Water quality in the Björkdal gold mine recipient, northern Sweden

Abstract: The Björkdal mine is the largest operating gold mine in the Skellefte
district, Northern Sweden. One important objective of this study was to give
a general description of dissolved and particulate metals (As, Cd, Co, Cr,
Cu, Hg, Mo, Ni, Pb, V, Zn, Al) and sulfate in the Lillträskbäcken-Kågeälven
system. Samples were collected from streams and tailings and compared to
concentrations according to the Swedish EPA classification systems. Chemical
analyses and leaching tests indicate that the tailings metal content is
generally low, except for Cr, and tailings can be approved as suitable for
construction purposes. This study shows general seasonal trends in element
concentrations, pH and conductivity downstream of the mine. Metal
concentrations increase during spring melt and periods of rainfall, and
decrease during summer. In general, element concentrations decrease
downstream of the mine property. To define background metal concentrations
upstream of the Björkdal mine a new sampling station (St D) was created. Most
of the metals in the discharge waters from the mining area are close to or do
not exceed background levels, except for Mo, V and As, that fairly often
exceed background levels at different sampling locations. Metal partitioning
between suspended and dissolved phases was estimated. The result shows that
close to the mine most elements dominate in the suspended phase, while the
dissolved phase of As, Ni, V and Mo dominates at some stations. Element
concentrations in the Björkdal area were compared with those in drainage
waters from acid sulfate soils. The result shows that natural occurrences of
acid sulfate soils can result in metal concentrations equal to or higher than
those in the Björkdal area.