the new material is assigned to Tritonophon grimsbyensis n. sp. As Conrad’s original specimens are lost and where he collected them is unknown, a neotype from the Grimsby Formation is designated. These bellerophonts are preserved as casts on the soles of thin, fine-grained, sandstone beds interbedded with shale. These beds are probably tempestites Most are juvenile forms oriented on their sides, but in some beds adults with a widely expanded aperture are oriented aperture-down. Some specimens exhibit a V-shaped sinus on the median lobe, which is rarely preserved in Silurian examples. The aperture-down orientation suggests that this was the stable position during gentle wave action as well as probably their life position. Beds containing only juveniles may be evidence that the bellerophonts occasionally experienced a population boom but then were killed off during the storm event. Fine-grained sandstone fills the shell interiors, likely emplaced during wave-induced agitation. However, the shell walls are cast in mudstone, indicating that they dissolved during shallow burial and mud was pumped into the moulds. This may have been aided by episodic ground motion due to earthquakes that mobilized the adjacent sediment.
Geochronology (zircon U-Pb, Hf, O isotopes), provenance analysis, and tectonic setting of the Paleoproterozoic Karrat Group and supracrustal rocks of the Rinkian fold belt, West Greenland
(Elsevier, 2024-10) Partin, Camille A.; McDonald, Brayden S.; McConnell, Michael; Thrane, Kristine; Pearson, D. Graham; Sarkar, Chiranjeeb; Luo, Yan; Stern, Richard A.
We use zircon U-Pb, Hf and O isotopes to constrain the depositional ages and provenance of metasedimentary rocks of the Paleoproterozoic Karrat Group of West Greenland and to understand the tectonic processes leading to basin development on the eastern Rae craton. An older supracrustal assemblage (Qeqertarssuaq complex) deposited after ca. 2.6 Ga is separated by an unconformity with a younger supracrustal assemblage (the Karrat Group). The Qaarsukassak Formation at the base of the Karrat Group was deposited after ca. 2.0 Ga, with dominantly Archean age modes. The youngest siliciclastic rocks (Nûkavsak and Mârmorilik formations) in the Karrat Group have maximum depositional ages ranging from ca. 1980 to 1950 to 1900 Ma and contain dominant detrital zircon age modes between ca. 2.50 and 1.93 Ga. A ca. 1.92 Ga supracrustal assemblage referred to as the northern domain (Karrat Group, sensu lato) is geographically separated from the Karrat Group (sensu stricto) by the Prøven igneous complex. The stratigraphy and detrital zircon profiles are compared to broadly coeval sedimentary units on the Rae craton and a unifying model of their deposition is presented. The Rae craton is the dominant detritus source; initially these sources were mostly local, changing to a mix of local and distal sources including the western Rae craton. The tectonic setting of the Karrat basin transitioned from extensional to convergent to collisional during its basin evolution, reflecting Wilson cycle phases within an epeiric sea. Accordingly, zircon Hf isotopes in our dataset track the evolution of the opening and closing of the Manikewan Ocean. Detrital zircon Hf isotopes in our dataset reveal a greater proportion of juvenile detritus (especially ca. 2.15–1.95 Ga) than is known from the currently exposed crustal record, pointing to the importance of the detrital zircon record for understanding Paleoproterozoic crustal and tectonic evolution.
Recommended nomenclature of epidote-group minerals
(GeoScience World, 2006) Armbruster, Thomas; Bonazzi, Paola; Akasaka, Mashide; Bermanec, Vladimir; Chopin, Christian; Giere, Reto; Heuss-Aßbichler, Soraya; Liebscher, Axel; Menchetti, Silvio; Pan, Yuanming; Pasero, Marco
Epidote-group minerals are monoclinic in symmetry and have topology consistent with space group P21/m and the general formula A2M3[T2O7][TO4](O,F)(OH,O). Zoisite is an orthorhombic polymorph of clinozoisite Ca2Al3[Si2O7][SiO4]O(OH) and is thus not considered a member of the epidote-group. Epidote-group minerals are divided into three subgroups. (1) Members of the clinozoisite subgroup are derived from the mineral clinozoisite Ca2Al3[Si2O7][SiO4]O(OH) by homovalent substitutions only. The key cation- and anion-sites are A1 = M2+, A2 = M2+, M1 = M3+, M2 = M3+, M3 = M3+, O4 = O2-, O10 = (OH)-. In other words, the dominant valence as listed above must be maintained. (2) Members of the allanite subgroup are REE-rich minerals typified by the eponymous mineral “allanite”. This subgroup may be derived from clinozoisite by homovalent substitutions and one coupled heterovalent substitution of the type A2(REE)3+ + M3M2+ → A2Ca2+ + M3M3+. Thus the valences on the key sites are: A1 = M2+, A2 = M3+, M1 = M3+, M2 = M3+, M3 = M2+, O4 = O2-, O10 = (OH)-. (3) Members of the dollaseite subgroup are REE-rich minerals typified by the eponymous mineral “dollaseite”. This subgroup may be derived from clinozoisite by homovalent substitutions and two coupled heterovalent substitutions of the type A2(REE)3+ + M3M2+ → A2Ca2+ + M3M3+ and M1M2+ + O4F-→ M1M3+ + O4O-2. Thus the valences on the key sites are: A1 = M2+, A2 = M3+, M1 = M2+, M2 = M3+, M3 = M2+, O4 = F-, O10 = (OH)-. The key cation-sites M3 and A1 (and, in principle, M2) determine the root name. In both clinozoisite and allanite subgroups no prefix is added to the root name if M1 = Al. The prefixes ferri, mangani, chromo, and vanado indicate dominant Fe3+, Mn3+, Cr3+, and V3+ on M1, respectively. In the dollaseite subgroup no prefix is added to the root name if M1 = Mg. Otherwise a proper prefix must be attached; the prefixes ferro and mangano indicate dominant Fe2+ and Mn2+ at M1, respectively. The dominant cation on A2 (other than Ca) is treated according to the Extended Levinson suffix designation. This simple nomenclature requires renaming of the following approved species: Niigataite (old) = clinozoisite-(Sr) (new), hancockite (old) = epidote-(Pb) (new), tweddillite (old) = manganipiemontite-(Sr) (new). Minor modifications are necessary for the following species: Strontiopiemontite (old) = piemontite-( Sr) (new), androsite-(La) (old) = manganiandrosite-(La) (new). Before a mineral name can be assigned, the proper subgroup has to be determined. The determination of a proper subgroup is made by the dominating valence at M3, M1, and A2 expressed as M2+ and or M3+, not by a single, dominant ion (i.e., Fe2+, or Mg, or Al). In addition, the dominant valence on O4: X- or X2- must be ascertained. [M2+]A2 > 0.50, [M3+]M3 > 0.50 → clinozoisite subgroup, [M3++ M4+]A2 > 0.50, [M2+]M3 > 0.50 → allanite subgroup, {[M2+]M3+M1 – [M3++ M4+]A2 } > 0.50 and [X-]O4 > 0.5 → dollaseite subgroup. Coupled heterovalent substitutions in epidote-group minerals require a special application of the so-called 50 % rule in solid-solution series. (1) Clinozoisite subgroup: The dominant trivalent cation on M3 determines the name, whereas the A2 cation appearing in the suffix has to be selected from among the divalent cations. (2) Allanite and dollaseite subgroups: For the sites involved in the charge compensation of a heterovalent substitution in A2 and O4 (i.e. M3 in the allanite subgroup; M3 and M1 in the dollaseite subgroup), identification of the relevant end-member formula must take into account the dominant divalent charge-compensating octahedral cation (M2+) and not the dominant cation in these sites. Formal guidelines and examples are provided in order to determine a mineral “working name” from electron-microprobe analytical data.
Widespread Archean basement beneath the Yangtze craton
(GeoScience World, 2006) Zheng, Jianping; Griffin, William L; O’Reilly, Suzanne Y.; Zhang, Ming; Pearson, Norman; Pan, Yuanming
The age distribution of the crust is a fundamental parameter in modeling continental evolution and the rate of crustal accretion through Earth’s history, but this is usually estimated from surface exposures. The exposed Yangtze craton in eastern China consists mainly of Proterozoic rocks with rare Archean outcrops. However, the U-Pb ages and Hf isotope systematics of xenocrystic zircons brought to the surface in lamproite diatremes from three Proterozoic outcrop areas of the craton suggest the widespread presence of unexposed Archean basement, with zircon age populations of 2900–2800 Ma and 2600– 2500 Ma and Hf model ages of 2.6 to ca. 3.5 Ga or older. The zircons also record thermal events reworked on the craton ca. 2020 Ma (remelting of older crust) and 1000–850 Ma (addition of juvenile mantle material). The observation of deep crust significantly older than the upper crust will require revision of models for the rates of crustal generation through time.
Equilibrium shapes of two and three dimensional two-phase rotating fluid drops with surface tension: effects of inner drop displacement
(American Institute of Physics, 2022-11-01) Butler, Samuel
The shapes of rotating fluid drops held together by surface tension is an important field of study in fluid mechanics. Recently, experiments with micron-scale droplets of liquid helium have been undertaken and it has proven useful to compare the shapes of the resultant superfluid droplets with classical analogs. If the helium is a mixture of He3 and He4, two phases are present. In a recent paper, the shapes of rotating two phase fluid droplets were calculated where the inner drop was constrained to stay at the drop center. The outer shapes and dimensionless rotation rate-angular momentum relationships were shown to be similar to single phase drops provided that the density and surface tension scales were chosen appropriately. In the current paper, I investigate models in which the inner drop can displace from the centre. In order to simplify the analyses, two dimensional drops are first investigated. I show that the inner drop is unstable in the centre position if its density is greater than the outer density and that the inner drop will move towards the outer boundary of the drop in these cases. When the inner drop has a higher density than the outer drop, the moment of inertia of displaced inner drops is increased relative to centered drops and hence the kinetic energy is decreased. Shapes of two and three dimensional drops, rotation rate-angular momentum and kinetic and surface energy relationships are investigated for off-axis inner drops with parameters relevant to recent liquid He experiments.
Trace element-mineral associations in modern and ancient iron terraces in acid drainage environments
(Elsevier, 2016-07-31) Cruz-Hernandez, Pablo; Pérez-López, Rafael; Parviainen, Annika; Lindsay, Matthew B. J.; Nieto, José M.
Iron-rich sediments commonly cover riverbeds that have been affected by acid drainage associated with sulfide-mineral oxidation. Freshly-formed precipitates correspond to poorly-crystalline oxyhydroxysulfates that recrystallize over time. This study examined the distribution and mineral association of trace elements (e.g., As, Cu, Zn) in modern and ancient (~ 6 Ma) Fe terraces in the Tinto river basin, Spain. The mineral composition of the terraces was determined by Raman μ-spectroscopy. Chemical digestions, electron probe microanalyses, and synchrotron-based μ-X-ray fluorescence mapping were used to examine As, Cu, and Zn distribution and corresponding mineral associations. Fresh precipitates at modern terrace surfaces were dominated by schwertmannite, which contained high As, Cu, Mn, and Zn concentrations. However, schwertmannite transforms into goethite over days to weeks in the deeper part of the current terraces and into hematite over centuries. Affinity for trace elements was generally highest for schwertmannite and lowest for hematite, which suggests that their retention by Fe terraces decreases during mineral transformation. Hence, schwertmannite acts as temporary sink for contaminants, which are again released over long time periods. These findings should be considered for management and treatment of possible water resources affected by acid mine drainage.
Influence of As(V) on precipitation and transformation of schwertmannite in acid mine drainage-impacted waters
(Schweizerbart science publishers, 2018-12-07) Cruz-Hernandez, Pablo; Carrero, Sergio; Pérez-Lópeza, Rafael; Fernandez-Martinez, Alejandro; Lindsay, Matthew B. J.; Dejoie, Catherine; Nieto, José M.
Iron-rich sediments commonly cover riverbeds affected by acid mine drainage (AMD). Initial precipitates are often dominated by schwertmannite, which has an exceptionally high capacity to sequester As and other toxic elements. This poorly crystalline Fe oxyhydroxysulfate rapidly recrystallizes to goethite; however, the influence of trace elements on ageing rates and products is poorly understood. This study examined the influence of As(V) concentrations on the kinetics of schwertmannite precipitation and transformation. Schwertmannite was synthesized in the presence of various initial dissolved As concentrations (i.e., 0–2 mM) and subsequently aged at 40, 60 or 85 °C for 1 h to 300 d. The initial As concentration had a profound impact on schwertmannite precipitation and transformation. Schwertmannite precipitation was inhibited at higher initial As concentrations in favor of pseudo-amorphous Fe-hydroxyarsenate formation. Schwertmannite transformation to goethite was accompanied by sulfate release and, over longer time, As release. Pair distribution function (PDF) analysis of high-energy X-ray diffraction (HEXD) patterns revealed that increasing initial As concentration produced structural defects in associated precipitates. Schwertmannite precipitation exerts an important control on As mobility in AMD-impacted waters; however, this study has demonstrated that the long-term stability of schwertmannite and associated precipitates should be considered when designing AMD remediation strategies and AMD treatment systems.
X-ray absorption spectroscopy and X-ray diffraction data for molybdenum minerals and compounds
(Elsevier, 2022-09-13) Schoepfer, Valerie; Lindsay, Matthew B. J.
We report Mo K- and LIII-edge X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) data collected for 15 molybdenum minerals and compounds sourced from museum collections, mineral dealers, and chemical suppliers. The samples were finely ground and analyzed at the Canadian Light Source synchrotron (Saskatoon, Canada). The L III-edge XAS data were collected in fluorescence and total electron yield mode, while the K-edge XAS data were collected in transmission and fluorescence modes. Molybdenum L III-edge spectra cover the X-ray absorption near edge structure (XANES) region and Mo K-edge spectra cover the extended X-ray absorption fine structure (EXAFS) region. Tabulated XAS data are provided to support analysis of XAS data obtained for geological or environmental research. Furthermore, Mo K-edge EXAFS and L III-edge XANES spectra, the k3 weighted oscillatory χ(k) functions, and the Fourier-transforms in χ(R) of these K-edge data are presented graphically. Corresponding XRD data were collected as two-dimensional images against an area detector and integrated to form line scans. The data were collected at a wavelength of 0.68866 Å (18 keV) and is tabulated and presented graphically over a 0-40 °2Q range. This dataset is intended to be used as reference material for a variety of rare and common Mo phases.
Repartitioning of co-precipitated Mo(VI) during Fe(II) and S(-II) driven ferrihydrite transformation
(Elsevier, 2022-08-29) Schoepfer, Valerie; Lindsay, Matthew B. J.
Molybdenum is an essential element for most biological systems. Biosynthesis of Mo-enzymes that support global biogeochemical cycles of N, C, and S depends upon bioavailable molybdate (MoO42−). Interactions with Fe(III) (oxyhydr)oxides can limit Mo bioavailability in aerobic environments, while redox-driven mineral transformations can enhance Mo sequestration. Here, we examine Mo repartitioning during Fe(II) and S(-II) driven ferrihydrite transformation under anaerobic conditions. We reacted Mo(VI) co-precipitated 2-line ferrihydrite with Fe(II)(aq) or S( II)(aq) and monitored geochemical and mineralogical changes over time. Inductively coupled plasma–mass spectrometry (ICP–MS) and synchrotron powder X-ray diffraction (XRD) results revealed rapid Fe(II)(aq) and S(-II)(aq) uptake and limited Mo release during extensive ferrihydrite transformation to goethite [α-FeOOH] and lepidocrocite [γ-FeOOH] in the Fe(II) and S( II) experiments. Transmission electron microscopy–selected area electron diffraction (TEM-SAED), coupled with Mo LIII-edge and K-edge X-ray absorption near edge structure (XANES) spectroscopy, revealed partial Mo(VI) reduction and precipitation of kamiokite [Fe2MoIV3O8] and sidwillite [MoVIO3‧2H2O] in both experiments. Extended X-ray absorption fine structure (EXAFS) spectroscopy at the Mo K-edge revealed Mo-O, Mo-Fe and Mo-Mo bonding consistent with kamiokite precipitation in both Fe(II) and S(-II) experiments, and the absence of Mo-S bonding in the S(-II) experiments. Similar Mo(VI) repartitioning pathways during Fe(II) and S( II) driven ferrihydrite transformation suggests that: (i) Fe(II) served as the electron donor for ferrihydrite transformation in both experiments, with Fe(II)(aq) likely produced in situ via ferrihydrite sulfidation in the S( II) experiments; and (ii) co-precipitation inhibited Mo release and limited subsequent interactions S(-II)(aq) during ferrihydrite transformation. Overall, our findings indicate that initial association with FeOx phases can strongly influence Mo sequestration pathways in anaerobic environments.
Geochemical characteristics of oil sands fluid petroleum coke
(Elsevier, 2016-11-30) Nesbitt, Jake A.; Lindsay, Matthew B. J.; chen, ning
The geochemical characteristics of fluid petroleum coke from an oil sands mine in the Athabasca Oil Sands Region (AOSR) of northern Alberta, Canada were investigated. Continuous core samples were collected to 8 m below surface at several locations (n = 12) from three coke deposits at an active oil sands mine. Bulk elemental analyses revealed the coke composition was dominated by C (84.2 ± 2.3 wt. %) and S (6.99 ± 0.26 wt. %). Silicon (9210 ± 3000 mg kg−1), Al (5980 ± 1200 mg kg−1), Fe (4760 ± 1200 mg kg−1), and Ti (1380 ± 430 mg kg−1) were present in lesser amounts. Vanadium (1280 ± 120 mg kg−1) and Ni (230 ± 80 mg kg−1) occurred at the highest concentrations among potentially-hazardous minor and trace elements. Sequential extractions revealed potential for release of these elements under field-relevant conditions. Synchrotron powder X-ray diffraction revealed the presence of Si and Ti oxides, organically-complexed V and hydrated Ni sulfate, and provided information about the aromatic carbon matrix. X-ray absorption near edge structure (XANES) spectroscopy at the V and Ni K-edges revealed that these metals were largely hosted in porphyrins and similar organic complexes throughout coke grains. Slight variations among V and Ni K-edge spectra were largely attributed to slight variations in local coordination of V(IV) and Ni(II) within these organic compounds. However, linear combination fits were improved by including reference spectra for phases with octahedrally-coordinated V(III) and Ni(II). Sulfur and Fe K-edge XANES confirmed that thiophenic coordination and pyritic-ilmenitic coordination are predominant, respectively. These results provide new information on the geochemical and mineralogical composition of oil sands fluid petroleum coke and improve understanding of potential controls on associated water chemistry.
Aqueous- and solid-phase molybdenum geochemistry of oil sands fluid petroleum coke deposits, Alberta, Canada
(Elsevier, 2018-11-12) Robertson, Jared M.; Nesbitt, Jake A.; Lindsay, Matthew B. J.
Fluid petroleum coke generated at oil sands operations in the Athabasca Oil Sands Region of northern Alberta, Canada, contains elevated concentrations of molybdenum (Mo) and other metals including nickel (Ni) and vanadium (V). Solid-phase Mo concentrations in fluid petroleum coke are typically 10 to 100 times lower than V and Ni, yet dissolved Mo concentrations in associated pore waters are often comparable with these metals. We collected pore water and solids from fluid petroleum coke deposits in the AOSR to examine geochemical controls on Mo mobility. Dissolved Mo concentrations increased with depth below the water table, reaching maxima of 1.4 to 2.2 mg L-1, within a mixing zone between slightly acidic and oxic meteoric water and mildly alkaline and anoxic oil sands process-affected water (OSPW). Dissolved Mo concentrations decreased slightly with depth below the mixing zone. X-ray absorption spectroscopy revealed that Mo(VI) and Mo(IV) species were present in coke solids. The Mo(VI) occurred as tetrahedrally coordinated MoO42- adsorbed via inner- and outer-sphere complexation, and was coordinated in an environment similar to Fe-(hydr)oxide surface complexes. The OSPW likely promoted desorption of outer-sphere Mo(VI) complexes, resulting in higher dissolved Mo concentrations in the mixing zone. The principal Mo(IV) species was MoS2, which originated as a catalyst added upstream of the fluid coking process. Although MoS2 is likely stable under anoxic conditions below the mixing zone, oxidative weathering in the presence of meteoric water may promote long-term Mo release.
Mineralogy and geochemistry of oil sands froth treatment tailings: Implications for acid generation and metal(loid) release
(Elsevier, 2019-02-04) Lindsay, Matthew B. J.; Vessey, Colton; Robertson, Jared M.
Froth treatment tailings (FTT) are one of three principal tailings streams generated during bitumen extraction at oil sands mines in northern Alberta, Canada. Unlike the coarse tailings and fluid fine tailings, FTT are enriched in sulfide-minerals content and exhibit the potential for acid generation and metal(loid) leaching. However, the mineralogical and geochemical characteristics of this sulfide-bearing tailings stream remain poorly constrained. We examined samples of fresh FTT (n = 3) and partially-weathered FTT collected from a sub-aerial beach deposit (n = 15). X-ray diffraction revealed that weathering-resistant silicates, phyllosilicates, and oxides dominated (85 ± 7.3 wt. %) the FTT mineral assemblage, while sulfides (6.2 ± 3.6 wt. %) and carbonates (8.9 ± 4.3 wt. %) were relatively minor phases. Pyrite [FeS2] was the principal sulfide in all samples, while minor amounts of marcasite [FeS2] occurred only in beach samples. Sulfide mineral textures were highly variable and included euhedral to subhedral pyrite crystals, discrete and clustered pyrite framboids, and marcasite replacements of pyrite framboids. Siderite [FeCO3] accounted for 55 to 90 % of all carbonates, while dolomite [CaMg(CO3)2], calcite [CaCO3] and ankerite [Ca(Fe,Mg,Mn)(CO3)2] accounted for the remainder. Statistical analysis of bulk geochemical compositions suggested that environmentally-relevant metal(loid)s, including As, Cu, Co, Fe, Mn, Ni, Pb and Zn, were likely associated with sulfides, carbonates and, to a lesser extent, phyllosilicates. Electron probe microanalyses revealed a wide range of As, Cu, Co, Mn, Ni and Zn concentrations in pyrite, with As and Cu concentrations elevated in framboids. Rare earth elements (REEs), Th and U also occurred at elevated concentrations and statistical analyses suggest they are associated with zircon and, potentially, monazite and xenotime. Static acid-base accounting (ABA) tests indicated that all FTT samples are potentially acid generating. Our study describes the mineralogical and geochemical characteristics of oil sands FTT, and indicates that oxidative weathering has the potential to generate acidic drainage containing elevated dissolved concentrations of several metal(loid)s.
Aqueous vanadate removal by iron(II)-bearing phases under anoxic conditions
(American Chemical Society (ACS) Publications, 2020-03-06) Vessey, Colton; Lindsay, Matthew B. J.
Vanadium contamination is a growing environmental hazard worldwide. Aqueous vanadate (HxVVO4(3−x)− (aq)) concentrations are often controlled by surface complexation with metal (oxyhydr)oxides in oxic environments. However, the geochemical behaviour of this toxic redox sensitive oxyanion in anoxic environments is poorly constrained. Here we describe results of batch experiments to determine kinetics and mechanisms of aqueous H2VVO4− (100 μM) removal under anoxic conditions in suspensions (2.0 g L−1) of magnetite, siderite, pyrite, and mackinawite. We present results of parallel experiments using ferrihydrite (2.0 g L−1) and Fe2+(aq) (200 μM) for comparison. Siderite and mackinawite reached near complete removal (46 µmol g−1) of aqueous vanadate after 3 h and kinetic rates were generally consistent with ferrihydrite. Whereas magnetite removed 18 µmol g−1 of aqueous vanadate after 48 h and uptake by pyrite was limited. Uptake by Fe2+(aq) was observed after 8 h, concomitant with precipitation of secondary Fe phases. X ray absorption spectroscopy revealed V(V) reduction to V(IV) and formation of bidentate corner-sharing surface complexes on magnetite and siderite, and with Fe2+(aq) reaction products. These data also suggest that V(IV) is incorporated into the mackinawite structure. Overall, we demonstrate that Fe(II)-bearing phases can promote aqueous vanadate attenuation and, therefore, limit dissolved V concentrations in anoxic environments.
Adsorption of (Poly)vanadate onto Ferrihydrite and Hematite: An In Situ ATR–FTIR Study
(American Chemical Society (ACS) Publications, 2020-03-25) Vessey, Colton; Schmidt, Michael P.; Abdolahnezhad, Mojtaba; Peak, Derek; Lindsay, Matthew B. J.
Vanadium (V) has been a useful trace metal in describing Earth’s biogeochemical cycling and development of industrial processes; however, V has recently been recognized as a potential contaminant of concern. Although Fe (oxyhydr)oxides are important sinks for aqueous V in soils and sediments, our understanding of adsorption mechanisms is currently limited to mononuclear species (i.e., HxVO4(3–x)–). Here we use in situ attenuated total reflectance – Fourier transform infrared spectroscopy to examine sorption mechanisms and capacity for (poly)vanadate attenuation by ferrihydrite and hematite from pH 3 to 6. Adsorption isotherms illustrate the low affinity of polyvanadate species for ferrihydrite surfaces compared to hematite. Mononuclear V species (i.e., [HxVO4](3−x)− and VO2+) were present at all experimental conditions. At low surface loadings and pH 5 and 6, H2VO4− adsorption onto ferrihydrite and hematite surfaces results from formation of inner sphere complexes. At [V]T above 250 µM, adsorbed polynuclear V species in this study include H2V2O72− and V4O124−. Whereas, HV10O286−, H3V10O285−, and NaHV10O284− are the predominant adsorbed species at pH 3 and 4 and elevated [V]T. Surface polymers were identified on hematite at all experimental pH values, whereas polymeric adsorption onto ferrihydrite was limited to pH 3 and 4. These results suggest that hematite offers a more suitable substrate for polymer complexation compared to ferrihydrite. Our results demonstrate the pH and concentration dependant removal of (poly)vanadate species by Fe(III) (oxyhydr)oxides, which has implications for understanding V mobility, behaviour, and fate in the environment.
Structural Incorporation of Sorbed Molybdate during Iron(II)-Induced Transformation of Ferrihydrite and Goethite under Advective Flow Conditions
(American Chemical Society (ACS) Publications, 2020-06-08) Schoepfer, Valerie; Qin, Kaixuan; Robertson, Jared M.; Das, Soumya; Lindsay, Matthew B. J.
Aqueous Fe(II) can induce recrystallization of ferrihydrite and goethite [α‑FeOOH] to their more crystalline or molecularly homogenous counterparts. Despite common association with these and other Fe(III) (oxyhydr)oxides, relationships between Fe(II)-induced transformation and Mo mobility remain poorly constrained. We conducted laboratory column experiments to examine repartitioning of sorbed Mo during Fe(II)-induced transformation of ferrihydrite and goethite under advective flow conditions. We first pumped (~0.25 L d−1) artificial groundwater containing 0.1 mM MoO42− and buffered to pH 6.5 through columns packed with ferrihydrite- and goethite-coated sand until > 90 % Mo breakthrough was observed. Extended X-ray absorption fine structure (EXAFS) spectroscopy shows that initial MoO42− attenuation resulted from inner sphere complexation of MoO4 tetrahedra at ferrihydrite and goethite surfaces. We then pumped Mo-free anoxic artificial groundwater containing 0.2 mM or 2.0 mM Fe(II) through the columns until effluent Mo concentrations remained < 0.005 mM. Raman spectroscopy shows that Fe(II) introduction induced transformation of both ferrihydrite and goethite to lepidocrocite. Additionally, Fe(II) introduction mobilized 4 to 34 % of sorbed Mo and total mass release was greater for (i) ferrihydrite compared to goethite columns and (ii) low Fe(II) compared to high Fe(II) influent. Effluent pH decreased to ~5.8 for columns receiving the high Fe(II) influent and returned to pH 6.5 after 5 to 10 pore volumes. EXAFS spectroscopy indicates that structural incorporation of MoO6 octahedra into neoformed phases contributes to Mo retention during Fe(II) induced transformation. Our results offer new insight into Mo repartitioning during Fe(II)-induced transformation of Fe(III) (oxyhydr)oxides and, more generally, controls on Mo mobility in geohydrologic systems.
Molybdenum(VI) sequestration mechanisms during iron(II)-induced ferrihydrite transformation
(American Chemical Society (ACS) Publications, 2021-08-04) Schoepfer, Valerie; lum, jullieta; Lindsay, Matthew B. J.
Adsorption and coprecipitation reactions with Fe(III) (oxyhydr)oxides contribute to Mo(VI) attenuation within geohydrologic systems. Redox transitions within these systems can promote transformation of metastable phases, including ferrihydrite, and repartitioning of associated Mo(VI). Recent studies show that Mo(VI) coordination shifts from tetrahedral to octahedral during Fe(II)-induced ferrihydrite transformation. However, effects of initial conditions including solution pH, the Mo(VI) uptake mechanism, and Mo(VI) loading on repartitioning are not known. We performed batch experiments using ferrihydrite suspensions prepared with adsorbed or coprecipitated Mo(VI) (0, 25, and 100 μmol g–1) at two initial pH values (pH0; 5.0 and 6.5). We catalyzed ferrihydrite transformation under anoxic conditions by adding Fe(II)(aq) (0.5 mM) and monitored pH, [Mo]T, and [Fe]T over time. After 168 h, we collected reacted solids for analysis by powder X-ray diffraction (XRD), transmission electron microscopy-selected area electron diffraction (TEM-SAED), and Mo K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. XRD data indicate that bulk ferrihydrite transformation was limited in all but the pH0 6.5 coprecipitated Mo(VI) experiments. The TEM-SAED results reveal that nanoscale lepidocrocite and goethite formed at ferrihydrite surfaces in all experiments, whereas nanoscale bamfordite [FeMo2O6(OH)3·H2O] crystallites were observed in pH0 6.5 experiments. EXAFS models reveal changes in Mo(VI) coordination and bonding consistent with bamfordite precipitation combined with structural incorporation into neoformed goethite and lepidocrocite. Our results improve the understanding of Mo(VI) retention pathways in geohydrologic systems.

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