Gregory Dipple

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Doctoral Student Supervision

Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.

Mechanisms of carbon mineralization from the pore to field scale: Implications for CO2 sequestration (2015)

Innovative technologies to stabilize atmospheric CO₂ concentrations are essential in order to mitigate the harmful effects of anthropogenic greenhouse gas (GHG) emissions on the global climate system. Mineralization of carbon in solid, stable carbonate minerals through reaction of CO₂ with Mg-rich mining wastes is a promising CO₂ sequestration strategy that offers the potential to render certain mines GHG neutral. Here, the physical and chemical controls on rates of and capacity for CO₂ sequestration in systems representative of mine tailings are examined from the mineral-fluid interface to field scale using a combination of experimental techniques. These experimental data and existing field data are used to develop a comprehensive reactive transport model that captures the processes governing carbon mineralization in the shallow subsurface. Stirred batch reactor, microfluidic pore scale, and decimeter to meter scale column carbonation experiments using brucite [Mg(OH)2] revealed that the primary controls on carbonation include the rate of CO₂ supply, the distribution of the reactive phase, the mineral grain size/surface area, and the availability and distribution of water. The rate-limiting step during carbonation varied from CO₂ supply to mineral dissolution depending on the experimental variables. Surface passivation and water-limited reaction resulted in a highly non-geometric evolution of reactive surface area. The extent of reaction was also limited at high water content because viscous fingering of the gas streams supplied to the columns resulted in narrow zones of highly carbonated material, but left a large proportion of brucite unreacted. More robust predictions of the CO₂ sequestration rate and capacity that can be expected at the field scale are possible due to the incorporation of water consumption, water-limited reactivity, and surface passivation functions into the reactive transport code, MIN3P. This research imparts a better understanding of fundamental mechanisms and chemical processes relevant to CO₂ sequestration in mine tailings, with implications for mineral carbonation in other settings that have greater CO₂ sequestration capacity, such as shallow subsurface formations with similar mineralogy. Aspects of this research, such as water-limited reactivity, have broader implications for reactive transport processes in the vadose zone in general, including mineral weathering and groundwater remediation.

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A comparative study of the origin of carbonate-hosted gem corundum deposits in Canada (2013)

This detailed scientific study of the carbonate-hosted gem corundum occurrences near Revelstoke, British Columbia and Kimmirut, Nunavut, Canada was completed in order to: (1) characterize the gem corundum mineralization; (2) develop genetic models for gem corundum mineralization; and (3) develop exploration strategies for gem corundum in carbonate-hosted deposits. These unique localities were chosen to help develop exploration strategies for gem corundum deposits in Canada since existing models of gem corundum genesis are unable to explain their origin.The Revelstoke occurrence is located in the Monashee Complex of the Omineca belt of the Canadian Cordillera. Pink (locally red or purple) corundum crystals occur in thin, folded and stretched layers containing the assemblage of green muscovite + Ba-bearing K-feldspar + anorthite ± phlogopite ± Na-poor scapolite. Mineral assemblages and textures in these silicate layers and thermodynamic modeling suggest that corundum formed from muscovite dehydration at the peak of metamorphism (~650-700 °C at 8.5-9 kbar). Observed trends in whole rock geochemical data indicate that the corundum-bearing silicate (mica-feldspar) layers formed by mechanical mixing of carbonate with the host gneiss protolith; the bulk composition of the silicate layers was modified by Si and Fe depletion during prograde metamorphism. High element mobility is supported by homogenization of δ¹⁸O and δ¹³C values in carbonates and silicates for the marble and silicate layers. The Kimmirut Sapphire Occurrence is located in the Lake Harbour Marble of the Baffin Island segment of the Trans Hudson Orogen. Blue and colourless zoned gem corundum crystals occur in coarse-grained calc-silicate pods with albite + calcite + muscovite ± K-feldspar. Corundum-bearing zones are separated from a phlogopite + plagioclase symplectite around violet diopside crystals by scapolite which fluoresces in UV light. Corundum likely formed during retrograde metamorphism at P-T
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The mineralogical, geochemical and isotope characteristics of alteration, mineralization and metamorphism of the Red Lake gold mines, Ontario (2012)

Archean lode-gold deposits are a significant source of gold. However, exploration of this deposit type is hindered by their poorly understood genetic models and geochemical features. This project investigated the geochemical expression surrounding the Archean lode-gold Red Lake Gold Mines (RLGM) in the Superior Province, Canada. Mineral chemistry, whole rock and isotope geochemistry were used to establish how hydrothermal and metamorphic events influenced ore genesis. The RLGM is a basalt-hosted lode-gold deposit that formed from multiple superposed hydrothermal and metamorphic events. This study defined three significant superposed events which were important for gold mineralization. The first event was a widespread hybridized seafloor-magmatic event which caused reduction with FeO, MnO, K2O, SO3, SiO2, Rb, As and Cu enrichment. Seawater interaction created abundant micas-clays-chlorite-carbonate-FeMn oxides. Localized acidic magmatic fluids, in syn-volcanic faults, caused advanced argillic alteration. Subsequent peak-regional metamorphism created a widespread (>7km) occurrence of metamorphosed altered basalts. The micas-clays-chlorite-carbonate-FeMn oxides were metamorphosed to form Fe-biotite-Ti-magnetite±carbonate and Fe-chlorite-Fe-amphibole-FeMn-garnet-epidote/clinozoisite-magnetite-calcite-biotite assemblages. The metamorphosed argillic alteration created a quartz-muscovite-andalusite assemblage. Overprinting the widespread metamorphosed altered basalt was the significantly narrower (
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The geology and genesis of the Central Zone deposit, Galore Creek alkalic Cu-Au porphyry district, northwestern British Columbia, Canada (2011)

Located in the Late Triassic Galore Creek alkalic Cu-Au porphyry district in northwestern British Columbia, the Central Zone deposit represents the end-member of the silica-undersaturated class of alkalic porphyry systems. The deposit is hosted by volcano-sedimentary rocks of the Middle to Upper Triassic Stuhini Group that were intruded by a syenite-monzonite complex and hydrothermal breccias. Post-mineral tilt (45 to 60° W-SW) provides an opportunity to examine a vertically extensive depth range of the system, and the impact of host rocks and a redox control on the precipitation of sulfide and silicate alteration minerals.Early mineralization associated with potassic alteration is dominated by gold-bearing chalcopyrite + bornite (Cu:Au ~ 2:1). A second gold-poor mineralization event is associated with calc-potassic alteration and dramatically changes the Cu:Au ratio (5:1) in the core of the Central Zone. In general, greatest Cu-Au concentrations overlap lithological contacts characterized by contrasting ferromagnesian mineral content, thus forming redox gradients. Sulfur isotopic compositions emphasize the importance of fO₂ conditions in ore deposition. Sulfides in highly mineralized centers are characterized by moderately negative δ₃₄Ssulfide values (-10.66‰ to -7.84‰), whereas sulfides deposited distally show highly negative δ₃₄Ssulfide values (-17.13‰ to -4.03‰). These data suggest that the interaction of sulfate-rich (SO₄²-(aq)) fluids with varying amounts of Fe²⁺-bearing minerals in host rocks increased H₂S/SO₄²- leading to formation of reduced S, and precipitation of sulfide minerals.Trace elements such as V and As in host rocks and Eu²⁺ in hydrothermal garnet reflect the same redox influence. Vanadium and As are soluble under highly oxidizing conditions. The shift in oxidation state facilitates their incorporation in alteration minerals. Thus, highest V (>700ppm) and As (>40ppm) concentrations form halos distally to the redox gradients and ore bodies. Hydrothermal garnets near lithologic contacts contain excess Eu²⁺. In contrast to V and As, Eu²⁺ is soluble in reduced fO₂ conditions and precipitates close to the redox gradient.This study demonstrates that redox is the dominant control on ore deposition in the Central Zone. Recognizing redox changes may provide a valuable guide for future exploration in the Galore Creek district and perhaps other alkalic Cu-Au porphyry systems worldwide.

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Mineral Traps for Greenhouse Gases in Mine Failings: A Protocol for Verifying and Quantifying CO2 Sequestration in Ultramafic Mines (2010)

Mineralization of CO₂ in ultramafic mine tailings can occur on a scale that is significant relative to the greenhouse gas emissions of a mine. Consequently, some active mining operations may be able to take advantage of carbon mineralization within their tailings to offset part of their greenhouse gas emissions. The secondary Mg-carbonate minerals that form in mine tailings are safe and durable traps for carbon and their presence can represent substantial disposal of atmospheric CO₂. Hydrated Mg-carbonate minerals precipitate within mine tailings from the Diavik Diamond Mine, Northwest Territories, Canada, and the Mount Keith Nickel Mine, Western Australia, Australia. An improved understanding of the carbon cycle in mine tailings, and the contribution of mineralogical and geochemical strategies for assessing carbon mineralization in ultramafic mine tailings, are achieved by studying these sites.Quantitative mineralogical procedures, which use X-ray powder diffraction data, are developed for quantifying low abundances of mineral traps for CO₂ within mine tailings. Quantitative mineralogical results are used to assess the amount of CO₂ stored within hydrated Mg-carbonate minerals at both mine sites, and to assist in determining which gangue minerals are the primary sources for Mg in these minerals.Radiocarbon and stable isotopes of carbon and oxygen are used to identify the sources for carbon in secondary Mg-carbonate minerals. Isotopic analogue experiments are used to study the fractionation of stable carbon isotopes during precipitation of dypingite, a hydrated Mg-carbonate mineral, under conditions that simulate those in the tailings storage facilities at Mount Keith. The results of these experiments suggest that hydrated Mg-carbonate minerals may be precipitating out of isotopic equilibrium with the atmosphere. A carbon isotopic fractionation factor obtained for dypingite, and computational models for isotopic mixing scenarios, are used to interpret stable isotope and radiocarbon data for carbonate minerals. Although models for mixing scenarios can provide convincing fits to stable isotopic data, they are commonly inconsistent with field observations, trends in quantitative mineralogical data, and radiocarbon results. Ultimately, radiocarbon data are used to determine that most of the carbon trapped and stored within hydrated Mg-carbonate minerals at Diavik and Mount Keith is sourced from the modern atmosphere.

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Patterns of Distal Alteration Zonation Around Antamina Cu-Zn Skarn and Uchucchacua Ag-based Metal Vein Deposits, Peru (2008)

No abstract available.

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Measuring enhanced carbon dioxide exchange between the atmosphere and mine waste derived from ultramafic hosted mineral deposits (2023)

The full abstract for this thesis is available in the body of the thesis, and will be available when the embargo expires.

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Carbon mineralization in ultramafic mine tailings via CO2 injection (2021)

As CO₂ emissions continue to rise, the threat posed by anthropogenic climate change grows. To combat this crisis, technologies are needed to capture and store CO₂. Carbon mineralization is one approach, which reacts cations with CO₂ to form stable carbonate minerals. Ultramafic mine tailings are one cation feedstock that could be used to advance this strategy at scale. CO₂ injection into the porous medium is required to accelerate the mineralization rates.Ultramafic mine tailings vary widely in their reactivity to CO₂. One important mineral, brucite, reacts rapidly with CO₂. Thermogravimetric analysis was used to identify and quantify brucite abundances. The developed method improved brucite detection limits and could quantify brucite when phases, which interfere with identification by X-ray diffraction, are present.Centimetre-scale injection experiments were conducted on well-graded tailings grain size distributions on serpentinite (brucite-rich) and kimberlite (brucite-poor) samples. Well-graded grain size distributions enabled the permeability to inject into the porous medium. Reactive fine-grained brucite released most of its Mg, while lizardite leached a minority of its Mg in the brucite-poor samples. 0.1 to 1 wt.% CO₂ was sequestered into major hydromagnesite and minor nesquehonite. Metre-scale experiments in kimberlite tailings increased the scale and designed methods to achieve mine-scale injection. Compaction testing evaluated the relationship between the dry density and moisture content of the tailings. 6-metre-long pipe experiments replicated the reactivity of the centimetre scale. Scalable pad experiments injected CO₂ through a perforated pipe into a layer of mixed coarse and fine tailings. Plume development throughout the pad led to homogeneous reactivity. Heterogeneity and low abundances of sequestered carbon madeconfirming the gas-phase mass balance on the injected CO₂ using total inorganic carbon difficult. A similar magnitude of carbon was sequestered in PK, as observed at the centimetre-scale, varying from 0.1 to 0.2 wt.% CO₂.Carbon mineralization in mine tailings via CO₂ injection has been shown to be effective in accelerating passive sequestration rates. This observed reactivity equates to a minor reduction in mine emissions at carbon-intensive mines while being enough capacity to make low-carbon mines carbon neutral.

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Carbonation of the Oman Ophiolite during subduction and emplacement (2021)

Fully carbonated peridotite, known as listvenite, is well exposed along the basal thrust of the Oman ophiolite. Outcrops of listvenite are a fossilized record of fluid-rock interactions that resulted in the storage of billions of tonnes of CO₂, providing researchers insight into an important global carbon sink and a potential natural analogue to in situ carbon sequestration. The goal of this thesis is to investigate the formation of listvenite using samples from the Oman Drilling Project to 1) characterize the petrology and geochemistry of listvenite, 2) determine the mineral reaction sequence and the physical and chemical conditions required and 3) constrain the potential sources of CO₂ bearing fluids.Three carbonated lithologies were observed: 1) serpentine with variable amounts magnesite and dolomite veining (ophicarbonate); 2) serpentine with abundant vein and matrix hosted magnesite, dolomite, talc and quartz (talc-ophicarbonate); and 3) intergrown magnesite, dolomite and quartz (listvenite). With the exception of H₂O, CO₂ and variable amounts of Ca, the major element geochemical composition of all three lithologies approximates unaltered peridotite. Fluid mobile trace elements such as Cs, Rb and Sr are enriched in listvenite to over 100-times that of unaltered peridotite and correlate with increasing δ¹³C values. δ¹³C values increase with carbonation from ~-7 δ¹³C in ophicarbonate samples through to ~+2 δ¹³C in listvenite, representing the progressive dilution of mantle-derived carbon with marine-derived carbon.Detailed petrography and thermodynamic phase equilibria modelling demonstrate that listvenite formed via a series of mineral reactions resulting in the breakdown of serpentine and the formation of magnesite, dolomite, talc and quartz. Crosscutting relationships between carbonate minerals and deformation structures, in combination with oxygen isotopic exchange thermometry, reveal that carbonation reactions were driven by at least two pulses of CO₂-bearing fluids that originated from, or interacted with, the metamorphic rocks below. The first pulse is associated with deformed matrix- and vein-hosted magnesite carbonation at 150-250 ℃, which potentially occurred pre-syn obduction at shallow depths within a subduction zone. This was followed by a later pulse of calcium-rich fluids associated with late undeformed dolomite carbonation at 50-100 ℃, which potentially occurred syn-post obduction during thrusting over carbonate shelf sediments.

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Formation and preservation of brucite and awaruite in a serpentinized ultramafite, central British Columbia: implications for carbon sequestration and nickel recovery (2021)

The Trembleur ultramafite in the Decar area in central British Columbia consists of severalultramafic protolith lithologies that are variably altered to serpentinite, ophicarbonate, soapstoneand listwanite. Alteration minerals include brucite (Mg[OH]₂), which can be used to sequesteratmospheric CO₂ and awaruite (Ni₃Fe), which is an economically attractive nickel alloy. Thesetwo minerals are formed during serpentinization and destroyed during carbonate alteration. Thisstudy examines the formation and preservation of these two minerals. The abundance, grain sizeand morphology of brucite and awaruite are variable, and the underlying controls on theirdistribution have been unclear. We use petrographic observations (textures, mineral assemblages), whole-rock and mineral major-element chemistry, and physical properties to characterize the formation, stability, and distribution of brucite and awaruite in order to optimize their utilization within the processing circuit should the deposit be mined. Brucite comprises up to ~13 wt.% of serpentinite and occurs as fine (
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Characterization of ultramafic mine tailings reactivity for carbon capture and storage (2020)

The carbon capture and storage potentials of ultramafic mine tailings are essential for assessing if mineral carbonation is a promising CO₂ sequestration strategy. CO₂ gas is mineralized in solid, stable carbonate minerals through dissolution and reaction with Mg-rich mining wastes. Here, the physical and chemical controls on reactivity and capacity for CO₂ sequestration in systems representative of mine tailings are examined using a combination of experimental techniques including flow-through, batch dissolution and disk carbonation. The reactivity of tailings is measured as a number of Mg²⁺ that is loosely bounded and readily leached (termed labile Mg). The study deploys the definition of labile Mg and understands its variability for advancing carbon sequestration techniques on the pilot and field scale. Flow-through and batch dissolution experiments on pure mineral phases and tailings show that labile Mg can be sourced from the bulk dissolution of Mg-hydroxides and the transient surface-reaction of Mg-silicates. Labile Mg is dependent primarily on mineralogy as well as the surrounding geochemical environment. CO₂ is the optimized acid that imposes a parallel and addictive effect towards promoting mineral dissolution and therefore enhances the quantity of labile Mg (reactivity). Characterizing mine tailings’ reactivity based on the capacity of labile Mg extraction is fundamental for accurate estimation of the carbon sequestration potential of the deposits and decisions on employment of the proper carbon sequestration techniques. This research imparts methods for quantitatively determine the reactivity of carbon capture and storage using mine tailings. Aspects of this research, such as serpentine surface-exchange reaction, also enabled more in-depth observations into the dissolution pathways of Mg-silicates and the feasibility of using ultramafic mine tailings for long-term carbon capture and storage.

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Mapping the carbonate alteration footprint of the Cortez Hills Carlin-type gold deposit, Nevada using carbon-oxygen isotopes, and geochemistry as a vectoring tool (2018)

The Cortez Hills deposit is located along the Battle-Mountain Eureka Trend in North-Central Nevada and is a world-class Carlin-type (CTD) gold deposit. Visible and cryptic alteration associated with mineralization were used to define footprints, alteration haloes, mineralization targets and fluid pathways. Approximately 2,500 carbon and oxygen isotope analyses from a mm- to m-scale using core, chips, pulped rock and surface samples together with geology and geochemistry provided an integrated dataset for evaluating fluid transport and alteration in the Cortez Hills plumbing system.The Cortez Hills plumbing system was described using calcite veins. Timing of calcite veins were based on crosscutting relationships relative to alteration and mineralization events. Three main vein stages were identified which includes ten vein types and two stylolite events. Cross-cutting relationships were supported by vein physical characteristics to improve identification. Calcite veins at Cortez Hills have distinct physical and chemical characteristics that can be identified with a variety of methods. Chemical characteristics were used to understand the processes that formed veins. V2 veins associated with Carlin fluids could be a significant fluid pathway contributing to the hydrothermal plumbing system. Calcite veins have the potential to be used as an exploration tool for Carlin systems.Invisible alteration was described using carbon and oxygen stable isotopes, and Carlin pathfinder elements (As, Au, Hg, Sb, and Tl) as a vectoring tool. Oxygen isotopes represented the most far-field detectable feature of CTDs and were used to define the cryptic carbonate alteration of Cortez Hills. Defining thresholds for carbon and oxygen isotopes, and pathfinder elements were integral to map alteration haloes (lower threshold), define mineralization targets (upper threshold) and map fluid flow pathways. Isotopes and pathfinder elements were described in order of greatest distance travelled outboard of economic gold orezones and utilized as a vectoring tool for alteration and mineralization: 18O>As>Hg>Sb>Tl-13C>Au. The defined 18O deposit footprint (lower threshold) was >3.5km and the pathfinder element alteration halo was 2.2km in size. The defined 18O mineralization target (upper threshold) was 1km in width and 0.6km in height.

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