Tin isotopes via fs-LA-MC-ICP-MS analysis record complex fluid evolution in single cassiterite crystals
Tin isotopes via fs-LA-MC-ICP-MS analysis record complex fluid evolution in single cassiterite crystals
复制标题
通过 fs-LA-MC-ICP-MS 分析锡同位素记录了单个锡石晶体中复杂的流体演化
DOI：
10.2138/am-2021-7558
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发表时间：
2021-02
影响因子：
3.1
通讯作者：
Zhenhua Zhou
中科院分区：
文献类型：
--
作者：
Peng Liu;Jingwen Mao;Bernd Lehmann;Stefan Weyer;Ingo Horn;Ryan Mathur;Fangyue Wang;Zhenhua Zhou
摘要锡锡矿的锡同位素地球化学特征可用于恢复锡矿流体演化过程。本文采用飞秒激光烧蚀多接收电感耦合等离子体质谱（fs-LA-MC-ICP-MS）对中国东南部西岭脉型锡存款矿床早期和晚期的两种锡锡石晶体进行了阴极发光（CL）成像、微量元素和原位Sn同位素组成研究。研究结果表明，来自高温辉长岩-稳定热液环境的早期辉长岩具有核、幔和边缘带，其δ124/117 Sn 3161 A（相对于Sn标准NIST 3161 A）从晶核的+0.38 ± 0.06‰降低到地幔带的-0.12 ± 0.06‰（2 SE）。这种同位素演变，也被钽含量减少了两个数量级，表明流体批次向同位素轻锡演变。该晶体的边缘区域具有中等的锡同位素组成，约为+0.05‰ δ124/117 Sn 3161 A，并伴有高Ta，表明存在第二批流体。白云母稳定热液环境中形成的晚期钙铝榴石晶体，其核部Sn同位素组成为δ124/117 Sn 3161 A =-0.15‰，Ta含量较低，边缘Sn同位素组成为δ124/117 Sn 3161 A =+0.30 ± 0.08‰，Ta含量较高。对于早期晶体，该晶体的形成必须涉及两种不同的流体批次。我们的试点研究突出了空间分辨分析的优势相比，传统的，解决方案锡同位素分析散装钙钛矿晶体。锡同位素在微观尺度上的变化揭示了封闭和开放系统的流体演化和同位素分馏相结合的钙镁矾晶体生长的复杂性。
Abstract Tin isotope geochemistry of cassiterite may allow for reconstructing the fluid evolution of tin ore deposits. Here, we present cathodoluminescence (CL) imaging, trace element, and in situ Sn isotope compositions of two cassiterite crystals from an early and a relatively late stage of ore formation of the Xiling vein-style Sn deposit, southeastern China, by femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICP-MS). Our results show that the early-stage cassiterite from a high-temperature feldspar-stable hydrothermal environment has core, mantle, and rim zones with a systematic decrease in δ124/117Sn3161A (relative to the Sn standard NIST 3161 A) from +0.38 ± 0.06‰ in the crystal core to –0.12 ± 0.06‰ (2 SE) in the mantle zone. This isotopic evolution, also paralleled by a decrease in Ta content by two orders of magnitude, suggests a fluid batch evolving toward isotopically lighter Sn. The very rim zone of this crystal has an intermediate tin isotope composition at about +0.05‰ δ124/117Sn3161A, combined with elevated Ta, suggestive of a second fluid batch. The late-stage cassiterite crystal from a muscovite-stable hydrothermal environment has a core with an evolved Sn isotope composition at about –0.15‰ δ124/117Sn3161A combined with low Ta, and a rim with heavier Sn isotope compositions up to +0.30 ± 0.08‰ δ124/117Sn3161A and higher Ta contents. As for the early-stage crystal, two diferent fluid batches must be involved in the formation of this crystal. Our pilot study highlights the advantage of spatially resolved analysis compared to conventional, solution Sn-isotope analysis of bulk cassiterite crystals. The Sn isotope variations at the microscale reveal the complexity of cassiterite crystal growth by a combination of closed- and open-system fluid evolution and isotope fractionation.