MICRO-SR-XRF STUDIES OF GOLD PROVENANCE IN ARCHAEOLOGY

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1 NUCLEAR PHYSICS MICRO-SR-XRF STUDIES OF GOLD PROVENANCE IN ARCHAEOLOGY ANGELA VASILESCU, B. CONSTANTINESCU, ROXANA BUGOI National Institute for Nuclear Physics and Engineering, P.O.Box MG-6, RO Bucharest- Magurele, Romania, Received November 11, 2009 Micro-Synchrotron Radiation X-Ray Fluorescence (SR-XRF) studies can help in the establishment of a typical signature (fingerprint) of gold coming from specific sources. The presence of trace elements (Sb, Sn, Te, Pb) in Transylvanian gold and the analysis of their concentrations in archaeological artifacts found on the territory of Romania can lead to conclusions related to the provenance of the gold used in their manufacture. This work attempted to establish the origin of the gold used for the mint of two different types of coins and for a Bronze Age hair ring from the Tauteu hoard. Except for the kosons with monogram, which were manufactured from refined gold, the other objects show an alluvial signature. Key words: provenance, gold, SR-XRF. 1. INTRODUCTION The study of trace elements in archaeological gold artifacts can provide important clues about the metal provenance and the involved manufacturing procedures, leading to conclusions regarding the commercial, cultural and religious exchanges between the old populations and their way of life. Ancient metallic objects have been manufactured in a quite primitive manner, the metallurgy and techniques being developed over time; they are inhomogeneous on the micrometer scale, containing remains of imperfect smelting and inclusions (small areas with composition different from the surroundings) [1]. The basic composition of various types of gold coins discovered in Romania was established by energy-dispersive X-ray fluorescence (XRF) using radioactive sources ( 238 Pu and 241 Am) and by proton activation analysis (PAA) [2]. XRF allows the fast study of the finds as they are, without any damage or modification. The intervention on the archaeological items is permitted for sampling, in the least damaging way, only when supported by the need for more accurate analysis to clear details or controversies concerning their provenance. In such cases, more refined studies by micro-sr XRF (Synchrotron Radiation X-Ray Fluorescence) are possible, e.g. at the spatially resolved set-ups like the BAM-line at BESSY in Berlin or the ANKA/ISR FLUO beamline in Rom. Journ. Phys., Vol. 56, Nos. 3 4, P , Bucharest, 2011

2 2 Studies of gold provenance in archaeology 367 Karlsruhe, where the accuracy and high excitation energy allows for the measurement of trace element concentrations: Sb, Te, Pb known fingerprints for the Carpathian mines, and Sn characteristic for the panned alluvial gold [3]. These elements have been identified in geological samples using the same technique. The present study aims at more detailed insight into the provenance of Dacian kosons. We report also results on a Bronze Age gold hair ring from the Tauteu treasure. A host of gold samples (grains, nuggets, fine gold sand) from various Transylvanian mines and rivers and some very small (few-milligram) fragments of archaeological objects (coins, jewelry) were investigated by micro-sr XRF, in point analysis and scanning. Additional results obtained at BESSY are in course of publication [4]. 2. EXPERIMENTAL The studies were performed by micro-synchrotron Radiation X-Ray Fluorescence (SR-XRF) at the BAM-line [5] at BESSY and the FLUO-beam [6] at ANKA/ISR in Karlsruhe. At BESSY, point spectra for 15 natural gold samples from Transylvania and 12 sub-mm-sized samples from archaeological objects, were acquired using a Silicon Drift Detector (SDD). The beam was focused to an area of µm 2. The typical collection time was 300 s for a point spectrum. At the ANKA/ISR FLUO-line, we performed 2-dimensional scans with the beam focused to µm 2. The scan area could be visualized with an optical microscope and recorded with a camera. We obtained elemental maps for 6 archaeological samples. The detector used was a HPGe crystal. The maximum excitation energy of the X-rays at both sites was 32.5 kev. The samples were mounted in air on a dedicated frame, put on a motorized xyz stage and positioned at an angle of 45 to the primary X-ray beam. The identification of the peaks and the off-line data analysis was performed with PyMCA [7] and AXIL [8]. Relative concentrations of minor and trace elements were determined using a procedure based on various standards and fundamental parameter calculations. The samples analyzed in this work were archaeological and geological ones. The archaeological samples were tiny fragments (~ µm chips) coming from coins or jewelry, taken in the least destructive manner possible from parts of the objects with little relevance as to their shape and decoration. Twelve coin pieces representing two types of kosons [9,10] with or without a monogram (from Tarsa-Luncani, near Sarmizegetusa, the capital of Dacia) were analyzed in comparison with their contemporary pseudo-lysimachus stater (2

3 368 Angela Vasilescu, B. Constantinescu, Roxana Bugoi 3 samples). The other sample was a tiny fragment coming from a Late Bronze Age hair ring from the Tauteu hoard (Bihor County) [11]. This treasure contains 6 gold items, out of which 5 hair rings of a specific shape and design, obtained by hammering and cresting the fir-tree -style decoration. The archaeological samples come from the National Museum of Romanian History, Bucharest and the Vasile Parvan Institute of Archaeology, Bucharest. a b c Fig. 1 Gold artifacts and native gold: a) A gold nugget; b) A koson with a complex monogram (reverse); c) Tauteu hair ring #8993. The geological gold comes from the Brad Gold Museum and the collection of the Babes-Bolyai University Cluj-Napoca. 3. RESULTS AND DISCUSSION The study of the origin of the koson treasures is of special interest to archaeologists and historians. The kosons are considered as the only gold coins issued by the Dacians. Our experiments intended to determine whether the gold used for these coins is native or refined, and as such, to give some insight into the workmanship of those days. We identified clearly that the kosons without monogram contain Sn (figure 2 left), while the ones with monogram do not (figure 2 right). Tin is the characteristic X-ray signature of alluvial gold, due to riverbed cassiterite most likely. The absence of Sn is a sign for other gold sources: mine or refined; figure 2 (b) and 3 illustrate the lack of Sn in a typical spectrum for a koson with monogram and for a pseudo-lysimachus sample, respectively.

4 4 Studies of gold provenance in archaeology 369 Fig. 2 Sn: present in a koson without monogram, KFM left, and absent in a koson with monogram KCM 587 -right (ANKA). Fig. 3 SR-XRF spectrum for a pseudo-lysimachus sample (no Sn) (BESSY). Sn is present both in the Tauteu hair ring spectrum and native gold /alluvial samples (Figure 4).

5 370 Angela Vasilescu, B. Constantinescu, Roxana Bugoi 5 Fig. 4 Sn in the Tauteu hair ring sample (left) and in alluvial gold (right) (BESSY). We have also found a micro-inclusion of Sb in one koson without monogram sample, which could point at the possible use of primary (mine) gold associated with alluvial in the manufacture of these coins (figure 5). This is a hypothesis that needs further investigation. Fig. 5 Sb microinclusion in sample IA-92 koson without monogram (ANKA). The concentrations have been evaluated for all of the samples and added to previous XRF evaluations. Our up-to-date knowledge on the Transylvanian native gold can be summarized as in table 1:

6 6 Studies of gold provenance in archaeology 371 Table 1 Summary of elemental composition of Transylvanian native gold Primary deposits Ag [%] Cu [%] Sb [ppm] Sn [ppm] Te [ppm] Pb [%] general Rosia Montana Sacarimb ! 0.25% Fizesti trace trace 1 Placer deposits * 2-8 ~0.2 ~50 only Stanija * Valea Oltului, Stanija, Valea Ariesului, Valea Pianului metal and chalcopyrite mix. All the native gold samples are inhomogeneous mixtures of Au-Ag-Cu metallic alloys containing small quantities of telurides and antimonates, with galena (PbS), pyrite (FeS 2 ), chalcopyrite (CuFeS 2 ) and sphalerite ((Zn,Fe)S) inclusions. In the XRF analysis performed at the Horia Hulubei National Institute of Nuclear Physics and Engineering the composition of the Tauteu hair-ring was found: Au 92.9%, 6.0% Ag and 0.95% Cu. Sn was below the detection limit of the employed set-up. The Au-Ag content suggests a native alluvial gold (from Transylvania), containing chalcopyrite (a Cu-Fe sulphide), a mineral looking like gold. Gold with a somewhat similar composition can be found in the Apuseni Mountains at Rosia Montana. The kosons without monogram and the Tauteu ring are made of alluvial gold, as shown by the presence of Sn in their composition. They represent a rather primitive manufacture, using nuggets of gold as found, only by hammering. It is also possible that some coins were minted using preexisting gold in objects captured in the wars, the tribes being more occupied to fight than with mining or metallurgy. CONCLUSIONS The present study shows that the kosons with monogram are made from refined (more than 97%) gold with no Sb or Sn traces, and the ones without monogram are manufactured mainly from native alluvial gold (Sn traces). No Te was found, but being a volatile element, the refining technology would eliminate it. The presence of Sb traces needs more investigation, which could be performed if more samples were available. Contemporary with the kosons, the Greek pseudo-lysimachus staters are made of refined gold (no Sn, Sb). The gold in the Bronze Age Tauteu hair ring is also of alluvial origin.

7 372 Angela Vasilescu, B. Constantinescu, Roxana Bugoi 7 Micro-SR-XRF is a valuable tool for the identification and classification of various gold sources, by the characterization of each region by a fingerprint. It can be used for provenancing archaeological and museum items, but by itself it is not enough proof in historical controversies. But combined with information related to deeper geological research and historical insight, it can provide support for the hypotheses on the civilization, life and habits of ancient populations. Acknowledgements. We acknowledge the support from EU grant RII 3 CT for transnational access and mobility and the funding by CEX research programs. Special thanks go to our collaborators in archaeology and geology for providing the samples and for the valuable comments on the geological features of the Transylvanian gold. We are deeply indebted to the experimental support teams: Martin Radtke, Uwe Reinholz and Oliver Scharff at BESSY and Rolf Simon at ANKA. REFERENCES 1. E. Pernicka, Nucl. Instrum. Meth. Phys. Res. B14, (1986). 2. V. Cojocaru, B. Constantinescu, I. Stefanescu, C.M. Petolescu, J. Radioanal. Nucl. Chem. 246 (1), (2000). 3. B. Constantinescu, R. Bugoi, V. Cojocaru, D. Voiculescu, D. Grambole, F. Herrmann, D. Ceccato, Nucl. Instrum. Meth. Phys. Res. B 231, (2005). 4. B. Constantinescu, A. Vasilescu, M. Radtke, U. Reinholz, Micro-SR-XRF studies for archaeological gold identification the case of Carpathian gold and Romanian museal objects, Proc. Conf. Synchrotron Radiation in Art and Archaeology, October 2008, Barcelona, Spain, Appl. Phys. A99, (2010). 5. H. Riesemeier, K. Ecker, W. Gorner, B.R. Muller, M. Radtke, M. Krumrey, X-Ray Spectrometry 34, (2005). 6. R. Simon, G. Buth, M. Hagelstein, Nucl. Instrum. Meth. Phys.Res. B199, (2003). 7. V.A. Sole, E. Papillon, M. Cotte, Ph. Walter, J. Susini, Spectrochim.Acta B62 (2007) B. Vekemans, K. Janssens, L. Vincze, F. Adams, P. Van Espen, X-Ray Spectrometry 23, (1994). 9. O. Iliescu, Quaderni ticinesi di numismatica e antichità classiche 19, 185 (1990). 10. C. M. Petolescu, The treasure of King Koson(Booklet), Romanian National History Museum, Bucharest (2000). 11. D. Popescu, Prelucrarea aurului in Transilvania inainte de cucerirea romana (Gold processing in Transylvania before the Roman Conquest), in Materiale şi Cercetări Arheologice II, (1956) (in Rom.).