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The present work was devised to address the systematic analysis of samples from a range of Roman non-ferrous metal artefacts from different archaeological contexts and sites in the Roman provinces of Germania Superior. One of the focal points of this study is the provenancing of different lead objects from five important Roman settlements between 15 BC and the beginning of fourth century AD. For this purpose, measurements were made on lead and copper ore samples from the Siegerland, Eifel, Hunsrück and Lahn-Dill area in Germany and supplemented with data from the literature to create a data bank of lead isotope ratios of European deposits. Compositional analysis of lead objects by Electron Microprobe analysis showed that Romans were able to purify lead from ore up to 99%. Multi-Collector Inductively Coupled Plasma Mass-Spectrometry was used to determine the source of lead, which played an important role in nearly all aspects of Roman life. Lead isotope ratios were measured for ore samples from German deposits from the eastern side of the Rhine (Siegerland, Lahn-Dill, Ems) and the western side of the Rhine (Eifel, Hunsrück), which contained enough ore reserves to answer the increasing local demand and are believed to have been mined during the Roman period. This data together with those from Mediterranean ore deposits from the literature was used to establish a data bank. The Mediterranean ore deposits range from Cambrian (high 207Pb/206Pb) to tertiary (lower 207Pb/206Pb) values. In particular, the Cypriot deposits are younger, while the Spanish deposits fall either with the younger Sardic ores or close to the older Cypriot ores. The lead isotope ratios of most German ore deposits fall in between the 208Pb/206Pb vs. 207Pb/206Pb ratios of Sardinia and Cyprus, where the lead isotope signature of ore deposits from France and Britain are also found. Over 240 lead objects were measured from Wallendorf (second century BC to first century AD) Dangstetten (15-8 BC), Waldgirmes (AD 1-10), Mainz (AD 1-300), Martberg (first to fourth centuries AD) & Trier (third to fourth centuries AD). Comparing the lead isotope ratios of lead objects and those from German ores shows that the source of over 85 percent of objects are Eifel ore deposits, but the Roman’s had also imported lead from the Southern Massif Central and from Great Britain. A further topic of this work was the systematic study of the variation of copper isotope ratios in different copper minerals and the mechanisms, which controls copper isotope fractionation in ores deposits. For this purpose, copper isotope analyses were made by Multi-Collector Inductively Coupled Plasma Mass-Spectrometry from a series of hydrothermal copper sulphides and their alteration products. Copper and lead isotope ratios were measured in coexisting phases of chalcopyrite and malachite and also coexisting malachite and azurite. No significant fractionation was observed in malachite-azurite phases, but in chalcopyrite-malachite coexisting phases, malachite always shows a positive fractionation to heavier isotope values. Zhu et al. and Larson et al. showed that isotopic variations in copper principally reflect mass fractionation in response to low temperature processes rather than source heterogeneity. The low temperature ore formation processes are mostly represented by weathering of primary sulphide ores to produce secondary carbonate phases and therefore are usually observed on the surface of ore deposits, which were probably removed during the early Bronze Age. Using this concept, copper isotope ratios were measured in some Early Bronze Age copper alloys and Roman copper alloys. However, no large copper isotope fractionation has been observed. Lead and copper isotope ratios were measured on samples from the Kupferschiefer. Two profiles were investigated; 1) Sangerhausen, which was not directly influenced by the oxidizing brines of Rote Fäule and 2) Oberkatz, where both Rote Fäule-controlled and structure-controlled mineralization were observed. Results from maturation studies of organic matter suggest the maximum temperature affecting the Kupferschiefer did not exceed 130°C. delta-65-Cu ranges between -0.78-+0.58‰, shows a positive correlation with copper concentration. Maximum temperature in the Kupferschiefer profile from Oberkatz is supposed to be around 150°C. delta-65Cu in this profile ranges between -0.71-+0.68‰. The pattern of copper isotope fractionation and copper concentration is same as the for profile of Sangerhausen. Origina lead isotope ratios are strongly overprinted by high concentrations of uranium in bottom of both profiles causing more radiogenic lead.
This PhD thesis has been carried out within an interdisciplinary cooperational project between the Deutsches Bergbau-Museum Bochum and the Goethe-Universität Frankfurt, which is dedicated to ancient Pb-Ag mining and metal production in the hinterland of the municipium Ulpiana in central Kosovo. Geochemical analysis (OM, XRD, EMP, MC-ICP-MS) of ores, metallurgical (by-) products and metal artefacts allowed to reconstruct the local chaîne opératoire and to decipher significant chronological differences between presumably Roman/late antique and medieval/early modern metallurgical processing. Pb isotope provenance studies documented the relevance of local metal production within the Roman Empire and confirmed the actual existence of a Metalla Dardanica district, which until now solely has been suspected on basis of epigraphy.
The predominant abundance of the by-products matte (Cu, Pb, Fe and Zn sulphides) and speiss (ferrous speiss: Fe-As compounds; base metal speiss: ~(Cu,Ni,Fe,Ag )x(Sb,Sn,As )y ) at smelting sites with a preliminary Roman/late antique dating points to treatment of complex polymetallic ore. Pb isotope analysis demonstrated that the mining district of Shashkoc-Janjevo (partially) supplied six of the ten investigated metallurgical sites. In this mineralisation, parageneses with elevated Cu, As and Sb abundances comprise significant proportions of particularly tennantite-tetrahedrite minerals, chalcopyrite, arsenopyrite and were generated during the early and main stages of ore formation. Later precipitated ore in contrast is marked by a significantly less versatile mineralogy and consists almost exclusively of galena, sphalerite and pyrite/marcasite. Besides increased Cu, As and Sb contents, ore from the main formation stage also exhibits generally higher Ag abundances, which are mainly hosted by fahlore and locally abundant secondary Cu sulphides (chalcocite, digenite and covellite) and oxidised phases (e.g. malachite, azurite). The higher precious metal grades of this ore type, whose geochemical signature (i.e. higher proportions of Cu, As and Sb) is mirrored by the abundance of the metallurgical by-products matte and speiss (almost exclusively found at potentially Roman/late antique smelting sites; see above), presumably were a pivotal factor leading to its preferential exploitation in earlier times. Matte and base metal-rich speiss contain notable amounts of Ag, which are mainly present in Cu-(Fe) sulphides and particularly antimonides ((Cu,Ni)2Sb, Ag3Sb), respectively. While the speiss compounds due to their close association with Pb bullion presumably were cupelled automatically, the metallurgical treatment of matte could not have been proven unambiguously, but overall certainly is highly likely.
The beneficiated ore (i.e. crushed and sorted, potentially also treated by more lavish techniques such as grinding, sieving or wet-mechanical methods) possibly was partially roasted and subsequently together with fluxes and charcoal submitted to the furnaces. The working temperatures approximately ranged between 1100 and 1400 °C. Slags from all presumably Roman/late antique dated and few of their potentially medieval/early modern analogues were produced from smelting of (partially roasted) ore with charcoal and added siliceous material, thus resulting in fayalite-dominant phase assemblages or rarely observed glassy parageneses. Even though several subtypes of fayalite slags have been established on basis of the abundance of Fe-rich oxide phases (i.e. spinel ss and wüstite), late clinopyroxene and the general solidification sequence of the slags, the process conditions (i.e. temperature, fO2, added fluxing agents) must have been widely similar; chemical variations could be explained by varying degrees of interaction of the slag melt with charcoal ash and furnace material. The other investigated metallurgical remains indicate employment of a calcareous flux, which led to formation of Ca-rich olivine-, olivine+clinopyroxene-, clinopyroxene- or melilite-type slags. These types as well as glassy slags were generated at more oxidising conditions outside the fayalite stability field (FMQ buffer equilibrium, cf. Lindsley, 1976) than their olivine-dominant analogues. Conclusions on the furnace construction could be drawn on basis of the typology of the slags, which mostly were tapped into a basin located outside the furnace, but partially (at two presumably medieval/early modern sites) also accumulated in a reservoir within the smelter.
Lead artefacts excavated in Ulpiana could be isotopically related to ores from mineralisations in its vicinity and demonstrate that the resources were at least utilised for local metal production. However, also ship wreck cargo from Israel - including several lead ingots with the inscription 'MET DARD' (Raban, 1999) - and late antique lead-glazed pottery from Serbia and Romania (Walton & Tite, 2010) could be related to a possible Kosovarian/Serbian provenance of the raw material and thus indicate flourishing trade of metal from the Metalla Dardanica district within the Roman Empire.
References:
Lindsley, D. H. (1976). Experimental studies of oxide minerals. In D. Rumble, III (Hrsg.), Oxide minerals (61-88). Reviews in Mineralogy, Volume 3. Washington, DC: Mineralogical Society of America.
Raban, A. (1999). The lead ingots from the wreck site (area K8). Journal of Roman Archaeology, Supplementary Series, 35, 179-188.
Walton, M. S., & Tite, M. S. (2010). Production technology of Roman lead-glazed pottery and its continuance into late antiquity. Archaeometry, 52(5), 733-759.