Fluid Inclusion and EPR Spectroscopic Study of Ta–Nb Mineralization in Kadavur, Tamil Nadu, India

Kadavur is a significant Proterozoic anorthosite–gabbro complex, located within the Madurai block of the southern granulite terrain, India. In Kadavur complex, the marginal zone is made up of rapakivi granites and dolerite dykes and the core of this complex is made up of late-stage intruded pegmatites. Tantalum–niobium (Ta–Nb)-rich pegmatites (n = 20) and barren pegmatites (n = 5) were studied for fluid inclusion and electron paramagnetic resonance (EPR) characterization. Five and two distinct fluid inclusions are identified in the Ta–Nb-rich pegmatites, and barren pegmatites respectively. In the mineralized samples, carbonic inclusions show depression in the CO₂ melting temperature indicating the presence of volatile phases of N₂, C and CH₄, which is also confirmed by a laser Raman microprobe. The similar range of trapping temperatures and different modes of homogenization (liquid and vapour) are attributed to the fluid immiscibility process for Kadavur Ta–Nb mineralization. The EPR is one of the exploration tools for many mineral deposits. EPR spectra signals for mineralized pegmatite and barren pegmatite samples show the paramagnetic induced defect centres of E₁ and peroxyl types identified in Kadavur, India.