Very little is known about the environmental mobility of many critical metals, particularly how they are leached from primary host minerals, mobilized under different conditions of pH and redox, and potentially sequestered in secondary phases. We have conducted field and laboratory studies of weathered wastes from operating or formerly operating Canadian mines to study mineral-water interaction of rare earth elements (REEs), antimony (Sb), tungsten (W), and cobalt (Co). For REE, concentrations are expected to increase substantially as pH decreases in water associated with mining activity. Antimony is mobile over a range of pH values but can be sequestered in secondary minerals, although their stability is variable. Tungsten is relatively mobile at alkaline pH values and is commonly sorbed to Fe-oxyhydroxide minerals at lower pH. Cobalt is leached relatively easily from mixtures of primary sulfide minerals and secondary weathering products in the presence of near-neutral water. In Canada, no mine effluent regulations currently exist for any of these elements and, for REE and W, there are no guidelines for either drinking water or ecological protection. Expertise from geochemists and toxicologists needs to be combined to guide future mine waste management at critical mineral mines.

The Yellowknife area was one of the most productive and profitable gold districts in Canadian history. The early years of operation were associated with large releases of mining waste to local water bodies that have resulted in an enduring environmental legacy in the region. Here, we compile, for the first time, archival information on the scale of impact to local waterbodies during the highest environmental emissions (1949–1956). More than 800 measurements of arsenic (As) concentrations from local waterbodies, ponded surface water, and domestic water sources were extracted from archived government documents during this period. The compilation of these data revealed extreme and widespread arsenic contamination of local waterbodies from mining operations with concentrations up to 47 000 µg L−1 As. The archived correspondence included documentation of public health effects revealing that local mining emissions were a public health risk during this period. Comparison of the archived water quality records with contemporary data for the same lakes indicated widespread reductions of lake water arsenic concentrations across the region over half a century. These data provide evidence of the extent of historical environmental impacts of mining on Indigenous territory and of government and industry failure to stop emissions when faced with evidence that local mines were causing environmental pollution and risks to public health. By bringing these data to light, it is hoped that this information will support reconciliation efforts between the federal and territorial governments and local Indigenous Peoples.

The environmental fate of antimony (Sb) in aquatic ecosystems has been less studied compared to other metal(loid)s released by mining. This study investigated Sb flux from lake sediments of Yellowknife Bay (Great Slave Lake, Northwest Territories, Canada), which were contaminated by gold mining operations. Sediment Sb fluxes were measured in the field by short term (2-6 day) incubations of intact sediment cores and in the laboratory by incubating bulk sediment over a longer 30-day period. Antimony diffusion from sediment to overlying water was observed in 17 of 28 intact cores (61%), with flux rates ranging from 10 to 279 mu g/m(2)/day. Overlying water and surface sediment remained oxic during the field measurements. Sediment Sb concentration (0.7-47 mu g/g) was positively correlated with Sb flux, and the mineralogy of the sediment, characterized in a companion study, likely influenced flux spatial patterns. Other environmental factors, specifically season, temperature, organic matter content, and iron or manganese concentrations of sediment did not explain Sb flux. Porewater Sb concentrations were low (0.2-9.6 mu g/L), and porewater depth profiles were not related to solid-phase Sb concentration, suggesting limited post-depositional mobility within sediments. Laboratory incubation of mixed bulk sediments showed higher Sb fluxes of 185-1555 mu g/m(2)/day over the course of a 30-day experiment. Temperature warming from 7 to 22 degrees C did not enhance the Sb flux. Higher Sb fluxes in the laboratory versus field measurements may have been due to (i) more Sb in the laboratory sediments (similar to 160 mu g/g), and (ii) oxidative dissolution of stibnite and Sb sulfosalt minerals that were previously stable in deeper anoxic sediments but disturbed and exposed to oxygen during laboratory manipulation. This study demonstrated that Sb can diffuse from mining-contaminated sediments into overlying water under oxic conditions, with fluxes influenced by sediment Sb concentrations and mineralogy.

Soils in the Yellowknife region were contaminated with arsenic by >50 years of atmospheric mining emissions from ore roasting operations. Persistent community concern regarding contamination of local garden soils prompted this investigation. One hundred and fifteen soil samples were collected from 110 resident gardens and were analysed by inductively coupled plasma mass spectrometry for elemental analysis. Arsenic concentrations were below local remediation soil quality guidelines for residential areas (160 mg kg-1) in all soil samples, but 62 % of samples exceeded national Canadian soil quality guidelines (12 mg kg-1) for the protection of environmental and human health. Ten samples, with relatively high arsenic concentrations, were analysed by scanning electron microscope with automated mineralogy to identify solid phase arsenic hosts; four samples were further analysed by synchrotron-based microanalysis to identify crystal structure of target mineral grains. The predominant mineral host of arsenic in the garden soils was identified as arsenopyrite, which could be geogenic, anthropogenic (e.g., repurposed mine waste), or both. Arsenic trioxide from ore roaster stack emissions was identified in five garden soils mineralogically analysed. Arsenic-bearing iron oxides were detected in nine of the soils mineralogically analysed; in three of these soils, roaster-generated iron oxides generated by ore roasting were identified. Garden soil arsenic concentrations (14 mg kg-1 median) were substantially lower than values determined by a previous study for undisturbed, Public Health Layer soils in the region (390 mg kg-1 median); likely, mixing of surface soils with soil beneath, and use of purchased soils in gardening has dispersed the surficial arsenic enrichment consequent of ore roasting.

This study investigates the controls on metal(loid) mobility from mine tailings and pond sediments near Cobalt, Ontario with a focus on arsenic (As), which is present at high concentrations throughout this former mining district. Mineralogical and geochemical analyses were performed on tailings from four abandoned mill sites and nearby pond sediments. The mass of readily soluble metal(loid)s in the tailings and sediments was evaluated using shake flask experiments. Horsetails (Equisetum spp.) growing on these tailings were collected for chemical characterization, backscattered electron imaging, and synchrotron-based chemical analysis. Results indicate that mineralogical hosts of As vary between depositional environments. Authigenic, oxidized phases (e.g., erythrite and an iron- and calcium-bearing arsenate) sequester As in near-surface environments. Ore minerals (e.g., cobaltite and safflorite) and authigenic reduced phases (e.g., realgar) host As in submerged tailings and anoxic pond sediments. Short-term exposure of tailings and sediments to oxidized, ultrapure water releases As from the ore minerals and reduced phases (1.31-325 mg L-1 As; median = 19.1 mg L-1 As). Horsetails growing on these tailings sequester As via formation of an oxidized iron-bearing plaque on the outside of the plant roots and shoots. This study demonstrates that As mobility in mine-impacted environments is controlled by geochemical reactions, mineral dissolution and precipitation, and vegetation growth. These processes must be considered when developing long-term management decisions for legacy mine sites.

Historical mine tailings in the Cobalt Mining Camp in northern Ontario are both a source of environmental contamination and a potential resource of critical metals. Widespread mining in the Cobalt area during the 20th century resulted in dozens of unremediated mine sites and at least 18 unconfined tailings deposits, which contain potentially hazardous metals and metalloids, including arsenic (As). Economic metals, including cobalt (Co), also occur in the waste and could be recovered. Geochemical and mineralogical analyses of tailings and pond sediments were performed to assess the mobility of Co and other metal(loid)s in different depositional environments and implications for reprocessing of the mine wastes. Tailings from four sites and benthic sediments from a pond impacted by tailings were characterized using ICPES/MS, various mineralogical techniques, and shake flask experiments. Cobalt concentrations in the tailings and sediments (96.8-8900 mg kg- 1 Co; median = 470 mg kg- 1) exceed Canadian environmental quality guidelines for residential soils (50 mg kg- 1 Co) at all sample sites. Mineralogical investigations reveal that Co is hosted in oxidized alteration phases in near-surface tailings along with primary sulfide and arsenide minerals, which persist in this environment. In submerged tailings, Co is contained mainly within primary sulfide and arsenide minerals and reduced secondary phases. Cobalt-bearing chlorite is a major host of Co in half of the tailings samples, containing up to 50 wt% of the total Co content; the presence of Co-bearing chlorite may impact potential recovery of Co from the tailings in the future. The mineralogy of the benthic pond sediments is heterogeneous; however, Co is sequestered in both primary sulfide and arsenide minerals and authigenic reduced phases such as Co-bearing sulfide. The results of shake flask experiments reveal that Co in the tailings and sediments dissolves in deionized water under oxidizing conditions. The concentration of Co in the leachate (30-126,000 mu g L- 1 Co) consistently exceeds Canadian water quality guidelines for Co (1 mu g L- 1). The results of this study provide new insight about the controls on metal(loid) mobility, including the processes which impact metal(loid) cycling in reduced pond sediments and the occurrence of Co-bearing chlorite in the tailings. In addition to characterizing the risks associated with mine waste contamination and informing long-term waste management decisions, the results of this study may be applied to understand the potential for future Co recovery from mine waste and sediments in the Cobalt area.

With climate change, conditions for dust generation are expected to be more prevalent. A potential dust source of concern are mine wastes due to the likelihood of potentially toxic elements which pose a human health risk if ingested or inhaled. This study analysed sieved mine tailings from a legacy mine in Nova Scotia, Canada. The aim of the research was to analyse total concentrations of Cu and Pb in tailings samples sieved to represent dust; to determine gastric bioaccessibility of Cu and Pb in these samples; and to analyse the impact of mineralogy on Cu and Pb bioaccessibility. Mineralogy was determined with a scanning electron microscope and automated mineralogy software. Tailings were sampled from an uncovered, subaerial, tailings impoundment. Copper bioaccessibility had a strong positive correlation with carbonate and oxide copper hosts. Lead bioaccessibility had a strong positive correlation to one oxidation product, cerussite (lead carbonate). Lead was predominantly hosted in cerussite and had greater bioaccessibility than copper which was predominantly hosted in chalcopyrite. The results highlight the increased human-health risk posed by subaerial tailings at an abandoned mine.

A holistic understanding of the chemical recovery of lakes from arsenic (As) pollution requires consideration of within-lake biogeochemical cycling of As and processes occurring in the surrounding catchment. This study used a watershed mass balance approach, complemented by experimental sediment incubations, to assess the mobility and transport of As within a subarctic watershed (155 km 2 ) impacted by more than 60 years of atmospheric mining emissions. The period of record spanned a transition from drought to high streamflow between September 2017 and September 2019, which yielded insights into the interacting effects of hydrology and within-lake biogeochemical cycling of As. Internal loading of As from contaminated lake sediments (25 - 46 kg As year-1 ) and contributions from terrestrial sources (16 - 56 kg As yr- 1 ) continue to negatively impact lake water quality (19 - 144 mu g As L-1 ), but the relative importance of these loads varies seasonally and inter-annually in response to changing hydrological conditions. Wet conditions resulted in greater transport of As from terrestrial reservoirs and upstream areas, shorter lake water retention time, and increased the downstream export of As. During dry periods, the lake was disconnected from the surrounding watershed resulting in limited terrestrial contributions and longer lake water residence time, which delayed recovery due to the greater relative influence of internal loading from contaminated sediments. This study highlights that changing hydroclimatic regimes will alter trajectories of chemical recovery for arsenic impacted lakes through the coupling of within-lake and watershed transport processes.

Here, we present As K-edge X-ray absorption spectroscopy (XAS) data for 28 arsenic minerals and compounds. These minerals and compounds were obtained from mineral dealers, museum collections, and chemical suppliers, and were positively identified by synchrotron-based powder X-ray diffraction (XRD). All samples were analyzed for both XRD and XAS at the Canadian Light Source synchrotron (Saskatoon, Canada). The As K-edge XAS data were collected in both transmission and fluorescence modes and cover the extended X-ray absorption fine structure (EXAFS) region. Raw XAS data in both modes are provided to support XAS analysis obtained for geological or environmental research. Furthermore, As K-edge EXAFS spectra, the k3 weighted oscillatory χ(k) functions, and the Fourier-transforms in χ(R) of these K-edge data are processed and presented graphically. Corresponding XRD data was collected to confirm phase identity. Two-dimensional powder diffraction images were collected against an area detector and integrated to produce line scans. The XRD data were either collected at a wavelength of 0.68866 Å (18 keV) or 0.3497 Å (35.45 keV). Raw, tabulated asc files are available, while the patterns are also presented graphically over a 0-40 °2Θ range or 0-26.5 °2Θ range, respectively. The intent of this dataset is to provide reference XAS spectra to researchers conducting environmental or geological research on As.

The leaching kinetics of tungsten in scheelite tailings in sodium carbonate solutions at low temperatures (25-75 & DEG;C) were found to closely follow the predicted values based on the shrinking core model (SCM), originally developed at elevated temperatures (150-190 & DEG;C). Temperature demonstrated a profound positive effect on the leaching kinetics of scheelite. The apparent rate constants, k values, determined from leaching the scheelite tailings at low temperatures, were found to be a few orders of magnitude lower than those obtained at elevated temperatures (i.e. & SIM; 10-7 vs. 10-4 s-1). The time required to extract over 90% of tungsten was estimated to be 15 days at 75 & DEG;C, in contrast to 2 h at 200 & DEG;C. The experimental kinetic data from leaching the scheelite tailings were found to consistently outperform the kinetic model prediction, by as much as 70% and 400% at 50 and 25 & DEG;C, respectively. As observed at elevated temperatures, an increase in sodium carbonate concentration or agitation speed had little effect on the leaching kinetics at low temperatures. This study demonstrated the potential use of sodium carbonate solutions as a non-aggressive lixiviant in a percolation or dump leach operation, which could be considered as an environmentally viable reprocessing option for scheelite tailings. Il a ete constate que la cinetique de lixiviation du tungstene des residus de scheelite dans des solutions de carbonate de sodium a basse temperature (25-75 & DEG;C) suivait de pres les valeurs predites basees sur le modele a c & OELIG;ur retrecissant (SCM), originellement developpe a des temperatures elevees (150-190 & DEG;C). La temperature a demontre un effet positif profond sur la cinetique de lixiviation de la scheelite. Les constantes cinetiques apparentes, valeurs k, determinees a partir de la lixiviation des residus de scheelite a basse temperature, se sont revelees etre de quelques ordres de grandeur inferieures a celles obtenues a des temperatures elevees (c.-a-d. & SIM;10-7 contre 10-4 s-1). Le temps requis pour extraire au-dela de 90% du tungstene a ete estime a 15 jours a 75 & DEG;C, contre 2 heures a 200 & DEG;C. On a trouve que les donnees cinetiques experimentales de la lixiviation des residus de scheelite surpassaient regulierement les predictions du modele cinetique, jusqu'a 70% et 400% a 50 et 25 & DEG;C, respectivement. Comme observe a des temperatures elevees, une augmentation de la concentration du carbonate de sodium ou de la vitesse d'agitation avait peu d'effet sur la cinetique de lixiviation a basse temperature. Cette etude a demontre l'utilisation potentielle de solutions de carbonate de sodium comme lixiviant non agressif dans une operation de percolation ou de lixiviation de decharge, ce qui pourrait etre considere comme option de retraitement ecologiquement viable pour les residus de scheelite.

We studied the occurrence of dissolved thiolated Arsenic (As) in legacy tailings systems in Ontario and Nova Scotia, Canada, and used aqueous and mineralogical speciation analyses to assess its governing geochemical controls. Surface-accessible and inundated tailings in Cobalt, Ontario, contained ∼1 wt-% As mainly hosted in secondary arsenate minerals (erythrite, yukonite, and others) and traces of primary sulfide minerals (cobaltite, gersdorffite and others). Significant fractions of thiolated As (up to 5.9 % of total dissolved As) were detected in aqueous porewater and surface water samples from these sites, comprising mostly monothioarsenate, and smaller amounts of di- and tri-thioarsenates as well as methylated thioarsenates. Tailings at the Goldenville and Montague sites in Nova Scotia contained less (<0.5 wt-%) As, hosted mostly in arsenopyrite and As-bearing pyrite, than the Cobalt sites, but exhibited higher proportions of dissolved thiolated As (up to 17.3 % of total dissolved As, mostly mono- and di-thioarsenate and traces of tri-thioarsenate). Dissolved thiolated As was most abundant in sub-oxic porewaters and inundated tailings samples across the studied sites, and its concentrations were strongly related to the prevailing redox conditions and porewater hydrochemistry, and to a lesser extent, the As-bearing mineralogy. Our novel results demonstrate that thiolated As species play an important role in the cycling of As in mine waste systems and surrounding environments, and should be considered in mine waste management strategies for high-As sites.

Arsenic contamination from mining poses an environmental challenge due to the mobility of this redox-sensitive element. This study evaluated arsenic mobility in sediments of Yellowknife Bay (Canada), a large subarctic water body impacted by gold mining during the 20th century. Short-term measurements of arsenic flux from sediment, arsenic profiling of the water column and sediment porewater, and mass balance modelling were conducted to assess the importance of sediment as an arsenic source. Sediment arsenic fluxes were highly variable throughout Yellowknife Bay and ranged from - 65-1520 µg m-2 day-1. Elevated fluxes measured near the mine site were among the highest published for well-oxygenated lakes. Redox boundaries were typically 2-3 cm below the sediment surface as indicated by porewater profiles of iron, manganese, and arsenic, with arsenic maxima of 65-3220 µg L-1 predominately as arsenite. Sediment arsenic flux was positively related to its solid-phase concentration. Modelling indicated sediment was a principal source of arsenic to the water column. Adsorption and precipitation processes in the oxidizing environment of near-surface sediments did not effectively attenuate arsenic remobilized from contaminated sediments. Internal recycling of legacy arsenic between sediment and surface water will impede a return to background conditions in Yellowknife Bay for decades.

The Cantung mine is a formerly operating tungsten mine located in western Northwest Territories. As part of the Northern Abandoned Mine Reclamation Program, the Canadian government is looking to remediate the property. This may include reprocessing the tailings to isolate potentially acid-generating sulphide minerals, mitigating any possible environmental liability to the nearby Flat River and its confluences. Cantung’s mineral processing operations produced three concentrates and one tailings product: a high-grade WO3 concentrate; medium grade WO3 concentrate; a copper concentrate; and sulphidic tailings. During periods of low copper prices, chalcopyrite was not recovered from the ore and was instead directed to tailings. Poor recovery from the scheelite gravity separation circuit combined with intermittent chalcopyrite flotation resulted in the tailings containing notable quantities of copper and tungsten, which could potentially be recovered during reprocessing to offset costs. Experimental work was completed on tailings samples collected from tailings pond #3, Cantung’s largest tailings impoundment. Ideal flotation conditions were determined to remove potential acid-generating minerals (mainly pyrrhotite) while also recovering residual valuable minerals, primarily chalcopyrite. A polish grind of the tailings sample prior to flotation was found to increase sulphide mineral recovery. Up to 86

Yellowknife Bay (Great Slave Lake, Northwest Territories, Canada) is a water body valued by surrounding communities for its subsistence, recreational, and cultural use. Located directly downstream of the former Giant Mine and Con Mine, Yellowknife Bay has received inputs from mine waste streams enriched in arsenic (As), antimony (Sb), and metals since the late 1930s. Lake sediments in Yellowknife Bay provide a record of metal(loid) contamination from aerially deposited roaster stack emissions, mine effluent, and Giant Mine tailings. A sediment sampling program was conducted in Yellowknife Bay to characterize As and Sb mineralogy using scanning electron microscopy-mineral liberation analysis. Mineralogical analysis of As- and Sb-hosted minerals in nine sediment cores suggests that arsenic trioxide (As2O3), originally deposited during the period of peak-mining emissions, has since been transformed into authigenic sulfides (interpreted to be realgar) down core from peak-mining emissions. Arsenic has also been attenuated by iron (Fe)-oxyhydroxides and roaster-generated iron oxides up-core from peak-mining emissions, near the sediment–water interface. The Sb-bearing minerals appear to be stable in Yellowknife Bay sediments, with no conclusive evidence of post-depositional mobility having been identified. The observed prevalence of arsenic trioxide in surface sediments proximal to Giant Mine suggests that As and Sb contamination is ongoing, likely from terrestrial weathering of contaminated soils and shoreline outcrops. Arsenic-bearing oxide minerals prevalent in surface sediments may become unstable should redox conditions in the hypolimnion change; prolonged anoxia could destabilize the As hosting minerals and release As to bottom waters. Therefore, long-term monitoring of the water column, including hypolimnion conditions, in Yellowknife Bay is recommended.

Other| July 29, 2023 Minerals from Mines to Mountaintops from Earth to Mars and BeyondPreface Roberta L. Flemming; Roberta L. Flemming Search for other works by this author on: GSW Google Scholar Lee A. Groat; Lee A. Groat Search for other works by this author on: GSW Google Scholar Bryan C. Chakoumakos; Bryan C. Chakoumakos Search for other works by this author on: GSW Google Scholar Heather E. Jamieson Heather E. Jamieson Search for other works by this author on: GSW Google Scholar Author and Article Information Roberta L. Flemming Lee A. Groat Bryan C. Chakoumakos Heather E. Jamieson Publisher: Mineralogical Association of Canada Received: 31 May 2023 Accepted: 31 May 2023 First Online: 29 Jul 2023 The Canadian Journal of Mineralogy and Petrology (2023) 61 (4): 651–652. https://doi.org/10.3749/INT014 Article history Received: 31 May 2023 Accepted: 31 May 2023 First Online: 29 Jul 2023 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Roberta L. Flemming, Lee A. Groat, Bryan C. Chakoumakos, Heather E. Jamieson; Minerals from Mines to Mountaintops from Earth to Mars and BeyondPreface. The Canadian Journal of Mineralogy and Petrology 2023;; 61 (4): 651–652. doi: https://doi.org/10.3749/INT014 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyThe Canadian Journal of Mineralogy and Petrology Search Advanced Search Ronald C. Peterson completed his Ph.D. in Geology with special emphasis in mineralogy at Virginia Tech in 1980. At that time, the Department of Geology had an exceptional group of mineralogy, crystallography, and petrology professors, including Donald Bloss, Gerry Gibbs, Paul Ribbe, James Craig, Charles Gilbert, David Wones, and others. Professor Gibbs worked closely with Professor Monte Boisen (Department of Mathematics) to develop and deliver an altogether new way of teaching mineralogy that was truly enlightening, making clear all of crystallography through an elegant and simple mathematical approach. This was so empowering that all the mineralogy and crystallography minded graduate... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Historical mining and mineral processing at the former Giant Mine (Yellowknife, NT, Canada) created an enduring legacy of arsenic (As) and antimony (Sb) contamination. Approximately 237,000 tonnes of arsenic trioxide roaster waste (ATRW) generated between 1948 and 1999 remains stored on-site in underground chambers. We studied the chemical forms and phase associations of As and Sb to improve understanding of ATRW environmental behavior. Although arsenolite [As2O3] is the principal As and Sb host, we also observed minor associations of As with Fe oxides. Arsenic K-edge X-ray absorption spectroscopy (XAS) revealed As(III) dominated ATRW, with some As(V) and As(-I) also present. Arsenic coordination and bonding is consistent with arsenolite, while scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) showed minor As association with Fe oxides and arsenopyrite [FeAsS]. Antimony K-edge XAS revealed variable proportions of Sb(III) and Sb(V), with Sb-O, Sb-Sb and Sb-As bonding consistent with stibioclaudetite [AsSbO3] or Sb-substituted arsenolite. Electron microprobe analysis (EMPA) results showed variable but quantitative Sb substitution for As in arsenolite grains, possibly influencing ATRW solubility and reactivity under environmental conditions. Overall, our results reveal complex As and Sb phase associations with important implications for ongoing remediation efforts and long-term environmental fate of ATRW solids.

This study compares select dust sampling apparatuses and monitoring methods by investigating fugitive tailings dust transport and deposition at an abandoned Zn-Pb-Cu mine located in eastern, Canada. The sampling apparatuses and monitoring methods are compared in terms of capturing seasonal trends and spatial extent, as well as the ability to evaluate impacts to aquatic ecosystems. Methods evaluated include satellite imagery, lichen tissue analysis, passive dry deposition collectors (Pas-DDs) with two different configurations, dust deposition gauges (DDGs) and a high volume total suspended particulate (Hi-Vol TSP) sampler. All methods utilized demonstrated benefits and challenges in relation to seasonal sampling and determining spatial extent of dust deposition. Results indicate that the polyurethane foam disk configuration of the Pas-DD sampler efficiently accumulates dust in comparison to the glass fiber filter configuration and DDGs which both likely underestimate dust deposition. Lichen and satellite imagery were shown to be effective tools for identifying areas of interest and extent of contamination. At the study site, it was observed that dust deposition was highest in the winter months and lowest in the summer months, likely due to increased erosion in winter weather conditions (higher wind speeds and/or freeze drying effect).

Arsenic (As) is commonly sequestered at the sediment–water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulfides. The results of this study demonstrate that the accumulation of organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories, Canada. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially derived OM (e.g., cutinite, funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulfide minerals (e.g., goethite, orpiment, lepidocrocite, and mackinawite); however, grain-scale synchrotron-based analysis shows that As is also associated with amorphous OM. Mixed As oxidation states in porewater (median = 62% As (V), 18% As (III); n = 20) and sediment (median = 80% As (-I) and (III), 20% As (V); n = 9) indicate the presence of variable redox conditions in the near-surface sediment and suggest that post-depositional remobilization of As has occurred. Detailed characterization of As-bearing OM at and below the SWI suggests that OM plays an important role in stabilizing redox-sensitive authigenic minerals and associated As. Based on these findings, it is expected that increased concentrations of labile OM will drive post-depositional surface enrichment of As in mining-impacted lakes and may increase or decrease As flux from sediments to overlying surface waters.

Arsenic (As) is commonly sequestered at the sediment-water interface (SWI) in mining-impacted lakes through adsorption and/or co-precipitation with authigenic iron (Fe)-(oxy)hydroxides or sulphides. The results of this study demonstrate that the accumulation of solid-phase organic matter (OM) in near-surface sediments also influences the mobility and fate of As in sub-Arctic lakes. Sediment gravity cores, sediment grab samples, and porewaters were collected from three lakes downstream of the former Tundra gold mine, Northwest Territories. Analysis of sediment using combined micro-X-ray fluorescence/diffraction, K-edge X-ray Absorption Near-Edge Structure (XANES), and organic petrography shows that As is associated with both aquatic (benthic and planktonic alginate) and terrestrially-derived OM (cutinite; funginite). Most As is hosted by fine-grained Fe-(oxy)hydroxides or sulphide minerals ( e.g., goethite, orpiment, lepidocrocite, mackinawite); however, grain-scale synchrotron-based analysis shows that As is also associated with amorphous OM. Mixed As oxidation states in porewater (median = 62 % As (V), 18 % As (III); n = 20) and sediment (median = 80 % As (-I) and (III), 19 % As (V); n = 9) indicate the presence of variable redox conditions in the near-surface sediment and suggest that post-depositional remobilization of As has occurred . Detailed characterization of As-bearing OM at and below the SWI suggests that OM plays an important role in stabilizing redox-sensitive authigenic minerals and associated As. Based on these findings, it is expected that increased concentrations of labile OM will drive post-depositional surface-enrichment of As in mining-impacted lakes and may increase or decrease As flux from sediments to overlying surface waters.