Flash Presentations of the Geoscience Research Challenge – Master’s Level

The Mont Albert ophiolite complex and its metamorphic sole, the Diable Amphibolite, located on the Gaspé Peninsula, are relics of a fossil subduction system set up on the passive margin of Laurentia during the Taconian Orogeny. The metamorphic sole corresponds to segments made up of mafic crustal rocks and sedimentary rocks from the lower plate accreted to the base of the thrusting plate. This makes it possible to study the processes active at the start of a subduction event. The Diable Amphibolite is one of the best-preserved metamorphic sole in Quebec, but remains poorly studied.

Some of the data needed to properly characterise this unit are missing or incomplete, making it difficult to understand the processes explaining the origin of this subduction zone.

The aims of the project are therefore to determine the protoliths of the metamorphic sole and to define the source of the sedimentary rocks in order to reconstruct the Perilaurentian margin and understand the onset of the subduction zone. To achieve this, fieldwork was carried out to collect representative samples of the entire metamorphic sequence. The mafic rocks were analysed to quantify major and trace element concentrations in order to determine the nature of the protoliths. U-Pb dating will also be carried out on the detrital zircons contained in the sedimentary rocks to determine the age and depositional environment. Geochemical results indicate a gradual variation in rare earth element (REE) content between the mafic rocks at the base of the sequence and those at the top. The former have a REE composition similar to enriched mid-ocean ridge basalts (E-MORB), while the latter show a depleted signature. The rocks located towards the centre of the sole have an intermediate signature between these two poles. The composition of the mafic rocks at the base of the sequence, characterised by an enriched signature, is similar to that of the basalts of the Shick Shock Group located structurally beneath the Diable Amphibolite and corresponding to the end of the Laurentian margin. It is possible to conclude that the subduction zone began close to the Laurentian margin. For the rest of the project, the U-Pb dating data from the detrital zircons still needs to be analysed in order to better characterise the early stages of subduction zone formation.

The Superior Province is made up of several sub-provinces with distinct lithological and metamorphic characteristics, separated from each other by deformation zones. The nature of these contacts is poorly understood and requires characterisation work, especially as they often represent significant metallotects on a regional scale.

The Ministère des Ressources naturelles et des Forêts carried out mapping work north of Chibougamau, covering the Mesoarchean to Neoarchean subprovinces of Opatica and La Grande. These two subprovinces are bounded by the Poste Albanel Shear Zone. In this area, metamorphic conditions increase from lower amphibolite facies in the Opatica to upper amphibolite facies in the La Grande, while the major shear zones are characterised by transitional facies between greenschist and amphibolite. We propose to carry out a detailed metamorphic study to quantify the pressure-temperature (P-T) conditions of the metamorphism in each of the two subprovinces in order to determine whether the metamorphic conditions vary progressively or abruptly and to correlate these changes with the major structures. The second objective of this study is to date the metamorphic episodes in order to clarify the chronology (t) of the events revealed by the P-T data and their possible synchronism in the two subprovinces. Dating the metamorphism will also highlight the differences and similarities in the metamorphic and geodynamic evolution of these subprovinces. It will thus be possible to better understand the tectonic evolution linked to the juxtaposition of the Opatica and La Grande subprovinces in this region.

During the summer of 2024, the first fieldwork was carried out to collect metapelite samples in the La Grande (Voirdye Formation) and Opatica (Michaux Group) subprovinces. In each of these subprovinces, the metamorphic assemblage is biotite ± garnet ± sillimanite, but cordierite and muscovite are found locally in the rocks of the La Grande Subprovince. Detailed transects across the Poste Albanel Shear Zone enabled us to sample highly deformed lithologies close to the Opatica-La Grande contact, particularly in the tonalitic gneisses of the Théodat Complex. Nearly 40 samples collected on either side of this contact will be used to characterise the geochemistry of the metapelites, determine the relationships between the metamorphic minerals, quantify the P-T conditions and, eventually, establish the age of the metamorphic events using garnet and/or monazite dating.

Orientation 1 of the Quebec Plan for the Development of Critical and Strategic Minerals (CSM) aims to increase knowledge of these essential resources. With this in mind, our project aims to improve CSM exploration methods by vectorising LCT (Li-Cs-Ta) pegmatites associated with hyperaluminous plutons.

The best-known model for the formation of LCT pegmatites proposes that they formed from volatile- and rare-element-rich residual liquids originating from the fractional crystallisation of magma derived from the partial melting of sedimentary rocks. These dykes show spatial and genetic zonation with hyperaluminous granites, as in several examples in the Superior Province, western Ontario and southeastern Manitoba. In addition, some of these granites also show mineralogical zonation with increased content of certain minerals, such as garnet, tourmaline and beryl, in areas where spodumene pegmatites have been identified. Our project focuses on mineralogical and chemical zonations within the La Motte Batholith (LMB) in Abitibi, with the aim of identifying vectors for targeting these potentially LCT pegmatite-rich zones. Since these zonations are not always obvious, machine learning will be used to highlight them.

This project began with the compilation of recent (Rajhi, 2024) and historical (SIGÉOM and Leduc [1980]) chemical and mineralogical data relating to the LMB. The data was then checked for quality and compatibility, and integrated into a database for further analysis. This process involved the use of advanced statistical methods and machine learning to define vectorisation indicators and assess their effectiveness. Given the small amount of lithiniferous pegmatites in the LMB area, we plan to validate the indicators identified by testing them in the Simard Lake area, which has a similar geological environment and where we have collected recent data. This validation will enable us to assess the robustness and versatility of the indicators in two different hyperaluminous granites. By combining existing geological data with modern techniques, this project aims to improve the efficiency of exploration for lithiniferous pegmatites.

Most of the gold mined in Canada today comes from quartz veins in orogenic gold mineralisation. In the Abitibi Belt, it is estimated that more than half of the gold is associated with the quartz-carbonate veins in the syn- to late-deformational orogenic deposits (2660 to 2640 ±10 Ma). However, data on the age and source of the gold mineralisation is still lacking for several deposits in the region. The Bonnefond intrusion, located near Val-d'Or, is the ideal site for gaining a better understanding of these Archean orogenic systems. This cylindrical, tonalitic intrusion is surrounded by a zone of porphyritic diorite and was emplaced in a deformation corridor. The host rock at the roof of the deformation zone is composed of basalts and mafic tuffs belonging to the Jacola Formation, while the wall consists mainly of andesites of the Val-d'Or Formation. Omnipresent propylitic alteration is suggested by the presence of the secondary assemblage chlorite ± epidote ± sericite. In the Bonnefond mineralised zones, typical shear veins composed of quartz + tourmaline + carbonate ± chlorite ± pyrite ± chalcopyrite ± scheelite ± sulphates ± muscovite (QTC) average ~3.0 g/t gold. These QTC veins are concentrated in the tonalite-diorite intrusion along secondary shear zones. QTC veins cutting the tonalite are associated with intense bleaching (albite ± sericite) of the host rock. The mafic tuff xenoliths present in the intrusion tend to show fuchsite alteration. This alteration also appears to be associated with a significant loss of original structures in the host rock. In situ U-Pb geochronological analyses using LA-ICPMS were used to determine the chronology of the gold mineralisation. Analyses of xenotime, a mineral paragenetically associated with mineralisation in the QTC veins, suggest an episode of main mineralisation contemporaneous with deformation, followed by a second post-deformation episode. The rare earth element composition of the xenotime combined with geochronological data facilitates the characterisation of these grains. In addition, infrared imaging and trace elements in the pyrite provide a better understanding of the formation of the QTC veins. There is a clear zonation of Co, Ni and As content in the pyrite, suggesting that at least two different fluids contributed to its formation. The two episodes highlighted by the geochronology and the zonations in the pyrite must therefore have contributed to the development of the gold mineralisation at Bonnefond.

Located at the roof of the Grenville Front thrust (Parautochtonous Zone), the Grenville Front Tectonic Zone (GFTZ) contains high-grade gneisses that were variably metamorphosed during the Kenorean (around 2.6 Ga) and Grenvillian (around 1.0 Ga) orogenies. The polymetamorphic history of these gneisses remains poorly understood, but is essential for proposing a tectonic model for the evolution of both the Grenville and Superior provinces.

Near Val-d'Or, the GFTZ marks the boundary of the Neoarchean Pontiac Subprovince (Autochthonous Zone). This subprovince is composed of migmatitic paragneisses, Neoarchean pegmatite dykes and, locally, lenses and decametric dykes of metabasite whose origin and age are uncertain. We present here new field observations and the results of in situ LA-ICP-QQQ-MS geochemical and geochronological analyses (U-Pb on titanite; Lu-Hf on garnet) to determine the nature and metamorphic evolution of these metabasites. Our work has enabled us to distinguish three units: 1) migmatitized mafic garnet + clinopyroxene granulites cut by pegmatites which have a geochemical signature of uncontaminated basalt from a primitive mantle-type source; 2) granulitic metagabbros intersecting the pegmatites and composed of the assemblage hornblende + plagioclase + clinopyroxene + garnet ± orthopyroxene ± quartz ± ilmenite ± titanite which are characterised by a geochemical signature of contaminated basalt derived from a primitive mantle type source; 3) subophitic and coronitic metagabbros with plagioclase + clinopyroxene + garnet + biotite + ilmenite ± olivine ± hornblende ± hercynite which have a geochemical signature of contaminated basalt from an enriched mantle-type source. These three units are respectively correlated with 1) the synsedimentary basalts of the Pontiac Group (about 2.7 Ga); 2) the Matachewan Dyke Swarm (about 2.4 Ga) and 3) the Sudbury Dykes (about 1.2 Ga), all recognized units in the Pontiac Subprovince. The metamorphic ages on garnet and titanite are Archean (around 2.6 Ga) for the mafic granulites and paragneisses, while they are Grenvillian (around 1.0 Ga) for the two metagabbro units. These results suggest the presence of two superimposed granulite metamorphic events in the GFTZ: a first Kenorean event recorded in the Archean mafic granulites and paragneisses, and a second Grenvillian event recognized only in the metamorphosed Proterozoic dykes. Thus, granulite assemblages formed during metamorphic episodes separated by more than 1.6 Ga coexist within the GFTZ near Val-d'Or. Estimates of pressure and temperature conditions are currently being made.

The first observation of carbonatites and fenites in the area north of Ottawa, in the Grenville Province, was made by Hogarth (1966) in Gatineau Park. Subsequent research demonstrated the existence of several carbonatite dykes and associated fenites (0.9 to 1.1 Ga) at several other locations eastward to Buckingham, with the carbonatites north of Gatineau showing the greatest enrichment in light rare-earth elements (REE).

Mapping surveys undertaken as part of this study revealed the presence of centimetric to metric carbonatite dykes showing a massive to brecciated structure and trending generally NNE-SSW to NE-SW, subparallel to the regional foliation. They are hosted by a metasedimentary basement of paragneisses, quartzites, marbles and calcosilicate rocks. This assemblage is cut by orthogneisses, granites, pegmatites and syenite dykes.

Carbonatite mineralogy is dominated by carbonates (>50%) (predominantly calcite, and dolomite), with apatite, quartz, micas, barite and iron oxides in smaller proportions. The breccias contain decimetric enclaves of fenitized gneiss and/or granite, surrounded by a reaction ring rich in phlogopite and apatite. Geochemically, the dykes are calciocarbonatites and magnesiocarbonatites that show Sr (< 0.3%) and Ba (< 11%) enrichments attributable respectively to the presence of celestine and barite disseminations. These carbonatites also show high REE contents of up to 4% REE_tot. These values are associated with REE phosphates (monazite) and REE carbonates (parisite).

Metasomatism of the surrounding rock (fenitization) is spatially associated with carbonatite dykes, alkaline intrusions and/or the presence of non-outcropping carbonatites. A distinction is made between proximal potassic fenitization, dominated by microcline (hematitized) and phlogopite, and distal sodic fenitization with pyroxene (ægyrine) and amphibole (richterite and riébeckite). These potassic fenites are enriched in iron and REE (up to 1% REE_tot) and contain disseminated monazite and REE carbonates. The fenite - iron oxide association has already been invoked to explain the emplacement of the nearby Haycock iron deposit (Lapointe, 1979). Our observations suggest that the REE-Fe mineralized system is genetically linked to a hydrothermal metasomatic system energized by late carbonatite dykes and controlled by a regional fault system (NE-SE, E-W to NW-SE).

U-Pb petrochronology on monazite enables dating of metamorphic processes and interpretation of their geological significance on the basis of the textural context and the chemical composition of monazite, which is controlled by (re)crystallization conditions and metamorphic reactions.

Six samples from the Wabash metasedimentary complex, with a maximum depositional age of 1204 ± 12 Ma, were selected to constrain the metamorphic evolution in the Haute-Mauricie area during the Grenvillian orogeny. The samples are Grt-Sil-Bt-Kfs-Pl-Qz-Ilm±Gr±Rt±Hc-Mnz-Zrn-Ap migmatitic paragneisses metamorphosed to upper amphibolite or granulite facies. Inclusion patterns and garnet chemical composition in some samples suggest two periods of garnet growth.

Monazite dates in the six samples are predominantly Grenvillian, although two samples also yielded older dates (ca. 1.4 Ga), whose significance remains to be assessed. Grenvillian prograde monazite forms inclusions in garnets and cores in matrix grains, and are characterized by a high Y+HREE content and a weakly negative Eu anomaly. Crystallization of prograde monazite began at ca. 1100-1080 Ma in five samples, and at ca. 1150 Ma in the sixth. The increase in the negative Eu anomaly and the increase in the Th/U ratio imply stabilization of K-feldspar during the metamorphic peak and crystallization of the partial melt during regional cooling that began between ca. 1050 Ma and ca. 1020 Ma. Y+HREE variations in monazite <1050 Ma vary throughout samples. Monazite in one sample associated with biotite that replaces garnet and defines the foliation is rich in Y+HREE and is dated at ca. 980 Ma. This indicates that this sample was deformed late, during garnet resorption. By contrast, in another sample, Y+HREE-poor monazite inclusions in garnet overgrowths that contain sillimanite and former melt inclusions are dated at ca. 1005 Ma, consistent with late garnet growth under suprasolidus conditions, possibly due to thermal input from late-Grenvillian alkaline intrusions. The metamorphic context during the Ottawan phase (1090-1020 Ma) is relatively homogeneous across the study area, while the Rigolet phase (1005-980 Ma) is marked by garnet growth or resorption, or absence of monazite crystallization, depending on the sample.

The St-Fulgence Deformation Zone, located in the Saguenay-Lac-Saint-Jean region, has a complex geological history that affects several of the region's lithodemic units. The deformation zone extends over 400 km in length and more than 2 km in width, and is the result of several deformation phases linked to the Grenville Orogeny. This structure has played a major role in the regional tectonics and magmatic evolution of the area.

This research project proposes to study this zone in detail in order to improve understanding of the geological structures and timing of deformation episodes, as well as to assess its influence on the tectonic, magmatic and metallogenic evolution of the region. The deformation structures show three main orientations: (1) NE-SW moderately dipping to the SE with reverse dextral motion, (2) N-S moderately dipping to the east with reverse dextral motion and, more rarely, (3) N-S to NW-SE moderately dipping to the SW and NE with reverse sinistral motion. The lineations associated with dextral structures show three orientations: moderate dips to the dominant NNE and NE, weak to moderate dips to the south to SSW developed locally and weak dips to the north associated with N-S structures. These different families of lineations could be associated with distinct deformation episodes or variable responses depending on the lithologies. The sinistral structures intersect the dextral NE-SW structures and therefore have a later origin. The relative chronology of the other structures has not yet been established.

Metamorphic assemblages and microstructures (mineral deformation mechanisms, kinematic indicators) developed in the various lithologies examined (paragneisses, quartzites, orthogneisses, mylonites, ultramylonites, amphibolites, alkali feldspar granites, mangerites, syenogranites, charnockites, syenites with or without hypersthene, gabbronorite and leuconorite) will be studied in oriented thin sections. Quartz-rich samples will be subjected to crystallographic axis orientation analysis using electron backscatter diffraction (EBSD) to confirm the direction and temperature of deformation. Samples of mylonitized paragneiss and asymmetrically boudinized leucosome will be dated by U-Pb geochronology on monazite and zircon to determine the age of the deformation and assess its relationship with regional metamorphism, respectively. Field observations will be complemented by analysis of LiDAR and aeromagnetic data to delineate structural domains and the extent of shear zones.

Proterozoic anorthositic massifs are known worldwide for their large magmatic Fe-Ti-P ± V deposits (e.g., Lac Tio, Qc). Although these massifs contain an abundance of critical and strategic minerals, the formation and distribution of these deposits are still poorly understood, which complicates exploration. In the Grenville Province, the Lac-Saint-Jean Anorthositic Suite (LSJAS) hosts numerous Fe-Ti-V-P showings, including the Saint-Charles-de-Bourget deposit.

This project essentially concerns a mineralized corridor in the Saint-Charles-de-Bourget and Bégin-Lamarche sectors, along the southern margin of the LSJAS (Saguenay). The objective of this study is to better understand the relationship between Fe-Ti-V ± P mineralization and the anorthositic host rocks in this sector using anorthositic facies mapping, total rock lithogeochemistry and plagioclase chemistry by portable XRF. A total of 224 samples were collected from the 96 outcrops visited during the field campaigns (summers 2023 and 2024) along three E-W transects: Saint-Charles-de-Bourget (29 km), Bégin-Lamarche (18 km) and one in between (9 km). These transects, centred on the mineralized corridor, are oriented perpendicular to the stratigraphy, local structures and megadykes of diorite (Lac Chabot Diorite) and leucotroctolite (Bégin Megadyke). The dominant lithologies observed are: anorthosite (± olivine and/or orthopyroxene), leuconorite (± olivine), leucotroctolite (± orthopyroxene or clinopyroxene) and (leuco)gabbronorite (± olivine). The mineralization includes lenses of massive magnetitite (Fe-Ti ± V) containing olivine (± orthopyroxene) and of massive or banded nelsonite (Fe-Ti-P) ± olivine (and/or orthopyroxene). These mineralizations are directly associated with anorthosite (± olivine and/or orthopyroxene), leucotroctolite (± orthopyroxene) or ferrodiorite and/or leucogabbronorite dykes containing olivine. These lithologies are also found in enclaves within the mineralizations.

The composition of the plagioclase in the 3 transects has enabled the distinction of 3 domains. The Central domain (mineralized corridor) is characterized by anorthosites ( containing olivine and/or orthopyroxene) and leucotroctolites (± orthopyroxene) with a plagioclase of andesine composition (An30-50) exhibiting high strontium contents (≥ 0.1%). The Eastern and Western domains, on either side of the mineralized corridor, are dominated by leuconorites with a few leucotroctolitic bands distinguished by a plagioclase varying in composition from andesine to labradorite (An36-62) and generally low strontium contents (≤ 0.1%).

The Proterozoic anorthositic suites of the Grenville Province, such as the Lac-Saint-Jean Anorthositic Suite (LSJAS), host critical and strategic metal mineralizations, notably Ni-Cu-Co and Fe-Ti-V-P. However, the relationships between these mineralizations and the various facies of the anorthosite are not well defined. The aim of this master's project is to map the facies and geochemical composition of plagioclase in the anorthosites of the northern margin of the LSJAS, in the Lac à Paul area, known for its Fe-Ti-P and Ni-Cu showings, in order to gain a better understanding of the relationships between lithologies and Ni-Cu mineralization.

In the summer of 2024, mapping and sampling of the northern margin of the LSJAS, mainly around the Nourricier, MHY and Léo-Charl showings, and an E-W transect across this sector, resulted in the collection of 84 samples from 59 outcrops. This sector exposes various mafic (anorthosite, [leuco]norite, [leuco]troctolite) and ultramafic (orthopyroxenite) lithologies of the LSJAS.

Analysis of the data reveals that (leuco)norite dominates, with minor proportions of (leuco)troctolite, anorthosite and orthopyroxenite. (Leuco)norite and (leuco)troctolite commonly contain iron oxides (1 to 25%) and apatite (1 to 20%), with local clusters of nelsonite. Norite and orthopyroxenite are the main host rocks for Ni-Cu mineralization, particularly at the Léo-Charl showing. In this zone, sulphidic mineralization (pyrrhotite with minor pyrite and chalcopyrite) occurs as veins in an orthopyroxenite dyke and as small massive to semi-massive clusters in norite associated with the dyke. Analyses of plagioclase calcicity, carried out by portable XRF on flat surfaces of sawn samples, reveal that the eastern part of the study area is dominated by andesine (An_38-47), with a tendency towards a transitional composition (An_48-51) in the south-western and northern parts. Lithologies containing labradorite (An_50-70) are rare. The Sr values measured in these rocks suggest the existence of two distinct populations: a dominant population with low Sr values (0.07-0.08%) located on the periphery and a second with higher values (up to 0.107%) concentrated in the centre of the area. Future work, including the study of mineralization from drill core, petrography and geochemical analyses, will aim to confirm these observations and further our understanding of the relationships between Ni-Cu mineralization and LSJAS lithologies in this highly favourable sector.

Rare earth elements (REE) are vital to industrial technologies. These elements include the lanthanides, as well as scandium and yttrium. Exploiting REEs in Canada has the potential to generate considerable economic gains by reducing the country's dependence on China, which is the main producer.

As with other metals, mining REE can present a risk of drainage water contamination from waste rock piles. Our work focuses on 4 waste rock lithologies (lamprophyre, carbonatite, fenite and breccia) from a carbonatite REE deposit. Waste rock samples were characterized for their physical, chemical and mineralogical properties. Samples weighing 10 kg were then tested in columns (14 cm internal diameter, 50 cm to 1 m height) rinsed every two weeks with 1.8 l of deionized water for 1 year. The leachates were analyzed after each rinse.

This work demonstrates that the tailings are not potentially acid-generating, containing only traces of sulphides and sufficient neutralizing minerals. The pH of the leachates fluctuates between 7.9 and 8.7, while the electrical conductivity and alkalinity are stable between 250 and 600 µS/cm and between 100 and 175 mg CaCO₃/l respectively. Cerium, lanthanum and neodymium are the main REEs detected in waste rock leachates, followed by praseodymium, samarium and yttrium. Breccia is the most REE-generating lithology among those studied. Lead (up to 0.06 mg/l), barium (0.1 to 0.  mg/l) and fluorine (decreasing trend, from 8 to 16 mg/l at the beginning of the test to 2 to 4 mg/L at the end) were among the main metals detected in leachates.

In conclusion, the preliminary results suggest that the waste rock is low in contaminants, with concentrations of dissolved metals generally below regulatory limits. However, the risk associated with some elements such as lead, barium and fluorine needs to be clarified as the project progresses.

Environmental desulphurization is a method of managing mine tailings that is increasingly used to restore tailings sites. Although desulphurized tailings do not generate acid mine drainage, they may still contain residual sulphides. It has become essential to study the geochemical behaviour of desulphurized tailings from the moment they are deposited and over the long term to reduce the risks associated with the generation of AMD and metal-contaminated effluents.

The aim of this study is to assess the impact of desulphurized tailings used as a monolayer cover to control AMD. The tailings used come from the Doyon and Éléonore mines. The materials underwent initial characterization to determine their physical, chemical and mineralogical properties. Six column tests were set up in the laboratory with the following characteristics: 80 m high, 14 mm in diameter, a 2 m deep water table, a 30 cm thick layer of tailings and volumetric water content probes. Oxidized and weakly oxidized Doyon tailings as well as oxidized Éléonore tailings were covered by sand, desulphurized tailings or fresh tailings in order to quantify the influence of desulphurized tailings on effluent quality. The columns underwent eight flushing/draining cycles (1 cycle/month), after which the composition of the leachate was analyzed.

The results indicate that leachates from the Doyon tailings columns (oxidized and weakly oxidized) and from the covers of desulphurized Westwood tailings and sand have acid pHs below 3.2, high alkalinity (7486 to 1000 mg CaCO₃/l) and high metal contents (Zn, Fe). In contrast, the fresh Éléonore tailings and the inert sand used as a cover layer over the oxidized Éléonore tailings displayed a fairly similar geochemical behaviour, with slightly basic pH values (above 7) and low metal contents. Leachates from the column covered with fresh Éléonore tailings revealed high arsenic concentrations that gradually decreased. However, arsenic concentrations increased with time in the test carried out with an inert sand cover. The results demonstrate that the geochemical behaviour of tailings sites covered with desulphurized tailings varies mainly according to the nature of the underlying tailings. Thus, the use of desulphurized tailings as a cover has little influence on the quality of the leachate.

Alkaline drainage (AD), an emerging environmental issue, is characterized by a high pH and alkalinity, as well as by concentrations of metallic contaminants that can exceed current standards. The objective of this study is to assess the hydrogeochemical behaviour of Fe-Ti slag that generates AD in order to understand the evolution of pH, alkalinity and the potential mobility of contaminants over time.

To this end, six samples of Fe-Ti slag residues (PH1, PH2, PH3, Pkiln, UGS and UAE Oxides) were taken from the Rio Tinto Iron and Titanium smelter in Sorel-Tracy. A detailed physicochemical and mineralogical characterization of these residues was carried out. Simple leaching tests (TCLP and SPLP) and kinetic leaching tests (columns and humidity cells) were then carried out to assess the short- and long-term mobility of the contaminants. Leachates from the humidity cells and columns were collected weekly or monthly and analyzed.

The main results obtained indicate that leachates from Fe-Ti residues contain very small concentrations of As, Ba, Cd, Cr, Pb and Se (TCLP test), with values that do not exceed the ‘high risk’ criteria of Directive 019. The leachates from the Pkiln and UGS Oxides residues have higher concentrations in Ca and Mg (SPLP test), with values of 100 and 222.4 mg/l Ca and 21.9 and 12.2 mg/l Mg respectively. The results of the kinetic tests show that the pH and alkalinity of the leachates tend to increase with time. Leachates from the humidity cells have a pH ranging from 8 to 11.79 and an alkalinity ranging from 33.68 to 145.92 mg CaCO₃/l. In addition, the columns returned a pH between 7.65 and 10.06 and an alkalinity ranging from 24.88 to 348.08 mg CaCO₃/l. Finally, ammoniacal nitrogen in the column leachates presents a high initial concentration in the Pkiln residues, which decreases rapidly over time. In contrast, the humidity cell leachates revealed ammoniacal nitrogen concentrations below the detection limit (<0.1 mg/l). Detailed mineralogical characterization of the samples is in progress.

Mining activity, although essential to Quebec’s economy, generates vast tailings parks that present major environmental challenges, requiring revegetation. The former Gagnon iron mine, abandoned since 1985, is an example, with 95% of its surface still unvegetated. Stress factors limit natural succession and recolonization of this habitat, making it imperative to better understand recolonization dynamics. Among these factors, soil microorganisms play a key role. Indeed, pioneer plants do not colonize new environments alone: their roots interact with a wide diversity of microorganisms, which are essential for plant and soil health. The biodiversity of this microbiome is generally correlated with plant performance and soil quality. However, most knowledge on these interactions comes from natural or semi-natural ecosystems, and few studies concern primary successions like those observed in mining tailings parks. It is therefore crucial to better understand these habitats to ensure their sustainable management and to select optimal plants and microorganisms to effectively restore the Gagnon mine.

This project aims to characterize the influence of microorganisms on the recolonization of mining tailings parks. We will analyze two types of microbiomes: that of uncolonized soils and that of the rhizospheric soils of the five plants present on the site, using advanced biomolecular approaches. This analysis will distinguish microorganisms present in the soil in the absence of plants from those specifically associated with plant soils. We will also conduct an in vitro greenhouse experiment to measure plant-soil feedback between different species and rhizospheres at the site. By correlating these data with microbiome diversity, we will identify the microorganisms that have the greatest impact on plant performance and how plant microbiomes affect coexistence between plants. This information will be essential to understanding how the microbiome of these plants has enabled them to colonize and coexist in this hostile environment. This research will allow us to identify which plant species have microbial communities with complementary functions. We can then propose synergistic plant assemblages to accelerate the ecological recovery of sites disturbed by mining activities. More broadly, this study will contribute to understanding the role of the microbiome in the restoration of damaged habitats.

Despite its economic benefits, mining operations produce large volumes of output, particularly fine tailings. Although these tailings sites are hostile environments for plants, they must be revegetated. This revegetation process is the first step towards returning a mine site to its natural state. The site of the former Gagnon-Lac Jeannine iron ore mine includes a 4 km² tailings facility. Despite the low level of nutrients, the area is slowly being colonized by pioneer plants, but remains largely devoid of plant life.

The first part of our study looked at the changes that these colonizing plants make to their environment. To determine the extent of their effect on the site's fine residues, we studied two types of soil: rhizospheric soil associated with five (5  plant species present on the site, and soil not colonized by plants (tailings). The plants studied were the: Drummond's mountain-avens, mountain alder, sandwort, littletree willow and bryophyte covers. On these 54 rhizosphere samples and 50 samples of uncolonized tailings, we measured microbial nitrogen fixation, carbon content, soil respiration rate and cation exchange capacity. These variables are all important, as they play key roles in ecosystem recovery. In the second part of the study, our team paid particular attention to a symbiotic plant (Drummond's mountain avens) known to have a significant effect on nitrogen fixation. This species is very present on the mine site, even in the most stressed areas, and is sparsely distributed across the province. The Lac Jeannine site is one of the few places where the mountain avens has been recorded in Quebec. We are therefore going to study in depth the fixing communities associated with this pioneer plant, in particular its ability to establish a symbiosis with the actinobacterium Frankia sp.

This research will allow us to make recommendations to improve plant biodiversity in sites undergoing remediation and to reduce the environmental and monetary cost of these operations. More specifically, we aim to determine whether certain plants present on the Lac Jeannine site have complementary functions that could facilitate plant succession.

The rise of industrialization has had a considerable impact on people's daily lives, leaving a negative mark on the environment. In the context of mining, an activity in the primary sector of the economy, a great deal of research has demonstrated the undeniable impact of poorly managed tailings on the surrounding ecosystems (surface water, groundwater and the pedosphere). When mine tailings come into contact with oxygen and water, they tend to oxidize and release contaminants into the environment: this is known as acid mine drainage. To manage this problem, several mining rehabilitation methods have been tested, including desulphurization and the recycling of mine tailings during reclamation work. The use of desulphurized mine tailings as a reclamation material offers a number of economic and environmental advantages. However, there are still uncertainties surrounding the long-term effectiveness of this practice and the geochemical interactions under anaerobic conditions.

The main purpose of this research is to understand the geochemical behaviour of desulphurized mine tailings under aerobic and anaerobic conditions. To this end, kinetic tests were carried out on mine tailings from the Doyon, Éléonore and Westwood mines, both in the presence and absence of oxygen. Analyses of physico-chemical parameters (Eh, pH, electrical conductivity, acidity, alkalinity) and geochemical parameters (cations, anions and metals) were carried out on the leachates. The post-rinse samples underwent final characterization (mineralogical analysis [MO, SEM, XRD]) and parallel extraction in order to identify the different phases leached during the kinetic test.

The sulphide discharges behave similarly under the two conditions: leachates from the Doyon tailings have acid pH values, whereas tailings from Eleonore are neutral with very low concentrations of Zn, Fe, Ni, Cu and Pb. The As contents are almost zero in the Doyon tailings, but they are higher than the levels indicated in Directive 019 for Éléonore. Leachates from desulphurized tailings also have neutral pH values, and metal concentrations comply with Directive 019 standards. Geochemical modelling was also carried out to visualize the thermodynamic equilibrium during flushing.