Earth and Environmental Scienceshttp://hdl.handle.net/10012/99432024-03-29T00:59:18Z2024-03-29T00:59:18ZEvolution of the Laurentide Ice Sheet in north-central Ontario from subglacial sedimentsTaves, Robinhttp://hdl.handle.net/10012/203942024-03-13T02:31:01Z2024-03-12T00:00:00ZEvolution of the Laurentide Ice Sheet in north-central Ontario from subglacial sediments
Taves, Robin
Till stratigraphic analysis of 10 sediment bluffs near Ogoki Post in the Hudson and James Bay Lowlands.
2024-03-12T00:00:00ZProterozoic zircon dates from auriferous zones at the Island Gold deposit: implications for late gold remobilization in the Superior ProvinceGagnon, Sophie Mariehttp://hdl.handle.net/10012/203412024-02-14T03:30:58Z2024-02-13T00:00:00ZProterozoic zircon dates from auriferous zones at the Island Gold deposit: implications for late gold remobilization in the Superior Province
Gagnon, Sophie Marie
The Island Gold deposit is a high-grade Archean orogenic gold deposit within the Michipicoten greenstone belt of the Superior Province. Hosted within the ~2750 Ma felsic to intermediate Wawa metavolcanic assemblage, gold mineralization has been constrained to between ~2680 and 2673 Ma. However, anomalous Proterozoic ages have been discovered within auriferous alteration zones, suggesting that late hydrothermal activity may have affected the deposit and potentially remobilized gold. Mineralization is hosted within quartz (± carbonate) veins, with minimal mineralization within the surrounding altered host rock. To investigate the occurrence and spatial distribution of these anomalous young ages within the deposit, samples along an alteration gradient (weakly to strongly altered) adjacent to auriferous quartz ± carbonate veins, and from differing depths within the ore zone were examined. U–Pb LA-ICP-MS analyses of zircon from strongly altered auriferous zones yielded Archean protolith dates as well as Mesoproterozoic and early Paleozoic to late Mesozoic dates. Compared to Archean zircons in the host metavolcanic rocks, the younger zircons have generally higher concentrations of heavy rare earth elements and moderate enrichment in Y, Ta, U, and Th. We interpret the Mesoproterozoic ages to represent fluid–rock interaction during the Mid-Continent Rift, whereas the Paleozoic to Mesozoic grouping may be related to alkalic/kimberlitic activity within the area associated with the Great Meteor Hotspot track. It is unclear if these fluids had compositions amenable for large-scale gold mobilization, but they may have played a role in locally distributing gold throughout the Island Gold deposit. An increasing number of reported Proterozoic dates from accessory minerals in Archean gold deposits suggests that post-Archean processes are a potential complication for understanding the distribution of gold and has regional implications for gold exploration in the Superior Province.
2024-02-13T00:00:00ZUse of Fe isotopes to examine Fe cycling in Boreal Shield lakes: implications for cyanobacterial bloom development and ancient biogeochemical cyclingLIU, KAIhttp://hdl.handle.net/10012/203052024-01-27T03:31:28Z2024-01-26T00:00:00ZUse of Fe isotopes to examine Fe cycling in Boreal Shield lakes: implications for cyanobacterial bloom development and ancient biogeochemical cycling
LIU, KAI
Stable iron (Fe) isotopes have only been used recently to explore biogeochemical Fe processes in terrestrial and aquatic ecosystems. The δ⁵⁶Fe values in natural samples range from −4‰ to 4‰. An increasing number of studies have focused on Fe isotopes in marine settings. However, few studies have focused on lake systems and only in extreme environments such as meromictic ferruginous lakes. This thesis has applications in two distinct fields, freshwater eutrophic research and early Earth evolution. Phytoplankton blooms have been studied extensively in lake ecosystems. Despite the fact that macronutrients phosphorus and nitrogen are commonly known as dominant factors controlling the blooms, the critical role of micronutrient Fe has been proposed in recent studies. However, current understanding of the sources and availability of Fe for phytoplankton blooms and Fe cycling in lakes in general remains limited. Although the mechanisms that result in the deposition of banded iron formation in the Archean ocean remain a subject of debate, it is proposed that photoferrotrophy played a significant role in the oxidation of Fe(II) in anoxic Archean oceans. Studies investigating the occurrence and significance of photoferrotrophy have primarily focused on meromictic and ferruginous lakes. However, such lakes are thought to be rare on a global scale.
To explore the potential application of stable Fe isotopes for tracing biogeochemical Fe cycling in Boreal Shield lakes, δ⁵⁶Fe values of dissolved, particulate, and sediment Fe were measured in two small dimictic Boreal Shield headwater lakes: manipulated eutrophic Lake 227, with annual cyanobacterial blooms, and unmanipulated oligotrophic Lake 442. Within these small lakes, the range in δ⁵⁶Fe is large (ca. −0.9 to +1.8‰), spanning more than half the entire range of natural Earth surface samples. Two layers in the water column with distinctive δ⁵⁶Fe of dissolved (DFe) and particulate Fe (PFe) were observed in both lakes, despite large differences in trophic states. During cyanobacterial blooms in Lake 227, selective uptake of isotopically light Fe modifies δ⁵⁶Fe, resulting in Δ⁵⁶Fe dis-part of up to 1‰ between dissolved and particulate Fe in the epilimnion while little fractionation was observed in the epilimnion of Lake 442. In the anoxic layers in both lakes, upward flux from sediments dominates the dissolved Fe pool with an apparent Δ⁵⁶Fe dis-part of −2.2 to −0.6‰. Large Δ⁵⁶Fe dis-part and previously published metagenome sequence data suggest active Fe cycling processes in anoxic layers, such as microaerophilic Fe(II) oxidation or photoferrotrophy, could regulate biogeochemical cycling. Large fractionation of stable Fe isotopes in these lakes provides a potential tool to probe Fe cycling and the acquisition of Fe by cyanobacteria, with relevance for understanding biogeochemical cycling of Earth’s early ferruginous oceans.
To further explore the effect of phytoplankton blooms on biogeochemical Fe cycling in the epilimnion and metalimnion of L227, seasonal variations in Fe concentrations, Fe speciation and Fe isotope compositions of dissolved Fe (DFe), particulate Fe (PFe) and total Fe (TFe) were reported in the oxic layers of L227 and L442. Biological uptake of Fe by phytoplankton results in a decrease in DFe, an increase in PFe and a decrease in TFe in the oxic epilimnion and metalimnion during the blooms. The prevalence of Fe(II) in the particulate Fe coupled with the depletion of Fe(II) in the dissolved Fe during the blooms suggest that diazotrophic cyanobacteria and chlorophytes in L227 likely utilize dissolved inorganic Fe(II) rather than organic complexed Fe(III), highlighting the importance of Fe(II) during iron acquisition. Uptake of isotopically light Fe by phytoplankton results in a diagnostic change in the dissolved and particulate δ⁵⁶Fe in the oxic layers. As a result, dissolved δ⁵⁶Fe is more positive than particulate δ⁵⁶Fe in the oxic layers of L227, with Δ⁵⁶Fe dis-part of 1.02 ± 0.33‰ (2σ) during the peak of the first bloom and Δ⁵⁶Fe dis-part of 0.56 ± 0.05‰ (2σ) during the second bloom. The difference in Δ⁵⁶Fe dis-part observed during the first bloom and the second bloom suggests that uptake of Fe by chlorophytes might produce distinct Fe isotope fractionation compared to diazotrophic cyanobacteria, possibly due to the differences in their uptake kinetics, the specific Fe-uptake mechanisms and associated enzymatic processes. The consistency in TFe concentration and Fe isotope composition of TFe in the epilimnion throughout the first and second blooms suggest that the settling flux of particulate Fe is limited during the blooms, likely due to efficient retention by phytoplankton. In contrast, during the decline of the bloom, the settling of isotopically light particulate Fe(II) associated with biomass to profundal sediment caused total δ⁵⁶Fe in the epilimnion to become isotopically heavier. During the peak of the first bloom, the large Δ⁵⁶Fe dis-part, the more negative particulate δ⁵⁶Fe, and the more particulate Fe concentrations in the metalimnion compared to what has been observed in the epilimnion suggest that cyanobacteria could migrate to the upper zone of the anoxic hypolimnion to uptake Fe under Fe-limited conditions. Modelling results showed that isotopically light PFe and TFe measured in the metalimnion during the peak of the first bloom are best explained by the migration of cyanobacteria below the redox boundary for the uptake of dissolved Fe(II). The observed seasonal variation in Fe concentration, speciation and isotope compositions associated with the progression of two annual blooms show great potential in understanding the role of Fe in the formation of cyanobacterial bloom and determining the availability and source of Fe for cyanobacterial uptake.
To explore the Fe processes and Fe sources in the anoxic hypolimnia of Boreal Shield lakes, seasonal variation in Fe concentrations and Fe isotope compositions of dissolved Fe and particulate Fe in the anoxic hypolimnia along with the Fe concentrations and Fe isotope compositions of porewater Fe and bulk sediment Fe in bottom sediment cores were reported in four Boreal Shield lakes: one eutrophic Lake 227 and three oligotrophic Lake 221, Lake 304 and Lake 442. In the oxic layers of all lakes, dissolved δ⁵⁶Fe is more positive than particulate δ⁵⁶Fe, likely modified by a combination of multiple processes including biological uptake, photochemical reduction of particulate Fe(III), complexation of dissolved Fe and dissolved organic matter, photolysis and microbial decomposition. The observed Δ⁵⁶Fe dis-part in the oxic layers of all lakes ranges from 0.06 ± 0.09‰ (2σ) to 1.02 ± 0.33‰(2σ), with the higher values likely arising from biological uptake. In contrast, the δ⁵⁶Fe values of dissolved and particulate Fe are reversed in the anoxic hypolimnia of all lakes, with negative Δ⁵⁶Fe dis-part fractionations of −0.91 ± 0.58‰ (2σ) in L221, −0.87 ± 0.81‰ (2σ) in L227, −1.06 ± 0.26‰ (2σ) in L304 and −0.72 ± 0.25‰ (2σ) in L442. Particulate Fe from the epilimnia is likely reduced completely by dissimilatory iron-reducing bacteria at the redox boundary, supported by the similarity in δ⁵⁶Fe between dissolved Fe in the anoxic hypolimnia and particulate Fe in the epilimnia of all lakes. The highly positive δ⁵⁶Fe values of particulate Fe in the anoxic hypolimnion and the large Δ⁵⁶Fe dis-part fractionations indicate in situ active Fe cycling in the anoxic hypolimnion. The most plausible explanation for the large Δ⁵⁶Fe dis-part fractionations in the anoxic hypolimnion is microbial oxidation, possibly photoferrotrophy, supported by the 16S rRNA gene sequencing and genome-resolved metagenome sequencing analysis. An increase in the magnitude of Δ⁵⁶Fe dis-part with depth and over time was observed in L221, L227 and L304, likely due to the variation of the oxidation rates, supported by increased particulate Fe concentrations with depth and time. The high concentration and negative δ⁵⁶Fe values of porewater Fe(II) suggest that DIR dominates organic mineralization pathways in sediment cores from the bottoms of L227, L304 and L442. The DIR-produced porewater δ⁵⁶Fe is further modified by the diagenetic formation of siderite in the upper section of sediment cores and the diagenetic formation of pyrite in the deeper section. Temporal and spatial variation in Fe isotope fractionation in the anoxic hypolimnia, along with the Fe isotope signatures in the sediment, suggest active Fe cycling in four lakes, highlighting the potential of seasonally anoxic Boreal Shield lakes to serve as analogues of the late Archean ocean.
2024-01-26T00:00:00ZHydrogeochemistry and Trace Element Mobility in an Acidic High-Sulfide Tailings Impoundment After 40 Years of OxidationStarzynski, Hannah Lucyhttp://hdl.handle.net/10012/202872024-01-26T03:30:56Z2024-01-25T00:00:00ZHydrogeochemistry and Trace Element Mobility in an Acidic High-Sulfide Tailings Impoundment After 40 Years of Oxidation
Starzynski, Hannah Lucy
Abandoned mine sites can create a legacy environmental contamination issue when the generation of acid mine drainage is allowed to continue with insufficient or absent remediation measures. The South Bay mine, a former underground Cu-Zn mine located in northwestern Ontario, is once such site with historical contamination. The mine wastes at South Bay contain high concentrations of sulfide minerals which continue to oxidize decades following mine closure, leading to acidic seepage with high concentrations of dissolved metals impacting the surrounding lakes. This aim of this study is to provide a characterization of the current hydrogeology, geochemistry, mineralogy, and microbiology of the South Bay tailings so that this information can inform future remediation work.
Instrument installation and collection of core samples of the tailings was performed at five locations within the tailings impoundment area. Pore-water samples were collected from piezometer and soil water sampler nests. Sub-samples of tailings cores were collected and analysed using optical microscopy, scanning electron microscopy, selective extractions, total carbon/sulfur, X-ray diffraction, X-ray fluorescence, synchrotron, and DNA sequencing techniques. Mineralogical analysis indicated that pyrite was the main sulfide mineral in the tailings, with lesser amounts of sphalerite and chalcopyrite and trace amounts of pyrrhotite, galena, and arsenopyrite. The oxidation zone in which sulfide minerals are depleted is restricted to the upper 0-15 cm of tailings. The moisture content within the tailings is relatively high, contributing to a low O2 diffusion rate into the tailings. High proportions of acidophilic microorganisms capable of catalyzing Fe and S oxidation reactions were found in the shallow tailings. Sulfide oxidation modelling has indicated that oxidation of sulfide minerals in the South Bay tailings may continue for decades to millennia before all sulfide minerals are depleted in the vadose zone.
Prolonged sulfide mineral oxidation has led to acidic pore waters with pH as low as 1.26 with high concentrations of dissolved metals, including Fe, Zn, Cu, As, Pb, and Co. The lowest pH and highest concentrations of dissolved metals tends to occur in the shallow tailings near the region of active sulfide-mineral oxidation. High concentrations of dissolved rare earth elements (REEs), up to 9.45 mg/L total REEs, were also found within the shallow acidic pore-waters. Dissolution of gangue minerals and secondary minerals contributes to acid neutralization, with pH increasing to circumneutral values below the water table. Metals and metalloids may be attenuated through adsorption or co-precipitation with secondary mineral phases. Copper was found to be attenuated through covellite precipitation, Pb was attenuated through anglesite precipitation, and As was attenuated by adsorption or co-precipitation with Fe(III) (oxy)hydroxides. Metal(loid)s sequestered within Fe(III) (oxy)hydroxides may be susceptible to remobilization through reductive dissolution should environmental conditions imposed by future remediation efforts induce strong reductive conditions.
2024-01-25T00:00:00Z