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.

中文翻译：

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锡金属中的混合铅源：使用铅同位素研究锡制品的意义


利用铅的同位素组成来寻找铜、铅和银的方法已经很成熟。铅同位素分析也为锡金属的研究带来了希望，只要考虑到锡石 （SnO2） 的 U-Th-Pb 系统学和锡生产的 chaîne opératoire。尽管前寒武纪锡石可能含有 10 ppm 的 Pb 或更多（主要是放射性 206Pb），但显生代的例子通常只含有百万分之几的 Pb。然而，从欧洲青铜时代沉船中出土的 133 个原始锡锭中，除了一个之外，其他所有锡锭的铅含量都超过了单独来自锡石的铅含量，在分析的 12 个锡器中，有 6 个被解释为来自南部非洲的矿石。因此，几乎所有的锡制品都必须含有来自外部锡石来源的铅，对 LIA 的解释必须考虑到这种污染。污染物的性质（硫化物、含铀钍矿物、硅酸盐）可以从 Pb 浓度和 LI 值的模式中推断出来。在锡制品中通常可以识别的 Pb 的 3 个主要来源是锡矿石中的原始 Pb、由于 U 衰变而原位产生的放射性 Pb，以及锡石冶炼和铸锭生产过程中添加的外部 Pb。由于锡石的 U/Pb 高但 Th/Pb 低，因此 208Pb/204Pb 可能代表矿物中掺入的初始 Pb。这是假设在矿石加工过程中没有添加外部 Pb，或者添加的 Pb 来自来自同一 Pb 矿石来源的同代硫化物。在这种情况下，208Pb/204 Pb 可用于估计 Pb 模型年龄，而 Pb 模型年龄又可用于锭的来源估计。 如果 Pb 的添加来自铀-钍矿物污染物到精矿中，那么这也将增加 208Pb/204Pb，并指向错误的年轻型 Pb 年龄。在这种情况下，问题在 206Pb/204Pb 和 208Pb/204Pb 的正相关值中很明显。如果 Pb 浓度高于某个阈值（约 5 ppm）。LIA 典型的常见 Pb 同位素比值将清楚地表明外部的非锡石 Pb 被添加到锡伪影中。这种锡可能来自矿石中的杂质（例如，锡石中的夹杂物、精矿中的杂质），或在矿石冶炼和/或金属加工过程中添加。总体而言，Pb 浓度升高伴随着常见 Pb 的典型非放射性 Pb 同位素，清楚地表明锡伪影中添加了大量的外部（污染物）Pb。