Describe the geological characteristics of any three important types of uranium deposits in India. Draw neat sketches illustrating the geological setting of these deposits.

1. Sandstone-Type Uranium Deposits

These deposits are the most significant contributors to India’s uranium production, particularly in the East Coast Gondwana basins of Odisha and Andhra Pradesh. They are hosted within coarse-grained sandstones of the Proterozoic age, typically belonging to the Talchir and Raniganj Formations. The uranium mineralization is primarily associated with carbonaceous matter within the sandstone, acting as a reducing agent. The process involves the precipitation of uranium from groundwater enriched in uranium, often sourced from surrounding granitic rocks.

Geological Characteristics:

• Host Rock: Coarse-grained, permeable sandstones with significant porosity.
• Mineralization: Uranium occurs as finely disseminated uraninite (UO₂) and pitchblende, often coating sand grains and filling pore spaces. Secondary minerals like carnotite (K₂(UO₂)₂(VO₄)₂·3H₂O) are common due to weathering.
• Structural Control: Faults and fractures play a role in fluid flow and uranium deposition.
• Regional Setting: Gondwana basins characterized by fluvial and deltaic environments.

Sketch: Illustrates a cross-section of a sandstone deposit, showing uranium mineralization concentrated within a permeable sandstone layer, overlain by impermeable shale. Faults are shown facilitating fluid flow.

2. Unconformity-Type Uranium Deposits

These deposits are found in the Proterozoic basins of Rajasthan, specifically in the Bhilwara and Udaipur regions. They occur at the base of the Cuddapah Supergroup, where uranium-bearing conglomerates and sandstones overlie Archaean crystalline basement rocks. The unconformity surface acts as a trap for migrating uranium-rich fluids.

Geological Characteristics:

• Host Rock: Conglomerates, sandstones, and shales of the Cuddapah Supergroup overlying Archaean granite and gneiss.
• Mineralization: Uraninite is the primary uranium mineral, concentrated along the unconformity surface and within permeable layers.
• Structural Control: The unconformity surface and associated faults are crucial for uranium accumulation.
• Regional Setting: Proterozoic rift basins with a distinct unconformity between basement rocks and sedimentary cover.

Sketch: Shows a cross-section of an unconformity-type deposit, highlighting the uranium mineralization concentrated at the contact between the Cuddapah sediments and the Archaean basement.

3. Vein-Type Uranium Deposits

Vein-type uranium deposits are less common in India but are found in the Southern Granulite Terrain of Tamil Nadu and Kerala. These deposits are associated with hydrothermal activity related to granitic intrusions and fault systems. Uranium-bearing fluids circulate along fractures and faults, precipitating uranium minerals in veins.

Geological Characteristics:

• Host Rock: Charnockites, granites, and gneisses of the Southern Granulite Terrain.
• Mineralization: Uraninite, pitchblende, and other uranium minerals occur within quartz veins and along fault planes.
• Structural Control: Faults, fractures, and shear zones are the primary conduits for hydrothermal fluids.
• Regional Setting: High-grade metamorphic terrains with a history of granitic magmatism and tectonic activity.

Sketch: Illustrates a vein-type deposit, showing uranium mineralization filling a quartz vein within a granitic rock mass, associated with a fault zone.