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.

锡钨矿床中金属的富集、输运和结晶是高度演化的岩浆-热液系统中熔融和流体驱动过程的复杂组合。然而，目前还没有很好地限定各个成矿阶段的确切条件和控制参数。除了构造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可以提供金属运输过程中最终导致金属沉积的关键变化的重要信息，因为它们的分馏关键取决于它们的结合环境的变化。因此，假设金属键变化与同位素分馏之间的关系被很好地理解，甚至被校准，同位素特征可以识别金属运输和结晶的条件。在这里，我们提出了一种互补的方法，将实验和案例研究相结合：(1)在精心设计的实验室实验中更好地理解和校准熔融流体和锂云母之间的Li同位素分异；(2)将Li和Sn同位素代理应用于两个已经很好表征但化学和结构上不同的花岗岩Sn- w -Li矿床（Sadisdorf， Erzgebirge和Argemela，葡萄牙）。用飞秒激光烧蚀（LA-） MC-ICP-MS原位分析Li同位素（主要是Li云母）和锡石的Sn同位素。我们期望从这两种同位素系统中获得互补的信息：Li同位素预计对流体的性质和熔体-流体析出（第一次和第二次沸腾）或两种流体（蒸汽-盐水）之间的分馏反应敏感，这将进行实验校准。预计锡同位素主要是由于氧化还原变化（从Sn2+到Sn4+），在汽卤分离或锡石结晶过程中（如文献中的几项研究所示）。在汉诺威已经建立了本研究计划中调查的实验和分析装置，并且将Li和Sn同位素系统应用于Sn- w -Li矿床的宿主矿物有望提供关于金属运输和结晶条件的非常有价值的信息。如果时间允许，我们计划用LA-MC-ICP-MS对黑钨矿进行原位W同位素分析，并对相同的黑钨矿晶体（在科隆）进行高精度溶液双尖峰分析。在黑钨矿的结晶过程中，W同位素分馏不受氧化还原过程的控制，而黑钨矿通常与热液脉中的锡石有关，因此W的同位素组成可以限制温度降低在成矿演化中的作用。