Disruption of the geochemical metal cycle during mining: Multiple isotope studies of lake sediments from Schefferville, subarctic Québec

• Published in: Chemical Geology
• Main Authors: Aebischer, Stéphane, Cloquet, Christophe, Carignan, Jean, Maurice, Charles, Pienitz, Reinhard
• Other Authors: Takuvik Joint International Laboratory ULAVAL-CNRS, Université Laval Québec (ULaval)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Paléoécologie Aquatique CEN - Laval, Centre d'Etudes Nordiques (CEN), Université Laval Québec (ULaval)-Université Laval Québec (ULaval), Centre de Recherches Pétrographiques et Géochimiques (CRPG), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Lorraine (UL)-Centre National de la Recherche Scientifique (CNRS), Bureau de la connaissance géoscientifique du Québec, Ministère de l’Énergie et des Ressources naturelles
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2015
• Subjects: Isotopes; Geochemistry; Mining; Environmental changes; Lake sediments; Schefferville; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Subarctic
• Online Access: https://hal.univ-lorraine.fr/hal-01769718; https://doi.org/10.1016/j.chemgeo.2015.07.028

International audience Iron mining in Schefferville (1939–1977) in subarctic Quebec has left behind large numbers and quantities of tailing deposits. The impact of past mining activity on aquatic ecosystems in the Schefferville area has been studied using geochemical and isotopic (Pb, Zn and Fe) analyses of lake sediments, ore deposits, tailings and epiphytic lichens. Analysis of two sediment cores from Lakes Dauriat and Oksana reveals that the surface geochemical cycle of the Schefferville area has been profoundly disturbed by anthropogenic activity such as mining. Disturbances were particularly abrupt at the transitions from pre-mining to mining and mining to post-mining periods.Elemental and isotopic analyses of the lake sediments reveal four different end-member contributions to the lake sedimentation, with changes in terms of sources and source contribution observed throughout the sedimentation history. End-members were identified using Pb, Zn and Fe isotopes and are consistent for each element. Lead isotope ratios vary from highly radiogenic (206Pb/204Pb = 27) to less radiogenic (206Pb/204Pb = 17.7) from the bottom to the top of the sediment cores. Iron isotope compositions vary from − 0.2‰ to 1‰, the latter value remaining constant throughout the sedimentary history of Lake Oksana. A systematic difference in the Zn isotope ratios of the two lakes is also observed, and can be explained by local differences in basin lithology. In order to identify pollution sources, samples from ores and tailings and epiphytic lichens were measured as proxies of mining activity, lithology, and atmospheric deposition, respectively.The impact of anthropogenic activity is clearly evident in the sediment records and results from mining activity, as well as local urban and industrial activities (waste water inputs). Long-range atmospheric deposition also accounts for some of the variations in isotopic composition measured in the sediments. The systematic coupling of Pb isotopes with Zn or Fe isotopes allows us to identify and ...