ItemIncomplete Sulfide Oxidation in Oxygen-Depleted Mine Waste Systems and Consequences for Aqueous Sulfur SpeciationGeological Sciences and Geological Engineering; Vriens, BasThe oxidative dissolution of sulfide minerals in mine wastes can lead to oxygen depletion and redox gradients, impacting the mobility of redox-sensitive solutes, especially in heterogeneous tailings systems. However, the controls of these gradients on sulfide reactivity and sulfur (S) mobilization are not well-understood, posing challenges to long-term drainage quality assessments. This research explored the weathering of pyrite, Fe-rich sphalerite, and S-bearing mineralogy in controlled conditions (6 ItemDiagenesis of Groundwater Calcrete and Paleochannel Sediments: Implications for the Genesis of Channel and Playa Uranium Deposits and the Dolomite ProblemDrummond, Justin Barclay Rogers; Geological Sciences & Geological Engineering; Pufahl, Peir; James, Noel; Layton-Matthews, DanielChannel and playa uranium deposits are a sub-type of surficial uranium deposits that form in Tertiary to Recent groundwater calcrete and associated dolomitic, clay-rich, paleochannel and playa sediments. The primary ore mineral in most deposits is the potassium-uranyl-vanadate, carnotite (K2(UO2)2(VO4)2.1-3H2O). Despite the economic potential of channel and playa deposits, there is a dearth of contemporary research focused on understanding their genesis. As a result, there remains significant uncertainty about how these deposits form. Research herein integrates petrography, mineralogy, hydrogeochemistry, stable isotope geochemistry, and lithogeochemistry to develop a paragenetic framework that illuminates key processes mediating carnotite precipitation at Lake Way and Lake Maitland, Western Australia. Significant findings include: 1) a key mineral assemblage of authigenic Mg-clays and sedimentary dolomite with carnotite in both groundwater calcrete and associated clastic sediments that post-dates calcrete formation; 2) authigenic Mg-clays are an essential nucleation substrate for both sedimentary dolomite and carnotite; 3) comparison with other channel and playa uranium deposits in Western Australia and Africa reveals that this Mg-clay-carbonate association is common in channel and playa uranium deposits across the globe. Carnotite precipitation is interpreted to be fostered by evaporation-driven sedimentary dolomite precipitation, which establishes a positive feedback loop that dissociates uranyl-carbonate complexes increasing carnotite saturation in pore water. Potassium ions adsorbed to authigenic Mg-clay surfaces probably assist with promoting carnotite nucleation. The kinetics of such Mg-clay mediated nucleation also provide new insight into the dolomite problem. This longstanding quandary focuses on the disconnect between the abundance of dolostone in the rock record and the inability to precipitate low temperature dolomite under laboratory conditions. The recognition of synsedimentary dolomite in channel and playa uranium deposits is important because it preserves a primary isotopic composition of shallow groundwater aquifers. Integrating these findings with previously published data into a mineral systems framework identifies seven factors that are required to form economic carnotite deposits: 1) sources of uranium and vanadium; 2) low hydraulic gradient; 3) high precipitation deficit; 4) shallow, unconfined, high permeability aquifers; 5) focusing of U-bearing groundwater into the zone of evaporation; 6) evaporation to drive the physico-chemical processes mediating carnotite precipitation; and 7) time. ItemGrenville Marble-Hosted Zinc Mineralization at the Salerno Lake Deposit, Canada: Stratigraphic, Mineralogical, and Lithogeochemical ConstraintsTurkalp, Erkan; Geological Sciences and Geological Engineering; Olivo, Gema R.Previous studies in the zinc mineralization hosted in the high-grade metamorphosed marbles of the Grenville Supergroup suggest that the zinc mineralization formed syngenetically with the sedimentation of the carbonate sequence (SEDEX-type). However, observation of drill cores, mineralogical composition of rock types, texture of mineralized samples, paragenesis, and lithogeochemistry data reveal that magmatic- hydrothermal fluids may have contributed to the formation and/or transformation of the zinc mineralization. The main ore mineral, yellow and red sphalerite occurring as disseminated, banded, and semi-massive, is hosted mainly in the dolomitic marble units containing up to 25 % silicate minerals (dominantly phlogopite, tremolite +/- diopside), which are intercalated with siliciclastic, calcitic marble, diopside-tremolite dolomitic marble, pyritic dolomitic marble, and quartz-diopside rich marble. The sedimentary sequence is cut by syenite and calciocarbonatite intrusions exhibiting contact metasomatic zones with endoskarn and exoskarn alteration. Most of the intrusive rocks were found in close proximity (1-10 m) to the zones with higher grade zinc, and sphalerite was found included in calcite in a sample of calciocarbonatite. Significantly, enrichment of Ag, As, Co, K2O, Rb, and REE in both intrusions and mineralized zones proximal to the intrusions compared to the distal dolomite marbles may suggest magmatic fluid-rock interaction. Furthermore, zinc enrichment in the siliciclastic rock, which does not typically contain high concentrations of zinc, was found in proximity to the calciocarbonatite intrusion. Nevertheless, we cannot exclude the possibility that zinc mineralization has occurred during sedimentation and was transformed or enriched during a subsequent magmatic event. In this case, the permeable zones that acted as conduits for the early mineralizing fluids could have been exploited by the magma. This could explain the early occurrence of pyrite and yellow sphalerite during an early event (exhalative?) and red sphalerite in higher- grade zinc zones found in close proximity to intrusions. However, further research is required to verify this hypothesis. ItemComparison of Informed and Un-Informed Shear Strength Reduction Procedures for Finite Element Method Slope Stability AnalysisKelly, Liam; Geological Sciences and Geological Engineering; Hutchinson, D. Jean; Diederichs, MarkGeotechnical engineers commonly rely on numerical models such as the Finite Element Method (FEM) to analyze natural, civil, and mining slope stability problems. One of the goals of these analyses is typically to determine a Factor of Safety (FoS) like that obtained using Limit Equilibrium Methods (LEM). To compute the FoS, Shear Strength Reduction (SSR) techniques are commonly employed. The SSR procedure involves the systematic computation of elastic-plastic FEM slope models with differing strength parameters to solve for the FoS within a specified tolerance. This is generally achieved using a monotonically increasing or a bracketing and bisecting technique. These procedures are standard in most geotechnical FEM software packages. The advances in personal computing technology have aided the adoption of the SSR technique into engineering practice. The technique provides significant advantages over LEM techniques primarily pertaining to the lack of assumption about failure surface and forces, and the ability to compute deformation. One of the major drawbacks of the FEM compared to LEM is the time required to complete the analysis. A single FEM SSR analysis can take hours to days to complete if using a very fine mesh. There has been limited academic literature on the topic of improving SSR procedure runtime, structurally. This thesis presents a framework for a technique called “informed” SSR. Informed SSR procedures utilize previously computed SSR stages to provide information to subsequent SSR stages to develop a better initial guess for the FEM solution. These informed procedures are compared to “un-informed” procedures included in Rocscience’s RS2 which solve each SSR stage independently of all other SSR stages. This thesis also assesses optimization of informed SSR procedures for modified Strength Reduction Factor (SRF) step sizes and constant strength parameter reduction techniques. The cases analyzed in this thesis show that informed SSR results in drastically decreased run times when compared to analogous un-informed procedures. This is achieved whilst not drastically changing the values, such as FoS and nodal displacement, output by the un-informed procedures. ItemThermal History of the Frontenac Arch in Southeastern Ontario, Canada Constrained From Low-temperature ThermochronologyGarcia Ramos, Daniela; Geological Sciences and Geological Engineering; Godin, Laurent; Coutand, IsabelleThe Frontenac Arch is an intraplate low-relief ridge of Precambrian rocks that connects the southeastern Ontario part of the Canadian shield with the Adirondack Massif in New York State. The NW-SE trending ridge is oriented perpendicular to the major tectonic fabric of the Grenville, Appalachian, and St Lawrence rift systems. This thesis research aims to understand the building mechanism(s) and timing of this basement topography. New apatite and zircon (U-Th)/He and apatite fission track data from 19 samples collected along three transects in the Frontenac Arch provide cooling ages ranging from 183.7 - 19.5 Ma (AHe), 196.2 - 109.6 Ma (AFT), and 732.5- 144.1 Ma (ZHe). The T-t paths for the Frontenac Arch define a thermal history dominated by one stage of progressive cooling since the post-Shawinigan phase of the Grenville Orogeny (~1140 Ma) to surface temperatures by ~525 Ma after the culmination of the breakup of Rodinia. This is followed by sediment burial (~ 3-4 km) and reheating to ~160 °C with heating peaks at different times during the Paleozoic resulting in partial resetting of the ZHe dates, and a third cooling stage (0.3-0.5 °C/Ma ) starting during the breakup of Pangea and opening of the Atlantic Ocean in the Early Mezosoic. The last pulse of cooling in the thermal models between 175-225 Ma coincides with Mesozoic normal fault reactivation documented through AFT age discontinuities in the St. Lawrence and Saguenay fault system at ca. 200 -250 Ma caused by NW-SE extension and breakup of Pangea. A younger faulting event resulting in differential exhumation is likely recorded in the Frontenac Arch along the NE-trending Rideau-Lake normal Fault between 150-190 Ma. A period of differential unroofing started at least since the Late Cretaceous and eroded most of the Early Paleozoic sediments left in the last 120 Ma, as recorded by Devonian clasts in Cretaceous diatremes and kimberlites in Montreal and Lake Timiskaming, respectively.