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

花岗岩大省与锡、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的基本新绿色技术所必需的。花岗岩熔体被输送到地壳中层，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岩浆-热液矿床，其中蕴藏着这些关键金属。然而，尽管所有的花岗岩熔体都放出挥发物，但这些系统很少形成经济矿藏，而且当它们形成时，它们的寿命非常短暂。这些系统内有多代岩浆作用，并不总是知道哪一次岩浆事件与经济成矿有关。岩基的增量侵位、侵位速率和岩浆系统中存在的熔融量对矿床形成的作用尚不清楚。这些都是基本问题，将导致更好的成矿地质模型。通常情况下，岩浆事件是通过锆石U-Pb等工具测定的，但现在可以使用新的高精度分析技术来产生新的矿物计时仪。这些工具将使热液事件的准确测年成为可能，因为从这些事件中沉淀出来的矿石(锡石U-铅)将直接测年。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相结合(通过高精度ID-TIMS使用锆石U-Pb)，将使岩基建造与经济矿化联系起来。来自寄主花岗岩的锆石还将通过分析现场示踪剂，如Lu-Hf同位素(对来源敏感)和经济金属的微量元素，提供熔体演化的记录。因此，首次将岩浆事件来源和金属含量的潜在变化与其最终成矿联系起来，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布什维尔德杂岩的LeBowa花岗岩套的A型花岗岩和伴生的锡矿床，以及英格兰西南部康沃尔的科努比安岩基和伴生的锡省。这些野外遗址具有良好的曝光性，这将使样本采集变得容易，是两个独特的岩浆系统。这两个截然不同的系统将允许进行比较，重点是花岗岩的侵位历史，以及岩体结构和熔体体积的速度如何影响成矿潜力。分析工作将在BGS和圣安德鲁斯同位素地球化学实验室使用激光烧蚀技术进行，而关于岩浆锆石和热液锡石的ID-TIMS年代学将在BGS地质年代学和示踪设施进行。

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.