Mineral Resources of Kerala: Applied and Basic Research

Primary and secondary rutile – a case study from Kerala

Rutile is the best source of titanium in nature. This mineral has widespread occurrence in rocks, alluvial sediments and in beach placers and, therefore, are used as an indicator mineral for provenance analysis. The rutile that is obtained from source rocks is known as primary rutile and it is postulated that ilmenite alteration can also produce rutile, which is a secondary rutile. Loss of rutile (secondary origin) along ilmenite is a drain in the economy. Such rutile if characterized can be separated out from the factory grade ilmenite and could be treated as a separate product with higher Ti content than leucoxene. Similarly presence of iron contaminated rutile or leucoxene along with the primary rutile crop will drastically reduce the price of the rutile. So if the primary rutile can be characterized it will be possible to separate primary rutile from the mixture of primary and secondary rutile along with traces of leucoxene.

The study was designed to decipher the chemical and physical characteristics of primary and secondary rutile.
The salient output of the study are:

 Primary rocks (granulites) with garnet in Kerala Khondalite Belt seldom contain appreciable amounts of rutile, which is “primary”.
       
Ti/ Ti+Fe of the leucoxene samples are of the range 0.6-0.7, which indicates a pseudo-rutile alteration stage only. XRD also corroborateschemical data.
In granulites with garnet, rutile is unstable.

1.2 and 1.4 Amp fractions were found to contain maximum leucoxene – source of secondary rutile.

 Deciphering of “secondary” rutiles from the separates of high current  strength fraction of leucoxene is impossible.

The source of rutile in the beach placer could be postulated mainly of  offshore origin. This has to be studied further. A minor contribution to  placer rutile could be due to secondary enrichment in the weathering   front related to laterization. This hypothesis needs further studies.