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Personne :
Makvandi, Sheida

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Makvandi

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Sheida

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Université Laval. Département de géologie et de génie géologique

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ncf13701002

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  • PublicationAccès libre
    PCA of Fe-oxides MLA data as an advanced tool in provenance discrimination and indicator mineral exploration : case study from bedrock and till from the Kiggavik U deposits area (Nunavut, Canada)
    (Association of Exploration Geochemists, 2018-11-26) Makvandi, Sheida; Beaudoin, Georges; McClenaghan, Margaret Beth; Quirt, D.; Ledru, Patrick
    Magnetite and hematite grains from the 0.25–0.5 mm and 0.5–2.0 mm ferromagnetic fractions of ten till samples collected up-ice, overlying and down-ice of the Kiggavik U deposits (Nunavut, Canada), as well as eight bedrock samples from Kiggavik igneous and metasedimentary basement and overlying sedimentary rocks were characterized for their grain size and mineral association using optical microscopy, scanning electron microscopy (SEM) and mineral liberation analysis (MLA). Principal component analysis (PCA) was used to evaluate the MLA data for Fe-oxide mineral association and grain size distribution. PCA shows that mineralogical and granulometric differences in Fe-oxides from Kiggavik igneous rocks distinguish them from that of Kiggavik metasedimentary and sedimentary rocks. In addition, The PCA results indicate that the composition and abundance of minerals associated/intergrown with Fe-oxides are not only different in various till samples, but also in different size fractions of the same sample. Higher proportions of hornblende, quartz, gahnite, grunerite, apatite, chromite and sulfides are intergrown with Fe-oxides in the 0.5–2.0 mm till fraction, as compared to the 0.25–0.5 mm fraction in which Fe-oxides are mostly associated with pyroxene, titanite, rutile, feldspars, calcite and zircon. The mineral associations and grain sizes of proximal bedrocks are reflected in smaller size fractions of Kiggavik till, whereas detrital grains in the 0.5–2.0 mm fraction of Kiggavik till may have originated from distal sources. PCA also shows that Fe-oxides from the Kiggavik bedrock and till can be discriminated from those of volcanogenic massive sulfide (VMS) deposits because of smaller grain sizes and higher abundances of sulfides, gahnite, axinite, corundum, hypersthene and pyroxene intergrown with VMS Fe-oxides. This study emphasizes the importance of selecting suitable representative grain size fractions of till, or other sediments, when using indicator minerals for exploration. The results of PCA of Fe-oxides MLA data are consistent with the results of using Fe-oxides geochemical data in provenance discrimination of Kiggavik till.
  • PublicationAccès libre
    Geochemistry of magnetite and hematite from unmineralized bedrock and local till at the Kiggavik uranium deposit : implications for sediment provenance
    (Elsevier, 2017-09-23) Makvandi, Sheida; Beaudoin, Georges; McClenaghan, Margaret Beth; Quirt, David
    The petrography and mineral chemistry of magnetite and hematite from igneous, metasedimentary, and sedimentary bedrock in the area of the Kiggavik unconformity-related uranium deposit, and from till covering the deposit were investigated using optical microscopy, scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The R-package rob-Compositions method was used to treat censored values in the EPMA and LA-ICP-MS geochemical data, and the results were transformed using a centered log-ratio transformation prior to data analysis using partial least squares-discriminant analysis (PLS-DA). The Kiggavik rock samples are from a wide range of lithologies including granite, leucogranite, syenite, metagreywacke, quartzite, and quartz arenite. The integration of petrography and mineral chemistry identifies four origins for iron oxides in the Kiggavik bedrocks: magmatic, hydrothermal, diagenetic, and weathering. The igneous bedrocks mainly contain magmatic magnetite replaced by mostly hydrothermal and rarely by weathering related hematite. Higher concentrations of trace elements such as Mg, Al, Ti, and Zr in hydrothermal hematite from leucogranite, granite and Martell syenite relative to parent magnetite suggest that hematite crystallized from high-temperatures hydrothermal fluids. By contrast, relative trace elements depletion in hematite replacing V-Cr-rich magnetite from Schultz Lake Intrusive Complex syenite may indicate hematite precipitation from low-temperature oxidizing fluids. The high U content (450 ppm averagely), rounded shape, and altered edges of hematite grains from metagreywacke indicate that the iron oxide is detrital, originally precipitated from U-rich hydrothermal fluids. Quartzite also contains hydrothermal hematite. Distinct chemical compositions of hydrothermal hematite from Kiggavik metasedimentary and igneous basement demonstrate different compositions and temperatures of parental hydrothermal fluids, as well as different compositions of replaced minerals/host rocks. Magnetite rarely occurs in the Kiggavik sedimentary bedrocks as it has been partly or entirely replaced by hematite. The Thelon Formation quartz arenite contains detrital hematite mainly sourced from weathering of the Kiggavik igneous basement, and also diagenetic hematite that formed in situ replacing detrital magnetite, ilmenite, sulfides and/or Fe-bearing silicates. PLS-DA distinguishes different compositions of magnetite and hematite characterizing the various Kiggavik rock samples. The PLS-DA latent variable subspaces defined by the bedrock samples were used to classify the sources of iron oxides in Kiggavik till. The results show that magnetite and hematite from the till are mainly derived from local rocks, with a small proportion from unknown host rocks. PLS-DA identifies Si, Ca, Pb, Zr, Al, Ge, Nb, Ga, Mn, Mg, Ti, Co, Y U, V, Ni, and Cr as main discriminator elements. Their variable concentrations in iron oxides can be used to separate different Kiggavik rocks. PLS-DA also demonstrates that lower concentrations of Si, Ca, Al, Mn, Mg, Ti, Zn, Co and Ni discriminate Kiggavik iron oxides from magnetite from porphyry, iron oxide copper gold ore deposits (IOCG), Iron Oxide-Apatite (IOA), and Bayan Obo Fe-Nb-REE deposit types. Nickel enrichment and higher Ca values also differentiate magnetite from Ni-Cu, and from VMS deposits and VMS-related BIF, respectively, from Kiggavik iron oxides. The PLS-DA discrimination models suggest that volcanogenic massive sulfide (VMS)-related banded iron formations (BIF) are the potential source for some of the unclassified iron oxide grains in Kiggavik till. Retention of U contents by iron oxides during phase transformation or in detrital hematite indicates the ability of iron oxides to act as a long term repository of U. Overall, this study shows that magnetite and hematite are efficient minerals for provenance studies and mineral exploration in uranium rich environments, and also indicates that robust models for classification of indicator minerals origins in unconsolidated sediments can be established from PLS-DA of LA-ICP-MS data.