Deciphering the metal stable isotope record of Sn-W ore deposits: a complementary approach based on experiments and case studies

破译锡钨矿床的金属稳定同位素记录：基于实验和案例研究的补充方法

• 批准号: 521732943
• 负责人: Professor Dr. Stefan Weyer, Ph.D.
• 金额: --
• 依托单位: Institut für Mineralogie
• 依托单位国家: 德国
• 项目类别: Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/521732943?language=en
• 关键词: Deciphering; metal; stable; isotope; record

Enrichment, transport and crystallisation of metals in Sn-W deposits results from a complex combination of melt- and fluid-driven processes in highly evolved magmatic-hydrothermal systems. However, the exact conditions and controlling parameters in the various stages of ore formation are not yet well constrained. In addition to structural and classical geochemical and mineralogical investigations, the stable isotope fractionation of the metals may provide important information on crucial changes during metal transport that finally result in metal deposition, as their fractionation critically depends on changes in their bonding environment. Thus, provided that the relationship between metal bonding changes and resulting isotopes fractionation is well understood, or even calibrated, isotopic signature may fingerprint the conditions of metal transport and crystallisation. Here, we propose a complementary approach, combining experiments and case studies (1) to better understand and calibrate the fractionation of Li isotopes between melt-fluid and Li-micas in well-designed laboratory experiments and (2) to apply the Li and Sn isotope proxy to two already well-characterized, but chemically and structurally distinct granitic Sn-W-Li deposits (Sadisdorf, Erzgebirge and Argemela, Portugal). For Li isotopes (mostly) Li micas and for Sn isotopes cassiterite will be analysed, both in situ with femtosecond laser-ablation (LA-) MC-ICP-MS. We expect complementary information from these two isotope systems: Li isotopes are expected to be sensitive to the nature of the fluid and to fractionate during melt-fluid exsolution (first and second boiling) or between to fluids (vapour-brine), which will be experimentally calibrated. Sn isotopes are expected to mostly fractionate as a result of a redox change (from Sn2+ to Sn4+), during vapour-brine separation or during the crystallization of cassiterite (as indicated by several studies of the literature). The experimental and analytical set up for the investigations planed in this study are already established in Hannover and application of the Li and Sn isotope systems to their host minerals in Sn-W-Li deposits is expected to provide very valuable information on the conditions of metal transport and crystallization. If time allows we plan to establish in situ W isotope analyses of wolframite with LA-MC-ICP-MS, validated with high-precision solution double spike analyses of the same wolframite crystals (in Cologne). As W isotope fractionation during the crystallization of wolframite, which is frequently associated with cassiterites in hydrothermal veins, is not controlled by a redox process, the isotope compositions of W may allow us to constrain the role of decreasing temperatures during the metallogenic evolution.

SN-W沉积物中金属的富集，运输和结晶是由于高度演化的岩浆 - 热热系统中熔体和流体驱动的过程的复杂组合而产生的。但是，在矿石形成的各个阶段的确切条件和控制参数尚未受到良好约束。除了结构和经典的地球化学和矿物学研究外，金属的稳定同位素分馏还可能提供有关金属转运过程中关键变化的重要信息，最终导致金属沉积，因为它们的分馏非常取决于其粘结环境的变化。因此，只要金属键变化与产生的同位素分馏之间的关系得到充分理解，甚至校准了同位素特征，可以指纹金属传输和结晶的条件。 Here, we propose a complementary approach, combining experiments and case studies (1) to better understand and calibrate the fractionation of Li isotopes between melt-fluid and Li-micas in well-designed laboratory experiments and (2) to apply the Li and Sn isotope proxy to two already well-characterized, but chemically and structurally distinct granitic Sn-W-Li deposits (Sadisdorf, Erzgebirge and Argemela，葡萄牙）。对于LI同位素（主要）li云母和SN同位素，将分析碳耐岩，均与飞秒激光燃烧（LA-）MC-ICP-MS进行原位。我们期望这两个同位素系统的互补信息：LI同位素有望对液体的性质敏感，并在熔融液体溶液中（第一和第二沸腾）或对流体（Vapour-Brine）之间的分馏敏感，这将经过实验校准。由于氧化还原的变化（从SN2+到SN4+），在蒸气 - 棕北方分离期间或在Cassiterite的结晶过程中（如文献研究所示），因此SN同位素大多是由于氧化还原变化（从SN2+到SN4+）的大部分。在汉诺威（Hannover）和SN同位素系统在SN-W-LI沉积物中的寄主矿物质中的应用中，预计在本研究中计划的研究和分析性的研究已建立，预计将提供有关金属运输和结晶状况的非常有价值的信息。如果时间允许，我们计划用LA-MC-ICP-MS对Wolframite进行原位的同位素分析，并用同一Wolframite晶体（在Cologne）进行高精度溶液双峰分析验证。由于Wolframite的结晶过程中的W同位素分馏（通常与水热静脉中的硬质岩相关，因此不受氧化还原过程的控制，因此W的同位素组成可能使我们能够限制金属生成进化过程中温度降低的作用。