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

锡（Sn）和钨（W）的资源主要与岩浆热液系统有关，已被确立为战略金属，成功勘探具有经济价值的矿床取决于对成矿过程的基本理解，包括来源和原生富集、迁移、沉积和再活化。与其他高场强（HFSE;即，Nb和Ta）和助熔元素（例如，Li、P、F）、Sn和W通常与晚至造山后地壳过铝质花岗岩系统（包括稀有金属花岗岩（RMG）和伟晶岩）以及相关热液活动存在密切的空间关系。锡和钨集中到经济等级是由于熔体（即，预浓缩）和流体驱动（即，再动员）过程。这些元素在地壳内的迁移和再分配取决于不同的因素，如它们在与含矿矿物平衡的熔体和流体中的溶解度，以及它们在岩浆-热液过渡期在熔体和流体之间的分配。虽然熔体和流体组成是两种元素的重要参数，但W对温度高度敏感，Sn对氧化还原条件高度敏感（即，以Sn 2+或Sn 4+形式储存和运输）。虽然已经确定了主要控制参数，但需要进一步调查，以解决文献中的差异（例如，与这种系统的复杂性和潜在的实验问题有关）。为了达到这个目的，我们计划使用不同的方法集中在几个方面：（i）考虑到熔体和流体的地球化学变化以及与锡钨矿床有关的P-T-fO 2条件，进行含锡和钨矿物在熔体和流体中的溶解度实验，（ii）旨在准确确定岩浆-热液过渡期锡和钨的流体/熔体和盐水/蒸汽/熔体分配的实验，（iii）对Argemela花岗岩系统（葡萄牙）的一个突出实例进行流体包裹体研究，以定性和定量地调查Sn和W在流体中的浓度以及在岩浆-热液过渡期的迁移情况，（iv）调查Sn在不同地壳环境中的氧化态，以评估氧化还原对Sn在地壳内迁移和再分布的影响。总之，我们的研究结果将有助于重新评估现有的锡钨矿床的形成模型。

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.