Epithermal mineralisation related to carbonatites: a key potential source of critical heavy rare earth elements for clean energy

稀土元素（稀土）是由16种化学性质相似的元素组成的一组，它们自然地一起出现。稀土元素钕、镨、钐、镝和铽在经济上非常重要，因为它们被用于制造高强度的永磁体。这些磁铁是生产电动汽车的电动机和风力涡轮机发电所必需的。为了实现清洁能源目标和减少二氧化碳排放，预计到2026年，对这些技术的需求将大幅增长。对稀土磁铁的需求也将跟随这一上升趋势，但存在与稀土矿石稳定供应有关的问题。一个问题是，目前的生产仅限于中国，中国控制着全球90%以上的稀土供应。​第二个问题是，与“轻”稀土（如钕）相比，目前开采的“重”稀土（如铽和镝）还不够。这是因为重稀土天然储量较少，但也因为目前稀土的主要来源——一种被称为“碳酸盐岩”的岩石——主要是富含轻稀土的。在拟议的项目中，我将通过调查在现有的富含轻稀土的碳酸盐岩矿床附近发生的一种新型重稀土矿化来解决重稀土供应有限的问题。如果一起开采，这些矿床类型可以提供磁铁工业所需的稀土的正确组合。然而，希望发现和开发这些矿床的矿产勘探公司面临着几个问题：-不清楚它们的位置，它们为什么出现或它们如何变化；-没有明确的方法可以轻松找到这些新矿床；-目前还不确定是否有可能经济地开采这些矿床。我提议与英国矿产勘探公司合作开展的研究，将通过开发“地质模型”来解决这些问题。地质模型根据矿床的形成过程重新想象矿床；在这种情况下，可能是火山系统与水相互作用形成温泉。当温泉在地下深处形成矿床时，它们被称为“浅成热液”矿床。我将测试浅成热液矿床地质模型的某些方面是否适用于碳酸盐岩周围的重稀土元素矿化。为了开发和测试地质模型，地质学家有一个广泛的工具包。然而，一个关键的起点是研究不同岩石和矿物之间的关系，以便了解矿化的时间。这是通过对岩石样品的实地和微观观察得出的。矿物成分的微小变化可以揭示其形成的时间和条件。在这个项目中，我将研究矿物的组成，以确定矿化的时间，以及流体的温度和组成。此外，将对矿物中被困水的微观量进行分析，以反算原始地层温度。这些技术将用于地球不同深度的五个不同矿床的样本。五个测试地点的观测结果将与浅成热液模型进行比较，以产生适合矿产勘探行业的最终地质模型。由此产生的地质模型将有利于工业，使其能够迅速发现和评价新的重稀土资源，并通过更有信息的勘探减少矿物勘探的成本和对环境的影响。从长远来看，低热液重稀土矿床的开采将为英国的供应链带来安全、平衡的重稀土供应，而重稀土对磁铁生产至关重要。

Rare earth elements (rare earths) are a group of 16 elements with similar chemical properties, which naturally occur together. The rare earths neodymium, praseodymium, samarium, dysprosium, and terbium are highly economically important as they are used in high-strength permanent magnets. These magnets are essential for producing electric motors in electric vehicles and for generating power from wind turbines. Demand for these technologies is forecast to grow substantially to 2026 in order to meet clean energy targets and reduce CO2 emissions. Demand for rare earth magnets will also follow this upward trend, but there are issues relating to the stable provision of rare earth ore. One issue is that existing production is limited to China, who control over 90% of the World's rare earth supply. This limited supply is unstable, as demonstrated by China's 2010 restriction of rare earths to Japan over a territorial dispute. A second issue is that not enough 'heavy' rare earths (e.g., terbium and dysprosium), are currently mined compared to the 'light' rare earths (e.g. neodymium). This is because heavy rare earths are naturally less abundant, but also because the current major source of rare earths, a rock type termed a 'carbonatite', is predominantly only light rare earth-rich.During the proposed project, I will address the problem of limited heavy rare earth supplies by investigating a new type of heavy rare earth mineralisation occurring near existing light rare earth-rich carbonatite deposits. If mined together, these combined deposit types could provide the correct mix of rare earths required for the magnet industry. However, there are several problems facing mineral exploration companies who wish to find and exploit these deposits:- It is unclear where they are located, why they occur, or how they vary,- There is no clear way to easily find these new deposits,- It is currently uncertain if it is possible to economically mine these deposits.My proposed research, undertaken in collaboration with UK-based mineral exploration companies, will resolve these issues through the development of 'geomodels'. Geomodels re-imagine ore deposits in terms of their formation process; in this case, likely to be a volcanic system interacting with water to form hot springs. When hot springs form mineral deposits deep underground they are termed 'epithermal' deposits. I will test if some of the aspects of an epithermal deposit geomodel are applicable to heavy rare earth element mineralisation around carbonatites.Geologists have a wide toolkit in order to develop and test geomodels. A key starting point, however, is to study the relationships between different rocks and minerals in order to understand the timing of mineralisation. This is obtained from field and microscopic observations of rock samples. Small variations in what a mineral is made of can reveal the timing and conditions in which it formed. In this project, I will investigate the composition of minerals in order to determine the timing of mineralisation, as well as fluid temperature and composition. Furthermore, analyses of microscopic amounts of trapped water within minerals will be undertaken to back-calculate the original formation temperature. These techniques will be used on samples from five different deposits from different depths in the Earth. Observations from the five test localities will be compared with an epithermal model, in order to produce a final geomodel suitable for the mineral exploration industry.The resulting geomodel will be of benefit to industry by enabling the rapid discovery and assessment of new heavy rare earth resources and reducing the cost and environmental impact of mineral exploration through better-informed prospecting. In the long run, exploitation of epithermal heavy rare earth deposits will lead to a secure and balanced supply of the heavy rare earths, essential for magnet production, into the UK supply chain.