Geochemical baseline study of gold mineralization in theBarsele Area, North Sweden

Abstract: Two lake sediment cores and 10 lake water samples were sampled at differentdepths to assess trace metal content and water quality prior to thepossibility of mining two orogenic gold deposits at Barsele, North Sweden.Existing regional water data sampled at different seasonal conditions wasprovided. Data from the Swedish Environmental Protection Agency (SEPA), theKalix River and Lake Kutsasjärvi were also used as reference data to quantify metal pollution and assess their possible impact on aquatic systems. Bedrock composition, location of ore body and existing assay data were equally reviewed.Till close to gold deposits has high As but low base metal enrichment.Streams B7and B4 interacting with the ore bodies and mineralized till has aneutral pH and a good buffering capacity due to the weathering of calciteveins associated with ore bodies. Arsenic (18.2µg/l, SEPA class 4, Stream B7) is the most elevated in the drainage basin while Zn, Ni, Cu Hg, Mo, Cd and Pb in all surface waters are within the tolerance limit (SEPA class 1or2). Sorption onto Fe- oxy hydroxides in addition to a near neutral pH seems to limit greatly the mobility of heavy metals but less on the mobility of As due to its ability to form mobile complex anions. Lake water has a relatively low metal content due to its neutral pH and its near stable oxygen concentration. Arsenic (SEPA class 4) is particularly enriched in lake sediments, in association with precipitation of Fe-oxyhdroxide. Copper and Ni are equally elevated in lake sediments. Generally, metal enrichment in lake sediment is higher at sampling station A compared to station B and reflects variations in redox processes and the recycling of Fe-Mn. Although lake water and mineralized streams have a good buffering capacity, their metal content could be upgraded once mining begins because large volumes of rocks will be exposed to weathering. Thus, adequate measures should be taken to dispose waste rocks and monitor water chemistry.