Uranium Deposits

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Patrice Bruneton - One of the best experts on this subject based on the ideXlab platform.

  • Mineralogy and Geochemistry of the Host-Rock Alterations Associated with the Shea Creek Unconformity-Type Uranium Deposits (Athabasca Basin, Saskatchewan, Canada). Part 1. Spatial Variation of Illite Properties
    Clays and Clay Minerals, 2006
    Co-Authors: Emmanuel Laverret, Patrice Bruneton, Daniel Beaufort, David Quirt, Philippe Kister, Patricia Patrier Mas, Norbert Clauer
    Abstract:

    Unconformity-related Uranium Deposits, which represent a significant high-grade Uranium resource, are systematically surrounded by a host-rock alteration halo enriched in clay minerals. Illite is often the major clay mineral component of the halo and it displays a variable crystal structure. New data are provided on the crystal structure and the chemistry of illite encountered within and outside of the alteration halo surrounding the Shea Creek deposit. Two illite populations were distinguished using textural and structural criteria: samples rich in the tv -1 M polytype display thin (sub-micrometer) and ‘hairy’ shapes, while samples richer in the cv -1 M polytype contain illites with rigid lath-like shapes several micrometers wide. In barren ‘regional’ sandstone, the trends with depth of the textural and microstructural properties of illite particles are: (1) an increase of particle size, (2) an evolution to a more isometric form, and (3) a dominance of the cv -1 M polytype over the tv -1 M polytype. These trends record diagenetic processes under conditions of deep burial and differ from those observed in altered sandstone around the Uranium mineralization. The altered sandstone is characterized by enrichment in the tv -1 M polytype near the unconformity and/or brittle structural features. This tv -1 M illitization took place in response to structurally-controlled infiltration of basement rocks by diagenetic brines which were further recycled after interaction into the overlying basin. Variations of the illite structural and textural properties may result from nucleation/growth kinetics and may be indicative of a change in the flow regime, and/or a change of saturation state of the fluid vs. illite. The tv -1 M illite may be favored in environments characterized by a high fluid/rock ratio and a high supersaturation state of the fluids in proximity to mineralization.

  • Mineralogy and Geochemistry of the Host-Rock Alterations Associated with the Shea Creek Unconformity-Type Uranium Deposits (Athabasca Basin, Saskatchewan, Canada). Part 2. Regional-Scale Spatial Distribution of the Athabasca Group Sandstone Matrix Minerals
    Clays and Clay Minerals, 2006
    Co-Authors: Philippe Kister, Daniel Beaufort, David Quirt, Emmanuel Laverret, Michel Cuney, Patricia Patrier Mas, Patrice Bruneton
    Abstract:

    The spatial distribution of the dominant matrix minerals present in the middle-Proterozoic Athabasca Group sandstone (kaolin, illite, sudoite, dravite, hematite) was studied at a regional scale in the Shea Creek region (Saskatchewan, Canada), in which two epigenetic unconformity-type Uranium Deposits have been discovered. 3D models of matrix mineral distribution were derived from normative mineral calculations and 3D interpolation using whole-rock geochemical analyses of sandstone samples collected from both mineralized and barren areas. The calculations were constrained by information obtained from petrographic and crystal-chemical clay mineralogical studies on representative samples. The 3D mineral distribution models were compared to the lithostratigraphy and structural features of the Athabasca Group sandstone to ascertain the source and mobility of the main elements involved in the sandstone host-rock alteration processes related to the U mineralization. The distribution of Al is conformable with the lithostratigraphy throughout the studied area, regardless of proximity to basement-rooted structures and U ore bodies. The distribution of illite displays similar features, but the intensity of the illitization of kaolin decreases with increasing distance from the structures and U ore bodies. Hematite bleaching and neoformation of sudoite and dravite were restricted to the vicinity of the fault zones above the U ore bodies. The spatial configurations of the mineral anomalies show that syn-ore fluids flowed from the basement towards the sandstone cover via the fault zones, as described in current metallogenic models. Although Al remained immobile (mass transfer), the anomalous K, B and Mg present in the host-rock alteration haloes were probably imported from the basement rocks (mass transport). Unlike B and Mg, K migrated laterally at least several kilometers from the basement-rooted faults. The mineral distribution models were used to quantify the volume of altered sandstone (10^−2−10^−1 km^3) and the amounts of K, Mg and B which were imported to the alteration haloes above the Shea Creek U ore bodies: 186,000 t of K, 66,000 t of Mg, and 11,000 t of B above the Anne ore body, and 24,000 t of K, 185,000 t of Mg, and a similar 11,000 t of B above the Colette ore body.

  • clay alteration associated with proterozoic unconformity type Uranium Deposits in the east alligator rivers Uranium field northern territory australia
    Economic Geology, 2005
    Co-Authors: Daniel Beaufort, Patrice Bruneton, Patricia Patrier, Emmanuel Laverret, J Mondy
    Abstract:

    Clay minerals associated with the unconformity-type Uranium Deposits of the East Alligator Rivers Uranium field have been used to determine the spatial distribution of hydrothermal alteration and the conditions of Uranium deposition within the altered basement underlying the Kombolgie unconformity. Alteration develops a similar pattern at regional and smaller scales, with a close relationship between the degree of alteration and the amount of structural discontinuities observed on both sides of the unconformity (e.g., faults, fractures, breccias). These discontinuities were mechanically active during the hydrothermal activity. The hydrothermal clay minerals partly to totally replace diagenetic dickite and illite in the Kombolgie sandstones and metamorphic phengite and chlorite in the basement rocks. The time-space alteration sequence established in this study can be summarized as follows: (1) early crystallization of illite ± illite-smectite (I-S) mixed layer minerals + LREE-Sr–bearing aluminum phosphate-sulfates (APS) in sandstones above the unconformity, illite ± I-S mixed layer minerals + sudoite + APS on both sides of the unconformity and in fault gouges, and illite ± I-S mixed layer minerals + chlorite ± apatite deeper in the basement; and (2) late precipitation of chlorite in the open fracture network mainly centered below the unconformity. The main stage of Uranium deposition was associated with chloritization in the basement rocks. Smaller particle size, lath-shaped or flaky morphology, common interstratification with expandable layers, lower crystallinity, and Mg-rich chemical compositions can be used to distinguish the hydrothermal clays from the other diagenetic and metamorphic illite and/or chlorite. Hydrothermal illite can be distinguished from diagenetic and metamorphic illite-phengite by its poor crystallinity along the c-axis, interstratification with minor amounts of smectite layers, and a 1M polytype in which trans-vacant octahedral sites predominate (1 Mt). Chemically, the hydrothermal illite differs from diagenetic illite by a lower interlayer charge and a higher Mg content. The hydrothermal chlorite is distinguished from the metamorphic chlorite by its smaller particle size, spherulitic habit, poor crystallinity along the c-axis, and common association with corrensite and/or chlorite-corrensite mixed layers. Most of the hydrothermal chlorite is Mg rich and has a structural formula close to that of clinochlore (XFe <0.20). Near the Uranium Deposits, the spherules of hydrothermal chlorite are chemically zoned (from XFe <0.10 to XFe <0.40), which is interpreted as the result of a change in the oxidation state of the hydrothermal solution during the chlorite crystallization. The space-time alteration sequence established for clay minerals and the observed transition of APS to apatite are interpreted as the result of an increasing degree of interaction of the basement rocks with infiltrating acidic and oxidizing sub-basinal brines. In turn, these fluids tend to be neutralized and reduced by their ongoing interaction with ferrous iron-bearing phyllosilicates (Fe chlorite and biotite) and iron sulfides of metamorphic origin. The ore Deposits are surrounded by zones in which the degree of fluid-rock interaction was very high and chloritization is most abundant. The octahedral Mg content of the associated hydrothermal illite from the sandstone can be used as a guide to indicate the possible presence of Uranium orebodies in the basement rocks, tens to hundreds of meters below. The crystal structures of the hydrothermal illite and chlorite suggest that these minerals crystallized at temperatures approximatively 30° to 50°C lower than those expected at the peak diagenesis of the Kombolgie sandstones near the unconformity.

  • aluminum phosphate sulfate minerals associated with proterozoic unconformity type Uranium Deposits in the east alligator river Uranium field northern territories australia
    Canadian Mineralogist, 2005
    Co-Authors: Stephane Gaboreau, Daniel Beaufort, Patricia Patrier, Philippe Vieillard, Patrice Bruneton
    Abstract:

    Aluminum phosphate–sulfate (APS) minerals occur as disseminated crystals in a wide range of geological environments near the Earth’s surface, including weathering, sedimentary, diagenetic, hydrothermal, metamorphic and also postmagmatic systems. Their general formula is AB3(XO4)2(OH)6, in which A, B and X represent three different crystallographic sites. These minerals are known to incorporate a great number of chemical elements in their lattice and to form complex solid-solution series controlled by the physicochemical conditions of their formation (Eh, pH, activities of constituent cations, P and T). These minerals are particularly widespread and spatially related to hydrothermal clay-mineral parageneses in the East Alligator River Uranium Field (EARUF) environment associated with Uranium orebodies in the Proterozoic Kombolgie basin of the Northern Territories, Australia. This field contains several high-grade unconformity-related Uranium Deposits, including Jabiluka and Ranger. Both petrography and chemical data are used to discuss the significance of APS minerals in the alteration processes from the EARUF. The wide range of chemical compositions recorded in APS is essentially due to coupled substitutions of Sr for the LREE and of S for P at the A and X sites, respectively. The major variations of the APS solid-solution series mainly consist of the relative proportions of svanbergite, goyazite and florencite end-members. The APS minerals result from the interaction of oxidizing and relatively acidic fluids with aluminous host-rocks enriched in monazite. The spatial distribution of these minerals and their compositional variation around the Uranium orebodies allow us to consider them as good tracers of redox and pH paleo-conditions responsible for the development of fronts during the alteration processes, and hence as potential tools for mineral exploration.

  • a detailed fluid inclusion study in silicified breccias from the kombolgie sandstones northern territory australia inferences for the genesis of middle proterozoic unconformity type Uranium Deposits
    Journal of Geochemical Exploration, 2003
    Co-Authors: Donatienne Derome, Patrice Bruneton, Michel Cathelineau, Michel Cuney, C Fabre, Jean Dubessy, Amelie Hubert
    Abstract:

    The relative chronology and detailed chemistry of paleofluids circulating at the base of the Kombolgie Sub-basin were investigated in the East Alligator River district (Northern Territory, Australia), where world-class unconformity-type Uranium Deposits are located. The chemistry of fluid inclusions was determined using in-situ analysis (Raman microprobe and laser-induced breakdown spectroscopy [LIBS]) and by observing the melting sequences by microthermometry. This study revealed the occurrence of three distinct fluids: (i) a sodium-rich brine that corresponds to a diagenetic fluid percolating at the bottom of the Kombolgie sandstones at a temperature close to 150±15 °C; (ii) a calcium-rich brine, probably corresponding to a residual brine in evaporitic environment that has evolved by fluid–rock interactions with the basement lithologies; and (iii) a low salinity fluid, heated in the basement, injected into the base of the sandstone cover. H2 and O2 and/or traces of CH4 were detected in the vapor phase of some fluid inclusions, especially in the low salinity ones in quartz breccia samples taken above mineralized areas. Hydraulic brecciation of the sandstone was associated with a pressure decrease favoring fluid mixing and the subsequent cementation of breccias. According to the fluid inclusion study and other geologic constrains, the minimum thickness of the Sub-Kombolgie Basin is estimated at 4 km. Drusy quartz breccias with evidence of fluid mixing are quite common at the base of the Kombolgie Basin, but not necessarily linked to U-mineralization. However, it is proposed that the presence of gases such as H2 and O2 in fluid inclusions, which results from water radiolysis, constitutes an indicator of gas linked to significant U concentrations deeper in the basement rocks.

Michel Cuney - One of the best experts on this subject based on the ideXlab platform.

  • origin of Uranium Deposits revealed by their rare earth element signature
    Terra Nova, 2011
    Co-Authors: Julien Mercadier, Mariechristine Boiron, Antonin Richard, Michel Cuney, Philippe Lach, Jessica Bonhoure, Mathieu Leisen, Philippe Kister
    Abstract:

    Uranium Deposits form in a wide range of geological settings, including deep magmatic to surficial conditions, and range in age from Archaean to recent. These temporal and spatial variations have given rise to an extreme diversity of ore Deposits. However, understanding their conditions of formation has remained challenging. This article reports rare earth element (REE) abundances, measured by microbeam methods in Uranium oxides, for a series of worldwide Uranium occurrences. The REE patterns are very specific to each deposit type and directly reflect the conditions of their genesis. We propose an evaluation of the first-order parameters controlling the REE behaviour in each mineralised system. This study demonstrates that the REE pattern is the most efficient tool for constraining the geological models of Uranium Deposits and for genetically discriminating new Uranium discoveries. This approach may form the starting point for a new procedure in the fight against nuclear trafficking.

  • origin of Uranium Deposits revealed by their rare earth element signature
    Terra Nova, 2011
    Co-Authors: Julien Mercadier, Mariechristine Boiron, Antonin Richard, Michel Cuney, Philippe Lach, Jessica Bonhoure, Mathieu Leisen, Philippe Kister
    Abstract:

    Uranium Deposits form in a wide range of geological settings, including deep magmatic to surficial conditions, and range in age from Archaean to recent. These temporal and spatial variations have given rise to an extreme diversity of ore Deposits. However, understanding their conditions of formation has remained challenging. This article reports rare earth element (REE) abundances, measured by microbeam methods in Uranium oxides, for a series of worldwide Uranium occurrences. The REE patterns are very specific to each deposit type and directly reflect the conditions of their genesis. We propose an evaluation of the first-order parameters controlling the REE behaviour in each mineralised system. This study demonstrates that the REE pattern is the most efficient tool for constraining the geological models of Uranium Deposits and for genetically discriminating new Uranium discoveries. This approach may form the starting point for a new procedure in the fight against nuclear trafficking.

  • an evaporated seawater origin for the ore forming brines in unconformity related Uranium Deposits athabasca basin canada cl br and δ37cl analysis of fluid inclusions
    Geochimica et Cosmochimica Acta, 2011
    Co-Authors: Antonin Richard, Julien Mercadier, Mariechristine Boiron, Michel Cuney, David Banks, Michel Cathelineau
    Abstract:

    Abstract Analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity-related Uranium Deposits from the Paleoproterozoic Athabasca Basin (Canada) were performed in order to determine the origin of chloride in the ore-forming brines. Microthermometric analyses show that samples contain variable amounts of a NaCl-rich brine (Cl concentration between 120,000 and 180,000 ppm) and a CaCl2-rich brine (Cl concentration between 160,000 and 220,000 ppm). Molar Cl/Br ratios of fluid inclusion leachates range from ∼100 to ∼900, with most values between 150 and 350. Cl/Br ratios below 650 (seawater value) indicate that the high salinities were acquired by evaporation of seawater. Most δ37Cl values are between −0.6‰ and 0‰ (seawater value) which is also compatible with a common evaporated seawater origin for both NaCl- and CaCl2-rich brines. Slight discrepancies between the Cl concentration, Cl/Br, δ37Cl data and seawater evaporation trends, indicate that the evaporated seawater underwent secondary minor modification of its composition by: (i) mixing with a minor amount of halite-dissolution brine or re-equilibration with halite during burial; (ii) dilution in a maximum of 30% of connate and/or formation waters during its migration towards the base of the Athabasca sandstones; (iii) leaching of chloride from biotites within basement rocks and (iv) water loss by hydration reactions in alteration haloes linked to Uranium deposition. The chloride in Uranium ore-forming brines of the Athabasca Basin has an unambiguous dominantly marine origin and has required large-scale seawater evaporation and evaporite deposition. Although the direct evidence for evaporative environments in the Athabasca Basin are lacking due to the erosion of ∼80% of the sedimentary pile, Cl/Br ratios and δ37Cl values of brines have behaved conservatively at the basin scale and throughout basin history.

  • Evolution of Uranium Fractionation Processes through Time: Driving the Secular Variation of Uranium Deposit Types
    Economic Geology, 2010
    Co-Authors: Michel Cuney
    Abstract:

    Uranium deposit types have evolved considerably from the Archean to the Present. The major global drivers were (1) change of geotectonic conditions during the Late Archean, (2) strong increase of atmospheric oxygen from 2.4 to 2.2 Ga, and (3) development of land plants during the Silurian. Other significant variations of Uranium deposit types are related to unique conjunctions of conditions such as those during phosphate sedimentation in the Cretaceous. Earth’s Uranium fractionation mechanisms evolved through four major periods. The first, from 4.55 and 3.2 Ga, corresponds to formation of a thin essentially mafic crust in which the most fractionated trondheimite-tonalite-granodiorite (TTG) rocks attained Uranium concentrations of at most a few parts per million. Moreover, the Uranium being essentially hosted in refractory accessory minerals and free oxygen being absent, no Uranium deposit could be expected to have formed during this period. The second period, from about 3.1 to 2.2 Ga, is characterized by several widespread pulses of highly fractionated potassic granite strongly enriched in U, Th, and K. Late in this period peraluminous granite was selectively enriched in U and to a lesser extent K. These were the first granite and pegmatite magmas able to crystallize high-temperature uraninite. The erosion of these granitic suites liberated thorium-rich uraninite which would then be concentrated in placer Deposits along with pyrite and other heavy minerals (e.g., zircon, monazite, Fe-Ti oxides) within huge continental basins (e.g., Witwatersrand, South Africa, and Bind River, Canada). The lack of free oxygen at that time prevented oxidation of the uraninite which formed the oldest economic Uranium deposit types on Earth, but only during this period. The third period, from 2.2 to 0.45 Ga, records increased oxygen to nearly the present atmospheric level. Tetravalent Uranium from uraninite was oxidized to hexavalent Uranium, forming highly soluble uranyl ions in water. Uranium was extensively trapped in reduced epicontinental sedimentary successions along with huge quantities of organic matter and phosphates accumulated as a consequence of biological proliferation, especially during the Late Paleoproterozoic. A series of Uranium Deposits formed through redox processes; the first of these developed at a formational redox boundary at about 2.0 Ga in the Oklo area of Gabon. All known economically significant Uranium Deposits related to Na metasomatism are about 1.8 Ga in age. The high-grade, large tonnage unconformity-related Deposits also formed essentially during the Late Paleoproterozoic to early Mesoproterozoic. The last period (0.45 Ga-Present) coincided with the colonization of continents by plants. The detrital accumulation of plants within continental siliciclastic strata represented intraformational reduced traps for another family of Uranium Deposits that developed essentially only during this period: basal, roll front, tabular, and tectonolithologic types. However, the increased recognition of hydrocarbon and hydrogen sulfide migration from oil or gas reservoirs during diagenesis suggests potential for sandstone-hosted Uranium Deposits to be found within permeable sandstone older than the Silurian. Large Uranium Deposits related to high-level hydrothermal fluid circulation and those related to evapotranspiration (calcretes) are only known during this last period of time, probably because of their formation in near-surface environments with low preservation potential.

  • micrometer scale carbon isotopic study of bitumen associated with athabasca Uranium Deposits constraints on the genetic relationship with petroleum source rocks and the abiogenic origin hypothesis
    Earth and Planetary Science Letters, 2007
    Co-Authors: Laure Sangely, Michel Cuney, Marc Chaussidon, Raymond Michels, Marc Brouand, Vincent Huault, Patrick Landais
    Abstract:

    Abstract In situ analytical techniques – Fourier transform infrared microspectroscopy (μFTIR) and ion microprobe – have been used to unravel the origin of solid bitumen associated with the Uranium Deposits of Athabasca (Saskatchewan, Canada). Both aliphaticity and carbon isotopic compositions within the samples are heterogeneous but spatially organized in concentric zonations at the micrometer scale. Finally, the δ 13 C values are positively correlated to the aliphatic contents over an extremely large isotopic range from ∼ − 49‰ to ∼ − 31‰. We infer that this positive correlation may be related to the carbon isotopic fractionations associated with the synthesis of bitumen through the catalytic hydrogenation of CO 2 , rather than the result of pre-existing petroleum product precipitation and/or alteration (such as radiolysis). This explanation is consistent with (i) published results of abiogenic synthesis experiments, in which the differences in δ 13 C values between saturated and unsaturated hydrocarbons range from + 2 and + 19‰, in contrast to the differences systematically observed in conventional bitumen and petroleum ranging from 0‰ to − 4‰; (ii) the absence of a similar positive correlation between aliphatic contents and δ 13 C values in the other bitumen analyzed in the present study, for which a biogenic origin has been unequivocally established (samples from Oklo, Gabon, and Lodeve, France, Uranium Deposits); (iii) the presence of CO 2 and H 2 in the gas-phase of fluid inclusions in the Athabasca Uranium Deposits, H 2 resulting from water radiolysis. The present results suggest that the δ 13 C vs. aliphaticity correlation could be used as a criterion to discriminate between abiogenic vs. biogenic origin of macromolecular organic matter.

Daniel Beaufort - One of the best experts on this subject based on the ideXlab platform.

  • alteration related to Uranium Deposits in the kiggavik andrew lake structural trend nunavut canada new insights from petrography and clay mineralogy
    Canadian Mineralogist, 2014
    Co-Authors: Thomas Riegler, Jeanluc Lescuyer, Peter Wollenberg, Dave Quirt, Daniel Beaufort
    Abstract:

    The Kiggavik project, located 70 km west of Baker Lake (Nunavut), is a major Uranium exploration project in the Canadian arctic, with three significant basement-hosted Uranium Deposits (Kiggavik, End, and Andrew) which spread along a NE SW trend a few kilometers from the south-eastern border of the Thelon Basin. These Deposits are closely associated with alteration zones in which clay minerals are abundant. At the scale of the whole structural trend, the alteration paragenesis is composed of illite +/- sudoite +/- hematite +/- aluminum phosphate sulfate minerals (APS). Alteration petrography and mineral paragenesis are similar to those identified in basement-hosted Uranium Deposits related to Paleoproterozoic unconfornaities in the Athabasca Basin (Canada) or Alligator River (Australia). The alteration haloes are characterized by two similar types of phyllosilicate assemblages (dioctahedral micas or illite and chlorites) corresponding to a regional retrograde metamorphic stage that was overprinted by hydrothermal alteration during the mineralization event. These two assemblages can be distinguished on the basis of crystallographic and chemical properties and mapping of structural parameters, such as the variation of crystallinity along the c-axis or the polytypes of phyllosilicates, which can be used as a vector to mineralization. The crystal chemistry of the hydrothermal phyllosilicates replacing the previous metamorphic minerals indicates a release of iron. This last point is fundamental to the occurrence of hematite in alteration zones and points out the potential effects of the iron redox state in the control of Uranium precipitation during the hydrothermal event

  • evidence of native radiation induced paramagnetic defects in natural illites from unconformity type Uranium Deposits
    Pacific Rim Conference on Multimedia, 2008
    Co-Authors: Thierry Allard, Daniel Beaufort, E Morichon, Patricia Patrier
    Abstract:

    This study presents the first unequivocal identification of natural radiation-induced defects in illites. Middle Proterozoic illites related to unconformity-type Uranium Deposits of Canada and Australia were studied using electron paramagnetic resonance (EPR) spectroscopy at X- and Q-band frequencies. The saturation behaviour of EPR spectra as a function of power demonstrates that native defects of illites are different from those known in other clays as kaolinite, dickite or smectite. Q-band spectra indicate the presence of several––at least two––native defects. The EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g ∥ = 2.032 and g ⊥ = 1.993. The corresponding defect is named as Ai center. The study of oriented specimen confirms the strong anisotropy, and shows that the main defect has its g ∥ component perpendicular to the (ab) plane of illite. These defects in illite correspond to electron holes located on oxygen atoms of the structure and likely associated to Si, according to the lack of hyperfine structure. The Ai center in illite has similar EPR parameters to the A center in kaolinite and dickite. The isochronal annealing data suggest that illite can be used as a dosimeter in the geosphere. However, the determination of half-life and activation energy of the Ai center requires additional work.

  • Mineralogy and Geochemistry of the Host-Rock Alterations Associated with the Shea Creek Unconformity-Type Uranium Deposits (Athabasca Basin, Saskatchewan, Canada). Part 1. Spatial Variation of Illite Properties
    Clays and Clay Minerals, 2006
    Co-Authors: Emmanuel Laverret, Patrice Bruneton, Daniel Beaufort, David Quirt, Philippe Kister, Patricia Patrier Mas, Norbert Clauer
    Abstract:

    Unconformity-related Uranium Deposits, which represent a significant high-grade Uranium resource, are systematically surrounded by a host-rock alteration halo enriched in clay minerals. Illite is often the major clay mineral component of the halo and it displays a variable crystal structure. New data are provided on the crystal structure and the chemistry of illite encountered within and outside of the alteration halo surrounding the Shea Creek deposit. Two illite populations were distinguished using textural and structural criteria: samples rich in the tv -1 M polytype display thin (sub-micrometer) and ‘hairy’ shapes, while samples richer in the cv -1 M polytype contain illites with rigid lath-like shapes several micrometers wide. In barren ‘regional’ sandstone, the trends with depth of the textural and microstructural properties of illite particles are: (1) an increase of particle size, (2) an evolution to a more isometric form, and (3) a dominance of the cv -1 M polytype over the tv -1 M polytype. These trends record diagenetic processes under conditions of deep burial and differ from those observed in altered sandstone around the Uranium mineralization. The altered sandstone is characterized by enrichment in the tv -1 M polytype near the unconformity and/or brittle structural features. This tv -1 M illitization took place in response to structurally-controlled infiltration of basement rocks by diagenetic brines which were further recycled after interaction into the overlying basin. Variations of the illite structural and textural properties may result from nucleation/growth kinetics and may be indicative of a change in the flow regime, and/or a change of saturation state of the fluid vs. illite. The tv -1 M illite may be favored in environments characterized by a high fluid/rock ratio and a high supersaturation state of the fluids in proximity to mineralization.

  • Mineralogy and Geochemistry of the Host-Rock Alterations Associated with the Shea Creek Unconformity-Type Uranium Deposits (Athabasca Basin, Saskatchewan, Canada). Part 2. Regional-Scale Spatial Distribution of the Athabasca Group Sandstone Matrix Minerals
    Clays and Clay Minerals, 2006
    Co-Authors: Philippe Kister, Daniel Beaufort, David Quirt, Emmanuel Laverret, Michel Cuney, Patricia Patrier Mas, Patrice Bruneton
    Abstract:

    The spatial distribution of the dominant matrix minerals present in the middle-Proterozoic Athabasca Group sandstone (kaolin, illite, sudoite, dravite, hematite) was studied at a regional scale in the Shea Creek region (Saskatchewan, Canada), in which two epigenetic unconformity-type Uranium Deposits have been discovered. 3D models of matrix mineral distribution were derived from normative mineral calculations and 3D interpolation using whole-rock geochemical analyses of sandstone samples collected from both mineralized and barren areas. The calculations were constrained by information obtained from petrographic and crystal-chemical clay mineralogical studies on representative samples. The 3D mineral distribution models were compared to the lithostratigraphy and structural features of the Athabasca Group sandstone to ascertain the source and mobility of the main elements involved in the sandstone host-rock alteration processes related to the U mineralization. The distribution of Al is conformable with the lithostratigraphy throughout the studied area, regardless of proximity to basement-rooted structures and U ore bodies. The distribution of illite displays similar features, but the intensity of the illitization of kaolin decreases with increasing distance from the structures and U ore bodies. Hematite bleaching and neoformation of sudoite and dravite were restricted to the vicinity of the fault zones above the U ore bodies. The spatial configurations of the mineral anomalies show that syn-ore fluids flowed from the basement towards the sandstone cover via the fault zones, as described in current metallogenic models. Although Al remained immobile (mass transfer), the anomalous K, B and Mg present in the host-rock alteration haloes were probably imported from the basement rocks (mass transport). Unlike B and Mg, K migrated laterally at least several kilometers from the basement-rooted faults. The mineral distribution models were used to quantify the volume of altered sandstone (10^−2−10^−1 km^3) and the amounts of K, Mg and B which were imported to the alteration haloes above the Shea Creek U ore bodies: 186,000 t of K, 66,000 t of Mg, and 11,000 t of B above the Anne ore body, and 24,000 t of K, 185,000 t of Mg, and a similar 11,000 t of B above the Colette ore body.

  • clay alteration associated with proterozoic unconformity type Uranium Deposits in the east alligator rivers Uranium field northern territory australia
    Economic Geology, 2005
    Co-Authors: Daniel Beaufort, Patrice Bruneton, Patricia Patrier, Emmanuel Laverret, J Mondy
    Abstract:

    Clay minerals associated with the unconformity-type Uranium Deposits of the East Alligator Rivers Uranium field have been used to determine the spatial distribution of hydrothermal alteration and the conditions of Uranium deposition within the altered basement underlying the Kombolgie unconformity. Alteration develops a similar pattern at regional and smaller scales, with a close relationship between the degree of alteration and the amount of structural discontinuities observed on both sides of the unconformity (e.g., faults, fractures, breccias). These discontinuities were mechanically active during the hydrothermal activity. The hydrothermal clay minerals partly to totally replace diagenetic dickite and illite in the Kombolgie sandstones and metamorphic phengite and chlorite in the basement rocks. The time-space alteration sequence established in this study can be summarized as follows: (1) early crystallization of illite ± illite-smectite (I-S) mixed layer minerals + LREE-Sr–bearing aluminum phosphate-sulfates (APS) in sandstones above the unconformity, illite ± I-S mixed layer minerals + sudoite + APS on both sides of the unconformity and in fault gouges, and illite ± I-S mixed layer minerals + chlorite ± apatite deeper in the basement; and (2) late precipitation of chlorite in the open fracture network mainly centered below the unconformity. The main stage of Uranium deposition was associated with chloritization in the basement rocks. Smaller particle size, lath-shaped or flaky morphology, common interstratification with expandable layers, lower crystallinity, and Mg-rich chemical compositions can be used to distinguish the hydrothermal clays from the other diagenetic and metamorphic illite and/or chlorite. Hydrothermal illite can be distinguished from diagenetic and metamorphic illite-phengite by its poor crystallinity along the c-axis, interstratification with minor amounts of smectite layers, and a 1M polytype in which trans-vacant octahedral sites predominate (1 Mt). Chemically, the hydrothermal illite differs from diagenetic illite by a lower interlayer charge and a higher Mg content. The hydrothermal chlorite is distinguished from the metamorphic chlorite by its smaller particle size, spherulitic habit, poor crystallinity along the c-axis, and common association with corrensite and/or chlorite-corrensite mixed layers. Most of the hydrothermal chlorite is Mg rich and has a structural formula close to that of clinochlore (XFe <0.20). Near the Uranium Deposits, the spherules of hydrothermal chlorite are chemically zoned (from XFe <0.10 to XFe <0.40), which is interpreted as the result of a change in the oxidation state of the hydrothermal solution during the chlorite crystallization. The space-time alteration sequence established for clay minerals and the observed transition of APS to apatite are interpreted as the result of an increasing degree of interaction of the basement rocks with infiltrating acidic and oxidizing sub-basinal brines. In turn, these fluids tend to be neutralized and reduced by their ongoing interaction with ferrous iron-bearing phyllosilicates (Fe chlorite and biotite) and iron sulfides of metamorphic origin. The ore Deposits are surrounded by zones in which the degree of fluid-rock interaction was very high and chloritization is most abundant. The octahedral Mg content of the associated hydrothermal illite from the sandstone can be used as a guide to indicate the possible presence of Uranium orebodies in the basement rocks, tens to hundreds of meters below. The crystal structures of the hydrothermal illite and chlorite suggest that these minerals crystallized at temperatures approximatively 30° to 50°C lower than those expected at the peak diagenesis of the Kombolgie sandstones near the unconformity.

J Mondy - One of the best experts on this subject based on the ideXlab platform.

  • clay alteration associated with proterozoic unconformity type Uranium Deposits in the east alligator rivers Uranium field northern territory australia
    Economic Geology, 2005
    Co-Authors: Daniel Beaufort, Patrice Bruneton, Patricia Patrier, Emmanuel Laverret, J Mondy
    Abstract:

    Clay minerals associated with the unconformity-type Uranium Deposits of the East Alligator Rivers Uranium field have been used to determine the spatial distribution of hydrothermal alteration and the conditions of Uranium deposition within the altered basement underlying the Kombolgie unconformity. Alteration develops a similar pattern at regional and smaller scales, with a close relationship between the degree of alteration and the amount of structural discontinuities observed on both sides of the unconformity (e.g., faults, fractures, breccias). These discontinuities were mechanically active during the hydrothermal activity. The hydrothermal clay minerals partly to totally replace diagenetic dickite and illite in the Kombolgie sandstones and metamorphic phengite and chlorite in the basement rocks. The time-space alteration sequence established in this study can be summarized as follows: (1) early crystallization of illite ± illite-smectite (I-S) mixed layer minerals + LREE-Sr–bearing aluminum phosphate-sulfates (APS) in sandstones above the unconformity, illite ± I-S mixed layer minerals + sudoite + APS on both sides of the unconformity and in fault gouges, and illite ± I-S mixed layer minerals + chlorite ± apatite deeper in the basement; and (2) late precipitation of chlorite in the open fracture network mainly centered below the unconformity. The main stage of Uranium deposition was associated with chloritization in the basement rocks. Smaller particle size, lath-shaped or flaky morphology, common interstratification with expandable layers, lower crystallinity, and Mg-rich chemical compositions can be used to distinguish the hydrothermal clays from the other diagenetic and metamorphic illite and/or chlorite. Hydrothermal illite can be distinguished from diagenetic and metamorphic illite-phengite by its poor crystallinity along the c-axis, interstratification with minor amounts of smectite layers, and a 1M polytype in which trans-vacant octahedral sites predominate (1 Mt). Chemically, the hydrothermal illite differs from diagenetic illite by a lower interlayer charge and a higher Mg content. The hydrothermal chlorite is distinguished from the metamorphic chlorite by its smaller particle size, spherulitic habit, poor crystallinity along the c-axis, and common association with corrensite and/or chlorite-corrensite mixed layers. Most of the hydrothermal chlorite is Mg rich and has a structural formula close to that of clinochlore (XFe <0.20). Near the Uranium Deposits, the spherules of hydrothermal chlorite are chemically zoned (from XFe <0.10 to XFe <0.40), which is interpreted as the result of a change in the oxidation state of the hydrothermal solution during the chlorite crystallization. The space-time alteration sequence established for clay minerals and the observed transition of APS to apatite are interpreted as the result of an increasing degree of interaction of the basement rocks with infiltrating acidic and oxidizing sub-basinal brines. In turn, these fluids tend to be neutralized and reduced by their ongoing interaction with ferrous iron-bearing phyllosilicates (Fe chlorite and biotite) and iron sulfides of metamorphic origin. The ore Deposits are surrounded by zones in which the degree of fluid-rock interaction was very high and chloritization is most abundant. The octahedral Mg content of the associated hydrothermal illite from the sandstone can be used as a guide to indicate the possible presence of Uranium orebodies in the basement rocks, tens to hundreds of meters below. The crystal structures of the hydrothermal illite and chlorite suggest that these minerals crystallized at temperatures approximatively 30° to 50°C lower than those expected at the peak diagenesis of the Kombolgie sandstones near the unconformity.

Philippe Kister - One of the best experts on this subject based on the ideXlab platform.

  • origin of Uranium Deposits revealed by their rare earth element signature
    Terra Nova, 2011
    Co-Authors: Julien Mercadier, Mariechristine Boiron, Antonin Richard, Michel Cuney, Philippe Lach, Jessica Bonhoure, Mathieu Leisen, Philippe Kister
    Abstract:

    Uranium Deposits form in a wide range of geological settings, including deep magmatic to surficial conditions, and range in age from Archaean to recent. These temporal and spatial variations have given rise to an extreme diversity of ore Deposits. However, understanding their conditions of formation has remained challenging. This article reports rare earth element (REE) abundances, measured by microbeam methods in Uranium oxides, for a series of worldwide Uranium occurrences. The REE patterns are very specific to each deposit type and directly reflect the conditions of their genesis. We propose an evaluation of the first-order parameters controlling the REE behaviour in each mineralised system. This study demonstrates that the REE pattern is the most efficient tool for constraining the geological models of Uranium Deposits and for genetically discriminating new Uranium discoveries. This approach may form the starting point for a new procedure in the fight against nuclear trafficking.

  • origin of Uranium Deposits revealed by their rare earth element signature
    Terra Nova, 2011
    Co-Authors: Julien Mercadier, Mariechristine Boiron, Antonin Richard, Michel Cuney, Philippe Lach, Jessica Bonhoure, Mathieu Leisen, Philippe Kister
    Abstract:

    Uranium Deposits form in a wide range of geological settings, including deep magmatic to surficial conditions, and range in age from Archaean to recent. These temporal and spatial variations have given rise to an extreme diversity of ore Deposits. However, understanding their conditions of formation has remained challenging. This article reports rare earth element (REE) abundances, measured by microbeam methods in Uranium oxides, for a series of worldwide Uranium occurrences. The REE patterns are very specific to each deposit type and directly reflect the conditions of their genesis. We propose an evaluation of the first-order parameters controlling the REE behaviour in each mineralised system. This study demonstrates that the REE pattern is the most efficient tool for constraining the geological models of Uranium Deposits and for genetically discriminating new Uranium discoveries. This approach may form the starting point for a new procedure in the fight against nuclear trafficking.

  • Mineralogy and Geochemistry of the Host-Rock Alterations Associated with the Shea Creek Unconformity-Type Uranium Deposits (Athabasca Basin, Saskatchewan, Canada). Part 1. Spatial Variation of Illite Properties
    Clays and Clay Minerals, 2006
    Co-Authors: Emmanuel Laverret, Patrice Bruneton, Daniel Beaufort, David Quirt, Philippe Kister, Patricia Patrier Mas, Norbert Clauer
    Abstract:

    Unconformity-related Uranium Deposits, which represent a significant high-grade Uranium resource, are systematically surrounded by a host-rock alteration halo enriched in clay minerals. Illite is often the major clay mineral component of the halo and it displays a variable crystal structure. New data are provided on the crystal structure and the chemistry of illite encountered within and outside of the alteration halo surrounding the Shea Creek deposit. Two illite populations were distinguished using textural and structural criteria: samples rich in the tv -1 M polytype display thin (sub-micrometer) and ‘hairy’ shapes, while samples richer in the cv -1 M polytype contain illites with rigid lath-like shapes several micrometers wide. In barren ‘regional’ sandstone, the trends with depth of the textural and microstructural properties of illite particles are: (1) an increase of particle size, (2) an evolution to a more isometric form, and (3) a dominance of the cv -1 M polytype over the tv -1 M polytype. These trends record diagenetic processes under conditions of deep burial and differ from those observed in altered sandstone around the Uranium mineralization. The altered sandstone is characterized by enrichment in the tv -1 M polytype near the unconformity and/or brittle structural features. This tv -1 M illitization took place in response to structurally-controlled infiltration of basement rocks by diagenetic brines which were further recycled after interaction into the overlying basin. Variations of the illite structural and textural properties may result from nucleation/growth kinetics and may be indicative of a change in the flow regime, and/or a change of saturation state of the fluid vs. illite. The tv -1 M illite may be favored in environments characterized by a high fluid/rock ratio and a high supersaturation state of the fluids in proximity to mineralization.

  • Mineralogy and Geochemistry of the Host-Rock Alterations Associated with the Shea Creek Unconformity-Type Uranium Deposits (Athabasca Basin, Saskatchewan, Canada). Part 2. Regional-Scale Spatial Distribution of the Athabasca Group Sandstone Matrix Minerals
    Clays and Clay Minerals, 2006
    Co-Authors: Philippe Kister, Daniel Beaufort, David Quirt, Emmanuel Laverret, Michel Cuney, Patricia Patrier Mas, Patrice Bruneton
    Abstract:

    The spatial distribution of the dominant matrix minerals present in the middle-Proterozoic Athabasca Group sandstone (kaolin, illite, sudoite, dravite, hematite) was studied at a regional scale in the Shea Creek region (Saskatchewan, Canada), in which two epigenetic unconformity-type Uranium Deposits have been discovered. 3D models of matrix mineral distribution were derived from normative mineral calculations and 3D interpolation using whole-rock geochemical analyses of sandstone samples collected from both mineralized and barren areas. The calculations were constrained by information obtained from petrographic and crystal-chemical clay mineralogical studies on representative samples. The 3D mineral distribution models were compared to the lithostratigraphy and structural features of the Athabasca Group sandstone to ascertain the source and mobility of the main elements involved in the sandstone host-rock alteration processes related to the U mineralization. The distribution of Al is conformable with the lithostratigraphy throughout the studied area, regardless of proximity to basement-rooted structures and U ore bodies. The distribution of illite displays similar features, but the intensity of the illitization of kaolin decreases with increasing distance from the structures and U ore bodies. Hematite bleaching and neoformation of sudoite and dravite were restricted to the vicinity of the fault zones above the U ore bodies. The spatial configurations of the mineral anomalies show that syn-ore fluids flowed from the basement towards the sandstone cover via the fault zones, as described in current metallogenic models. Although Al remained immobile (mass transfer), the anomalous K, B and Mg present in the host-rock alteration haloes were probably imported from the basement rocks (mass transport). Unlike B and Mg, K migrated laterally at least several kilometers from the basement-rooted faults. The mineral distribution models were used to quantify the volume of altered sandstone (10^−2−10^−1 km^3) and the amounts of K, Mg and B which were imported to the alteration haloes above the Shea Creek U ore bodies: 186,000 t of K, 66,000 t of Mg, and 11,000 t of B above the Anne ore body, and 24,000 t of K, 185,000 t of Mg, and a similar 11,000 t of B above the Colette ore body.

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