The geology and petrology of Cainozoic basaltic rocks in the Cooktown area, North Queensland

Over most of the area, the McLean Basalt, southwest of Cooktown, and the Piebald Basalt, north of Cooktown, were erupted on to a land surface generally similar to that of the present day. The basalts form horizontal flows, and a number of vents have been identified. In the main, the lavas consist of olivine basalt; these are shown by chemical analysis to be alkaline, transitional to olivine tholeiite. In the McLean Basalt, several flows consisting of olivine analcimite have been discovered. An olivine nephelinite flow is associated with the Piebald Basalt. Chemical analyses of olivine analcimites and the olivine nephelinite are presented and discussed.