Lead isotopic feature of the Besshi-type deposits and its bearing on the ore lead evolution
Lead isotopic feature of the Besshi-type deposits and its bearing on the ore lead evolution
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别子型矿床铅同位素特征及其对矿石铅演化的影响
DOI：
10.2343/geochemj.14.303
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发表时间：
1980
影响因子：
0.8
通讯作者：
A. Sasaki
中科院分区：
文献类型：
--
作者：
Kazuo Satō;A. Sasaki
对加拿大Flin Flon地区中生代和古生代Besshi型矿床的黄铁矿样品和元古代层状矿化的方铅矿样品进行了额外的铅同位素测量。Besshi型矿化的补充数据一方面证实了先前的观察结果，即这种类型的存款中的铅同位素可变，相对于主要铅（整合）矿石系统，207 Pb一直不足，另一方面表明，在某些情况下，即使在单个存款中，也存在小但显著的同位素变化。这些矿床的同位素模式类似于洋脊玄武岩的同位素模式，但与所研究的一个中生代矿床中发现的主要铅矿体的同位素组成及其演化模式的一致性形成鲜明对比，从而加强了以前的观点，即大多数贝西型矿床中的铅可能主要来自地幔。在Flin Flon地区，还发现了与主要铅矿石系统相关的207 Pb缺乏和其他两个与大多数Besshi型矿床共同的显著特征，这些特征与镁铁质岩浆活动密切相关，且通常为Pb贫乏性质。类似的层状沉积物的例子似乎存在于其他地区。Besshi型和其他207Pb缺乏矿床似乎表明存在幔源矿铅系统。此类矿床的成矿作用似乎最常见于太古代至早元古代和晚古生代至中生代地体，但也可能发生在其他硅质环境中，而推测为地壳成因的大型富铅矿体可能仅发现于元古代至晚古生代的硅铝质环境中。目前全球构造史的概念似乎与层状成矿带的两个主要演化系统的观点大体一致。
Additional lead isotope measurements have been made on pyrite samples from the Mesozoic and Paleozoic Besshi-type deposits and on a galena sample from the Proterozoic stratiform mineralization in the Flin Flon area, Canada. The supplemented data for the Besshi-type mineralization confirm, on the one hand, the previous observation that leads in this type of deposit are isotopically variable and are consistently deficient in 207Pb relative to the major lead (conformable) ore system, and reveal, on the other hand, that, in some cases, a small but significant isotopic variation exists even within a single deposit. The isotopic pattern of these deposits, which is similar to that of the ocean-ridge basalts, is in striking contrast with a uniform isotopic composition and its conformity with the evolutionary pattern of the major lead orebodies found in one of the Mesozoic deposits examined, and thus reinforces the previous view that the lead in most Besshi-type deposits may have been derived mainly from the mantle. The 207Pb deficiency relative to the major lead ore system and other two remarkable features common to most Besshi-type deposits, close association with mafic magmatism and generally Pb-impoverished nature, are also recognized in the Flin Flon area. Similar examples of stratiform deposits seem to exist in other areas. The Besshi-type and other 207Pb deficient deposits appear to indicate the presence of a mantle-derived ore-lead system. The mineralization of such deposits seems to occur most commonly in Archean to early Proterozoic and late Paleozoic to Mesozoic terrains, but might occur also in other simatic environments, whereas the large Pb-rich orebodies presumably of crustal origin may only be found in Proterozoic to Phanerozoic sialic environments. The current concept of global tectonic history appears to be generally consistent with the view of two major evolutionary systems of stratiform ore leads.