Reconstruction of the chemical composition of the metal from the bronze age site gonur depe (Turkmenistan), according to the analysis by mass spectrometry with inductively coupled plasma

The chemical composition of copper alloys from Bronze Age site of ancient Margiana (ancient delta of Murghab river, Turkmenistan) Gonur Depe were studied by mass spectrometric analysis (ICP-MS) for 63 elements. Four types of alloys are identified. Chemical composition of the parent metal of five fully oxidized items were completely reconstructed by developed technics. This allowed to compare them with other metal artifacts of the area. It is shown that the typical Gonur copper alloys can also be differentiated by their micro-composition into smaller subgroups. Spectral analysis traditionally used to determine the chemical elemental composition of the products of copper alloys allows to determine mainly macro-composition of the alloy and only a few elements of micro-composition. The quantitative content of copper - alloy matrix is not defined by it. ICP-MS multielemental analysis has much more possibilities in terms of accuracy, sensitivity, and the number of elements determined in comparison with spectral analysis. By our method it allows to quantify 63 elements: Li Be Na Mg Al Si P K Ca Ti Cr Mn Fe Co Cu Zn Ga Ge As Se Rb Sr Y Nb Mo Ru Pd Ag Cd In Sn Sb Te Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Ta W Re Pt Au Hg Tl Pb Bi Th U. Chemical element composition of the copper alloys products from Gonur by ICP-MS was not studied yet. We have studied 10 samples of artifacts from various places of Gonur Depe by ICP-MS: fragments of pins, seals, bracelets, mirrors, plates, unknown object and metallurgical slag, found by Margiana archaeological expedition (under the direction of V.I. Sariandi) in 1988, 1994 and 2010. As some artifacts were completely oxidized a special technique of reconstruction of the chemical composition of the parent metal by the chemical composition of the oxidized copper alloys has been developed. The oxygen content in the oxides and the initial chemical composition of copper alloys of five artifacts were determined by calculation. The chemical composition on 63 elements which was determined by the ICP-MS analyses is presented for all the studied artifacts. In this collection of copper-bronze artifacts of Gonur Depe we identified four types by macro-composition: copper (Cu), arsenic bronze (Cu-As), tin bronze (Cu-Sn), lead-bismuth-arsenic bronze (Cu-Pb-Bi-As). Criteria of similarity and difference by micro-composition allow additionally dividing these types of alloys into several subgroups and clarify the genesis of copper alloys of Margiana.

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