First Report of Florencite from the Singhbhum Shear Zone of the East Indian Craton

Abstract EN

Metamorphic florencite is being reported from kyanite-rich rocks from the eastern part of the Palaeo- to Mesoproterozoic Singhbhum shear zone.

This is the first report of florencite from the Precambrian rocks of the Indian Shield.

Host rock of florencite is a kyanite-rich rock (>80 vol%) with small and variable amounts of quartz, lazulite, augelite, and rutile.

Florencite forms small (<20 microns) idioblastic-to-subhedral crystals that are included in large kyanite grains.

Rarely, florencite replaces kyanite.

The florencite has small proportion of crandallite (8.7–11.8 mol%) and goyazite (<2 mol%) components.

Florencite of this study is dominated by Ce (~49 mol%) with significant La (~30 mol%) and Nd (~21 mol%).

Compared to other florencite occurrences of the world, florencite of the studied rock is impoverished in S, Sr, and Ba and rich in P.

Stability of the assemblage florencite-kyanite-augelite-lazulite and the quantitative thermobarometry in the adjoining rocks suggest that florencite was formed during Palaeoproterozoic metamorphism that culminated at the P-T range of 490±40∘C and 6.3±1 kbar.

Integrating all the geological features it is postulated that florencite was formed due to metasomatism of some aluminous protolith by infiltration of acidic fluids charged with PO4-3 and LREE.