Micro-sr-xrf and Micro-pixe Studies for Archaeological Gold Identification

For gold, the most promising elements for provenance are Platinum Group Elements (PGE), Sn, Te, Sb, Hg, Pb, but also high melting point elements, such as Ta and Nb. Small fragments of native Carpathian gold placer and primary were studied using Synchrotron Radiation X-Ray Fluorescence at ANKA synchrotron. The goal of the study was to identify the trace elements, especially Sn, Sb and Te. The measurements were performed in air by using a 32.5 keV beam to excite the characteristic X-lines in Sn-Sb-Te region. We found Sn to be present in placers, Sb, Te and Pb in primary gold. Native gold nuggets, fragments of objects coming from Visigothic Pietroasa “The Golden Brood Hen with Its Chickens” hoard and small (less than 250 microns diameter) fragments from ancient Dacian and Grek gold coins were analyzed using micro-PIXE technique at the Rossendorf TANDETRON and at the Legnaro AN2000 microbeam facilities. We found Te and Sb in primary gold and Sn and traces of Sb in placers. For Pietroasa hoard, we found Sn in the Oenochoe cup and small fibula, indicating that alluvial gold probably from Anatolia (Pactolus river) was used. We also detected Ta inclusions in the large fibula, indicating that Ural Mountains (the only region where Ta and Au minerals are together) gold was (at least partially) used. As concerning the gold coins, two type of Dacian staters were identified: one from remelted refined gold and other from native (alluvial) Carpathian gold. A spectacular application to nine Dacian gold bracelets (armbands), identified as made from native placer and primary Carpathian gold, is also presented. INTRODUCTION Trace elements are more significant for provenancing archaeological metallic artifacts than the main components. For gold, the most promising elements are Platinum Group Elements (PGE), Sn, Te, Sb, Hg, Pb [Pernicka, 1986]. To help Romanian archaeologists in authentication and provenance studies on ancient gold artefacts (jewelry and coins) found on Romania’s territory [Bugoi et al, 2005], the very possible use of Carpathian gold must be considered. This analysis involves the compositional study of Carpathian native gold samples – placer (gold sand or nuggets found in rivers bed) and primary (gold obtained from mining), to determine the fingerprints of gold from this geological area. In this paper, the investigation of several small fragments of natural Carpathian gold by using micro Proton Induced X-ray Emission (micro-PIXE) technique at the microbeam facility of Forschungszentrum Dresden-Rossendorf, Germany and by using micro Synchrotron Radiation X-Ray Fluorescence (micro SR-XRF) at ANKA Synchrotron Radiation Facility of the Forschungszentrum Karlsruhe, Germany is presented. The analytical results obtained for the Carpathian gold were applied to the authentication of the most spectacular Romanian archaeological recovery in the last 100 years, the one of nine huge spiraled gold Dacian bracelets. Inclusions of Platinum Group Elements (PGE) Ru, Rh, Pd, Os, Ir and Pt in gold were released into rivers by the decomposition of rocks and occur in placer deposits in the form of grains and nuggets of complex alloys. The melting point of PGE is higher than that of gold; thus, PGE grains remain unchanged during the metallurgical processing of the gold ore. Apart 1 9th International Conference on NDT of Art, Jerusalem Israel, 25-30 May 2008 For more papers of this publication click: www.ndt.net/search/docs.php3?MainSource=65