Petrographic Characteristics of Rock Types in Parts of Khammam Schist Belt, Andhra Pradesh, India

The Khammam Schist Belt (KSB) is unique from other schist belts in the granite greenstone terrain of the Dharwar Craton by the presence of workable deposits of corundum in this belt. The petrographic studies on the rocks of KSB are vital and of significant value for not only demarcating the mineralized zone but also for understanding the genesis of corundum.
The KSB is predominantly composed of schistose and gneissose rocks of the Precambrian age. These rocks form the entire plain country of the KSB and occur as discontinuous deformed interlayers/bands. Hornblende schists, Schistose amphibolites and Tremolite-actinolite-talc-chlorite schists occur as dark bands, streaks and lenses within the tonalite gneisses and pelitic gneisses in the KSB, forming the basement for younger anorthosites, amphibolite dykes, mafic and felsic granulites, meta-dolerites and granitoids. All these rocks are deformed and metamorphosed under upper amphibolite to lower granulite facies conditions. (Appavadhanulu, K. et al., 1976)
A number of representative samples were collected for the close examination of various rock types in the area. As many as 100 thin sections were prepared to establish the petrographic character of the rocks. Modal Analysis were carried out for some important rock types to estimate the approximate percentage of various minerals present in them.