Kenneth Hickey
Relevant Thesis-Based Degree Programs
Graduate Student Supervision
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.
Metal precipitation in several types of hydrothermal ore deposits is a product of fluid-rock interaction. The degree to which fluids can interact with rocks is, therefore, a fundamental control on the metal endowment of such deposits. This dissertation investigates hydrothermal flow paths and fluid-rock interactions along these flow paths in the Osiris cluster of Carlin-type Au deposits, Nadaleen trend, Yukon. The main findings of the dissertation are that steeply-plunging folds in the deposits were rotated to their modern steep geometry during progressive thrusting and flattening against the northern margin of the Selwyn basin, which acted as a rigid backstop. The vein networks that formed during this folding were later preferentially exploited by the ore fluids, which altered the pre-existing veins to Mn-rich, Sr-poor, Fe-poor, Mg-poor, UV-fluorescent (UVF) calcite veins. The chemistry and δ¹³C and δ¹⁸O composition of these UVF veins suggest that they formed during the progressive mobilization of carbonate cations down the flow path from carbonate dissolution zones. Most fluid flow occurred where the pre-existing vein network was closest spaced, such as in rigid carbonate units and steeply-plunging fold closures. This interpretation is supported by lithogeochemical relationships between Mn, Sr, Au, As, δ¹³C and δ¹⁸O that suggest the fluids generally exploited numerous flow paths smaller than the ~3 m lithogeochemical sample interval. Gold grades are higher in parts of the deposit where fluids could percolate through the rock mass rather than being confined to veins. Their ability to partition between fractures or veins and the wall-rock is controlled by the ratio of the fracture network’s bulk permeability to the rock layer’s permeability. Consequently, changes in the pre-existing vein network permeability are equally, if not more important, than changes in host rock permeability for promoting fluid-rock interaction. Variations in time-integrated fluid flux between flow paths also significantly influence fluid-rock interaction along the flow path. Laser ablation U-Pb carbonate geochronology of ore-stage carbonate veins indicates that the deposit likely formed from multiple hydrothermal events over several tens of millions of years and that magmatism was probably not a heat, fluid, or metal source.
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Physical-chemical fluid evolution, timing of fluid-migration and driving forces for fluid-flow are factors that fundamentally control the mass transport that leads to the formation of sedimentary rock hosted copper deposits. This thesis constrains these factors for Kupferschiefer-type mineralization in a sequence of Neoproterozoic rocks of the Redstone Copperbelt, Mackenzie Mountains, Northwest Territories, Canada. Stratiform copper mineralization is located in rift-basins that formed during the break-up of the supercontinent Rodinia within a period of Earth’s history that witnessed evolution of Precambrian life and dramatic climate changes associated with the Snowball Earth glaciations. A U-Pb zircon date is presented, constraining the eruption of a marker unit within the Neoproterozoic sequence that heralded the prolonged period of rifting that led to supercontinent fragmentation. The age also constrains the deposition of the host rocks for stratiform copper mineralization. Dating monazite grains associated with mineralization at the Coates Lake stratiform copper deposit demonstrates that mineralization occurred ~100 My after host rock deposition, following 2-4 km of burial. Mapping, fluid inclusion, paragenetic, and S-Sr-O-C isotope evidence show that mineralizing fluids were ~190 to 250 °C, had salinities of ~32 wt. % NaCl equivalent, were overpressured and circulated through red-beds that underlie mineralization. Fluid-pathways have been traced through the red-beds, up basin-margin faults and back laterally along stratigraphy in mineralized zones, suggesting that flow was circulatory and evidence is presented for free-convection. Two significant glacial episodes may have produced cryogenic brines that are a potential source of salinity for mineralizing fluids. Modelling the behavior of H-O-Cu-S-Cl over a range of temperature and salinity representative of stratiform copper mineralization suggests that significant solubilities of copper can be attained by even weakly oxidized fluids. This study contributes to a growing body of evidence that Kupferschiefer-type deposits are not only formed during early-diagenesis, but can form after significant periods of burial from saline, moderate temperature fluids that are not highly oxidized. A separate style of ‘vein-vug’ copper mineralization has been dated and occurred later in the basin-history, possibly as remobilization of stratiform mineralization; vein-vug mineralization may have formed in association with regional Zn-Pb mineralization across the northern Canadian Cordillera.
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Mapping relative patterns of mineral alteration and metasomatism reveal the visible manifestation of a hydrothermal system, but the visible expression of the hydrothermal system at the distal margins of fluid circulation may be limited owing to significant kinetic barriers to mineralogical and chemical alteration. Light stable isotopes of oxygen and carbon in carbonate minerals can be sensitive indicators of the interaction between hydrothermal fluids and wall rocks that can be used to delineate fluid flow pathways, evaluate the permeability network and source of fluids, estimate integrated fluid fluxes, and define the distal extent of alteration in carbonate-bearing lithologies. Carlin-type Au deposits in northeastern Nevada, USA are predominately sediment-hosted Au deposits formed by large hydrothermal systems. Typically, hydrothermal alteration including silicification, carbonate dissolution, clay alteration, and sulfidation are spatially restricted. The Blue Star-Goldstrike district on the Northern Carlin trend is the largest known occurrence of Carlin-type Au with a reported Au endowment of ~1,960 t. At the northern end of the Goldstrike district, the Banshee Au deposit represents a relatively small Carlin-type deposit primarily hosted within Jurassic lamprophyre dike (west Banshee) and polymict breccia units (east Banshee). Proximal alteration at west Banshee consists of silicification, illitization, and sulfidation with the addition of Au, Cs, Hg, K, Rb, Sb, Tl, and W and depletion in Ba, Ca, Mg, Mn, Na, and Sr. The breccia unit and limestone adjacent to the west Banshee lamprophyre exhibit carbonate dissolution and silicification. Outside of visible alteration, δ18O depletion in wall rock and vein calcite defines a more distal expression of alteration. Analysis of down hole δ¹⁸O in limestone from two transects across the Goldstrike district show that the isotopic alteration footprint surrounding Au mineralization may extend 2 km or more out from the main ore bodies. Reactive transport modeling of δ¹⁸O alteration at Banshee provides a tool for evaluating time integrated fluid flux associated with observed isotopic alteration. The combined datasets form the basis of an alteration model for Carlin-type Au deposits where alteration zones outward from proximal clay alteration, silicification, sulfidation, and carbonate dissolution to distal trace element metasomatism and δ¹⁸O alteration.
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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.
An abundance of Paleoproterozoic orogenic belts are distributed globally, as peripheral terranes accreted against the margins of Archean cratons. The abundance of these terranes indicates a period of tectonic activity between 2.1 and 1.8 Ga. The study of such belts has offered insight into the nature and rate of tectonic activity in the Paleoproterozoic. Analysis of thermo-tectonic events, paired with the collection of geochronological data has led to the discovery of a supercontinent that existed before the formation of Rodinia, called Columbia. The 1.9 Ga Wopmay Orogen in northern Canada is a Paleoproterozoic belt, comprising a complex amalgamation of tectonic elements, which is thought to have formed during the assembly of Columbia.The advent of new geochronological data has demanded that the current P-T-t-d (Pressure-Temperature-time-deformation) model of the Wopmay Orogen be reconsidered. To reconstruct the evolution of an orogenic belt, structural analysis of overprinting kinetic fabrics, thermodynamic analysis of metamorphic mineral assemblages, and the determination of absolute timing of thermo-tectonic events are required.Two map areas were chosen to conduct an analysis of the kinetic and metamorphic evolution of the southern Wopmay Orogen, a region of the belt that has historically been under-studied. The Brown Water and the Little Crapeau Lake areas are situated south of 65˚N in the Metamorphic Internal zone of the orogen, and are bounded to the east and west by the Archean Slave craton and the ca. 1850 Ma Great Bear Magmatic zone, respectively. The areas comprise a sequence of pelitic to semi-pelitic schists and gneisses that overlie parautochthonous Archean basement. Rocks in both areas show evidence for five generations of overprinting fabrics, S₁C-S₅C at Little Crapeau Lake, and S₁B-S₅B at Brown Water Lake. Conditions of peak metamorphism were attained synchronous with the intrusion of the ca. 1877 Ma Little Crapeau Sill, and the regionally expansive ca. 1850 Ma Rodrigues granite. At Brown Water Lake peak metamorphic conditions were reached syn-S₅B at 3.1-4.2 kbars and 570-670˚C, and syn-S₂C at 3.1-3.9 kbars and 570-630˚C at Little Crapeau Lake. Chemical and isotopic geochronological dating of monazite provided metamorphic age constraints that concurred with ages of local intrusions.
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Samples were collected from Jurassic intrusions in the northern Carlin Trend to determine the thermal history of the region that was strongly affected by Late Cretaceous exhumation and Eocene hydrothermal fluid flow. Low-temperature apatite fission track and apatite and zircon (U-Th)/He thermochronology of the northern Carlin Trend records 3-4 km exhumation since the Late Jurassic. At least 1-2 km exhumation occurred during a phase of rapid exhumation between 85-60 Ma that is coincident with extensional collapse of the overthickened hinterland of the Sevier orogeny. Late Cretaceous exhumation ages provide a background against which ~40 Ma thermal anomalies associated with the formation of the Carlin-type Au deposits can be observed. In the northern Carlin Trend, a thermal halo defined by apatite fission track resetting was observed up to 400 m out from major fluid flow conduits around the Goldstrike Stock that is immediately south of the multi-million ounce Betze-Post deposit. A lack of hydrothermal alteration within the stock shows that Eocene hydrothermal fluid flow was concentrated around its edge, and that heating of the stock was predominantly conductive. Finite element modelling and forward modelling of time-temperature paths constrain the duration of a hydrothermal fluid event to on order of 10 kyr. Multiple phases of this duration of fluid flow are possible, but were either thermally isolated or were shorter-lived. The high rates of fluid flux associated with short fluid flow durations are similar to those observed in hydrothermal systems driven by forced convection or pressure-driven flow, suggesting fluid flow responsible for the formation of Carlin-type Au deposits was driven by a magmatic source or seismicity rather than free convection.
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The Long Canyon deposit is a sediment-hosted gold deposit located in northeastern Nevada, over 150 km east of the Carlin Trend. The deposit geology, geochemistry and mineralogy suggest that it is a Carlin-type deposit. This project tests the extents of auriferous hydrothermal fluid infiltration through carbonate rocks at Long Canyon using patterns of ¹⁸O/¹⁶O depletion to define the limits of fluid-rock interaction. Patterns of isotope depletion are used to assess the structural and lithologic controls on fluid flow, and the lateral extent of fluid rock interaction beyond the limits of trace element halos genetically associated with gold mineralization. Carbon and oxygen isotope ratios were measured using the Mineral Deposit Research Unit’s Mineral Isotope Analyzer (MIA) at the University of British Columbia.Gold mineralization at Long Canyon occurs predominantly within deeply oxidized, limestone-hosted solution breccias, located within necklines of an 80 metre thick boudinaged dolomite unit. Alteration associated with gold mineralization comprises decalcification of limestones>>dolomite, fine-grained pyrite growth within Fe-rich host rocks, argillization and silicification. Clay minerals include dickite within the core of the system, flanked by illite and kaolinite. Assuming typical Carlin-type fluid temperatures of 180° to 240°C, δ¹⁸O values of ore fluids are calculated at ≤1.6 to 6.3‰. Calculated δ¹⁸OH₂₀ that deposited dickite within the core of the mineralized system was calculated at 2.3‰ for a 200°C fluid.In this study several scales of sampling were tested including: contiguous drill assay pulps over cross sections; surface sampling along traverses; closely spaced hand sample coverage down drillholes; and micro-drilled hand samples. Presented here are the results of over 2,800 unique ¹⁸O/¹⁶O carbonate sample compositions from across the deposit. Results indicate stable isotope depletion mapping around carbonate-hosted ore bodies with sufficient sample density can provide far field vectors to fluid flow paths beyond what traditional lithogeochemistry alone may show. Additionally, it is evident from the pattern of oxygen isotope depletion that hydrothermal fluid flow responsible for mineralization was largely constrained to brittle damage zones within boudin necks, or incipient boudin necks, within massive dolomite units. There was minimal lateral flow within or vertically across stratigraphic units without pre-existing structural damage.
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The genesis of the Minto copper-gold deposit, YT, Canada, has been variously interpreted since its discovery although no existing model accounts for ductile deformation as a control on mineralization. Results from this study show that Minto ore is hosted within ductiley deformed granitoid host rocks emplaced as multiple intrusions into an actively deforming environment, with the variably sheared host rocks separated by incipiently deformed granodiorites essentially barren of mineralisation. Contacts between deformed/mineralized rock and incipiently deformed/barren rock range from abrupt to gradational, and are the product of pre-existing igneous contacts, variably partitioned deformation, or a combination of these. Deformation of granitoids is interpreted to have controlled fluid flow, with associated alteration promoting further deformation and fluid flow. Potassic alteration, in the form of biotite-magnetite, is the dominant alteration associated with mineralisation, and analysis of alteration using isocon diagrams indicates that K, Fe, Si, Cu, Au, and Ag have been added during alteration, although mass has been lost overall due to a relative reduction in Na and Ca. Host rock intrusion, mineralization, and deformation are interpreted via geochronology and crosscutting relationships as ongoing over at least 5 m.a., from about 202 Ma until about 197 Ma, based on U-Pb SHRIMP geochronology of zircons in granitoids and Re-Os ICP-MS geochronology of molybdenite. The trend of mineralisation is now coincident with the strike of foliation on short steep limbs and of axial planes of folded foliation. This geometry may not be representative of original processes, but of remobilization of ore during continued deformation. The above observations, coupled with data from existing studies, strongly suggest Minto is representative of deposit generation within an arc subduction environment at depths not typically considered for copper-gold deposit formation.
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Multiple analytical techniques were employed to investigate distal patterns in low temperature hydrothermal fluid flow into and out of Carlin-type gold deposits in two study areas: the Leeville deposit and the Shoshone range including the Pipeline, Gold Acres and Elder Creek deposits. Previous studies indicate that gold is hosted in lower Paleozoic carbonate rocks overlain by thick sequences of similarly aged siliciclastic rocks. Patterns in δ¹⁸O depletion (
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