SCREED: Supergene enrichment of carbonatite REE deposits

SCREED：碳酸岩稀土矿床的表生富集

• 批准号: NE/X015114/1
• 负责人: Martin Smith
• 金额: $ 103.6万
• 依托单位: University of Brighton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FX015114%2F1
• 关键词: SCREED; Supergene; enrichment; carbonatite; REE

The rare earth elements (REE), and in particular neodymium and dysprosium, are essential for renewable energy devices such as wind turbines and the development of electric motors for transport. At present the REE are sourced from either low concentration weathered granitoid (ion adsorption clay) deposits, or from high concentration carbonatite-related deposits, especially the World's dominant REE mine in hard-rock, altered carbonatite at Bayan Obo, China. The one major mine operator outside of China is the Mount Weld weathered carbonatite, Australia. Weathered carbonatites such as Mount Weld are some of the world's richest REE deposits and several are subject to active exploration. As part of the NERC Global Partnerships Seedcorn fund project WREED, we have carried out preliminary investigations of weathering products on carbonatite hosted REE deposits. Three end member weathering products have been identified (1) carbonate mineral dissolution leaves behind primary REE minerals, forming residual deposits; (2) dissolution and reprecipitation of REE phosphates and fluorcarbonate minerals results in the formation of new hydrated REE-phosphate or -carbonate minerals producing supergene enrichment; and (3) the formation of clay and iron-manganese oxide caps (either from weathering of the deposit itself, or from soil transport from surrounding rocks) that may hold the REE adsorbed to mineral surfaces (c.f. the ion adsorption deposits). High grade, weathered carbonatite deposits typically consist of a range of soil and weathered horizons, that may be phosphate-rich due to dissolution and re-precipitation of apatite and monazite during the weathering process (Mount Weld, Australia), overlain by later sediments that may be REE enriched either by accumulation of residual minerals in lake sediments (Tomtor, Russia). The mineralogy of the ore zone is linked to, but distinct from, the unweathered carbonatite rock, and includes phosphates, crandallite-group minerals, carbonates and fluorcarbonates and oxides. In this study we will utilise bulk rock geochemistry, sequential leaching techniques, mineral chemistry and microbiology to investigate the processes producing different weathered REE deposit styles in carbonatites and their influence on the economic REE grade and environmental impact of deposits. Bulk rock geochemistry will be used to quantify element enrichments and depletions relative to bedrock, and to investigate the potential for ion adsorption style mineralisation in weathered carbonatites. Mineral chemical techniques will be used to investigate the timing of weathering, host minerals of the REE, potential beneficial or harmful changes in chemistry relative to primary minerals, and proxies for the environmental controls on weathering style. These data will be combined with existing records of surface morphology and weathering depth to produce overall genetic models linking climate, geomorphology and geochemistry that will allow prediction of the resource potential of the carbonatite weathered zone. The results will be communicated with industry and the public to raise awareness of the resource requirements of decarbonisation, and potential routes to increased extraction efficiency and reduced impact.

稀土元素（REE），特别是钕和镝，对于风力涡轮机等可再生能源设备和运输电机的开发至关重要。目前稀土元素主要来源于低浓度风化花岗质（离子吸附粘土）矿床和高浓度碳酸盐岩相关矿床，特别是世界上主要的硬岩蚀变碳酸盐岩稀土矿位于中国白云鄂博。中国以外的主要煤矿运营商是澳大利亚的Mount Weld风化碳酸盐矿。风化的碳酸盐岩，如芒特维尔，是世界上最丰富的稀土矿床之一，其中一些正在积极勘探。作为NERC全球伙伴关系种子基金项目WREED的一部分，我们对碳酸盐岩含稀土矿床的风化产物进行了初步调查。确定了3个端元风化产物：(1)碳酸盐矿物溶蚀留下原生稀土矿物，形成残余矿床；(2)稀土磷酸盐和氟碳酸盐矿物的溶蚀和再沉淀形成新的水合稀土磷酸盐或氟碳酸盐矿物，形成表生富集；(3)粘土和铁锰氧化物盖层的形成（要么来自矿床本身的风化作用，要么来自围岩的土壤迁移），它们可能将稀土元素吸附到矿物表面（如离子吸附矿床）。高品位的风化碳酸盐岩矿床通常由一系列土壤和风化层组成，由于风化过程中磷灰石和独居石的溶解和再沉淀，可能富含磷酸盐（Mount Weld，澳大利亚），其上覆有后来的沉积物，这些沉积物可能通过湖泊沉积物中残余矿物的积累而富集稀土元素（Tomtor，俄罗斯）。矿带的矿物学与未风化的碳酸盐岩有联系，但又不同，包括磷酸盐、辉长岩群矿物、碳酸盐和氟碳酸盐以及氧化物。在这项研究中，我们将利用大块岩石地球化学、顺序浸出技术、矿物化学和微生物学来研究在碳酸盐岩中产生不同风化稀土矿床类型的过程，以及它们对矿床的经济稀土品位和环境影响的影响。大块岩石地球化学将用于量化相对于基岩的元素富集和消耗，并研究风化碳酸盐中离子吸附式矿化的潜力。矿物化学技术将用于研究风化的时间、稀土元素的宿主矿物、相对于原生矿物的潜在有益或有害的化学变化以及环境控制风化类型的代用物。这些数据将与现有的地表形态和风化深度记录相结合，产生将气候、地貌和地球化学联系起来的整体遗传模型，从而可以预测碳酸盐岩风化带的资源潜力。研究结果将与工业界和公众进行沟通，以提高对脱碳资源需求的认识，以及提高提取效率和减少影响的潜在途径。