Department of Geological Sciences and Geological Engineering Graduate Theses
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Item Potential Human Exposures to Hg in Staple Crops from Agricultural Areas Impacted by Artisanal Small-Scale Gold Mining Activities(2025-01-28) Eboigbe, Excellent Oluwakemi; Geological Sciences and Geological Engineering; McLagan, DavidArtisanal small-scale gold mining (ASGM) is a rapidly expanding sector that manifests complex political, social, and environmental issues. Chief among these problems are the emissions (air) and releases (terrestrial/aquatic) of mercury (Hg) that is employed as the primary method of recovering gold from mined ores and sediments (Hg-gold amalgam burning). Recent work with stable Hg isotopes has demonstrated stomatal uptake of elemental Hg (Hg(0)) by higher plants to dominate Hg deposition in vegetated systems. ASGM activities are indiscriminate in where they occur and often impact highly productive forests, wetlands, and agricultural areas. Considering the importance of the latter for sustaining human populations and the extensive atmospheric emissions of Hg from ASGM activities, the stomatal uptake pathway of Hg by staple crops in agricultural areas impacted by ASGM is worthy of scientific investigation. In this study, we examine potential human exposure pathways in ASGM impacted agricultural areas in Nigeria using a total systems approach. The study works collaboratively with a local mining community in Nigeria to facilitate knowledge dissemination with impacted individuals and to ensure a more holistic study design. Samples of tubers/grains, foliage, roots, and stems of maize, cassava, and peanuts were collected from two farms along a transect away from an active ASGM site (Farm 1 closest; Farm 2 furthest). Air (passive samplers) and soils were sampled at the ASGM site and both farms. Results reveal contamination of farms and crops in the farm closest to the ASGM area, with the control farm at background levels, confirming Hg exposure gradient away from the mine. Stable isotope data also reveal the atmosphere as the dominant source for the uptake of Hg in staple crops for all species, with minimal translocations to other parts of the crops. In assessing potential human health impacts from consuming these crops, MeHg levels in crop tissues measured were consistently less than 1% of THg, suggesting minimal risk from MeHg exposure. However, elevated levels of inorganic Hg highlight a significant potential for harm.Item Reconciling Quantitative Mineralogy and Drainage Dynamics in Weathering Mine Waste Rock(2025-01-24) Saberi, Nima; Geological Sciences and Geological Engineering; Vriens, BasMineral resource extraction generates vast amounts of mine waste, which can release poor-quality drainage upon weathering, including acid rock drainage (ARD). Effective storage and wastewater treatment strategies are essential to mitigate the environmental impact of these materials. However, forecasting the long-term mineral reactivity and drainage behavior in large-scale mine waste storage systems remains a significant challenge for the mining industry. A proactive, predictive approach to mine waste management, rather than reactive stabilization or remediation, is needed. This PhD thesis investigates mineral weathering processes in mine waste rock under diverse geochemical conditions to support this shift to predictive approaches. The first study examines sample preparation biases in quantitative mineralogical analyses of granular mine wastes. It demonstrates that particle size segregation during epoxy molding introduces significant error, which can be mitigated by cutting molds perpendicular to the settling direction. Variability due to unresolved heterogeneity is shown to be minor when particle counts exceed 25,000 at sizes >150 μm. The second study quantifies the relationship between mineralogical parameters (size, association, and liberation) and leachate chemistry at different water saturation levels (100-5%). Leachate pH decreased from 6.14 at full saturation to 5.37 at 5% saturation, accompanied by a reduction in average carbonate grain size from 200 to 145 μm. Iron (Fe) and copper (Cu) concentrations in solution increased significantly at lower saturation, with Cu levels rising 24-fold at 5% saturation compared to full saturation. Conversely, arsenic (As) concentrations increased with higher moisture content due to changes in pyrite oxidation behavior. The third study investigates trace metal scavenging by secondary minerals in mine waste, focusing on Fe(oxy)hydroxides and Ca-sulfates. High-resolution LA-ICP-MS element mapping reveals strong enrichment of trace elements such as Cr and Cd at grain rims, whereas other elements reveal a more uniform distribution, indicating isomorphic substitution within Fe-oxides. Factor analysis highlights distinct element associations, suggesting different sequestration mechanisms based on primary mineral sourcing or compatibility with the secondary mineral structure. By combining kinetic testing, geochemical leachate analysis and quantitative mineralogical assessments, as well as statistical evaluations, this thesis provides insights into mineral reactivity and heterogeneity of mine waste materials across various storage conditions.Item CHEMICAL CONTROLS ON THE DISTRIBUTION OF CRITICAL METALS IN THE HACKETT RIVER ZN-PB-CU-AG MAIN ZONE VOLCANOGENIC MASSIVE SULFIDE DEPOSIT, NUNAVUT(2025-01-03) Keane, Siobhan Tara; Geological Sciences and Geological Engineering; Layton-Matthews, Daniel; Peter, JanThe 2.68 Ga Zn-Pb-Cu-Ag Hackett River Main Zone volcanogenic massive sulfide (VMS) deposit is in the Hackett River Greenstone Belt (Nunavut), part of the Slave Craton. VMS deposits are polymetallic and host a variety of critical metals. Samples from a drill hole that stratigraphically transects the mineralization were studied. Within this hole, copper is enriched in the footwall, and this decreases in abundance higher in the mineralized lens; this is followed upward by enrichment in Zn, and finally Pb enrichment towards the top of the mineralized lens. “Ore” minerals present are: chalcopyrite, galena, pyrite, pyrrhotite, sphalerite, and tetrahedrite. Samples were analyzed for bulk geochemistry, and mineralogy and mineral chemistry by SEM-MLA and LA-ICP-MS. The residence, zonation, and deportment of fifteen critical metals (Mn, Mn, Cd, Co, Ni, As, Sb, Ag, Bi, Se, Sn, In, Ga, Ge, Mo, Tl) were determined. Towards the stratigraphic top of the mineralized lens Ag (and Sn) is resident in tetrahedrite and galena. Galena is the dominant host for these elements where tetrahedrite is not present (i.e., not precipitated), suggesting that both elements are controlled by temperature of the mineralizing fluid. Cadmium, Mn, and Ga reside in sphalerite. Manganese2+ and Cd2+ substitute for Zn2+ in the sphalerite crystal structure. Similarly, Ga2+ substitutes for Zn2+ and there is element competition between Ga and Zn for space in the sphalerite crystal lattice. Bismuth and Tl occur as substitutions for Pb due to “incremental” crystallization from a circulating hydrothermal fluid, wherein the “reservoir” of these elements is quickly depleted once galena starts to precipitate. The highest Co concentrations in pyrite are toward the middle of the mineralized lens and the highest Ni concentrations occur toward the top of the mineralized lens. Both Co2+ and Ni2+ substitute for Fe2+ in the pyrite crystal structure. The difference in their enrichment through the mineralized lens indicates that the elements are in competition with each other for residence in pyrite. Arsenic and Se are enriched in pyrrhotite and chalcopyrite at the base of the lens. Higher in the mineralized lens As is enriched in pyrite and tetrahedrite, and Se is enriched in galena.Item Petrogenesis of mantle-hosted granitoids from the Samail ophiolite(2024-11-21) Angelo, Tiago Valim; Geological Sciences and Geological Engineering; Spencer, ChristopherThe Samail ophiolite in Oman and the United Arab Emirates comprises Cretaceous oceanic lithosphere, from mantle peridotite below the petrologic Moho to crustal gabbro, sheeted dykes, and basalt pillows, with intercalated sediments. Obducted onto the passive margin of the Arabian plate, the Samail ophiolite is interpreted as a supra-subduction zone (SSZ) ophiolite. This study focuses on minor but important components of the Samail ophiolite: granitoids that intrude both its crustal and mantle sections, referred as crust- (CHG) and mantle-hosted granitoids (MHG), respectively. Through major and trace element compositions, stable and radiogenic isotopes, and fluid inclusion studies, this work explores their petrogenesis and implications in SSZ environments. Geochemical and isotopic evidence reveals distinct formation processes for CHG and MHG. CHG are metaluminous tonalites and trondhjemites, low-K, with flat to light rare earth element-depleted patterns. Positive εNd and low δ18O values suggest a mid-ocean ridge basalts-like affinity. They are interpreted to reflect fractionation of basalt/gabbro or anatexis of oceanic crust. In contrast, MHG range from granite to tonalite and are mostly peraluminous, similar to peraluminous sediment-derived granitoids. However, they show scattered K2O, Na2O, CaO, Rb/Sr, higher SiO2, and lower Al2O3+FeO+MgO+TiO2 wt.% compared to typical sediment-derived granitoids. MHG likely formed from the interaction of sediment (pelitic to siliceous) derived melts with basaltic melts from an underthrust oceanic plate within the mantle wedge, without involvement of the overriding oceanic crust. This mixing is supported by low whole-rock εNd values and Sr and Pb isotopic signatures. However, variable δ18O (3-28‰) and εHf values, along with elevated δ7Li in muscovite from MHG, suggest the involvement of deep-sea ferromanganese sediments as an alternative source. Fluid inclusion studies on the MHG provide further insight into fluid evolution and migration within ophiolite systems. Low δ13Ctot (-27‰) values from quartz-hosted fluid inclusions are hydrocarbon-bearing, probably derived from carbonate-bearing rocks below the base of the ophiolite during obduction. The granitoids studied here offer insights into petrogenetic processes in SSZ where CHG represent products of processes operating within the ophiolite, while MHG reflect inputs derived externally to the ophiolite. The MHG record crustal material transport into the mantle, contributing to mantle heterogeneity over time.Item Chemistry of the pearl oyster Pinctada radiata and implications for palaeoceanography(2024-11-07) Yousif, Ruqaiya; Geological Sciences and Geological Engineering; Pufahl , Peir; James, NoelOyster shell chemistry offers major potential for palaeoceanographic studies and temperature reconstructions, particularly bimineralic oysters such as Pinctada radiata. This thesis explores the efficacy of using P. radiata shells from the shallow subtidal environment of the Qatari coast, Persian/Arabian Gulf, as recorders of oceanographic conditions. Collected from the Qatar coast, the chemistry of growth lines from calcitic and aragonitic layers within the shells was analysed and compared with known ocean buoy data (including temperature, salinity, and pH). The oxygen isotopic composition (δ18O) of calcite and aragonite ranges from -1.2 to 2.2‰ and -1.1 to 1.3‰, respectively, with seasonal δ18O temperatures derived from calcite mirroring recorded seawater temperatures. However, δ18O values in aragonite show no temperature correlation to seawater values, suggesting vital effects influence its composition. Carbon isotopic compositions (δ13C) for both minerals also indicate vital effects, with no direct correlation to buoy data. Trace element concentrations and ratios in both minerals correlate with salinity and pH, allowing for the reconstruction of Holocene and Pleistocene seawater conditions using fossilized P. radiata. Additionally, the application of carbonate clumped isotope (Δ47) thermometry to the bimineralic shells reveals discrepancies in temperature estimates. TΔ47 values from calcite layers accurately track seasonal temperature variations, while aragonite layers show consistently higher temperatures due to kinetic fractionation and vital effects. Elevated Ca and Mg concentrations further contribute to temperature overestimation. This thesis also examines the role of environmental stressors on living P. radiata, including temperature fluctuations and tidal exposure. These stressors affect the inner extrapallial fluid (iEPF), pH, and magnesium ion concentrations, facilitating dissolution and Mg-rich carbonate precipitation within the aragonite matrix. This research highlights that diagenesis is an active process throughout the organism's life and can be induced by the mantle itself. It offers new insights into biogenic carbonate preservation and diagenesis prior to its export to the geological record. Collectively, results highlight the potential of P. radiata shells as valuable proxies for understanding past environmental conditions and the complexities of carbonate chemistry in marine settings.