Scientific analysis of bronze objects of the first millennium to the second century BCE excavated from the Jiangkou Site, Pengshan, Sichuan

The Jiangkou site is located in the Min River channel in Pengshan County, Sichuan Province, China. One hundred and four bronze weapons and tools of the First millennium to the second century BCE were found throughout five excavations from 2016 to 2022. Typology and radiocarbon dating suggest that the bronze objects could be dated as early as the early Western Zhou dynasty. There is a great variety of object types, and some types have not been discovered before. In order to study the technical characteristics and the sources of raw materials of these bronze objects, through analysis of observation of the wood handles in the socket of the axes and alloy composition, we found that the wood handles were most likely sourced locally, and the people at that time consciously chose tree species suitable for tool and agricultural implement handles. Compositional analysis shows that Jiangkou bronzes have diachronic differences in alloy compositions, Western Zhou bronzes exhibited the highest copper content, with lower lead and tin content, but the copper content in the bronzes of the Eastern Zhou dynasty declined significantly, while lead and tin content increased to varying degrees. Furthermore, the alloy compositions of the Jiangkou bronzes were directly related to their forms and functions. The lead isotope study indicates that the copper materials used in the Western Zhou bronzes from Jiangkou were found to be diverse, including both Central Plains-type materials and local materials. Moreover, six bronzes displayed highly radiogenic lead. Compared with the Western Zhou bronzes, the lead isotope ratios of Eastern Zhou bronzes from Jiangkou site are more concentrated, some of the copper used in Eastern Zhou bronzes may have originated from local sources in Sichuan. Through scientific analysis, this research provides new understandings and a new perspective for the study of early bronzes in the Chengdu Plain.