EPMA geochemistry and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbhum Shear Zone, eastern India: Implications for REE mineralization vis-à-vis tectonothermal events in the Proterozoic Mobile Belt

Abstract

The Singhbhum shear zone (SSZ), eastern India, located close to the boundary between the Proterozoic North Singhbhum Mobile Belt and the Archaean Singhbhum craton, is the best known uranium province and one of the most important copper districts in India. The uranium ores and associated rocks are enriched in rare earth elements (REEs). This study integrates texture, composition and in situ LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit in the SSZ. The earliest LREE-rich allanite (Allanite-Ce) formed at 1883 ± 14 Ma and was subsequently replaced and overgrown respectively by LREE-depleted allanite and epidote at 1637 ± 11 Ma and 1107 ± 18 Ma. The earliest monazite (Monazite-Ce) formed at ca. 1809 ± 9 Ma, while a new generation of monazite and florencite are dated at 952.2 ± 7.9 Ma and 959 ± 83 Ma respectively. Titanite, discordant to the pervasive foliation, records ancient Pb-loss and probably new titanite growth at 978 ± 17 Ma.The SSZ witnessed protracted evolutionary history with accompanying multi-stages REE mineralization and mobilization, spanning over ca. 900 Ma. The Paleoproterozoic LREE-mineralization occurred in two different pulses at ca. 1.88 Ga and ca. 1.80 Ga predating the known ages of metamorphism. It is envisaged that extension-related faults developed at the present location of the SSZ acted as fluid conduits and localized the earliest ca. 1.88 Ga hydrothermal REE mineralization. It is unclear whether the ca 1.80 event is the continuation of the ca 1.88 Ga event or represents a separate and discrete pulse of mineralization in the same locale under different geotectonic environment. The ca. 1.64 Ga event associated with LREE-removal is related to either reactivation of the existing faults or partial closure of the mobile belt with concomitant shear deformation and metamorphism in the shear zone when the rocks in the northern mobile belt were thrust southwards along existing mineralized faults. The status of the ca. 1.11 Ga event is ambiguous. The 950 ± 50 Ma event, which primarily redistributed REEs from existing mineralization is related to the final closure of the mobile belt and reactivation of the SSZ associated with the formation of the greater Indian land mass in Peninsular India.