金属矿床中磁铁矿和黄铁矿的逐步淋滤Pb-Pb同位素等时线直接定年

The Pb stepwise-leaching isotopic isochron has been used occasionally by researchers to determine the ages of some special geological events since 1990s. The methdolody is as follows. Different types and concentrations of acids are used to leach out stepwisely the common and radiogenic leads in different lettice positions of single minerals; the leaching solutions of different steps with various common lead to radiogenic lead proportions can be obtained; the Pb isotopic composions in the leaching solutions are analyzed by mass spectrometer and a Pb-Pb isochron can be yielded. The proponents of this project will choose pyrite and magnetite as research subjects. The pyrite and magnetite with relatively rich radiogenic Pb will be selected by means of in situ LA-MC-ICPMS analysis. The Pb stepwise leaching procedure will be optimized gradually through systematic experiment. We will strive to establish a feasible stepwise leaching Pb-Pb isochron method on pyrite and magnetite. Therefore the mineralization ages of some metallic mineral deposits can be obtained by directly analyzing the ore minerals, pyrite and magnetite.

20世纪90年代以来，陆续有学者尝试利用逐步淋滤法Pb-Pb同位素等时线定年来探索一些特殊地质事件的年龄。该技术是用不同种类、不同浓度的酸对单矿物进行逐步淋滤，将处于不同的晶格位置的放射成因铅和普通铅分步淋滤出来，不同阶段可以获得具有不同的放射成因铅和普通铅比例的淋滤液，对淋滤液进行质谱测定，从而获得Pb-Pb等时线年龄。本项目选用黄铁矿和磁铁矿为研究对象,用LA-MC-ICPMS原位铅同位素分析技术筛选放射成因铅较高的样品,通过系统地实验研究，不断优化逐步淋滤实验流程,建立针对黄铁矿、磁铁矿的逐步淋滤Pb-Pb同位素等时线定年方法，为金属矿床研究提供直接的定年数据。

逐步淋滤技术是用不同种类、不同浓度的酸对单矿物进行逐步淋滤，将处于不同的晶格位置的放射成因铅和普通铅分步淋滤出来，不同阶段可以获得具有不同的放射成因铅和普通铅比例的淋滤液，对淋滤液进行质谱测定，从而获得Pb-Pb等时线年龄的实验技术。本项目选用黄铁矿和磁铁矿为研究对象,用LA-MC-ICPMS微区原位Pb同位素分析技术筛选放射成因铅较高的样品, 根据设计的逐步淋滤流程，对筛选出的4件黄铁矿和2件磁铁矿样品进行了测定，获得了2个有意义的成矿年代学信息，另外4件样品测试结果虽不具有明确的地质意义，但可以反映Pb同位素物质的来源。