|Titre||Occurrence and environmental impact of oxide-sulphide gossans and their reactive zones in permafrost|
|Auteur||Williamson, M -C; Harris, J; Percival, J B; Bédard, J; Froome, J; Peterson, R C; Rainbird, R|
|Source||40th Annual Yellowknife Geoscience Forum, abstracts of talks and posters; par Watson, D M (éd.); Northwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume 2012, 2012 p.
|Liens||Online - En Ligne |
|Séries alt.||Secteur des sciences de la Terre, Contribution externe 20120291|
|Réunion||40th annual Yellowknife Geoscience Forum; Yellowknife; CA; Novembre 13-15, 2012|
|Document||publication en série|
|Province||Territoires du Nord-Ouest|
|Sujets||effets sur l'environnement; pergélisol; congélation du sol; glace fossile; chapeaux ferrugineux; contamination des métaux lourds; géologie des dépôts meubles/géomorphologie; géologie de
|Programme||adaptation et impacts sur l'environnement, environnement du nord, Géosciences environnementales|
|Résumé||(disponible en anglais seulement)|
The bioavailability of potentially toxic trace elements, such as As, Cd, Co, Cr, Cu, Hg, Ni, and Pb, is strongly related to their mineral chemistry and
oxidation state in the environment. Environmental assessments of future mine sites in the North require knowledge of the conditions under which trace metals released during the oxidation of sulfides are subsequently concentrated and contained in
permafrost, or dissolved in fluids and released from it. Previous investigations of base metal gossans in arctic regions suggested a complex acid rock generation process in which freeze-thaw cycles promote the chemical weathering of sulfide-rich
rocks accompanied by the production of reactive gossanous soil.
We report the results of a collaborative activity based on the following scientific hypothesis: Arctic gossans constitute analogues of how mine waste would behave in a permafrost
environment. The objectives of the activity in Years 1 and 2 were to: (1) locate gossans in central Victoria Island using satellite imagery; (2) measure the spectral signatures of surficial materials at key locations to improve the accuracy of remote
predictive maps; (3) carry out detailed mapping and sampling of surface materials of alteration zones in permafrost to characterize them; (4) determine the stratigraphy, mineralogy, and geochemistry of deposits to document facies and determine their
origin. Our results show that remote predictive mapping of oxide-sulphide gossans is best achieved using a combination of Landsat-7 and Worldview-2 images; and that the results obtained from in situ surface spectral analyses are robust, and validate
the remote predictive maps. The mineralogy of gossans at two different localities on Victoria Island consists predominantly of gypsum, jarosite and goethite, implying an important role for sulfate-evaporite rocks of the Kilian Formation in the
genesis of these deposits. In addition, frozen pore waters in gossan pyrite sands at one locality are extremely acidic, with a pH of 2, confirming our working hypothesis that the gossans constitute analogues of mine waste in permafrost, and provide
natural laboratories for the study of oxidation reactions, their environmental impact, and remediation. Finally, the long-term persistence of pyrite encased within the acidic permafrost indicates that oxidation and dissolution reactions are very slow
in permafrost environments. These conditions require close attention and further study as global temperatures rise and affect the depth of the active layer in permafrost at northern latitudes.