Copper-ore mining in Sweden since the pre-Roman Iron Age: lake-sediment evidence of human activities at the Garpenberg ore field since 375Â BCE.

Historical documents, archaeological evidence and lake-sediment records indicate thus far that significant mining of iron and copper ores in the Berglsagen mining region in central Sweden did not begin until the late 12th century - first with iron in Norberg - and thereafter spreading rapidly throughout the region during the 13th century when also copper was included (e.g. Falun). Prior to this, iron was produced domestically from secondary sources such as bog iron, while geochemical analyses of bronze artefacts indicate copper was imported. The parish of Garpenberg was at the intersection between historical iron- and copper-mining districts, and consequently we expected our sediment record from the lake Gruvsjön ('mine lake') to follow the established 13th century development. However, a 2-3-fold enrichment in copper and lead occurred already during 375-175 BCE (pre-Roman Iron Age), together with small increases in zinc, magnesium and charcoal particles, and changes in pollen. Together these indicate a clear pattern of human disturbance connected with the ore body bordering the lake. A second distinct phase occurred 115-275 CE, but with an 8-9-fold increase in copper and lead along with other indicators. From 400 CE a permanent increase in copper and lead occurred, which then accelerated from the 13th century as seen elsewhere in the region. Our results push back the evidence for early ore mining in Sweden from the Middle Ages to the pre-Roman Iron Age.