Abstract:

Mining sites, comprising rock walls in open pit or underground mines, tailings dams, waste-rock dumps, and ore stockpiles, pose a risk of uranium mobilization through the weathering of uranium-bearing minerals. The discharge of water containing high uranium concentrations from mine sites into environmental recipients is concerning due to uranium’s chemical toxicity (Kurttio et al., 2002, 2005; Seldén et al., 2009) and radioactivity (Radespiel-Tröger & Meyer, 2013; Wagner et al., 2011).

This study investigated the sources of elevated uranium concentrations in mine water, pumped from an open-pit iron ore mine site in Northern Sweden. The elevated uranium concentrations in the mine water result from two main sources: uranium released through the chemical and physical weathering of uranium-bearing minerals in the open pit walls and uranium present in groundwater. The groundwater has the potential to leach out uranium-bearing minerals along its flow path before it permeates into the open pit through pore spaces and fractures.

Minewall weathering stations were installed on major rock types in the open pit to identify rock types that can potentially leach out high amounts of uranium. The uranium leaching rate was highest from pegmatite compared to other rock types potentially due to a prevalent uraninite-pyrite association observed during mineral characterization. Drainage pipes installed at different locations in the open pit for pit slope stability were sampled to assess the groundwater contribution. We identified different areas in the open pit with varying groundwater uranium concentrations, suggesting that it might be possible to pinpoint uranium inflow hotspots.

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Mr. Torbjörn Karlsson