Geochemistry of the Precambrian Alkaline Rocks and Carbonatites of India-Gaps in our Knowledge

Abstract

The carbonatites in India are closely associated with alkaline rocks, and are restricted to the stable continental area along major deep-seated faults. The detailed structural settings of all the carbonatite-alkaline complexes are yet to be worked out. Alkali metasomatism (fenitisation) that commonly accompanies carbonatite eruption also remains to be studied for most of the carbonatites so far discovered. Very little geochemical work has been done to prove or disprove the concept of associational major and minor element characteristics of the alkaline rocks and carbonatites. Whereas highly diagnostic isotope ratios have been reported for the igneous carbonate rocks from various parts of the world, only very few determinations have been done on the Indian carbonatites. Since experimental data have proved the magmatic origin of carbonatites and it is presumed that carbonatites are secondary magmas out of either kimberlitic or alkali-basaltic magmas, the ultrabasic rocks associated with the alkaline rocks and carbonatites of India need to be studied from the point of view of establishing the parent magma. Carbonatites have proved to be hosts for numerous economic mineral deposits. It is, therefore, necessary to undertake extensive geochemical surveys of the known outcrops as well as of the soils overlying and surrounding the outcrops.