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Kokelj S.V.,Northwest Territories Geoscience Office
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.

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.

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

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.

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.

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