Textural and compositional evolution of niobium minerals in the Miaoya carbonatite-hosted REE-Nb deposit from the South Qinling Orogen of central China

• Published in: Mineralium deposita 2023, Vol.58 (1), p.197-220
• Main Authors: Ying, Yuan-Can, Chen, Wei, Chakhmouradian, Anton R., Zhao, Kui-Dong, Jiang, Shao-Yong
• Format: Article
• Language: English
• Subjects: Calcite; Carbonates; Crystallization; Depletion; Earth and Environmental Science; Earth Sciences; Evolution; Fluids; Geology; Hydrothermal fields; Hydrothermal systems; Mineral Resources; Mineralization; Mineralogy; Minerals; Niobium; Orogeny; Precursors; Silurian; Tantalum; Tantalum oxides; Trace elements; Uranium dioxide; Zirconium
• ISSN: 0026-4598; 1432-1866
• DOI: 10.1007/s00126-022-01126-y

The Miaoya carbonatite complex in the South Qinling Orogen hosts one of the largest REE-Nb deposits in China. The origin and evolution of REE enrichment in this Silurian intrusion have been extensively studied, whereas Nb mineralization remains less well understood. Here, we report detailed mineralogical and geochemical data on diverse Nb-bearing minerals from the Miaoya carbonatite to explain the development of Nb mineralization in these rocks. Ferrocolumbite is the dominant Nb mineral, which occurs principally as an alteration product of the earlier-crystallized Nb phases (uranopyrochlore, betafite, and fersmite). The ferrocolumbite varieties (Clb-1, Clb-2, Clb-3) inherited some compositional characteristics of its precursors, in particular a trend of decreasing Ta 2 O 5 and UO 2 from Clb-1 to Clb-3, which mimics the Ta-U depletion trend from uranopyrochlore to betafite and fersmite. Varieties Clb-1 and Clb-2 and associated calcite and altered uranopyrochlore show evidence of hydrothermal overprint such as positive Eu anomaly. Ferrocolumbite Clb-2 shows slightly higher Eu/Eu* and Zr/Hf ratios and contains fewer relicts of its precursor mineral in comparison with Clb-1, possibly indicating local enrichment of F in the hydrothermal system. Calcite associated with Clb-3 and fersmite shows a trace element signature characteristic of igneous carbonates, suggesting that this mineral paragenesis is least affected by metasomatic overprint with no contribution from external fluids. The study of the Miaoya REE-Nb deposit shows that late-stage metasomatism of carbonatites does not significantly enhance Nb grade in contrast to that of REE mineralization and leads to the formation of a secondary Nb paragenesis with specific trace element characteristics.