Fugitive dust from exposed tailings at an inactive gold mine in Québec, Canada, using the Pas-DD dust capture method

Abstract

Fugitive mine dust (i.e., particulate emissions) is a ubiquitous waste stream at all mine sites, including active, inactive, and abandoned. Although dust emissions can reasonably be expected to diminish after the cessation of mining activities, any waste products left uncovered have the potential to continue to emit dust to the near-mine environment. In this study, we capture and characterize dust using the Pas-DD dustfall method around the inactive gold-mine site of Joutel in the Abitibi-Témiscamingue region of Québec. The site has been inactive for 30 years, during which time the tailings storage area has been left mostly uncovered, with previously unknown amounts of dust entering the near-mine environment. The quantity of dust captured by our samplers was generally low and did not exceed 0.5 mg/dm²day. Areas of the bottom ∼2 mm of the polyurethane foam (PUF) disks used as a sampling substrate in the Pas-DD method partially degraded following deployment for 284–285 days in the field, resulting in a mass loss of up to 0.57 mg/dm²day. The low dust deposition rates and variable amounts of PUF degradation precluded net mass flux of the PUF disks providing meaningful insight into spatial variability of dust deposition. In contrast, element deposition rates and quantitative mineralogy of the dust are not impacted by PUF degradation and were the most useful datasets in this low-dust setting, allowing us to distinguish background environmental dust from local anthropogenic dust sources, including the tailings as well as other activities in the area. The major (average > 5 vol%) minerals in the dust are: muscovite (21 ± 6 vol%), quartz (22 ± 16 vol%), feldspars (18 ± 4 vol%), chlorite (13 ± 3 vol%), and olivine or serpentine (5 ± 3 vol%). All of these minerals except olivine or serpentine were also common in the tailings, in similar abundance except for reduced muscovite (3.9 ± 0.6 vol% muscovite, 27 ± 7 vol% quartz, 19 ± 3 vol% feldspars, 10 ± 5 vol% chlorite). The tailings also had iron (hydr)oxides (21 ± 8 vol%) and sometimes pyrite (14 ± 19 vol%) as major minerals. The minerals that were identified as being derived mainly from the tailings site are iron (hydr)oxides, ankerite, and pyrite whereas olivine or serpentine, amphibole, calcite, and dolomite originate primarily from the background Abitibi Greenstone Belt environment. Dust with the highest proportion of tailings-sourced minerals was captured downwind of the site and decreased in abundance with distance, pointing to wind as the primary control on dust dispersion from the tailings, with other activity in the forest near the site or along the roads producing discreet dust-generating events. The captured dust contained distinctly less Fe and As than the tailings, reflecting the much lower proportion of iron (hydr)oxides and pyrite in the dust compared to the tailings. Differences in the relative proportion of minerals in the dust compared to the tailings reflect the preferential mobilization of minerals with lower density and flaky mineral habits. Overall, this study demonstrates the utility of the Pas-DD dust monitoring method in a low-dust setting and the central role that the physical properties of minerals play in the resulting dust composition.