Work

Visean and Permian Sn-Nb-Ta Metallogeny in the Iberian Variscan Belt: insights from the Golpejas Rare-Metal granite

Year: 2026

Type: article

Abstract: The Golpejas Rare-Metal Granite (GRMG) is an atypical Variscan intrusion characterized by its sheet-like geometry, limited thickness, and remarkably rapid cooling (<210 years). Subsequent structural rotation (>90°) during D2–D3 deformation inverted the system, repositioning the original apical zone into the footwall. LA-ICP-MS U–Pb geochronology identifies two metallogenic stages: a syn -magmatic disseminated Nb–Ta–Sn event (ca. 340 Ma) and a Permian hydrothermal overprint (ca. 290 Ma) characterized by quartz–montebrasite–cassiterite–wodginite–tapiolite veins. Geochemical modeling links the GRMG to a coeval tourmaline-bearing leucogranite, whereas subsolidus re-equilibration temperatures (<470 °C) indicate emplacement of a near-water-saturated melt at ∼ 220 MPa (∼8 km). At the margins, combined thermal and chemical quenching promoted muscovite crystallization and preferential precipitation of columbite group minerals (CGM), but not cassiterite. Conversely, in the core, continued crystallization induced second boiling, exsolving a magmatic fluid responsible for albitization and phosphatization, and a subordinate hydrosaline liquid (HSL). Interaction with these fluids produced multiple CGM generations through selective dissolution and reprecipitation. Consequently, whole-rock Ta/Nb evolution reflects mixing among CGM generations rather than fractional crystallization. Finally, late-stage kaolinization nearly doubled Nb–Ta grades through mass loss. These results demonstrate that economically significant Nb–Ta enrichment resulted from the coupled effects of fractional crystallization, chemical quenching and fluid exsolved magmatic fluids, with fluids-mediated redistribution ultimately exerting the dominant control over deposit-scale Nb–Ta enrichment. This genetic model also identifies kaolinized zones, phosphatized domains, muscovite-rich margins and tourmaline-bearing granites as favorable exploration targets.

Source: Ore Geology Reviews

DOI: 10.1016/j.oregeorev.2026.107561