Critical metal enrichment in peralkaline granite systems: Constraints from multi-generation zircons in the large-scale Baerzhe Zr-REE-Nb deposit (northeastern China)

Rare metals and rare earth elements (REEs) are globally demanded critical metals that exhibit extreme enrichment in peralkaline granite mineralizing systems. However, the underlying mechanisms of this enrichment remain poorly understood. In this study, we investigated the textural and geochemical characteristics of zircons from the large-scale Baerzhe critical metal deposit in northeastern China, which hosts economic concentrations of Zr-REEs-Nb. Three distinct zircon types were identified: Type-I zircons crystallized from highly evolved melts enriched in REEs, Y, Th, and U. Type-II zircons irregularly overprint Type-I grains and formed through melt-mediated re-equilibration process during the magmatic-hydrothermal transition stage. Their anomalously high Y2O3 (5.1–6.0 wt%) and Nb (4866–9020 ppm) contents indicate formation in a F-rich melt. Type-III zircons are characterized by a spongy texture and a depletion in REEs, Y, Th, and U. They formed via dissolution-reprecipitation processes involving late-stage hydrothermal fluids. U-Pb dating shows all zircon types have indistinguishable ages at ca. 126 Ma, confirming that critical metal mineralization occurred in a brief, continuous pulse rather than prolonged multi-stage events. The magmatic-hydrothermal transition (Type-II) is the key interval for Y/Nb enrichment, while late hydrothermal processes (Type-III) drive light REE enrichment (via monazite and bastnäsite precipitation). This sequential model refines previous understanding of Baerzhe mineralization, highlighting F-rich liquids as the common mediator; i.e., they promote late-stage F-rich melt (magmatic stage) and fluid-rock interaction (hydrothermal stages) to concentrate Zr, REEs, and Nb. This study demonstrates that zircon not only can record the timing and environment of mineralization but also identify high-potential ore-forming stages—enhancing both the scientific study and exploration efficiency of critical metal deposits worldwide.