Geochemical evolution of uranium mineralization in the Mohuldih deposit, Singhbhum Shear Zone, India: constraints from uraninite and brannerite chemistry

Abstract

The study reports textures and compositions of uraninite and brannerite from the Mohuldih uranium deposit of the Singhbhum Shear Zone. Three types of texturally varied uraninite are identified: (i) pre-tectonic (U<inf>G−1</inf>), (ii) syn to post-tectonic (U<inf>G−2</inf>), and (iii) inclusions (U<inf>G−3</inf>). Based on UO<inf>2</inf> and PbO composition, these are further divided into five subgroups (U<inf>G−1a</inf>, U<inf>G−2a</inf>, U<inf>G−1b</inf>, U<inf>G−2b</inf>, and U<inf>G−3</inf>). The negative correlation between the rare-earth elements including Y (ΣREE<inf>2</inf>O<inf>3</inf> + Y<inf>2</inf>O<inf>3</inf>) and UO<inf>2</inf> of U<inf>G−1a</inf> and U<inf>G−2a</inf> uraninite indicates substitution of REE and Y for U4+ in the structure of these grains during primary crystallization, whereas U<inf>G−1b</inf> and U<inf>G−2b</inf> resulted from REE + Y + U-enrichment during secondary fluid-induced alteration. Compositional trends further reveal post-crystallization incorporation of Na, Si, K, Ca, Ti, and Fe, replacing radiogenic Pb in the structure of uraninite. The U-Th-Pb<inf>Total</inf> dating of uraninite yields two clusters: older (~ 1.71−1.64 Ga; preserved by U<inf>G−1a</inf> and U<inf>G−2a</inf>) and younger (~ 0.93 Ga; U<inf>G−1b</inf> and U<inf>G−2b</inf>). Additionally, the extrapolated best-fit linear trend for uraninite in U<inf>G−3</inf> population preserves chemical dates ranging from ~ 1.71 to ~ 1.64 Ga. The ~ 1.64 Ga represents a U + Y + HREE + Ca + Fe hydrothermal event, resulting in the precipitation of uraninite, followed by dissolution-reprecipitation of the mineral along the grain boundary and fractures at ~ 0.93 Ga. The oldest mesured date (~ 1.71 Ga) is attributed to partial Pb-loss by older uraninite during the ~ 1.64 Ga hydrothermal event, with no evident geological significance in the area. The dissolution-reprecipitation of the early-formed uraninite also resulted in the formation of brannerite and ilmenite during the ~ 0.93 Ga event. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025.