Gregory Dipple

Professor

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Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - Nov 2019)
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. Supplementary video material is available at: http://hdl.handle.net/2429/51487

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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 (2010 - 2018)
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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