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Acosta-Gongora P.,University of Alberta | Gleeson S.A.,University of Alberta | Samson I.M.,University of Windsor | Ootes L.,Northwest Territories Geoscience Office | Corriveau L.,Geological Survey of Canada
Economic Geology | Year: 2015

The NICO Au-Co-Bi(±Cu±W) deposit is located in the Great Bear magmatic zone, NWT, Canada, where numerous polymetallic, iron oxide-dominated mineralized systems have been recognized. Petrographic, electron microprobe analysis (EMPA), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICPMS) studies of host-rock alteration and ore mineralogy, together with sulfarsenide geothermometry, have been carried out to constrain the nature of alteration and/or mineralization assemblages in this deposit. Metasedimentary rocks of the Treasure Lake Group host NICO and are pervasively altered to an assemblage of ferrohornblende I + actinolite I + biotite I + magnetite I ± orthoclase, which is cut by barren veins composed of quartz ± ferrohornblende-orthoclase-calcite (Set 1). These alteration events are overprinted by metasomatic prograde and retrograde mineralized assemblages and both brittle and ductile deformation accompanied the metasomatism. The prograde assemblage (>400°C) consists of cobaltite, Co-rich loellingite, and Co-rich arsenopyrite (stage I), magnetite II, ferrohornblende II, actinolite II, biotite II, pyrite, and minor scheelite and orthoclase. The earliest retrograde mineralization consists of arsenopyrite (stages II and III), which contains variable amounts of Co, together with native Bi (±bismuthinite) and Au, with lesser magnetite, marcasite, pyrite, hastingsite, and minor quartz. The preservation of solidified native Bi droplets suggests a temperature range of 270° to <400°C for precipitation of this assemblage. The final stage of retrograde mineralization consists of a chalcopyrite-bismuthinite-hematite-chlorite assemblage, together with hastingsite ± emplectite, which formed at temperatures of less than 270°C. Textural and trace element evidence indicates that the Au and Bi present within arsenides and sulfarsenides in the NICO system resulted from the initial partitioning of structurally bound Au and/or "invisible" (nanometer-sized particles) of Au and Bi into the prograde sulfarsenide and arsenide phases, which contain up to 81 ppm Au. The Au and Bi were remobilized following retrograde alteration of those minerals to arsenopyrite II. Molten Bi droplets are interpreted to have scavenged Au insitu, resulting in the formation of the Bi-Au inclusions observed in arsenopyrite II. The second mechanism of gold refining is explained by the occurrence of contemporaneous Bi (±Te) melt and hydrothermal fluids that also could have fractionated gold during transport in solution and deposited it in fractures, interstitially to earlier mineral grains, and as disseminations within Ca-Fe-amphibole-magnetite-biotite-altered rocks. Overall, the gold upgrading at NICO is consistent with the liquid bismuth collector model, suggesting that this process was an important control on gold concentration in this and potentially other Au-Bi-Te-Fe-As-S-rich iron oxide-copper-gold (IOCG) deposits. ©2015 by Economic Geology


Acosta-Gongora P.,University of Alberta | Gleeson S.A.,University of Alberta | Samson I.M.,University of Windsor | Ootes L.,Northwest Territories Geoscience Office | Corriveau L.,Geological Survey of Canada
Economic Geology | Year: 2014

The Paleoproterozoic Great Bear magmatic zone is the focus of ongoing exploration for iron oxide copper-gold (IOCG) deposits and also hosts iron oxide-apatite occurrences. Examples of IOCG deposits in the Great Bear magmatic zone include Sue-Dianne and NICO, and other smaller prospects, including Damp, Fab, and Nori/Ra. The past-producing Terra mine property hosts significant IOCG-like alteration that contains dome-shaped, iron oxide-apatite bodies. Petrographic study has identified multiple generations of magnetite at NICO, Fab, and Nori/Ra and, for the most part, a single generation of magnetite at Sue-Dianne, Damp, and Terra. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) documents important geochemical differences in V, Ni, Cr, and Co concentrations within the magnetite. Variations of trace elements in magnetite from the Great Bear magmatic zone could be a result of (1) host rock-fluid equilibration during regional metamorphism, (2) postmetamorphic hydrothermal metasomatism of Treasure Lake Group metasedimentary rocks, (3) preferential solubility of Co over Ni within the Fe-rich fluids, (4) changes in oxygen fugacity (fO2), and (5) partitioning of elements into coprecipitating sulfides. Regionally, the Cr/Co ratio is higher in barren and pre-ore magnetite compared to magnetite coprecipitated with ore minerals and/or present in ore-rich veins and breccias. Locally, at the Nori/Ra prospect, the V/Ni ratio in magnetite differentiates between barren and ore-related magnetite, and at Damp and Sue-Dianne the Co/Ni ratio is extremely high and clearly different from that of other Great Bear magmatic zone magnetite samples. These results provide the first database for geochemically characterized magnetite from different stages of IOCG alteration and illustrate the potential use of magnetite as an indicator mineral in the exploration for IOCG deposits. ©2014 Society of Economic Geologists, Inc.


Fraser R.H.,Natural Resources Canada | Lantz T.C.,University of Victoria | Olthof I.,Natural Resources Canada | Kokelj S.V.,Northwest Territories Geoscience Office | Sims R.A.,Tetra Tech Inc.
Ecosystems | Year: 2014

Strong evidence for a pan-Arctic expansion of upright shrubs comes from analysis of satellite imagery, historical photographs, vegetation plots, and growth rings. However, there are still uncertainties related to local-scale patterns of shrub growth, resulting interactions among vegetation functional groups, and the relative roles of disturbance and climate as drivers of observed change. Here, we present evidence that widespread and rapid shrub expansion and lichen declines over a 15,000 km2 area of the western Canadian Arctic have been driven by regional increases in temperature. Using 30 m resolution Landsat satellite imagery and high resolution repeat color-infrared aerial photographs, we show that 85% of the land surface has a positive 1985–2011 trend (P < 0.05) in NDVI, making this one of the most intensely greening regions in the Arctic. Strong positive trends (>0.03 NDVI/decade) occurred consistently across all landscape positions and most vegetation types. Comparison of 208, 1:2,000 scale vertical air photo pairs from 1980 and 2013 clearly shows that this greening was driven by increased canopy cover of erect dwarf and tall shrubs, with declines in terricolous lichen cover. Disturbances caused by wildfires, exploratory gas wells, and drained lakes all produced strong, yet localized increases in NDVI due to shrub growth. Our analysis also shows that a 4°C winter temperature increase over the past 30 years, leading to warmer soils and enhanced nutrient mineralization provides the best explanation for observed vegetation change. These observations thus provide early corroboration for modeling studies predicting large-scale vegetation shifts in low-Arctic ecosystems from climate change. © 2014, UKCrown: Natural Resources Canada.


Spence C.,Environment Canada | Kokelj S.A.,Aboriginal Affairs and Northern Development Canada | Kokelj S.V.,Northwest Territories Geoscience Office | Hedstrom N.,Environment Canada
Hydrological Processes | Year: 2014

There have been widespread increases in winter streamflow across the circumpolar north since the mid to late 1900s. However, the physical processes that result in winter runoff generation are not well understood. The objective of this research was to determine the runoff generation processes and pathways of cold season streamflow, and to compare and contrast them with those of spring freshet in a subarctic Canadian Shield study catchment in which winter streamflow regime changes have been documented. Traditional hydrometric methods were used in conjunction with modelling and hydrochemistry to estimate runoff sources and pathways. Results suggest that while runoff generation processes do not necessarily differ between spring and winter runoff events, the timing at which pre-event and event water contributes does differ. Furthermore, the periods in which certain runoff pathways activate and deactivate are different. Runoff during the spring freshet is dominated by pre-event water that has not been exposed to the subsurface. In contrast, and most notably, isotopic chemistry reveals that 72% of high cold season streamflow is from new precipitation. In Precambrian Shield regions, or in other landscapes where there may be a large fraction of lakes, late autumn rainfall can increase lake levels, and in turn, storage, to ample volumes that can provide high amounts of winter runoff. Where autumn rainfall has been increasing, precipitation and surface water should be considered as a source of enhanced winter streamflow in these types of landscapes. These results have implications for how widespread environmental changes in the circumpolar north, especially those of aquatic chemistry and permafrost thaw, should be interpreted and predicted. © 2013 John Wiley & Sons, Ltd.


Lemieux Y.,Northwest Territories Geoscience Office | Lemieux Y.,Geological Survey of Canada | Hadlari T.,Northwest Territories Geoscience Office | Simonetti A.,University of Alberta | Simonetti A.,University of Notre Dame
Canadian Journal of Earth Sciences | Year: 2011

U-Pb ages have been determined on detrital zircons from the Upper Devonian Imperial Formation and Upper Devonian - Lower Carboniferous Tuttle Formation of the northern Canadian Cordilleran miogeocline using laser ablation - multicollector - inductively coupled plasma - mass spectrometry. The results provide insights into mid-Paleozoic sediment dispersal in, and paleogeography of, the northern Canadian Cordillera. The Imperial Formation yielded a wide range of detrital zircon dates; one sample yielded dominant peaks at 1130, 1660, and 1860 Ma, with smaller mid-Paleozoic (~430 Ma), Neoproterozoic, and Archean populations. The easternmost Imperial Formation sample yielded predominantly late Neoproterozoic - Cambrian zircons between 500 and 700 Ma, with lesser Mesoproterozoic and older populations. The age spectra suggest that the samples were largely derived from an extensive region of northwestern Laurentia, including the Canadian Shield, igneous and sedimentary provinces of Canada's Arctic Islands, and possibly the northern Yukon. The presence of late Neoproterozoic - Cambrian zircon, absent from the Laurentian magmatic record, indicate that a number of grains were likely derived from an exotic source region, possibly including Baltica, Siberia, or Arctic Alaska - Chukotka. In contrast, zircon grains from the Tuttle Formation show a well-defined middle Paleoproterozoic population with dominant relative probability peaks between 1850 and 1950 Ma. Additional populations in the Tuttle Formation are mid-Paleozoic (~430 Ma), Mesoproterozoic (1000-1600 Ma), and earlier Paleoproterozoic and Archean ages (>2000 Ma). These data lend support to the hypothesis that the influx of sediments of northerly derivation that supplied the northern miogeocline in Late Devonian time underwent an abrupt shift to a source of predominantly Laurentian affinity by the Mississippian.


Spence C.,Environment Canada | Kokelj S.V.,Northwest Territories Geoscience Office | Kokelj S.A.,Natural Resources Canada | McCluskie M.,Natural Resources Canada | Hedstrom N.,Environment Canada
Journal of Geophysical Research G: Biogeosciences | Year: 2015

Enhanced winter streamflow is a characteristic of a nival/pluvial regime that has emerged in parts of the subarctic Canadian Shield because of increasingly common late summer rains. This phenomenon is part of a widespread trend toward higher winter streamflow in watersheds across the circumpolar north. There may be implications for biogeochemical systems as streamflow regimes undergo these types of changes associated with climate warming. Streamflow and geochemical fluxes were observed over 2 years with different winter flow conditions in a subarctic Canadian Shield catchment. Results show that higher wintertime loads of carbon and solutes associated with enhanced winter streamflow were in association with an expansion of contributing areas to run off over what would have existed during typical winter recession. Furthermore, the wet fall conditions that lead to enhanced winter streamflow require water tables close to the topographic surface in highly conductive organic soil layers, which is a similar to the condition during the spring melt. Fall rainfall-runoff leaves an ample volume of water in the lakes that are ubiquitous in this landscape. This water maintains winter streamflow during a time when it traditionally would have ceased. A slowing of biological activity under lake ice increases net mineralization and nitrification rates. This convergence of nitrogen cycling and winter streamflow produced a disproportionate flux of inorganic nitrogen from the study catchment. A conceptual model of how enhanced winter streamflow changes water chemistry in a lake-dominated shield landscape is proposed and may be used as a benchmark to guide hypotheses of process interactions, change in other landscapes, or across scales. ©2014. American Geophysical Union. All Rights Reserved.


Rasmussen K.L.,University of British Columbia | Lentz D.R.,University of New Brunswick | Falck H.,Northwest Territories Geoscience Office | Pattison D.R.M.,University of Calgary
Ore Geology Reviews | Year: 2011

A field and petro-chemical classification of felsic magmatic phases (FMPs) at the world-class Cantung W skarn deposit was undertaken to document the evolution of magmatism and the relationships between different FMPs, metasomatism, and mineralization. Early FMPs include moderately differentiated (Zr/Hf=18-26, Ti/Zr=14-15) biotite monzogranitic plutons and early biotite-rich granitic dykes, and compositionally similar quartz-feldspar porphyry dykes. Late, highly fractionated (Zr/Hf=8-17, Ti/Zr=3-13) FMPs sourced from a deeper monzogranitic intrusion include: (1) leucocratic biotite- or tourmaline-bearing dykes derived from localized entrapments of residual magma; and, (2) sub-vertical NE-trending aplitic dykes derived from a larger segregation of residual fluid- and incompatible element-enriched magma. The aplitic dykes have textures, morphologies, spatial associations, and a pervasive calcic metasomatic mineral assemblage (Ca-plagioclase+quartz or clinozoisite) indicative of syn-mineralization emplacement. Very late-stage overpressuring and initiation of sub-vertical fractures into the overlying plutonic carapace and country rocks by supercritical magmatic fluid led to an interaction with calcareous country rocks that resulted in an increased aCa2+ in the fluid and the concurrent precipitation of W skarn. Residual magma also ascended with, and quenched in equilibrium with the magmatic fluid to from the aplitic dykes, then was metasomatized by the fluid as it interacted with calcareous country rocks. Overall, highly fractionated and moderately to very highly undercooled FMPs at Cantung provide evidence for a large and evolving felsic magmatic system at depth that segregated and maintained a stable fluid- and incompatible element-enriched residual magma until the latest stages of crystallization. The detailed study of FMPs associated with magmatic-hydrothermal mineral deposits allow us to refine our understanding of these mineralizing systems and better define metallogenic and exploration models for intrusion-related mineralization. © 2011 Elsevier B.V.


Lacelle D.,University of Ottawa | Fontaine M.,University of Ottawa | Forest A.P.,University of Ottawa | Kokelj S.,Northwest Territories Geoscience Office
Chemical Geology | Year: 2014

The knowledge of past permafrost conditions is of importance to assess the potential magnitude of changes that periglacial environments may experience as a result of climate warming or disturbance. To assess if past thaw unconformities may be preserved from isotopic and geochemical discontinuities within permafrost, this study investigates the distribution of ground ice, stable water isotopes and major cations in two permafrost cores collected in a hummocky terrain site near Inuvik, Northwest Territories, Canada; a site where the evolution of the active layer during a recent period of permafrost degradation and subsequent aggradation was documented. Based on the high-resolution isotope geochemistry profiles, closed-system Rayleigh-type ionic segregation and isotope fractionation occurred during thermally-induced water migration into shallow permafrost and its freezing along a negative soil temperature gradient. Due to thermally-induced water migration into permafrost, δ18O may not always be able to identify thaw unconformities; however the calculation of the 18O enrichment factors between ice and water (ε18Oi-w) may be used to determine position of thaw unconformities in permafrost, if thaw events are followed by permafrost aggradation. The approach of using ε18Oi-w provides additional information regarding past permafrost conditions that can complement change in cryostructures observed along natural exposures. © 2014.


Lacelle D.,University of Ottawa | Brooker A.,University of Ottawa | Fraser R.H.,Canada Center for Mapping and Earth Observation | Kokelj S.V.,Northwest Territories Geoscience Office
Geomorphology | Year: 2015

Retrogressive thaw slumps are one of the most active geomorphic features in permafrost terrain. This study investigated the distribution and growth of thaw slumps in the Richardson Mountains and Peel Plateau region, northwestern Canada, using Tasseled Cap (TC) trend analysis of a Landsat image stack. Based on the TC linear trend image, more than 212 thaw slumps were identified in the study area, of which 189 have been active since at least 1985. The surface area of the slumps ranges from 0.4 to 52ha, with 10 slumps exceeding 20ha. The thaw slumps in the region are all situated within the maximum westward extent of the Laurentide Ice Sheet. Based on relations between frequency distribution of slumps and that of terrain factors in the landscape, the slumps are more likely to occur on the ice-rich hummocky rolling moraines at elevations of 300-350m and 450-500m and along east-facing slopes (slope aspects of 15° to 180°) with gradients of 8° to 12°. Pixel-level trend analysis of the TC greenness transformation in the Landsat stack allowed calculating headwall retreat rates for 19 thaw slumps. The 20-year average retreat rates (1990-2010 period) for 19 slumps ranged from 7.2 to 26.7myr-1, with the largest slumps having higher retreat rates. At the regional scale, the 20-yr headwall retreat rates are mainly related to slope aspect, with south- and west-facing slopes exhibiting higher retreat rates, and large slumps appear to be generating feedbacks that allow them to maintain growth rates well above those of smaller slumps. Overall, the findings presented in this study allow highlighting of key sensitive landscapes and ecosystems that may be impacted by the presence and growth of thaw slumps in one of the most rapidly warming region in the Arctic. © 2015 published by Elsevier B.V. All rights reserved.


Kokelj S.V.,Northwest Territories Geoscience Office | Jorgenson M.T.,Alaska Ecoscience
Permafrost and Periglacial Processes | Year: 2013

The term thermokarst describes the processes and landforms that involve collapse of the land surface as a result of the melting of ground ice. We review the literature that has contributed to our understanding of patterns, processes and feedbacks, and the environmental consequences of thermokarst, focusing on hillslope, thaw lake and wetland processes. Advances in remote sensing techniques, and their application in a broad suite of change detection studies, indicate recent increases in the rates and magnitude of thermokarst including retrogressive thaw slumping, lake expansion and the transformation of frozen peatlands to collapsed wetlands. Field-based studies and modelling have enhanced the knowledge of processes and feedbacks associated with warming permafrost, changes in talik geometry and accelerated thaw slump activity, and thaw lake expansion. Hydrological processes can strongly influence the rates of thaw lake and gully development, and the degradation of frozen peatlands. Field studies and calibrated modelling efforts that investigate the drivers of thermokarst and test conceptual ideas of landscape evolution will be critical to further advance the prediction of landscape and ecosystem change. Thermokarst research provides an important context for studying the environmental implications of permafrost degradation. Hillslope thermokarst can alter the water quality of lakes and streams with implications for aquatic ecosystems. Investigation of the interactions between thermokarst and hydrologic and ecological processes has improved knowledge of the feedbacks that accelerate change or lead to stabilisation in terrestrial and thaw lake environments. Finally, the influence of permafrost thaw on soil carbon dynamics will be an important focus of thermokarst research because of feedbacks with the global climate system. © Her Majesty the Queen in Right of Canada 2013.

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