Journal of Archaeological Science 82 (2017) 31e39

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Journal of Archaeological Science

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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 0.23 0.15 0.97 2.03 0.17 0.15 11.58 0.03 0.62 0.32 13.62 2.63 LN104 e 0.61 1.55 72.60 0.34 0.14 0.63 3.68 0.12 0.21 8.97 0.04 0.63 1.34 7.43 1.70 LN105 0.45 0.96 3.68 61.99 0.77 0.21 1.43 4.41 0.24 0.10 8.70 0.01 0.22 0.54 12.09 4.19 LN106 e 0.39 2.49 76.14 0.62 0.06 1.29 2.58 0.37 0.38 7.83 0.08 1.21 0.42 4.96 1.18 LN107 0.30 2.08 2.95 35.13 0.53 0.18 1.25 15.59 0.20 1.01 22.68 0.09 1.81 2.72 8.86 4.61 LN108 0.86 1.38 8.10 52.29 0.60 0.08 3.27 6.82 0.54 0.30 11.98 0.06 0.46 1.03 9.87 2.34 LN109 0.22 2.16 2.57 45.71 0.41 0.28 1.10 11.05 0.16 0.64 18.53 0.07 1.11 1.82 10.32 3.84 LN110 0.25 1.50 3.50 34.53 0.64 0.10 1.70 14.23 0.26 0.72 21.37 0.07 1.86 3.57 10.10 5.62 LN111 0.22 1.41 4.63 38.31 0.45 0.31 2.06 10.13 e 0.56 17.33 0.08 1.52 2.64 13.57 6.79 LN112 0.40 1.43 4.48 36.11 0.64 0.21 1.79 10.74 0.27 0.59 17.10 0.06 1.68 2.58 16.41 5.50

Note: Normalized data; “–” means the concentration is below the detection limit. It should be note that copper (Cu) and arsenic (As) are presented here as oxides because an oxide standard was employed during the XFR analysis, but a big portion of these elements are existed in metallic form as numerous metal prills were observed frequently in all the samples. The calculation of iron (Fe) as Fe2O3 rather than FeO is based on the fact that hercynitic magnetite (Fe(Fe, Al)2O4) was identified in some samples, however, small particles/dendrites of wüstite are detectable under the microscope.

components of slag matrix, namely SiO2,Fe2O3 and CaO have few samples, pure copper prills were identified. Iron is also notably varied concentrations. Silica content of these samples frequently detected in these prills as impurity and in many cases, its ranges between 35 wt% and 78 wt% while their iron oxide contents concentration is over 1 wt%. Antimony was found in some arsenical are between 5 wt% and 23 wt%. The variation of lime content is copper prills, and occasionally its concentration can be more than even more significant, with a difference in one order of magnitude 2 wt%. Copper sulphide with a minor amount of iron was occa- between the richest and the poorest samples. Barium oxide and sionally found as halos surrounding metallic prills. zinc oxide are consistently present in these samples. Mineral remains containing a significant amount of copper and/ Microscopic analysis shows that most samples are heteroge- or arsenic were identified in some samples. A triangular inclusion neous with frequent semi-reacted quartz grains (Fig. 5). This was found embedded in a partially reacted matrix of sample LN107 observation explains the highly varied basic oxides concentration (Fig. 8). Microanalysis of the un-corroded strip (indicated by the in slags' bulk composition. SEM-EDS analysis of the fully molten/ white cross in Fig. 8) gave a Cu:S atomic ratio around 1.06, reacted areas of slags shows that they are mainly composed of SiO2 approximating the formula of covellite (CuS). In sample LN102 and and FeO, together with notable amounts of CaO, Al2O3, BaO and LN109, bright clusters were found in BSE images (Fig. 9, Table 3). MgO. Melilite and pyroxene group crystals were found in the glassy They mainly contain oxygen, iron, copper and arsenic. Chemical matrix (Fig. 6). Cuprite and magnetite-rich spinel clusters with a composition of the whole cluster and its sub-phases are shown in significant amount of iron oxide and alumina were also frequently Table 4. Both the “skeleton-frame” microstructure and chemical identified. Occasionally, delafossite crystals (CuFeO2) and small composition indicate these clusters are very likely to be unreacted wüstite particles/dendrites (FeO) were spotted, indicating the ore remains, probably secondary minerals of copper/iron sul- heterogeneous redox conditions inside the smelting container. pharsenide ores such as enargite and arsenopyrite (Hoppner€ et al., Large numbers of metallic prills (from several micrometres to 2005). millimetres in diameter) were found trapped in the slag matrix Cross-section of technical ceramics show that they have a (Fig. 7, Table 2). Most of them are rich in arsenic (up to 30 wt%), vitrified inner part with dark-grey/black colour and a thin layer of showing a dendrites and sometimes independent g phase. In only a glassy slag lining on the interior surface (Fig. 10). The chemical composition of ceramic body, vitrified ceramic and slag lining are

Fig. 6. Optical photomicrograph of sample LN107, showing grey pyroxene crystals Fig. 5. BSE image of sample LN101, showing large vacuoles and unreacted remnant in a together with clusters of iron oxides (light grey) and metal prills (bright) in a silicate heterogeneous substrate. matrix (dark) (Optical photomicrograph, as polished). K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39 35

Fig. 7. Examples of metal prills observed in the Laoniupo slags. Upper left: LN106, pure copper prill with cuprite inclusion formed (Cu þ Cu2O) eutectic structure; upper right: LN107, noting dendrites already visible due to a relatively high As content; lower left: LN111, high As content prill with dendrites and grey sulphide inclusions; lower right: LN112, a pure copper prill with copper sulphide on the rim. (Optical photomicrograph). determined by SEM-EDS area analysis (Table 4). It is noticed that in Radivojevic et al. (2010) analysed slag pieces from the site of comparison to the ceramic body, the levels of iron oxide, lime, Belovode in eastern Serbia dated back to the 5th millennium BC. barium oxide, arsenic and copper considerably increased in the These samples are rich in copper (10.1e27.8% Cu2O) and contain vitrified part of ceramic and slag lining. The find of arsenic and delafossite as well. However, according to their consistently high copper in the inner part of ceramics clearly indicates they were iron, manganese, zinc and cobalt contents, these slags were inter- used for processing copper alloy while the enrichment of alkali and preted to be remains of a smelting process. Similar slags were found alkali earth oxides in this part might reflect the influence of fuel in a Portuguese site and dated to the Chalcolithic period. Analytical ash. The gradient in colour and degree of vitrification from the result and experimental smelting also suggested them as by- outside to inside suggest these vessels were heated from above products of a smelting process (Hanning et al., 2010). In this light, (Bayley and Rehren, 2007). the Laoniupo slags were likely to be remains from processing nat- ural ores due to their high zinc and barium content as well as the 5The nature of the Laoniupo slags in comparative perspective: presence of unreacted ore minerals in the slag matrix. However, it is technological pathways to arsenical copper not clear whether the crucible charge was one complex poly- metallic ore yielding both copper and arsenic or an arsenic rich ore The Laoniupo slag samples have relatively low iron oxide but together with pre-smelted metallic copper and/or high purity high silica content and heterogeneous substrate. The dominance of copper minerals (e.g. malachite and covellite). arsenic-bearing copper prills in all analysed samples indicates that Previous researchers have suggested several different routes to arsenical copper was produced at this site, however, a further produce arsenical copper: the direct smelting of polymetallic ores interpretation of its production mechanism is not straightforward. bearing both copper and arsenic (Müller et al., 2004), the co- Zinc and barium are consistently detected in the Laoniupo slags in a smelting of copper oxide minerals with copper/iron sulpharse- considerable level but generally absence in the body of technical nide ores, cementation of metallic copper with arsenic minerals ceramics. Additionally, the copper and arsenic rich minerals such as (Lechtman and Klein, 1999) or alloying of metallic copper with covellite and complex sulphurarsenide minerals are found in the arsenic-rich speiss (Thornton et al., 2009; Rehren et al., 2012). The slag matrix. These finds suggest that the charge inside the Laoniupo differentiation of these different processes, especially between crucibles included some complex ore minerals with barium and intentional alloying and unconsciously smelting naturally poly- zinc rich gangue. The existence of cuprite and delafossite in slag metallic ores has troubled many researchers. matrix indicates a relatively oxidising reaction condition. This type Müller et al. (2004) analysed a coherent assemblage of metal- of “dross” is usually considered to be related with copper melting or lurgical remains including slags, crucible slag lining, ores, crucible refining process (Bachmann, 1982; Craddock, 1995; Liu et al., 2015). fragments and metal prills unearthed from Chalcolithic layer at the However, Burger et al. (2010)'s experimental simulation has indi- site of Almizaraque in southeast Spain. Chemically, most of the cated, in a crucible smelting process, when the charge has a rela- slags are rich in copper (CuO up to 49%) and arsenic (As2O3 up to tively high O:S weight ratio (>2e3), magnetite, delafossite and 7.2%), and their magnesia and iron oxide contents are much higher even cuprite can become the dominant phases in the smelting slag. than that of the ceramic body of crucibles. The paragenesis of 36 K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39

Table 2 Composition and dimensions of metal prills in Laoniupo slag.

No. Number of prills Size of prills (um) Composition (wt%)

Cu As Fe Sb

LN101 5 10e40 Max 89.9 24.2 2.7 3.7 Mean 77.1 19.2 1.4 2.4 Min 70.4 8.6 ee SD. 7.9 6.3 0.9 1.5 LN102 10 5e20 Max 91.6 30.6 2.7 4.7 Mean 81.9 15.2 1.6 1.2 Min 63.2 8.4 ee SD. 12.7 10.1 1.2 2.0 LN103 7 15e1500 Max 100.0 5.6 3.1 e Mean 96.6 2.2 1.1 e Min 94.4 eee SD. 2.4 2.3 1.4 / LN104 11 5e150 Max 96.5 24.7 ee Mean 85.9 10.9 ee Min 75.3 eee SD. 8.5 9.0 / / LN105 3 10e250 Max 67.0 31.0 25.5 15.9 Fig. 8. Covellite particle embedded in a partly reacted matrix (LN107), cross shows the Mean 49.1 21.9 12.8 6.6 position of EDS microanalysis. Min 27.7 5.5 ee SD. 19.9 14.2 12.8 8.3 LN106 10 5e400 Max 98.7 29.5 2.8 e Mean 83.8 14.3 1.9 e Min 68.2 e 1.3 e SD. 11.4 11.1 0.7 / LN107 4 5e700 Max 88.4 22.8 ee Mean 83.2 16.8 ee Min 77.2 11.6 ee SD. 5.6 5.6 / / LN108 10 5e50 Max 100.0 4.9 1.8 e Mean 96.8 3.0 0.3 e Min 94.9 eee SD. 2.3 2.1 0.7 / LN109 7 5e50 Max 100.0 32.4 3.8 e Mean 81.3 17.3 1.5 e Min 67.5 eee SD. 13.2 13.6 1.5 / LN110 5 10e150 Max 89.7 15.1 2.7 e Mean 87.4 11.1 1.5 e Min 84.9 7.8 ee SD. 1.8 3.1 1.4 / LN111 8 10e200 Max 96.8 31.5 2.2 e Mean 90.7 8.4 0.9 e Min 68.5 1.4 ee Fig. 9. BSE image of complex ore remnant, compositions of different phases are shown SD. 10.0 10.6 1.1 / in Table 3. LN112 11 5e300 Max 98.4 11.0 2.6 3.3 Mean 91.1 7.7 0.6 0.5 Min 86.9 eee Table 3 SD. 3.7 3.7 1.0 1.2 Chemical composition of different phases showing in Fig. 9. Note: “–” means the concentration is below the detection limit; “/” means the SD is Position Composition (wt%) not applicable. OCuAsFeSiAlCaMnZnP

1 9.2 87.7 e 2.4 0.7 eee ee magnetite, cuprite and delafossite in the slags indicates a fairly 2 16.3 61.7 e 15.7 4.3 2.0 ee ee oxidising condition during the smelting process, although tempo- 3 22.3 19.5 36.0 9.9 0.8 1.1 5.1 1.7 2.8 0.9 rally and regionally, conditions could have been reducing enough to Note: Normalized data; “–” means the concentration is below the detection limit. smelt copper indicated by the notable iron content in the trapped arsenical copper prills. The authors argued the Almizaraque slags indicated a crucible smelting process using secondary altered fah- degree of specialization was used to reduce complex ores directly in lore ores, but they also pointed out that the possibility of alloying crucibles and produced copper with a range of arsenic contents. copper metal with arsenic-rich ores at this site. Rehren et al. (2012) suggested that smelted speiss had been Murillo-Barroso et al. (2017) presented a detailed analysis of used as the source of arsenic to produce arsenical copper at the ores and copper production remains from the 3rd millennium BC Early Bronze Age site of Arisman in northwest Iran. The speiss site Las Pilas in Spain not far from Almizaraque. The ore analysis might have been added to an oxidic copper ore during the smelting shows that most samples contain oxidic copper minerals such as process, or later mixed with metallic copper in an alloying process. azurite and malachite while arsenic and zinc bearing minerals such Either operation would result in an iron silicate slag with notable as zincolivenite was frequently identified. Most slags were not fully amounts of CaO and Al2O3. Bulk chemical composition of slag liquefied and highly heterogeneous, bearing a large quantity of samples shows they are rich in copper (2.0 wt% CuO in average) but partially reacted arsenic and copper rich minerals. The authors relatively poor in arsenic (0.1 wt% As2O3 in average). However, suggested a low efficiency smelting technology with a limited metal prills trapped in the slag are mainly arsenical copper with K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39 37

Table 4 Analytical result of technical ceramic fragments from the Laoniupo site (wt%).

Sample No. Defined areas Number of analysis Na2O MgO Al2O3 SiO2 K2O CaO FeO BaO CuO As2O3 LN113 Ceramic body 1 1.9 2.8 12.8 65.5 4.3 7.7 5.2 eee Vitrified ceramic 3 1.8 2.8 11.8 60.1 3.1 12.5 5.0 0.8 2.2 e Slag lining 3 0.6 1.3 8.7 46.8 2.4 18.6 8.7 2.3 5.9 4.8 LN114 Ceramic body 2 1.8 2.5 13.6 66.6 3.8 6.1 5.6 eee Vitrified ceramic 1 1.3 e 11.4 58.8 3.2 12.3 6.1 1.6 2.1 3.3 Slag lining 1 1.2 e 8.2 46.0 2.1 20.2 7.9 2.2 5.9 6.3 LN115 Ceramic body 1 1.8 2.4 13.7 68.2 4.0 4.7 5.2 eee Vitrified ceramic 1 1.7 2.5 12.3 65.6 3.9 9.0 5.0 eee Slag lining 3 1.2 e 10.0 51.6 2.7 14.6 8.0 2.0 3.7 6.0

Note: Normalized data; “–” means the concentration is below the detection limit.

located to east of the Guanzhong Plain just on the other side of the (see Fig. 1). The excavation in 1990s revealed small pieces of metallurgical remains at this site. One slag sample shows a significant arsenic content in the matrix and numerous trapped arsenical copper prills (Arsenic up to 36 wt%). The similar cementation/co-smelting process was proposed to explain the formation of this slag ( et al., 2005). This find provides important evidence that can potentially fills the chronological gap between Laoniupo and Xichengyi, and indicate the existence of this technology in the further east areas. Considering the relatively high and stable arsenic content in the Laoniupo slag and a potentially long history of producing arsenical copper via alloying process in north China exemplified by the site of Xichengyi and Yuanqu Shang city, it is argued that the Laoniupo slag were also derived from a cementation/co-smelting process involving arsenic-rich mineral and metallic copper/high purity Fig. 10. Binocular photomicrograph of cross-section of a technical ceramic fragment copper minerals. During this process, copper metal/mineral and (LN114, width of image is 15 mm). arsenic-rich ores (potentially copper-bearing as well) were charged together in the reaction vessel, probably a crucible, to produce arsenical copper. The ores might contain sulphide minerals which high iron content (3.1 wt% in average). accounts for the sulphide rim surrounding the metal prills and Arsenical copper production in the Bronze Age China did not unreacted sulphide minerals observed in the slag. Since no evi- receive much attention until a copper smelting site at Xichengyi dence of pure copper production has been found at the Laoniupo near Zhangye, in the middle of the Hexi Corridor, Gansu province site so far, the metallic copper, if used, was more likely to be was identified (see Fig. 1). The site provides important reference smelted at other sites and then imported. material for the study of early arsenical copper production in China. Dated to the early second millennium BC, Xichengyi is one of the earliest copper smelting sites excavated in China so far (Chen et al., 7. Discussion 2014). Li et al. (2015) reported analytical results of metallurgical fi remains, including 32 slags, 29 ores and 5 furnace lining from this The study of the Laoniupo slags for the rst time provides evi- site. All slag samples have similar iron silicate matrix with several dence of local arsenical copper production in the Guanzhong Plain. to tens percent of copper. They can be clearly divided into two The technical features of the Laoniupo slags including their rela- groups on the basis of their different metallic inclusions. In most tively low quantity and small size, heterogeneous slag matrix with slag samples (27 of 32), pure copper prills are consistently found abundant unreacted minerals, high copper content, and presence of and occasionally matte prills are also identified. The remaining 5 magnetite, delafossite and metal prills with sulphidic rim are samples are, however, dominated by arsenical copper prills (up to consistent with early smelting slag derived from a relatively low 30 wt% of arsenic) with some of them also containing notable temperature and oxidising process. fi amounts of iron and antimony. The analysis of furnace lining shows Though the ore source of this site has still not been con rmed, it the similar pattern that only one sample has arsenical copper prills is suggested that the Qinling Mountain at the southern boundary of while the other 4 are dominated by pure copper prills. The ore the Guanzhong Plain is currently the best candidate (see Fig. 1). samples from this site are mainly oxidic minerals of copper (26 of There are a number of important metallogenetic belts in this region 29) with a small proportion of them (3 samples) rich in arsenic and bearing copper minerals such as bornite, chalcopyrite often co-exist lead bearing minerals such as fahlore, cerrusite, galena and mem- with fahlores in polymetallic deposits (Qi and Hou, 2005; Ren et al., tite. Chen (2015) then divided these materials into two different 2007). Geographically, some of the deposits are accessible through categories referring to two separated metallurgical processes or the valleys of small rivers originated from the mountain, such as the two different stages of the same process. Copper metal was very Ba River passing by the site of Laoniupo. Although we do not have likely to be smelted first from relatively clean copper ores, and then any direct evidence for the copper mining in this area so far, the alloyed with arsenic-rich ores in a separated cementation/co- recent discovery of ancient turquoise mining site dated back to the smelting process. late Neolithic period in the Luonan County (see Fig. 1) provided Another evidence of arsenical copper production dated to the solid evidence for the early exploration of mineral resources in the 2nd millennium BC was from a Shang city site at Yuanqu in Shanxi, Qinling region (Xian et al., 2016). Metalliferous deposits in the Qinling Mountain have been proposed as the potential source of the 38 K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39

Shang period metalwork found in the Hanzhong Basin, south of the this site. Its potential relationship with the ore resource in the mountain range (Chen et al., 2009) and might also be explored by Qingling Mountain should be examined as well. It is also interesting the Bronze Age people living to the north in the Guanzhong plain. to conduct comparative studies of bronze production in the Considering its chronological context, the production of arsen- Guanzhong Plain and other regions of China to find out how varied ical copper at the Laoniupo site is worth more attention since it is in social contexts and different production and consumption models conflict with the traditional view that tin bronze metalwork (lea- of bronzes influenced the technological choices of ancient workers. ded or not) played a dominant role in most of the Bronze Age sites in China. Kwang-chih Chang (1980) pointed out that in contrast to Acknowledgments many other regions of the world, the use of bronze in ancient China was mainly linked to politics, in the form of ritual vessels and The authors are grateful to Professors Thilo Rehren, Ernst Per- weapons, rather than to economic functions. However, in a regional nicka and Marcos Martinon-Torres as well as colleagues from USTB fi level, signi cant diversity of bronze metalwork in terms of function, for their insightful comments, support and assistance. The com- style and alloy composition have been noticed. Chen et al. (2009, ments made by four anonymous reviewers helped to improve the 2016) revealed a remarkable regional compositional characteristic quality of the manuscript and are gratefully acknowledged. This of Hanzhong bronzes in southern Shaanxi and challenged the work was supported by research grants awarded by the National ‘ ’ simplistic core-periphery interpretation paradigm, which Natural Science Foundation of China (51304020, 51474029) and the emphasized the cultural predominance of the Central Plain but National Administration for Cultural Heritage (2014220). The fi oversimpli ed the complex historical trajectories and interactions revision of this paper is finished at the UCL Institute of Archaeology, fi among many different geographical regions. The identi cation of where Chen Kunlong is working as a Newton International Fellow arsenical copper production at the site of Laoniupo provides (2017e2019, NF160456) supported by the Newton International another important example of this regionalised characteristic of Fellowship awarded by the British Academy. metal production during the Shang period. Last but not least, as it has been widely discussed for decades, the cultural exchange with Northwest China could have played an References important role for the early development of metallurgical tech- An, Z., 1981. Some problems concerning China's early copper and bronze artefacts. nology in the Central Plain during the Bronze Age, and part of the Kaogu Xuebao Archaeol. Sin. 3, 269e285 (in Chinese). Central Plain's technological know-how might be originated from Bachmann, H.G., 1982. The Identification of Slags from Archaeological Sites. Insti- the northwest (e.g. An, 1981; Fitzgerald-Huber, 1995; Li, 2005; Mei tute of Archaeology, London. Bagley, R., 2009. Anyang mold-making and the decorated model. Artibus Asiae 69, et al., 2012, 2015). However, due to the lack of research on the 39e90. production remains, this hypothesis remains untested. In consid- Bayley, J., Rehren, Th, 2007. Towards a Functional and Typological Classification of eration of the important geographic position of Laoniupo, the re- Crucibles. Metals and Mines: Studies in Archaeometallurgy. Archetype Publi- cations, London, pp. 46e55. sults presented here may have the potential to provide empirical Burger, E., Bourgarit, D., Wattiaux, A., Fialin, M., 2010. The reconstruction of the first evidence for technological connections between Northwest China copper-smelting processes in Europe during the 4th and the 3rd millennium and the Central Plain. As mentioned before, in spite of its later date, BC: where does the oxygen come from? Appl. Phys. A 100 (3), 713e724. Chang, K., 1980. Shang Civilization. Yale University Press, New Haven. the technology of Laoniupo are generally in the same line with Chen, G., 2015. Studies on the Early Copper Mining and Metallurgy Sites in the those revealed at Xichengyi and Yuanqu, showing a potential Valley of Heishuihe River. Doctoral Thesis. University of Science and Technology technological continuity. It should also be noted that the site of Beijing, Beijing, pp. 157e162. Chen, K., Rehren, Th., Mei, J., Zhao, C., 2009. Special alloys from remote frontiers of Laoniupo had been occupied continuously since the Neolithic the Shang Kingdom: scientific study of the Hanzhong bronzes from southwest period and its cultural connection with the Hexi corridor and the Shaanxi, China. J. Archaeol. Sci. 36 (10), 2108e2118. Central Plain started at least in the first half of the second millen- Chen, G., Wang, H., Li, Y., Zhang, L., Yang, Y., 2014. The Xichengyi site at the Zhangye e nium BC. During this period, the copper artefacts have been used by city, Gansu province. Kaogu Archaeol. 7, 3 17 (in Chinese). Chen, K., Mei, J., Rehren, Th., Zhao, C., 2016. Indigenous production and interre- the people living in those two regions. Thus, it is worth paying gional exchange: late second-millennium BC bronzes from the Hanzhong basin, attention in the future investigation to check whether there are China. Antiquity 90 (351), 665e678. earlier evidence of metallurgical production at the site of Laoniupo, Craddock, P.T., 1995. Early Metal Mining and Production. Edinburgh University Press, Edinbergh. testing whether the metallurgical technology had spread via the Fitzgerald-Huber, Louisa G., 1995. Qijia and Erlitou: the question of contacts with Guangzhong plain. distant cultures. Early China 20, 17e67. Han, J., 2009. On the rise of bronze culture of Er-Li-Tou. Zhongguo Lishi Wenwu Chin. Hist. Cult. Relics) 1, 37e47 (in Chinese). 6. Conclusion Hanning, E., Gauß, R., Goldenberg, G., 2010. Metal for Zambujal: experimentally reconstructing a 5000-year-old technology. Trab. De. Prehist. 67, 287e304. Scientific analyses of metallurgical remains from the Laoniupo Hauptmann, A., 2007. The Archaeometallurgy of Copper: Evidence from Faynan, fi Jordan. Springer, Berlin, New York. site have, for the rst time, revealed evidence of arsenical copper Hoppner,€ B., Bartelheim, M., Huijsmans, M., Krauss, R., Martinek, K., Pernicka, E., production in the Guanzhong plain during the late second millen- Schwab, R., 2005. Prehistoric copper production in the Inn Valley (Austria), and nium BC. Complex ores consisting of arsenic-bearing minerals may the earliest copper in central Europe. Archaeometry 47, 293e315. “ ” Lechtman, H., Klein, S., 1999. The production of copperearsenic alloys (arsenic have been used as the source of alloying element and smelted bronze) by cosmelting: modern experiment, ancient practice. J. Archaeol. Sci. 26 together with raw copper/high purity copper minerals to produce (5), 497e526. arsenical copper. Similar cementation/co-smelting process was Li, S., 2005. Early metallurgy variability and interaction between Northwest and the e identified at the Xichengyi site in the Hexi Corridor and the Shang Central Plain. Kaogu Xuebao Archaeol. Sin. 3, 239 278 (in Chinese). Li, Y., Chen, G., Qian, W., Wang, H., 2015. Research on the metallurgical remains City site at Yuanqu. This result throws new light on the under- unearthed from the Xichengyi site at the Zhangye city. Kaogu yu Wenwu standing of regional metalwork development in the Bronze Age Archaeol. Cult. Relics) 2, 119e128 (in Chinese). Guanzhong Plain and its potential role as a bridging zone con- Liang, H., Li, Y., Sun, S., Tong, W., 2005. Analyses on as-contained slag unearthed from city site in of Shanxi China. Youse Jinshu necting Northwest China and the Central Plain during the spread Nonferr.s Met. 57 (4), 127e130 (in Chinese). metallurgical technology. Future research is expected to provide Liu, S., 2002. The Archaological Report of the Laoniupo Site. Shaanxi People’s information about the general archaeological background and Publishing House, Xi'an (in Chinese). Liu, S., Rehren, Th., Pernicka, E., Hausleiter, A., 2015. Copper processing in the oases technical details of the smelting activity at the site of Laoniupo, of northwest Arabia: technology, alloys and provenance. J. Archaeol. Sci. 53, especially the nature of the ores and other crucible charges used at 492e503. K. Chen et al. / Journal of Archaeological Science 82 (2017) 31e39 39

Martinon-Torres, M., Rehren, T., 2014. Technical ceramics. In: Roberts, B.W., Qi, W., Hou, M., 2005. Copper ore deposit types and prospecting direction in Thornton, C.P. (Eds.), Archaeometallurgy in Global Perspective. New York. Shaanxi Province. North Western Geol. 38 (3), 29e40 (in Chinese). Springer, Heidelberg, Dordrecht, London, pp. 107e131. Radivojevic, M., Rehren, Th., Pernicka, E., Sljivar, D., Brauns, M., Boric, D., 2010. On Mei, J., 2009. Early metallurgy in China: some challenging issues in current studies. the origins of extractive metallurgy: new evidence from Europe. J. Archaeol. Sci. In: Mei, J., Rehren, Th (Eds.), Metallurgy and Civilisation: Eurasia and beyond. 37, 2775e2787. Archetype Publication, London, pp. 9e16. Rehren, Th., Boscher, L., Pernicka, E., 2012. Large scale smelting of speiss and Mei, J., Xu, J., Chen, K., Shen, L., Wang, H., 2012. Recent research on early bronze arsenical copper at Early Bronze Age Arisman, Iran. J. Archaeol. Sci. 39 (6), metallurgy in northwest China. In: Jett, P., McCathy, B., Douglas, J.G. (Eds.), 1717e1727. Scientific Research on Ancient Asian Metallurgy: Proceeding of the Fifth Forbes Ren, X., Wang, R., Mao, J., Li, C., Xiang, T., Wang, J., 2007. Regional geochemistry Symposium at the Freer Gallery of Art. Archetype Publication, London, characters and exploration direction for mianxian-lueyang-ningqiang multi- pp. 37e46. metal deposit cluster Area, Shaanxi Province, China. J. Earth Sci. Environ. 29, Mei, J., Wang, P., Chen, K., Wang, L., Wang, Y., Liu, Y., 2015. Archaeometallurgical 221e226 (in Chinese). studies in China: some recent developments and challenging issues. J. Archaeol. Thornton, C.P., Rehren, Th., Pigott, V.C., 2009. The production of speiss (iron arse- Sci. 56, 221e232. nide) during the Early Bronze Age in Iran. J. Archaeol. Sci. 36 (2), 308e316. Müller, R., Rehren, Th., Rovira, S., 2004. Almizaraque and the early copper metal- Xian, Y., Li, Y., Yang, Q., 2016. Investigation report on the ancient turquoise mining lurgy of southeast Spain: new data. Madr. Mittl. 45, 33e56. site of Hekou in the Luonan county, Shaanxi province. Kaogu yu Wenwu Murillo-Barroso, M., Martinon-Torres, M., Massieu, Mª Dolores C., Socas, Dimas M., Archaeol. Cult. Relic 3, 11e17 (in Chinese). Gonzalez, Fernando M., 2017. Early metallurgy in SE Iberia. The workshop of Las Zhang, T., 2000. On the cultural remains in the Xia period eastern Guanzhong plain. Pilas (mojacar, Almería, Spain). Archaeol. Anthropol. Sci. http://dx.doi.org/ Wenbo Relics Museol. 3, 3e10 (in Chinese). 10.1007/s12520-016-0451-8. Zhao, C., 2004. Chemical compositional analysis and study of bronzes unearthed Ottaway, B.S., 2001. Innovation, production and specialization in early prehistoric from the Yinxu site, Anyang. Kaoguxue Jikan Collect. Pap. Archaeol. 15, 243e268 copper. Eur. J. Archaeol. 4, 87e112. (in Chinese).