Lamproites in the West B¾c Bé of ViÖt Nam were first described by Lacroix and named as cocite. Later, they were classified as dark-coloured, highly potassic porphyrite by Russian and Vietnamese geologists, but their origin has not been dealed with. Studying the behaviour of trace elements and calculating the compositional melting of the rocks have been showing that the source rock is garnet-bearing peridotite melted from 3 to 5.7% at over 30 kbar and 1600⁰C.