Provenancing copper in the middle Shang period through isotopic analysis of metallurgical remains

Archaeological investigations recently conducted at the site of Tajiasi, a Middle Shang bronze casting workshop, have led to the discovery of abundant metallurgical micro-remains from various stages of bronze production processes. Lead isotope analysis of these samples has given fresh insights into the discussion about the origin of the metal sources employed during this period. The copper melting and refining slags, characterized by ²⁰⁶Pb/²⁰⁴Pb around 18.0 and very low lead concentrations (＜4,000 ppm), provided the first reliable indicator about the geological origin of copper used in the Middle Shang period. It is suggested the Jiurui metallogenic district in the Middle Yangtze River, home to the Shang period copper smelting site of Tongling, was the copper source for the Taijiasi site. On the other hand, alloying slags and bronze objects bearing highly radiogenic lead (²⁰⁶Pb/²⁰⁴Pb > 19.0) show an elevated, but still relatively low Pb content (＜2 wt%), suggesting that the source of tin introduced Pb which was characterized by HRL. Items including alloying slags, dross, spillages and bronze objects have similar HRL characteristics to the Middle Shang bronzes from other sites. This result indicated the Taijiasi site was involved in a multi-line metal circulation during this period, and elucidated the complexity and multiplicity of supply networks for different kinds of metals in the Middle Shang period. It also highlighted the great potential of copper melting and refining slags for detecting the copper provenance.