via Geology.com, the USGS has released a pretty useful primer on the geology of Rare Earth elements. The types of host rocks are described along with the challenges of mineral processing for element extraction.
A table summarizes the host rock types along with examples of their occurrence. ... a bit surprised that no examples from India have been given. There is active mining in India of placer sand type deposits from the coasts of Kerala. These sands are rich in monazite a phosphate derived from granitic rocks which has been used as a source of Thorium but is increasingly now gaining importance as a source of Rare Earths too. Inland placers have also been identified as potential sources.
There are two other potential geological sources of Rare Earths in India. Alkali and carbonatite intrusives and volcanic flows. These broadly fall in two age groups; through the Proterozoic, developed during episodic magmatic events. Tamil Nadu and Rajasthan carbonatites are well known but their Rare Earth potential needs to be evaluated in detail. The younger ones are late Cretaceous in age, related to the Deccan volcanic episodes and are located in the western regions around Gujarat.
The third potential source of Rare Earths are the thick residual clay and lateritic soils developed on granitic source rocks. These types of deposits are being exploited in south China. Such soils are present through the western parts of south India. They formed during intense weathering of Precambrian terrains during the Cenozoic. I am not sure how well they have been characterized in terms of their Rare Earth element concentrations.
Even if they are recognized as a resource, it will be tough to exploit them. Most of these thick soils are covered with tea and coffee plantations... a mighty industry of its own.