辉钼矿微区原位Re-Os同位素定年方法研究

The metallogenic geochronology problems of large number of metal deposits have been solved by traditional solution method of molybdenite Re-Os dating. However, the solution method is composed of time-consuming mineral separation and complex chemical preparation. Moreover, some deposits cann’t be dated using this kind of solution analysis because very few molybdenite could be found, and some Re-Os age differences and variations in the mineral scale may be missed, especially for the multi-stage deposits. With the improvement of analytical methods and instruments, in situ isotopic analysis are developing rapidly because of the advantages of fast, low cost and no pollution. Base on the study of mass fractionation correction and age calculation methods, some molybdenite standard samples dated by NTIMS will be chosen as external standard to date the molybdenites using femtosecond laser ablation- multicollector mass spectrometry. In situ Re-Os dating of molybdenite will provide a rapid and effective method for the direct dating of metal deposits. High spatial resolution Re-Os age for different occurrences and multiple episodes molybdenite from Suoerkuduke Cu-Mo deposit will be obtained using this method, and the problem of metallogenic chronology and mineralization processes will be researched.

传统的辉钼矿溶样Re-Os定年方法解决了大量内生金属矿床成矿年代学问题，但是需要繁杂的矿物分选和化学前处理，并且很难解决多期次叠加矿床和样品量少辉钼矿定年问题。随着分析方法的不断提高和仪器的不断改进，原位同位素分析技术以其快速、低成本、无污染等优势得到了迅速发展。本申请拟在质量分馏校正和年龄计算方法研究基础之上，选取已知年龄不同时代辉钼矿样品作为外标，采用飞秒激光-多接收质谱联用技术对未知辉钼矿样品进行原位Re-Os定年，为金属矿床直接定年提供一种快速、有效的技术手段。并以此对存在多期叠加成矿的新疆索尔库都克Cu-Mo矿床中不同部位、不同产状辉钼矿开展高空间分辨率Re-Os定年，解决其成矿年代学问题，精细地刻画其成矿过程。

传统的辉钼矿溶样Re-Os定年方法解决了大量内生金属矿床成矿年代学问题，但是需要繁杂的矿物分选和化学前处理，并且很难解决多期次叠加矿床和样品量少辉钼矿定年问题。随着分析方法的不断提高和仪器的不断改进，原位同位素分析技术以其快速、低成本、无污染等优势得到了迅速发展。本项目研制了3件不同时代辉钼矿原位Re-Os同位素定年标准物质研制，采用双外标校正法实现了元素分馏和质量歧视效应的有效校正，建立了飞秒激光-多接收质谱联用辉钼矿样品进行原位Re-Os定年技术，并对不同含量、不同时代辉钼矿样品进行原位Re-Os定年，与传统的溶液方法相比，年龄越老的辉钼矿样品获得的原位Re-Os年龄准确度越高，对于Re 含量大于37 ppm并且年龄老于57 Ma辉钼矿样品，能够获得较为精确的原位Re-Os年龄。该方法具有快速、低成本、高空间分辨率等优势，为存在多期次叠加成矿的辉钼矿样品以及小颗粒、难挑选辉钼矿样品Re-Os年龄精确测定提供了一种有力的技术手段。采用火试金法制备的NiS基体标样作为外标，建立了低含量硫化物原位Re准确测定技术，该方法能够快速实现几百pg/g级低含量硫化物Re的准确分析，对于识别低含量硫化物是否适合进行Re-Os同位素定年研究以及探讨Re-Os同位素定年机理都具有重要意义。通过详细的野外和矿相学工作，将新疆索尔库都克Cu-Mo成矿事件主要分为三期，早期矽卡岩金属矿物主要为磁铁矿、黄铁矿、磁黄铁矿、黄铜矿和辉钼矿，即Fe-Cu-Mo组合，早期辉钼矿、黄铜矿Re-Os年龄介于386-391Ma；与晚期矽卡岩有关的金属矿物为黄铁矿、黄铜矿、辉钼矿及闪锌矿，即Cu-Mo-Zn组合晚期辉钼矿Re-Os年龄为288-297Ma；此外，还识别出一起主要以绿帘石化为特征的Mo矿化事件，辉钼矿Re-Os年龄为337Ma。