Late Holocene periods of copper mining in the Eisenerz Alps (Austria) deduced from calcareous lake deposits

Abstract

• Geochemical proxies indicate mining activity during the Bronze and Iron Ages. • Variations of δ 15N and δ 34S point towards lake catchment changes. • Pb enrichments in the calcareous deposits are not consistent with supra-regional amtospheric Pb peaks. Palynological studies and archaeological discoveries suggest repeated extensive prehistoric copper mining in the Eisenerz Alps (Styria, Austria). In an attempt to reconstruct the specific temporal evolution of copper (Cu) mining activity in this area from the Bronze Age to the medieval period, this article presents records of elemental variations, trace elemental enrichments of Cu, nickel (Ni), zinc (Zn), arsenic (As), cadmium (Cd), antimony (Sb) and lead (Pb) as well as light stable isotopes of nitrogen ( δ 15 N) and sulfur ( δ 34 S) as preserved in a calcareous sediment core retrieved from Lake Leopoldstein (Eisenerz). While the multi-element geochemical approach covers a time period from the Early Bronze Age to the mid-medieval period (2070 BCE – 850 CE), isotopic analyses were conducted up to a core depth of 660 cm, corresponding to about 3100 BCE. A comparative study of the parameters revealed strong indications of regional mining during the mid-Bronze Age (∼15th – 14th century BC), the Hallstatt period (∼8th – 6th century BC) and in the late La Tène period (∼3st century BC). Statistical evaluation of the data highlighted a good correlation of trace elements associated with local copper ores (fahlores, chalcopyrite). Enrichments of Pb, in contrast, are characterised by a more substantial deviation from the general trace element trend and are mainly linked to lithogenic input. Overall, the results of this study underscore the necessity of a broad-based multi-proxy approach in order to reconstruct periods of past mining activity based on the analysis of calcareous lake sediments. Especially, δ 15 N and δ 34 S revealed no particular potential for identifying past mining activity. However, both proxies were helpful for inferring erosional changes in the lake catchment, and thus for unraveling the interdependencies between geogenic and anthropogenic signals. Our study sheds new light on prehistoric copper mining in Central Europe.