The leucite lamproites of the Fitzroy Basin, Western Australia∗

Abstract

A re‐examination in the field of the lamproites of the Fitzroy Basin, Western Australia, shows that for the most part they occur in concentrically‐zoned plugs occupying diatremes. The zonal distribution of the lamproites in each plug is due to the different rates of cooling in different parts of the plug and the peculiar nature of the lamproite magma (high potash dominant over alumina, absence of soda, and abundance of titania, zirconia, baryta and fluorine) is ascribed to upward gas transfer of these constituents in the diatremes, the parental magma being of peridotitic character.