Fluid inclusion and stable isotope fingerprints of the Paraná emerald deposit, Borborema Province, northeastern Brazil: implications for a tectonic–magmatic origin

Emerald from the Paraná deposit, in northeastern Brazil, is found in metasomatic phlogopite schists formed after fluid interactions between Be-bearing granitic pegmatites and Cr-rich mafic rocks within the Portalegre shear zone. This study combines fluid inclusion petrography, microthermometry, X-ray microtomography and stable isotope analyses to fingerprint the Paraná emerald deposit, providing critical insights into its formation within a tectonic–magmatic environment. Fluid inclusion analysis revealed two distinct fluid inclusion assemblages, with evidence of boiling processes triggered by tectonic stress. The distribution of fluid and phlogopite inclusions evidenced by X-ray microtomography indicate the presence of three stages of crystal growth, highly influenced by regional metamorphism and deformation. On the other hand, stable isotope data ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM1" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> 18 O: +6.9 to +7.1‰; <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="IM2" overflow="scroll"> <mml:mi>δ</mml:mi> </mml:math> D: −76 to −93‰) are consistent with a magmatic origin for the hydrothermal fluids. These findings contribute to the understanding of emerald formation in the Borborema Province and to the discussion of the role of tectonic structures in emerald genesis, with the Portalegre shear zone interpreted as the main conduit for Be-rich pegmatite melts and fluids that led to the formation of the Paraná emerald during the final stage of the Brasiliano orogeny ( c. 528–524 Ma).