Transport processes of Sn and W within the crust: From a peraluminous granitic melt to a mineralising fluid

锡(锡)和钨(W)的资源主要与岩浆-热液系统有关，已被确定为战略金属，成功勘探具有经济价值的矿床取决于对成矿过程的基本了解，包括来源和原生浓缩、运输、沉积和再活化。与其他高场强元素(如Nb、Ta)和熔剂元素(如Li、P、F)一起，锡和钨通常与晚造山至后造山地壳过铝花岗岩系统(包括稀有金属花岗岩和伟晶岩)及其相关的热液活动存在密切的空间关系。锡和钨浓缩到经济品位是熔体(即预浓缩)和流体驱动(即再活化)过程的综合结果。这些元素在地壳中的迁移和再分布取决于不同的因素，如它们在熔体和流体中的溶解度与含矿矿物的平衡以及它们在岩浆-热液转变过程中在熔体和流体之间的分配。虽然熔体和流体成分是这两种元素的重要参数，但对于给定的成分，W对温度高度敏感，而锡对氧化还原条件(即，以Sn2或Sn4形式储存和运输)高度敏感。虽然已经确定了主要的控制参数，但还需要进一步的研究来揭示文献中的差异(例如，与此类系统的复杂性和潜在的实验问题有关)。为此，我们计划使用不同的方法集中于几个方面：(I)考虑熔体和流体的地球化学变化以及与锡-钨矿床相关的P-T-fO2条件的含锡和钨矿物在熔体和流体中的溶解实验，(Ii)旨在准确确定岩浆-热液转变过程中锡和钨的流体/熔体和卤水/蒸汽/熔体分配的实验，(Iii)对阿尔吉拉花岗岩系(葡萄牙)的一个杰出例子的流体包裹体研究，以定性和定量地研究岩浆-热液转变过程中流体中的锡和钨的浓度和迁移，(4)研究锡在不同地壳环境中的氧化状态，以评价氧化还原对锡在地壳内迁移和再分布的影响。总之，我们的结果将有助于重新评估现有的锡钨矿床形成模式。

Tin (Sn) and tungsten (W), whose resources are mainly associated with magmatic-hydrothermal systems, have been established as strategic metals and successful exploration of economically valuable deposits depend on a fundamental understanding of ore-forming processes including source and primary concentration, transport, deposition and remobilisation. Together with other high-field-strength (HFSE; i.e., Nb and Ta) and fluxing elements (e.g., Li, P, F), Sn and W commonly occur in close spatial relationship with late to post-orogenic crustal peraluminous granitic systems - including rare-metal granites (RMGs) and pegmatites - and related hydrothermal activity. Tin and W concentration to economic grades results from a combination of melt- (i.e., preconcentration) and fluid-driven (i.e., remobilisation) processes. The transport and redistribution of these elements within the crust depend on different factors such as their solubility in melt and fluid in equilibrium with ore-bearing minerals and their partitioning between melt and fluid at the magmatic-hydrothermal transition. While melt and fluid compositions are important parameters for both elements, W is highly sensitive to temperature and Sn to redox conditions (i.e., storage and transport as Sn2+ or Sn4+) for a given composition. Although main controlling parameters have been identified, there is a need for further investigations to unravel the discrepancies in the literature (e.g., related to the complexity of such systems and to potential experimental problems). To serve that purpose, we plan to focus on several aspects using different approaches: (i) Sn- and W-bearing minerals solubility experiments in melt and fluid considering the geochemical variety of melt and fluid and P-T-fO2 conditions relevant to Sn-W deposits, (ii) experiments designed to determine accurately the fluid/melt and brine/vapour/melt partitioning of Sn and W at the magmatic-hydrothermal transition, (iii) fluid inclusion study on one outstanding example of the Argemela granite system (Portugal) to qualitatively and quantitatively investigate Sn and W concentration in fluids and transport at the magmatic-hydrothermal transition, (iv) investigation of the oxidation state of Sn in different crustal environments to evaluate the redox effect on Sn transport and redistribution within the crust. Altogether, our results will help to reassess the existing models for the formation of Sn-W deposits.