The attractive and rare kick-back shape on the long arm of this boomerang is perhaps relevant to its usage - the collector, who was a prospector in the seems to be indicating that it is a fighting boomerang (see second image.
Unusual Painted Ceremonial AUSTRALIAN ABORIGINAL SHIELD from Central Queensland
Very Old and Fine South East Australian Aboriginal Fighting Club - Rare
Rare Antique, Tribal Art, Wood Work
Australian Aboriginal Art by Ronald Berndt, with bark paintings, carved figures