Diapiric marbles and dolomitic siltstone breccia of presumed Willouran age intrude younger Umberatana Group rocks which have been folded into an elongate domal structure and, in part, rest unconformably on the diapiric core. Within the diapir several rafts of coarse-grained dolomitic marble carry disseminated copper sulphides with copper content ranging up to 1.1% while along the southern flank a number of mines have worked secondary chalcocite, cuprite and malachite in veins within the Tapley Hill Formation; these veins appear to originate from within the diapir. Drilling has shown that secondary copper mineralisation is very erratic.