What Controls critical metal Sn-W-Ta deposit formation in granite batholiths? Unravelling the magmatic and hydrothermal evolution of the Bushveld Comp

是什么控制着花岗岩岩基中关键金属 Sn-W-Ta 沉积物的形成？

• 批准号: 2599261
• 金额: --
• 依托单位: University of St Andrews
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2599261
• 关键词: What; Controls; critical; metal; Sn

Large granite provinces are associated with the development of critical metal resources such as tin, tungsten, tantalum and lithium. These metals are required for essential new green technologies to push forward into a low-carbon economy. Granitic melts are transported to mid crustal levels where fractional crystallisation can concentrate metals of interest. Exsolved volatiles from these granitic systems can then form a magmatic-hydrothermal ore deposit which hosts these critical metals. However, while all granitic melts exsolve volatiles, economic ore deposits rarely form from these systems and when they do, they are very short-lived. There are multiple generations of magmatism within these systems and it not always known which magmatic event is linked to the economic mineralisation. The role that incremental batholith emplacement, the rates of emplacement and the amount of melt present within the magmatic system have on the formation of ore deposits is not known. These are fundamental questions which will lead to better geological models for ore formation. Typically, magmatic events have been dated via tools such as zircon U-Pb, however now novel high-precision analytical techniques can be used to yield new mineral chronometers. These are tools which will allow the precise dating of hydrothermal events as the ore (cassiterite U-Pb) which precipitated from them will be directly dated. Combining geochronology of the ore-forming event with high-precision temporal records on the host granitic system (through the use of zircon U-Pb via high-precision ID-TIMS) will enable a link of batholith construction to the economic mineralisation. Zircons from the host granite will also provide a record of melt evolution through the analysis of in-situ tracers such as Lu-Hf isotopes (which are sensitive to source) and trace elements of economic metals. Thus, for the first time linking potential changes in source and metal contents of magmatic events to their eventual mineralization will provide new perspectives on the nature of these complex ore-forming systems. These analytical techniques will be applied to the A-type granites and associated Sn-deposits of the Lebowa Granite Suite, Bushveld Complex, South Africa and to the Cornubian batholith and associated Sn-province of Cornwall, SW England. These field sites have good exposure which will make sample collection easy and are two unique magmatic systems. The two contrasting systems will allow a comparison focusing on the emplacement history of the granites and how the rates of pluton construction and melt volumes affect ore formation potential. Analytical work will be carried out by laser ablation techniques at both the BGS and the St Andrews Isotope Geochemistry Laboratories, while the ID-TIMS geochronology on magmatic zircons and hydrothermal cassiterite will take place at the BGS Geochronology and Tracers Facility.

大型花岗岩省与锡、钨、钽和锂等关键金属资源的开发有关。这些金属是推动低碳经济发展的重要绿色新技术所必需的。花岗岩熔体被输送到地壳中部，在那里分步结晶可以浓缩感兴趣的金属。从这些花岗岩系统中溶出的挥发物可以形成含有这些关键金属的岩浆热液矿床。然而，虽然所有花岗岩熔体都会溶解挥发物，但经济矿床很少从这些系统中形成，即使形成，它们的寿命也非常短暂。这些系统内存在多代岩浆活动，但并不总是知道哪一次岩浆活动与经济矿化有关。增量岩基侵位、侵位速率和岩浆系统内存在的熔体量对矿床形成的作用尚不清楚。这些都是基本问题，将有助于建立更好的成矿地质模型。通常，岩浆事件是通过锆石 U-Pb 等工具来测定年代的，但现在新型高精度分析技术可用于生产新的矿物计时器。这些工具可以对热液事件进行精确测年，因为从热液中沉淀出来的矿石（锡石 U-Pb）将被直接测年。将成矿事件的地质年代学与宿主花岗岩系统的高精度时间记录（通过高精度 ID-TIMS 使用锆石 U-Pb）相结合，将能够将岩基构造与经济矿化联系起来。来自主花岗岩的锆石还将通过分析原位示踪剂（例如 Lu-Hf 同位素（对来源敏感）和经济金属的微量元素）提供熔体演化记录。因此，首次将岩浆事件的来源和金属含量的潜在变化与其最终矿化联系起来，将为了解这些复杂成矿系统的性质提供新的视角。这些分析技术将应用于南非 Bushveld 杂岩区 Lebowa 花岗岩组的 A 型花岗岩和相关锡矿床，以及英格兰西南部康沃尔郡的 Cornubian 岩基和相关锡矿床。这些现场地点暴露良好，使样品采集变得容易，并且是两个独特的岩浆系统。这两个对比系统将允许对花岗岩的侵位历史以及岩体构造速率和熔体体积如何影响成矿潜力进行比较。分析工作将在 BGS 和圣安德鲁斯同位素地球化学实验室通过激光烧蚀技术进行，而岩浆锆石和热液锡石的 ID-TIMS 地质年代学将在 BGS 地质年代学和示踪设施进行。