Capture and characterization of fugitive mine dust around an open pit gold mine in Québec, Canada

Abstract

Monitoring and managing dust (i.e., particulate emissions) remains a ubiquitous challenge to the mining industry resulting in outstanding questions regarding the nature and spatial-temporal distribution of fugitive dust emissions to the near-mine environment. In this study, fugitive dust samples were captured up to 1 km from the mine perimeter over a ∼2-year study period using passive dry deposition samplers (PAS-DD) deployed around an active open-pit gold mine in Northwestern Québec, Canada. This study demonstrates the utility of the recently developed PAS-DD for long-term (84–285 days) dust sampling under a wide-range of weather conditions (−37 to 32 °C), allowing for measurement of the mine-dust footprint, the flux of dust-transported metal to the near-mine environment, and the micro-characterization of dust including its mineralogy. The results show that net dust deposition is highest near mine operations occurring near the open pit and the mine-access road, and that dust deposition reaches reference-site levels between 200 and 1000 m from the mine perimeter. Captured dust comprised 87–99 vol% silicates (primarily chlorite, quartz, muscovite, plagioclase, and amphibole), 1–9 vol% carbonates (calcite, ankerite, and dolomite), and <2 vol% sulfides (pyrite, pyrrhotite, sphalerite and arsenopyrite). Trace amounts (<0.2 vol%) of arsenopyrite in the dust is primarily responsible for the atmospheric deposition of As to the near-mine environment. The highest flux of As to the near-mine environment (<0.003 mg/dm²day) was recorded by samplers north of the open pit and mine access road, where net dust deposition is highest. In contrast, south of the mine dust has much lower net deposition rates (comparable to reference site levels), but delivers a higher concentration of As to the environment, resulting in As deposition rates up to 0.001 mg/dm²day (∼300x reference site levels). Dust captured south of the mine was enriched in arsenopyrite and is interpreted to reflect increased particulate input from the adjacent tailings storage area. The higher concentration of As in dusts reaching the southern near-mine environment correlates with As-enrichment in the organic layer of soils characterized in an earlier study. Overall, this study demonstrates how the geochemical and mineralogical characterization of dust captured by PAS-DD can be used to understand the role of fugitive mine dust in the transport of environmental contaminants to the near-mine environment.