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Writer's pictureNoel Ong

Emerging insights into nepheline syenite-derived regolith-hosted rare earth element deposits

Emerging insights into nepheline syenite-derived regolith-hosted rare earth element deposits | Samso Insights

The Puxiong deposit in Southwest China represents a significant shift in the exploration of regolith-hosted rare earth element (REE) deposits, traditionally dominated by granites and felsic volcanic substrates.


Recent discoveries and studies, such as those at Puxiong, underscore the potential of silica-undersaturated alkaline igneous rocks like nepheline syenite in contributing to REE resources [1].

 

Geology and mineralogy of the Puxiong deposit


Located in Southwest China, the Puxiong deposit is notable for its formation through the weathering of nepheline syenite, which has undergone partial hydrothermal enrichment in REEs.


This syenite registers REE concentrations that range dramatically from 177 to 9,336 parts per million (ppm).


The mineralogical composition includes significant percentages of REEs hosted in minerals such as britholite-(Ce), tritomite-(Ce), and cerite-(Ce), which collectively contribute to approximately 60% of the total REE content.


Additional REEs are found in secondary minerals within the K-feldspar and less abundantly in other minerals like titanite and hiortdahlite.


Figure 1: Puxiong Geology (Source: Economic Geology) | Samso Insights

Figure 1: Puxiong Geology (Source: Economic Geology) 


Weathering and REE Mobilisation


The weathering process is critical in the formation of regolith hosted REE deposits.

 At Puxiong, REEs are released from primary minerals into soil solutions.


Subsequently, they adsorb onto clay minerals or precipitate as supergene phases such as rhabdophane.


The clay minerals, particularly illite and halloysite, exhibit higher ion exchange capacities than those derived from granitic sources, enhancing their ability to capture and concentrate REEs.


Figure 2: Photographs of the regolith and parent nepheline syenite (Source: Economic Geology) | Samso Insights

Figure 2: Photographs of the regolith and parent nepheline syenite (Source: Economic Geology)


Spatial distribution of REEs 


The spatial distribution of REEs within the deposit reveals that the highest concentrations of heavy REEs (HREEs) occur at the footslope, averaging 110 ppm. 


Meanwhile, the lighter REEs (LREEs) are more abundant in the B horizon at hilltops.  


This distribution pattern is influenced by the topographical features and the mobility of REEs within the weathering profile, driven by groundwater and soil solutions. 


 

Strategic Significance and Environmental Considerations 


REEs are increasingly crucial due to their applications in high-technology and defence industries.  


The ease of mining and processing regolith-hosted deposits, such as those at Puxiong, offers a strategic advantage over more conventional hard-rock mining methods.  Moreover, the development of new mining technologies, such as electrokinetic mining, promises to enhance REE recovery while minimising environmental impacts. 


Global Implications 


The Puxiong deposit provides a new perspective on the potential for nepheline syenite-derived regolith-hosted REE deposits. 


it also invites further exploration and study in other regions with similar geological settings.  

Understanding the geochemical behaviour of REEs in these unique environments can guide future exploration and exploitation strategies, potentially leading to the discovery of new economically viable deposits. 


Conclusion 


The study of the Puxiong REE deposit not only expands the geological understanding of regolith hosted REE deposits but also underscores the importance of alternative sources for these critical materials.  


As global demand for REEs continues to rise, the insights gained from Puxiong and similar deposits are crucial for securing a sustainable supply of these indispensable elements. 


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Disclaimer


The information or opinions provided herein do not constitute investment advice, an offer or solicitation to subscribe for, purchase or sell the investment product(s) mentioned herein. It does not take into consideration, nor have any regard to your specific investment objectives, financial situation, risk profile, tax position and particular, or unique needs and constraints.



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References: 


[1} Min Wang, Martin Yan Hei Li, Mei-Fu Zhou, Jia-Xi Zhou, Guotao Sun, Ye Zhou, Yin Li; Enrichment of Rare Earth Elements During the Weathering of Alkaline Igneous Systems: Insights from the Puxiong Regolith-Hosted Rare Earth Element Deposit, SW China. Economic Geology 2024;; 119 (1): 161–187. doi: https://doi.org/10.5382/econgeo.5024 

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