Original paper

Compositional variation of aeschynite-group minerals in the Bayan Obo Nb-REE-Fe ore deposit, Inner Mongolia, China

Yang, Zhuming; Smith, Martin; Henderson, Paul; LeBas, Michael J.; Tao, Kejie; Zhang, Peishan


The aeschynite-group minerals occurring in an aegirine-fluorite-dolomite-aeschynite vein in the Bayan Obo Nb-REE-Fe deposit show complex compositional zoning in BSE images. Microprobe analyses revealed that the concentrations of REE2O3are globally high in aeschynite-group minerals, ranging from 36.72 to 40.32 wt.%. Four species were identified in the same sample, these being aeschynite-(Ce), aeschynite-(Nd), nioboaeschynite-(Ce) and nioboaeschynite-(Nd). The correlations among cations suggest two special coupled substitutions with charge-balanced described by the exchange vectors as CaNb(Nd,Sm,Pr)-1Ti-1 and LaNbTh-1Ti-1. The chondrite-normalized REE patterns are hump-shaped with the maximum at Pr or Nd. The chondrite-normalized La/Nd ratios vary in the range ~0.15 to 0.40. It indicates that at Bayan Obo aeschynite minerals are relatively strongly La-depleted and Nd-enriched. The compositional variations in aeschynite-group minerals were controlled by the crystal chemistry and affected by fluid composition.


aeschynite-groupmicroprobe analysiscompositional variationbayan obo