Journal of Archaeological Science 151 (2023) 105728 0305-4403/© 2023 Elsevier Ltd. All rights reserved. Resolving the complex mixing history of ancient Chinese bronzes by Manifold Learning and a Bayesian Mixing Model Zhenfei Sun a , Siran Liu a, * , Ji Zhang a, b , Kunlong Chen a , Brett Kaufman a, c a Institute for Cultural Heritage and History of Science & Technology, University of Science and Technology, Beijing, China b School of Archaeology and Museology, Peking University, China c Department of the Classics and the Materials Research Laboratory, University of Illinois Urbana-Champaign, USA A R T I C L E INFO Keywords: Metal provenance Mixing Lead isotope Bayesian mixing model Zhou period China ABSTRACT Provenance of metals is a major theme in Bronze Age archaeology since it can help to reveal complex cultural and economic entanglements in ancient times. However, where complex societies with diversifed trading relation- ships are concerned, identifying metal provenance has often proved to be challenging due to the frequent mixing of metals from different sources in antiquity. This research addresses this question by developing an innovative method for interpreting lead isotope data of bronze artefacts. Manifold learning and a Bayesian mixing model are combined to reconstruct quantitatively the contribution of metal sources to ancient bronzes. The methodology is employed to resolve the complex metal circulation system in the Zhou period (11th-3rd century BC) of China, and reveals a signifcant diachronic change of metal resources from North, Central, and South China. The North China metal sources were mainly employed in the Early Western Zhou period (1046–950 BC). In the following ages, the Yangtze River Valley and Qinling Mountains became the major metal sources for Zhou people. The Middle Spring and Autumn period (660 BC-560 BC) witnessed a major shift of dependence between these two sources, demonstrating a fundamental transformation in the metal circulation system. The South China metal sources were exploited throughout the entire Zhou period and probably associated with polymetallic deposits in the Nanling area. This research reveals the long-term patterns of metal exploration and mixing in the Zhou period of China, and also demonstrates the great potential this new methodology promises in addressing the complex metal mixing history in other cultural contexts. 1. Introduction The exploitation of metal materials was a key factor in the devel- opment of complex society (Erb-Satullo, 2020; Xia, 1985). By the Bronze Age, people were able to obtain metals from remote regions and distribute them in a fairly large network. The fow of metal in a vast geographical region is a refection of cultural and economic interactions among early societies (Renfrew and Bahn, 2016). These processes are exemplifed, for instance, by the extensive metal trading network in the Late Bronze Age Mediterranean (Berger et al., 2022; Powell et al., 2021; Stos-Gale et al., 1997) and Shang period of China (Liu et al., 2018; Zhangsun et al., 2021; Jin, 2003). The provenance of ancient metals therefore becomes a primary method for archaeologists to reconstruct the relationship among past human civilizations. Lead isotope analysis has been employed toward this end since the 1960s (Brill and Wampler, 1967), and was introduced to infer the geological provenance of ancient copper-based materials in the 1980s (Gale and Stos-Gale, 1982). Variability of lead isotope signatures in metal artefacts is a refection of ore bodies from different crustal origins. As the abundance of three radiogenic lead isotopes ( 208 Pb, 207 Pb, 206 Pb) increase with time, ore bodies of different ages that formed with source materials from different reservoirs tend to have varied lead isotope signatures (Faure, 1977). In addition, as isotope fractionation in metallurgical processes is insignifcant (Baron et al., 2009; Cui and Wu, 2011; Gale and Stos-Gale, 2000; Pernicka, 1992), lead isotopes can be a highly promising proxy to connect metal artefacts and geological ore sources. The method has been widely applied to resolving metal prov- enancing issues in East Asia (Jin et al., 2017; Liu et al., 2018; Jin, 2003), Southeast Asia (Pryce et al., 2011), the Mediterranean (Berger et al., 2022; Powell et al., 2021; Stos-Gale et al., 1997), Central Europe (Radivojevi´ c et al., 2018), Egypt (Rademakers et al., 2017) and the Americas (Cooper and Simonetti, 2021; Farquhar and Fletcher, 1984). * Corresponding author. E-mail address: siran.liu@ustb.edu.cn (S. Liu). Contents lists available at ScienceDirect Journal of Archaeological Science journal homepage: www.elsevier.com/locate/jas https://doi.org/10.1016/j.jas.2023.105728 Received 28 November 2022; Received in revised form 18 January 2023; Accepted 19 January 2023