Degassing-Driven Oxidation Promotes HREE Enrichment in South China Granites.

This article focuses on the geochemical and isotopic characteristics of two Mesozoic granites from the Zhaibei heavy rare earth element (HREE) deposit in South China, investigating the origin of HREE enrichment and unusual cerium (Ce) depletion. The older porphyritic granite (~188 Ma) exhibits higher HREE contents, negative Ce anomalies, and evidence of oxidation during post-magmatic hydrothermal stages, attributed to metasomatism by REE-rich, oxidizing fluids derived from flat subduction of a sediment-bearing slab. In contrast, the younger medium–coarse-grained granite (~170 Ma) shows mantle-derived isotopic signatures and lacks Ce anomalies or elevated oxidation states. The study proposes that fluid-induced oxidation increased oxygen fugacity, causing Ce3+ to oxidize to Ce4+, which fractionated Ce from other REEs and promoted HREE enrichment in the granites, highlighting the role of slab-derived fluids and oxygen fugacity in HREE mineralization.