MINERALOGY AND AR-40 AR-39 GEOCHRONOLOGY OF ORANGEITES (GROUP-II KMBERLITES) FROM THE DAMODAR VALLEY, EASTERN INDIA/

A suite of ultramafic-mafic alkaline igneous rocks in the Damodar Vall ey, eastern India, contains carbonate, phosphate and titanate minerals that are nor characteristic or common in minettes or lamproites, but are typical of orangeites (Group II kimberlite) from southern Africa. Phlogopite grains from the Damodar alkaline rocks yield mean Ar-40/Ar- 39 ages of 116.6 +/- 0.8 Ma, 113.5 +/- 0.5 Ma and 109.1 +/- 0.7 Ma (1 sigma errors) using laser dating techniques. These ages are similar to the Rb-Sr ages of African orangeites, which lie mostly in the range 1 21 to 114 Ma. Prior to this study, only one possible occurrence of ora ngeite (the similar to 820 m.y.-old Aries pipe, Western Australia) was known outside the Kaapvaal craton and its environs. If the Damodar al kaline rocks are bona fide orangeites, it is likely that they were gen erated at depths of >150 km, within the stability field of diamond.