Abstract
One of the greatest enigmas in the study of Bronze Age China is the source of highly radiogenic lead discovered in the copper-based objects of the Shang period (ca. 1500–1046 BC). Although being relatively rare in nature, such lead contributed over half of the lead consumed across a vast area from the Yellow River to the Yangtze. Identifying its source and supply network would significantly contribute to our understanding of how China achieved the largest metal production across Eurasia. The past thirty years of research have seen various proposals for the origin of this lead, including south-western China, the middle Yangtze River valley, the Qinling and Zhongtiao mountains, and even Africa. This paper attempts to illustrate the tempero-spatial pattern of this highly radiogenic lead using the largest possible databank. Furthermore, by going beyond the bronze data and investigating lead isotopes in non-metal objects, we confirm that multiple sources of highly radiogenic lead must have been used across Chinese history. In turn, this implies the feasibility of a multi-source model for the lead in the Shang bronzes.
Highlights
A major application of lead isotope geochemistry in archaeology has been in provenance studies, of which metal sources employed in the Mediterranean Bronze Age has undoubtedly attracted most attention[1,2]
In the absence of unusually high concentrations of uranium and thorium, and in a closed geological environment, the isotope ratios of lead in a mineral deposit will evolve along predictable lines over geological time, and the geological age of such deposits can be calculated from a measurement of these isotope ratios[8,9]
The lead isotope ratios of minerals formed in the presence of excess uranium and/or thorium, evolve along different lines as a result of the production of additional amounts of 206Pb, 207Pb, and 208Pb, the exact enrichment depending on time and the amounts of uranium and thorium present
Summary
The future and are generally referred to as anomalous (Joplin-type or J-type) leads. The other type of anomalous lead, Bleiberg type or B-type, formed in the early stages of the Earth’s evolution but has been remobilised, transported and re-emplaced at a later date and mixed with younger normal and/or radiogenic leads from sources with greater depletion in U/Pb than in Th/Pb (usually in the lower crust). We must assume that Bronze Age metallurgical workers in China (as elsewhere) had no means of distinguishing lead with anomalous isotopic values, beyond the unwitting selection of such metal by the preferential use of raw materials from a particular source In this case, the observation that all of the major sites approximately contemporary with Shang, stretching from the Yangtze River to the Central Plains, used highly radiogenic lead for a maximum period of three hundred years is in itself remarkable. The data by Cui et al from another set of eight glass-based objects (seven ear pendants and one eye bead dated to the Eastern Zhou period) unearthed from the site of Lijiaba in the Sichuan Basin are considerably important They are all lead-barium glass, and five of them contain highly radiogenic lead[30]. Its occurrence in these glass objects undoubtedly extends this picture into the later period
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