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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
- Emmanuel Laverret, Patricia Patrier Mas, Daniel Beaufort, Philippe Kister, David Quirt, Patrice Bruneton, Norbert Clauer
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- Journal:
- Clays and Clay Minerals / Volume 54 / Issue 3 / June 2006
- Published online by Cambridge University Press:
- 01 January 2024, pp. 275-294
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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-1M polytype display thin (sub-micrometer) and ‘hairy’ shapes, while samples richer in the cv-1M 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-1M polytype over the tv-1M 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-1M polytype near the unconformity and/or brittle structural features. This tv-1M 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-1M 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.
Clay Minerals in Basalt-Hawaiite Rocks From Mururoa Atoll (French Polynesia). I. Mineralogy
- Antoine Mas, Alain Meunier, Daniel Beaufort, Patricia Patrier, Patrick Dudoignon
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- Journal:
- Clays and Clay Minerals / Volume 56 / Issue 6 / December 2008
- Published online by Cambridge University Press:
- 01 January 2024, pp. 711-729
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Clay minerals in chilled or brecciated margins (altered glass) and massive inner crystalline parts (mesostasis) of three basalt-hawaiite bodies from Mururoa Atoll (French Polynesia) have been studied in order to compare their chemical and mineralogical compositions. Polyphase assemblages comprise di- and trioctahedral phases, both of which consist of non-expandable layers (chlorite, celadonite) and two types of expandable layers (saponite and Fe-rich smectite or ‘nontronite-like’ material). The presence of the Fe-rich clays is supported by the presence of the X-ray diffraction 060 peak at 1.51–1.52 Å and of the infrared absorption bands at 875 and 822 cm−1 (Fe3+-Al-OH and Fe3+-Fe3+-OH groups, respectively). The chemical composition of the Fe-rich smectites does not fit with the theoretical nontronite field. The layer charge averages 1 per Si4O10 making these Fe-rich smectites close to ‘celadonite-type’ clays. This could explain the presence of mixed-layer celadonite-smectite. Plotted in an M+/4Si vs. Fe/sum octahedral cations diagram, the chemical compositions of clay minerals in the mesostasis form a continuous field limited by the celadonite-high-charge nontronite-like smectite and chlorite end-members. The clay assemblages are different from those formed in hydrothermal systems or low-grade metamorphic conditions which are characterized by the sequence: saponite → randomly ordered chlorite-smectite mixed-layered minerals (MLMs) → corrensite → chlorite. The systematic presence of Fe-rich clays either in the altered chilled margins or in the massive inner parts of the basalt-hawaiite bodies (high-charge nontronite-like smectite and mixed-layer nontronite-celadonite) makes the Mururoa sea-mount a potential terrestrial analogue for Mars surface exploration.
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
- Philippe Kister, Emmanuel Laverret, David Quirt, Michel Cuney, Patricia Patrier Mas, Daniel Beaufort, Patrice Bruneton
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- Journal:
- Clays and Clay Minerals / Volume 54 / Issue 3 / June 2006
- Published online by Cambridge University Press:
- 01 January 2024, pp. 295-313
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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 km3) 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 Minerals in Basalt-Hawaiite Rocks From Mururoa Atoll (French Polynesia). II. Petrography and Geochemistry
- Alain Meunier, Antoine Mas, Daniel Beaufort, Patricia Patrier, Patrick Dudoignon
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- Journal:
- Clays and Clay Minerals / Volume 56 / Issue 6 / December 2008
- Published online by Cambridge University Press:
- 01 January 2024, pp. 730-750
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The clay minerals formed in chilled margins and massive crystallized inner parts of three basalt-hawaiite bodies of Mururoa Atoll (French Polynesia) exhibit contrasting textures. Glass alteration textures are observed around fractures crosscutting the quenched margins: Fe-rich clays grow inward into the glass (retreating surface) while Mg-rich clays grow outward (open space). The textures of clay deposits filling the diktytaxitic voids (mesostasis) in the massive inner parts of the three volcanic bodies are different: unoriented clay matrix with embedded euhedral apatite and pyroxene microcrysts (submarine flow); pallisadic clays coating the void walls and the crystal surfaces of apatite and K-feldspar microcrysts (subaerial flow); and clay muffs covering all the apatite needles, with the central part of the void remaining empty (dike). The unoriented texture could result from the alteration of a glass precursor concomitant with the olivine phenocrysts (clay pseudomorphs). However, such an alteration implies important chemical transfers which are not observed. The pallisadic and muff textures form through heterogeneous nucleation on the solid surfaces and crystal growth from a saline solution. No glass precursor existed. As the center of the diktytaxitic voids in the dike is empty, the residual liquid was probably boiling. The amounts of light rare earth elements (LREE), Sr, and the most incompatible elements are greater in clays from diktytaxitic voids relative to the amounts formed in the altered glass of the chilled margins. Thus, diktytaxitic clays formed from a residual liquid which gave either an evolved glass or a saline solution after cooling (fractionation process). The δ18O variation vs. loss on ignition (LOI) indicates that sea water was involved either in rock alteration or magma contamination. This is confirmed by the 87Rb/86Sr ratio of bulk rocks and clay fractions from the quenched and massive inner parts of the three volcanic bodies which do not fit with the 11.5 Ma isochron indicating that the Rb-Sr system was not closed at any stage during the magmatic history.
Application of chemical geothermometry to low-temperature trioctahedral chlorites
- Atsuyuki Inoue, Alain Meunier, Patricia Patrier-Mas, Cecile Rigault, Daniel Beaufort, Philippe Vieillard
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- Journal:
- Clays and Clay Minerals / Volume 57 / Issue 3 / June 2009
- Published online by Cambridge University Press:
- 01 January 2024, pp. 371-382
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Low-temperature chlorites formed in diagenetic to low-grade metamorphic environments generally have greater Si contents and larger numbers of octahedral vacancies, and smaller Fe+Mg contents than higher-grade metamorphic chlorites. The compositional variations are characterized approximately by four end-member components: Al-free trioctahedral chlorite, chamosite, corundophilite, and sudoite. The solid solution is considered to be a random mix of cations and vacancies in the octahedral sites. Using the compositions of chlorites from Niger, Rouez, and Saint Martin diagenetic-hydrothermal series, a new, more convenient geothermometer, applicable to low-T chlorites is proposed and comparison made with geothermometers proposed previously. The chlorites studied contain appreciable amounts of Fe(III) (>14% of the total Fe), determined by Mössbauer spectroscopy. The calculations under which all Fe was regarded as ferrous gave considerable overestimates for the formation temperature, irrespective of the geothermometer used. This problem was reduced by taking into account the presence of Fe(III) in the octahedral sites. The geothermometer from this study gave more reasonable estimates than the geothermometers proposed by Walshe (1986) and Vidal et al. (2001), particularly in the case of the Niger chlorites which crystallized in the lowest-temperature conditions. The ordered-site substitution model of solid solution developed by Vidal et al. (2001) predicted satisfactorily the formation temperature of the Rouez chlorites and of some of the Saint Martin chlorites, suggesting that the chlorite compositions are controlled by the exchange at low-T conditions while they are controlled by Tschermak exchange at higher temperatures. The decreasing number of vacancies with temperature are poorer in Fe-rich than in Fe-poor chlorites. Furthermore, the ordered-site occupation of cations and vacancies in trioctahedral chlorite occurs concomitantly with the compositional changes ruled by increasing temperature conditions.
Spatial and temporal evolution of hydrothermal alteration at Lavras do sul, Brazil: Evidence from dioctahedral clay minerals
- Everton Marques Bongiolo, Patricia Patrier-Mas, André Sampaio Mexias, Daniel Beaufort, Milton Luiz Laquintinie Formoso
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- Journal:
- Clays and Clay Minerals / Volume 56 / Issue 2 / April 2008
- Published online by Cambridge University Press:
- 01 January 2024, pp. 222-243
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TheAu-Cu (±Pb, Zn, Ag) prospects of Lavras do Sul, southernmost Brazil, arehosted in Neoproterozoic granitic and volcanogenic rocks. Mineralization occurs in structurally controlled N40°W to E-W quartz veins; sericite (±chlorite) and sulfides are the main secondary minerals in associated wall rocks.
In the present contribution we use petrography (optical microscopy and scanning electron microscopy (SEM)), mineralogy (X-ray diffraction (XRD) with polytypes, FWHM, decomposition of diffraction patterns), and crystal chemistry of samples from several prospects to document the spatial and temporal evolution of sericitic alteration of veins and wall rocks associated with gold.
Hexagonal, coarse-grained 2M1 phengite-rich alteration (± illite) is best developed with coarse-grained primary growth (comb) quartz + pyrite ± Au veins and altered wall rock from the western portion of the granitic complex (phyllic alteration). Pure phengite was recognized by narrow XRD profiles (FWHM ⩽ 0.2°2θ CuKα) of the <5 µm particle-size fraction, non-expandable d001 X-ray reflections and interlayer charge (IC) >0.9 per O10(OH)2.
Towards the eastern zones of the granitic complex and in the volcanogenic rocks, wider XRD profiles (FWHM values ⩾ 0.2°2θ CuKα) were decomposed. They contain mixtures of coarse- to fine-grained, lath-like crystals of both 2M1 and 1M illite (non-expandable d001 X-ray reflections, IC between 0.85 and 0.89 per O10(OH)2) with expandable d001 reflections associated with lath-like, fine-grained crystals of ordered (R ⩾ 1) illite-rich I-S (80–90% of illite; IC of ∼0.8 per O10(OH)2), and minor amounts of regularly ordered (R = 1), illite-rich I-S mixed layers (75% of illite; IC of ∼0.74 per O10(OH)2). The dioctahedral clay association of illite + illite-rich I-S mixed layers (intermediate argillic alteration) is best developed in quartz + pyrite ± Au veins, breccias, and wall-rock alteration from the eastern portion of the granitic complex and in the volcanic area. Quartz from veins and breccias has fine-grained primary growth, recrystallization, and replacement textures, similar to those in epithermal deposits.
The overall distribution of the dioctahedral clays indicates that the study area represents a fracture-controlled, tilted, porphyry to epithermal deposit, with telescoping alteration features observed in the east of the mining district. Deeper levels of exposure of a large hydrothermal system are observed in the west of the mining district, as shown by higher-rank dioctahedral minerals (phengite) that crystallize at relatively high temperatures (Tphe ≈ 300°C, phyllic alteration) associated with coarse-grained, primary-growth quartz veins, similar to those observed in porphyry deposits. On the other hand, shallower levels of exposure are observed in the east of the study area, associated with abundant, lower-rank dioctahedral clay minerals (illite + illite-rich I-S mixed layers, intermediate argillic alteration) that crystallize at relatively lower temperatures (TI-S ≈ 120–200°C).
Available data show that gold is associated with phengite, but that lower-rank, overprinting alteration characterized by illite-I-S may have locally modified the original gold grades.