The Provenance of Copper Materials for Bronze Chariot-horse Unearthed from Yang’an Han Tomb in Qionglai, Sichuan Province revealed by the lead isotope analysis and trace elements analysis

doi:10.21203/rs.3.rs-3218981/v1

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The Provenance of Copper Materials for Bronze Chariot-horse Unearthed from Yang’an Han Tomb in Qionglai, Sichuan Province revealed by the lead isotope analysis and trace elements analysis

https://doi.org/10.21203/rs.3.rs-3218981/v1

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The high-grade bronze chariot-horse was unearthed in Yang’an Han tomb in Qionglai city, Sichuan Province, and its owner may be a vassal. In this study, metallographic microscopy, scanning electron microscope energy dispersive (SEM-EDS), multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), and inductively coupled plasma-atomic emission spectrometer (ICP-AES) were used to analyze samples from the bronze chariot-horse. The bronze chariot-horse samples were all Sn bronze, and the metallographic structure showed that the bronze chariot-horse was cast. The provenance of the copper material for the bronze chariot-horse was clearly different from that of the late Warring States period and other Western Han period bronzes excavated in the Sichuan area. According to historical documents and archaeological findings, the bronze chariot-horse unearthed in the Sichuan area may be related to the migration of the Liu Yue family, and the analysis of the lead isotope data indicated that the copper material probably came from the southeastern Hebei and western Shandong. This result provided an appropriate evidence for the relationship between the bronze chariot-horse and the family of Liu yue from the perspective of resource circulation.

bronze chariot-horse

the Western Han Dynasty

the circulation of copper materials

lead isotope analysis

trace elements analysis

The large-scale development of the Sichuan region began in the late Warring States Period. Li Bing, the local governor of the Shu State, was responsible for building Dujiangyan Irrigation Project, greatly promoting the development of agriculture and economy. The Western Han Dynasty further strengthened its rule over the Sichuan region through immigration, cultural transmission and economic support (Duan 1999). According to The Book of Han (the History of the former Han Dynasty, written by Bangu), during the Western Han Dynasty to the Xinmang Period, Chengdu, Luoyang, Linzi (now Zibo City, Shandong Province), Handan (now Handan City, Hebei Province) and Wan (now Nanyang City, Henan Province) were known as the “Five Metropolis”五都, and developed into regional economic centers second only to the capital Chang’an (now Xi’an City, Shaanxi Province). Archaeological data showed that the Western Han government established Xigong西工(official handicraft institutions) in Sichuan region, mainly producing lacquerware, textile and bronze for the royal family (Bai 2014). The inscriptions on bronze and lacquerware recorded that the artifacts were made in Xigong, Shu county蜀郡西工造, indicating that handicraft production in Sichuan area was an important component of the official handicraft industry during the Western Han Dynasty.

Qionglai City was a county-level city under the administration of Chengdu City, Sichuan Province. Geographically, it was located on the western edge of the Sichuan Basin and in the foothills of the Qionglai Mountains. During the 2009 excavations, more than 60 Han tombs were discovered in Yang’an Industrial Park, Qionglai city. Archaeologists found a bronze chariot-horse in tomb M39. It was composed of a chariot and four horses with typical Han Dynasty features. The bronze chariot-horse was crushed by the collapsed coffin, causing the bronze chariot-horse to be crushed into several pieces. Based on the pottery, lacquerware, and other artifacts unearthed from the same tomb, it was inferred that the tomb could be dated to the middle and late Western Han Dynasty (around 140BC ~ 8AD) (Suo 2013).

Based on current archaeological discoveries, about 8 bronze chariot-horse have been discovered in Guizhou, Sichuan and Gansu Province (Ren 2019). The owner of the bronze chariot-horse found in Wuwei city, Gansu Province was Zhang Xiu张绣, the Duke of Xuanwu宣武侯in the Eastern Han Dynasty (Chu 1982), while that of other bronze chariot-horses were unclear. The Book of Etiquette and Ceremonial仪礼 (a classic Confucian text describing details of ceremonies) recorded that the number of burial horses represented the identity and status of the tomb owner during his lifetime in the Zhou Dynasty (771BC-221BC). The Emperor’s chariot was drawn by six horses, the vassal’s chariot by four horses. The Han Dynasty continued this burial system. Although we did not find any information identifying the owner of the tomb in Yang’an Han tomb M39, the number of buried horses matched the status of the vassals in the literature. Therefore, it was inferred that the tomb owner may have been a high-ranking noble.

In this paper, we analyzed the alloy composition and manufacturing process of bronze chariot-horse unearthed from Yang’an Han tomb in Qionglai. Lead isotope analysis and trace elements analysis have been used to discuss the circulation of mineral materials in Sichuan area during the Western Han Dynasty. These two methods were the most commonly used methods for exploring the circulation of metal resources in metallurgical archaeological research (Jin 2008; Wei 2007). This paper aimed to determine the possible provenance of copper materials for bronze chariot-horse combined with relevant historical literature and archaeological discoveries.

Seventeen samples were taken from the edges of fragments from different parts of bronze chariot-horse. The detailed introduction of samples was listed in Table 1 and shown in Fig. 2.

Table 1

the introduction of samples from bronze chariot-horse
No.	Sample type	Archaeological No.	Lab. No.	Sampling location
1	bronze horse	M39:1	TM1-1	fragment on the chest
2	bronze horse	M39:1	TM1-2	fragment on the chest
3	bronze horse	M39:1	TM1-3	right hind leg
4	bronze horse	M39:1	TM1-4	left front leg
5	bronze horse	M39:1	TM1-5	right hind leg
6	bronze horse	M39:2	TM2-1	the fracture of the neck
7	bronze horse	M39:2	TM2-2	left hind leg
8	bronze horse	M39:3	TM3-1	right front leg
9	bronze horse	M39:4	TM4-1	the mane of horse
10	bronze horse	M39:4	TM4-2	right front leg
11	bronze horse	M39:4	TM4-3	left front leg
12	bronze horse	M39:4	TM4-4	fragment on the chest
13	chariot	M39:7	CX7-1	chariot fragment
14	chariot	M39:7	CX7-2	bottom plate
15	chariot	M39:11	CX7-3	bottom plate
16	wheel	M39:8	CL8-1	wheel rims
17	wheel	M39:8	CL8-2	wheel spoke

Chemical compositional analysis

Chemical compositional analysis was conducted by using SEM (Dutch FEI Sirion200 field emission scanning electron microscope) and EDS (Oxford INCA spectrometer, UK.) at the Physics and Chemistry Experiment Center of University of Science and Technology of China. Considering the component segregation of the sample, 2–3 areas with a well preserved substrate were selected for scanning under a low-power microscope, and the average value was taken as the final result. The alloy composition of the 10 bronze chariot-horse samples were listed in Table 2.

Metallographic analysis

The samples were inlaid with polymer and polished before being tested. Using ferric chloride hydrochloric acid ethanol solution to etch the sample, we then took images and observed using a ultra-depth microscope (KEYENCE,VHX-2000C) at the Laboratory of Archaeometry in Anhui University.

Lead isotopic analysis

Lead isotope ratios were carried out by MC-ICP-MS (VGELEMENTAL) at the School of Earth and Space sciences of Peking University in Beijing, China. In order to ensure the accuracy and stability of the instrument, the international lead isotope standard SRM981 was measured respectively before and after the sample measurement, the overall analytical 2σ error of ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb for all bronze samples were 0.000019 and 0.00018, respectively. The results of MC-ICP-MS analysis were listed in Table 3.

Trace elements analysis

Trace elements were carried out by ICP-AES (iCAP 7400DUO, Thermo) in the Modern Experimental Technology Center of Anhui University. Based on previous research, the trace elements Co, Ni, As, Sb, Au, Ag, Se, Te, and Bi were indicative of the provenance of the raw materials for the bronzes (Qin et al 2004; Li 2004; Wei 2007). We carried out the trace element analysis on 11 samples. The results of ICP-AES analysis were listed in Table 4.

3.1 Chemical composition

Table 2 showed that Cu content of the samples ranged from 47 ~ 67% and Sn content from 2 ~ 8%; Pb content was generally low, and the highest was only 0.7%. The bronze samples were severely corroded, so the alloy compositional data were for reference only. The overall copper content was lower than the general measurement value, and the elements C, Cl, Na, K were detected, which may be related to the loss of Cu due to corrosion.

Lead concentration was a major concern when using lead isotope analysis to investigate the provenance of copper-based metals in antiquity (Gale and Stos-Gale 1982). There was no agreement on the type of raw material reflected by the lead isotope data. Some scholars believed that lead should come from lead impurities in copper ore residues if the lead content was between 50 ppm to 4% (Gale and Stos-Gale 2000), while other scholars proposed 1 wt% of lead as intentional alloy component. Given that Chinese scholars often use 2% as the threshold to discuss the related issues of lead isotope, in this paper, we also used the conventional threshold of 2 wt%. Based on this criterion, it was concluded that the bronze chariot-horse samples were all tin bronze, which meant that the lead present in these objects was considered to be associated with the copper ore sources and that the lead isotopic composition was representative for that of the copper sources.

Table 2

SEM-EDS analysis results of the samples from Yang’an Han Tomb in Qionglai (wt%)
No.	Lab. No.	Cu	Sn	Pb	other elements	Alloy type
1	TM1-2	63.37	6.77	0.17	29.69	Cu-Sn
2	TM1-3	58.27	4.37	0.40	36.96	Cu-Sn
3	TM2-1	53.43	7.90	0.07	38.60	Cu-Sn
4	TM2-2	50.43	5.10	0.70	43.77	Cu-Sn
5	TM3-1	66.17	2.97	0.07	30.25	Cu-Sn
6	TM4-2	47.57	3.97	0.13	48.33	Cu-Sn
7	TM4-3	47.07	2.10	0.07	50.76	Cu-Sn
8	CX7-1	53.33	5.07	0.30	41.30	Cu-Sn
9	CX7-2	58.47	2.23	--	39.30	Cu-Sn
10	CL8-1	60.07	5.33	0.67	27.93	Cu-Sn

3.2 Metallographic microstructure

Figure 3 presented the metallographic pictures of the bronze chariot-horse. All analyzed samples were typical casting microstructure, which shows a dendritic microstructure with (α + δ) eutectoid, lead inclusions and sulfide inclusions scattered throughout the matrix. There was no sign of secondary processing. The lead existed in fine particles, such lead distribution had little effect on the matrix cutting and the mechanical properties of the alloy. Moreover, free copper particles were also found in the rusted parts of some samples (TM2-1). There was no consensus on the mechanism of free copper particles formation, some scholars argued that it was caused by electrochemical corrosion of bronze alloys (Sun 1996), while others believed that it was the result of dealloying effect (Wan 1989).

3.3 Pb isotope ratios

As can be seen in Table 3, lead isotope ratios of bronze chariot-horse samples ranged from 0.861 ~ 0.883 for ²⁰⁷Pb/²⁰⁶Pb, from 2.12 ~ 2.183 for ²⁰⁸Pb/²⁰⁶Pb, from 17.616 ~ 18.30 for ²⁰⁶Pb/²⁰⁴Pb, from 15.560 ~ 15.763 for ²⁰⁷Pb/²⁰⁴Pb, and from 38.461 ~ 38.831 for ²⁰⁸Pb/²⁰⁴Pb. All the lead isotope ratios conformed to the characteristics of common lead (Jin 2008).

Table 3

The results of lead isotope ratios of bronzes chariot-horse samples
Lab. No.	²⁰⁷Pb/ ²⁰⁶Pb	Error	²⁰⁸Pb/ ²⁰⁶Pb	Error	²⁰⁶Pb/ ²⁰⁴Pb	Error	²⁰⁷Pb/ ²⁰⁴Pb	Error	²⁰⁸Pb/ ²⁰⁴Pb	Error
TM 1–3	0.8654	0.00002	2.148	0.00016	18.0458	0.00165	15.6169	0.00133	38.7626	0.00631
TM 1–4	0.8643	0.00002	2.1455	0.00003	18.086	0.00286	15.6324	0.0022	38.8029	0.00655
TM 1–5	0.8614	0.00002	2.122	0.0021	18.2992	0.023	15.7625	0.0198	38.8308	0.00802
TM 4 − 1	0.8684	0.00001	2.1515	0.00013	17.9649	0.0009	15.6016	0.00071	38.6514	0.00271
TM 4–4	0.8687	0.00005	2.1408	0.00058	18.1033	0.00851	15.7261	0.00821	38.7555	0.00811
CS 11 − 1	0.8833	0.00003	2.1833	0.00024	17.6156	0.00472	15.5602	0.00459	38.4605	0.00826

3.4 Trace elements

As can be seen in Table 4 and Fig. 4, the As amount of the bronzes was extremely high, the Zn, Co, Sb, Au amount were low. The trace elements characteristics of the bronze chariot-horse were generally similar, indicating that their copper materials may have the same source.

Table 4

Analysis results of bronze chariot-horse unearthed from Yang’an Han Tomb (µg/g)
Lab. No.	Zn	As	Co	Ni	Sb	Bi	Ag	Au
TM1-1	595.23	1678.6	184.52	666.67	464.3	1315.5	1333.33	56.62
TM1-2	498.8	2040.3	168.2	596.8	535.7	1188.9	967.7	52.36
TM1-3	562.1	1992.1	198.4	814.81	839.95	837.3	1113.76	56.63
TM2-1	472.38	1854.48	160.82	545.62	408.69	871.51	737.76	53.08
TM2-2	584.23	2185.6	197.63	666.97	478.62	1064.09	1303.09	5.74
TM4-2	73.4	1147.8	114.2	441.46	444.34	483.69	740.89	72.58
TM4-3	597.59	1418.06	96.38	491.56	506.02	966.26	862.64	65.38
CX7-1	47.1	188.63	14.5	60.56	62.69	150.88	88.11	57.43
CX7-2	571.15	2120.17	188.46	637.5	353.84	1594.22	694.22	65.91
CL8-1	625.9	2320	193.6	703.08	514.25	1092.6	1222.1	148.8
CL8-2	468.84	1830.08	153.56	561.2	400.02	767.68	630.61	70.1

4.1 Comparison between bronze chariot-horse with bronzes from the Warring States Period and Western Han Dynasty in Sichuan area

We used the copper groups (CG) method to classify the trace element of the bronze chariot-horse. This method makes use of the absence or non-absence (using 0.1% as the cut-off to distinguish) of arsenic (As), antimony (Sb), silver (Ag) and nickel (Ni) to build 16 trace element groups for discussing the circulation of raw materials (Bray 2009; Bray and Pollard 2012; Bray et al. 2015; Pollard et al. 2017a, 2017b). The trace elements grouping results showed that the copper groups of the bronze chariot-horse were distributed CG1, CG2 and CG9. Combined with previous studies on trace elements grouping, the copper groups of the late Warring States Period bronzes excavated in Sichuan area were mainly concentrated in CG2, CG4, and CG7 (Li 2020). Other groups, like CG1 and CG12, constituted only a small proportion. Although CG2 accounted for a certain percentage in both the copper groups of the Xinghelu bronzes and the bronze chariot-horse, the differences in the trace elements grouping should not be ignored, and reflected the possibility of different sources of copper materials.

Table 5

Grouping of trace elements in bronzes chariot-horse, bronzes from Xinghelu cemetery and Baishoulu cemetery, Chengdu
Site	CG1 NNNN	CG2 YNNN	CG4 NNYN	CG7 NYYN	CG9 YNYN	CG12 YYYN	Total No.	Data source
Xinghelu cemetery	1%	20%	29%	49%		1%	224	Li et al. 2020
Baishoulu cemetery	11%		32%	54%			28	Li et al. 2020
Bronze chariot-horse	9%	55%			36%		11	This paper

Due to the limitation of trace elements of the Western Han bronzes unearthed in Sichuan area, it was currently unclear about the relationship between the bronze chariot-horse and other Western Han bronzes excavated in Sichuan area from the perspective of trace elements grouping.

We further discussed the utilization of the copper materials between the bronze chariot-horse and the bronzes excavated in Sichuan area by comparing the lead isotope data. Some published lead isotope data of bronzes unearthed in Sichuan area were collected, including the Western Han copper spearheads from Huili County (Du 2016), the bronze wares from Baishoulu cemetery (Li 2020) and the willow-leaf shaped bronze swords from Shuangyuan cemetery (Wang 2021). The latter two were the late Warring States period sites found in Chengdu. It should be noted that the lead isotopes of these artifacts selected in this paper all indicated the source of copper materials.

By comparing lead isotope data of these bronzes with that of the bronze chariot-horse, it can be seen in Fig. 5 that all data can be divided into three groups: Group A, Group B and Group C. The lead isotope data of the bronze chariot-horse distributed in group A (except TM1-5). The artifacts falling within Group B included the Warring States Period bronzes and a portion of the Western Han copper artifacts excavated in Huili, Sichuan, while other the Western Han copper spearheads from Huili fell within Group C. One interesting finding was that the provenance of copper materials for the bronze chariot-horse was different from that for the bronzes of the late Warring States period and the Western Han Dynasty in Sichuan area, which indicated that its copper materials had other sources. It was consistent with the result of trace elements analysis.

The lead isotope data of the Warring States Period bronzes and a portion of the Western Han copper atifacts from Huili overlapped in Group B, suggesting that the supply of raw materials may be more stable at that time in the Sichuan basin, which may be related to the abundant copper resources and the closed geographical environment in this area. The modern geological survey data revealed that southwest Sichuan and northeast Yunnan were one of the famous copper ore distribution belts in China, namely the Sichuan-Yunnan Copper Belt (Huang 2001). A large number of bronzes unearthed from Sanxingdui, Jinsha and other pre-Qin sites indicated that there was no shortage of the copper materials in this area, even though some copper materials may have been imported. It was important to note that we did not collect lead isotope ratios indicated the copper source of Qin Dynasty bronzes, so it is uncertain whether the source of copper materials changed during the Warring States Period to the Western Han Dynasty. Although Chen et al. published lead isotope data for Qin Dynasty Ban Liang coins from the Chengdu Plain, they indicated the source of the lead materials (Chen 2021).

The artifacts falling within Group C had ²⁰⁷Pb/²⁰⁶Pb<0.81 and ²⁰⁶Pb/²⁰⁴Pb>19.5, which showed the characteristics of the highly radiogenic lead (HRL) (Jin 2008). Based on previous studies, the use of minerals containing HRL was from the Erligang Period to the Yinxu III Period, after which it was no longer used on a large scale (Jin 2017). Wang et al. research showed that the lead isotopic signature of Huili copper spearheads was consistent with those of the local copper deposits, so it was more likely that the spearheads were made from the local ores (Wang 2020).

What caused the change of copper materials for bronze chariot-horse? Was it related to the use of bronze chariot-horses as high-grade burial objects? Addressing the provenance of the copper materials for bronze chariot-horse would be a very meaningful archaeological issue.

4.2 The provenance of copper materials for bronze chariot-horse

In this section of the paper, we attempted to discuss the possible copper materials provenance of the bronze chariot-horse. Due to lack of trace element data of copper ingots unearthed in Sichuan area, we compared the published trace element data of copper ingots from Daye, Zhongtiao Mountain, and the Southern Anhui (Wei 2007; Luo 2008) with those of bronze chariot-horse by using Principal Component Analysis (PCA). In Fig. 6, the data of the bronze chariot-horse were distributed in the separate area except for one point that overlapped with the copper ingots from Daye, it seemed impossible that the copper materials of the bronze chariot-horse derive from the compared areas.

In order to further determine the copper source of bronze chariot-horse, the lead isotope data of bronze chariot-horse were analyzed. According to the Geo-chemical province theory in China (Zhu 1998), most of the data in this paper belonged to the lead isotope zone of the Geo-chemical province of Yangtze (²⁰⁶Pb/²⁰⁴Pb=17.5 ~ 18.2, ²⁰⁷Pb/²⁰⁴Pb=15.33 ~ 15.6, ²⁰⁸Pb/²⁰⁴Pb=37.5 ~ 39.0), which suggested that the copper material of the bronze chariot-horse should be mainly sought within the scope of Yangtze province.

The lead isotope data of the bronze chariot-horse were compared with several potential ore sources in Southern Anhui, Hubei, and Sichuan-Yunnan in order to identify the most probable copper source. Documents and archaeological findings proved that copper mines in these areas were already exploited during the Western Han Dynasty.

The Southern Anhui was one of the important copper belts in the middle and lower reaches of the Yangtze River. During the reign of Emperor Wu of Han Dynasty, he adopted a series of economic policies and centralized the right of iron, salt and coin under the central government. The dedicated official was established to manage copper mining in Danyang (now the southern Anhui province and parts of Jiangsu and Zhejiang province). Due to the high quality of Danyang copper, it was shipped to Cang’an (the capital of the Western Han) and other regions for bronze casting during the Western Han period.

Based on historical documents, the copper mines in Sichuan and Yunnan were exploited on a certain scale during the Han Dynasty. “Records of the Historian” recorded that Emperor Wen of Han rewarded Dengtong邓通with copper deposit within the territory of Yan Dao严道 (present-day Xingjing荥阳, Ya’an雅安, Sichuan province) for making coins, indicating copper ore was mined and used locally. Moreover, according to The Book of Han, copper mining in Qiongdu邛都, Yuexi Jun越嶲郡 (present-day Xichang, Sichuan ), Laiwei 来唯(present-day Mengzi, Yunnan) and Yuyuan俞元(present-day Chengjiang, Yunnan), Yizhou Jun益州郡were also exploited in the Western Han Dynasty.

In addition to the above two regions, lead isotope data from copper deposits in the middle reaches of the Yangtze River in Hubei were selected for comparative study. The middle reaches of the Yangtze River was one of the areas with concentrated distribution of skarn copper deposits in China. During the Shang and Zhou Dynasties, it was a very important source of copper material and continued to be mined in the Han Dynasty (Huangshi Municipal Museum 1999).

We carried out 2D kernel density estimation analysis method to compare lead isotope ratios of bronze chariot-horse with modern copper ores and polymetallic ores from the three areas mentioned above. The data were plotted to discuss the probable source of copper materials (Fig. 7). The concentration of lead isotope data for the bronze chariot-horse differed significantly from those of the copper ores of the southern Anhui and Hubei (Fig. 7a and Fig. 7b), which indicated that the copper material could not derive from these area. Although the Sichuan-Yunnan area had better matches, its kernel density data centers did not overlap with lead isotope data distribution of the bronze chariot-horse (Fig. 7c). By comparison, it was believed that the copper materials for bronze chariot-horse could not be determined at present.

This conclusion did not discourage us, on the contrary, it stimulated our interest in exploring the source of the copper material for the bronze chariot-horse. Once again, we focused our attention on the bronze chariot-horse itself. As mentioned previously, the bronze chariot-horse was a high-grade burial object, and its user could have been a vassal. However, the central government of the Western Han Dynasty ruled the Sichuan area through establishment of prefectures and counties, and no one was enfeoffed as a vassal in Sichuan area during the Western Han Dynasty (Duan 1999), so was it possible that he migrated to Sichuan from elsewhere?

Based on such considerations, An important archaeological discovery not far from the Yang’an Han tomb had to be brought up. From 2017 to 2018, a brick tomb of the Han Dynasty was found in Fankuai Village, Qionglai City (Wang 2018). Archaeologists found a seal (consisting of a big hollow seal and a small seal) in the tomb, with seal characters: Liu Yue 刘越 and Zi Zhong 子仲 (Fig. 8). According to The Book of Han, Liu Yue was the son of the Emperor Jing of the Western Han Dynasty, and was enfeoffed as King of Guangchuan. His fiefdom was in the present-day Jing County, Hengshui City, Hebei Province. It was speculated that the appearance of his private seal in Qionglai may be related to the migration of future generations. Although we could not hastily link the owners of the bronze chariot-horse to the Liu Yue family, this discovery offered at least a possibility. If the owner of the bronze chariot-horse was related to the Liu Yue family, was it possible that the copper material came from the northern China?

To confirm our reasoning, lead isotope data from copper mines in southeastern Hebei and western Shandong were collected. In addition, lead isotope data from the slags in the Linzi city site of Qi State were also selected because Linzi was not far from Guangchuan State, and was an important copper casting workshop in the Western Han Dynasty (Cui 2021). Figure 7d showed that the lead isotope data of the bronze chariot-horse overlapped well with the kernel density data centers. Thus, on balance, we were inclined to believe that the copper materials for the bronze chariot-horse could come from southeastern Hebei and western Shandong. This result was also consistent with the previous hypothesis. The significance of this result not only identified the possible source of copper materials for the bronze chariot-horse, but also provided an appropriate evidence for the relationship between the bronze chariot-horse and the Liu Yue family from the perspective of resource circulation.

Another question aroused our great interest. Was the bronze chariot-horse circulated to the Sichuan area as finished object or made locally in Sichuan? Assuming that the bronze chariot-horse was cast locally, it seemed unlikely that the copper material was transported over long distances, since there was no shortage of copper material in the Sichuan area. The more reasonable possibility was that the bronze objects from the Guangchuan state were remelted and reused for casting the bronze chariot-horse. Due to the limitation of sample quantity, it was difficult to further discuss this issue. Several hypotheses could be formulated, and either explanation was not readily accepted until further research was conducted.

In this paper, the alloy composition, metallographic microstructure, lead isotopes and trace elements of the bronze chariot-horse excavated from the Yang’an Han tomb in Qionglai were analyzed, and the conclusions of the study were drawn as follows:

(1) The bronze chario-horse was a high-grade buried object, which consisted of a chariot and four horses. The number of the horses matched the status of the vassals in the literature. it was inferred that the tomb owner may have been a high-ranking noble.

(2) All the bronze chariot-horse samples were tin bronze. The lead isotope data conformed to the characteristics of the common lead and represented the source of copper materials. The metallographic images showed typical casting microstructure, indicating that the bronze chariot-horses were cast.

(3) Trace elements analysis and lead isotope analysis showed that the provenance of the copper materials for the bronze chariot-horse was clearly different from that of the late Warring States period and other Western Han period bronzes excavated in the Sichuan area. The copper materials for the bronze chariot-horse probably came from southeastern Hebei and western Shandong, which provided an appropriate evidence for the relationship between the bronze chariot-horse and the Liu Yue family from the perspective of resource circulation.

We confrm that neither the manuscript nor any parts of its content are currently under consideration or published in another journal. All authors have approved the manuscript and agree with its submission to the Archaeological and Anthropological Sciences.

Acknowledgements We would like to thank Yangmin Gong and Yumao Liu from Chengdu Municipal Institute of Cultural Relics and Archaeology for providing the samples.

Funding This research was funded by The National Social Science Fund of China (grant number 21BKG019) .

Author contribution Guofeng Wei and Ruixiang Zhang performed the data analysis, and wrote and edited the manuscript. They contributed equally to the manuscript and should be regarded as co-first authors. Hongyan Shi collected the study samples and analysed the data. Ning Wang and Tao Yang provided the archeological samples and took part in the sampling. All authors read and approved the final manuscript.

Data Availability All the data generated or analyzed during this study are included in this published article.

Competing interests The authors declare no competing interests.

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No competing interests reported.

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The Provenance of Copper Materials for Bronze Chariot-horse Unearthed from Yang’an Han Tomb in Qionglai, Sichuan Province revealed by the lead isotope analysis and trace elements analysis

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Version 1

Abstract

Figures

1 Introduction

2 Samples and methods

3 Results

3.1 Chemical composition

3.2 Metallographic microstructure

3.3 Pb isotope ratios

3.4 Trace elements

4 Discussion

4.2 The provenance of copper materials for bronze chariot-horse

5 Conclusions

Declarations

References

Additional Declarations

Status:

Version 1