Lead isotope and trace element analysis of the Wuzhu coins from Doujiaqiao hoard, Tianjin City, North China

Abstract

The minting of coins in almost all societies is related to the central authority. The evolution of the central government's control over the coinage power in the Han Dynasty (202 BC-220 AD) of ancient China reflects the rise and decline of the central authority. Unfortunately, there is no historical record referring to the condition of coinage material management in the HD. Thus, in this paper, XRF, metallography, MC-ICP-MS and ICP-AES were used to study the alloy composition, microstructure, lead isotope and trace element characteristics of 11 Wuzhu (五铢) coins of the Eastern Han Dynasty (25-220 AD) from the Doujiaqiao hoard, Tianjin city, North China. The XRF results showed that there were two kinds of alloy in these coins: one group with high lead content more than 7.6 wt.%, while the other with low lead content less than 1.9 wt.%. And all of these samples had tin content less than 2.9 wt.%. The metallography results indicated that all of these samples were cast, while one sample showed annealing signs. According to the lead isotopic ratios, the lead material of the five high-lead coins had two different provenances: the Yangtze and the Southern China geochemical province. In addition, the copper material of the other six low-lead coins may be derived from several different copper mines. Furthermore, the data of trace elements confirmed that the copper source of the EHD coins in the Doujiaqiao hoard came from different mines, which is consistent with the lead isotope analysis results and further indicates that the copper and lead mines for coinage might be exploited by several local authorities in the EHD.