Personne : Makvandi, Sheida
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Université Laval. Département de géologie et de génie géologique
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- PublicationAccès libreGeochemistry 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, DavidThe 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.
- PublicationAccès libreChemical composition of tourmaline in orogenic gold deposits(Société de géologie appliquée aux gîtes minéraux, 2020-06-10) Makvandi, Sheida; Sciuba, Marjorie; Beaudoin, GeorgesTourmaline from eighteen orogenic gold deposits and districts, hosted in varied country rocks and metamorphic facies, was investigated by EPMA (Electron Probe Micro-Analyzer) and LA-ICP-MS (Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry) to establish discriminant geochemical features to constrain indicator mineral surveys for gold exploration. Such tourmaline most commonly belongs to the alkali group, with a dravitic composition. LA-ICP-MS results were investigated with binary plots and PLS-DA (Partial Least Square-Discriminant Analysis). PLS-DA suggests that the major element composition of tourmaline from orogenic gold deposits is buffered by the hydrothermal fluid, whereas trace element composition is strongly controlled by the composition and the metamorphic facies of the country rocks. Contents of Sn, Ga, Ti, Rare Earth Elements (REE), Zr, Hf, Nb, Ta, Th and U vary with the metamorphic facies of the country rocks. Tourmaline from orogenic gold deposits has high contents of Sr, V, and Ni and low Li, Be, Ga, Sn, Nb, Ta, U, and Th compared to tourmaline from other deposit types and geological environments. Binary plots such as Sr/Li vs. V/Sn, Sr/Sn vs. V/Nb, Sr/Sn vs. Ni/Nb and Sr/Sn vs. V/Be, as well as PLS-DA, discriminate tourmaline from orogenic gold deposits from that of other settings. Binary plots highlight a transitional variation in the trace element composition of tourmaline from metamorphic, to magmatic-hydrothermal, to magmatic environments.
- PublicationAccès libreTrace element composition of igneous and hydrothermal magnetite from porphyry deposits : relationship to deposit subtypes and magmatic affinity(Society of Economic Geologists (États-Unis), 2019-06-30) Makvandi, Sheida; Beaudoin, Georges; Boutroy, Émilie; Sappin, Anne-Aurélie; Xiaowen, HuangTrace element compositions of igneous and hydrothermal magnetite from nineteen well-studied porphyry Cu ± Au ± Mo, Mo, and W-Mo deposits, combined with partial least squares-discriminant analysis (PLS-DA), were used to investigate the factors controlling magnetite chemistry during igneous and hydrothermal processes, as divided by magmatic affinity and porphyry deposit subtypes. Igneous magnetite can be discriminated by relatively high P, Ti, V, Mn, Zr, Nb, Hf, and Ta contents but low Mg, Si, Co, Ni, Ge, Sb, W, and Pb contents, in contrast to hydrothermal magnetite. Compositional differences between igneous and hydrothermal magnetite are mainly controlled by the temperature, oxygen fugacity, co-crystallized sulfides, and element solubility/mobility that significantly affect the partition coefficients between magnetite and melt/fluids. Binary diagrams based on Ti, V, and Cr contents are not enough to discriminate igneous and hydrothermal magnetite in porphyry deposits. Relatively high Si and Al contents discriminate porphyry W-Mo hydrothermal magnetite, probably reflecting the control by high Si, highly differentiated, granitic intrusions for this deposit type. Relatively high Mg, Mn, Zr, Nb, Sn, and Hf, but low Ti and V contents, discriminate porphyry Au-Cu hydrothermal magnetite, most likely resulting from a combination of mafic to intermediate intrusion composition, high chlorine in fluids, relatively high oxygen fugacity, and low temperature conditions. Igneous or hydrothermal magnetite from Cu-Mo, Cu-Au, and Cu-Mo-Au deposits cannot be discriminated from each other probably due to similar intermediate to felsic intrusion composition, melt/fluid composition, and conditions such as temperature and oxygen fugacity for the formation of these deposits. The magmatic affinity of porphyritic intrusions exerts some control on the chemical composition of igneous and hydrothermal magnetite in porphyry system. Igneous and hydrothermal magnetite related to alkaline magma is relatively rich in Mg, Mn, Co, Mo, Sn, and high field strength elements (HFSE), perhaps due to high concentrations of chlorine and fluorine in magma and exsolved fluids, whereas those related to calc-alkaline magma are relatively rich in Ca but depleted in HFSE, consistent with the high Ca but low HFSE magma composition. Igneous and hydrothermal magnetite related to high-K calc-alkaline magma is relatively rich in Al, Ti, Sc, and Ta, due to a higher temperature of formation or enrichment of these elements in melt/fluids. PLS-DA on hydrothermal magnetite compositions from worldwide porphyry Cu, iron oxide-copper-gold (IOCG), Kiruna-type iron oxide-apatite (IOA), and skarn deposits identify important discriminant elements for these deposit types. Magnetite from porphyry Cu deposits is characterized by relatively high Ti, V, Zn, and Al contents, whereas that from IOCG deposits can be discriminated from other types of magnetite by its relatively high V, Ni, Ti, and Al contents. IOA magnetite is discriminated by higher V, Ti, and Mg but lower Al contents, whereas skarn magnetite can be separated from magnetite from other deposit types by higher Mn, Mg, Ca, and Zn contents. Decreased Ti and V contents in hydrothermal magnetite from porphyry Cu and IOA, to IOCG, and to skarn deposits may be related to decreasing temperature and increasing oxygen fugacity. The relative depletion of Al in IOA magnetite is due to its low magnetite-silicate melt partition coefficient, immobility of Al in fluids, and earlier, higher-temperature magmatic or magmatic-hydrothermal formation of IOA deposits. The relative enrichment of Ni in IOCG magnetite reflects more mafic magmatic composition and less competition with sulfide, whereas elevated Mn, Mg, Ca, and Zn in skarn magnetite results from enrichment of these elements in fluids via more intensive fluid-carbonate rock interaction.
- PublicationAccès libreTrace element composition of iron oxides from IOCG and IOA deposits : relationship to hydrothermal alteration and deposit subtypes(Springer, 2017-07-17) Makvandi, Sheida; Beaudoin, Georges; Boutroy, Émilie; Xiaowen, Huang; Corriveau, Louise; Franco De Toni, AnthonyTrace element compositions of magnetite and hematite from 16 well-studied iron oxide–copper–gold (IOCG) and iron oxide apatite (IOA) deposits, combined with partial least squares-discriminant analysis (PLS-DA), were used to investigate the factors controlling the iron oxide chemistry and the links between the chemical composition of iron oxides and hydrothermal processes, as divided by alteration types and IOCG and IOA deposit subtypes. Chemical compositions of iron oxides are controlled by oxygen fugacity, temperature, co-precipitating sulfides, and host rocks. Iron oxides from hematite IOCG deposits show relatively high Nb, Cu, Mo, W, and Sn contents, and can be discriminated from those from magnetite + hematite and magnetite IOA deposits. Magnetite IOCG deposits show a compositional diversity and overlap with the three other types, which may be due to the incremental development of high-temperature Ca–Fe and K–Fe alteration. Iron oxides from the high-temperature Ca–Fe alteration can be discriminated from those from high- and low-temperature K–Fe alteration by higher Mg and V contents. Iron oxides from low-temperature K–Fe alteration can be discriminated from those from high-temperature K–Fe alteration by higher Si, Ca, Zr, W, Nb, and Mo contents. Iron oxides from IOA deposits can be discriminated from those from IOCG deposits by higher Mg, Ti, V, Pb, and Sc contents. The composition of IOCG and IOA iron oxides can be discriminated from those from porphyry Cu, Ni–Cu, and volcanogenic massive sulfide deposits.
- PublicationAccès libreIndicator mineral exploration methodologies for VMS deposits using geochemistry and physical characteristics of magnetite(2015) Makvandi, Sheida; Beaudoin, GeorgesPour évaluer le potentiel de la magnétite en tant que minéral indicateur des dépôts de Sulfures Massifs Volcanogènes (SMV), la composition des éléments traces et les caractéristiques (morphologie, taille des grains et textures de surface) de la magnétite provenant de différents contextes ont été investiguées. Les caractéristiques physiques et les associations minérales de la magnétite du dépôt d’Izok Lake (Nunavut, Canada), de la roche encaissante et du till recouvrant la zone à proximité ont été étudiés en utilisant la microscopie optique, le Microscope Électronique à Balayage (MEB) et l’Analyseur de Libération Minérale (MLA). Les résultats permettent de distinguer la magnétite magmatique, métamorphique et supergène dans un environnement de SMV, et indiquent que 1) la taille des grains de magnétite et leur relation texturale avec les associations minérales caractérisent la roche encaissante, 2) l’angularité de la magnétite du till est indicatrice de la forme originel du minérale, et 3) les textures de surface de la magnétite détritique sont diagnostiques des processus affectant les grains durant l’érosion, le transport, et après la déposition dans les sédiments glaciaire. La composition de la magnétite provenant d’Izok Lake (Nunavut, Canada) et d’Halfmile Lake (Nouveau-Brunswick, Canada) et de leurs roches encaissantes a été étudiée en utilisant le MEB, la microsonde électronique, et l’ablation laser- spectrométrie de masse à plasma à couplage inductif (LA-ICP-MS). Les données censurées ont été transformées en utilisant la routine R robCompositions, puis converties en utilisant les log-ratios centrés pour éviter tout effet de fermeture. L’analyse en Composantes Principales (ACP) permet de discriminer différents types de roche encaissantes et des dépôts basés sur la teneur de la magnétite en Si, Ca, Zr, Al, Ga, Mn, Mg, Ti, Zn, Co, Ni et Cr. Les données de composition de la magnétite de seize dépôts SMV (mafique, bimodal mafique, bimodal felsique, felsique-silicoclastique), et de trois Formations de Fer Rubanées (FFR) associés à des SMV ont été investiguées par analyse discriminante par les moindres carrés partiels (PLS-DA) pour distinguer les différentes compositions de magnétite basées sur les teneurs en Si, Ca, Al, Mn, Mg, Ti, Zn, Co et Ni. Le résultat indique quatre types de magnétite en association avec les dépôts de SMV: magmatique, hydrothermale, métamorphique, et la magnétite zonée. L’analyse des données par PLS-DA sépare la magnétite des SMV et BIF des autres types de gites minéraux. Les analyses en PCA et PLS-DA des échantillons de la roche encaissante/dépôt SMV et FFR produisent un modèle de discrimination de la composition de la magnétite dans le till qui peut être utilisé pour identifier, en exploration minérale, la magnétite dérivée de l'érosion d'un SMV par un glacier.
- PublicationAccès librePCA 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, PatrickMagnetite 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 libreTrace element composition of scheelite in orogenic gold deposits(Société de géologie appliquée aux gîtes minéraux, 2019-09-11) Makvandi, Sheida; Sciuba, Marjorie; Beaudoin, Georges; Grzela, DonaldScheelite from 25 representative orogenic gold deposits from various geological settings was investigated by EPMA (electron probe micro-analyzer) and LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometer) to establish discriminant geochemical features to constrain indicator mineral surveys for gold exploration. Scheelite from orogenic gold deposits displays five REE patterns including a bell-shaped pattern with a (i) positive or (ii) negative Eu anomaly; (iii) a flat pattern with a positive Eu anomaly and, less commonly, (iv) a LREE-enriched pattern, and (v) a HREE-enriched pattern. The REE patterns are interpreted to reflect the source of the auriferous hydrothermal fluids and, perhaps, co-precipitating mineral phases. Scheelite from deposits formed in rocks metamorphosed at upper greenschist to lower amphibolite facies have low contents in REE, Y, and Sr, and high contents in Mn, Nb, Ta, and V, compared to scheelite formed in rocks metamorphosed below the middle greenschist facies. Scheelite from deposits hosted in sedimentary rocks has high Sr, Pb, U, and Th, and low Na, REE, and Y, compared to that hosted in felsic to intermediate rocks. Statistical analysis including elemental plots and multivariate statistics with PLS-DA (partial least square-discriminant analysis) reveal that the metamorphic facies of the host rocks as well as the regional host rock composition exert a strong control on scheelite composition. This is a result of fluid-rock exchange during fluid flow to gold deposition site. PLS-DA and elemental ratio plots show that scheelite from orogenic gold deposits have distinct Sr, Mo, Eu, As, and Sr/Mo, but indistinguishable REE signatures, compared to scheelite from other deposit types.