Carbonatite Alkali Complex of Samalpatti Dharmapuri District, Tamil Nadu

Dunites, pyroxenites, alkali syenites and carbonatites form the complex. The complex intrudes in a discordant fashion, hornblende gneisses which form the country rock.

The carbonatites are distributed mainly in pyroxenite as fracture fillings and to a lesser extent as dykes in syenites. The carbonatite bodies form a distinct but discontinuous ring. The calcite-dolomite carbonatite and para-ankerite carbonatite are the main types. Varieties having mica, monazite, riebeckite and ilmenite are identified. Quartz-baryte-galena veins, pegmatites of syenitic composition and albitites are associated with the carbonatites. Evidences for fenitisation are not much. Feldspathoids, normally associated with carbonatite activity are absent. Xenoliths of gneisses, pyroxenite and syenite in carbonatites, compositional banding and primary foliation, are some of the features of the carbonatites. On the basis of mineral assemblage, the temperature of formation of this complex is assigned 325°C. Analyses indicate relatively high values for barium, cerium, yttrium, zirconium, vanadium and boron.