锡金属中的混合铅源:利用铅同位素研究锡文物的意义

IF 2.6 1区 地球科学 Q1 ANTHROPOLOGY
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引用次数: 0

摘要

利用铅的同位素组成对铜、铅和银进行探矿的方法已经非常成熟。只要考虑到锡石(SnO)的铀-钍-铅系统学和锡的生产过程,铅同位素分析也有望用于锡金属的研究。尽管前寒武纪锡石可能含有十数ppm的铅或更多(主要是放射性铅),但新生代的锡石通常只含有百万分之几的铅。然而,在欧洲青铜时代沉船出土的 133 块锡锭中,除了一块之外,其他所有锡锭的铅含量都超过了锡石本身的铅含量,而在 12 件经过分析的锡器中,有 6 件锡器被解释为来自南部非洲的矿石。因此,几乎所有锡器都必须含有来自外部锡石来源的铅,而对 LIA 的解释必须考虑到这种污染。污染物的性质(硫化物、含铀-锡矿物、硅酸盐)可以从铅浓度和铅含量的模式中推断出来。锡文物中的铅通常有三个主要来源:锡矿石中的原始铅、因铀衰变而在原地产生的放射性铅,以及锡石冶炼和铸锭生产过程中添加的外部铅。由于锡石具有较高的 U/Pb 值,但 Th/Pb 值较低,因此 Pb/Pb 值可能代表矿物中的初始 Pb 含量。这是假设在矿石加工过程中没有添加外部铅,或者添加的铅来自同一铅矿石产地的共生硫化物。在这种情况下,208Pb/204 Pb 可用于估算铅模型年龄,进而用于估算铸锭的出处。如果精矿中的 U-Th 矿物污染物增加了 Pb,那么也会增加 Pb/Pb,并导致错误的年轻 Pb 模型年龄。在这种情况下,Pb/Pb 和 Pb/Pb 的正相关值就会显示出问题。如果铅浓度超过一定的临界值(约 5 ppm)。这将清楚地表明,锡器中添加了外部的、非钙钛矿的铅。这些锡可能来自矿石中的杂质(如锡石中的夹杂物、精矿中的杂质),也可能是在矿石冶炼和/或金属加工过程中添加的。总之,Pb 浓度升高,并伴有普通 Pb 典型的非辐射 Pb 同位素,清楚地表明锡文物中添加了大量外部(杂质)Pb。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Mixed lead sources in tin metal: Implications for using lead isotopes to study tin artifacts

Methods for provenancing copper, lead, and silver using the isotopic composition of lead are well-established. Lead isotope analysis holds promise for the study of tin metal as well, as long as one accounts for the U-Th-Pb systematics of cassiterite (SnO2) and chaîne opératoire of tin production. Although Precambrian cassiterite may contain 10s of ppm Pb or more (predominantly radiogenic 206Pb), Phanerozoic examples typically contain only a few parts per million Pb. However, all but one of the 133 raw tin ingots excavated from European Bronze Age shipwrecks contains more Pb than could have come from cassiterite alone, as do six of the twelve analyzed tin objects interpreted to have been derived from the ores of southern Africa. Accordingly, almost all tin objects must contain Pb from external cassiterite sources and interpretation of LIA must account for this contamination. The nature of the contaminant (sulfides, U-Th-bearing minerals, silicates) can be inferred from patterns in Pb concentration and LI values. The 3 major sources of Pb that can typically be identified in tin artifacts are original Pb from the tin ore, radiogenic Pb produced in-situ due to U decay, and external Pb added during the cassiterite smelting and ingot production. As cassiterite has high U/Pb but low Th/Pb, the 208Pb/204Pb may be representative of the initial Pb incorporated in the mineral. This is assuming either that no external Pb is added during the ore processing or that the added Pb is from coeval sulfides from the same Pb ore provenance. In such cases 208Pb/204 Pb can be used to estimate a Pb model age, which in turn can be used for provenance estimate of the ingots. If the addition of Pb is from U-Th-mineral contaminants to the ore concentrate, then this will also increase 208Pb/204Pb and point to erroneously young model Pb ages. In such cases, the problem would be evident in positively correlated values of 206Pb/204Pb and 208Pb/204Pb. If Pb concentrations are above a certain threshold (approximately 5 ppm). LIA typical common Pb isotope ratios will be clear indication that external, non-cassiterite Pb, is added to the tin artifact. This tin could be from impurities in the ore (e.g., inclusions in cassiterite, impurities in the ore concentrate, or added during ore smelting and/or metal processing. Overall, elevated Pb concentrations accompanied with non-radiogenic Pb isotopes typical for common Pb, is a clear indication that significant amount of external (contaminant) Pb is added to the tin artifact.

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来源期刊
Journal of Archaeological Science
Journal of Archaeological Science 地学-地球科学综合
CiteScore
6.10
自引率
7.10%
发文量
112
审稿时长
49 days
期刊介绍: The Journal of Archaeological Science is aimed at archaeologists and scientists with particular interests in advancing the development and application of scientific techniques and methodologies to all areas of archaeology. This established monthly journal publishes focus articles, original research papers and major review articles, of wide archaeological significance. The journal provides an international forum for archaeologists and scientists from widely different scientific backgrounds who share a common interest in developing and applying scientific methods to inform major debates through improving the quality and reliability of scientific information derived from archaeological research.
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