Discovery and Petrogenetic Significance of Strontianite‐rich Carbonatite in the Muluozhai REE Deposit, Western Sichuan, China

Abstract Strontianite‐rich carbonatite, containing over 30 vol% carbonate minerals predominantly composed of strontianite (SrCO 3 ), is identified in the Zhengjialiangzi ore segment of the Muluozhai rare earth element (REE) deposit, western Sichuan Province, China. It exhibits a unique mineral assemblage dominated by strontianite, fluorite, bastnäsite, barite, calcite and dolomite, distinguishing it from conventional calcio‐, magnesio‐, ferro‐, or natro‐carbonatites. The rock shows extreme enrichment in REEs (ΣREE = 47335–64367 ppm), with strong LREE/HREE fractionation [(La/Yb) N = 1151–2119] and notably high concentrations of high‐value critical REEs (e.g., Pr, Nd, Tb, Dy), 5–10 times greater than those in local calcite‐dominated carbonatites. Trace element patterns indicate significant enrichment in REEs, Sr, and Ba, along with depletion in high‐field‐strength elements (HFSEs; e.g., Nb, Ta, Zr, Hf). In‐situ Sr isotopes of strontianite [( 87 Sr/ 86 Sr) i = 0.706190–0.707305] indicate an enriched mantle source (EMI–EMII). Sr enrichment is attributed to initial mantle source enrichment and extensive fractional crystallization, possibly accompanied by minor wall‐rock assimilation. We propose that the strontianite‐rich carbonatite formed from a highly evolved, Sr‐ and REEs‐rich carbonatitic magma that intruded into shallow structural breccias, followed by rapid cooling. Its formation is associated with a continuous melt‐fluid evolutionary process that is characteristic of carbonatitic systems.