Thanks Con. Beautiful photos of the flower-covered nest. Could be one of several Iridomyrmex which construct raised areas of vegetable matter to catch the sun and make a warm place to raise brood. Below is a quote from Shattuck, S. O., & McMillan, P. (1998). Revision of the species of the Iridomyrmex conifer group (Hymenoptera: Formicidae), with notes on their biology. Australian Journal of Zoology, 46(3), 301–315. https://doi.org/10.1071/ZO98033.
"The conifer species-group of the ant genus Iridomyrmex .... The species I. conifer Forel, I. setoconus, sp. nov. and I. turbineus, sp. nov. are placed in the group, which is limited to south-western Australia. ... These ants show unusual nesting habits in that thatched mounds are used during the cooler winter months and subterranean nests are constructed during the hot summer months. This habit is not known to occur in any other ant."