India has huge Thorium reserve, a potential source of nuclear energy. This…

Concept

Thorium is not mined as a free metal; it occurs chemically locked inside the mineral monazite, a rare-earth phosphate. Monazite is heavy and resistant to weathering, so rivers carry the grains to the sea, where wave action sorts and concentrates them into 'placer' deposits in beach and coastal sand. A thorium reserve therefore depends on a coastal sand belt that is rich in monazite, formed by this river-to-shore sorting process.

Application

India's monazite-bearing beach-sand belt is richest along the south-west coast, where the Kerala coastal sands (the Chavara belt near Kollam and adjoining beaches) hold a major share of the country's monazite and hence its thorium. India's atomic-energy programme (BARC / Department of Atomic Energy) is built on this coastal monazite resource, which is why the reserve is described as confined to the coastal sands of the Kerala sea.

How the geological setting decides it

• A monazite placer needs hard rock to weather, rivers to carry the heavy grains, and a wave-worked shore to concentrate them: that combination is a coastal beach-sand belt.

• Inland plateau rock such as Chhota Nagpur weathers in place and is mined for coal, iron and mica, not sorted into a coastal monazite placer.

• A tidal delta such as the Sunderban lays down fine, light silt and clay, the opposite of the heavy-mineral sorting that builds a placer.

• A wind-built desert such as the Thar moves light quartz dunes far inland with no river-to-shore transport, so no heavy-mineral placer forms.

Cross-check

Reading the four settings against that placer requirement points to the Kerala sea coast, which is consistent with the BARC / IAEA record of India's thorium occurring in Kerala beach sands.