Geological resources of scandium: a review from a Chinese perspective

ABSTRACT

Scandium (Sc) is a dispersed metal in Earth’s lithosphere, with an average abundance of 16 to 22 ppm. In the meantime, it is widely considered as a critical metal because of its paramount significance in scientific research and technical innovation. With surging demands that are not backed-up by current supplies globally, the market price of Sc oxide is astonishingly five times more than the most expensive rare earth oxide of terbium (Tb). Production of Sc is significantly held back due to scarcity of economically viable grades at explorable depths within the crust, compared with other critical metals such as REE, Nb and Ta. Nevertheless, typical high- to intermediate-grade Sc deposits, as compiled in this review, consistently show close relationships to specific magmatic (e.g. ultramafic-mafic and carbonatitic), supergene and hydrothermal processes during Sc enrichment, especially the former two. Known potential Sc deposits are tentatively classified based on their host rocks and metallogeny, including those hosted in the ultramafic-mafic rocks and related laterites, in carbonatite and related laterites, in bauxite residue and processed coals, hydrothermal Sc deposits and Sc deposits related to syenite intrusions, pegmatites or marine sediments. We also discuss the Sc enrichment mechanism and associated tectonics and partition coefficients of Sc among diverse minerals and melts, which reveal the preference of Sc for clinopyroxene, garnet and iron oxides by isomorphic replacement or ion absorption during diverse magmatic and supergene Sc enrichment processes. Lastly, Sc resources in the world-class Bayan Obo deposit are discussed in detail as an illustrative benchmark example, where hydrothermal aegirine may host majority of carbonatite-derived Sc.

Graphical Abstract

KEYWORDS:

• Scandium deposit
• dispersed metal
• SC deposit classification
• SC enrichment
• metallogeny
• bayan obo deposit

Highlights

• This integrated review classified known global Sc deposits into five categories.

• Sc is mainly enriched to economic grade by magmatic and supergene processes.

• Sc was enriched in laterites by absorption or isomorphism in iron oxides.

• Sc was occasionally enriched in coarse-grained Sc minerals in veins or pegmatites.

• Polymetallic Sc deposits are primary targets for geological research and mining.

Acknowledgments

We appreciate PhD student Shuang-Liang Liu for his support and opinion during discussion, and we are grateful for the precious and detailed comments from Prof. Axel Müller, Prof. Robert J. Stern and other reviewers. This review and related work are financially supported by the National Natural Science Foundation of China under Grant No. 41902066 and 41930430, the Fundamental Research Funds for the Central Universities under Grant No. lzujbky-2021-7, and the Open Program of the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization [2021Z2360] and the Joint Projects of the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization (2022Z2413).

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/00206814.2023.2169842

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [41902066,41930430]; the Open Programme of the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization [2021Z2360]; the Joint Research Programme of the State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization [2022Z2413]; Key Research Program of the Institute of Geology and Geophysics (Chinese Academy of Sciences) [IGGCAS-201901]; Fundamental Research Funds for the Central Universities of China [lzujbky-2021-7].