中文摘要:在铅同位素研究中，异常铅是经常遇到并难于解释的问题。在一个矿区或矿带范围内，某些矿床的铅同位素资料中往往显示存在两种类型的铅：具有单阶段演化 历史的正常铅和具有两个(或多个)阶段演化历史的异常铅。在常规的铅同位素组成图解上，这两种铅的数据点有时构成异常铅等时线，正常铅则位于等时线上含放射性成因铅最低的位 置处。如果这种正常铅能给出合理的矿化年龄，并且该年龄与容矿围岩的成岩年龄基本一致 ，但显著老于异常铅瞬间增长模式年龄，那么，这种正常铅可能是异常铅等时线的起点，笔 者称其为P点铅。显然，异常铅是后期放射性成因铅加入到P点铅形成的，P点铅的模式年龄 为异常铅来源区的年龄。利用P点铅及异常铅等时线的资料，可以计算获得异常铅的矿化年 龄。因此，P点铅这个概念的提出，为探讨矿化年龄问题开辟了一条新途径。文章还以加拿 大和北欧地区某些矿床的铅同位素资料为例，讨论了在实际成矿过程中是否有P点铅存在的 问题，讨论了P点铅在矿床成因研究中的重要意义，并给出了如何判断P点铅的具体条件。
Abstract:In the study of the lead isotopes of a particular orebody or a special ore distr ict, anomalous leads frequently constitute a quite complicated problem whose int erpretation is rather difficult. Among the lead isotope ratio data from some ore deposits in a certain orefield or metallogenic belt, there often exist two kind s of leads, namely ordinary leads with single_stage model of evolution and anoma lous leads with multi_stage model of evolution. The isotope ratios of these lead s sometimes form a secondary isochron in coordinates of 206Pb/204 Pb and 207Pb/204Pb or 206Pb/204Pb and 208Pb/204Pb, and ordinary leads are located at the position of the least radiogenic leads in the isochron. If the ordinary leads can yield an acceptable age for the mineralization which corresponds to the age of surrounding rocks bu t is much older than the instantaneous growth model age of anomalous leads, the component of ordinary leads may be the initial lead of the anomalous line. In th is case, such ordinary leads are defined as the P point lead. Obviously, anomalo us compositions result from the addition of radiogenic leads to the common lead as represented by the P point lead, and the model age of the P point lead is ide ntical with the source age of anomalous leads. Mineralization age of anomalous l eads extracted from the surrounding rocks can be computed by using the model age of the P point lead and the anomalous line slope. Therefore, the proposed idea of P point lead has opened a new way to study the mineralization ages. Exemplifi ed by the lead isotope data from such deposits as Geneva Lake deposit, Kirkland Lake veins and Temagami Mine Road occurrence in Canada, and base metal sulfide d eposits in the Rappen area, northern Sweden, this paper discusses the problem wh ether or not the idea of P point lead corresponds to the reality of the minerali zation process, and illustrates the significance of applying the P point lead to the study of ore deposit genesis. Finally, this paper puts forward the identifi cation criteria for the existence of P point lead in a certain ore deposit or mi neralization belt.
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韩 发；孟祥金.2004.P点铅及其应用意义[J].矿床地质,23(1):77~81.2004.P Point Lead and Its Application to Metallogeny[J].Mineral Deposits23(1):77~81
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