Copper Smelting

Since the 1990s, archaeological investigations of prehistoric copper mines have been conducted in the famous mining district of Schwaz/Brixlegg in the Lower Inn Valley, North Tyrol (Austria). A large number of sites (mainly from the Late Bronze Age and up to the Early Iron Age) have been investigated so far with the aim to record and to analyse this extraordinary prehistoric mining landscape. A focal point of research is the reconstruction of the process chain connected to the prehistoric copper production comprising ore mining, beneficiation, and smelting processes. This paper discusses the final step of metal production, the smelting of copper ores. Whereas dozens of prehistoric mines and several sites with traces of mechanical ore treatment have been examined in the last years, only two smelting sites from the period under consideration are known so far. One of these sites, the smelting site Rotholz (municipality of Buch in Tyrol), could be prospected by geophysical methods (geomagnetic) and partly excavated during several campaigns in 2010 and 2015-2017. A detailed documentation of the archaeological remains could be performed in the frame of the DACH-project “Prehistoric copper production in the eastern and central Alps - technical, social and economic dynamics in space and time” (supported by the Austrian Science Fund FWF, the German research foundation DFG and the Swiss National Research Foundation SNF, 2015-2018). The Rotholz smelting site dates into the 12th/11th cent. BC (Late Bronze Age, Urnfield culture, dated by 14C-analysis). The basic raw material used for the local copper production were fahlores which occur in considerable quantities in the Devonian dolomitic hostrock (Schwazer Dolomit). As a result of the excavations a multiphase roasting bed, a battery of four furnaces, a slag heap (crushed slag, slag sand) and many other informative structures could be uncovered and documented. The findings (ceramic, slags, ores, stone tools, animal bones,…) have been furnished to archaeological and archaeometrical analysis.

The project from which the data derived aimed to establish the first systematic study of Cu isotope fractionation during the prehistoric smelting and refining process. For this reason, an experimental approach was used to smelt sulfide copper ore according to reconstructed prehistoric smelting models. The ore was collected by E. Hanning as part of her PhD thesis work from a Bronze Age mining site, the Mitterberg region, Austria (Hanning and Pils 2011) and was made available for the experiments.

All starting materials for the experiments such as the natural ore, roasted ore, construction clay, flux, dung (used for the roasting), wood and charcoal (fuel) were natural materials. All firing conditions including the amount of fuel or charging material and the temperatures in the furnaces were recorded, and the experimental procedures were documented in the very detail. In total, 30 experiments were carried out in 4 experimental series. The smelting products, both intermediate products and final products were sampled during or after the respective experiment. Slag, matte and copper metal were the major smelting products. All other materials used in and produced by the experiments were sampled, too. Materials used and produced in the two most promising experimental series with regard to potential Cu isotope fractionation were analyzed. Based on the analytical results, the potential of Cu isotopes as a tool in archaeometallurgical research was systematically evaluated and consequences for the copper isotope application as a provenance tool in archaeometry were identified.

The data include the documentation of the experiments, laboratory procedures and analytical methods. An experimental outline was previously published in Rose et al. (2019). Analytical methods applied were ICP-MS (elemental analysis, 80 samples), MC-ICP-MS (copper isotopes, 98 samples), and XRD (phase analysis, 25 samples). The experiments were carried out at the Römisch-Germanisches Zentralmuseum, Labor für Experimentelle Archäologie, Mayen, Germany. Laboratories used for the analytical part of the project were the research laboratories at the Deutsches Bergbau-Museum Bochum and FIERCE (Frankfurt Isotope and Element Research Center), Goethe-University Frankfurt, both Germany. Data were processed and plots created with R (R Core Team 2019) in RStudio®. Data are provided as data tables or text files, the R scripts used to create the time-temperature plots of the smelting experiments are also included.

The annual panel UK-Gespräche – “Get Together” will in this year focus on the metallurgy of the Middle and Late Bronze Age in the area of the Urnfield Culture and contemporary cultural phenomena in Europe. Starting from the ongoing project “Bronze Age metallurgy in western and central Balkans“ of the host institute OREA in cooperation with the Institute for Archaeological Science (VIAS) of the University Vienna, the aim of the workshop is to pool experts working on different aspects of copper mining and copper metallurgy, including ore processing, casting, distribution of raw metals and ingots as well as use and function of the metal objects. A special interest lies on the social and environmental impact of metallurgical activities. Furthermore the establishment of relations between Bronze Age communities based on the exchange of raw material and metal products is in the focus.

The program of the workshop will include a wide range of regional studies as well as region-spanning contributions dealing with specific topics. The final objective is to gain a better understanding of the technological and social processes that led to the interweaving of the metallurgical know-how across the different Urnfield Culture societies in Europe.
The event is free, but space is limited. For more information and to register, please contact mario.gavranovic@oeaw.ac.at or mathias.mehofer@univie.ac.at

see:
https://www.orea.oeaw.ac.at/veranstaltungen/event-detail/article/uk-gespraeche-bronze-age-metallurgy/