Identification and Classification of Archeological Materials From Bronze Age Gold Mining Site Ada Tepe (Bulgaria) Using Rock Magnetism

Archeological materials from the most ancient open-pit gold mine in Europe have been investigated using mineral magnetic methods as part of the multidisciplinary research of the site. The aim of the study was to employ rock-magnetic characteristics (magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization and various magnetic grain-size dependent ratios) for classification of a collection of 177 samples, taken from Late Bronze age waste heaps, pristine rocks, natural soils and soils from cultural layers. Factor analysis and k-means cluster analysis revealed that four clusters explain the best mineral magnetic data. Results from the thermomagnetic analysis and thermal demagnetization of composite isothermal remanence proved that the main magnetic minerals in the collection are magnetite/maghemite, hematite, and goethite. Based on the magnetic properties, samples from clusters 1 and 3 were identified as influenced by fire-archeological structures and waste heaps with the use of fire setting, respectively. Samples belonging to cluster 2 were dominated by goethite and hematite, thus identified as rock residues. Materials grouped in cluster 4 showed magnetic characteristics typical of natural soils and were thus related to this class of materials. The obtained clustering of the samples agreed well with their archeological assignment. Spatial distribution of cluster members across the site provides valuable environmental information for the location of the mining activities, their lateral spread and the technology used. It was concluded that magnetic mineral analysis is a precise, sensitive, and a highly effective method for characterization and classification of materials from ancient mining.