Earth and Environmental Sciences Undergraduate Honours Theses

Permanent URI for this collectionhttps://hdl.handle.net/10222/75089

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Open Access
Characterization of Calcite Amygdules in Devonian Basalts, in the McArras Brook Formation, Nova Scotia
(2024-04) Helmke, Ingrid
Along the North Shore of Nova Scotia, Canada vesicular basalts in the McArras Brook Formation are host to carbonate amygdules and veins. These basalts are interbedded within a well characterized Devonian strata but have not been directly dated. Through previous studies with U-Pb dating, the ages for calcite amygdules have been shown to form shortly after the eruption of the host basaltic lava. Secondary processes lead to the formation of overgrowths on existing calcite amygdules and low-T veins. These may form during tectonic emplacement and thus, multiple generations of calcite can also be found in the same suite of basaltic rocks. Before the U-Pb ages of both volcanism (amygdule formation) and later tectonic activity (secondary calcite) can be accurately measured and used as a proxy for the age of the basalt flows, the growth history of the calcite amygdules and viens must be carefully characterized. In this study we have used basic textural relationships and UV fluorescence to examine calcite growth history, both in the field and in collected samples. In-situ UV-fluorescence shows the growth of several generations of calcite amygdules and veins in the basalts from McArras Brook. We will use the UV characterization to help target analysis of different generations of calcite using a scanning electron microscope (SEM) to analyse the relationships between the fluorescence and the major elements. The results are expected to identify activator elements in the calcite which correspond to the differences in fluorescence colour, and correlate element compositions to the growth history. This will allow us to target the best areas for subsequent U-Pb dating of calcite to determine the absolute (volcanic) ages of these basalts, and the ages of secondary processes.
Open Access
Quantifying the Impacts of Nova Scotia Forest Management Practices on Forest Stand Albedo and Surface Temperatures
(2024-04) Rusnak, Evelyn
In an effort to mitigate climate change, the Canadian government has increased focus on natural carbon sequestration through afforestation (i.e., the planting of forests where there were previously no forests) and reforestation (i.e., the planting of forests to replace a forest than was removed or disturbed). Traditionally, these forest management practices have preferred coniferous (softwood) tree species, which has led to wide scale species conversion across Europe and North America, increasing coniferous forest cover. Recent studies have linked these forestation practices to increased surface temperatures in managed forests. Coniferous forests have lower albedo than deciduous forests, absorbing a greater ratio of solar energy, which is re-emitted as heat and raises surrounding temperatures. This thesis tested the hypothesis that forest management practices in Nova Scotia increase coniferous tree cover, which in turn reduces canopy albedo and raises surface temperatures. Remote sensing methods were used to test the relationship between forest treatments and stand biophysical characteristics. Albedo, surface temperature, and Normalized Difference Water Index outputs for Nova Scotia were derived from multispectral and thermal satellite imagery collected by Landsat 8 over July and August 2022. Forest stand data shared by the Nova Scotia department of Natural Resources and Renewables identify 216,235 forest stands, classified into two groups: 89,171 treated forest stands, and 127,064 natural forest stands. Analysis successfully demonstrated relationships between forest management practices and forest stand biophysical characteristics using remote sensing derived measurements. Contradicting the original hypothesis, treated stands exhibited higher mean albedo than natural stands, a process partially explained by the scarce canopy cover of young replanted forests. Further, mean surface temperatures in treated stands were 0.4-1.2 °C warmer than comparable natural stands. This relationship indicates current forestry policies may, in fact, be increased surface temperatures in managed forests. While further discriminant analyses failed to meet confidence thresholds, classification accuracies of ~70% suggest some discriminant ability within the predictor variables (albedo, surface temperature, and NDWI). The overall results of this thesis indicated that forest management is creating higher forest surface temperatures, but this phenomena is not related to decreased albedo in treated stands, and is likely caused by underlying processes not addressed in this study. The outcomes of this work call into question the efficacy and validity of using forests as climate change mitigators. Specifically, whether Canada should continue to implement climate change policies that promote reforestation and afforestation if these methods may warm surface temperatures. In-depth analysis assessing the value forestation as a climate mitigation strategy should be conducting; contrasting the cost of increased surface temperatures caused by forest management against the considerable carbon sequestration ability of forests.
Open Access
The impact of precipitation phase and aquifer type on changing groundwater levels in mountain regions of Canada and the United States
(2024-04) Salehi, Sana
Groundwater in alpine regions plays an essential role in downstream water supply. As the climate warms, mountain water resources are under threat with reduced snowpack, glacier recession, and precipitation phase change that can negatively impact summer streamflow. However, the extent to which such global changes can impact the mechanisms that contribute to groundwater recharge remains poorly understood. This project aims to address the limited spatial and temporal extents of observational studies and enhance our understanding of long-term trends across various geographical boundaries of groundwater in mountainous regions. We analysed a dataset of 171 observation wells from mountain regions across Canada and the US, categorizing wells as snow-dominated, rain-dominated, and high-temperature rain-dominated hydrological regimes based on temperature thresholds. Additionally, we considered three aquifer types (confined, unconfined, and mixed) and the well depth as the potential explanatory variables. We conducted Kruskal- Wallis and Spearman correlation analysis on the above against the groundwater level trends, respectively. Our results indicated a non-significant difference (p = 0.1687) between the three hydrological regimes, a statistically significant difference (p = 0.0182 < 0.05) in the trends observed between the three-aquifer type, and lastly a weak negative Spearman correlation of ρ = -0.01089 between trend and well depth, which is not statistically significant (p<0.05). This study emphasizes the value of extending research on mountain groundwater to a larger spatial extent and offers significant insights into how various factors can influence groundwater recharge in mountains.
Open Access
Halifax Residential Air Quality: Public Perceptions and PM2.5 Concentrations
(2024-04) Russell, Sadie
Residents of Halifax's North End have raised concerns over air quality in their neighbourhood. Exposure to elevated levels of airborne particulate matter pose serious risks to human health and increases strain on local healthcare systems. This study sought to quantify local concentrations of PM2.5 and compare them to Canadian Ambient Air Quality Standards (CAAQS). Additionally, it aimed to understand public perceptions of air quality and sources of pollution within their neighborhood. PM2.5 concentrations were collected remotely from the 2600 block of Agricola Street from November 2022 and November 2023. A total of 276 usable days were recorded. The observed 24-hour 98th percentile PM2.5 average is 50.1 μg/m3 and the annual average is 12.6 μg/m3. Averages exceeded the highest CAAQS threshold of both 24-hour and annual averages. Daily trends showed that the highest concentrations occurred between 8 am and 6 pm on weekdays and showed no variation from the downtown control site on weekends. The highest PM2.5 concentrations were recorded in the presence of northwesterly winds. A local butcher shop and meat smoker to the northwest of the study site, was identified as a likely source of the local elevated air pollution A self-selecting, online survey was circulated by mail flyer and email. People who live or work within a 200 m radius of the air quality sensor were eligible to participate. Participants were asked to rate their perception of local air quality trends, level of concern, and perceived sources of pollution. Based on census population density, it is estimated that 900 respondents lived within the study area. Survey results were based upon 61 usable responses. Respondents to the survey confirmed that they perceived the nearby meat smoking operation to be one of the top three sources of air pollution within their community. A Posteriori coding of open-ended questions yielded numerous sentiments of frustration and reduced quality of life due to local air pollution. However, most respondents indicated that they perceived air quality to be at least acceptable. Regardless of perception, long-term exposure to elevated PM2.5 levels pose health risks to the public in the immediate vicinity; especially seniors, children, and those with pre-existing medical conditions.
Open Access
Assessing Eutrophication Vulnerability as an Indicator of Cyanobacteria Presence in Kejimkujik National Park
(2024-04) Macdonald, Sarah
Kejimkujik National Park (KNP) and National Historic Site (Nova Scotia, Canada) is home to numerous lakes that support a multitude of recreational activities and aquatic habitats. The park is comprised of camp sites, canoeing routes, and hiking trails, making it a popular tourist attraction during the summer months. Aquatic systems in the park not only support these recreational activities, but also support diverse organisms that are important to the park’s ecosystem. This thesis was the first study to assess the cyanobacterial populations within KNP. The objectives of this study were to identify lakes within the park that are susceptible to cyanobacteria blooms. Several factors could influence the proliferation of cyanobacteria in KNP, including nutrient abundance, light availability, water temperature, mixing regimes, and flushing rates. This study involves a phosphorus loading model, which uses publicly available spatial and water quality data, to characterize the lakes in KNP based on their eutrophication vulnerability, using the factors known to contribute to harmful cyanobacterial blooms. The results of the model were compared to information collected from a park-wide cyanobacteria sampling program and toxin survey conducted in 2023 to assess the applicability of this model for identifying lakes vulnerable to blooms. Next generation MiSeq illumina sequencing results indicate that cyanobacteria were present in small abundances in 10 of the 16 study lakes within the park, but little is known about whether these photosynthetic bacteria populations could proliferate and form blooms that could be harmful to humans and other animals. Three of the study lakes contained potentially toxin-producing cyanobacteria of the order Nostocales. Anatoxins and microcystins were detected in small quantities in several locations in the park. Water quality parameters collected from 2008 to 2021 indicate that cyanobacteria were primarily present in oligotrophic lakes. Cyanobacteria were additionally only shown to exist within certain thresholds of certain water quality parameters. Cyanobacteria were only found in lakes with a total phosphorus concentration between 4 to 10 μg/L, and a total organic carbon concentration between 2 to 5 mg/L. More research needs to be conducted to determine exactly what is driving the cyanobacteria proliferation in KNP.
Open Access
Identifying and prioritizing barriers to Atlantic salmon habitat connectivity in Napu’saqnuk (St Mary’s River), Mi’kma’ki (Nova Scotia, Canada)
(2024-04) Bleyer, Rosie
Atlantic salmon (Salmo salar) are an anadromous fish species that migrate from headwaters of their home rivers out to the open ocean and back; this ecologically, economically, and culturally significant species requires extensive and well-connected freshwater habitat to successfully reproduce and maintain viable populations. However, the installation of road culverts can fragment aquatic habitat and impede Atlantic salmon from reaching their spawning grounds. In mainland Nova Scotia, Napu’saqnuk, known as the St. Mary’s River, represents important habitat for a population of Atlantic salmon that has been assessed as ‘Endangered.’ Removing and remediating culverts that cause habitat fragmentation in the area is therefore of utmost importance, however it can be time and resource intensive. Through field assessments in the West Branch of the river over the summer of 2023 I collected data on 75 culverts’ abilities to successfully pass Atlantic salmon and general information on their structure and state of function. I have combined this information with remotely collected landscape scale characteristics of each site to further investigate the relationship between culvert characteristics and passability. Logistic regression modelling identified the characteristics of shape, diameter, change in elevation, and position in the watershed to be the best predictors of a culvert being able to successfully pass salmon. The results of field assessments indicated that the river continues to experience severe fragmentation, with 77% of culverts assessed to be a partial or full barrier to fish passage. Culverts previously recommended for remediation by the St Mary’s River Association in 2009 were revisited to find some had been removed or modified; other sites continue to be legacy barriers potentially fragmenting the watershed habitat for up to several decades. Using collected data on fish passage and estimated upstream habitat, I prioritized additional sites in the West Branch for further assessment and remediation. My research provides a framework for future culvert assessments and remediation in this important watershed by leveraging data collected through a combination of fieldwork and remote sensing.
Open Access
Mapping lobster habitat in the Northumberland Strait using multibeam echosounders to assess juvenile lobster conservation zone placement
(2024-04) Metcalfe, Kate
The Northumberland Strait, located in the southern Gulf of Saint Lawrence, is an important area for scallop and lobster fishing. To mitigate the negative ecological effects of fishing, marine management strategies in the form of scallop fishing buffer zones are in place, and informed through dive surveys and fishing data aim to protect juvenile lobster habitat. Current scallop fishing buffer zone locations (shoreline to 1km offshore) align with where hard bottom is expected to be. There are multibeam datasets covering this area, but our understanding of the benthic ecosystem composition and marine conservation strategies could be greatly improved by creating benthic habitat maps of the area using multibeam echosounder (MBES) technology. Using a combination of bathymetry and backscatter collected by MBES, and drop camera footage, substrate distribution maps and habitat suitability maps for adult lobster were created using Random Forest and Maximum Entropy modelling respectively. The sediment was classified into three substrate categories using a modified Folk 5 classification: mud to muddy sand and sand, mixed sediment, and rock & boulders. The placement of the scallop fishing buffer zones from a species conservation standpoint is discussed based on the modelled habitat suitability and distribution of bottom type. Patterns of habitat suitability for adult lobster were spatially compared against the various bottom types. The sediment distribution results showed that there was a higher proportion of rock & boulder and mixed sediment within the scallop fishing buffer zones than outside of the protected zones. From the observed higher proportion of rock & boulders and mixed sediment inside the buffer zones, it can be inferred that substrate distribution inside the buffer zones is suitable for adult lobster conservation. There is however suitable habitat outside of the conservation zones that could be further protected. The observed adult lobster habitat preference can then inform juvenile lobster juvenile lobster habitat preference from what is known about juvenile lobster and adult lobster behaviour. Increased understanding of the distribution of bottom type and of adult lobster habitat suitability will allow for more informed juvenile lobster conservation decisions in the Northumberland Strait based on relationships that have been observed in order studies to work towards meeting Canada’s 2030 marine conservation goals.
Open Access
Determining the Effectiveness of Forestry Beneficial Management Practices for Olive-sided Flycatcher, a Species at Risk Bird in Nova Scotia
(2024-04) Freeman, Hannah
The Olive-sided Flycatcher (OSFL) is a bird species at risk that breeds across Canada, including in Nova Scotia's forests. It is considered threatened in the province, experiencing recent population declines. While OSFL occupies protected areas in Nova Scotia (NS), research indicates that these areas alone are insufficient for conservation, emphasizing the need for conservation efforts in working forests. Species-specific beneficial management practices (BMPs) were developed for OSFL in the context of forest harvesting and applied in a stand in Cape Breton in 2022. However, their effectiveness in conserving OSFL is undetermined. This study assesses BMP effectiveness by evaluating OSFL reproductive success inferred from vocalization activity as a measure for successful conservation. Bioacoustic data from the harvested site in Cape Breton a non-BMP control site in Southwest NS were collected using autonomous recording units and analyzed in Raven Pro/Lite. Songs and calls were counted independently using visual and auditory clues, as well as aid by BirdNET identification highlights. These counts were averaged over varied time periods, and vocal activities were compared to expected patterns observed for pairing, successful nesting, and failed nesting. In the harvested site, results on song rate activity were consistent with patterns expected for male OSFL that pair and reproduce successfully. On the other hand, those at the control site displayed song rate activity consistent with patterns expected for male OSFL that pair but experience a failed nest. This indicates that harvesting with BMPs allowed OSFL to occupy the area and did not inhibit the bird from breeding successfully, thus highlighting the potential effectiveness of the BMPs in OSFL conservation.
Open Access
Predicting Olive-sided Flycatcher (Contopus cooperi) Breeding Habitats in Southwestern Nova Scotia Using LiDAR Metrics Informed by Drone Data.
(2024-04) Burns, Declan
The Olive-sided Flycatcher (OSFL) is a migratory species at risk bird, currently listed as “Threatened” in Nova Scotia, and “Special Concern” federally. The strategy to promote the recovery of OSFL population is expected to revolve around protecting existing breeding habitat as soon as these locations are found. Two studies have previously modeled OSFL habitat in Nova Scotia using tree-stand level input layers which makes it impossible to identify the within-stand characteristics used by the bird when choosing their habitat. These characteristics of fine-scale forest structure are closely tied to their foraging strategies and are the main driver determining OSFL occupancy rates in these habitats. The goal of this study is to use high-resolution drone imagery to inform LiDAR metrics as inputs for a model that predicts OSFL breeding habitat locations in Nova Scotia. The canopy height models (CHM) for the two data types were compared at 19 known OSFL habitat sites across the province by assessing tree spacing, canopy cover, and the vertical heterogeneity of the treetops to determine which LiDAR metrics can show the within-stand characteristics of OSFL habitat. A correlation test identified three metrics in the drone CHM that could be comparatively measured in the LiDAR CHM: canopy cover and the mean and standard deviation of tree heights. These metrics were then used as inputs for a Maximum Entropy (MaxEnt) model alongside other environmental layers important for characterizing OSFL habitat. MaxEnt created a predicted distribution of the species from occurrence data and the environmental input layers to identify where habitat with similar environmental characteristics could occur. After each run of the model, the performance of each input covariate was assessed, and the worst performing covariate was removed before the model ran again. This process was repeated until the best fit model was identified. The final model consisted of four environmental covariates used to predict OSFL habitat locations: proportion of canopy cover, distance to wetlands, mean canopy heights, and distance to spruce stands. The model performed comparatively well to previous predictive habitat models for the OSFL and identified 48.90% of the Kespukwitk area as being suitable habitat for the OSFL. The results showed the importance of capturing the variation within the OSFL’s habitat for predicting habitat locations, evident by the LiDAR-derived covariate measuring the proportion of canopy cover performing better than all other covariate used in any model predicting OSFL habitat in Nova Scotia. Locating where these habitats occur throughout the province is crucial to inform where recovery strategies would be most effectively implemented to protect the OSFL Atlantic population.
Open Access
Characterizing the Conifer Density Gradient from the Halifax Peninsula to the Hinterlands of the Halifax Regional Municipality
(2023-04) Radomske, Levyn
The urban-forest tree-species composition is influenced by the urban environment and thus by daily anthropogenic activity. However, in the naturalized woodlands, species composition is primarily influenced by natural disturbances. In moving away from the urban setting to the naturalized forest, there is a shift in the environment leading to a transition of dominant species, ultimately creating a species composition gradient. This study characterized the conifer gradient through assessing the Halifax Peninsula, surrounding communities, and the hinterlands of the HRM. The assessment of the conifer density on the Halifax Peninsula followed a probabilistic sampling technique in which ocular estimates were conducted to produce a conifer inventory for the study area. To assess the conifer density in the other study areas, two independent datasets were analyzed. Further analyses on other cities’ conifer densities were conducted to develop benchmark values for the HRM. Through these assessments, it became apparent that there is a steep conifer gradient in the transition from the urban environment to the naturalized environment. These data can be used to question the lack of conifers in the urban forest despite their prominence in the naturalized setting and in other cities. Key Words: Conifer, Urban Forest, Urban Forest Values, Urban Environment, Density
Open Access
An Analysis of Introductory Environmental Science Textbooks’ Approaches to Commonly Held Climate Change Misconceptions
(2023-04) Lowther, Lauren
A climate literate public is becoming increasingly important as the threats of climate change grow (Johnston 2019). Climate literacy is taught across introductory environmental science courses in higher education institutions in Canada with textbooks being used as a key tool in facilitating climate literacy in these cases (Choi et al. 2010). This study aims to evaluate how these textbooks are approaching their delivery of commonly held climate change misconceptions. A literature review was conducted to determine prevalent misconceptions and key textbook elements that enhance learning while also combatting misconceptions. The climate change and atmospheric science chapters from eight textbooks used among the top 15 research universities in Canada were analyzed to determine the presence or absence of the six most commonly recorded misconceptions and whether or not the misconceptions were presented using the key five textbook elements. A checklist containing the misconceptions and textbook elements was used to identify and further code textbook elements; each time a check mark was given, the key terms and associated content segments were also recorded. The results show that some key textbook elements were heavily underrepresented across all misconceptions and textbooks. Misconceptions were only directly refuted by the textbooks in 6.25% of the time. Some misconceptions were frequently presented without the inclusion of select textbook elements. Only one out of eight textbooks used examples when presenting misconceptions around the greenhouse effect. Two out of eight textbooks used prompting questions and none used case studies or examples when presenting concepts related to misconceptions of water vapour’s role as a greenhouse gas. The results also showed some similarities in the presentation of concepts across all textbooks. The phrases ‘short term’ and ‘long term’ were used across all but one book when presenting the difference between weather and climate. Refuting misconceptions is one of the most effective strategies that can be used to help learners overcome these misunderstandings (Nussbaum et al. 2018). Despite this, the results in the present study showed that this was the most underrepresented key textbook element. The inclusion of this element into future textbooks could lead to more effective comprehension and a reduction in misconceptions held by students (Schroeder and Kucera 2022). Misconceptions regarding water vapour as a greenhouse gas and the greenhouse effect and climate change being a natural phenomenon require better representation in textbooks as the key elements used were lacking. Ultimately, textbooks should be written with common misconceptions in mind to diminish their prominence and better facilitate a climate literate society. Keywords: misconceptions, climate literacy, key textbook elements, climate change, conceptual change
Open Access
Telling the North American beaver tale: modelling Castor canadensis distribution in Mi'kma'ki (Nova Scotia, Canada)
(2023-04) Bahen, Geneva
The American beaver (Castor canadensis) is a keystone species of both significant ecological and biocultural importance in Mi'kma'ki (Nova Scotia). In North America, several environmental covariates are known to influence C. canadensis habitat selection, including distance to watercourse, stream gradient, and distance to preferred hardwoods; however, specific distances and species vary greatly throughout their continental range, prompting the need for local study. In Nova Scotia, occurrence data have never been systematically collected as C. canadensis is a common and unthreatened species, resulting in geographic knowledge gaps. This thesis remedied this knowledge gap by using Maximum Entropy modelling (Maxent) to create a species distribution model using environmental conditions present in areas of known occurrences to predict areas of C. canadensis distribution across the province. Input layers consisted of predominantly citizen-science occurrence data, and environmental covariates which characterized geomorphology and forest composition. Correlation analysis and reverse stepwise elimination were used to generate two models: an ecological model, and a human footprint model, where the latter investigated the influence of anthropogenic disturbance. Each model was an average of 10 replicates, using 500 iterations, 10,000 background pseudo-absence points, and a jackknife test to measure variable importance. The ecological model produced a high averaged area under the receiver operating characteristic curve (AUC) for the replicated runs (0.80 +/- 0.02), where the strongest contributors to distribution based on the permutation importance were 'Watercourse' (26.6%), 'Elevation' (15.1%), 'Red Oak' (11.8%), 'Aspen' (11.4%), and 'Gray Birch' (9.9%). Response curves indicated proximity to watercourses, low elevation, proximity to aspen, and distance from red oak and gray birch were important habitat associations. The human footprint model showed a positive relationship between occurrence points and human footprint, likely due to citizen-science collected occurrence data. Areas of known historic usage overlap at a landscape scale with distribution. The habitat association findings are consistent with previous studies suggesting watercourses, elevation and specific hardwood tree species are the main drivers of distribution, highlighting important areas of the predicted distribution of C. canadensis in the Wabanaki-Acadian Forest. Modelling this distribution is a practical conservation and management tool, which can contribute to future efforts to map biocultural connectivity in Mi'kma'ki (Nova Scotia), inform land use management, and provide insight into future species' sampling needs. Keywords: American beaver, Castor canadensis, SDM, Maxent, Nova Scotia
Open Access
Where is the Carbon? Spatially Mapping Organic Carbon on the Seafloor in the Eastern Shore Islands, Nova Scotia, Canada
(2023-04) Brenan, Catherine
Coastal sediments contain some of the largest stocks of organic carbon on earth and play a vital role in influencing the carbon cycle. Protecting organic carbon hotspots is essential to mitigating climate change since coastal development and bottom trawling can disturb the seafloor, driving the remineralization of organic carbon into carbon dioxide. Terrestrial carbon stocks are well studied and mapped, but our knowledge of standing stocks of marine sedimentary carbon and the role that it can play in minimizing the effects of climate change are poorly understood. One of the challenges in mapping the seafloor environment is the issue of characterizing spatial heterogeneity of different substrata, which is critical in estimating organic carbon standing stocks in the marine environment. In this study, we use high-resolution multibeam echosounder (MBES) data from the Eastern Shore Islands off Nova Scotia to predict the distribution of percent organic carbon in surface sediments. We applied benthic habitat mapping approaches, utilizing high-resolution continuous coverage environmental variables (bathymetry, backscatter, ruggedness, and slope) combined with subsea video and sediment grab sample ground truthing to generate thematic maps of sediment types for the area. We then compared that to organic carbon measurements from the sediment samples to estimate organic carbon standing stocks by substrate type. The sediment map had a 60 % mean of the squared prediction error, yet the substrate pattern was like previous substrate maps that were done in the Eastern Shore Islands. We also found that the standing stock of carbon range was 613,536 to 10,915,548 kg/km2. Our findings demonstrated that high-resolution sediment classification maps are necessary to improve our understanding of spatial patterns of OC. They can also help identify carbon hotspots, which are essential for seabed management and climate mitigation strategies. Key words: Organic Carbon, Ocean Sediment, Seafloor Mapping, Marine Carbon Stocks, Seabed Acoustics
Open Access
Investigating pyrite genesis and relation to gold at the Lone Star Deposit, YT
(2023-04) Hilliard, Arthur
The Klondike region of the Yukon Territory, Canada, is famous for extensive placer deposits, recovering over 20 million oz since discovery, but lacks any major defined bedrock resources. As a result of a surge in exploration activity, recent drilling efforts have delineated several new bedrock targets, including the Lone Star deposit near Dawson City, Yukon. The Lone Star deposit is hosted by a suite of Late Permian plutonic, volcanic, and sedimentary units known as the Klondike Assemblage. This assemblage formed because of subduction-related arc-magmatism, followed by Late Permian-Early Triassic regional greenschist-amphibolite facies metamorphism during accretion onto Laurentia as part of the Yukon-Tanana Terrane. Gold deposition is thought to be mid-late Jurassic, mainly occurring within discordant quartz veins with common pyrite mineralization but overall low sulfidation (galena, sphalerite, chalcopyrite, etc. only trace). This study adds to the overall understanding of the Lone Star deposit by establishing relations between pyrite paragenesis and gold mineralization. This is done through detailed examination of a suite of samples, selected based on differences in pyrite occurrence. Observations by reflected light and SEM have delineated at least 3 major pyrite types from a textural perspective: syn-tectonic, post-tectonic and vein. Samples have been analyzed by LA-ICPMS using individual spot analyses on pyrite core and rim, and trace element mapping on a subset of samples. Of the trace element suite measured, we found consistently detectable levels of Co, Ni, Cu, As, Sb, Pb, Te and Bi. Spot analyses have revealed both discrete core-rim trace element concentrations and grains that are relatively homogeneous, providing evidence for pyrite growth events involving different trace element sources. Trace element maps reveal these relations in more detail with grains displaying internal chemical structure. Some elements (Co, Ni, As, in some cases Se) are present as a dissolved component, but others (Cu, Sb, Pb, Te, and Bi) are typically found as inclusions along with Au and Ag in small amounts. Cores tend to be enriched in Co, Ni, or As, with rims depleted relatively. Gold concentrations are below detection in pyrite grains and is present as sparse inclusions of an Au or Au-Te phase. The occurrence of Au as a discrete phase, and not a dissolved component, suggest that a disconnect exists between the processes that precipitated gold and those that formed pyrite in the Lone Star system. iv Keywords: orogenic gold, pyrite, trace elements, LA-ICPMS mapping
Open Access
Machine Learning Focal Mechanism Inversion for Hydraulic Fracturing Induced Earthquakes
(2023-04) MacDonald, Megan
Hydraulic fracturing has been found to be a major contributor to the increase in induced seismicity worldwide, with pore pressure, poroelasticity, and coulomb stress transfer identified as the three main triggering mechanisms. However, there is still much to be learned about how these mechanisms operate in hydraulic fracturing-induced earthquakes. The accurate discrimination of these mechanisms requires a complete and precise earthquake catalog, particularly with regards to focal mechanisms, which provide insight into the changes in stress in the area surrounding the hypocenter. Determining the polarities of first motions by hand is a traditional method for identifying earthquake focal mechanisms, but it is not suitable for microearthquakes due to their low signal-noise ratio and the large volume of data involved. Machine learning, on the other hand, provides a reliable and efficient way to classify polarities. Thus, in this study we apply a machine learning-based first motion classifier to automatically invert focal mechanisms for induced earthquakes in the Tony Creek Dual Microseismic Experiment (ToC2ME). We then discuss the accuracy and efficiency of the application of machinelearning- based first motion classifier – DiTingMotion for hydraulic fracturing-induced earthquakes and investigate the associated mechanisms for earthquake triggering during the hydraulic fracturing. We have demonstrated that DiTingMotion is capable of classifying the polarities of earthquake first motions and characterizing focal mechanisms for induced earthquakes. By analyzing three major earthquake sequences during the ToC2ME experiment, our results illustrate that pore pressure, poroelasticity, and coulomb stress transfer can coexist during the hydraulic fracturing, although each may dominate during different stages. We suggest that a comprehensive understanding of geological settings, hydraulic fracturing operations, and the distribution of pre-existing faults/fractures is critical to comprehending the triggering of induced earthquakes. These factors play important roles in seismic activity and comprehending them is essential to mitigate the seismic hazard associated with hydraulic fracturing and optimize shale gas production. Keywords: Hydraulic Fracturing, Induced Seismicity, Machine Learning, Focal Mechanisms, Earthquake Triggering Mechanisms, Microearthquakes
Open Access
Petrology and Geochemistry of Ignimbrites from the Bears Brook Volcanic Group, Arisaig, Antigonish County, Nova Scotia.
(1978-03-15) Eames, Alexandra J.
A chemical study of the ignimbrites of Arisaig, Nova Scotia, was undertaken to determine their geochemical character, any variations within flow units, and their relationship to associated volcanics. The ignimbrites are rhyolitic in composition and there seems to be no primary chemical variation within individual flow units. The area has been subjected to low-grade regional metamorphism, probably to greenschist facies, which accounts for most of the variation within each ignimbrite. The rock type previously called "andesite" is found to be more appropriately classified as a spilite. Some possible indicators of the nature of the rock suite are investigated, including trace- and rare-earth element distributions, and possible interpretations of the origin of this bimodal occurrence are discussed. The chemical evidence favours a model involving fractional crystallization. Keywords: Pages: 92 Supervisor: D. B. Clarke
Open Access
Structural Analysis of the George River Group at North Mountain, Cape Breton, Nova Scotia
(1978-03-15) McFall, Gail H.
Several different explanations of the structure of the George River rocks at North Mountain have been suggested in the past, none of which has proved to be very satisfactory. Milligan has proposed that the structure is that of diverging, fan-like folds plunging westerly at about 40 degrees. This hypothesis was tested by plotting the detailed information on fold axis plunges, gathered by Keating, on stereonets and comparing the predicted and observed plunges. The results proved to be quite different from what was expected. Further analysis of the distribution of rock types, combined with the stereogram results, suggested that more than one period of folding had occurred and that the structure is that of a primary set of folds plunging very steeply to the southeast on which a secondary set of folds, plunging to the west-southwest at about 30 to 40 degrees, have been superimposed. Keywords: Pages: 38 Supervisor: G. C. Milligan
Open Access
Regional Geochemical Variations of Upper Cenozoic Volcanic Rocks in the Andes
(1978-03-15) Palma, Vincent V.
Regional variations in the chemical composition of Miocene-to-Recent volcanic rocks from the Central Andes are investigated on the basis of 260 chemical analyses compiled from the literature in addition to 25 new analyses for 5 trace elements. Correlations are established between major and trace element compositions and other variables such as distance from the eruptive centres from the Peru-Chile trench or crustal thickness, using the computer and multigraphic techniques. Among the most striking correlations are the confirmation of the previously established continent-ward increase of K2O for all rock types, a surprising negative correlation of Na2O with distance from the trench in one large segment of the Cordillera and the positive correlation of Li, U and Rb with crustal thickness. Comparisons are also made between Andean rocks and those of island arcs and other tectonic regimes. Keywords: Pages: Supervisor: Marcos Zentilli
Open Access
An Application of Pleistocene Geology to Mineral Exploration in Southwestern Nova Scotia
(1978-03-15) Sinclair, Paul
An esker complex near Yarmouth, Nova Scotia has been investigated to determine the mode of origin of the eskers and to evaluate their usage in mineral exploration. Field work involved describing sections through eskers, boulder counts, collecting esker materials, and geochemical sampling. Lab work involved grain size analysis, heavy mineral identification and geochemical analysis. Stratigraphic units of glaciofluvial material within the eskers range from well sorted sandy units to poorly sorted units containing clay to boulder size material. The eskers appear to have formed in subglacial tunnels and are composed of a series of nodes or beads of massive material connected by a topographically lower ridge of relatively well sorted material. Most esker material is derived from local bedrock and the presence of mineralized clasts in eskers may be used to define regions of interest for mineral exploration. Geochemical sampling for elements of As, Zn, Cu and Pb in the hydromorphic dispersal zone of eskers appears to indicate the abundance of mineralized clasts presents. This type of geochemical sampling may be useful in areas where exposure to esker material is masked by a cover of vegetation. Keywords: Pages: 119 Supervisor: Marcos Zentilli
Open Access
Gravity and Magnetic Investigations of the Deep Cove Intrusive, Cape Breton County, Nova Scotia
(1978-03-15) Toews, Richard
Gravity and magnetic surveys were conducted on the Deep Cove quartz monzonite intrusive to ascertain its subsurface configuration and, in particular, the attitude of its west contact with the surrounding Fourchu volcanic rocks. Laboratory measurements of both intrusive and volcanic rock samples from Deep Cove indicate a density contrast of 0.10-0.15 g cm-3 and a magnetic susceptibility contrast of 1.5 x 10-3 measured in cgs units. The Koenigsberger Q-ratios of the samples are, in general, considerably less than unity. The expected anomalies caused by these contrasting properties are observed in the survey data. Using a two-dimensional modelling computer program, models were developed which result in calculated gravity and magnetic anomalies that approximate the observed data. Gravity models suggest that the west contact of the intrusive is almost vertical, perhaps dipping steeply to the west. The calculated anomalies of magnetic models are less sensitive to the attitude of contacts. Magnetic models require: (1) a great susceptibility contrast than that measured in the laboratory and (2) a depth to the top of the "magnetic body" of approximately 30 metres. These requirements possibly indicate weathering of ferrimagnetic minerals in the uppermost volcanic rocks. Keywords: Pages: 69 Supervisor: John Pierce