Micro-pixe studies for archaeological gold identification – the case of transylvanian gold and of dacian gold staters (kosons)

Trace elements are more significant for provenance of archaeological metallic artifacts than the main components. For gold, the most promising elements are Platinum Group Elements (PGE), Sb, Hg, Pb, and, especially for alluvial (panned) gold, Sn and Pt. Several small fragments of ancient gold objects from some Bronze Age objects and Greek and Dacian (KOSON – type) coins were analyzed. To check if the Transylvanian gold was used, some fragments of nuggets from Transylvanian mines and alluvial gold were also studied. The measurements were performed by using the AGLAE accelerator of the Centre de Recherche et de Restauration des Musees de France. The samples were bombarded with a 3 MeV proton micro-beam (roughly 50 µm diameter). The employed beam current was around 10 nA. We also used the micro-PIXE technique at the nuclear microprobe facility of the Forschungszentrum Dresden-Rossendorf. A 3 MeV proton beam was employed; the beam diameter was roughly 150 μm. The total accumulated charge was around 3 μC.
As conclusions of the performed experiments, one can quote the following findings:

• Sn was detected as a trace-element in all the KOSON without monogram coins; in one of them we could acquire spectra in several spots; in one of them a very high concentration of Sn was found but not in the surrounding areas, most probably a cassiterite grain;
• No trace-elements were detected in the KOSON with monogram coins and the pseudo-Lysimach staters issued by the Greek colonies at the Black Sea coast; it was concluded that highly refined gold was used to manufacture these coins; the above findings led us to the idea that the two kind of KOSON coins were manufactured by using different gold sources
• Sn was also found as trace element in a fragment taken from a Early Bronze Age bracelet from Tauteu, hoard (Transylvania) and in a fragment from the Vulchitrun-like disk (Late Bronze Age) found in Calarasi, Oltenia; we could conclude that alluvial gold was most likely used to manufacture these Bronze Age objects;
• Te was found in several geological samples (e.g. in the ones from Rosia Montana), a fact that is of particular importance, since this element appears to be a characteristic of the Transylvanian gold minerals, but it is easily evaporated during the native gold melting, so, its presence in gold objects is very improbable;
• A very interesting finding was the presence of Pd traces in one of the alluvial gold samples, the one coming from Mures river.