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Byrne K.,University of British Columbia | Byrne K.,Teck Resources Ltd | Tosdal R.M.,University of British Columbia
Economic Geology | Year: 2014

The Late Triassic Southwest zone alkalic porphyry Cu-Au deposit in the Galore Creek district, northwestern British Columbia, is hosted in hydrothermally cemented breccias that overprinted older matrix-rich breccia and megacrystic orthoclase-phyric syenite and monzonite dikes. Synmineralization cemented breccias and biotite-phyric monzodiorite dikes are localized at the contact of the matrix-rich breccia and host syenite and monzonite dikes, as well as in crosscutting faults. Regional shortening tilted the Southwest zone deposit so that the cemented breccias now dip 50° to 60° southwest. Four paragenetic stages formed the deposit. A premineralization stage (1) consists of the emplacement of coherent syenite and monzonite host rocks that are cut by a matrix-rich breccia. The synmineralization stage (2) produced potassic-altered rocks and phlogopite-magnetite-K-feldspar-cemented breccia and veins, and most of the Cu-Fe sulfides. A halo of stage 2 diopside-magnetite-grandite-phlogopite calcic-potassic veins and altered rocks formed around the potassic domains and Cu ore zones. Alteration during stage 2 probably formed at temperatures of about 500° to 425°C from oxidized saline magmatic-hydrothermal fluids. Contemporaneous high (aCa 2+)/(aH +)2 conditions peripheral to the potassic domains are required to form the marginal calcicpotassic and calcic assemblages. The potassic and calcic-potassic alteration domains were overprinted by propylitic and calcic alteration assemblages due to the retrograde influx of an admixture of cooler magmatic and nonmagmatic fluids. Sphene from a stage 2 calcic-potassic vein yielded a 202.8 ± 2.1 Ma age (U-Pb SHRIMP-RG) that is interpreted to reflect the approximate time of hydrothermal alteration. Late-mineralization stage (3) alteration overprinted the cemented breccias and comprises sericite-anhydrite (sericitic), grandite (calcic), and chlorite-epidote- carbonate-pyrite (propylitic) assemblages. Localized latemineralization and Cu-poor stage (4) K-feldspar-Fe carbonate-specularite (carbonate-potassic) and quartzpyrite veins (quartz veins) cut stage 2 and 3 assemblages. Chalcopyrite and bornite dominate the core of the deposit, and grade outward to chalcopyrite > pyrite and to pyrite > chalcopyrite, flanked by a pyrite-only halo. The core of the system is Cu-Au rich, grading outward to an Au-enriched, Cu-poor halo coincident with pyrite-bearing propylitic alteration. Gold-copper ratios increase upward within stage 2 potassic zones and outward from the core. Variations in pH, redox, and temperature along and across fluid flow paths best explain the change to higher Au/Cu values upward and away from the Cu-rich potassic domains. © 2014 Society of Economic Geologists, Inc.

Micko J.,University of British Columbia | Micko J.,University of Tasmania | Tosdal R.M.,University of British Columbia | Bissig T.,University of British Columbia | And 2 more authors.
Economic Geology | Year: 2014

The Late Triassic Galore Creek porphyry district is the largest accumulation of Cu-Au prospects in British Columbia, Canada, in terms of contained metal. The principal economic resource is the Central zone deposit. It comprises three high-grade centers: the Au-rich North and South gold lenses and the Cu-dominated Central replacement zone. Alteration footprints, ore shells, and porphyry intrusions in these centers dip 45° to 60° to the west in the North gold lens and southwest in the South gold lens and Central replacement zone, indicative of significant postmineral tilting. This inclination created an oblique vertical expression of the Central zone at surface and at depth, providing a +700-m depth profile through the deposit. Galore Creek is considered to be the end-member of the silica-undersaturated class of alkalic porphyry Cu- Au deposits. It displays a unique hydrothermal alteration footprint, generally devoid of quartz veining. Despite the lack of crosscutting veins, a paragenetic sequence of several discrete potassic and calcic alteration events has been established. During main-stage alteration, two mineralization events occurred that formed the economic resource in the Central zone. Highly oxidizing fluids derived from porphyritic syenite to monzonite intrusions produced initial potassic alteration and sulfide mineralization in the North gold lens and South gold lens. Cu-Au ore shells are characterized by a gold-rich core dominated by bornite associated with hematitedusted orthoclase, specular hematite, and anhydrite. The second period of hydrothermal activity caused brecciation and calcic alteration in the Central replacement zone. The calcic fluids formed hydrothermal cement grading from Ti-rich andraditic to grossularitic garnet in the core of the breccia to a diopside and magnetitedominated assemblage at the margins. Calcic alteration also formed in the surrounding host rock. This alteration event was followed by potassic alteration and mineralization, characterized by biotite, anhydrite, and chalcopyrite in the Cu-rich ore shell of the Central replacement zone. Most of the Au is hosted in bornite that is spatially associated with oxidized (reddened) rock units dominated by an alteration assemblage of orthoclase ± hematite ± specular hematite ± garnet ± anhydrite. High-grade Cu in the Central zone is related to abundant chalcopyrite that has commonly replaced an assemblage of biotite ± magnetite ± diopside. This distinct spatial separation strongly suggests that the local redox environment within the wall rocks governed sulfide and gold distributions. The switch from early Au-rich mineralization to late-stage Cu-dominated mineralization appears to have been controlled by varying redox conditions within the magma. The change from more oxidized alteration assemblages (Fe3+ > Fe2+) to more reduced assemblages (Fe3+ ≤ Fe2+) is indicative of a change in oxidation potential that may have propelled sulfide saturation in the magma and, thus, the subsequent depletion of most of the Au. © 2014 Society of Economic Geologists, Inc.

Duuring P.,Monash University | Duuring P.,University of Western Australia | Bleeker W.,Geological Survey of Canada | Beresford S.W.,Monash University | And 2 more authors.
Mineralium Deposita | Year: 2010

Perseverance is a world-class, komatiite-hosted nickel sulphide deposit situated in the well-endowed Leinster nickel camp of the Agnew-Wiluna greenstone belt, Western Australia. The mine stratigraphy at Perseverance trends north-northwest (NNW), dips steeply to the west, and is overturned. Stratigraphic footwall units lie along the western margin of the Perseverance Ultramafic Complex (PUC). The PUC comprises a basal nickel sulphide-bearing orthocumulate- to mesocumulate-textured komatiite that is overlain by a thicker, nickel sulphide-poor, dunite lens. Hanging wall rocks include rhyodacite that is texturally and compositionally similar to footwall volcanic rocks. These rocks separate the PUC from a second sequence of nickeliferous, E-facing, spinifex-textured komatiite units (i. e. the East Perseverance komatiite). Past workers argue for a conformable stratigraphic contact between the PUC and the East Perseverance komatiite and conclude that the PUC is extrusive. This study, however, clearly demonstrates that these komatiite sequences are discordant, implying that the PUC may have intruded rhyodacite country rock as a sill with subsequent structural juxtaposition against the East Perseverance komatiite. Early N-S shortening associated with the regional DI deformation event (corresponding to the local DP1 to DP3 events at Perseverance) resulted in the heterogeneous partitioning of strain along the margins of the competent dunite. A mylonite developed in the more ductile footwall rocks along the footwall margin of the PUC, while isoclinal F3 folds, such as the Hanging wall limb and Felsic Nose folds, formed in low-mean stress domains along the fringes of the elongated dunite lens. Strata-bound massive and disseminated nickel sulphides were passively fold thickened in hinge areas of isoclinal folds, whereas basal massive sulphides lubricated fold limbs and promoted thrust movement along shallowly dipping lithological contacts. Massive sulphides were physically remobilised up to 20 m from their primary footwall position into deposit-scale fold hinges to form the 1A and Felsic Nose orebodies. First-order controls on the geometry of the Perseverance deposit include the thermomechanical erosion of footwall rocks and the channelling of the mineralised komatiitic magma. Second- or third-order controls are several postvolcanic deformation events, which resulted in the progressive folding and shearing of the footwall contact, as well as the passive fold thickening of massive and disseminated sulphide orebodies. Massive sulphides were physically remobilised into multiple generations of fold hinges and shear zones. Important implications for near-mine exploration in the Leinster camp include identifying nickeliferous komatiite units, defining their three-dimensional geometry, and targeting fold hinge areas. Fold plunge directions and stretching lineations are indicators of potential plunge directions of massive sulphide orebodies. © 2010 Springer-Verlag.

Teck Resources Ltd is seeking regulatory approval for its Frontier Oil Sands Project, a proposed 260,000 bpd oil sands mining and bitumen production operation located north of Fort McMurray, Alberta. As part of the feasibility design process for the Project, 70 ton of oil sand were collected from the Frontier leases during the winter of 2014 to determine oil sands processing characteristics of specific geological facies and bitumen grades. The targeted collection of 70 ton oil sands from a remote greenfield site via large diameter coring was completed with no first aids, medical aids, or lost time incidents. Productivity exceeded expectations with core recovery of 100% and an average coring time for each of the 44 holes of 30 hr. The 2014 large diameter coring program has successfully completed and offers a proven methodology for other operators looking to collect large bulk oil sand samples from remote greenfield sites. The scope and learnings from the large diameter coring program are discussed. Tar sands.

Reynolds M.A.,University of Alberta | Gingras M.K.,University of Alberta | Gleeson S.A.,University of Alberta | Stemler J.U.,Teck Resources Ltd
Geology | Year: 2015

Sediment-hosted massive sulfide (SHMS) deposits are an important source of global zinc resources, and the Red Dog Pb-Zn-Ag ± Ba district in Alaska (USA) contains giant deposits of this type. The existing model for ore formation at Red Dog involves early diagenetic replacement of sediment deposited in a restricted basin with stratified suboxic bottom waters. We present new observations of trace fossils Schaubcylindrichnus ichnospecies (isp.) and Chondrites isp. in several Red Dog deposits. The presence of the trace fossils, the size of the largest burrows, and the pervasiveness of the ichnofabric indicate that at least some intervals of the host sediment were deposited in an oxygenated middle to outer shelf environment. The burrow linings and infill are replaced by barite, hydrothermal quartz, and sulfide minerals, and the lack of compaction suggests that mineralization was diagenetically early. To reconcile these data with those from previous regional sedimentological and lithogeochemical studies, we propose a new model whereby the ore-hosting sediment was deposited in a shelfal setting in which redox conditions were affected by a fluctuating oxygen minimum zone. The strong spatial correlation between bioturbation and Red Dog SHMS deposits suggests that the presence of trace fossils may have played an important role in controlling the flow of ore-forming fluids by increasing host sediment permeability. © 2015 Geological Society of America.

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