Analytical Assessment of Chaltasian Slag: Evidence of Early Copper Production in the Central Plateau of Iran

Abstract

This study reports the archaeometallurgical analyses results on six slag remains obtained from Chaltasian, Iron Age II, in the Central Plateau of Iran, excavated by Islamic Azad University, VaraminPishva Branch. Metallurgical studies were carried out to identify oxides, Ca-rich silicates and metallic phases in the slag material, using wavelength dispersive X-Ray fluorescence (WDXRF), followed by an analysis of one sample under the polarizing microscope: plane polarized light (PPL) and cross polarized light (XPL). Based on the analyses, it has been concluded that these six copper slag remains have a considerable amount of silica, which had been added to the smelt to increase its fluidity. Analyses showed a clinopyroxene microstructure in a glassy matrix for five samples, and a barite source, from a probable lead-zinc source in limestone, for the other sample. The absence of arsenic in these copper slags could show a paradigm shift in copper production in this space-time grid. According to the low amount of slag present on site, on the one hand, and the application of relatively advanced extraction technology on the other, this research introduces Chaltasian as an Iron Age II small copper production centre in the Central Plateau of Iran with a locally-developed copper extraction technology. IANSA 2017 ● VIII/2 ● 137–144 Bita Sodaei, Poory Kashani: Analytical Assessment of Chaltasian Slag: Evidence of Early Copper Production in the Central Plateau of Iran 138 Figure 1. Map of Iran. Figure 2. Aerial Photo, Chaltasian (Yousefi Zoshk 2012) IANSA 2017 ● VIII/2 ● 137–144 Bita Sodaei, Poory Kashani: Analytical Assessment of Chaltasian Slag: Evidence of Early Copper Production in the Central Plateau of Iran 139 Figure 3. Topographical Map, Chaltasian (Yousefi Zoshk 2012) Figure 4. Chaltasian, central mound (Yousefi Zoshk 2012). is currently a common technique to reach an understanding of the specialization in alloy production. Elemental analyses are a type of characterization research in archaeometry. The comparative assessment of chemical composition can lead to the determination of metal manufacturing processes. Archaeologists, therefore, prefer to employ chemical and physical techniques to identify both the elemental composition and production technology (Kashani et al. 2013a). In this work, six slag remains have been analyzed to obtain information about the quantitative elemental composition of the slag material and its mineral resources. 2. Theoretical background The production and use of copper and its alloys on the Iranian Plateau might have been started in the Neolithic site of “Ali Kosh” in the south west of Iran, where a rolled bead of native copper was found (Moorey 1969; Pigott 1999a; Thornton 2009). The bead from “Ali Kosh” has been dated to between the 8th and 7th Millennium BC (Hole 2000; Thornton 2009). It has been further specified that copper extraction technology on the Iranian Plateau had local developments during the Bronze Age (Dyson, Voigt 1989; Oudbashi et al. 0 120 m IANSA 2017 ● VIII/2 ● 137–144 Bita Sodaei, Poory Kashani: Analytical Assessment of Chaltasian Slag: Evidence of Early Copper Production in the Central Plateau of Iran 14