Nepheline Syenite from Rairakhol, Sambalpur District, Orissa

Abstract A newly identified body of nepheline syenite with associated non-feldspathoidal syenites from the Rairakhol area of Sambalpur district in the Eastern Ghat belt of Orissa sector adds to the present population of such complexes in this segment of Precambrian crust of Indian Peninsula. Recent researches have emphasized the significance of these bodies as a major Late-Proterozoic tectonothermal marker event in this belt. The Rairakhol syenitc complex consists mainly of nepheline syenite, syenite and minor quartz syenite. Biotite and hornblende are the chief mafic constituents which occur as accessories in varying proportions. This body is emplaced within an interbanded sequence of quartzite, khondalite and charnockite. Syenitic rocks have a flow banding/foliation well-developed at many localities. A pink pegmatitic K-feldspar sycnite possibly represents a late-magmatic product. Occurrences of a few relatively smaller bodies of similar composition are also recorded.