PETROLOGY AND GEOCHEMISTRY OF THE LAMPROPHYRIC ROCKS FROM THE BOKARO COALFIELD, BIHAR AND THEIR ECONOMIC-POTENTIAL

The dyke swarms intruding the Gondwana sequence in the east Bokaro Coa lfrield, Bihar include lamprophyres and lamproites such as olivine lam proties, olivine-leucite lamproites and leucite lamproites. Basic intr usives and rare siderite rich carbonates (carbonatite ?) are also foun d. The olivine lamproites contain xenocrysts of olivine and rare xenol iths of harzburgite. Gold Values upto 3.6 ppm on grab samples have bee n noted from the intrusive rocks in the area. These lamprophyric rocks are considered to have formed from a highly incompatible element enri ched metasomatised mantle source probably of harzburgitic composition.