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Journal of Archaeological Science 82 (2017) 31e39 Contents lists available at ScienceDirect Journal of Archaeological Science journal homepage: http://www.elsevier.com/locate/jas Evidence of arsenical copper smelting in Bronze Age China: A study of metallurgical slag from the Laoniupo site, central Shaanxi * ** Kunlong Chen a, Siran Liu a, , Yanxiang Li a, , Jianjun Mei a, b, Anding Shao c, Lianjian Yue c a Institute of Historical Metallurgy and Materials, University of Science and Technology Beijing, Beijing 100083, China b Needham Research Institute, Cambridge CB3 9AF, UK c Shaanxi Provincial Institute of Archaeology, Xi'an 710043, China article info abstract Article history: Previous archaeometallurgical studies on Bronze Age China mainly focused on finished artefacts, Received 21 October 2015 whereas our understanding of copper smelting technology of this period is still limited. This paper, for Received in revised form the first time, presents analytical results of metal production remains from the site of Laoniupo in 20 April 2017 Guanzhong Plain, central Shaanxi. It reveals that arsenical copper was produced at this site by smelting Accepted 25 April 2017 arsenic-rich polymetallic ores with raw copper or high purity copper ores. The identification of metal production in the Guanzhong Plain is significant for the investigation of regional development and inter- regional interaction of Bronze Age cultures in China. The possible exploitation of ores from deposits in Keywords: Bronze age the Qinling Mountain region during this period is also discussed in this article. © China 2017 Elsevier Ltd. All rights reserved. Arsenical copper Slag Polymetallic ore 1. Introduction Materials, University of Science and Technology Beijing (IHMM, USTB). Much attention has been paid to the production debris Research into the metalwork of the Early-Middle Bronze Age found at ancient metallurgical sites, aiming at a direct under- China (ca. 2000 BCE e 1000 BCE) has made significant progress in standing of ancient metal production activities. Investigation on the the past decades. Issues such as the beginning of metallurgy in metal production remains unearthed from the site of Laoniupo, as China, and compositional characteristics and casting technology of presented in this paper, is one of the initial results of these efforts. Shang-Zhou bronze ritual vessels have kept attracting scholars and resulted in a large number of crucial publications in both Chinese 2. Archaeological context and samples and English (e.g. Zhao, 2004; Mei, 2009; Chen et al., 2009; Bagley, 2009; Mei et al., 2012, 2015). However, most of these studies are The site of Laoniupo is located at the eastern suburb of Xi'an City, artefacts-based, only reflecting information of the final few steps of Shaanxi Province. This area in the lower valley of the Wei River is ancient metallurgical chaine^ operatoire (Ottaway, 2001; called “Guanzhong Plain” meaning “Inside the Passes”. Neighboured Hauptmann, 2007) and, unavoidably, leaving many research la- by the Loess Plateau in the north and the Qinling Mountains in the cunas. For example, we still have little knowledge about the early South, this area connects the Central Plain of China and Northwest smelters' choice of ores and details of their smelting and alloying China, and has long been occupied by many archaeological cultures technologies. In recent years, a series of archaeometallurgical field (Fig. 1). The site of Laoniupo was first inhabited during the Yang- investigations and analytical work have been carried out by a shao period (6th to 4th millennia BC), and was continuously used as research group at the Institute of Historical Metallurgy and a settlement by the following Late Neolithic cultures such as Keshengzhuang II culture (24th to 21st centuries BC) and Don- glongshan culture (ca. 20th to 18th centuries BC). Pottery typology * Corresponding author. suggests that during the Donglongshan period the site received fl ** Corresponding author. in uences from both the Erlitou culture (19th to 16th centuries BC) E-mail address: [email protected] (S. Liu). in the Central Plain and the Qijia culture (23rd to 18th centuries BC) http://dx.doi.org/10.1016/j.jas.2017.04.006 0305-4403/© 2017 Elsevier Ltd. All rights reserved. 32 K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39 Fig. 1. Map of the Guanzhong Plain and adjacent regions, showing the locations of Laoniupo and other Shang period sites. in Hexi corridor, Gansu province, demonstrating its important role remains such as slags and technical ceramics (Fig. 3). All samples in the cultural exchanges of this period (Liu, 2002; Zhang, 2000; analysed in this research are collected from this layer. The typology Han, 2009). of pottery sherds suggest this layer can be dated to the Shang By the late second millennium BC, contemporary with the Shang period. A charcoal inclusion found in one slag piece (No. LN112) was Culture in the Central Plain, the Laoniupo site reached its most sent for radiocarbon dating at the School of Archaeology and flourishing stage. Having a maximum extension of 20 km2, the site Museology and the School of Physics, Peking University (lab code: controlled a great strategic landscape on the north bank of the Ba BA090234). The calibrated age with 2s confidential level is be- River, a tributary of the Wei River. In the late 1980s, Northwest tween 1415 BCE and 1295 BCE. This result places the specimen to University in Xi'an carried out six seasons of excavations at Lao- the Middle-Late Shang period, and corresponds well with the niupo and revealed a total area of 5000 m2. The site is divided into 4 chronology suggested by the associated pottery sherd (Fig. 4). sub-zones by the excavators according to their different landscapes Twelve slag and four technical ceramic fragments shown in and topographies (Fig. 2). These excavations have yielded abundant Fig. 3 (No. 1e12) were selected for more detailed analyses due to archaeological features including rammed-earth foundations for their relatively large size. The specimens are irregular lumps with large buildings, pottery kilns, house foundations, tombs, sacrificial dark grey, dark brown and black colours. Vacuoles in different sizes pits of chariots and horses, and ash pits. A large number of artefacts as well as green and/or some red-brown corrosion products are made with various materials were unearthed while the most regularly identified. Flowing patterns were not observed on any of interesting ones are fragments of casting moulds and slags, directly them, indicating they were not tapped from the furnace. Technical suggesting a copper processing workshop at this site. (Liu, 2002). ceramic samples (Fig. 3: No.13e15) are also small fragments, From 2008 to 2011, the IHMM carried out four field surveys at showing reddish ceramic body on one side and dark brown to black Laoniupo and its neighbouring regions. Metal working remains, slag linings on the other side. The relatively small sizes and fairly mainly slag fragments, were found in the sub-zone I and II. Ac- fine texture of these ceramics suggest they are fragments of cru- cording to the published excavation reports and recent fieldwork, it cibles rather than furnace walls, which is likely to be thicker and is clear that the metalworking remains are concentrated in the coarser (Martinon-Torres and Rehren, 2014). central-south part of the site facing southward to the Ba River (Fig. 2). In April 2010, a small landslide on top of a local cave-house 3. Analytical methods at the southern edge of the site exposed the profile of a cultural layer. This layer mainly consist of grey podzolic soil and ash, bearing Bulk chemical composition of slag samples were analysed with domestic pottery sherds, bone fragments, and metallurgical Shimadzu Lab Center XRF-1800 Wavelength Dispersive X-ray K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39 33 Fig. 2. Map of the Laoniupo site, showing the general location, sub-zones and excavated areas. Fig. 3. Photographs of metallurgical remains discovered at the Laoniupo site; No. 1 to 12 are slag pieces while No. 13 to 15 are technological ceramics. Fluorescence Spectrometer (XRF) at the School of Metallurgical and Ecological Engineering, USTB. Samples were first powdered and then prepared into pressed pellets for analysis. Microscopic ana- lyses of slag and technical ceramic were conducted with an optical microscopy (OM) at the IHMM, USTB and a Hitachi SN-3200 Scanning Electron Microscope equipped with an EDAX Energy Dispersive Spectrum analyzer (SEM-EDS) at the Chinese Academy of Cultural Heritage (CACH). Samples were mounted with epoxy resin and polished with diamond paste down to 0.25 mm. The analytical conditions of SEM-EDS were set as an acceleration voltage of 20 kV, a working distance of 10e15 mm and an acqui- sition time of 60s. 4. Analytical results Bulk composition of 12 slag pieces are shown in Table 1. Remarkably, all samples have high copper and arsenic contents with an average of 11.2 wt% CuO and 3.6 wt% As2O3. The main Fig. 4. Calibrated date of charcoal inclusion found in slag LN112. 34 K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39 Table 1 WD-XRF bulk chemical analytical results of the Laoniupo slag (wt%). Sample Na2O MgO Al2O3 SiO2 P2O5 SO3 K2O CaO TiO2 MnO Fe2O3 NiO ZnO BaO CuO As2O3 LN101 e 0.45 3.25 56.11 0.30 0.18 1.49 1.88 e 0.25 10.13 0.11 1.12 0.47 21.29 2.95 LN102 0.08 0.33 2.43 77.43 0.31 0.31 1.19 1.47 0.10 0.10 5.76 0.01 0.23 1.10 6.95 2.20 LN103 0.11 0.28 2.02 65.09

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