Tectonics and Fluid Coupling in Critical Metal Enrichment

This study investigates the coupled roles of solid-state deformation, hydrothermal fluid flow, and critical metal enrichment mineralization. Integrating structural analysis, mineral microtextures, EBSD, fluid inclusions, and H-O isotopes, we show that the deposit experienced Neoproterozoic Nb pre-enrichment in alkaline volcanic rocks, later overprinted by Early Paleozoic tectonic-hydrothermal events. Ductile shear zones that characterized by foliation and lineatio enhanced permeability and channeled F⁻-Cl⁻-CO₂-rich fluids from deep sources, with fluid inclusion planes confirming foliation-parallel migration. Syn-tectonic breakdown of amphibole, pyroxene, and titanite released Nb, Y, and REEs into solution as soluble complexes.

Fluid evolution—driven by alkali consumption and CO₂ influx, lowered pH and increased Nb solubility. Nb enrichment occurred via water-rock interaction within shear zones, though complex stability initially inhibited precipitation. Localized Nb deposition took place at altered mineral margins, where Fe²⁺ spikes destabilized complexes. Ore bodies formed in brittle–ductile to brittle domains, governed by the interplay of deformation-controlled permeability and chemical feedbacks.

Strain regime shifts further enhanced permeability, enabling mixing between deep NbF₆⁻- YF₆³⁻-CO₂-rich fluids and external alkaline magmatic or Ca-rich fluids. This mixing triggered pH and redox changes that destabilized metal complexes, precipitating Nb minerals as magnetite/ilmenite-hosted inclusions or microveins, which direct evidence of strain and fluid pulsation. Fault-valve cycling induced fluid immiscibility and boiling, further disrupting complex stability. Our findings underscore that tectonically driven fluid migration is fundamental to Nb enrichment, providing a structural framework for exploring orogenic rare-metal deposits.