The geochemical dynamics of mine tailings at Laver and Stekenjokk, Northern Sweden

Sammanfattning: This thesis presents geochemical studies of tailings and waters sampled at two closed mines; the Laver mine in Norrbotten where the tailings have not been remediated, and the Stekenjokk mine in Västerbotten where the tailings have been flooded. Oxidation of sulfide minerals in the tailings at Laver has led to the development of a distinct chemical zonation with an oxidised zone above the unoxidised tailings. Metals released from oxidation and weathering of sulfide minerals are retained within the tailings impoundment. This retention mechanism is today very efficient and only 5-10 % of the released masses of metals reaches the surface water system. Areas of the tailings deposit with shallow groundwater table are at present the main source of metal release. The water column of the water cover at Stekenjokk was sampled four times at various stations. The pond water contains higher concentrations of Ca, S (as sulfate), Cd and Zn than local background. The flow of Ca, S, Cd and Zn to the water column from the pore water of the tailings is an effect of both in-situ oxidation and buffering in the uppermost part of the tailings, and the fact that some parts of the tailings material were oxidised prior to the remediation with water cover. Resuspension of sulfides from the tailings surface itself is insignificant. Flooding as remediation method works well at Stekenjokk.