In April 2018, a project called ACUDEMAB (Analyses of composition of non-ferrous
metals, used for decorations in Early Middle Ages in Bulgaria) was successfully implemented
in the Laboratory of Ion Beam Applications, MTA Atomki, Debrecen, in the framework of the
EU H2020 IPERON CH (Integrated Project for the European Research Infrastructure ON
Cultural Heritage) Trans-National Access program. Analysis of metal used for the casting
of all these products, which is found in workshops and near furnaces can give convincing
argument that this is precisely the metal used by medieval craftsmen. The results would give
us the opportunity to identify ways of receipt of raw materials – import or reuse of waste
products for new castings.
The appearance of elements in the analysis depends on the geological and metallurgical conditions. According to the mineralogy of typical lead ores and the behaviour of
the elements during the melting process, antimony Sb, arsenic As, bismuth Bi, copper Cu
and silver Ag are among the leading elements in lead analysis. Similarly, with much less
concentration than the actual melting of the ore, elements such as cobalt, iron, nickel and
zinc, and gold, arsenic, selenium and tellurium may appear in the metal. Tin is not a typical
ingredient for lead ores hence its absence in lead ingots.
They belong to the so called Balkan metallogenic belt, where there are two basic
types of mineralization: lead-zinc mineralization with key representatives of galenite,
sphalerite, chalcopyrite, pyrite (there were some ancient galenite mines found) and gold
bearing polymetal minerals, represented by galenite, sphalerite and gold-bearing pyrite.
Gold is placed in the oxidising zone of the galenite and pyrite. Investigations made on the
remains of antique copper mines make us say with great certainty that the major portion of
raw materials (copper and bronze) came from the Burgas-Strandja mining region. Numerous traces of mining activities were found in that region. In the Burgas sub-region only there
are more than 250 ancient ore mines