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、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关键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，分块结晶可以使感兴趣的金属浓缩。从这些花岗质体系中析出的挥发物可以形成岩浆热液矿床，其中含有这些关键金属。然而，虽然所有的花岗岩熔体都会溶解挥发物，但经济矿床很少从这些体系中形成，即使形成，也非常短暂。在这些系统中存在多代岩浆活动，但并不总是知道哪一次岩浆活动与经济矿化有关。岩基增量侵位、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。这些基本问题将导致更好的成矿地质模型。通常，岩浆事件的年代是通过锆石U-Pb等工具来确定的，但是现在新的高精度分析技术可以用来产生新的矿物计时器。这些工具将允许对热液事件进行精确测年，因为从热液事件中析出的矿石（锡石U-Pb）将被直接测年。将成矿事件的地质年代学与寄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，将使基岩构造与经济矿化联系起来。寄主花岗岩的锆石也将通过对原位示踪剂（如对来源敏感的Lu-Hf同位素）和经济金属微量元素的分析，提供熔体演化的记录。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的成矿作用联系起来，将为研究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Lebowa花岗岩组的a型花岗岩和伴生锡矿床，以及英格兰西南部Cornwall的Cornubian基岩和伴生锡省。这些地点暴露良好，容易采集样品，而且是两个独特的岩浆系统。这两个对比系统将使我们能够比较花岗岩的侵位历史，以及岩体的构造速度和熔体体积如何影响成矿潜力。分析工作将在英国地质调查局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地质年代学将在英国地质调查局地质年代学和示踪剂设施进行。

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.