Department of Geological Sciences and Geological Engineering Graduate Theses

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    Investigating Trace Element Sourcing and Biogeochemical Cycling in the Great Lakes
    (2024-05-02) Pereira Junqueira, Tassiane; Geological Sciences and Geological Engineering; Vriens, Bas; Leybourne, Matthew
    The Great Lakes are a group of five interconnected lakes that form one of the world’s largest freshwater systems, containing about 21% of the world's liquid surface freshwater. However, urbanization and industrialization throughout the basin have increased the discharge of various pollutants into the lakes, including metals, such as copper (Cu), zinc (Zn), and rare earth elements (REE). Furthermore, agricultural development, urbanization, and other hydrological management and land-use practices contribute to water and sediment contamination through runoff that can lead to nutrient enrichment and increased metal accumulation, potentially disrupting aquatic ecosystems and posing risks to the environment. Copper and zinc are trace metals with long histories as anthropogenic contaminants. In contrast, the REE are considered potential emerging contaminants in this system, and their baseline levels as well as biogeochemical cycling are not as well understood. Environmental, economic, and public health consequences may be associated with elevated levels of these trace elements in aquatic ecosystems, but the sources, sinks and processes controlling the occurrence of Cu, Zn and REE, particularly at baseline levels, remain poorly understood in many locations in the Great Lakes. This PhD thesis first summarizes current knowledge on biogeochemical Cu, Zn and REE dynamics in the Great Lakes, including current concentrations and loads, potential sources, and major processes controlling their occurrence. Results from Cu and Zn isotope analyses of river waters and sediments are presented to address critical knowledge gaps pertaining to their cycling and sources. Furthermore, REE concentrations in Great Lakes waters and sediments are assessed to investigate the biogeochemical processes governing REE variability in the Great Lakes, and to quantify the role of sedimentation as a mechanism in lake-wide REE dynamics. Overall, this thesis reveals the highly variable spatiotemporal dynamics of Cu, Zn, and REE across the basin, and reveals the distinct behaviors of trace elements within and between the lakes. This thesis expands the understanding of the biogeochemical processes controlling Cu, Zn, and REE dynamics in the Great Lakes, assisting in the preservation of this globally distinctive freshwater reserve against legacy and emerging trace metal pollution.
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    Enhanced Laboratory Testing and Characterization Related to the Mechanics of Anisotropic Rock
    (2024-03-28) Packulak, Timothy; Geological Sciences and Geological Engineering; Diederichs, Mark; Day, Jennifer
    Geological engineering is a complicated field to practice in, especially when engineering solutions have to be designed to interact and sometimes be hosted in anisotropic geomaterials. This anisotropic environment is composed of two components, discontinuities and intact blocks. In many cases, these intact blocks of rock are anisotropic, specifically transverse isotropic, where empirical methods do not accurately predict behaviour and analytical solutions are not always available, leaving numerical methods to help predict their behaviour. As civil infrastructure continues to be built in increasingly complex rockmasses at greater depths, it is important to use testing methods measuring geomechanical properties with a high degree of accuracy and repeatability. Tensile strength is commonly measured via the indirect tensile strength test, intact elastic components and compressive strength are measured via the unconfined compressive strength test, and joint deformation is measured via the direct shear test. However, the testing methods were historically designed for rock materials that were homogenous and isotropic. This research addresses the limitations of some of the most common laboratory testing methods used in rock engineering design and proposes modifications to the testing methods, as well as recommendations for instrumentation and guidelines for data processing. For joint stiffness this thesis recommends that an intact control specimen be tested to account for both machine and system deformations. In order to quantify joint roughness, a method using Structure-from-Motion photogrammetry and statistical analysis is proposed to understand the anisotropic behaviour of joint surfaces. For tensile strength testing, it is recommended that specimens be instrumented to measure strain and determine strain thresholds in order to measure crack initiation as well as confirm proper loading. For anisotropic tensile strength, a new three-part failure criterion based on stress transformation mechanics is proposed, and validated using digital image correlation. For compressive loading, recommendations for the use of dynamic elastic constants are presented as an alternative to static measurements which typically have a high degree of scatter. Finally, a new behaviour model is presented for anisotropic materials suggesting the onset of two crack initiation points: shear along foliation and tensile fracturing in the matrix.
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    Application of Computational Methods to Data Integration and Geoscientific Problems in Mineral Exploration and Mining
    Trott, McLean R; Geological Sciences and Geological Engineering; Leybourne, Matthew; Layton-Matthews, Daniel
    The application of computational methods to data integration and interpretation problems in the mineral exploration and mining space was examined at two distinct scales: deposit-scale studies at the Pimentón and Josemaría epithermal and porphyry copper deposits, and a tectonic examination of the Caribbean at the plate scale using public domain data. Much commonality was found, suggesting that some components of objective workflows are relevant at nearly any scale, with a few modifications. Quality control assessment of data is critical and extends beyond geochemical datasets to any data type required for downstream machine learning processes. Dimensionality reduction, although it may vary in form, is a useful and informative preprocessing step at any scale. Signal analysis techniques like continuous wavelet transform tessellation are relevant to noise reduction and boundary detection for linear data at any scale, when framed appropriately. Examination of workflows for incorporating multiple input feature families was key for this research; again, similarities were found in all cases. Textural metrics were found informative for geological classifications, particularly when involved with geochemical inputs, forming a complementary combination of features with more holistic representation of the rocks in numeric terms, a theme first illustrated at Pimenton and reinforced in Josemaria. Incorporation of distinct datatypes is aided by principal components analysis (PCA) and consideration to spatial coincidence during acquisition and processing of acquired data. Articulation of the concept that classic model metrics like accuracy, precision, and recall are highly influenced by the scale of labelling compared with the scale of feature inputs for many geoscientific problems led to an in-depth examination of this problem during the Josemaría study. The proposed solution, involving the removal of ‘noise’ and generalization of class membership probabilities for linear data predictions, is effective, and incorporates an element of spatial coherency into predictions. The same technique for noise reduction and generalization, continuous wavelet transform tessellation, proved useful on an entirely different scale during examination of hypocenters in the Caribbean region. The method provided an empirical means of locating significant hypocenter density minima along the trend of the arc. Ultimately, it is hoped that this research can facilitate the adoption of semi-automated workflows for large/high-dimensioned datasets or routine tasks and permit human ingenuity to be used on the tasks where creativity is essential.
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    Water-rock Interactions in Geologically Diverse Regional Aquifers of Northeastern Ontario
    Dell, Kayla; Geological Sciences and Geological Engineering; Leybourne, Matthew
    Information regarding the characterization and controls of groundwater chemistry in Precambrian silicate aquifers of northeastern Ontario is limited. This study utilizes the analysis of halogens, major ions, select trace ions, δ18OH2O, δ2HH2O, δ34SSO4, δ18OSO4 and tritium of 271 groundwater samples collected from Precambrian bedrock aquifers to present a characterization of groundwater chemistry for northeastern Ontario, in addition to 55 groundwater samples collected from Paleozoic aquifers of Manitoulin Island in Lake Huron. The analysis of 87Sr/86Sr on 98 of the total groundwater samples collected are also presented here. Aquifers are hosted in a variety of rock types including Archean rock of the Superior Province to the north of the study area, Paleoproterozoic Huronian Supergroup rocks in the west, metamorphosed Precambrian rock of the Grenville Province in the southeast, and Paleozoic carbonate rocks on Manitoulin Island. Water-types, Cl- versus Cl/Br bivariate plots, and other geochemical and isotopic methods were employed to discern sources of salinity and to identify zones of anomalous groundwater chemistry. The sources of salinity were identified as mixing with trace amounts of deep brines, water-rock interaction, and influence by surface contaminants, including road salt. A zone of anomalous chemistry forms a northeast-southwest linear trend within the Grenville Province running parallel to the Grenville Front. This zone is characterized by reducing conditions (as low as -130.8 mV), elevated TDS (up to 1250.7 mg/L), Br- (up to 3.44 mg/L), Cl- (up to 386.08 mg/L), I- (up to 192 µg/L), B (up to 2249.7 µg/L), and depleted Sr isotope values (as low as 0.708667). A group of samples characterized by Na-Cl geochemical facies, unconfined aquifer conditions, and parameters reflective of surface influence (oxidizing conditions, low pH, elevated TDS (up to 1304.4 mg/L) are commonly spatially associated with major highways. A zone of groundwater with a Na-K-HCO3 geochemical facies coincides with thick overlying Quaternary units of glaciolacustrine material deposited along the north shore of Lake Nipissing. The presence of a confining layer over this area reduces surface influence and allows for longer residence times leading to alkaline and reducing conditions and increased F- concentrations as a result of ion exchange. Groundwater along the north shore of Manitoulin Island with higher TDS (up to 7664.3 mg/L), Br- (up to 8.0 mg/L), Cl¬- (up to 4357.55 mg/L), I¬- (up to 134.0 µg/L), and B (up to 10475.0 µg/L) concentrations relative to the south shore of the island is likely related to the presence of shale and reducing conditions in the Georgian Bay and Blue Mountain formations. These results provide a general characterization of groundwater geochemistry in a geologically diverse region in northeastern Ontario and improved understanding of the controls of groundwater chemistry in silicate Precambrian aquifers.
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    Evaluation of Ultrasonic Pulse Velocity Measurements and Resultant Elastic Moduli of Hard Rock Core Specimens
    McDonald, Mark R.; Geological Sciences and Geological Engineering; Diederichs, Mark
    Material behaviour and strength characterization is a critical aspect of site investigation programs when designing engineered structures in rock. The measurement of Ultrasonic Pulse Velocities (UPV) in rock core is a straightforward non-destructive test used for estimating fundamental rock properties. UPV measurements emit high frequency acoustic waves through rock core specimens. The velocities of compressional and shear waves (P- and S-waves, respectively) are influenced by the unique microstructural characteristics of each rock sample. Upon calculating P- and S-wave velocities and bulk density, dynamic elastic constants can be calculated. A common problem with UPV derived elastic constants is that these measurements are often different than the static elastic parameters derived from destructive mechanical tests. Improving the understanding of why differences in elastic moduli occur between dynamic and static testing methods is investigated in this research. Factors including rock specimen lithology, density, core dimensions, saturation, pre-existing damage, and the impact of applied uniaxial and isotropic stress are investigated to evaluate their impact on P- and S-wave velocities and dynamic properties for commonly researched homogenous rock types. Further, the relationship between UPV core specimen measurements and in situ sonic borehole testing data is compared in a practical case study using new laboratory testing completed as part of this research, and published data from the Geological Survey of Canada. This study provides an opportunity for determining the impact of saturation and in situ stresses on measured wave velocities. The findings of this research demonstrate the significant impact of saturation, and uniaxial and isotropic stresses on P- and S-wave velocities and resultant elastic moduli on tested rock core specimens. Further, the non-linear axial stress-strain behaviours of UCS core specimens are related to the dynamic elastic measurements with and without compressive stress using UPV testing methods. Dynamic measurements of Young’s moduli taken at equivalent stress magnitudes where static Young’s moduli are measured are shown to better agree with static moduli data. Finally, axial and lateral P- and S-wave velocity changes under uniaxial compressive stress are analyzed with respect to critical damage thresholds, including crack closure, crack initiation, and crack damage for Lac du Bonnet core specimens.