The long arcuate Singhbhum Shear Zone (SSZ) of around 160 km length having roughly an E-W trend hosts many uranium deposits and working uranium mines viz., Mohuldih, Bandhuhurang, Turamdih, Narwapahar, Bhatin, Jaduguda and Bagjata from west to east in addition to Cu deposits viz., Rakha, Mosabani etc. REE is well known from Kanyaluka area. Recent sub-surface exploration for uranium by AMD unravelled occurrence of thorite (ThSiO4)-bearing bands in a number of locations in western, central and eastern sectors of uranium mineralisation in SSZ, spanning over the entire shear zone. Thorite is observed in various host rocks involving metapelites of Dhanjori and Singhbhum Group and also in the Soda Granite/ feldspathic schist unit emplaced along the shear zone at the contact between the two groups. The individual lithounits that host thorite-bearing bands are restricted along the Singhbhum Shear Zone and include feldspathic schists (possible derivative of Soda Granite), albite veins, quartz-chlorite schists, quartz-biotite schists and sericite/muscovite-quartz schists. The thorite bearing zones transgresses lithology, stratigraphy as well as uraniferous zones along the shear zone evidently placing them as epigenetic hydrothermal mineralisation possibly later to major uranium metallogeny. Thorite occurs as discrete, rounded as well as subhedral to euhedral grains in various metapelites. They also form veins of their own besides occurring as phases within veins of albite and magnetite-apatite along the shear zone. Such multiple modes of occurrence and varied associated mineralogy suggest hitherto unknown thorium related hydrothermal mineralisation in SSZ. Presence of secondary thorium phases such as brockite (Ca-Th-phosphate) as well as post tectonic vein-type occurrence, points towards the mobility of thorium under a hydrothermal regime as well. However, present study thus, for the first time, establish the occurrence of thorite along with REE-Th minerals showing definite evidences of thorium mobilisation in several sectors of the well know U-Cu province of Singhbhum Shear Zone. Thorium-REE mobility is a widely understudied domain and the present findings place the SSZ as an ideal ground for exploring the concept with more understanding of this metal.

Allanite, being one of the most common REE bearing mineral phases in the multimetallic mineralized domain of Singhbhum Shear Zone, has always attracted attention from researchers. The present paper outlines a detailed petromineralogical study on various textural types of allanites. The allanite is categorized into 6 different types falling under three major categories on the basis of deformation, metamictisation and darkening of pleochroic halos. On the basis of mineral assemblage and probe analysis of allanite it follows that the optical and textural variations are an implication of not only multiple generations of their formation but rather significant variation in nature of hydrothermal fluids as evidenced by the differences in co-crystallized assemblages. They hint at relatively reducing hydrothermal conditions in Singhbhum Shear Zone responsible for REE-U-Th mineralization overprinting earlier event of oxidizing hydrothermal mineralization in which the well-known Th-poor uraninite, crystallized. Majority of the allanite appeared post or at the most syn-tectonic in their formation. The available geochronological data of allanite suggests them to be formed around 1.8 Ga. Considering textural criteria as seen in the present study, it appears that the majority of allanite owing to their undeformed morphology must have formed later to or at the most during waning stages of shearing and hence the minimum age of shearing in SSZ could be considered around 1.8 Ga instead of 1.6 Ga.