The Rare Earth Elements: Demand, Global Resources, and Challenges for Resourcing Future Generations

This thematic issue is composed of the papers presented at the symposium “Rare Metals–Rare Earth Resources” of the annual meeting of the Society of Resource Geology held in Tokyo, Japan, on 19 July 2007. The symposium was organized by Shunso Ishihara, Hajime Hishida and Yasushi Watanabe. Seven of the 11 topics presented in the symposium were related to rare earth elements (REE), reflecting their recent increasing demand and prices (Fig. 1). The Japanese REE market and industry expect new REE suppliers to develop outside China, because of the decreased availability of rare earth materials for import from China. Production of rare earth elements (REE) and prices of dysprosium (Dy), neodymium (Nd) and neodymium-praseodymium (Nd-Pr) in the last two decades. CIF, cost, insurance and freight; REO, rare earth oxides. The articles in this thematic issue include a review of rare earth deposits in North America (Castor, 2008), a recent interpretation of the genesis of the world’s largest Bayan Obo deposit in China (Wu, 2008), and two papers and a note that describe the relationship between rare earth mineralization and granite (Ishihara, 2008; Ishihara et al., 2008; Murakami & Ishihara, 2008). This issue also includes a review article on the rare earth magnet by Minowa (2008), and an article on rare earth enrichment in stratabound manganese deposits in India (Moriyama et al., 2008). Minowa (2008) provides basic information on recent demand for neodymium and dysprosium, which is caused mainly by the production of dysprosium-bearing neodymium magnets in China and Japan. He estimates that 16,000 t of neodymium and 2600 t of dysprosium will be necessary to produce alloys for the magnets in 2010 for the world market. The review of rare earth deposits of North America by Castor (2008) concludes that world reserves are sufficient to meet international demand for most REE commodities in the 21st century and the development of new REE deposits in North America is unlikely in the near future because Chinese producers, especially those at Bayan Obo, are capable of large REE production at low prices. Details of Bayan Obo are reviewed by Wu (2008), who suggests a hydrothermal origin related to carbonatite magmatism for the deposit. Ishihara et al. (2008) describe the mineralogical and geochemical characteristics of the granites related to ion-adsorption REE deposits in southern China, which are the current source for heavy REE. Ishihara (2008) also discusses the occurrence of REE-enriched zircon in the Naegi granite in Japan. Murakami and Ishihara (2008) investigate REE abundance in the weathered crust and clay sediment above granitic rocks in Japan and China, and describe the ore grade and composition of the currently mined Dingnan deposit in southern China. Moriyama et al. (2008) explore manganese deposits for a new heavy REE source. They have found REE enrichment up to 975 ppm in stratabound or stratiform manganese deposits in Orissa, India, and suggest that this enrichment was caused by hydrothermal activity during deposition. The papers in the present issue conclude collectively that heavy REE such as dysprosium will become scarce in the future despite the large reserves of total REE in the world, because the current supply source of heavy REE is limited to ion adsorption deposits in China. I am convinced that the studies of the geneses of the ion adsorption deposits and related granites, some of which are presented in this issue, will be utilized for future world exploration of this type of deposit.

Recent process developments in beneficiation and metallurgy of rare earths: A review

A comparison of global rare earth element (REE) resources and their mineralogy with REE prospects in Sri Lanka

Rare earth is widely used in various fields, especially electronics, new energy and other issues involving the military and high technology. From electric cars to energy-saving bulbs and large wind turbines—rely on a special set of material to present. Although 29 countries and regions worldwide have their Rare earth resources, but mainly concentrated in several countries and regions. According to the U.S. Geological Survey Bureau, 2009 World reserves of rare earth resources, about 98.5 million tons, of which China accounted for 36.5%, the CIS countries accounted for 19.3%, U.S. 13.2%, Australia 5.5%, India 3.1%, Other countries and regions accounted for 22.3%. According to statistics, in 2009, China's Rare earth production accounts for 97% of world production, in sharp contrast, the CIS countries, the United States and Australia are zero Rare earth production. For a long time, China is the Rare earth supplier to Japan, the United States, France and other countries, shows the Sustainable Development of China's Rare earth resources development dangerous. China's rare earth resources areas mainly consist of two ore zones: North and South. Bayan Obo rare earth deposit, the mainly REE deposit in north, is a light rare earth deposit. Second are the Mianning of Sichuan, Weishan of Shandong, etc. Bayan Obo REE deposit is sedimentary metamorphic hydrothermal metasomatic type deposit, Mianning deposit is masanaga magma-related magmatic hydrothermal vein type deposit, Weishan rare earth deposit is alkaline magmatic hydrothermal type deposit. South Ore zone, including Jiangxi, Fujian, Guangxi, Guangdong and Hunan provinces, are the ionic rare earth based deposits, bears very valuable medium-heavy rare earth resources, widely distributed, large reserves, low radioactivity, mining easily, extraction of rare earth simple process, low production costs, and good product quality. Currently, the Inner Mongolia rare earth raw materials industry already have a considerable size and production capacity, processing of rare earth products and functional materials based on the proportion has improved significantly, has formed a strong cluster, in order to create a world-class industrial cluster of rare earth and laid a solid foundation. New rare earth materials and new energy industry is “second Five-Year planning” of Inner Mongolia during the two big strategic focus on the development of new industries, will achieve the Inner Mongolia rare earth resources advantages into economic advantage. Therefore, the government should further improve the investment environment and integrate the Inner Mongolia desert solar and wind power generation resources advantage and rare earth new energy material industry advantages, build new energy base in Inner Mongolia, accelerate national strategic rare earth resources strategic reserve base construction.

The story of rare earth elements (REEs): Occurrences, global distribution, genesis, geology, mineralogy and global production

Carbonatite and alkaline intrusive complexes, as well as their weathering products, are the primary sources of rare earth elements. A wide variety of other commodities have been exploited from carbonatites and alkaline igneous rocks including niobium, phosphate, titanium, vermiculite, barite, fluorite, copper, calcite, and zirconium. Other elements enriched in these deposits include manganese, strontium, tantalum, thorium, vanadium, and uranium. Carbonatite and peralkaline intrusion-related rare earth element deposits are presented together in this report because of the spatial, and potentially genetic, association between carbonatite and alkaline rocks. Although these rock types occur together at many locations, carbonatite and peralkaline intrusion-related rare earth element deposits are not generally found together. Carbonatite hosted rare earth element deposits are found throughout the world, but currently only five are being mined for rare earth elements: Bayan Obo, Daluxiang, Maoniuping, and Weishan deposits in China and the Mountain Pass deposit in California, United States. These deposits are enriched in light rare earth elements, including lanthanum, cerium, praseodynium, and neodynium. The principal rare earth element-minerals associated with carbonatites are fluocarbonates (bastnäsite, parisite, and synchysite), hydrated carbonates (ancylite), and phosphates (monazite) with bastnäsite being the primary ore mineral. Calcite and dolomite are the primary gangue minerals. At present, the only rare earth element production from a peralkaline intrusion-related deposit is as a byproduct commodity at the Lovozero deposit in Russia. Important rare earth element minerals found in various deposits include apatite, eudialyte, loparite, gittinsite, xenotime, gadolinite, monazite, bastnäsite, kainosite, mosandrite, britholite, allanite, fergusonite, and zircon, and these minerals tend to be enriched in heavy rare earth elements. Carbonatite and alkaline intrusive complexes are derived from partial melts of mantle material, and neodymium isotopic data are consistent with the rare earth elements being derived from the parental magma. Deposits and these associated rock types tend to occur within stable continental tectonic units, in areas defined as shields, cratons, and crystalline blocks; they are generally associated with intracontinental rift and fault systems. Protracted fractional crystallization of the magma leads to enrichment in rare earth elements and other incompatible elements. Rare earth element mineralization associated with carbonatites can occur as either primary mineral phases or as mineralization associated with late stage orthomagmatic fluids. Rare earth element mineralization associated with alkaline intrusive complexes may occur as primary phases in magmatic layered complexes or as late-stage dikes and veins. The greatest environmental challenges associated with carbonatite and peralkaline intrusion-related rare earth element deposits center on the associated uranium and thorium. Considerable uncertainty exists around the toxicity of rare earth elements and warrants further investigation. The acid-generating potential of carbonatites and peralkaline intrusion-related deposits is low due to the dominance of carbonate minerals in carbonatite deposits, the presence of feldspars and minor calcite within the alkaline intrusion deposits, and only minor quantities of potentially acid-generating sulfides. Therefore, acid-drainage issues are not likely to be a major concern associated with these deposits. Uranium has the potential to be recovered as a byproduct, which would mitigate some of its environmental effects. However, thorium will likely remain a waste-stream product that will require management since progress is not being made towards the development of thorium-based nuclear reactors in the United States or other large scale commercial uses. Because some deposits are rich in fluorine and beryllium, these elements may be of environmental concern in certain locations.

China has been the world’s leading rare earth element (REE) and yttrium producer for more than 20 years and hosts a variety of deposit types. Carbonatite-related REE deposits are the most significant REE deposit type, with REY (REE and yttrium)-bearing clay deposits, or ion adsorption-type deposits, being the primary source of the world’s heavy REEs. Other REY resources in China include those hosted in placers, alkaline granites, pegmatites, and hydrothermal veins, as well as in additional deposit types in which REEs may be recovered as by-product commodities. Carbonatite-related REE deposits in China provide nearly all the light REE production in the world. Two giant deposits are currently being mined in China: Bayan Obo and Maoniuping. The carbonatite-related REE deposits in China occur along the margins of Archean-Paleoproterozoic blocks, including the northern, southern, and eastern margins of the North China craton, and the western margin of the Yangtze craton. The carbonatites were emplaced in continental rifts (e.g., Bayan Obo) or translithospheric strike-slip faults (e.g., Maoniuping) along reactivated craton margins. The craton margins provide the first-order control for carbonatite-related REE resources. Four REE metallogenic belts, including the Proterozoic Langshan-Bayan Obo, late Paleozoic-early Mesozoic eastern Qinling-Dabie, late Mesozoic Chishan-Laiwu-Zibo, and Cenozoic Mianning-Dechang belts, occur along cratonic margins. Geologic and geochemical data demonstrate that the carbonatites in these belts originated from mantle sources that had been previously enriched, most likely by recycled marine sediments through subduction zones during the assembly of continental blocks. Although the generation of carbonatite magma is debated, a plausible mechanism is by liquid immiscibility between silicate and carbonate melts. This process would further enrich REEs in the carbonatite end member during the evolution of mantle-derived magma. The emplacement of carbonatite magma in the upper crust, channeled by translithospheric faults in extensional environments, leads to a rapid decompression of the magma and consequently exsolution of a hydrothermal fluid phase. The fluid is characterized by high temperature (600°–850°C), high pressure (up to 350 MPa), and enrichment in sulfate, CO2, K, Na, Ca, Sr, Ba, and REEs. Immiscibility of sulfate melts from the aqueous fluid, and phase separation between CO2 and water may take place upon fluid cooling. Although both sulfate and chloride have been called upon as important ligands in hydrothermal REE transport, results of our studies suggest that sulfate is more important. The exsolution of a sulfate melt from the primary carbonatite fluid would lead to a significant decrease of the sulfate activity in the fluid and trigger REE precipitation. The subsequent unmixing between CO2 and water may also play an important role in REE precipitation. Because of the substantial ability of the primary carbonatite fluid to contain REEs, a large-volume magma chamber or huge fluid flux are not necessary for the formation of a giant REE deposit. A dense carbonatite fluid and rapid evolution hinder long distance fluid transportation and distal mineralization. Thus, carbonatite-related alteration and mineralization occur in or proximal to carbonatite dikes and sills, and this is observed in all carbonatite-related REE deposits in China. Ion adsorption-type REE deposits are primarily located in the South China block and are genetically linked to the weathering of granite and, less commonly, volcanic rocks and lamprophyres. Indosinian (early Mesozoic) and Yanshanian (late Mesozoic) granites are the most important parent rocks for these REE deposits. Hydrothermal alteration by fluids exsolved from late Mesozoic granites or related alkaline rocks (e.g., syenite) may have enriched the parent rocks in REEs, particularly the heavy REEs. Furthermore, this alteration process led to the transformation of some primary REE minerals to secondary REE minerals that are more readily broken down during subsequent weathering. During the weathering process, the REEs are released from parent rocks and adsorbed onto kaolinite and halloysite in the weathering profile, and further enriched by the loss of other material to form the ion adsorption-type REE deposits. A warm and humid climate and a low-relief landscape are important characteristics for development of ion adsorption REE deposits.

Introduction: China is a large country of REE resources and production, supplying more than 90% of the world’s rare earth consumption market, China’s traditional REE resources, although rich, but reserves are also declining, in recent years, scholars have shown that the REEs in the specific geological conditions in the coals can be enriched, and even reach the industrial grade, the search for more REE mineral resources will be of great strategic significance.Methods: The article has selected the Zibo, Taozao, Huainan, Datong, Huozhou, Jungar, and Weibei coalfields in North China as the research objects. Based on inductively coupled plasma mass spectrometry (ICP-MS) analyses, the study provides a detailed analysis of the enrichment rules and distribution patterns of rare earth elements (REEs) in coal under different geological conditions.Results: The REE distribution patterns in Late Palaeozoic coals in North China are characterized by enrichment of LREEs, deficit of HREEs with gentle changes, and obvious negative anomalies of Eu, the enrichment of REE in coal is controlled by provenance and volcanism, and is related to distance of transport terrigenous material and the sedimentary environment. The REEs concentrations in North China indicates that Late Palaeozoic coals in the mining areas of the north, northwest, and western parts of North China are significantly enriched in REEs. In addition, REEs in Late Palaeozoic coals in the southeastern mining areas are relatively enriched, and the central and eastern regions are significantly depleted.Discussion: Large coal-type rare earth deposits are expected to be developed in North China, particularly the Datong coalfield, Jungar coal mine and the Weibei coal mine in the eastern margin of the Ordos Basin, and the Zibo coalfield.

The rare earth elements (REE) are fifteen elements with atomic numbers 57 through 71, from lanthanum to lutetium ('lanthanides'), plus yttrium (39), which is chemically similar to the lanthanide elements and thus typically included with the rare earth elements. Although industrial demand for these elements is relatively small in tonnage terms, they are essential for a diverse and expanding array of high-technology applications. REE-containing magnets, metal alloys for batteries and light-weight structures, and phosphors are essential for many current and emerging alternative energy technologies, such as electric vehicles, energy-efficient lighting, and wind power. REE are also critical for a number of key defense systems and other advanced materials. Section 843 of the National Defense Authorization Act for Fiscal Year 2010, Public Law 111-84, directs the Comptroller General to complete a report on REE materials in the defense supply chain. The Office of Industrial Policy, in collaboration with other U.S. Government agencies, has initiated (in addition to this report) a detailed study of REE. This latter study will assess the Department of Defense's use of REE, as well as the status and security of domestic and global supply chains. That study will also address vulnerabilities in the supply chain and recommend ways to mitigate any potential risks of supply disruption. To help conduct this study, the Office of Industrial Policy asked the U.S. Geological Survey (USGS) to report on domestic REE reserves and resources in a global context. To this end, the enclosed report is the initial USGS contribution to assessing and summarizing the domestic REE resources in a global perspective. In 2009, the Mineral Resources Program of the USGS organized a new project under the title Minerals at Risk and For Emerging Technologies in order to evaluate mineral resource and supply issues of rare metals that are of increasing importance to the national economy. Leaders and members of this project, with the assistance of the USGS National Minerals Information Center, prepared the enclosed USGS report on domestic REE resources. The USGS Mineral Resources Program has investigated domestic and selected foreign REE resources for many decades, and this report summarizes what has been learned from this research. The USGS National Minerals Information Center (formerly Minerals Information Team) has monitored global production, trade, and resources for an equally long period and is the principal source of statistics used in this report. The objective of this study is to provide a nontechnical overview of domestic reserves and resources of REE and possibilities for utilizing those resources. At the present time, the United States obtains its REE raw materials from foreign sources, almost exclusively from China. Import dependence upon a single country raises serious issues of supply security. In a global context, domestic REE resources are modest and of uncertain value; hence, available resources in traditional trading partners (such as Canada and Australia) are of great interest for diversifying sources of supply. This report restates basic geologic facts about REE relevant to assessing security of supply, followed by a review of current United States consumption and imports of REE, current knowledge of domestic resources, and possibilities for future domestic production. Further detail follows in a deposit-by-deposit review of the most significant domestic REE deposits (see index map). Necessary steps to develop domestic resources are discussed in a separate section, leading into a review of current domestic exploration and a discussion of the value of a future national mineral resource assessment of REE. The report also includes an overview of known global REE resources and discusses the reliability of alternative foreign sources of REE.

Rare earth element enrichment in sedimentary phosphorites formed during the Precambrian–Cambrian transition, Southwest China

An initial life cycle assessment of rare earth oxides production from ion-adsorption clays

Rare earth elements (REE) are indispensable to infrastructure, technology, and modern lifestyles, which has led to an increasing demand for these elements. The current global rare earth oxides (REO) market is dominated by Chinese production, which peaked in 2006 at 133,000 tonnes REO per year, accounting for some 97.1% of global production, causing concern about the long-term supply of REE resources. Although the REE consist of 17 individual elements (15 lanthanides plus scandium and yttrium) that are hosted by numerous types of mineralization, the relatively modest scale of the global REE mining sector has limited our knowledge of REE mineral resources and mineralizing systems compared to metals such as copper and iron, which are produced in much larger quantities. In order to quantitatively analyze the mineralogy, concentrations, and geologic types of REE deposits, we compiled a global dataset of REE mineral resources based on the most recently available data (2013–2014). This compilation yields minimum global contained total rare earth oxides plus yttrium oxide (TREO + Y) resources of 619.5 Mt split between 267 deposits. Deposits with available grade and tonnage data (260 of the 267 deposits in our database) contain some 88,483 Mt of mineral resources at an average concentration of 0.63% TREO + Y, hosting 553.7 Mt TREO + Y. Of the 267 total deposits in our database, some 160 have mineral resources reported using statutory mining codes (e.g., JORC, NI43-101, SAMREC), with the remaining 107 projects having CRIRSCO-noncompliant mineral resources that are based on information available in the industry literature and peer-reviewed scientific articles. Approximately 51.4% of global REO resources are hosted by carbonatite deposits, and bastnasite, monazite, and xenotime are the three most significant REE minerals, accounting for >90% of the total resources within our database. In terms of REE resources by individual country, China dominates currently known TREO + Y resources (268.1 Mt), accounting for 43% of the global REO resources within our database, with Australia, Russia, Canada, and Brazil having 64.5, 62.3, 48.3, and 47.1 Mt of contained TREO + Y resources, respectively. Some 84.3 Mt TREO + Y is hosted within tailings (dominated by tailings from Bayan Obo but with smaller resources at Palabora, Steenkampskraal, and Mary Kathleen) and 12.4 Mt TREO + Y is hosted by monazite within heavy mineral sands projects, illustrating the potential for REO production from resources other than traditional hard-rock mining. Global REE resources are dominated by the light REE, having an average light REO (LREO; La-Gd) to heavy REO (Tb-Lu and Y) ratio of 13:1. These REE deposits contain an average of 81 ppm Th and 127 ppm U, indicating that radioactive waste associated with REE extraction and refining could be a concern. Modeling the 2012 global production figures of 110 kt TREO + Y combined with an assumed 5% annual growth in REE demand indicates that known REE resources could sustain production until 2100 and that geologic scarcity is not an immediate problem. This suggests that other issues such as environmental, economic, and social factors will strongly influence the development of REE resources.

Rare earth elements (REE) play crucial roles in modern industry, technology applications, medical treatments and renewable energy system. Due to their unique physical and chemical properties, REE permanent magnets, alloys, phosphors, electronics and chemical catalysts have become indispensable components in a broad range of renewable energy technologies including wind turbines, electric vehicles (EV), photovoltaic (PV) thin films, and fluorescent lighting systems. The lack of comprehensive studies of current global REE supply chain severely limits our understanding of the comprehensive environmental burdens associated with the exploitation of these critical elements. There is an urgent need to establish a comprehensive and quantitative life cycle impact assessment (LCIA) based on robust REE mineral resources database and reliable rare earth elements (REE) processing information for global REE supply chain from the mining through refining to use stages which include impacts during production as well as benefits. In this way, the long-term future security of global REE supply can be modelled and assessed, thus ensuring sustainable REE uses. This thesis established a novel, systematic, comprehensive and transparent REE deposit geological classification system that covers all known and potential types of REE mineralization and deposit formation to categorize current available REE mineral resources. Then, based on this new classification scheme and mineral resources accounting, the first global REE mineral resources dataset based on statutory mining codes (e.g., JORC, NI43-101, SAMREC) has been compiled, which enables quantitative analyse the long-term REE resources availability and numerous key aspects (e.g. ore grade, mineral resources, principal mineralogy, by/co-products, deposit types, individual REE concentrations etc.) of future global REE supply. The results suggest REE geological scarcity is not an immediate problem. However, other issues such as associated environmental impacts, economic and social constraints will strongly influence the development of REE resources. Furthermore, a “cradle to gate” scale LCIA study based on 26 operating and potential REE mining projects in conjunction with their industrial reported REE mineral resources and processing data has been carried out. It showcases the possibility and necessity to systematically analyse the interconnections between critical aspects of REE production (e.g. project configurations, deposit types, ore grades, principal REE mineralogy, significant by/co-products) and consequent environmental impacts. Results suggest the development of cleaner REE refining technology based on project specific geological condition and mineralogy would be critical in optimizing the overall environmental performances long-term global REE supply chain. Finally, this thesis presents an indicative LCIA case study to assess future global REE demands and associated environmental implications in wind turbine industry, hence, It filled significant knowledge gaps between the comprehensive environmental benefits for REE consumption in downstream renewable energy system. The results suggest that the utilization of REE permanent magnet would not compromise but enhance the wind turbine’s sustainable performances. The consequential environmental benefits from wind energy generation significantly offset the environmental impacts for REE mineral production stages.

China started to produce rare earth elements (REEs) in the 1980s, and since the mid-1990s, it has become the dominant producer. Rare earth element export quotas first introduced by the Chinese government in the early 2000s were severely reduced in 2010 and 2011. This led to strong government-created disparity between prices within China and the rest of the world. Industrialized countries identified several REEs as strategic metals. Because of rapid price increases of REE outside of China, we have witnessed a world-scale REE exploration rush. The REE resources are concentrated in carbonatite-related deposits, peralkaline igneous rocks, pegmatites, monazite ± apatite veins, ion adsorption clays, placers, and some deep ocean sediments. REE could also be derived as a by-product of phosphate fertilizer production, U processing, mining of Ti-Zr-bearing placers, and exploitation of Olympic Dam subtype iron oxide copper gold (IOCG) deposits. Currently, REEs are produced mostly from carbonatite-related deposits, but ion adsorption clay deposits are an important source of heavy REE (HREE). Small quantities of REE are derived from placer deposits and one peralkaline intrusion-related deposit. The ideal REE development targets would be located in a politically stable jurisdiction with a pro-mining disposition such as Canada and Australia. REE grade, HREE/light REE (LREE) ratio of the mineralization, tonnage, mineralogy, and permissive metallurgy are some of the key technical factors that could be used to screen potential development projects. As REEs are considered strategic metals from economic, national security, and environmental points of view, technical and economic parameters alone are unlikely to be used in REE project development decision-making. Recycling of REE is in its infancy and unless legislated, in the short term, it is not expected to contribute significantly to the supply of REE.

Ion-adsorption rare earth element (REE) deposits represent strategic critical resources in China, which were traditionally considered to be predominantly hosted in granite weathering crusts. However, the recent discovery of new deposit types within the weathering crusts of shallow metamorphic rocks in South China has opened up novel exploration frontiers, while research on their metallogenic mechanisms remains insufficient. To elucidate the REE enrichment mechanisms in shallow metamorphic rock weathering crusts, this study focuses on the Getengzui ion-adsorption REE deposit in southern Jiangxi Province. Twenty-four samples were collected from the weathering crust profiles of the Qingbaikouan Shenshan and Kuli Formations. Multiple analytical approaches were employed, including major and trace element analysis, Chemical Index of Alteration (CIA), Base Leaching Index (BA), and quantitative evaluation of element mass transfer coefficients (τ). Trace element spider diagrams, REE distribution patterns, and A-CN-K diagram analysis were also utilized. The results reveal that the weathering crusts have progressed to the middle–late stage of chemical weathering. The average CIA value is 83 for the middle-upper part of the completely weathered horizon in the Kuli Formation. In contrast, for the completely weathered horizon in the Shenshan Formation, the value is 86. Intense chemical weathering has resulted in the near-complete decomposition of primary silicate minerals and extensive leaching of base cations. This progress has created an acidic pore water environment, which is critical for REE mobilization. REEs exhibit characteristics of in situ secondary enrichment, with significant enrichment of ΣREE in the middle-upper part of the completely weathered horizon. The peak τ(ΣREE) values reach 0.78 and 2.43 for the Kuli and Shenshan Formations, respectively. Apatite dissolution is identified as the primary source of REE ions. Differences exist in the geochemical mobility sequences of elements between the two formations. REE enrichment is controlled by multi-stage geochemical barriers, including an oxidation barrier and a clay adsorption barrier. The oxidation barrier preferentially fixes Ce4+, whereas the clay adsorption barrier serves as the dominant mechanism for large-scale REE enrichment. Parent rock lithology is the primary factor governing the efficiency, scale, and fractionation characteristics of REE enrichment. The Kuli Formation is favorable for forming the thick, large-scale orebodies enriched in light rare earth elements (LREEs). In the contrast, the Shenshan Formation tends to host higher-grade orebodies, characterized by a relatively balanced ratio of LREEs and heavy rare earth elements (HREEs). This study clarifies the main controlling factors for ion-adsorption REE mineralization in two shallow metamorphic rocks. It thereby provides a theoretical basis for future exploration. This framework is applicable to analogous REE resources within shallow metamorphic rock distributions across South China and nationwide.