一种新的稀有金属矿床定年技术：微区原位Sm-Nd定年

¹⁴⁷Sm-¹⁴³Nd放射性同位素体系在地球科学研究中得到了广泛的应用，经典的同位素稀释-热表面电离质谱法(ID-TIMS)一直是Sm-Nd同位素高精度测定的基准技术，但具有耗时长、成本高、样品需求量大等缺点，并且难以揭示微观尺度单矿物所蕴含的地球化学信息。近年来兴起的微区原位分析，具有简单、快速、高空间分辨率的特点，可以从微米尺度示踪岩浆和热液的起源及演化过程。本文通过同时测定Sm和Nd同位素质量分馏系数，实现¹⁴⁴Sm对¹⁴⁴Nd干扰的准确校正，获得了人造玻璃、磷灰石、榍石、独居石等几种不同基体标准样品(NIST610、Durango、MAD-2、BLR-1、117531)精确的¹⁴³Nd^/144Nd比值，与推荐值在误差范围内一致。然而，由于Sm和Nd元素性质的差异，在激光剥蚀和质谱电离过程中会产生明显的元素分馏，导致¹⁴⁷Sm/¹⁴⁴Nd很难进行精确校正，本文通过在进样系统中引入液态气溶胶，有效克服了基体效...

A new age determination technique for rare metal deposits: In situ Sm-Nd dating

¹⁴⁷Sm-¹⁴³Nd radioisotope system has been widely used in geoscience. The classical isotope dilution thermal ionization mass spectrometry (ID-TIMS) has always been the standard methods for high-precision determination of Sm-Nd isotopes. However, it is time-consuming, high cost and large demand for samples, and it is difficult to reveal the geological information especially in micro scale for a single crystal. In recent years, the in-situ analysis, which is simple, rapid and high spatial resolution, can trace the origin and evolution of ore deposits and magmas from the micro scale. In this study, the mass fractionation coefficients of Sm and Nd were determined simultaneously, the interference of ¹⁴⁴Sm on ¹⁴⁴Nd was corrected accurately. The accurately ¹⁴³Nd/¹⁴⁴Nd ratios of different matrix standard samples (NIST 610, Durango, MAD-2, BLR-1, 117531) were obtained, which were consistent with the recommended values within the error range. However, due to the different chemical properties of Sm and Nd, there will be obviously element fractionation in the process of laser ablation and mass spectrometry ionization, which makes it difficult to accurately correct ¹⁴⁷sm/¹⁴⁴Nd. In this study, the introduction of liquid aerosols in the sample inlet system can effectively overcome the influence of matrix effect. There are distinctly differences in Sm and Nd elemental fractionation coefficients between silicate minerals (artificial glass, sphene) and phosphate minerals (apatite, monazite, etc.), but the same type of minerals has stable and consistent elemental fractionation coefficients. Therefore, the external standard method can obtain accurate ¹⁴⁷Sm/¹⁴⁴Nd, which makes it possible for in-situ dating of ¹⁴⁷Sm-¹⁴³Nd. In situ Sm-Nd isotopic dating of monazite and bastnaesite in the Madi rare earth deposit, Hebei Province, has been carried out by using the newly established fs-LA-MC-ICPMS methods. It''s show that the age of monazite and bastnaesite is 177.2±6.3Ma, which is consistent with the in situ monazite U-Pb age of 175.6±1.1Ma. Those indicate that in-situ Sm-Nd isotopic analysis of monazite and bastnaesite can be used as a powerful technical tool to directly determine the formation age of rare earth deposits, and can also reveal the effective information of the source of ore-forming materials using the initial ¹⁴³Nd/¹⁴⁴Nd.