【作者】 汪常明；

【导师】 金正耀； Jiann-Yang Hwang；

【作者基本信息】 中国科学技术大学 ， 科学技术史， 2009， 博士

【摘要】 自然铜是人类使用最早的天然金属之一,它与人类早期文明存在重要联系。在全球范围内,北美地区不仅拥有最丰富的自然铜矿藏,而且拥有持续时间最长的自然铜文明。14C分析表明,北美印第安人约于6800年前开始利用自然铜,直至17世纪欧洲金属进入北美之后才逐渐停止使用。数千年来,北美土著人未能发展出冶铜技术,北美所有史前铜器皆自然铜直接打制而成。在哥伦布发现美洲大陆之前,北美还处于一种非常原始的社会状态,史前北美土著居民的生活图景,主要依赖考古研究去推断。探索这些早期铜器的矿料来源,对于了解北美史前矿业开发与利用、北美各部落间的商品交换和流通网络具有极其重要的意义。本文运用多种技术手段对北美自然铜进行了微量元素、铅同位素和铜同位素分析,目的是探索北美不同地区自然铜矿的上述3种地球化学特征,并由此探讨它们在北美铜器考古探源研究中的作用。在上述3种研究方法中,微量元素法是过去常用的一种探源分析法,本文着重了分析北美自然铜中的微量元素之一——铅元素在考古探源研究中的意义。铅同位素分析法是一种比较成熟的考古示踪研究方法,但在北美自然铜考古探源研究中的应用刚刚开始,本文对其开展了进一步的探索研究。铜同位素分析法是一种新兴的考古示踪法,本文首次将其应用于北美自然铜考古探源研究。本文运用这3种地球化学示踪法研究的具体内容及结论如下:首先,采用石墨炉原子吸收光谱法(GF-AAS)和电感耦合等离子体质谱分析法(ICP-MS)对北美多个矿区的66件自然铜样品进行了铅含量分析。分析结果表明,北美自然铜铅含量极低,且同一矿区甚至同一样品内部铅含量存在明显的不均匀性。自然铜的这种铅含量特征的发现为研究人员进行北美自然铜的铅同位素实验提供了重要参考信息。更重要的是,根据本实验及前人的分析结果,我们发现铅含量可作为判断北美自然铜与欧洲冶炼铜的一个有效标准。这对于区分北美遗址出土的北美自然铜铜器和欧洲冶炼铜铜器具有重要意义。此外,通过比较ICP-MS与GF-AAS所得到的实验结果发现,不同的分析方法所得到微量元素分析结果可能存在一定差异。因此,在进行微量元素分析时,分析方法的选择和实验室之间的比较十分重要。实验还通过扫描电镜能谱仪(SEM-EDS)对24个自然铜(包括5个冶炼自然铜)样品的成分进行了检测,结果表明,北美自然铜具有极高的纯度,通常高于99%。其次,采用热电离质谱法(TIMS)对北美4个自然铜矿区的13件自然铜样品进行了铅同位素分析。分析结果表明,所有自然铜样品中没有出现高放射性成因铅。Minong、Bisbee、Chititu三地的自然铜与北美史前人类利用最多的基维诺半岛自然铜铅同位素显示出了可区分的铅同位素特征,它们各自之间的铅同位素组成也存在一定差异。这一研究结果说明,铅同位素分析法在北美自然铜铜器的铜料来源研究中极可能是一种有效的示踪手段。最后,采用多接收电感耦合等离子体质谱分析法(MC-ICP-MS)对北美5个地区15个自然铜样品进行了铜同位素分析,分析结果显示它们的铜同位素(δ65Cu)变化范围相对较小。结合前人的分析数据发现,北美原生自然铜与次生自然铜具有明显不同的铜同位素组成,且较多数据表明密歇根地区的原生自然铜铜同位素组成较为均匀,与其它地区原生自然铜可能存在一定差别。此外,通过比较还发现北美原生自然铜与黄铜矿和辉铜矿的铜同位素组成具有显著差别,而后面两种矿物通常是生产冶炼铜的主要铜矿。综合上述分析结果认为,铜同位素分析技术在区分北美本土自然铜以及在区分欧洲冶炼铜和北美自然铜等考古研究中具有较大的应用潜力和广阔的发展前景。除了进行实验研究之外,本文对北美自然铜矿的利用史和北美铜文化进行了介绍与讨论;对过去北美自然铜的主要探源方法——微量元素示踪法的研究历史进行了梳理与评论;并对铅同位素和铜同位素考古探源研究进行比较详细的综述和讨论。更多还原

【Abstract】 Native copper is one of earliest metals used by human, it is an important material related to early civilization. There are the richest native copper deposits in North America, 14C dating indicates that native cooper had been utilized by American indigenous people in North America since 6800BP. The use continued until 17th century when European smelted copper entered North America. Archaeological studies show that native copper is the only material made into copper artifacts. For thousands of years, Indians fabricated a large number of copper artifacts by hammering, which were discovered in different prehistoric sites in North America. Before Columbus landed the America, North America was still in a primitive social stage. The life of aboriginals in North America could be only inferred through archaeological researches. Exploring the provenance of raw materials of those copper artifacts is an important content of North America prehistory. Understanding where native copper originated can provide critical information regarding trading routes, the interaction of cultures, the exploitation and use of mines.To establish the geochemical signatures of native copper of North America, three techniques: trace element, lead isotope and copper isotope analyses have been employed in this study. These three geochemical techniques are all important approaches to determine the geologic sources of artifact copper. Trace element analysis is a common method and has a history over one and half hundred years used to provenance study in North America. In this study, Pb, one of trace elements of native copper has been analyzed and its application to provenance study has been discussed. For the first time, the copper isotope technique is applied to archaeological provenance study of native copper in North America in this study. The analysis of lead isotope for native copper is also a pilot study in North America archaeology. Prior to experimental analysis, the history of mining of native copper and the copper culture in North America have been introduced and discussed. In order to understand the provenance study of native copper in North America better, reviews and discussion for three geochemical techniques have been made before the analyses.The main results and conclusions of this study are as following:Firstly, the Pb concentration of 66 native copper samples from several regions in North America has been determined by graphite furnace atomic absorption spectrometry (GF-AAS) and inductively coupled plasma mass spectrometer(ICP-MS). The results show that the native copper in North America has very low Pb content and exists obvious heterogeneity of Pb even in a single ore sample. By comparing GF-AAS and ICP-MS, we found different analytical techniques can yield different results. This indicates that care should be taken when choosing analytical technique in trace element study. According to the results of this study and previous analyses, it is found that Pb concentration may be used to distinguish native copper in North America and historical European smelted copper. Meanwhile, the analysis results also remind researchers need to pay special attention to Pb concentration and its heterogeneity when they are applying Pb isotope and trace element analysis to archaeology. The composition of 24 native copper samples (including 5 smelted native copper samples) has been analyzed by scanning electron microscope energy dispersive spectrometer (SEM-EDS). The results show that native copper is an extremely pure metal, generally purer than 99%.Secondly, the Pb isotope composition of 13 native copper samples from 4 regions has been measured by thermal-ionization mass spectrometry (TIMS). The result indicates there is no high-radiogenic Pb found in all samples. The Pb isotope compositiom of samples from Minong of Michigan, Bisbee of Arizona and Chititu of Alaska are different each other. Significant difference of Pb isotope signature also exists between these three regions and Keweenaw peninsula, Michigan where most quantity of native copper were mined by prehistoric Indians. The result of study suggests that Pb isotope can be used as a fingerprint to trace the geological sources of artifact copper in North America.Finally, the copper isotope signature of 15 samples from 5 native copper regions has been determined by multiple-collector plasma-source mass spectrometry (MC-ICP-MS). Results reveal a relative small range of variation (δ65Cu) of copper isotope within these samples. Along with previous analyses, we found that copper isotope composition of primary native copper is significantly different from secondary native copper. A relatively abundant data show that the primary native copper from Michigan has a relatively homogenous copper isotope composition and seems distinct from the other regions. In addition, significant different copper isotope variation exists between primary native copper in North America and chalcopyrite and chalcocite. In general, the latter two copper minerals are major sources for smelted copper. Conclusion can be drawn that copper isotope can be used as tracer in archaeological provenance studies of native copper. It will be a helpful tool in distinguishing native copper from different regions in North America as well as native copper of North America and European smelted copper.更多还原