In this post we present information extracted from two publications on the striking discovery of a huge Ore Trade Network from Cyprus to Scandinavia, and the reverse, during the Bronze Age.
A new and original Bronze Age culture, displaying a high level of technical and artistic mastery, emerged in Scandinavia about 1600BC (Kristiansen,1998; Vandkilde,1996). For instance, Scandinavia shows the highest amount of bronze swords in Europe dated to 1500-1300BC (mostly from barrows) and the Scandinavian hoard finds from the Late Bronze Age include numerous spectacular bronzes such as lures and shields (Harding, 2007; Kristiansen and Larsson, 2005). There are also lots of remains of crucibles and moulds from Bronze Ageworkshops in Scandinavia and some ingots of tin, copper and lead have also been found. These facts show that the metal was refined and alloyed in Scandinavia into finished objects, from about 1700BC and onwards (Hjärthner-Holdar, 1993; Oldeberg, 1942-1943). This sudden rise of the Nordic Bronze Age is an enigma that still lacks satisfactory economic and social explanatory models. Thus, a classic issue has been whether copper was imported to Scandinavia or mined locally.
Pb isotope geochemistry
A few theoretical aspects of lead isotope geochemistry may be recalled as an introduction to the section dealing with lead isotopes. In an archaeological approach the aim is to trace the source of lead in the artefact, i.e. use the lead isotopic signature of an artefact as a finger-print and match this with that of an appropriate ore, or ore district. For a bronze, a copper-tin alloy, it is most likely that two types of ores (Cu and Sn-bearing, respectively) have been used, and for geological reasons the lead component is assumed to be dominantly derived from the copper ore. This implies that conclusions drawn from lead isotope data typically involve a comparison between the isotope signatures of the artefacts and those of hypothetical copper ores which were mined in
pre-historic times.
Lead isotope signatures vary significantly between the ore provinces located adjacent to areas with bronze finds, which is due basically to large differences in ore formation ages. Such isotopic differences are favourable for pin-pointing the source of copper, and it is also fortunate that the “local” Swedish ores are generally much older than ores from continental Europe. The latter are normally of Phanerozoic age (i.e. around 500 million years old, or younger) and the implication is that ores occurring relatively close to the studied artefacts have strongly deviating lead isotope signatures from those characteristic for regions further south in Europe. This implies that the task of finding out if copper in the artefacts are made from Swedish or imported copper should be resolvable.
Description of the bronze objects
Priority has been given to artefacts that are considered to belong to the Nordic Bronze Age tradition (1700-500BC) (Baudou, 1960; Montelius, 1917, 1885; Sprockhoff, 1956; Vandkilde, 1996). Following this chronology, we have analysed 32 bronze items, dated between 1600BC and 700BC, and one artefact dated to Late Neolithic (LN). The analysed finds from three different, ore-bearing regions comprise e.g. material from bronze production and casting sites (sprues, melts, rods), which allow a direct comparison between bronze items and local Cu ores with respect to isotope and geochemical signatures.
Two samples are also included from the county of Västergötland; these are spatially related to samples from Dalsland, being found at the other side of Lake Vänern. To obtain a maximum chronological distribution and account for different functional aspect we have included various types of axes, swords and daggers of different kinds along with spearheads and fragments of shields, lures, sickles, armrings, and material from bronze casting.
Among the 33 studied artefacts 20 are derived from hoards and thirteen from stray find locations.
Analytical results – Element chemistry
The results from the elemental analyses of copper-based alloys show a compositional variation. Some general trends can be distinguished which form various groupings that may be compared to metal groups previously identified in other parts of Scandinavia and Europe. These are, at least to some extent, related to chronology, partly to geography and typology that to some extent also are mutually dependent. The following points summarise the overall results.
•One of the analysed artefacts, a dagger from Late Neolithic (LN), is copper with impurities. All the other artefacts are made of tin bronzes, varying from low tin (3%) to high tin (16%) bronzes. This variation is in part related to chronology
•The lead content is generally a few tenths of a percent, only occasionally reaching ca 1%. Accordingly, we can assume that no lead has been added to the alloys. Hence, the results from the lead isotope analyses are expected to successfully trace the relevant source of copper ore.
•The artefacts contain one or several elements at trace or impurity levels. Most objects have considerable amounts of one or several of arsenic, antimony, nickel and silver. A few artefacts have low concentration of iron and/or cobalt, whereas zinc in general is very low. The element ratios vary to such an extent that it is possible to distinguish groupings which may be identified as coming from different ore types or sources, most of which are sulphide ore sources and most prominently fahlores.
•Bronze compositions appear to show a complex relation to chronology. Tentatively, every single Bronze Age period has its own metal distribution pattern. Furthermore, within periods II and IV, the metal composition is quite homogeneous in the studied material. The opposite is true for the periods I and V.
•All analysed artefacts from the Bräckan scrap hoard in Dalsland (period IV), comprising items as well as casting debris, belong to a group with homogeneous metal characteristics. This is suggesting that the metalwas supplied from a single source. On the other hand, the personal hoard from Hjärpetan in Värmland (mainly period V), including a socketed axe, a sickle, a lure and a sword, has a far more heterogeneous metal composition implying several sources for the metal.
•The two Herzsprung shields (period V) from the county of Västergötland, are very similar in composition and can be distinguished from most other artefacts e.g. by their elevated content of cobalt.
Pb isotopes
•Although the artefacts display a considerable data range, it is obvious that the majority of published data from the local (and distal) ores plot far away from those of the artefacts. A few ore minerals plot in the same region as the artefacts and this merits some further attention.
•Artefact data tend to form different groups as defined by their chronological affiliation. This grouping is also, to some extent, illustrating geographical divisions as for instance all period IV artefacts are from Dalsland and almost all period V artefacts are finds from Värmland.
Discussion
Both the lead isotope and elemental analyses show that there are variations in metal supply related to chronology. The results also indicate that several ore types must have been processed during artefact production and that local ores were not used at all for producing the analysed artefacts.
From the trace element composition we can conclude that several ore sources are required to explain the variation in chemical signatures of artefacts. Furthermore, there is no strong chemical correlation between the artefacts and the hypothetically suggested local ore regions in Sweden and, importantly, more than one ore type is implied from the trace element pattern. Although certain chemical signatures are compatible with an origin from sulphide ores, like for instance chalcopyrite, the majority indicates that a particular type of sulphide ore, i.e. fahlore was used. In general, this ore type containing the combination of arsenic, antimony, silver and nickel is not present in the adjacent ore regions.
The discussed features allow us to conclude that although some of the artefacts with less characteristic elemental composition may be theoretically explained by local ores, the vast majority is not compatible with contemporaneous local ore production.
The trade routes for import of copper changed with time, and apparently copper was imported from different ore districts during discrete periods.
Conclusion
We are presenting analytical data for 33 bronze artefacts, ranging from the Late Neolithic to the Late Bronze Age from the copper ore bearing districts of Dalsland, Värmland and Småland, and none of these items matched the local ore signatures. This finding is consistent with previous analyses of bronze artefacts from Sweden (Kresten, 2005; Schwab et al., 2010). Moreover, there are no evident traces of Bronze Age copper mining from these districts, neither numerous finds of stone hammers nor prehistoric mines (Janzon,1984; cf. O’Brien, 2004). Another important fact to consider is that manufactured metal (typology) from a certain region should not automatically be equated with the use of ores from the same region (Chernykh, 1992; O’Brien, 2004). It is therefore important to stress that it could be vast distances between the different steps involved in the metallurgical “chaîne operatoire” (Ottaway, 2001): from ore extraction via refining, transport and exchange to local manufacture which will make the picture even more complex.
Thus, it is highly likely that copper was imported during the Bronze Age. From this follows that Sweden and Scandinavia took part in the complex maritime metal trade networks that existed in Europe in the Bronze Age where different sources of metal were dominating in certain periods. Thus, maritime networks, changing sources of metal and the trading of amber for metal seem to have been a crucial feature for Northern Europe during the Bronze Age (Beck and Shennan, 1991; Earle and Kristiansen, 2010; Kristiansen, 1998). At the same time, numerous ships were depicted on the Scandinavian rocks and bronze items, a praxis that might have reflected the maritime trade of precious metals (Kaul, 1998; Ling, 2008).
Both the lead isotope and chemical analyses have undoubtedly showed that the copper from the 33 Scandinavian Bronze Age artefacts diverges significantly from Scandinavian copper ores and that the copper must have been imported from elsewhere. The results furthermore indicate that there are variations in metal supply that are related to chronology, in resemblance with artefacts from Scandinavia as well as from other parts of Europe indicating analogous trade routes for copper, during the respective periods. Maritime networks and changing sources of metal seem to have been a key feature for Scandinavia in the Bronze Age.
(Source: “Moving metals or indigenous mining? Provenancing Scandinavian Bronze Age artefacts by lead isotopes and trace elements”, by Johan Ling et al., 2013)
In this second paper we report lead isotope and elemental data for 38 additional artefacts and metallurgical debris from southern Sweden with the aim to find out which ore bearing regions supplied copper to Scandinavia during different periods of the Bronze Age by comparing these data with the large body of archaeological, geological and archaeometallurgical publications pertaining to chronology of copper extraction and circulation in Bronze Age Europe.
An important part of our study has been to clarify whether or not copper was extracted locally or imported to Sweden during the Bronze Age. Although a local copper ore extraction was not supported by earlier results (Ling et al., 2013), we have enlarged not only the amount of artefacts from ore bearing districts in Sweden but also included objects from adjacent districts. Most of the artefacts derive from hoards or wetland locations and workshops, whereas a feware from graves or mortuary milieus and the rest are stray finds.
Special priority has been given to artefacts that belong to the Nordic Bronze Age tradition, 1700-500 cal. BC (Baudou, 1960; Montelius, 1885; Vandkilde, 1996). However, a metal-hilted dagger dated to about 2000-1700 cal. BC and a palstave of British type dated 1500-1400 cal. BC, were also included in this study. Additionally, exceptional finds, such as the Herzsprung shields (Ling et al., 2013: Fig. 6) and a piece of a lure from period V, have also been sampled. One important aim has been to analyse material from bronze production and workshop sites, like droplets of metal left in the crucibles, sprues, melts, rods/ingots and slag in order to capture the materials in the process of casting, rather than just as finished objects. Of special interest is the material from the workshop site at Hallunda, Botkyrka parish which also involves copper slag which is the only of its kind found in Sweden on a Bronze Age site.
The European ore deposits that could have supplied copper and tin in the 2nd-1st millennium BC for copper-based artefacts found in Sweden
There are many publications describing the ore deposits in Europe and their lead and their lead isotope and geochemical characteristics, mainly published in geological books and journals. However, for the metal provenance studies the most valuable are the archaeometallurgical surveys that have been conducted by many teams researching ancient mining and metallurgy.
For identification of the ore sources exploited in the Bronze Age it is necessary to have for comparisons three types of information: the geochemical characteristics of the ore deposit, lead isotope analyses of ore samples and indication of the periods of exploitation.
The lead isotope data obtained for the Swedish bronzes were compared with all available data for the Old World copper ores including the Near and Middle East, and some Asian deposits. The comparisons show that the Swedish bronzes are not consistent with the origin from the deposits located in the Near and Middle East, or Asia.
Results and discussion – General results
The conclusions as to the origin of the metal used for the copperbased artefacts from Bronze Age Sweden were obtained by comparing not only lead isotope ratios of the artefacts but also their elemental compositions and the geochemistry of ores from the deposits selected by their lead isotope ratios.
The majority of the analysed Swedish artefacts are tin-copper alloys, which also contain one or more of the impurities of arsenic, antimony, nickel and silver in the range from 0.2% to several percent. Iron and/or cobalt appear in smaller quantities.
The majority of the analysed objects have lead isotope and elemental compositions consistent mainly with the copper ores from central and southern Europe: North Tyrol in Austria, Sardinia and the Iberian Peninsula.
Six bronzes are isotopically fully consistent with the ores from the Eastern Mediterranean.
The specific identification of potential copper sources for Swedish BA artefacts in relation to regions and chronology – Austria, North Tyrol
Seventeen of the analysed artefacts spanning the chronology have lead isotope and chemical compositions that are consistent with the copper fahlores and slags from Brixlegg in North Tyrol.
Iberian Peninsula
Two shaft-hole axes (T1:2,3) and one flanged axe (T1:5) from period I. Given that one of the copper ores from the El Aramo mine has the same lead isotope composition as the shaft-hole axe T1:2 and in view of the strong evidence of exploitation of this mine in the 2nd millennium BC we accept that the copper for this axe most likely originated from north-west Spain.
Sardinia
The oldest artefact that has lead isotope composition fully consistent with the copper ores from the Sardinian mine of Calabona is a sword pommel (T1:6) from period I, with Sb, As, and Ni contents in the range of 0.3-0.4%.
British Isles, Cornwall
Amongst the artefacts from period V site of Vårdinge there is a very unusual find of pure tin ring-shaped rod (T1:60) that is fully consistent with the lead isotope compositions of ores from Cornwall, and a copper melt (T1:71), nearly free of impurities, that also could be from Cornwall, if copper was smelted then in Cornwall.
Cyprus
Three bronzes from period I (in particular 1600-1500 cal. BC): a flanged axe (T1:9) and two shaft-hole axes (T1:7,10) are fully consistent isotopically with the copper ores from Cyprus. The shaft-hole axe T1:10 has a content of As, Sb and Ni that is a little higher than usually found in Cypriot copper. The other two axes are made of relatively impurity free copper. From period II, a hilt-plate dagger (T1:20) has lead isotope composition fully consistent with the ores from Cyprus, and its trace element signature is similar to the shafthole axe T1:10. Finally, a socketed axe (T1:47) dated to period IV, very low in impurities, is fully consistent with the lead isotope compositions of the ores in the large Cypriot coppermine of Skouriotissa.
Greece
The analysed palstave from Öckerö (T:11), dated to period II, is a rather spectacular example of a type common in the British Isles (Butler,1963). However its lead isotope and chemical compositions, free of impurities, are fully consistent with the copper ores from Lavrion in Attica.
Implications of the inferred sources for metals in Swedish bronze artefacts
Accumulated data from Swedish bronze artefacts reinforce the view that all metals used in casting were imported. However, the presence of the copper slag from Botkyrka (T1:59) provides possible evidence of an attempt at smelting of the local ores in LBA, although such an attempt is not reflected in any of the analysed casting debris from the same site, or from any other BA site in Sweden. It is important to stress that the Swedish sulphide ores are highly complex mineralisations containing both copper and iron. These ores are difficult to reduce and at least four consecutive steps of roasting and smelting are required to reduce the sulphides to metal. This technologically complex procedure might have prevented a local extraction of copper during Bronze Age. Thus, the overall evidence of metallurgical activities in Sweden from the Bronze Age supports the assumption that at least some artefacts were produced locally using pure copper and tin respectively, as indicated by the presence of copper droplets in crucibles, some copper rods and the pure tin rod. This feature, in combination with the continuous flow of metal, very low levels of lead in the artefacts and their minor element and lead isotope compositions, seems quite indicative that the Swedish artefacts were not derived from a European ‘pool’ of re-used bronze, but from primary metals.
The presented interpretations of chemical and lead isotope analyses of Swedish metals dated to the Nordic Bronze Age are surprising and bring some information not known from previous work. Apart from a steady supply of copper from the Alpine ores in the North Tyrol (17), the main sources of copper are ores from the Iberian Peninsula (22) and Sardinia (18). Even more unexpected seems the identification of five objects made of Cypriot copper and one – a typical British palstave – of the copper from Lavrion in Greece. Equally interesting is that the obtained metal signatures clearly disfavour closer ore districts such as Scandinavia, Harz or Erzgebirge in Germany. This regards also regions that provide Scandinavia with artefacts during certain periods in the Bronze Age as for the Carpathian basin and Switzerland (Thrane, 1975; Vandkilde, 1996). On the other hand our material do also match copper and tin signatures with regions, like Austria, British Isles (1) and southern Germany (2), that traditionally have been argued as potential sources for Scandinavian metal.
The interpretation of the lead isotope and chemical ‘fingerprints’ of the analysed artefacts adds essential information to the picture of the ore bearing regions that supplied metal to Scandinavia in the Bronze Age. Generally speaking, artefacts dated to EBA (2000-1500 cal. BC) correlate to copper ores in the North Tyrol (2), Cyprus (3) and the west Mediterranean world (4), while most of the artefacts from the MBA (1500e1100 cal. BC) tie up neatly with copper ores in Sardinia (10) and south-Iberia (6). Most artefacts from the LBA (1100e700 cal. BC) correlate with ores in south Iberia and in North Tyrol. A tin ingot matches with Cornwall and two items with southern Germany.
From these results emerges a new complex picture of possible connections between Scandinavia and Europe in the Bronze Age that warrant further attention. The Baltic amber is of special interest here. In fact the Baltic amber constitutes the most concrete evidence of a Scandinavian “commodity” that was traded southwards for copper (Kristiansen, 1998; Montelius, 1888). This is indicated by the findings of Baltic amber, roughly in the same ore-bearing districts that show consistency with isotopes for Scandinavian artefacts (Beck and Shennan, 1991; Harding, 1984; Murillo-Barosso and Martinón-Torres, 2012).
Swords, shields and amber routes
When discussing the Baltic amber, the Scandinavia-Central Europe connection is of great importance, but also the link between Scandinavia and the late Wessex culture and its ties to the east Mediterranean world, so evident by the amber spacer-plates and other artefacts (c.p Eogan, 1990; Harding, 1984; Kristiansen and Larsson, 2005). It is notable that the main episodes for the traffic of amber to the Aegean world 1600, 1500 and 1200 cal. BC correspond well with the dating of some of the Scandinavian BA artefacts that in turn match the ores in Cyprus (Harding, 1990, 1984).
Regarding the Tyrolean copper in the Swedish artefacts it was probably transmitted to the north via the central European “amber routes” to Scandinavia (Navarro, 1925; Thrane, 1975). Thus, the analyses confirm earlier hypotheses that Austria provided metal to Scandinavia during EBA (3) and LBA (13), however, surprisingly not so much during the MBA (c.p Kristiansen, 1998). During the MBA, the west Mediterranean ores in Sardinia (10) and Spain (6) dominated. Interesting enough, all flange hilted swords and most of the hilt-plate swords and daggers from the MBA correspond to the copper ores from Sardinia or south Spain.
In addition to the importance of Austrian ores during the LBA, also Nuragic copper played a role, for example, most of the socketed axes from period IV can be correlated with the copper ores in this region. However, Spain (15) seems to have been the outermost dominant supplier of copper to Sweden during the LBA and this is in accordance with the evidence of mining in the region (Hunt-Ortiz, 2003). Perhaps the most intriguing correlation is the one between the two Swedish U-notched Herzsprung shields dated to about 1100-800 cal. BC (Uckelmann, 2011) and ores in the Ossa Morena district. In fact, there are about 70 stelae, dated to 1100-800 cal. BC, with depictions of mostly V-notched Herzsprung shields and horned warriors (Harrison, 2004), and in addition findings of Baltic amber at LBA sites in the same region (Murillo-Barosso and Martinón-Torres, 2012).
(Source: “Moving metals II: provenancing Scandinavian Bronze Age artefacts by lead isotope and elemental analyses”, by Johan Ling et al., 2014)
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