Identification and classification of archaeological materials from
Bronze age gold mining site Ada Tepe (Bulgaria) using rock magnetism
Abstract
Collection of materials from the most ancient open-pit gold mine in
Europe has been investigated using mineral magnetic methods as part of
the multi-disciplinary 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,
hematite and goethite. Based on the magnetic properties, samples from
clusters 1 and 3 were identified as influenced by fire – archaeological
structures and waste heaps with the use of fire setting, respectively.
Samples belonging to cluster 3 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 archaeological assignment. Spatial distribution
of cluster members across the site provides valuable environmental
information for the location of mining activities, their lateral spread
and the technology used. It was concluded that magnetic mineral analysis
is a precise, sensitive and highly effective method for characterization
and classification of materials from ancient mining.